Lewis Acid Activated Olefin Metathesis Catalysts · Lewis Acid Activated Olefin Metathesis Catalysts Adam Michael McKinty Doctor of Philosophy Department of Chemistry University of

Lewis Acid Activated Olefin Metathesis Catalysts

by

Adam Michael McKinty

A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy

Department of Chemistry University of Toronto

© Copyright by Adam Michael McKinty 2014

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Lewis Acid Activated Olefin Metathesis Catalysts

Adam Michael McKinty

Doctor of Philosophy

Department of Chemistry

University of Toronto

2014

Abstract

Since its discovery, catalytic olefin metathesis has been used as a powerful tool for the synthesis

of a variety of molecules. Over the last 20 years research in this area has received enormous

attention in the development of new catalysts and applications. The vast majority of the

ruthenium based catalysts developed have been modifications to the Grubbs Catalyst type

architecture. The research presented herein focuses on the development of new olefin metathesis

catalysts bearing tridentate, dianionic ligands and their activation with Lewis acids.

Complexes [(PPh3)2Ru(SCH2CH2)2O] and [(PPh3)2Ru(SC6H4)2O] were synthesized from

(PPh3)3RuCl2 and the corresponding dilithio-dithiolate salt or from (PPh3)4RuH2 and the

corresponding dithiol. These complexes were shown to react with BCl3 forming complexes

[(PPh3)2RuCl(Cl2B(SCH2CH2)2O)] and [(PPh3)2RuCl(Cl2B(SC6H4)2O)].

Complexes of the general structure [LRu(CHPh)(SC6H4)2O] and [LRu(CHPh)(XCH2CH2)2E]

where L = PCy3, SIMes, X = O, S, and E = O, S, PPh were prepared by ligand exchange with

Grubbs I and II. Alternatively, complexes [LRu(CHPh)(SC6H4)2O] and

[LRu(CHPh)(SCH2CH2)2E] where L = PCy3, SIMes and E = O, S were synthesized

independently of Grubbs Catalyst by the reaction of dithioacetals with Ru(0) sources. These

complexes proved to be inactive for catalytic olefin metathesis.

iii

The addition of BCl3 to these complexes resulted in the formation of new 6-coordinate ruthenium

alkylidene complexes of the general formula [LRuCl(CHPh)(Cl2B(SC6H4)2O)] and

[LRuCl(CHPh)(Cl2B(XCH2CH2)2E)] where L = PCy3, SIMes, X = O, S, and E = O, S, PPh.

These complexes also proved to be inactive for olefin metathesis. The addition of a second

equivalent of BCl3 results in the formation of 5-coordinate cationic ruthenium species of the

general formula [LRu(CHPh)(Cl2B(SC6H4)2O)][BCl4] and

[LRu(CHPh)(Cl2B(XCH2CH2)2E)][BCl4] where L = PCy3, SIMes, X = O, S, and E = O, PPh.

These cationic species proved to be active for a variety of olefin metathesis reactions including

ring closing metathesis (RCM), ring opening metathesis polymerization (ROMP) and cross

metathesis (CM).

iv

Acknowledgments

First and foremost I would like to thank Professor Doug Stephan for giving me the opportunity to

complete my degree in his group. His contagious enthusiasm, vast knowledge and continuous

support were invaluable in the completion and success of my degree. My grad school experience

has been nothing but a positive one. I am truly grateful for the experiences and opportunities

Doug gave me and I will always look back on my time in his group as a great chapter in my life.

I would also like to thank the Stephan group members, past and present, for their helpful

discussions, advice and friendship. I learned a lot from each one of them and they made a huge

contribution to my success. Outside of the lab I am thankful I could always count on them to

keep a healthy work-life balance.

I would like to thank my best friend and partner, Sanja for all her support and patience

throughout my degree. Her love and encouragement provided me with the strength and

determination to succeed and I could always count on her to provide support during difficult

times. Thank you so much.

Finally, I would like to thank my family for their unconditional support over the years.

Specifically I would like to thank my parents, Mike and Shirley McKinty. Without their

encouragement, support and love none of this would have been possible. I am extremely grateful

for the opportunities they've given me and the sacrifices they've made to enable me to pursue my

education.

v

Table of Contents

Acknowledgments .......................................................................................................................... iv

Table of Contents ............................................................................................................................ v

List of Tables ................................................................................................................................. ix

List of Schemes .............................................................................................................................. xi

List of Figures .............................................................................................................................. xiv

List of Abbreviations ................................................................................................................. xviii

Chapter 1 Introduction .................................................................................................................... 1

1.1 Catalysis .............................................................................................................................. 1

1.2 Catalytic Olefin Metathesis ................................................................................................. 1

1.2.1 Heterogenous Catalysis ........................................................................................... 1

1.2.2 Well-Defined Homogenous Catalysts ..................................................................... 2

1.2.3 Mechanism of Catalytic Olefin Metathesis ............................................................. 4

1.2.4 Variations of Grubbs Catalyst ................................................................................. 6

1.2.5 Z-selective Olefin Metathesis ................................................................................. 7

1.3 Lewis Acid Activation of Catalysts .................................................................................... 9

1.4 Nitrile Butadiene Rubber .................................................................................................... 9

1.5 Lanxess Project ................................................................................................................. 11

1.6 Scope of this Thesis .......................................................................................................... 11

Chapter 1 References .................................................................................................................... 14

Chapter 2 Coordination Chemistry of Tridentate, Dithiolate Ligands ......................................... 18

2.1 Introduction ....................................................................................................................... 18

2.1.1 Thiolate Ligands in Metal Complexes .................................................................. 18

2.2 Results and Discussion ..................................................................................................... 22

2.2.1 Synthesis of Ru Complexes .................................................................................. 22

vi

2.2.2 Reactivity of Complexes with BCl3 ...................................................................... 25

2.3 Conclusion ........................................................................................................................ 27

2.4 Experimental Section ........................................................................................................ 28

2.4.1 General Considerations ......................................................................................... 28

2.4.2 Synthetic Procedures ............................................................................................. 28


Chapter 3 Ruthenium Alkylidene Complexes with Tridentate, Dianionic Ligands ..................... 33

3.1 Introduction ....................................................................................................................... 33

3.1.1 Modifications to Grubbs Catalyst ......................................................................... 33

3.1.2 Halide Variations in Grubbs Catalyst ................................................................... 34

3.1.3 Pseudo-halides as Ligands on Ruthenium Metathesis Catalysts .......................... 35

3.1.4 Bidentate Monoanionic Ligands on Ruthenium Metathesis Catalysts ................. 36

3.1.5 Bidentate Dianionic Ligands on Ruthenium Metathesis Catalysts ....................... 37

3.1.6 Tridentate Ligands on Ruthenium Alkylidene Complexes ................................... 38


3.2.1 Synthesis of Ruthenium Alkylidene Complexes .................................................. 38

3.3 Conclusions ....................................................................................................................... 48




3.4.3 X-ray Crystallography .......................................................................................... 54


Chapter 4 Synthesis of Ru Alkylidenes via Dithioacetals ............................................................ 59

4.1 Introduction ....................................................................................................................... 59

4.1.1 First Well Defined Olefin Metathesis Catalyst ..................................................... 59

4.1.2 Synthetic Routes to Ruthenium Alkylidenes ........................................................ 59

vii


4.2.1 Attempted Synthesis Using Diazomethanes ......................................................... 62

4.2.2 Attempted Synthesis Using Propargyl Alcohol .................................................... 63

4.2.3 Synthesis of Ru Alkylidenes using Thioacetals .................................................... 63

4.3 Conclusion ........................................................................................................................ 67




4.4.3 X-ray Crystallography .......................................................................................... 72


Chapter 5 Lewis Acid Activation of Ruthenium Alkylidene Complexes ..................................... 77

5.1 Introduction ....................................................................................................................... 77

5.1.1 Lewis Acid Activation in Catalysis ...................................................................... 77

5.1.2 Lewis Acid Assisted Olefin Metathesis ................................................................ 77

5.1.3 Acid Activation of Olefin Metathesis Catalysts ................................................... 78


5.2.1 Reactivity with One Equivalent of BCl3 ............................................................... 81

5.2.2 Reactivity with Two Equivalents of BCl3 ............................................................. 91

5.2.3 Reactivity with Bronsted Acid .............................................................................. 94

5.2.4 Reversibility of Lewis Acid Reactivity ................................................................. 96

5.3 Conclusion ........................................................................................................................ 96




5.4.3 X-ray Crystallography ........................................................................................ 103

Chapter 5 References .................................................................................................................. 107

viii

Chapter 6 Catalytic Olefin Metathesis ........................................................................................ 109

6.1 Introduction ..................................................................................................................... 109

6.1.1 Types of Olefin Metathesis Reactions ................................................................ 109

6.1.2 Catalyst Screening .............................................................................................. 110

6.1.3 Cross Metathesis of NBR and 1-Hexene ............................................................ 112

6.1.4 Hydrogenation of NBR ....................................................................................... 113

6.2 Results and Discussion ................................................................................................... 113

6.2.1 Comparing Catalytic Activity of BCl3 'Activated' and 'Non-Activated' Species 113

6.2.2 Catalytic Olefin Metathesis Activity of Catalyst Derivatives ............................. 117

6.2.3 Comparisons of Active Catalysts ........................................................................ 124

6.2.4 Cross Metathesis of NBR and 1-hexene ............................................................. 129

6.2.5 Hydrogenation of NBR ....................................................................................... 133

6.3 Conclusion ...................................................................................................................... 135

6.4 Experimental Section ...................................................................................................... 136

6.4.1 General Considerations ....................................................................................... 136

6.4.2 Synthetic Procedures ........................................................................................... 137

Chapter 6 References .................................................................................................................. 150

Chapter 7 Summary and Future Work ........................................................................................ 152

7.1 Summary ......................................................................................................................... 152

7.2 Future Work .................................................................................................................... 153

ix

List of Tables

Table 3.4.1. Select Crystallographic Data for 3-1, 3-2 and 3-3 .................................................... 55

Table 3.4.2. Select Crystallographic Data for 3-5, 3-6 and 3-9 .................................................... 56

Table 4.4.1. Select Crystallographic Data for 4-1 ........................................................................ 74

Table 5.4.1. Select Crystallographic Data for 5-2, 5-4 and 5-5 .................................................. 105

Table 5.4.2. Select Crystallographic Data for 5-11 and 5-12 ..................................................... 106

Table 6.1.1. Standard Olefin Metathesis Reactions Using Common Catalysts .......................... 112

Table 6.2.1. Ring Closing Metathesis of Diethyl Diallylmallonate Using 5-17 at a 5 mol%

Catalyst Loading .................................................................................................................... 121

Table 6.2.2. Hydrogenation of NBR with 3-5, 5-5 and 5-12 ...................................................... 134

Table 6.2.3. Hydrogenation of NBR using 3-9, 5-9 and 5-17 .................................................... 134

Table 6.4.1. RCM of Diethyl Diallylmallonate with 3-4, 5-4 and 5-10 ..................................... 138

Table 6.4.2. RCM of Diethyl Diallylmallonate with 3-5, 5-5 and 5-12 ..................................... 138

Table 6.4.3. ROMP of 1,5-cyclooctadiene with 3-5, 5-5 and 5-12 ............................................. 139

Table 6.4.4. CM of 5-hexenyl Acetate and Methyl Acrylate with 3-5, 5-5 and 5-12 ................. 140

Table 6.4.5. RCM of Diethyl Diallylmallonate with 5-14 .......................................................... 140


Table 6.4.7. ROMP of 1,5-cyclooctadiene with 5-15 ................................................................. 142

Table 6.4.8. CM of 5-hexenyl Acetate and Methyl Acrylate with 5-15 ..................................... 142


Table 6.4.10. RCM of Diethyl Diallylmallonate with 5-17 with 5 mol% Catalyst Loading ...... 144

Table 6.4.11. RCM of Diethyl Diallylmallonate with 5-17 with 1 mol% Catalyst Loading ...... 144

Table 6.4.12. ROMP of 1,5-cyclooctadiene with 5-17 ............................................................... 145

Table 6.4.13. CM of 5-hexenyl Acetate and Methyl Acrylate with 5-17 ................................... 145

Table 6.4.14. GPC Data for the Metathesis of NBR and 1-hexene using 0.007 phr Grubbs 2 .. 146

x

Table 6.4.15. GPC Data for the Metathesis of NBR and 1-hexene using 5-12 .......................... 147



Table 6.4.18. Hydrogenation of NBR using 3-5, 5-5, 5-12 ........................................................ 149

Table 6.4.19. Hydrogenation of NBR using 3-9, 5-9, 5-17 ........................................................ 149

xi

List of Schemes

Scheme 1.2.1. Depiction of Olefin Metathesis ............................................................................... 1

Scheme 1.2.2. Olefin Metathesis with Tebbe's Complex ............................................................... 2

Scheme 1.2.3. Isolation of a Metalocycllobutane with Tebbe's Complex ...................................... 2

Scheme 1.2.4. Synthesis of 1-2 ....................................................................................................... 3

Scheme 1.2.5. Synthesis of the First Well-Defined Ru Olefin Metathesis Catalyst ....................... 4

Scheme 1.2.6. Chauvin Mechanism of Olefin Metathesis .............................................................. 5

Scheme 1.2.7. Olefin Metathesis Mechanism with 1st Gen. Grubbs Catalyst ................................ 6

Scheme 1.2.8. Synthesis of a Ruthenium Phosphonium Alkylidene Complex .............................. 7

Scheme 1.3.1. Activation of an Ethylene Polymerization Catalyst with TMA .............................. 9

Scheme 2.1.1. Synthesis of a Bridged Titanium Thiolate Borane Complex ................................ 19

Scheme 2.1.2. Mechanism of BH3 Addition to a Ruthenium Thiolate Complex ......................... 22

Scheme 2.2.1. Synthesis of 2-1 From Ru(PPh3)3Cl2 ..................................................................... 23

Scheme 2.2.2. Synthesis of 2-1 From Ru(PPh3)4H2 ...................................................................... 23

Scheme 2.2.3. Attempted Synthesis of a Thioether Dithiolate Ru Complex ................................ 23

Scheme 2.2.4. Synthesis of Phosphine Containing Ligand 2-2 .................................................... 24

Scheme 2.2.5. Attempted Synthesis of a Phosphino Dithiolate Ru Complex .............................. 24

Scheme 2.2.6. Synthesis of Dithiol Proligand 2-3 ........................................................................ 25

Scheme 2.2.7. Synthesis of 2-4 ..................................................................................................... 25



Scheme 3.2.1. Synthesis of 3-1 and 3-2 ........................................................................................ 39




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Scheme 4.1.1. Synthesis of the First Isolated Transition Metal Alkylidene ................................. 59

Scheme 4.1.2. Synthesis of the First Ruthenium Alkylidene ....................................................... 59

Scheme 4.1.3. Synthesis of Grubbs Catalyst Using Phenyldiazomethane ................................... 60

Scheme 4.1.4. Synthesis of Grubbs Catalyst Using a Sulfur Ylide .............................................. 60

Scheme 4.1.5. Synthesis of a Vinylalkylidene Using Propargyl Chloride ................................... 60

Scheme 4.1.6. Synthesis of Ru Alkylidenes from Phenyl Vinylsulfide ....................................... 61

Scheme 4.1.7. Synthesis of Grubbs Catalyst via Indenylidene Intermediate ............................... 61

Scheme 4.1.8. Synthesis of Grubbs Catalyst from Ru(0) Species ................................................ 62

Scheme 4.2.1. Failed Preparation of Ruthenium Alkylidene From Diazomethanes and 2-1 ....... 62

Scheme 4.2.2. Failed Preparation of Ruthenium Alkylidene From Diazomethanes and 2-3 ....... 63

Scheme 4.2.3. Failed Preparation of Ruthenium Indenylidene From Propargyl Alcohol and

2-3 ............................................................................................................................................ 63



Scheme 4.2.6. Synthesis of 3-4 From Dithioacetal 4-1 and Ru(cod)(cot) .................................... 65

Scheme 4.2.7. Synthesis of 3-4, 3-1 and 3-6 From Dithioacetals and Ru(PPh3)4(H)2 ................. 66

Scheme 4.2.8. Synthesis of 3-5, 3-2 and 3-7 From Dithioacetals and Ru(PPh3)4(H)2 .................. 66

Scheme 4.2.9. Ruthenium Alkylidene Formation From Dithioacetals ......................................... 67

Scheme 4.2.10. Synthesis of Grubbs II From 3-5 ......................................................................... 67

Scheme 5.1.1. Lewis Acid Catalyst Activation by Electronic Influence ...................................... 79

Scheme 5.1.2. Catalyst Activation by CuCl Ligand Abstraction ................................................. 80

Scheme 5.1.3. Synthesis of a Four-Coordinate Olefin Metathesis Catalyst by Halide

Abstraction ............................................................................................................................... 81


Scheme 5.2.2. Synthesis 5-2 ......................................................................................................... 83

Scheme 5.2.3. Synthesis of 5-3a and 5-3b .................................................................................... 86

xiii




Scheme 5.2.7. Synthesis of 5-10 - 5-13 ........................................................................................ 92

Scheme 5.2.8. Synthesis of 5-18 ................................................................................................... 95

Scheme 5.2.9. Reversibility of Lewis Acid Reactivity ................................................................. 96

Scheme 6.1.2. Standard Test Reaction for RCM ........................................................................ 111

Scheme 6.1.3. Standard Test Reaction for ROMP ...................................................................... 111

Scheme 6.1.4. Standard Test Reaction for CM ........................................................................... 111

xiv

List of Figures

Figure 1.2.1. Generalized Structure of a Schrock-type Catalyst ..................................................... 3

Figure 1.2.2. 1st and 2

nd Generation Grubbs Catalysts .................................................................... 4

Figure 1.2.3. Hoveyda-Grubbs Catalyst ......................................................................................... 7

Figure 1.2.4. Examples of Schrock Catalyst Based Z-Selective Olefin Metathesis Catalysts ........ 8

Figure 1.2.5. Ru-based Z-Selective Olefin Metathesis Catalyst ..................................................... 8

Figure 1.4.1. Depiction of Functional Groups Found in Nitrile Butadiene Rubber ..................... 10

Figure 1.4.2. Depiction of Hydrogenated Nitrile Butadiene Rubber with Functional Groups

Highlighted ............................................................................................................................... 10

Figure 2.1.1. The Active Sites of Hydrogenase Enzymes Containing Metal Thiolate

Structures.................................................................................................................................. 18

Figure 2.1.2. Titanium Thiolate Complexes ................................................................................. 19

Figure 2.1.3. Multimetallic Titanium Thiolate Complexes .......................................................... 19

Figure 2.1.4. Thiolate Bridged Bimetallic Complexes for Propargylic Alcohol Catalysis .......... 20

Figure 2.1.5. Tethered Ruthenium Thiolate Complex .................................................................. 20

Figure 2.1.6. Thiolate Complexes with Bridging BH2 Fragments ................................................ 21

Figure 2.1.7. Thiolate Bridged Ruthenium BH3 Complex ............................................................ 21

Figure 2.2.1. 31

P{1H} NMR Spectrum (top) and Ligand Backbone Region of

1H NMR

Spectrum (bottom) of 2-5 ......................................................................................................... 26

Figure 3.1.1. Generalized Structure of a Ruthenium Alkylidene Complex used for Catalytic

Olefin Metathesis ..................................................................................................................... 33

Figure 3.1.2. Generalized structures of NHCs Used as Ligands for Ruthenium Olefin

Metathesis Catalysts ................................................................................................................. 34

Figure 3.1.3. Electron Deficient Aryloxides as Ligands on Olefin Metathesis Catalysts ............ 35

Figure 3.1.4. Z-selective Olefin Metathesis Catalyst with a Thiolate Ligand .............................. 35

Figure 3.1.5. Ruthenium Olefin Metathesis Catalysts with Bidentate Monoanionic Ligands ..... 36

Figure 3.1.6. Ruthenium Metathesis Catalysts With Bidentate, Dianionic Ligands .................... 37

xv

Figure 3.1.7. Ruthenium Olefin Metathesis Catalysts with Tridentate, Dianionic Ligands ......... 38

Figure 3.2.1. POV-ray depiction of 3-1; C: black, P: orange, S: yellow, Ru: teal ........................ 40

Figure 3.2.2. POV-ray depiction of 3-2; C: black, N: blue-green, S: yellow, Ru: teal ................. 41

Figure 3.2.3. POV-ray depiction of 3-3; C: black, P: orange, S: yellow, Ru: teal ........................ 42

Figure 3.2.4. POV-ray depiction of 3-5; C: black, N: blue-green, O: red, S: yellow, Ru: teal ..... 44

Figure 3.2.5. POV-ray depiction of 3-6; C: black, O: red, P: orange, S: yellow, Ru: teal ........... 45

Figure 3.2.6. POV-ray depiction of 3-8; C: black, O: red, P: orange, Ru: teal. Insufficient data

for full solution ......................................................................................................................... 46

Figure 3.2.7. POV-ray depiction of 3-9; C: black, O: red, N: blue-green, Ru: teal ...................... 48

Figure 4.2.1. POV-ray depiction of 4-1; C: black, O: red, S: yellow, H: black ............................ 64

Figure 5.1.1. Latent Olefin Metathesis Catalysts which can be Activated by Bronsted or

Lewis Acids .............................................................................................................................. 79

Figure 5.1.2. Highly Active Bimetallic Olefin Metathesis Catalyst ............................................. 80

Figure 5.2.1. POV-ray depiction of 5-2a; B: pink, C: black, N: blue-green, S: yellow, Cl:

green, Ru: teal .......................................................................................................................... 83

Figure 5.2.2. (a) 31

P{1H} NMR spectrum and (b) alkylidene region of

1H NMR spectrum of

5-3 in CD2Cl2 ........................................................................................................................... 85

Figure 5.2.3. (a) 1H NMR Spectrum of 5-4. (b) Expansion of Ligand Backbone Region of

1H

NMR Spectrum of 5-4 .............................................................................................................. 87

Figure 5.2.4. POV-ray depiction of 5-4; B: pink, C: black, O: red, P: orange, S: yellow, Cl:

green, Ru: teal .......................................................................................................................... 88

Figure 5.2.5. POV-ray depiction of 5-5; B: pink, C: black, N: blue-green O: red, S: yellow,

Cl: green, Ru: teal .................................................................................................................... 89

Figure 5.2.6. POV-ray depiction of 5-11; B: pink, C: black, N: blue-green, O: red, P: orange,

S: yellow, Cl: green, Ru: teal ................................................................................................... 92

Figure 5.2.7. POV-ray depiction of 5-13; B: pink, C: black, N: blue-green, O: red, S: yellow,

Cl: green, Ru: teal. Anion omitted for clarity .......................................................................... 93

Figure 5.2.8. Complexes 5-14 - 5-17 ............................................................................................ 94

Figure 5.2.9. 1H NMR spectra of 3-4 (Top) and 5-18 (Bottom) ................................................... 95

Figure 6.1.1. Common Olefin Metathesis Reactions .................................................................. 110

xvi

Figure 6.2.1. Compounds used to Compare BCl3 Activation Effects on Catalysis .................... 113

Figure 6.2.2. Ring Closing Metathesis of Diethyl Diallylmalonate using Complexes 3-4

(Green Triangles), 5-4 (Red Squares), and 5-10 (Blue Diamonds) with 5 mol% Catalyst

Loadings at 25 ºC in CD2Cl2 .................................................................................................. 114

Figure 6.2.3. Ring Closing Metathesis of Diethyl Diallylmalonate With Complexes 3-5


Loadings at 25 ºC in CD2Cl2 .................................................................................................. 115

Figure 6.2.4. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene With

Complexes 3-5 (Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with

0.1 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ................................................................... 116

Figure 6.2.5. Cross Metathesis of 5-Hexenyl Acetate And Methyl Acrylate With Complexes

3-5 (Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with 5 mol%

Catalyst Loadings at 25 ºC in CD2Cl2 .................................................................................... 117

Figure 6.2.6. Compounds 5-14 and 5-15 .................................................................................... 118

Figure 6.2.7. Ring Closing Metathesis of Diethyl Diallylmalonate with 5-14 and 5-15 at a

5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ...................................................................... 118

Figure 6.2.8. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene with 5-15 at a

0.1 mol% Catalyst Loading at 25 ºC in CD2Cl2 ..................................................................... 119

Figure 6.2.9. Cross Metathesis of 5-Hexenyl Acetate and Methyl Acrylate With 5-15 at a

5 mol% Catalyst Loading at 25 ºC in CD2Cl2 ........................................................................ 119

Figure 6.2.10. Complexes 5-16 and 5-17 .................................................................................... 120

Figure 6.2.11. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-16 at a 5 mol%

Catalyst Loading at 25 ºC in CD2Cl2 ..................................................................................... 121

Figure 6.2.12. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-17 at a at a






Figure 6.2.15. Comparing the Activity of SIMes containing 5-12 and PCy3 Containing 5-10

for RCM of Diethyl Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ....... 124



xvii

Figure 6.2.17. Comparing the Activity of PCy3 Containing 5-16 and SIMes Containing 5-17


Figure 6.2.18. Comparing the Activity of 5-10, 5-14 and 5-16 for RCM of Diethyl

Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ........................................ 126


Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ........................................ 127

Figure 6.2.20. Comparing Activities of 5-12, 5-15 and 5-17 for ROMP of 1,5-Cyclooctadiene

at 0.1 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ............................................................... 128

Figure 6.2.21. Comparing Activities of 5-12, 5-15 and 5-17 for CM of 5-hexenyl Acetate and

Methyl Acrylate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2 ....................................... 129

Figure 6.2.22. Mw (Blue Diamonds) and Mn (Red Squares) Over Time of NBR Cross

Metathesis with 1-hexene Using 2nd

Gen. Grubbs Catalyst at a 0.007 phr Catalyst Loading

at 25 ºC in Chlorobenzene ...................................................................................................... 130

Figure 6.2.23. Mw Over Time of NBR Cross Metathesis With 1-Hexene at Various Catalyst

Loadings of 5-12 at 25 ºC in Chlorobenzene ......................................................................... 131





Figure 6.2.26. FTIR Spectrum of NBR (top) and Hydrogenated NBR (bottom) ....................... 135

xviii

List of Abbreviations

°C degrees Celsius

Å angstrom, 10-10

m

abs absorption

Ac Acetate

appt Apparent triplet

atm atmosphere

Ar Aryl

br broad

CD2Cl2 deuterated dichloromethane

calc calculated

cat. catalyst

CCD charge coupled device

CM cross metathesis

cm centimeter

coeff coefficient

Cp cyclopentadienyl

Cp* pentamethylcyclopentadienyl

Cy cyclohexyl

d doublet

dd doublet of doublets

DCM dichloromethane

deg degree

Dipp 2,6-diisopropylphenyl

equiv. equivalent

Et ethyl

Et2O diethyl ether

FTIR Fourier transform infrared

g gram

GOF goodness of fit

h hour

xix

H2 dihydrogen

Hz Hertz

I nuclear spin

Ind indenyl

iPr iso-propyl

m meta

m multiplet

Me methyl

Mes mesityl, 2,4,6-trimethylphenyl

min minute

mL milliliter

mm millimeter

mmol millimole

NHC N-heterocyclic carbene

nJxy n-bond scalar coupling constant between X and Y atoms

NMR nuclear magnetic resonance

o ortho

p para

Ph phenyl

phr parts per hundred

POV-Ray Persistence of Vision Raytracer

ppm parts per million, 10-6

py pyridine

q quartet

RCM ring closing metathesis

ROMP ring opening metathesis polymerization

r.t. room temperature

SIMes 1,3-Bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene

t triplet

tol toluene

thf tetrahydrofuran

TMS trimethylsilyl

1

Chapter 1 Introduction

1.1 Catalysis

A catalyst can be defined as a compound that lowers the activation energy for a given chemical

reaction.1 During the course of the reaction the catalyst is not consumed and therefore is only

required in a small amount. Enzymes are catalysts acting in our bodies everyday performing

tasks which are essential for our survival.2 Catalysis is used ubiquitously throughout industry

from the production of plastics such as polyethylene3-4

, to the synthesis of pharmaceuticals5, and

fine chemicals.6

1.2 Catalytic Olefin Metathesis

In chemistry, metathesis is described as a bimolecular reaction in which the products contain the

same groups as the reactants only redistributed over new bonds.7 This requires the breaking of

two bonds followed by the formation of two new bonds. Therefore, olefin metathesis can be

described as the redistribution of alkene groups by scission, redistribution and bond formation,

over two molecules containing an alkene fragment.8-9

A general scheme for olefin metathesis can

be seen in Scheme 1.2.1.10

Scheme 1.2.1. Depiction of Olefin Metathesis.

1.2.1 Heterogeneous Catalysis

The discovery by Karl Ziegler and Giulio Natta that combinations of Ti and alkylaluminum

species can catalyze the polymerization of olefins revolutionized industrial chemistry and the

way we live today.11

Modern polymerization of ethylene and propylene is done heterogeneously

on a silica support.4 Researchers at Dupont were investigating the polymerization of norbornene

with Ti-based Ziegler-Natta type catalysts. They were expecting the typical Ziegler addition

2

polymer as seen with ethylene and propylene but instead obtained a polymer that was highly

unsaturated.12

Following this discovery, early olefin metathesis catalysts were based on Ziegler-

Natta type systems involving early metal, high oxidation state species.13-14

1.2.2 Well-Defined Homogenous Catalysts

1.2.2.1 Tebbe's Complex

Initial studies of the mechanism of olefin metathesis suggested a pathway involving a metal

alkylidene and a metallocycle.15-17

In order to prove this hypothesis, well-defined species and

intermediates needed to be isolated. Fred Tebbe at DuPont discovered a reaction which

demonstrated the mechanism of olefin metathesis.18-19

Tebbe's Complex, 1-1 was shown to react

in a catalytic fashion with terminal olefins (Scheme 1.2.2).

Scheme 1.2.2. Olefin Metathesis with Tebbe's Complex

Subsequently, Grubbs and coworkers were able to trap a metallocyclobutane from a catalytic

metathesis reaction involving Tebbe's Complex (Scheme 1.2.3).20

The addition of a strong base

such as dimethylaminopyridine (DMAP) to the reaction mixture sequestered the Lewis acidic

allane and drove the equilibrium towards the metallocyclobutane.

Scheme 1.2.3. Isolation of a Metallocyclobutane with Tebbe's Complex

3

1.2.2.2 Schrock's Catalyst

In 1973, Schrock and coworkers were investigating alkyl complexes of tantalum. In an attempt to

synthesize Ta(CH2tBu)5, two equivalents of LiCH2

tBu were added to Ta(CH2

tBu)3Cl2.

21

However, tantalum alkylidene 1-2 was isolated which was formed by -hydrogen elimination

(Scheme 1.2.4).22

They went on to synthesize the first well defined Ta carbene species that was

active for catalytic olefin metathesis.23

Scheme 1.2.4. Synthesis of 1-2

Schrock and others went on to synthesize a number of other early transition metal alkylidene

complexes.24-25

Most notably are the W and Mo imido, alkylidene complexes. The Mo species

being commercially available as "Schrock's Catalyst" (Figure 1.2.1).26

These early metal

alkylidene species are extremely active for olefin metathesis but suffer from being extremely

reactive and functional group intolerant.

Figure 1.2.1. Generalized Structure of a Schrock-type Catalyst

1.2.2.3 Grubbs Catalyst

Due to the lengthy and laborious preparation of Schrock's W and Mo metathesis catalysts along

with their extreme sensitivity and functional group reactivity, new well-defined catalysts with

more tolerant metals were sought out. Based on earlier reports that Ru species could perform ring

opening metathesis polymerization (ROMP), the synthesis of Ru based catalysts was investigated

by the Grubbs group. The first well-defined Ru based catalyst to be isolated was from the ring

opening of a cyclopropene by Ru(PPh3)3Cl2 to give the alkylidene species 1-3 (Scheme 1.2.5).27

4

This complex was found to be active for ROMP and replacement of the PPh3 ligands with PCy3

resulted in a complex that was active for cross metathesis.28

Scheme 1.2.5. Synthesis of the First Well-Defined Ru Olefin Metathesis Catalyst

This opened up a new field of research in catalytic olefin metathesis chemistry. Although these

new Ru based systems were less active for olefin metathesis than the previous Mo and W based

systems, they were stable in the presence of water, acid, and many other functional groups. As

new methods were developed to prepare Ru alkylidenes (discussed in 5.1), a library of Ru based

catalysts began to become available.29

Of major significance to this field was the report of

(PCy3)2Ru(CHPh)Cl2 and (SIMes)(PCy3)Ru(CHPh)Cl2 known as 1st Generation and 2

nd

Generation Grubbs Catalyst respectively (Figure 1.2.2).28, 30

The substitution of a phosphine with

the N-heterocyclic carbene (NHC) in 2nd

Generation Grubbs increased the activity of the catalyst

dramatically. These catalysts are used in a variety of commercial applications.31-32

Figure 1.2.2. 1st and 2

nd Generation Grubbs Catalysts

1.2.3 Mechanism of Catalytic Olefin Metathesis

Initial speculation into the mechanism of olefin metathesis involved a number of hypotheses.9

Calderon proposed the formation of a cyclobutane in the coordination sphere of the metal

centre.33

An alternative mechanism by Grubbs involved a metallocyclopentane intermediate.15

Pettit proposed an intermediate in which four carbon atoms form sigma bonds with the metal

5

centre.34

In 1971, Chauvin proposed a mechanism for catalytic olefin metathesis which involved

a metal alkylidene species undergoing a 2+2 cycloaddition with an olefin to afford a

metallocyclobutane which could undergo constructive or non-constructive olefin and alkylidene

formation (Scheme 1.2.6).35

As the field of olefin metathesis grew, a number of other

mechanisms were proposed. Through labeling experiments and analyzing the distribution of

metathesis products the Chauvin mechanism gained support and is now the accepted mechanism

for olefin metathesis.16-17

Scheme 1.2.6. Chauvin Mechanism of Olefin Metathesis

More specifically, with a Grubbs type catalyst there are additional considerations that play a role

in the catalytic cycle. Based on kinetic data, it was determined that the five-coordinate ruthenium

species must undergo phosphine dissociation to give a four-coordinate active species (Scheme

1.2.7).36-38

This information was used in the rational design of 2nd

Generation Grubbs as well as a

number of other derivatives, some of which are discussed in 1.2.4. This four-coordinate species

could proceed in the mechanism by two different routes. One possibility is the incoming olefin

could coordinate trans to the phosphine. The second possibility is a ligand rearrangement around

the ruthenium centre and coordination cis to the phosphine. This coordination mode would

influence how the metallocyclobutane forms on the metal. In the case of Grubbs Catalyst it has

been determined that coordination trans to the phosphine is the favored pathway.39

An example

of when this distinction becomes important will be discussed in 1.2.5.

6

Scheme 1.2.7. Olefin Metathesis Mechanism with 1st Gen. Grubbs Catalyst

1.2.4 Variations of Grubbs Catalyst

The field of Ru based olefin metathesis catalysts has exploded since the report of Grubbs

catalyst. A number of variations have been made on these systems in an attempt to increase

activity and tailor them for specific applications.8-9, 31

This topic will be discussed in more detail

in 3.1 however, some systems are of significant importance and will be highlighted here. Based

on the accepted mechanism of olefin metathesis by a Grubbs type complex, the Hoveyda group

developed a catalyst which takes advantage of the initiation step and eliminates the phosphine

coordination-dissociation equilibrium that influences the amount of four-coordinate, active

species in the reaction mixture.40-41

The PCy3 present in 2nd

Generation Grubbs Catalyst is

replaced with a chelating ether group bound to the alkylidene fragment (Figure 1.2.3). After one

turn-over of the catalytic cycle, a new four-coordinate alkylidene complex is formed without this

chelate and this active species can enter the catalytic cycle again and an olefin can coordinate

without competitive coordination from a phosphine. Removing this competition creates an

increase in catalytic activity as seen by the ability for this Hoveyda-Grubbs Catalyst to perform

olefin metathesis on tetrasubstituted olefins.

7

Figure 1.2.3. Hoveyda-Grubbs Catalyst

A unique and more recent example of modification to the Grubbs framework came from the

Piers group in 2004.42

They found that protonation of the Ru carbide 1-4 with Jutzi's acid led to

the formation of the phosphonium alkylidene 1-5 (Scheme 1.2.8). These 14e- phosphonium

alkylidene complexes were found to be rapidly initiating olefin metathesis catalysts.43

Scheme 1.2.8. Synthesis of a Ruthenium Phosphonium Alkylidene Complex

1.2.5 Z-selective Olefin Metathesis

The product olefin from catalytic olefin metathesis can have one of two configurations. The E

isomer is the thermodynamically preferred product since the E configuration is more stable than

the Z configuration. A number of natural products and target pharmaceutical compounds contain

Z alkenes and therefore a catalyst that favors this configuration over the E would be desirable.

The use of bulky enantiopure ligands on transition metal catalysts to influence the selectivity of

catalysis has been exploited in a variety of transformations.44

This is the strategy employed by

the collaborative efforts of the Hoveyda and Schrock groups in olefin metathesis. By

incorporating large aryloxy ligands to the Schrock catalyst framework (Figure 1.2.4), they have

been able to produce catalysts with high Z-selectivities with up to 98% of the product being the Z

isomer.45-46

These monoaryloxide-pyrrolide (MAP) catalysts have been used in the total

synthesis of natural products.47

8

Figure 1.2.4. Examples of Schrock Catalyst Based Z-selective Olefin Metathesis Catalysts

Recently, there have also been reports of Z-selective Ru based olefin metathesis catalysts from

the Grubbs group.48-50

Their strategy uses a chelating NHC and a chelating anion. One of the

substituents on the NHC has been C-H activated and the anionic carbon is bound to Ru. The

other anionic ligands used are either a carboxylate or nitrate anion (Fig. 1.2.5). The Z-selectivity

comes from the chelating anion occupying the coordination site trans to the NHC carbon during

the catalytic cycle. This forces the incoming olefin to bind cis to the NHC which is itself also

locked in place by the chelate. The metallocyclobutane intermediate is formed in a side on

fashion which allows the Mes group on the NHC to influence the configuration. The substituents

on the metallocyclobutane are forced to point away from the Mes group and the resulting olefin

that is produced adopts a Z configuration.51

Figure 1.2.5. Ru-based Z-Selective Olefin Metathesis Catalyst

9

1.3 Lewis Acid Activation of Catalysts

The activation of transition metal catalysts with a Lewis acid has been exploited extensively in

the field of olefin polymerization.4 Specifically with metallocene catalysts for ethylene

polymerization, Lewis acids such as trimethylaluminum (TMA) are used to alkylate the complex

and abstract an anionic ligand to open up a coordination site and form a cationic metal complex

with a vacant coordination site where an olefin can bind and insert to start the polymerization

process (Scheme 1.3.1).

Scheme 1.3.1. Activation of an Ethylene Polymerization Catalyst with TMA.

Alternatively the alkylation and activation can be performed in discrete steps. This allows control

over the Lewis acid used for the alkyl-abstraction and therefore control over the resulting anion.

In many cases the Lewis acid used for the activation has a dramatic effect on the catalytic

activity of the system.52-53

1.4 Nitrile Butadiene Rubber

A specific industrial use of catalytic olefin metathesis is for the modification of nitrile butadiene

rubber (NBR). NBR is a co-polymer of butadiene and acrylonitrile. It is polymerized on an

industrial scale by anionic, emulsion polymerization.54

The resulting polymer contains cis- and

trans- alkene functionalities, vinyl groups, and nitrile groups (Figure 1.4.1). It's these nitrile

groups which give NBR many of its useful properties. NBR is stable in oils, fats and fuels, has

low permeability and high temperature resistance.55

It is used in a number of machine parts and

belts, for automotive tubing, and in the soles of running shoes.

10

Figure 1.4.1 Depiction of Functional Groups Found in Nitrile Butadiene Rubber

Modifications to crude NBR can give polymers with properties tailored for specific applications.

Such modifications include performing cross metathesis with 1-hexene and the C=C double

bonds of NBR.56-57

This decreases the molecular weight and narrows the polydispersity.

Following this olefin metathesis step, hydrogenation of the residual double bonds can be carried

out creating HNBR (Figure 1.4.2).55, 58

The resulting polymer is still extremely resistant to oils

and fuels, has better thermal stability than NBR, and is resistant to ozone and oxidative aging.

This high strength polymer has numerous oilfield and automotive applications.

Figure 1.4.1 Depiction of Hydrogenated Nitrile Butadiene Rubber with Functional Groups

Highlighted

11

1.5 Lanxess Project

Lanxess is a multinational specialty chemicals and polymers company. At the date of this thesis,

they are the world's largest manufacturer of NBR and HNBR. To accomplish the modifications

to NBR described in 1.4, 2nd

Generation Grubbs Catalyst is used for cross metathesis and

Wilkinson's Catalyst is used for hydrogenation. Both processes have considerable costs

associated with them. Wilkinson's catalyst is based on the precious metal Rh which is very

expensive. A system using a cheaper technology would be advantageous and economically

beneficial to Lanxess. The use of Grubbs Catalyst requires the licensing of this technology. This

also adds cost to the process. Ideally Lanxess would like their own technology to perform olefin

metathesis of NBR.

The work presented herein was sponsored by Lanxess. The goals of the project are twofold.

1) The development of new hydrogenation catalysts based on less expensive metals that are

effective for the hydrogenation of NBR; and 2) the development of new olefin metathesis

catalysts that are novel from any current patent literature and effective at performing cross

metathesis of 1-hexene and NBR. The majority of this thesis will focus on the development of

novel olefin metathesis catalysts. The current patent literature is extensive and covers a broad

range of catalysts. There is however, a large gap when it comes to complexes with tridentate

ligands.

1.6 Scope of this Thesis

The goal of this thesis was to develop proprietary olefin metathesis catalysts that could affect the

cross metathesis of NBR and 1-hexene. Recognizing the gap in the patent literature covering

tridentate ligands for olefin metathesis catalysts, an effort was made to explore their use for the

development of novel catalysts. In Chapter 2, the coordination chemistry of tridentate dithiolate

ligands on ruthenium is explored. In some cases the coordination chemistry of these types of

ligands proves to be more difficult than originally thought. The reactivity of the successfully

prepared compounds with BCl3 is also explored in an effort to determine if Lewis acid activation

of olefin metathesis catalysts with these ligands is a viable option.

In Chapter 3, the coordination chemistry of tridentate dianionic ligands on ruthenium alkylidene

species is described. The motivation was to easily prepare new ruthenium alkylidene species

12

from Grubbs catalyst as a convenient route to probe the reactivity and catalytic activity of these

species. This proved to be more successful than the coordination chemistry in Chapter 2. A

library of complexes was prepared with tridentate ligand variations to the anionic donors, central

neutral donor and the ligand backbone.

Chapter 4 describes the synthesis of ruthenium alkylidenes from Ru(0) sources and dithioacetals.

This newly developed method provides a synthetic route to some of the complexes described in

Chapter 3, however, this synthetic strategy is independent of any prior patent literature. An

independent route to these species was required in order to patent these new complexes and

provide Lanxess with the freedom to use these catalysts in their industrial processes.

The reactivity and activation of the ruthenium alkylidene species described in Chapters 3 and 4

with the Lewis acid BCl3 is explored in Chapter 5. The addition of one equivalent of BCl3

resulted in a ligand rearrangement and the formation of a 6-coordinate Ru centre. A second

equivalent of BCl3 resulted in the formation of a 5-coordinate, cationic Ru species via halide

abstraction.

Finally, in Chapter 6 the complexes synthesized in the previous chapters were tested for catalytic

olefin metathesis. They were tested for a variety of reactions including ring closing metathesis

(RCM), ring opening metathesis polymerization (ROMP), cross metathesis (CM) and the

metathesis of NBR and 1-hexene which was the ultimate goal of this thesis.

The work described herein was completed solely by the author with the exception of elemental

analysis which was completed in house by departmental staff.

Portions of each chapter that are published at the time of writing:

Chapter 3: McKinty, A. M., Lund, C., Stephan, D. W., "A Tridentate-Dithiolate Ruthenium

Alkylidene Complex: An Olefin Metathesis Catalyst Activated by BCl3" Organometallics, 2013,

32, 4730-4732.

Chapter 4: McKinty, A. M., Stephan, D. W., "A Facile Route to Ru-Alkylidenes" Dalton

Transactions, 2014, 43, 2710-2712.

13



32, 4730-4732.



32, 4730-4732.

14

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Schrock, R. R., Journal of Organometallic Chemistry 1993, 459 (1–2), 185-198.

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28. Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H., Angewandte Chemie

International Edition 1995, 34 (18), 2039-2041.

29. Trnka, T. M.; Grubbs, R. H., Accounts of Chemical Research 2000, 34 (1), 18-29.

30. Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H., Organic Letters 1999, 1 (6), 953-956.

31. Vougioukalakis, G. C.; Grubbs, R. H., Chemical Reviews 2009, 110 (3), 1746-1787.

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37. Sanford, M. S.; Love, J. A.; Grubbs, R. H., Journal of the American Chemical Society

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38. Sanford, M. S.; Ulman, M.; Grubbs, R. H., Journal of the American Chemical Society

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39. Tallarico, J. A.; Bonitatebus, P. J.; Snapper, M. L., Journal of the American Chemical

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43. Romero, P. E.; Piers, W. E., Journal of the American Chemical Society 2005, 127 (14),

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46. Jiang, A. J.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H., Journal of the American


47. Meek, S. J.; O'Brien, R. V.; Llaveria, J.; Schrock, R. R.; Hoveyda, A. H., Nature 2011,

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48. Endo, K.; Grubbs, R. H., Journal of the American Chemical Society 2011, 133 (22),

8525-8527.

49. Keitz, B. K.; Endo, K.; Herbert, M. B.; Grubbs, R. H., Journal of the American Chemical

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50. Keitz, B. K.; Endo, K.; Patel, P. R.; Herbert, M. B.; Grubbs, R. H., Journal of the


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54. Kaiser, A.; Brandau, S.; Klimpel, M.; Barner-Kowollik, C., Macromolecular rapid

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18

Chapter 2 Coordination Chemistry of Tridentate, Dithiolate Ligands

2.1 Introduction

2.1.1 Thiolate Ligands in Metal Complexes

Sulfur containing compounds are typically thought to be catalyst poisons which inhibit catalysis

and either slow it down or stop it completely.1-5

However, nature utilizes sulfur as a ligand in the

transition metal containing hydrogenase enzymes (Figure 2.1.1).6-9

These enzymes perform the

reversible oxidation of H2 in microorganisms.

Figure 2.1.1. The Active Sites of Hydrogenase Enzymes Containing Metal Thiolate

Structures

Thiolates have been used as ligands on transition metals across the periodic table for making

interesting complexes and to develop catalysts. In the 1990's the Stephan group explored their

chemistry on group 4 metals for the synthesis of piano stool complexes.10-12

They examined

bidentate, tridentate and tetradentate dithiolate ligands and their coordination chemistry around

Ti.13-14

They observed a number of monomeric and dimeric structures (Figure 2.1.2). They also

found that the coordinated thiolates were able to form bridged structures with other transition

metals (Figure 2.1.3). They exploited the bridging capabilities of the thiolate ligands to form

titanium hydride complexes with a B-S-Ti moiety when these complexes were reacted with

NaBH4 (Scheme 2.1.1).15

19

Figure 2.1.2. Titanium Thiolate Complexes

Figure 2.1.3. Multimetallic Titanium Thiolate Complexes

Scheme 2.1.1. Synthesis of a Bridged Titanium Thiolate Borane Complex

The examples of nature's hydrogenase enzymes and the work by Stephan and co-workers

demonstrates that thiolate ligands often form bimetallic species or bridged species with other

Lewis acids. Indeed, this is the case with a variety of examples from the literature. Nishibashi

and co-workers have developed a library of thiolate bridged bimetallic species that are

catalytically active for alkylation16-18

, cycloaddition19

, substitution20-21

and reduction22-23

of

20

propargylic alcohols (Figure 2.1.4). These catalytically active complexes are bimetallic

ruthenium and iron species bridged through two thiolate ligands.

Figure 2.1.4. Thiolate Bridged Bimetallic Complexes for Propargylic Alcohol Catalysis

When monometallic thiolate complexes can be synthesized, the thiolate ligand can act in a

non-innocent fashion where the thiolate functionality participates in bond activation with the

metal centre. Oestreich and co-workers have exploited this capability to catalytically activate C-

F bonds24

, generate borenium species25

, perform dehydrogenative C-H - silane coupling26-27

and

hydrosilyation.28

They used a tethered ruthenium thiolate species developed by Tatsumi and co-

workers who used this complex for dihydrogen activation (Figure 2.1.5).29

The activation of the

substrate occurs between the metal centre and the coordinated thiolate. The XH bond is cleaved

as H binds to the metal centre and X binds to the thiolate.

Figure 2.1.5. Tethered Ruthenium Thiolate Complex

Complexes of the first row transition metals with thiolate ligands bridging the metal centre and a

BH2 fragment were prepared in 1990.30

The proposed structures for Fe(III) and Cr(III) have three

21

bidentate borate ligands in the coordination sphere (Figure 2.1.6). Each ligand has two sulfur

donors bridged between a BH2 fragment. The Cu(II) complex is square planer with two bidentate

ligands coordinated. In these examples the bidentate borate ligands were prepared prior to

coordination to the metal centre.

Figure 2.1.6. Thiolate Complexes with Bridging BH2 Fragments

In 2004 Hille and co-workers reported two ruthenium complexes bearing tetradentate dithiolate

ligands.31

These complexes were shown to bind N2, H2 and BH3. Binding of N2 and H2 occur

exclusively at the metal centre. However, when BH3 was added to the complex the thiolate

ligand behaved non-innocently (Figure 2.1.7). The thiolate coordinated to boron and a hydride on

BH3 coordinated the ruthenium. They propose the coordination of the hydride to ruthenium

occurs first followed by the thiolate coordinating to boron to create the bridged species

(Scheme 2.1.2).

Figure 2.1.7. Thiolate Bridged Ruthenium BH3 Complex

22

Scheme 2.1.2. Mechanism of BH3 Addition to a Ruthenium Thiolate Complex

2.2 Results and Discussion

2.2.1 Synthesis of Ru Complexes

The deprotonation of the commercially available dithiols (HSCH2CH2)2O and (HSCH2CH2)2S

with two equivalents of n-BuLi provided the corresponding dilithiated dithiolate salts. These

salts were used to accomplish salt metathesis reactions with transition metals to provide a

convenient, straight forward method for the synthesis of new complexes bearing tridentate,

dithiolate ligands.

Mixing (LiSCH2CH2)2O with Ru(PPh3)3Cl2 in THF overnight at room temperature resulted in a

brown solution. After removing the solvent, the brown residue was dissolved in toluene and

filtered to remove the LiCl. Washing the isolated brown product with hexanes to remove PPh3

led to the isolation of 2-1 as a brown solid (Scheme 2.2.1). The 31

P{1H} NMR spectrum displays

a new chemical shift at 71.9 ppm. The 1H NMR spectrum has two triplets at 3.61 and 2.07 ppm

(3JHH = 5.54 Hz) suggesting symmetry of the ligand backbone. The only other signals in the

1H NMR spectrum are from the PPh3 protons which have a relative integration of 30:4:4 to the

ligand signals. Based on this and the one signal in the 31

P{1H} NMR there must be two

equivalent PPh3. Alternatively, mixing the dithiol (HSCH2CH2)2O with Ru(PPh3)4H2 in benzene

resulted in the formation of bubbles and a red-brown precipitate (Scheme 2.2.2). The spectral

parameters of this product match those of 2-1 demonstrating an alternative less laborious route to

these types of compounds.

23

Scheme 2.2.1. Synthesis of 2-1 From Ru(PPh3)3Cl2

Scheme 2.2.2. Synthesis of 2-1 From Ru(PPh3)4H2

Following similar procedures to the synthesis of 2-1, mixing the dithiol (HSCH2CH2)2S with

Ru(PPh3)4H2 resulted in H2 bubbling out of solution as a brown precipitate formed. A brown

solid was also collected from the reaction of (LiSCH2CH2)2S with Ru(PPh3)3Cl2 however in both

cases the collected solid was an intractable mixture of products which could not be identified by

NMR studies (Scheme 2.2.3).

Scheme 2.2.3. Attempted Synthesis of a Thioether Dithiolate Ru Complex

The influence of the central donor was further investigated by synthesizing a dithiolate ligand

with a central phosphine donor. The synthesis of (LiSCH2CH2)PPh was accomplished following

24

the procedure described by Escriche and co-workers.32

The nucleophilic ring opening of ethylene

sulfide by lithiated H2PPh provided half the ligand framework as LiSCH2CH2PHPh. Subsequent

lithiation followed by ring opening of a second equivalent of ethylene sulfide gave the dithiolate

ligand as a white solid (Scheme 2.2.4).

Scheme 2.2.4. Synthesis of Phosphine Containing Ligand 2-2

In an analogous fashion to the preparation of 2-1 the dithiolate ligand 2-3 was reacted with

Ru(PPh3)3Cl2 in THF overnight. Similar to the reaction with (LiSCH2CH2)2S the reaction of 2-2

with Ru(PPh3)3Cl2 results in the formation of an intractable mixture of unidentifiable products

(Scheme 2.2.5).

Scheme 2.2.5. Attempted Synthesis of a Phosphino Dithiolate Ru Complex

To investigate the influence of a more rigid and electron withdrawing ligand backbone, the aryl

analogue of diethylene glycol dithiol was prepared. (HSC6H4)2O (2-5) was prepared following

literature procedures (Scheme 2.2.5).33

Starting from diphenylether, dilithiation was

accomplished with n-BuLi in the presence of TMEDA. Elemental sulfur was added to the

dilithiated salt followed by the addition of LiAlH4 and refluxed. An acidic work up with HCl

resulted in formation of the dithiol as a pale yellow oil.

25

Scheme 2.2.6. Synthesis of Dithiol Proligand 2-3

Following an analogous procedure used to prepare 2-1, from Ru(PPh3)4H2 in benzene, when 2-3

was mixed with Ru(PPh3)4H2 bubbles evolved as 2-4 was formed. The 31

P{1H} NMR spectrum

displays a single shift at 72.1 ppm suggesting molecular symmetry and the 1H and

13C{

1H} NMR

spectra support the formulation of 2-4 as Ru(PPh3)2[(SC6H4)2O] (Scheme 2.2.6).


2.2.2 Reactivity of Complexes with BCl3

Interestingly, when 1 equivalent of BCl3 was added to a CH2Cl2 solution of 2-1, a color change

from brown to dark green was observed as 2-5 was formed (Scheme 2.2.8). The 31

P{1H} NMR

spectrum of the crude reaction mixture showed complete conversion to a single product with 2

unique phosphorus environments displaying doublets at 47.8 and 31.1 ppm (Figure 2.2.1). The

pair of doublets have a coupling constant of 37.3 Hz indicative of a cis phosphine geometry. The

11B NMR spectrum displays a sharp singlet at 12.0 ppm which suggests the presence of a

4-coordinate boron centre. The ligand backbone protons in the 1H NMR spectrum appear as 8

multiplets suggesting the loss of symmetry (Figure 2.2.1). The remaining signals in the aromatic

region are attributed to the phenyl rings of the two PPh3 ligands. These data support the

formulation of 2-5 as (PPh3)2RuCl[O(CH2CH2S)2BCl2] where a chloride has been transferred

from boron to ruthenium and the remaining BCl2 fragment is bridging the thiolate ligands. It is

26

this bridging of the thiolates and the 6-coordinate ruthenium centre which forces the PPh3 to

adopt a cis geometry. Similar reactivity with related compounds and structural evidence is

discussed in Section 5.2.1.


Figure 2.2.1. 31

P{1H} NMR Spectrum (top) and Ligand Backbone Region of

1H NMR

Spectrum (bottom) of 2-5

27

In an analogous fashion, when BCl3 was added to a solution of 2-4 the CH2Cl2 mixture

instantaneously changed from brown to dark green as 2-6 was formed (Scheme 2.2.9). The

31P{

1H} NMR spectrum is similar to that of 2-5 displaying two doublets. Compared to 2-5 the

peaks in the 31

P{1H} NMR spectrum are shifted slightly downfield and resonate at 52.5 and

33.2 ppm with a coupling constant of 36.1 Hz indicative of cis phosphines. The 11

B NMR

spectrum displays a sharp singlet at 12.9 ppm suggesting a four-coordinate boron centre. The 1H

NMR spectrum displays multiplets in the aromatic region assigned to the ligand backbone

protons and the PPh3 ligands. This data supports the formulation of 2-6 as

(PPh3)2RuCl[O(C6H4S)2BCl2] which is analogous to 2-5.


2.3 Conclusion

Two ruthenium complexes bearing tridentate dithiolate-ether ligands were prepared by two

different methods. Attempts to synthesize the analogous thioether and phosphino complexes

were unsuccessful. Based on NMR spectroscopy, the successfully prepared complexes contained

equivalent phosphines and a plane of symmetry. Upon the addition of BCl3 to these complexes

the thiolate ligands became bridged between the ruthenium centre and boron. A chloride was

transferred from the BCl3 to ruthenium and the BCl2 fragment bridged the two thiolates. The

NMR data of these 6-coordinate species suggests a loss in symmetry with two inequivalent

cis-phosphines and inequivalent ligand backbone protons. This reactivity with boranes and the

complexes obtained are similar to the examples presented in the introduction.

28

2.4 Experimental Section

2.4.1 General Considerations

All manipulations were carried out under an atmosphere of dry, O2-free N2 employing a Vac

Atmospheres glove box and a Schlenk vacuum-line. Solvents were purified with a Grubbs-type

column system manufactured by Innovative Technology and dispensed into thick-walled Schlenk

glass flasks equipped with Teflon-valve stopcocks. All solvents were thoroughly degassed after

purification (repeated freeze-pump-thaw cycles). CD2Cl2 was dried over CaH2 and vacuum

transferred into a Schlenk flask equipped with a Teflon-valve stopcock. 1H,

13C, and

31P NMR

spectra were recorded at 25 °C on Varian 300 and 400 MHz and Bruker 400 MHz spectrometers.

Chemical shifts are given relative to SiMe4 and referenced to the residual solvent signal (1H,

13C)

or relative to an external standard (31

P: 85% H3PO4). Chemical shifts are reported in ppm and

coupling constants as scalar values in Hz. Combustion analyses were performed in house

employing a Perkin-Elmer CHN Analyzer. All chemicals were obtained from Aldrich and used

as received unless stated. Pro-ligands were synthesized by the addition of two equivalents of

n-BuLi or KOtBu to the corresponding dithiol. (LiSCH2CH2)2PPh and (HSC6H4)O were prepared

according to literature procedures.32-33

2.4.2 Synthetic Procedures

Synthesis of 2-1: Ru(PPh3)3Cl2 (0.200 g, 0.209 mmol) was dissolved in 5 mL of THF. To this, a

THF solution (10 mL) of (LiSCH2CH2)O (37.6 mg, 0.250 mmol) was added. The solution was

stirred at room temperature overnight. The solvent was removed in vacuo and the resulting

brown solid was dissolved in CH2Cl2 (5 mL) and quickly filtered through celite. Pentane (15 mL)

was added to the solution to precipitate the brown product which was isolated by vacuum

filtration and washed with pentane (2 x 5 mL). 2-1 was isolated in 89% yield (0.142 g,

0.186 mmol).

Alternative synthesis of 2-1: Ru(PPh3)4H2 (0.200 g, 0.225 mmol) was dissolved in 10 mL of

benzene. (HSCH2CH2)2O (31 µL, 0.247 mmol) was added dropwise as bubbles of H2 evolved.

After the full addition of the dithiol, the reaction was stirred for 30 min. Pentane (10 mL) was

added to the mixture to fully precipitate the product which was collected by vacuum filtration

and washed with pentane (2 x 5 mL). The product was isolated as a brown solid in 93% yield

29

(0.159 g, 0.209 mmol). 1H NMR (CD2Cl2): 7.22 (br, 12H, PPh), 7.16 (t, 6H, PPh), 7.01 (t, 12H,

PPh), 3.61 (t, 4H, CH2), 2.08 (t, 4H, CH2). 13

C{1H} NMR (CD2Cl2): 134.2 (t, PPh), 133.6 (d,

PPh), 128.9 (s, PPh), 128.7 (s, PPh), 128.4 (d, PPh), 128.3 (s, PPh), 127.0 (t, PPh), 81.3 (s, CH2),

31.6 (s, CH2). 31

P{1H} NMR (CD2Cl2): 71.9. Analysis calculated for C40H38OP2RuS2: C, 63.06;

H, 5.03. Found: C, 62.63; H, 4.88.

Synthesis of 2-4: Ru(PPh3)4H2 (0.200 g, 0.225 mmol) was dissolved in 10 mL of benzene. 2-3

(58 mg, 0.247 mmol) was added dropwise as bubbles of H2 evolved. After the full addition of the

dithiol, the reaction was stirred for 30 min. Pentane (10 mL) was added to the mixture to fully

precipitate the product which was collected by vacuum filtration and washed with pentane (2 x 5

mL). The product was isolated as a light green solid in 88% yield (170 g, 0.198 mmol). 1H NMR

(CD2Cl2): 7.68, (m, 1H, (-SC6H4)2O), 7.59, (m, 1H, (

-SC6H4)2O), 7.51 (m, 1H, (

-SC6H4)2O), 7.37

(br, 6H, PPh), 7.25 (t, 12H, PPh), 7.10 (br, 12H, PPh), 6.87 (m, 1H, (-SC6H4)2O), 6.83 (m, 1H,

(-SC6H4)2O), 6.77 (m, 1H, (

-SC6H4)2O), 6.68 (m, 1H, (

-SC6H4)2O), 5.57 (m, 1H, (

-SC6H4)2O).

13C{

1H} NMR (CD2Cl2): 154.9 (Ph), 152.1 (Ph), 149.3 (Ph), 141.2 (Ph), 134.1 (PPh3), 133.7

(PPh3), 131.9 (PPh3), 131.8 (PPh3), 130.2 (PPh3), 129.4 (PPh3), 128.5 (PPh3), 127.5 (PPh3),

127.4 (PPh3), 126.6 (PPh3), 124.4 (PPh3), 124.2 (Ph), 123.5 (Ph), 123.1 (Ph), 120.6 (Ph), 119.2

(Ph), 118.5 (Ph), 118.4 (Ph), 115.2 (Ph). 31

P{1H} NMR (CD2Cl2): 72.1. Analysis calculated for

C40H38BCl3OP2RuS2: C, 54.65; H, 4.36. Found: C, 54.16; H, 3.98.

Synthesis of 2-5: To a CH2Cl2 solution of 2-1 (50 mg, 0.066 mmol) was added a hexanes

solution of BCl3 (1M, 66 µL, 0.066 mmol). The reaction mixture immediately turned from

brown to dark green. The solvent was removed in vacuo and the resulting green solid was

washed with 5 mL of hexanes and dried in vacuo to give 2-5 as a dark green solid in 94% yield

(54 mg, 0.061 mmol). 1H NMR (CD2Cl2): 7.59 (m, 6H, PPh), 7.45 (m, 7H, PPh), 7.34 (m, 4H,

PPh), 7.26 (m, 3H, PPh), 7.19 (m, 5H, PPh), 7.12 (m, 5H, PPh), 5.26 (m, 1H, CH2), 3.51 (m, 1H,

CH2), 3.27 (m, 1H, CH2), 2.94 (m, 1H, CH2), 2.61 (m, 1H, CH2), 2.57 (m, 1H, CH2), 2.26 (m,

1H, CH2). 13

C{1H} NMR (CD2Cl2): 136.8 (d,

1JPC = 48.1 Hz, PPh3), 135.3 (d,

1JPC = 38.5 Hz,

PPh3), 135.0 (d, 3JPC = 9.5 Hz, PPh3), 134.6 (d,

3JPC = 9.0 Hz, PPh3), 129.3 (d,

4JPC = 2.2 Hz,

PPh3), 128.8 (d, 4JPC = 1.9 Hz, PPh3), 127.4 (d,

2JPC = 9.1 Hz, PPh3), 126.8 (d,

2JPC = 10.1 Hz,

PPh3), 71.6 (CH2), 69.3 (CH2), 34.5 (CH2), 28.2 (CH2). 31

P{1H} NMR (CD2Cl2): 47.8 (d,

2JPP =

30

37.3 Hz, PPh3) 31.1 (d, 2JPP = 37.3 Hz, PPh3).

11B NMR (CD2Cl2): 12.0. Analysis calculated for

C48H38OP2RuS2: C, 67.20; H, 4.46. Found: C, 66.77; H, 4.31.

Synthesis of 2-6: To a CH2Cl2 solution of 2-4 (50 mg, 0.058 mmol) was added a hexanes

solution of BCl3 (1M, 58 µL, 0.058 mmol). The reaction mixture immediately turned from

brown to dark green. The solvent was removed in vacuo and the resulting green solid was

washed with 5 mL of hexanes and dried in vacuo to give 2-6 as a dark green solid in 90% yield

(51 mg, 0.052 mmol). 1H NMR (CD2Cl2): 7.84 (m, 1H, Ph), 7.60 (m, 6H, PPh3), 7.53 (m, 2H,

Ph), 7.41 (m, 2H, Ph), 7.24 (m, 12H, PPh3), 7.15 (m, 6H, PPh3), 7.06 (m, 6H, PPh3), 6.84 (m,

2H, Ph), 6.63 (m, 1H, Ph). 13

C{1H} NMR (CD2Cl2): 162.8 (Ph), 162.6 (Ph), 135.8 (d,

1JPC = 48.9

Hz, PPh3), 135.0 (d, 3JPC = 9.3 Hz, PPh3), 134.5 (Ph), 134.2 (d,

3JPC = 9.2 Hz, PPh3), 134.1 (Ph),

133.6 (Ph), 133.5 (Ph), 132.8 (Ph), 129.8 (Ph), 128.7 (Ph), 129.3 (Ph), 129.2 (d, 4JPC = 2.3 Hz,

PPh3), 129.0 (d, 4JPC = 2.3 Hz, PPh3), 127.3 (d,

2JPC = 9.2 Hz, PPh3), 127.0 (d,

2JPC = 9.9 Hz,

PPh3), 126.6 (Ph), 125.9 (Ph). 31

P{1H} NMR (CD2Cl2): 52.5 (d,

2JPP = 36.2 Hz, PPh3) 33.2 (d,

2JPP = 36.1 Hz, PPh3).

11B NMR (CD2Cl2): 12.9. Analysis calculated for C48H38BCl3OP2RuS2: C,

59.12; H, 3.93. Found: C, 58.43; H, 3.76.

31


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33

Chapter 3 Ruthenium Alkylidene Complexes with Tridentate, Dianionic

Ligands

3.1 Introduction

3.1.1 Modifications to Grubbs Catalyst

The discovery of well-defined ruthenium alkylidene complexes, specifically Grubbs catalyst, and

their ability to catalyze olefin metathesis has led to the development of a number of variations to

the Grubbs architecture being investigated.1 Based on the accepted mechanism of ruthenium

catalyzed olefin metathesis, the only essential ligand on the metal center is the alkylidene.2-4

This

leaves all other ligands including the anionic ligands (X), both neutral ligands (L) and even the

substituents on the alkylidene open for modification to adjust steric and electronic properties in

an attempt to increase catalyst activity, lifetime, stability and selectivity (Figure. 3.1.1). There's

also the possibility of introducing a sixth ligand to the coordination sphere and/or using chelating

ligands. A small sample of modified catalysts was discussed in 1.2.4. The replacement of PCy3

in 1st Generation Grubbs catalyst with SIMes in 2

nd Generation Grubbs catalyst led to increased

activity and stability.5 In an attempt to further increase these features, over 400 complexes

containing different NHC ligands have been prepared.6 A summary of generalized structures is

depicted in Figure 3.1.2.

Figure 3.1.1. Generalized Structure of a Ruthenium Alkylidene Complex used for Catalytic

Olefin Metathesis

34

Figure 3.1.2. Generalized structures of NHCs Used as Ligands for Ruthenium Olefin

Metathesis Catalysts

The modifications to the NHC have led to the synthesis of catalysts with increased activity for

specific applications and specific catalyst properties such as aqueous7-8

and asymmetric9-11

catalysis. However, the 2nd

Generation Grubbs Catalyst or Hoveyda-Grubbs Catalyst provide

reasonable activity and stability for most olefin metathesis applications and thus remain the most

popular catalysts in the ruthenium based family.5-6, 12

Modifications to the NHC in Grubbs

Catalyst has received an enormous amount of attention and by comparison the modification to

the anions of the complex has received very little.

3.1.2 Halide Variations in Grubbs Catalyst

To investigate the effect of exchanging the chloride ligands in Grubbs Catalysts for other halides

on catalytic activity, Grubbs and coworkers prepared [(PCy3)2RuX2(CHPh)] and

[SIMes(PCy3)RuX2(CHPh)] where X=Cl, Br, I.2 When X=I, initiation of catalysis occurs much

faster followed by X=Br and X=Cl. This is due to steric effects with the size of the halide

influencing the dissociation of the phosphine ligand. However, the activity of the catalysts

decreases in the order Cl>Br>I. This is due again to the size of the halide preventing the

coordination of the incoming olefin.

35

3.1.3 Pseudo-halides as Ligands on Ruthenium Metathesis Catalysts

Halides are not the only anionic ligands which have been used on ruthenium-based olefin

metathesis catalysts. A number of other X-type ligands have been investigated such as

alkoxides,13

aryloxides,14-18

carboxylates,19-21

and more recently, thiolates22-23

and nitrates.24

Grubbs and coworkers have prepared [(PCy3)Ru(OtBu)2(CHPh)] by simple salt metathesis with

KOtBu and [(PCy3)2RuCl2(CHPh)].

13 This compound is four-coordinate due to the ability of the

alkoxides to act as XL-type ligands and donate three electrons to the ruthenium centre. Even

though these complexes are 4-coordinate, they display low activity for olefin metathesis even at

elevated temperatures. Fogg and coworkers have successfully overcome this deleterious effect

using electron deficient, perfluorinated aryloxides as ligands (Figure 3.1.3).14-15

These catalysts

were showed to be active for ring closing metathesis.

Figure 3.1.3. Electron Deficient Aryloxides as Ligands on Olefin Metathesis Catalysts

More recently, Jensen and coworkers have prepared an olefin metathesis catalyst with a bulky

arylthiolate ligand (Figure 3.1.4).23

The large aryl group on the thiolate induces Z-selectivity on

the product olefin with up to 96% selectivity.

Figure 3.1.4. Z-selective Olefin Metathesis Catalyst with a Thiolate Ligand

36

3.1.4 Bidentate Monoanionic Ligands on Ruthenium Metathesis Catalysts

In the current literature there are a number of examples of bidentate, monoanionic ligands on

ruthenium alkylidene complexes. Grubbs et al. have reported a class of these compounds with

ligands containing a carboxylate donor and a neutral phosphine, ether or amine donor

(Figure 3.1.5).20

These catalysts proved to be active for ring closing metathesis of diethyl

diallymalonate at elevated temperatures. Interestingly, the activity of the catalysts was improved

with the addition of CuCl.

A related ruthenium alkylidene species with a phosphino-carboxylate ligand was reported by He

et al.19

This complex was active for olefin metathesis but again, elevated temperatures were

required. Verpoort has reported the use of an imino-aryloxide ligand on a ruthenium olefin

metathesis catalyst.25

This catalyst displayed high activity for ring opening metathesis

polymerization at 70 ºC. Herrmann et al. have reported a related pyridino-alkoxide ligand on a

ruthenium alkylidene complex.26

This catalyst displays low activity at room temperature but at

elevated temperatures it becomes a moderately active catalyst for ring opening metathesis

polymerization.

Figure 3.1.5. Ruthenium Olefin Metathesis Catalysts with Bidentate Monoanionic Ligands

37

3.1.5 Bidentate Dianionic Ligands on Ruthenium Metathesis Catalysts

Fogg and coworkers have also developed metathesis catalysts containing bidentate aryloxy

ligands.17-18

One variation which has a bidentate, dianionic sulfonato-aryloxide ligand exists as

two isomers (Figure 3.1.6). The mixture of these isomers is active for a limited number of

standard ring closing metathesis tests at elevated temperatures. The elevated temperatures are

required to labilize the pyridine ligand. A related catalyst bearing a catecholate ligand is active

for a wider variety of ring closing metathesis reactions at elevated temperatures.

Figure 3.1.6. Ruthenium Metathesis Catalysts With Bidentate, Dianionic Ligands

More recently, Hoveyda et al. have developed a class of olefin metathesis catalysts with

bidentate, dithiolate ligands.22

The bidentate nature of these catalysts forces monomer

coordination cis to the NHC ligand. This results in high Z-selectivity in ring opening metathesis

polymerization and ring opening cross metathesis reactions.

38

3.1.6 Tridentate Ligands on Ruthenium Alkylidene Complexes

Currently there is a limited number of examples of tridentate ligands on ruthenium alkylidene

complexes. Recently Stephan et al. have reported a ruthenium-O(CH2CH2PCy2)2 alkylidene

complex.27

This coordinatively saturated species is inactive for olefin metathesis. Attempted

activation of this species by halide abstraction with a Lewis acid resulted in the formation of a

ruthenium alkylidyne-hydride complex. Erker et al. have reported a dianionic pincer-type ligand

with amido donors on a ruthenium alkylidene complex (Figure 3.1.7).28

This species is active for

ring closing metathesis of 1,7-octadiene at 80 ºC. Jensen et al. have reported an ONO dianionic

ruthenium alkylidene complex.29

This complex displayed low catalytic activity for ring closing

metathesis at room temperature. At elevated temperatures or with the addition of a proton source

catalytic activity increased.

Figure 3.1.7. Ruthenium Olefin Metathesis Catalysts with Tridentate, Dianionic Ligands


3.2.1 Synthesis of Ruthenium Alkylidene Complexes

To investigate the potential of dianionic, tridentate ligands in olefin metathesis, the complexes

were first prepared from the commercially available 1st and 2

nd Generation Grubbs Catalysts. A

general strategy involves performing a salt metathesis reaction with the dilithiated ligand of

interest to eliminate two equivalents of LiCl and replace a phosphine. This route provided the

target compounds in exceptional yields.

39

The stoichiometric reaction of dithiolate (LiSCH2CH2)2S and (PCy3)2RuCl2(CHPh) gave rise to a

dark brown solution from which a dark brown solid 3-1 was isolated in 99% yield

(Scheme 3.2.1). The 1H NMR spectrum displays a doublet at 13.48 ppm with a

3JPH of 19.3 Hz

attributed to the proton on the alkylidene fragment. The ethylene backbone gives rise to four

signals between 3.41 and 1.93 ppm appearing as multiplets suggesting a plane of symmetry. All

other signals in the 1H NMR spectrum can be assigned to the PCy3 ligand and the phenyl

substituent of the alkylidene. The 13

C{1H} NMR resonance of the alkylidene carbon can be

observed at 235.2 ppm as a doublet with a 2JPC of 14.8 Hz. A resonance in the

31P{

1H} NMR

from the remaining PCy3 can be observed at 41.7 ppm. This data is consistent with the

formulation of 3-1 as (PCy3)Ru(CHPh)(SCH2CH2)2S. This was confirmed via an X-ray

crystallographic study (Figure 3.2.1). The geometry around Ru is best described as a distorted

trigonal bipyramidal. The phosphine and thioether ligands occupy the axial positions of the

distorted trigonal bipyramid. The Ru-P and Ru-S distances are 2.3720(3) and 2.3711(3) Å,

respectively, forming a S-Ru-P angle of 176.285(10)º. The Ru-S(thiolate) distances were found

to be 2.2916(3) and 2.2981(3) Å and the Ru-C bond length was determined to be 1.8639(11) Å.

The S-Ru-C angles are 110.51(3) and 110.97(3)º and the S-Ru-S' angle is 138.172(13)º.

Scheme 3.2.1. Synthesis of 3-1 and 3-2

40

Figure 3.2.1. POV-ray depiction of 3-1; C: black, P: orange, S: yellow, Ru: teal

A similar reaction was performed with (SIMes)(PCy3)RuCl2(CHPh) to give the analogous

complex 3-2 in a 97% yield. The 1H NMR spectrum has a resonance for the alkylidene at

14.41 ppm. All other signals are consistent with the NHC and ligand backbone. The resonance

for the alkylidene carbon appears at 211.18 ppm in the 13

C{1H} NMR. These data along with a

crystallographic study are consistent with a formulation of 3-2 as

(SIMes)Ru(CHPh)(SCH2CH2)2S. The geometry in the molecular structure is similar to that of

3-1 with a distorted trigonal bipyramidal Ru centre (Figure 3.2.2). The thioether and NHC

occupy the axial positions with bonds to ruthenium being 2.380(1) and 2.084(5) Å in length

respectively. The S-Ru-C(NHC) angle was found to be 173.54(13)º. The thiolates and alkylidene

fragments complete the trigonal plane with the Ru-S distances being 2.3126(13) and

2.3356(13) Å and the Ru-C distance being 1.860(5) Å. The S-Ru-C(alkylidene) angles were

found to be 108.91(16) and 111.43(16)º and the S-Ru-S' angle is 138.67(5)º.

41

Figure 3.2.2. POV-ray depiction of 3-2; C: black, N: blue-green, S: yellow, Ru: teal

In an attempt to investigate the effect of the central donor on the reactivity of the complexes,

variants were prepared. Stirring the dithiolate salt (LiSCH2CH2)2PPh in THF with

(PCy3)2RuCl2(CHPh) produced a dark brown solution. The 31

P{1H} NMR of the isolated brown

solid shows two doublets at 114.7 and 28.9 ppm with a 2JPP of 332 Hz suggesting trans-

phosphines. The alkylidene signal in the 1H NMR shifts upfield to 13.3 ppm and appears as a

doublet of doublets due to coupling to both phosphines. The alkylidene carbon gives rise to an

apparent triplet at 239.5 ppm in the 13

C{1H} NMR spectrum with a two bond coupling constant

of 12.57 Hz. All other signals account for the formation of 3-3 as

(PCy3)Ru(CHPh)(SCH2CH2)2PPh (Scheme 3.2.2). The formulation was confirmed via an X-ray

crystallographic study (Figure 3.2.3). The Ru-C distance is 1.873(2) Å. The Ru-PCy3 and

Ru-PPh distances are 2.4462(6) and 2.2869(7) Å respectively in length. The Ru-S bonds are

2.3004(7) and 2.2876(6) Å in length. The P-Ru-P angle is 172.47(2)º and the S-Ru-S angle is

130.94(3)º. The C-Ru-S angles are 119.12(8) and 109.73(8)º. Attempted coordination of this

ligand to (SIMes)(PCy3)RuCl2(CHPh) resulted in an intractable mixture of products with loss of

the alkylidene signal. This decomposition could be due to the extremely electron rich Ru centre

that would arise from coordination of this ligand facilitating undesired reactivity.

42


Figure 3.2.3. POV-ray depiction of 3-3; C: black, P: orange, S: yellow, Ru: teal.

In a similar fashion, compounds 3-4 and 3-5 were prepared from (LiSCH2CH2)2O and

(PCy3)2RuCl2(CHPh) and (SIMes)(PCy3)RuCl2(CHPh) respectively (Scheme 3.2.3). 3-4 was

isolated as a dark brown solid which displays a doublet in the alkylidene region of the 1H NMR

at 13.68 ppm, similar to that of 3-1. The 31

P{1H} NMR of the crude reaction shows free PCy3

and a resonance which had shifted significantly downfield from the starting material at 65.6 ppm.

The 13

C{1H} NMR spectrum shows an alkylidene signal at 207.95 ppm. The similarities between

this data and the chemical shifts of 3-1 led to the conclusion that the formulation of 3-4 is

(PCy3)Ru(CHPh)(SCH2CH2)2O.

43

The 1H NMR spectrum of red 3-5 is characterized by a singlet at 14.85 ppm attributable to the

proton of an alkylidene fragment. The remaining signals in the 1H NMR spectrum are assigned to

the presence of the dithiolate and NHC ligands and the phenyl substituent on the alkylidene. The

13C{

1H} NMR resonance of the alkylidene is observed at 209.98 ppm. Collectively these data

were consistent with the formulation of 3-5 as (SIMes)Ru(CHPh)(SCH2CH2)2O. This was

confirmed via a crystallographic study (Figure 3.2.4). The geometry about the Ru center in 3-5 is

best described as distorted trigonal bipyramidal with the NHC ligand and the central O atom of

the dithiolate ligand occupying the axial positions and the two S atoms and the alkylidene

completing the trigonal plane. The Ru-O and Ru-C(NHC) distances were found to be 2.218(2)

and 2.009(3) Å respectively with a O-Ru-C angle of 168.97(10)º. The alkylidene fragment gives

rise to a Ru-C distance of 1.853(3) Å, while the Ru-S distances were found to be 2.3017(9) and

2.3454(9) Å. The C-Ru-S angles are 110.61(11)º and 98.93(11)º while the S-Ru-S' angle was

determined to be 147.35(4)º. The remaining angles between the axial ligands and those in the

equatorial plane varied from 82.34(6)º to 101.88(9)º. These metric parameters reveal the marked

distortion of trigonal bipyramidal geometry.


44

Figure 3.2.4. POV-ray depiction of 3-5; C: black, N: blue-green, O: red, S: yellow, Ru: teal

In an effort to see the influence of the basicity of the thiolates and the rigidity of the backbone,

(LiSC6H4)2O was used as a ligand on Ru alkylidene complexes. After stirring with

(PCy3)2RuCl2(CHPh) in THF the isolated red solid displays a resonance at 14.7 ppm in the 1H

NMR spectrum from the alkylidene proton. The signal from the PCy3 ligand in the 31

P{1H}

NMR spectrum is shifted downfield from the starting material and appears at 68.6 ppm. In the

13C{

1H} NMR spectrum a resonance from the alkylidene carbon is observed at 192.2 ppm. The

structure of 3-6 was unambiguously determined by X-ray crystallography (Figure 3.2.5). The

geometry around the ruthenium centre is best described as distorted trigonal bipyramidal. The

axial phosphorus and oxygen atoms are located 2.2754(7) and 2.1931(19) Å away from

ruthenium respectively. The P-Ru-O angle is 175.32(6)°. The Ru-S distances in the trigonal

plane are 2.2870(8) and 2.3080(8) Å and the Ru-C distance is 1.848(3) Å. The S-Ru-S' angle is

138.96(3)° and the S-Ru-C angles are 107.70(9) and 110.34(9)°. All other angles range from

80.73(6) to 98.83(3)°.

45

Figure 3.2.5. POV-ray depiction of 3-6; C: black, O: red, P: orange, S: yellow, Ru: teal

The analogous compound 3-7 where PCy3 has been replaced with an NHC was prepared by

using (SIMes)(PCy3)RuCl2(CHPh) as a starting material (Scheme 3.2.4). The isolated red solid

gives rise to an alkylidene signal in the 1H NMR spectrum at 15.6 ppm. The

31P{

1H} NMR

spectrum of the crude reaction mixture shows only the presence of free PCy3. In the 13

C{1H}

NMR spectrum the signal at 209.1 ppm is due to the alkylidene carbon. All other signals can be

attributed to the formulation of 3-7 as (SIMes)Ru(CHPh)(SC6H4)2O.


46

The effect of the anionic donors in these tridentate systems was investigated by substituting the

thiolates for alkoxides. Stirring the related pro-ligand (KOCH2CH2)2O with

(PCy3)2RuCl2(CHPh) resulted in the isolation of the red compound 3-8 in 90% yield. A doublet

which can be assigned to the alkylidene proton is observed in the 1H NMR at 15.72 ppm with a

3JPH of 14.8 Hz. Four multiplets from 4.19 to 2.96 ppm arise from the ethylene linkers in the

backbone of the tridentate ligand. A singlet at 64.8 ppm is observed in the 31

P{1H} NMR and

signal at 192.2 ppm in the 13

C{1H} NMR spectrum is attributed to the carbon of the alkylidene.

From these data, along with an X-ray crystallographic study, the formulation of 3-8 was

determined to be (PCy3)Ru(CHPh)(OCH2CH2)2O. Although a molecular structure was obtained

from the X-ray study, the data was insufficient for a full solution therefore a discussion of metric

parameters is unavailable (Figure 3.2.6).

Figure 3.2.6. POV-ray depiction of 3-8; C: black, O: red, P: orange, Ru: teal. Insufficient

data for full solution

47

As with the previous ligands, the all oxygen tridentate ligand was reacted with

(SIMes)(PCy3)RuCl2(CHPh) to give 3-9 (Scheme 3.2.5). The alkylidene proton of the resulting

compound displays the characteristic chemical shift in the 1H NMR at 16.23 ppm. An X-ray

crystallographic study confirmed the formulation and structure of 3-9 as

(SIMes)Ru(CHPh)(OCH2CH2)2O (Figure 3.2.7). In the solid state, one of the alkoxy arms is

disordered over two positions. The alkylidene fragment gives rise to a Ru-C bond length of

1.830(3) Å. The Ru-O(ether) and Ru-C(carbene) bond lengths are 2.194(1) and 1.983(2) Å

respectively giving rise to a O-Ru-C angle of 165.18(2)°. The Ru-O(alkoxy) bond lengths range

from 1.944(3) to 2.020(4) Å. These parameters describe the distorted trigonal bipyramidal

geometry.


48

Figure 3.2.7. POV-ray depiction of 3-9; C: black, O: red, N: blue-green, Ru: teal.

3.3 Conclusions

A library of ruthenium complexes containing an alkylidene and a tridentate, dianionic ligand

along with either PCy3 or SIMes have been prepared. These compounds were easily prepared in

high yields from inexpensive, commercially available ligands and Grubbs Catalyst as a

convenient method to obtain the desired species for further investigation. Ligand variants include

dithiolates with a central thioether, ether, and phosphine donor. Ligands with both an alkyl and

an aryl backbone have been prepared and a dialkoxy ligand with a central ether donor has been

introduced. The obtained molecular structures display similar geometries which can be best

described as distorted trigonal bipyramidal with the central donor of the tridentate ligand trans to

the PCy3 or NHC. The alkylidene and the anionic donors complete the trigonal plane.

49



All manipulations were carried out under an atmosphere of dry, O2-free N2 employing a Vac

Atmospheres glove box and a Schlenk vacuum-line. Solvents were purified with a Grubbs-type

column system manufactured by Innovative Technology and dispensed into thick-walled Schlenk

glass flasks equipped with Teflon-valve stopcocks. All solvents were thoroughly degassed after

purification (repeated freeze-pump-thaw cycles). CD2Cl2 was dried over CaH2 and vacuum

transferred into a Schlenk flask equipped with a Teflon-valve stopcock. 1H,

13C, and

31P NMR

spectra were recorded at 25 °C on Varian 300 and 400 MHz and Bruker 400 MHz spectrometers.

Chemical shifts are given relative to SiMe4 and referenced to the residual solvent signal (1H,

13C)

or relative to an external standard (31

P: 85% H3PO4). Chemical shifts are reported in ppm and

coupling constants as scalar values in Hz. Combustion analyses were performed in house

employing a Perkin-Elmer CHN Analyzer. All chemicals were obtained from Aldrich and used

as received unless stated. Pro-ligands were synthesized by the addition of two equivalents of n-

BuLi or KOtBu to the corresponding dithiol or diol. (LiSCH2CH2)2PPh and (HSC6H4)2O were

prepared according to literature procedures.30-31


Synthesis of 3-1: A THF solution (5 mL) of (LiSCH2CH2)2S.2THF (0.020

g, 0.123 mmol) was added to a THF solution (5 mL) of Grubbs 1 (0.092

g, 0.112 mmol) and stirred overnight. All volatiles were removed from

the dark brown solution. The dark brown solid was taken up in CH2Cl2 (5

mL) and filtered through a celite packed pipette. Upon concentration to

dryness, the resulting dark brown solid was washed with hexane (2 20 mL) and dried to yield a

dark red solid (0.068 g, 97%). X-ray quality crystals were grown from a CH2Cl2/CH3CN

solution. 1H NMR (CD2Cl2): 13.48 (d,

3JPH = 19.3 Hz, 1H, Ru=CH), 7.12 (m, 3H, Ph), 6.93 (m,

2H, Ph), 3.41 (m, 2H, CH2), 3.24 (m, 2H, CH2), 2.45 (m, 2H, CH2), 1.93 (m, 2H, CH2), 2.28,

2.04, 1.73, 1.57, 1.19 (all m, P(C6H11)3). 13

C{1H} NMR (CD2Cl2): 235.16 (d,

2JPC = 14.78 Hz,

Ru=CH), 157.02 (ipso-C, Ph), 127.51 (2 CH, Ph), 125.84 (2 CH, Ph),125.40 (CH, Ph), 45.17

(2 CH2), 36.28 (2 CH2), 35.19 (d, 1JPC = 19.78 Hz, ipso-C of P(C6H11)3), 29.98 (m-C of

P(C6H11)3), 28.37 (d, 2JPC = 10.25 Hz, o-C of P(C6H11)3), 26.93 (p-C of P(C6H11)3).

31P{

1H}

50

NMR (CD2Cl2): 41.71. Analysis calculated for C29H47PRuS3: C, 55.83; H, 7.59. Found: C,

55.71; H,7.33.

Synthesis of 3-2: A THF solution (5 mL) of (LiSCH2CH2)2S.2THF

(0.020 g, 0.123 mmol) was added to a THF solution (5 mL) of

Grubbs 2 (0.095 g, 0.112 mmol) and stirred overnight. All volatiles

were removed from the dark brown solution. The dark brown solid

was taken up in CH2Cl2 (5 mL) and filtered through a celite packed

pipette. Upon concentration to dryness, the resulting dark brown

solid was washed with hexane (2 20 mL) and dried to yield a dark red solid (0.071 g, 98%). X-

ray quality crystals were grown from a CH2Cl2/CH3CN solution. 1H NMR (CD2Cl2): 14.41 (s,

1H, Ru=CH), 7.19 (t, 1H, p-H, Ph), 7.07 (t, 2H, m-H, Ph), 6.88 (d, 2H, o-H, Ph), 6.80 (s, 4H, 4

CH, Mes), 3.99 (s, 4H, 2 CH2, Im), 3.22 (m, 2H, CH2), 3.00 (m, 2H, CH2), 2.52 (s, 12H, 4

CH3, Mes), 2.24 (m, 2H, CH2), 2.19 (s, 6H, 2 CH3, Mes), 1.73 (m, 2H, CH2). 13

C{1H} NMR

(CD2Cl2): 211.18 (Ru=CH), 138.08 (ipso-C, Ph), 137.79 (ipso-C, NCN), 137.73 (ipso-C, Mes),

129.18 (4 CH, Mes), 127.25.18 (2 CH, Ph), 127.11 (2 CH, Ph), 125.14 (CH, p-C, Ph),

52.43 (2 CH2), 44.56 (2 CH2, Im), 34.77 (2 CH2), 20.98 (2 CH3, Mes), 19.68 (4 CH3,

Mes). Analysis calculated for C32H40N2RuS3+CH2Cl2 (In crystal lattice) : C, 53.94; H, 5.76; N,

3.81. Found: C, 55.69; H, 5.96; N, 3.81.

Synthesis of 3-3: A THF solution (5 mL) of (LiSCH2CH2)2PPh (0.032 g,

0.134 mmol) was added to a THF solution (5 mL) of Grubbs 1 (0.100 g,

0.122 mmol) and stirred overnight. All volatiles were removed from the

dark brown solution. The dark brown solid was taken up in CH2Cl2 (5


dryness, the resulting dark brown solid was washed with hexane (2 20 mL) and dried to yield a

dark red solid (0.076 g, 89%). 1H NMR (CD2Cl2): 13.31 (dd,

3JPH = 23.2 Hz,

3JPH = 1.8 Hz, 1H,

Ru=CH), 7.04 (m, 5H, PPh), 6.94 (d, 2H, Ph), 6.71 (m, 3H, Ph), 3.07 (m, 2H, CH2), 2.93 (m, 2H,

CH2), 2.47 (m, 5H, CH2, P(C6H11)3), 2.15 (m, 2H, CH2), 2.20, 1.86, 1.72, 1.33 (all m, P(C6H11)3.

13C{

1H} NMR (CD2Cl2): 235.90 (appt,

2JPC = 12.57 Hz, Ru=CH), 155.7 (dd,

3JPC = 10.50 Hz,

3.85 Hz, ipso-C, Ph), 130.74 (d, 2JPC = 9.27 Hz, 2 CH, PPh), 128.56 (CH, PPh), 128.55 (d,

1JPC

= 267.1 Hz, CH, PPh), 127.65 (d, 3JPC = 9.25 Hz, 2 CH, PPh), 127.09 (2 CH, Ph), 126.03 (2

51

CH, Ph),124.99 (CH, Ph), 34.16 (m, 2 CH2), 31.49 (m, 2 CH2), 29.53 (m-C of P(C6H11)3),

28.04 (d, 1JPC = 9.02 Hz, ipso-C of P(C6H11)3), 27.70 (d,

2JPC = 9.02 Hz, o-C of P(C6H11)3), 26.56

(p-C of P(C6H11)3). 31

P{1H} NMR (CD2Cl2): 114.7 (d,

2JPP = 330.6 Hz), 28.9 (d,

2JPP = 331.8

Hz). Analysis calculated for C35H52P2RuS2: C, 60.06; H, 7.49. Found: C, 59.58; H, 7.32.

Synthesis of 3-4: A THF solution (5 mL) of (LiSCH2CH2)2O.2THF

(0.020 g, 0.137 mmol) was added to a THF solution (5 mL) of Grubbs 1

(0.100 g, 0.126 mmol) and stirred overnight. All volatiles were removed

from the dark brown solution. The dark brown solid was taken up in

CH2Cl2 (5 mL) and filtered through a celite packed pipette. Upon

concentration to dryness, the resulting dark brown solid was washed with hexane (2 20 mL)

and dried to yield a dark red solid (0.075 g, 98%). 1H NMR (CD2Cl2): 13.68 (d,

3JPH = 11.8 Hz,

1H, Ru=CH), 7.27 (m, 2H, Ph), 7.14 (m, 3H, Ph), 3.84 (m, 2H, CH2), 3.21 (m, 2H, CH2), 2.74

(m, 4H, 2 CH2), 2.11, 1.98, 1.74, 1.61, 1.50, 1.19 (all m, P(C6H11)3. 13

C{1H} NMR (CD2Cl2):

207.95 (Ru=CH), 153.25 (ipso-C, Ph), 128.15 (2 CH, Ph), 125.58 (CH, Ph), 125.39 (2 CH,

Ph), 77.96 (2 CH2), 35.91 (d, 1JPC = 24.17 Hz, ipso-C of P(C6H11)3), 32.42 (2 CH2), 29.97

(m-C of P(C6H11)3), 28.31 (d, 2JPC = 10.25 Hz, o-C of P(C6H11)3), 26.93 (p-C of P(C6H11)3).

31P{

1H} NMR (CD2Cl2): 65.60. Analysis calculated for C29H47OPRuS2: C, 57.30; H, 7.79.

Found: C, 56.92; H, 7.55.

Synthesis of 3-5: Grubbs 2 (0.326 g, 0.384 mmol) in MeCN (5 mL)

was added to (LiSCH2CH2)2O.2THF (0.144 g, 0.489 mmol) in MeCN

(5 mL) and toluene (10 mL) and stirred for 16 h. All volatiles were

removed from the dark brown solution. CH2Cl2 (5mL) was added to

give a dark brown solution which was filtered through celite. Upon

concentration to dryness, the resulting dark brown solid was washed

with hexane (2 20 mL) and dried to yield a black-red solid. X-ray quality crystals were grown

from a CH2Cl2/CH3CN solution. (0.243 g, 99%). 1H NMR (CD2Cl2): 14.85 (s, 1H, Ru=CH), 7.14

(t, 1H, p-H, Ph), 6.97-7.05 (m, 4H, Ph), 6.86 (s, 4H, 4 CH, Mes), 3.92 (s, 4H, 2 CH2, Im),

3.65 (m, 2H, CH2), 2.82 (m, 2H, CH2), 2.45 (s, 12 H, 4 CH3, Mes), 2.32-2.41 (m, 4H, 2

CH2), 2.23 (s, 6H, 2 CH3, Mes). 13

C{1H} NMR (CD2Cl2): 209.98 (Ru=CH), 153.68 (ipso-C,

Ph), 137.89 (ipso-C, NCN), 137.38 (ipso-C, Mes), 137.31 (ipso-C, Mes), 127.27 (2 CH, Ph),

52

128.81 (4 CH, Mes), 125.02 (2 CH, Ph), 124.65 (CH, p-C, Ph), 77.56 (2 CH2), 51.84 (2

CH2, Im), 31.59 (2 CH2), 20.59 (2 CH3, Mes), 19.12 (4 CH3, Mes). Analysis calculated for

C32H40N2ORuS2: C, 60.63; H, 6.36; N, 4.42. Found: C, 60.19; H, 5.97; N, 4.30.

Synthesis of 3-6: A THF solution (5 mL) of (LiSC6H4)2O (0.033 g,

0.134 mmol) was added to a THF solution (5 mL) of Grubbs 1 (0.100


the dark brown solution. The dark brown solid was taken up in CH2Cl2

(5 mL) and filtered through a celite packed pipette. Upon concentration

to dryness, the resulting dark brown solid was washed with hexane (2

20 mL) and dried to yield a red solid (0.068 g, 97%). X-ray quality crystals were grown from a

CH2Cl2 solution. 1H NMR (CD2Cl2): 14.69 (d,

3JPH = 14.7 Hz, 1H, Ru=CH), 7.48 (d,

3JHH = 7.6

Hz, 2H, Ph), 7.48 (m, 3H, Ph), 6.90 (m, 4H, Ph), 6.82 (t, 3JHH = 7.3 Hz, 2H, Ph), 6.72 (m, 2H,

Ph), 2.15, 2.02, 1.77, 1.55, 1.19 (all m, P(C6H11)3. 13

C{1H} NMR (CD2Cl2): 192.20 (Ru=CH),

154.03 (2 ipso-C, Ph), 152.23 (ipso-C, Ph), 139.08 (2 ipso-C, Ph), 132.14 (2 CH, Ph),

130.14 (2 CH, Ph), 127.94 (2 CH, Ph), 126.31 (CH, Ph), 125.27 (2 CH, Ph), 123.97 (2

CH, Ph), 122.70 (2 CH, Ph), 115.86 (2 CH, Ph), 35.95 (d, 1JPC = 25.05 Hz, ipso-C of

P(C6H11)3), 31.62 (m-C of P(C6H11)3), 30.09 (p-C of P(C6H11)3), 28.19 (d, 2JPC = 10.24 Hz, o-C

of P(C6H11)3). 31

P{1H} NMR (CD2Cl2): 68.60. Analysis calculated for C37H47OPRuS2: C, 63.13;

H, 6.73. Found: C, 62.52; H, 6.30.

Synthesis of 3-7: A THF solution (5 mL) of (LiSC6H4)2O (0.038 g,

0.153 mmol) was added to a THF solution (5 mL) of Grubbs 2 (0.100


the dark brown solution. The dark brown solid was taken up in CH2Cl2

(5 mL) and filtered through a celite packed pipette. Upon concentration

to dryness, the resulting dark brown solid was washed with hexane (2

20 mL) and dried to yield a red solid (0.074 g, 86%). 1H NMR (CD2Cl2): 15.60 (s, 1H, Ru=CH),

7.41 (d, 2H, Ph), 6.91 (m, 8H, Ph, Mes), 6.79 (m, 5H, Ph), 6.64 (m, 2H, Ph), 4.08 (s, 4H, 2

CH2, Im), 2.51 (s, 12 H, 4 CH3, Mes), 2.22 (s, 6H, 2 CH3, Mes). 13

C{1H} NMR (CD2Cl2):

209.13 (Ru=CH), 153.13 (ipso-C, Ph), 151.45 (ipso-C, Ph) 139.53 (ipso-C, NCN), 137.97 (ipso-

C, Mes), 137.17 (ipso-C, Mes), 131.26 (2 CH, Ph), 129.18 (2 CH, Ph), 128.90 (2 CH, Ph),

53

128.14 (2 CH, Ph), 126.10 (4 CH, Mes), 127.42 (2 CH, Ph), 125.22 (CH, p-C, Ph), 122.90

(CH, Ph), 121.54 (2 CH, Ph), 114.78 (2 CH, Ph), 51.84 (2 CH2, Im), 20.71 (2 CH3,

Mes), 18.99 (4 CH3, Mes). Analysis calculated for C40H40N2ORuS2+CH2Cl2 : C, 60.43; H,

5.19; N, 3.44. Found: C, 61.08; H, 5.78; N, 2.88.

Synthesis of 3-8: A THF solution (5 mL) of (KOCH2CH2)2O (0.025 g,

0.137 mmol) was added to a THF solution (5 mL) of Grubbs 1 (0.100 g,

0.126 mmol) and stirred overnight. All volatiles were removed from the

dark brown solution. The dark brown solid was taken up in toluene (5


dryness, the resulting red solid was washed with hexane (2 20 mL) and dried to yield a red

solid (0.068 g, 90%). 1H NMR (CD2Cl2): 15.72 (d,

3JPH = 14.8 Hz, 1H, Ru=CH), 7.91 (d,

3JHH =

8.02 Hz 2H, Ph), 7.31 (m, 3H, Ph), 4.19 (m, 2H, CH2), 3.96 (m, 2H, CH2), 3.39 (m, 2H, CH2),

2.96 (m, 2H, CH2), 2.44, 2.22, 1.87, 1.67, 1.65 (all m, P(C6H11)3. 13

C{1H} NMR (CD2Cl2):

207.95 (Ru=CH), 128.6 (Ph), 128.2 (Ph), 126.4 (Ph), 124.7 (Ph), 79.5 (2 CH2), 72.1 (2 CH2),

33.2 (d, 1JPC = 26.1 Hz, ipso-C of P(C6H11)3), 28.8 (m-C of P(C6H11)3), 27.7 (d,

2JPC = 10.4 Hz,

o-C of P(C6H11)3), 26.5 (p-C of P(C6H11)3). 31

P{1H} NMR (CD2Cl2): 64.76. Analysis calculated

for C29H47O3PRu: C, 60.50; H, 8.23. Found: C, 59.94 H, 7.83.

Synthesis of 3-9: Grubbs 2 (0.100 g, 0.118 mmol) in THF (5 mL) was

added to (KOCH2CH2)2O (0.028 g, 0.153 mmol) in THF (10 mL) and

stirred for 16 h. All volatiles were removed from the dark brown

solution. Toluene (5mL) was added to give a dark brown solution

which was filtered through celite. Upon concentration to dryness, the

resulting dark brown solid was washed with hexane (2 20 mL) and dried to yield a dark red

solid. (0.63 g, 90%). 1H NMR (CD2Cl2): 16.23 (s, 1H, Ru=CH), 7.58 (d, 2H, Ph), 7.18 (m, 3H,

Ph), 6.87 (s, 4H, 4 CH, Mes), 3.78 (m, 4H, 2 CH2), 3.44 (s, 4H, 2 CH2, Im), 3.18 (m, 4H, 2

CH2), 2.57 (s, 12 H, 4 CH3, Mes), 2.19 (s, 6H, 2 CH3, Mes). 13

C{1H} NMR (CD2Cl2):

212.4 (Ru=CH), 153.3 (ipso-C, Ph), 138.7 (ipso-C, NCN), 137.5 (ipso-C, Mes), 137.4 (ipso-C,

Mes), 128.5 (2 CH, Ph), 128.2 (4 CH, Mes), 124.6 (2 CH, Ph), 123.6 (CH, p-C, Ph), 79.4

(2 CH2), 70.7 (2 CH2), 51.4 (2 CH2, Im), 20.7 (2 CH3, Mes), 18.4 (4 CH3, Mes).

54

Analysis calculated for C32H40N2O3Ru: C, 63.87; H, 6.70; N, 4.66. Found: C, 63.30 H, 6.43 N,

4.25.

3.4.3 X-ray Crystallography

3.4.3.1 X-ray Data Collection and Reduction

Crystals were coated in Paratone-N oil in the glove-box, mounted on a MiTegen Micromount

and placed under an N2 stream, thus maintaining a dry, O2-free environment for each crystal. The

data were collected on a Bruker Apex II diffractometer employing Mo Kα radiation (λ = 0.71073

Å). Data collection strategies were determined using Bruker Apex software and optimized to

provide >99.5% complete data to a 2θ value of at least 55°. The data were collected at 150(±2) K

for all crystals. The frames were integrated with the Bruker SAINT software package using a

narrow-frame algorithm. Data were corrected for absorption effects using the empirical multi-

scan method (SADABS).32

3.4.3.2 X-ray Data Solution and Refinement

Non-hydrogen atomic scattering factors were taken from the literature tabulations.33

The heavy

atom positions were determined using direct methods employing the SHELXTL direct methods

routine. The remaining non-hydrogen atoms were located from successive difference Fourier

map calculations. The refinements were carried out by using full-matrix least squares techniques

on F, minimizing the function (Fo–Fc)2 where the weight is defined as 4Fo2/2 (Fo

2) and Fo

and Fc are the observed and calculated structure factor amplitudes, respectively. In the final

cycles of each refinement, all non-hydrogen atoms were assigned anisotropic temperature factors

in the absence of disorder or insufficient data. In the latter cases atoms were treated isotropically.

C-H atom positions were calculated and allowed to ride on the carbon to which they are bonded

assuming a C-H bond length of 0.95 Å. H-atom temperature factors were fixed at 1.20 times the

isotropic temperature factor of the C-atom to which they are bonded. The H-atom contributions

were calculated, but not refined. The locations of the largest peaks in the final difference Fourier

map calculation as well as the magnitude of the residual electron densities in each case were of

no chemical significance.

55

Table 3.4.1. Select Crystallographic Data for 3-1, 3-2 and 3-3.

(3-1) (3-2) (3-3)

Formula C29H47PRuS3 C32H40N2RuS3

(CH2Cl2)

C35H52P2RuS2

Formula weight 623.92 734.87 699.92

Crystal System Triclinic Monoclinic Monoclinic

Space group P-1 P21/c P21/n

a(Å) 8.4357(4) 11.0572(10) 8.3215(10)

b(Å) 10.0451(4) 26.702(2) 17.7887(19)

c(Å) 17.6088(7) 12.1075(11) 22.489(3)

α(deg) 88.602(2) 90 90

β(deg) 80.783(2) 114.176(3) 96.735(5)

γ(deg) 86.310(2) 90 90

V(Å3) 1469.66(11) 3261.2(5) 3306.0(7)

Z 2 4 4

d(calc)gcm-3

1.410 1.497 1.406

R(int) 0.0290 0.0458 0.0731

Abs coeff,μ,mm-1

0.819 0.863 0.721

Data collected 11193 7483 7577

>2(FO2) 10137 6329 5988

Variables 331 370 406

R(>2) 0.0216 0.0616 0.0338

Rw 0.0538 0.1571 0.0795

GOF 1.022 1.123 1.039

56


(3-5) (3-6) (3-9)

Formula C32H40N2ORuS2

(CH3CN)

C37H47OPRuS C32H40N2O3Ru

Formula weight 674.92 703.93 601.73

Crystal System Monoclinic Monoclinic Monoclinic

Space group P21/n P21/c P21/n

a(Å) 14.1830(6) 10.4646(7) 9.6299(6)

b(Å) 10.3197(4) 18.4403(12) 14.408(1)

c(Å) 22.6405(11) 17.6740(11) 21.2995(14)

α(deg) 90 90 90

β(deg) 101.407(2) 94.848(2) 95.679(4)

γ(deg) 90 90 90

V(Å3) 3248.3(2) 3398.4(4) 2940.8(3)

Z 4 4 4

d(calc)gcm-3

1.380 1.376 1.359

R(int) 0.0349 0.0480 0.0313

Abs coeff,μ,mm-1

0.642 0.659 0.567


>2(FO2) 6375 6258 7309


R(>2) 0.0352 0.0398 0.0362

Rw 0.0817 0.0958 0.0904

GOF 0.975 0.983 1.026

57




2. Dias, E. L.; Nguyen, S. T.; Grubbs, R. H., Journal of the American Chemical Society

1997, 119 (17), 3887-3897.


2001, 123 (27), 6543-6554.


2001, 123 (4), 749-750.


6. Vougioukalakis, G. C.; Grubbs, R. H., Chem Rev 2010, 110 (3), 1746-87.

7. Lynn, D. M.; Mohr, B.; Grubbs, R. H.; Henling, L. M.; Day, M. W., Journal of the


8. Rolle, T.; Grubbs, R. H., Chemical Communications 2002, (10), 1070-1071.

9. Seiders, T. J.; Ward, D. W.; Grubbs, R. H., Organic Letters 2001, 3 (20), 3225-3228.

10. Funk, T. W.; Berlin, J. M.; Grubbs, R. H., Journal of the American Chemical Society

2006, 128 (6), 1840-1846.

11. Berlin, J. M.; Goldberg, S. D.; Grubbs, R. H., Angewandte Chemie International Edition

2006, 45 (45), 7591-7595.

12. Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H., Journal of the American


13. Sanford, M. S.; Henling, L. M.; Day, M. W.; Grubbs, R. H., Angewandte Chemie


14. Conrad, J. C.; Amoroso, D.; Czechura, P.; Yap, G. P. A.; Fogg, D. E., Organometallics

2003, 22 (18), 3634-3636.

15. Conrad, J. C.; Parnas, H. H.; Snelgrove, J. L.; Fogg, D. E., Journal of the American


16. Conrad, J. C.; Camm, K. D.; Fogg, D. E., Inorganica Chimica Acta 2006, 359 (6), 1967-

1973.

17. Conrad, J. C.; Snelgrove, J. L.; Eeelman, M. D.; Hall, S.; Fogg, D. E., Journal of

Molecular Catalysis A: Chemical 2006, 254 (1–2), 105-110.

58

18. Monfette, S.; Fogg, D. E., Organometallics 2006, 25 (8), 1940-1944.

19. Zhang, W.; Liu, P.; Jin, K.; He, R., Journal of Molecular Catalysis A: Chemical 2007,

275 (1–2), 194-199.

20. Samec, J. S. M.; Grubbs, R. H., Chemistry – A European Journal 2008, 14 (9), 2686-

2692.

21. Endo, K.; Grubbs, R. H., Journal of the American Chemical Society 2011, 133 (22),

8525-8527.

22. Khan, R. K. M.; Torker, S.; Hoveyda, A. H., Journal of the American Chemical Society

2013, 135 (28), 10258-10261.

23. Occhipinti, G.; Hansen, F. R.; Törnroos, K. W.; Jensen, V. R., Journal of the American


24. Cannon, J. S.; Grubbs, R. H., Angewandte Chemie International Edition 2013, 52 (34),

9001-9004.

25. De Clercq, B.; Verpoort, F., Tetrahedron Letters 2002, 43 (50), 9101-9104.

26. Denk, K.; Fridgen, J.; Herrmann, W. A., Advanced Synthesis & Catalysis 2002, 344 (6-

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27. Boone, M. P.; Brown, C. C.; Ancelet, T. A.; Stephan, D. W., Organometallics 2010, 29

(19), 4369-4374.

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4289-4297.

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30. Antonio Muñoz, J.; Escriche, L.; Casabó, J.; Pérez-Jiménez, C.; Kivekäs, R.; Sillanpää,

R., Inorganica Chimica Acta 1997, 257 (1), 99-104.

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59

Chapter 4 Synthesis of Ru Alkylidenes via Dithioacetals

4.1 Introduction

4.1.1 First Well Defined Olefin Metathesis Catalyst

The synthesis of alkylidenes has been done a number of ways. The first isolated transition metal

alkylidene complex was reported by Schrock and co-workers in 1974.1 It was formed by the

attempted formation of a homoleptic, pentaneopentyl Ta species (Scheme 4.1.1).2-3

This opened

up the field of well defined olefin metathesis catalysts.

Scheme 4.1.1. Synthesis of the First Isolated Transition Metal Alkylidene

4.1.2 Synthetic Routes to Ruthenium Alkylidenes

The first well-defined ruthenium based olefin metathesis catalyst was reported by Grubbs and

co-workers.4-5

It was synthesized by the ring opening of 2,2-diphenylcyclopropene with

Ru(PPh3)3Cl2 to give the vinylalkylidene (Scheme 4.1.2). Drawbacks of this method include the

laborious synthesis of the cyclopropene and the synthesis of the vinylalkylidene which initiates

slower than the typical benzylidene.6-7

Scheme 4.1.2. Synthesis of the First Ruthenium Alkylidene

Following this discovery, a number of new synthetic methods to prepare ruthenium alkylidenes

were discovered including direct routes to the faster initiating benzylidene present in

commercially available Grubbs Catalysts. These methods include the use of diazomethanes as

alkylidene transfer reagents (Scheme 4.1.3).4 This route is high yielding and provides a direct

60

pathway to the ruthenium benzylidene, however, diazomethanes are shock sensitive and

explosive and thus must be handled with extreme caution.

Scheme 4.1.3. Synthesis of Grubbs Catalyst Using Phenyldiazomethane

Milstein and co-workers developed a method using a sulfur ylide as an alkylidene transfer

reagent.8 This provides a safer starting material than using diazomethanes and a direct route to

the ruthenium benzylidene, however, there is a stoichiometric amount of thioether waste

generated (Scheme 4.1.4). This method is also patent protected and would require a licensing

agreement in order to use it commercially.

Scheme 4.1.4. Synthesis of Grubbs Catalyst Using a Sulfur Ylide

Starting from ruthenium hydrides, there are a variety of methods to convert these species to an

alkylidene. Reacting Ru(PPh3)3HCl with 3-chloro-3-methyl-1-butyne followed by phosphine

exchange affords the Ru vinylalkylidene in greater than 70% yield (Scheme 4.1.5).9 This

synthetic route has similar drawback to the cyclopropene route which also gives a

vinylalkylidene which have slower initiation rates compared to the benzylidene derivatives.

Scheme 4.1.5. Synthesis of a Vinylalkylidene Using Propargyl Chloride

61

Starting from [Ru(PiPr3)2HCl]2, this synthon can be converted to an alkylidene via the addition of

vinyl chloroformate.10

This results in the liberation of CO2 and transfer of the chloride to the Ru

centre as the ethylidene is formed. Similarly, reacting (Im(OMe)2)Ru(SIMes)(PPh3)HCl with

phenyl vinylsulfide results in the formation of the ruthenium thiolate alkylidene complex

(Scheme 4.1.6).11

Even though these compounds are active for catalytic olefin metathesis they

also suffer from forming an alkylidene which is slower initiating than a benzylidene.

Scheme 4.1.6. Synthesis of Ru Alkylidenes from Phenyl Vinylsulfide

By reacting Ru(PPh3)3Cl2 with 1,1-diphenyl-2-propyn-1-ol in THF with the loss of H2O,

followed by addition of PCy3 a ruthenium indenylidene can be isolated (Scheme 4.1.7).12

This

reaction is thought to be catalyzed by HCl and go through a ruthenium carbyne intermediate.

This ruthenium indenylidene complex is active for olefin metathesis but is slower initiating than

1st Generation Grubbs Catalyst. This species can be converted to Grubbs Catalyst by the

addition of 60 equivalents of styrene over 3 h.

Scheme 4.1.7. Synthesis of Grubbs Catalyst via Indenylidene Intermediate

Grubbs and coworkers have developed a method for preparing Grubbs Catalyst starting from a

Ru(0) species and dichloroalkanes.13

For example, heating Ru(cod)(cot) in the presence of PCy3

and Cl2CHPh results in the formation of 1st Generation Grubbs Catalyst in 50% yield

(Scheme 4.1.8). In a similar fashion, mixing RuH2(H2)2(PCy3)2 with cyclohexene results in the

62

formation of a Ru(0) species which reacts with Cl2CHPh to also give 1st Generation Grubbs

Catalyst in a 70% yield.

Scheme 4.1.8. Synthesis of Grubbs Catalyst from Ru(0) Species


4.2.1 Attempted Synthesis Using Diazomethanes

Reacting 2-1 with a diazomethane compound could lead to the synthesis of a ruthenium

alkylidene similar to 3-4 with a PPh3 in place of the PCy3 ligand (Scheme 4.2.1). This reaction is

conceptually related to the synthesis of Grubbs catalyst from Ru(PPh3)3Cl2 and a diazomethane.

To probe the potential of this synthetic strategy, commercially available, and less hazardous

TMSCHN2 was initially used as the diazomethane. Mixing 2-1 and TMSCHN2 in CD2Cl2 at

room temperature resulted in no observable change to the solution. NMR data showed no

evidence of a reaction taking place. In an optimistic attempt, PhCHN2 was prepared and mixed

with a CH2Cl2 solution of 2-1. A red solid was isolated from the reaction mixture. Multiple

alkylidene peaks were observed in the 1H NMR spectrum however they were very minor and

multiple attempts to increase the conversion proved unsuccessful and inconsistent.

Scheme 4.2.1. Failed Preparation of Ruthenium Alkylidene From Diazomethanes and 2-1

63

Replacing a phosphine with an alkylidene in 2-3 using a diazomethane reagent would lead to a

complex similar to 5-4 (Scheme 4.2.2). To see if this ruthenium starting material was more

reactive with diazomethanes it was mixed with either TMSCHN2 or PhCHN2 in CH2Cl2. In both

cases no reactivity was observed.

Scheme 4.2.2. Failed Preparation of Ruthenium Alkylidene From Diazomethanes and 2-3

4.2.2 Attempted Synthesis Using Propargyl Alcohol

In an attempt to prepare a ruthenium alkylidene using the propargyl alcohol route to an

indinylidene, 2-1 and 1,1-diphenylprop-2-yn-1-ol were refluxed in THF for 5 h in the presence of

a catalytic amount of acyl chloride (Scheme 4.2.3). This resulted in no observable reaction.

Scheme 4.2.3. Failed Preparation of Ruthenium Indenylidene From Propargyl Alcohol and

2-3

4.2.3 Synthesis of Ru Alkylidenes using Thioacetals

With unsuccessful attempts in synthesizing these ruthenium alkylidene complexes via

diazomethanes and propargyl alcohols, a more creative approach was developed. Based on the

work by Grubbs and co-workers using dihaloalkanes with Ru(0) sources to form

dihalo-ruthenium alkylidenes a related strategy using dithioacetals and Ru(0) sources to form

dithiolate-ruthenium alkylidene complexes was developed.

64

4.2.3.1 Synthesis of Thioacetals

The cyclic thioacetals were prepared employing a modification of the literature procedure

described by Hu and co-workers.14

Thus, to a solution of p-toluenesulfonic acid in MeOH heated

to 55 °C, was added a mixture of 2-mercaptoethyl ether and benzaldehyde in a slow drop-wise

fashion in order to selectively obtain the monomer. Following stirring overnight at 55 °C,

subsequent work-up afforded the cyclic thioacetal O(CH2CH2S)2CHPh 4-1 in 95% isolated yield

(Scheme 4.2.4). 1H NMR data for 4-1 confirmed the cyclic formation with the presence of the

S2CHPh proton resonating as a singlet at 5.80 ppm, the backbone protons resonating at 3.50,

2.90, 2.50 and 2.05 ppm as multiplets and the phenyl protons at 7.22, 6.84 and 6.75 ppm.


An X-ray crystallographic study confirmed the monomer formation (Figure 4.2.1). The eight

membered ring generated by the dithioacetal formation adopts a boat-chair conformation. This

reaction proved amenable to variation and was adapted to give the species S(CH2CH2S)2CHPh

4-2 and O(C6H4S)2CHPh 4-3 each isolated in greater than 90% yield (Scheme 4.2.5).

Figure 4.2.1. POV-ray depiction of 4-1; C: black, O: red, S: yellow, H: black

65


4.2.3.2 Synthesis of Ru Complexes

The dithioacetal 4-1 was reacted with Ru(cod)(cot)15

in the presence of 1.1 equiv of PCy3 in

C6H6 at 50 ºC for 2 h. Cooling the solution afforded a red solid in 73% yield. The 31

P{1H} NMR

of the red solid exhibits a single signal at 65.6 ppm and the 1H NMR spectrum is consistent with

the presence of the dithiolate ligand and PCy3 in a 1:1 ratio. In addition, a doublet resonance at

13.68 ppm with P-H coupling constant of 11.3 Hz is consistent with the presence of a ruthenium

alkylidene. This is further supported by the observation of the corresponding 13

C{1H} resonance

at 208.0 ppm. These NMR data is consistent with the formation of 3-4 (Scheme 4.2.6).

Scheme 4.2.6. Synthesis of 3-4 From Dithioacetal 4-1 and Ru(cod)(cot)

Due to the low yielding and tedious preparation of Ru(cod)(cot) a more convenient and higher

yielding Ru synthon was desired. Based on the success of Grubbs and co-workers using a

ruthenium dihydride as a Ru(0) source,13

Ru(PPh3)4(H)216

was reacted with dithioacetal 4-1 in

the presence of PCy3. During heating to 50 ºC for 4 h, the yellow solution became dark red with

the evolution of gas. Subsequent work-up afforded 3-4 in 89% isolated yield. Following a

similar process, the dithioacetals 4-2 and 4-3 were treated in a similar fashion with

Ru(PPh3)4(H)2 in the presence of PCy3 to give 3-1 and 3-6 in yields of 87, and 84%, respectively

(Scheme 4.2.7).

66

Scheme 4.2.7. Synthesis of 3-4, 3-1 and 3-6 From Dithioacetals and Ru(PPh3)4(H)2.

Replacement of PCy3 with SIMes in the reaction mixture with dithioacetal 4-1 lead to the

formation of a ruthenium alkylidene with a resonance at 14.85 ppm in the 1H NMR spectrum

indicating the formation of 3-5. However, the formation of a new hydride resonance at -26.5 ppm

as a doublet of doublets indicated the formation of a byproduct determined to be the C-H

activated SIMesRuH(PPh3)2.17

To prevent the formation of this byproduct, the dithioacetal was

reacted with Ru(PPh3)4(H)2 in the absence of SIMes to form the ruthenium alkylidene. After 4 h,

SIMes was added to the reaction mixture and heated for an addition 30 min. This led to an

increased yield of 86% of 3-5 (Scheme 4.2.8). This methodology was be applied with

dithioacetals 4-2 and 4-3 to give compounds 3-2 and 3-7 in 84 and 88 % yield, respectively.

Scheme 4.2.8. Synthesis of 3-5, 3-2 and 3-7 From Dithioacetals and Ru(PPh3)4(H)2

This synthetic route to Ru-alkylidene is thought to proceed by oxidative addition of the S-C

bonds to Ru followed by -thiolate transfer (Scheme 4.2.9). In these reactions Ru(PPh3)4(H)2

reacts as a Ru(0) source, presumably with loss of H2. This latter supposition is consistent with

the observation of gas evolution upon addition of the dithioacetal to the Ru-synthon. This

reaction is conceptually related to the oxidative addition of dihalomethanes to Ru(0), although

the present strategy affords the simultaneous delivery of a tridentate ligand and an alkylidene to

Ru, affording access to a family of new compounds.13

67

Scheme 4.2.9. Ruthenium Alkylidene Formation From Dithioacetals

These ruthenium alkylidene compounds can act as synthons for the preparation of Grubbs

Catalyst. Reacting 3-5 with 2 equivalents of PhC(O)Cl and 1 equivalent of PCy3 in CH2Cl2

cleanly liberated the dithioester (PhC(O)SCH2CH2)2O and 2nd

Generation Grubbs Catalyst

(Scheme 4.2.10). Thus this synthetic strategy offers a unique and facile, safe and high yielding

route to this catalyst.

Scheme 4.3.10. Synthesis of Grubbs II From 3-5.

4.3 Conclusion

In conclusion, a new method of preparing ruthenium alkylidenes from Ru(0) starting materials

and dithioacetals has been developed. This new method is amiable, high yielding, safe, and uses

inexpensive starting materials. This provides an alternative route to the ruthenium alkylidene

complexes with tridentate, dithiolate ligands presented in Chapter 3 avoiding the use of Grubbs

Catalysts. This method conveniently installs the alkylidene fragment as well as the tridentate

68

dithiolate ligand in one simple step. These complexes can be used as synthons to prepare Grubbs

catalyst.



All synthetic manipulations were carried out under an atmosphere of dry, O2-free N2 employing

a VAC Atmospheres glove box and a Schlenk vacuum-line. Hexanes, pentane and

dichloromethane were purified with a Grubbs-type column system manufactured by Innovative

Technology and dispensed into thick-walled glass Schlenk bombs equipped with Young-type

Teflon valve stopcocks. Acetonitrile was dried over CaH2 and distilled. Dichloromethane-d2 was

dried over CaH2 and benzene-d6 was dried over Na metal and vacuum-transferred into a Young

bomb. All solvents were thoroughly degassed after purification (three freeze-pump-thaw cycles).

1H,

13C, and

31P NMR spectra were recorded at 25 °C on Varian 300 and 400 MHz and Bruker

400 MHz spectrometers. Commercially available substrates were obtained from Sigma-Aldrich

and used without further purification. SIMes18

, Ru(cod)(cot)15

, Ru(PPh3)4(H)216

and thioacetal

4-219

were prepared according to literature procedures. Chemical shifts are given relative to

SiMe4 and referenced to the residual solvent signal (1H,

13C) or relative to an external standard

(31

P: 85% H3PO4). In some instances, signal and/or coupling assignment was derived from two-

dimensional NMR experiments. Chemical shifts are reported in ppm and coupling constants as

scalar values in Hz. Combustion analyses were performed in house employing a Perkin-Elmer

CHN Analyzer.


A general procedure for the synthesis of thioacetals is as follows. A solution of p-toluenesulfonic

acid (5 mg) in 200 mL of MeOH was heated to 55 oC in a 3-neck round bottom flask fitted with a

condenser, addition funnel and septum. A solution of 2-Mercaptoethyl ether (1.065 g, 7.7 mmol)

and benzaldehyde (0.817 g, 7.7 mmol) in 150 mL MeOH was added drop wise from the addition

funnel over 4 hours. The mixture was left at 55oC overnight. The reaction mixture was cooled

and filtered through a plug of alumina to remove the acid. All volatiles were removed and the

white solid was dissolved in 10 mL of toluene. The solution was passed through an alumina plug

to remove any oligomers that may have formed and all volatiles were removed from the filtrate.

69

Thioacetal 4-1 was crystallized from CH2Cl2 and obtained as colorless needles (1.65 g, 95%). X-

ray quality crystals were obtained from a CH2Cl2 solution at -35 o

C. 1H NMR (C6D6): 7.22 (s,

2H, Ph), 6.84 (t, 2H, Ph), 6.75 (t, 1H, Ph), 5.80 (s, 1H, CH), 3.50 (m, 2H, CH2), 2.90 (m, 2H,

CH2), 2.50 (m, 2H, CH2), 2.05 (m, 2H, CH2). 13

C{1H} NMR (C6D6): 143.2 (ipso-Ph), 128.7 (Ph),

128.0 (Ph), 127.8 (Ph), 127.6 (Ph), 72.7 (CH2), 59.2 (S2CHPh), 33.2 (CH2). Analysis calculated

for C11H14OS2: C, 58.37; H, 6.23. Found: C, 57.94; H, 6.38.

Thioacetal 4-3 was crystallized from CH2Cl2 and obtained as colorless needles. (2.26 g, 91%).

1H NMR (C6D6): 7.61 (m, 2H, Ph), 7.01 (m, 2H, Ph), 6.93 (m, 3H, Ph), 6.84 (m, 2H, Ph), 6.64

(m, 4H, Ph), 5.84 (s, 1H, S2CHPh). 13

C{1H} NMR (C6D6): 155.4, 140.4, 132.3, 130.3, 129.9,

128.8, 128.1, 127.8, 124.6, 123.0, 119.1 (all Ph), 61.3 (S2CH). Analysis calculated for

C19H14OS2: C, 70.77; H, 4.38. Found: C, 70.46; H, 4.11.

General procedures for synthesis of Ru alkylidene complexes

Procedure 1: Ru(cod)(cot) (20 mg, 0.063 mmol), PCy3 (20 g, 0.070 mmol) and thioacetal 4-1 (14

g, 0.063 mmol) were mixed and heated in C6H6 at 50oC for 4 h. The solution was cooled to room

temperature and the solvent was removed in vacuo. The resulting solid was washed with hexanes

and recrystallized from CH2Cl2 and pentane to give 3-4 as a red solid.

Procedure 2: To a C6H6 (1 mL) solution of Ru(PPh3)4(H)2 (20 mg, 0.022 mmol) was added PCy3

(9 mg, 0.033 mmol) and the thioacetal 4-1 (6 mg, 0.026 mmol). The mixture was heated at 50oC

in an oil bath for 4 h and the yellow solution turned dark red as bubbles evolved. Pentane was

added to the solution to crash out the red product, 3-4 which was washed with pentane. The

product was recrystallized from CH2Cl2 and pentane.

Procedure 3: To a C6H6 (1 mL) solution of Ru(PPh3)4(H)2 (20 mg, 0.022 mmol) was added

thioacetal 4-1 (6 mg, 0.026 mmol). The mixture was heated at 50oC in an oil bath for 4 h and the

yellow solution turned dark red as bubbles evolved. A solution of SIMes (10 mg, 0.033 mmol) in

C6H6 was added and the reaction was heated for another 30 min. Pentane was added to the

solution to crash out the red product 3-5 which was washed with pentane. The product was

recrystallized from CH2Cl2 and pentane.

70

Synthesis of 3-4: Isolated as a red solid in 73% yield (28 mg, 0.046 mmol) by

procedure 1 and 89% yield (12 mg, 0.020 mmol) by procedure 2 as a red

solid. 1

H NMR (CD2Cl2): 13.68 (d, 3JPH = 11.8 Hz, 1H, Ru=CH), 7.27

(m, 2H, Ph), 7.14 (m, 3H, Ph), 3.84 (m, 2H, CH2), 3.21 (m, 2H, CH2), 2.74

(m, 4H, 2 CH2), 2.11, 1.98, 1.74, 1.61, 1.50, 1.19 (all m, P(C6H11)3.

13C{

1H} NMR (CD2Cl2): 207.95 (Ru=CH), 153.25 (ipso-C, Ph), 128.15 (2 CH, Ph), 125.58

(CH, Ph), 125.39 (2 CH, Ph), 77.96 (2 CH2), 35.91 (d, 1JPC = 24.17 Hz, ipso-C of P(C6H11)3),

32.42 (2 CH2), 29.97 (m-C of P(C6H11)3), 28.31 (d, 2JPC = 10.25 Hz, o-C of P(C6H11)3), 26.93

(p-C of P(C6H11)3). 31

P{1H} NMR (CD2Cl2): 65.60. Analysis calculated for C29H47OPRuS2:

C, 57.30; H, 7.79. Found: C, 56.92; H, 7.55.

Synthesis of 3-1: Isolated in 87% yield (12 mg, 0.019 mmol) following

procedure 2 with thioacetal 4-2 as a dark red solid. X-ray quality crystals

were grown from a CH2Cl2/CH3CN solution. 1H NMR (CD2Cl2): 13.48

(d, 3JPH = 19.3 Hz, 1H, Ru=CH), 7.12 (m, 3H, Ph), 6.93 (m, 2H, Ph), 3.41

(m, 2H, CH2), 3.24 (m, 2H, CH2), 2.45 (m, 2H, CH2), 1.93 (m, 2H, CH2), 2.28, 2.04, 1.73, 1.57,

1.19 (all m, P(C6H11)3. 13

C{1H} NMR (CD2Cl2): 235.16 (d,

2JPC = 14.78 Hz, Ru=CH), 157.02

(ipso-C, Ph), 127.51 (2 CH, Ph), 125.84 (2 CH, Ph),125.40 (CH, Ph), 45.17 (2 CH2), 36.28

(2 CH2), 35.19 (d, 1JPC = 19.78 Hz, ipso-C of P(C6H11)3), 29.98 (m-C of P(C6H11)3), 28.37

(d, 2JPC = 10.25 Hz, o-C of P(C6H11)3), 26.93 (p-C of P(C6H11)3).

31P{

1H} NMR (CD2Cl2): 41.71.

Analysis calculated for C29H47PRuS3: C, 55.83; H, 7.59. Found: C, 55.71; H,7.33.

Synthesis of 3-6: Isolated in 84% (13 mg, 0.018 mmol) yield following

procedure 2 with thioacetal 3 as a red solid. X-ray quality crystals were

grown from a CH2Cl2 solution. 1H NMR (CD2Cl2): 14.69

(d, 3JPH = 14.7 Hz, 1H, Ru=CH), 7.48 (d,

3JHH = 7.6 Hz, 2H, Ph), 7.48

(m, 3H, Ph), 6.90 (m, 4H, Ph), 6.82 (t, 3JHH = 7.3 Hz, 2H, Ph), 6.72

(m, 2H, Ph), 2.15, 2.02, 1.77, 1.55, 1.19 (all m, P(C6H11)3. 13

C{1H} NMR (CD2Cl2): 192.20

(Ru=CH), 154.03 (2 ipso-C, Ph), 152.23 (ipso-C, Ph), 139.08 (2 ipso-C, Ph), 132.14

(2 CH, Ph), 130.14 (2 CH, Ph), 127.94 (2 CH, Ph), 126.31 (CH, Ph), 125.27 (2 CH, Ph),

123.97 (2 CH, Ph), 122.70 (2 CH, Ph), 115.86 (2 CH, Ph), 35.95 (d, 1JPC = 25.05 Hz,

ipso-C of P(C6H11)3), 31.62 (m-C of P(C6H11)3), 30.09 (p-C of P(C6H11)3), 28.19

71

(d, 2JPC = 10.24 Hz, o-C of P(C6H11)3).

31P{

1H} NMR (CD2Cl2): 68.60. Analysis calculated for

C37H47OPRuS2: C, 63.13; H, 6.73. Found: C, 62.52; H, 6.30.


procedure 3 as a red solid. 1H NMR (CD2Cl2): 14.85 (s, 1H, Ru=CH),

7.14 (t, 1H, p-H, Ph), 6.97-7.05 (m, 4H, Ph), 6.86 (s, 4H, 4 CH,

Mes), 3.92 (s, 4H, 2 CH2, Im), 3.65 (m, 2H, CH2), 2.82 (m, 2H,

CH2), 2.45 (s, 12 H, 4 CH3, Mes), 2.32-2.41 (m, 4H, 2 CH2), 2.23

(s, 6H, 2 CH3, Mes). 13

C{1H} NMR (CD2Cl2): 209.98 (Ru=CH), 153.68 (ipso-C, Ph), 137.89

(ipso-C, NCN), 137.38 (ipso-C, Mes), 137.31 (ipso-C, Mes), 127.27 (2 CH, Ph), 128.81

(4 CH, Mes), 125.02 (2 CH, Ph), 124.65 (CH, p-C, Ph), 77.56 (2 CH2), 51.84

(2 CH2, Im), 31.59 (2 CH2), 20.59 (2 CH3, Mes), 19.12 (4 CH3, Mes). Analysis

calculated for C32H40N2ORuS2: C, 60.63; H, 6.36; N, 4.42. Found: C, 60.19; H, 5.97; N, 4.30.


procedure 3 using thioacetal 2 as a dark brown solid. X-ray quality

crystals were grown from a CH2Cl2/CH3CN solution. 1H NMR

(CD2Cl2): 14.41 (s, 1H, Ru=CH), 7.19 (t, 1H, p-H, Ph), 7.07

(t, 2H, m-H, Ph), 6.88 (d, 2H, o-H, Ph), 6.80 (s, 4H, 4 CH, Mes), 3.99

(s, 4H, 2 CH2, Im), 3.22 (m, 2H, CH2), 3.00 (m, 2H, CH2), 2.52 (s, 12H, 4 CH3, Mes), 2.24

(m, 2H, CH2), 2.19 (s, 6H, 2 CH3, Mes), 1.73 (m, 2H, CH2). 13

C{1H} NMR (CD2Cl2): 211.18

(Ru=CH), 138.08 (ipso-C, Ph), 137.79 (ipso-C, NCN), 137.73 (ipso-C, Mes), 129.18

(4 CH, Mes), 127.25.18 (2 CH, Ph), 127.11 (2 CH, Ph), 125.14 (CH, p-C, Ph), 52.43

(2 CH2), 44.56 (2 CH2, Im), 34.77 (2 CH2), 20.98 (2 CH3, Mes), 19.68 (4 CH3, Mes).

Analysis calculated for C32H40N2RuS3+CH2Cl2 (In crystal lattice) : C, 53.94; H, 5.76; N, 3.81.

Found: C, 55.69; H, 5.96; N, 3.81.


procedure 3 using thioacetal 3 as a red solid. 1

H NMR (CD2Cl2): 15.60

(s, 1H, Ru=CH), 7.41 (d, 2H, Ph), 6.91 (m, 8H, Ph, Mes), 6.79 (m, 5H,

Ph), 6.64 (m, 2H, Ph), 4.08 (s, 4H, 2 CH2, Im), 2.51 (s, 12 H, 4 CH3,

Mes), 2.22 (s, 6H, 2 CH3, Mes). 13

C{1H} NMR (CD2Cl2): 209.13

72

(Ru=CH), 153.13 (ipso-C, Ph), 151.45 (ipso-C, Ph) 139.53 (ipso-C, NCN), 137.97

(ipso-C, Mes), 137.17 (ipso-C, Mes), 131.26 (2 CH, Ph), 129.18 (2 CH, Ph), 128.90

(2 CH, Ph), 128.14 (2 CH, Ph), 126.10 (4 CH, Mes), 127.42 (2 CH, Ph), 125.22

(CH, p-C, Ph), 122.90 (CH, Ph), 121.54 (2 CH, Ph), 114.78 (2 CH, Ph), 51.84

(2 CH2, Im), 20.71 (2 CH3, Mes), 18.99 (4 CH3, Mes). Analysis calculated for

C40H40N2ORuS2+CH2Cl2: C, 60.43; H, 5.19; N, 3.44. Found: C, 61.08; H, 5.78; N, 2.88.

Synthesis of 2nd Gen. Grubbs Catalyst from 3-5

To a CH2Cl2 solution of 3-5 (20 mg, 0.032 mmol) was added PCy3 (10 mg, 0.035 mmol) and

PhC(O)Cl (7.7 L, 0.066 mmol). The solution was stirred for 30 min and a color change from

red to purple was observed. Hexanes was added to precipitate the product which was collected

and washed with hexanes to give a purple solid in 93% yield (25 mg, 0.029 mmol). Spectral data

was identical to previous reports of 2nd

Gen. Grubbs.6













The heavy





2) and Fo

73










74

Table 4.4.1. Select Crystallographic Data for 4-1.

(4-1)

Formula C11H14OS2

Formula weight 226.36

Crystal System Monoclinic

Space group P21

a(Å) 5.74600

b(Å) 28.43100

c(Å) 13.44600

α(deg) 90

β(deg) 92.8400

γ(deg) 90

V(Å3) 2193.902

Z 8

d(calc)gcm-3

1.371

R(int) 0.0308

Abs coeff,μ,mm-1

0.449

Data collected 16225

>2(FO2) 14045

Variables 505

R(>2) 0.0474

Rw 0.1192

GOF 1.043

75



5288-5290.

2. Rupprecht, G. A.; Messerle, L. W.; Fellmann, J. D.; Schrock, R. R., Journal of the





5. Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H., Angewandte Chemie



7. Trnka, T. M.; Grubbs, R. H., Accounts of Chemical Research 2000, 34 (1), 18-29.

8. Gandelman, M.; Rybtchinski, B.; Ashkenazi, N.; Gauvin, R. M.; Milstein, D., Journal of

the American Chemical Society 2001, 123 (22), 5372-3.

9. Wilhelm, T. E.; Belderrain, T. R.; Brown, S. N.; Grubbs, R. H., Organometallics 1997,

16, 3867-3869.

10. Ferrando, G.; Coalter, I. I. I. J. N.; Gerard, H.; Huang, D.; Eisenstein, O.; Caulton, K. G.,

New Journal of Chemistry 2003, 27 (10), 1451-1462.

11. Dahcheh, F.; Stephan, D. W., Organometallics 2013, 32 (19), 5253-5255.

12. Dorta, R.; Kelly, A., III; Nolan, S. P., Advanced Synthesis & Catalysis 2004, 346, 917-

920.

13. Belderrain, T. R.; Grubbs, R. H., Organometallics 1997, 16, 4001-4003.

14. Xianming, H.; Kellogg, R. M.; Bolhuisb, F. v., J. Chem. Soc. Perkins Trans. 1994, 707-

714.

15. Frosin, K.-M.; Dahlenburg, L., Inorg. Chim. Acta 1990, 167, 83-89.

16. Nolan, S. P.; Belderrain, T. R.; Grubbs, R. H., Organometallics 1997, 16 (25), 5569-

5571.

17. Abdur-Rashid, K.; Fedorkiw, T.; Lough, A. J.; Morris, R. H., Organometallics 2003, 23

(1), 86-94.

18. Kuhn, K. M.; Grubbs, R. H., Organic Letters 2008, 10 (10), 2075-2077.

76

19. Xianming, H.; Kellogg, R. M.; van Bolhuis, F., Journal of the Chemical Society, Perkin

Transactions 1 1994, (6), 707.



77

Chapter 5 Lewis Acid Activation of Ruthenium Alkylidene Complexes

5.1 Introduction

5.1.1 Lewis Acid Activation in Catalysis

There are many examples of catalysts requiring activation from a Lewis acid co-catalyst. The

classic example employing this strategy is in the field of olefin polymerization with early

transition metals.1 The addition of a Lewis acid to a group 4 metallocene results in the

abstraction of an anionic ligand from the metal centre creating a metal-alkyl cation which is the

active species in olefin polymerization. The field of Lewis acid co-catalysts has been explored

extensively and a variety of Lewis acids have been used such as MAO2, boranes

3 and

carbocations4-5

to name a few. The choice of Lewis acid co-catalyst can result in a dramatic

effect on the structure of the resulting polymer, influencing the degree of branching, the

molecular weight, the PDI and the overall catalyst activity.6-7

Although Lewis acid activation of

catalysts has been explored extensively in the olefin polymerization field, the use of Lewis acid

co-catalysts has been relatively unexplored in olefin metathesis.

5.1.2 Lewis Acid Assisted Olefin Metathesis

The addition of Lewis acids to specific olefin metathesis reactions has proved to increase yields

when the substrates have a reactive or Lewis basic functional group. For example, the yield of

the cross metathesis product of various substrates and acrylonitrile is increased as much as

two-fold when Ti(OiPr)4 is added to the reaction catalyzed by Grubbs Catalyst.

8-9 Olefin

metathesis of acrylonitrile is difficult and often low yielding due to the nitrile functionality

poisoning the catalyst. When a Lewis acid is added to the reaction mixture, it quenches the

Lewis basicity of the nitrile group. This prevents the nitrile from binding to the ruthenium centre

and shutting down catalysis resulting in higher yields of metathesis product. With a similar

approach, the yield of the ring closed product of diallylamines can be dramatically increased by

the addition of Ti(OiPr)4

to the metathesis reaction mixture.

10 While useful for increasing yields

of specific reactions, this use of Lewis acids in olefin metathesis reactions is fundamentally

different from the direct activation of catalysts by Lewis acids.

78

5.1.3 Acid Activation of Olefin Metathesis Catalysts

There are a few examples of activation of olefin metathesis catalyst by Bronsted or Lewis acids

in the literature. The mechanism of activation can be by protonation of a ligand, abstraction of a

ligand via coordination to the Lewis acid or via halide abstraction. Similar to olefin

polymerization catalysts, the acid activation of olefin metathesis catalysts creates a vacant

coordination site. This results in a more Lewis acidic, coordinatively unsaturated metal centre

with a site for substrate to coordinate to the catalyst.

The activation of ruthenium alkylidene complexes bearing monoanionic, bidentate ligands with

Lewis or Bronsted acids for catalytic olefin metathesis has been explored in some detail

(Figure 5.1.1).11-15

In 2013, Pietraszuk reported a ruthenium alkylidene complex with a chelating

aryloxide ligand attached to the alkylidine.15

This complex is inactive for olefin metathesis on its

own but upon the addition of HCl the catalyst becomes active for ring opening metathesis

polymerization and cross metathesis. Activation is believed to occur by protonation of the

aryloxy ligand and coordination of the chloride to the metal centre to generate a

Hoveyda-Grubbs type species which is active for olefin metathesis. This catalyst can also be

activated by the Lewis acid CuCl, although the resulting catalyst is less active than when

activated with HCl. Hahn and co-workers reported a bispicolinate alkylidene complex which is

inactive for olefin metathesis.11

This catalyst also becomes activate for ring closing metathesis

upon the addition of HCl and in 2010 Grubbs and co-workers demonstrated its activity for cross

metathesis and ring opening metathesis polymerization.14

They also investigated the mechanism

of activation which was determined to be protonation of the picolinate ligands releasing two

equivalents of picolinic acid and generating a 14-electron ruthenium alkylidene species which is

active for olefin metathesis. In 2006, Verpoort et al. reported a Schiff base aryloxy ruthenium

alkylidene complex.12

Similar to the examples above, this catalyst is inactive for olefin

metathesis at room temperature but upon the addition of HCl or a Lewis acid such as CuCl,

AlCl3, silane, or BF3 the catalyst becomes active for ring opening metathesis polymerization.

Activation is believed to occur through protonation or coordination of the imine to the Lewis

acid.

79

Figure 5.1.1. Latent Olefin Metathesis Catalysts which can be Activated by Bronsted or

Lewis Acids

Grela and co-workers have published an example of acid activation of the catalyst periphery and

not on the metal centre resulting in an electronic influence.16

The protonation of an amine

functionality on the phenyl ring of a Hoveyda-Grubbs type catalyst creates an electronic effect

that results in greater lability of the ether ligand creating a more active catalyst for olefin

metathesis. They also describe a related compound that is activated by a Lewis acid following

the same principles (Scheme 5.1.1). The abstraction of a hydroxyl group from a quaternary

carbon attached to the phenyl ring of a Hoveyda-Grubbs type catalyst creates a tertiary

carbocation. This cationic charge results in an electronic effect labilizing the ether ligand and as

a result initiating catalysis more rapidly.

Scheme 5.1.1. Lewis Acid Catalyst Activation by Electronic Influence

A similar example where a Lewis acid creates an electronic effect labilizing a ligand was

published by Butenschön and co-workers (Figure 5.1.2).17

The coordination of chromium to the

phenyl ring of Hoveyda-Grubbs catalyst results in increased catalyst activity for ring closing

metathesis, ene-yne metathesis and cross metathesis reactions. Although in this example, the

80

Lewis acid is incorporated in the catalyst structure during the synthesis of the ruthenium

alkylidene and not by in situ addition, it still demonstrates activation of a olefin metathesis

catalyst by a Lewis acid.

Figure 5.1.2. Highly Active Bimetallic Olefin Metathesis Catalyst

Grubbs and co-workers have published an example of an olefin metathesis catalyst which can be

activated by a Lewis acid (Scheme 5.1.2).18

The pre-catalyst has an amino-carboxylate ligand

and upon the addition of CuCl the ligand coordinates to the copper metal centre creating a

bimetallic species bridged through the carboxylate. In order for this to happen the amine

disconnects from the ruthenium centre creating a four-coordinate ruthenium species with a

vacant site which can enter a catalytic cycle.

Scheme 5.1.2. Catalyst Activation by CuCl Ligand Abstraction

More recently, Cazin and co-workers reported a four-coordinate cationic olefin metathesis

catalyst.19

This catalyst is formed as a result of halide abstraction from a five coordinate Grubbs

type complex (Scheme 5.1.3). Both the parent neutral species and the cationic species are active

for ring closing metathesis and cross metathesis at 140 oC. Interestingly, even though the cationic

81

species is more active for olefin metathesis than the parent neutral complex, it is slower

initiating.

Scheme 5.1.3. Synthesis of a Four-Coordinate Olefin Metathesis Catalyst by Halide

Abstraction

In 2013, Wagener and co-workers published results demonstrating the effects of boron based

Lewis acids on olefin metathesis and isomerization tendency.20

They found that for Grubbs 1 and

Grubbs 2 Catalysts, the addition of triphenylborane, pinacol phenyl borane or boric acid resulted

in an increased yield of the cross metathesis product of 1-hexene. However, the addition of these

boranes to Hoveyda-Grubbs Catalysts resulted in a decreased yield of the cross metathesis

product. They speculate that the Lewis acid acts as a phosphine sponge for the Grubbs type

catalysts whereas with the Hoveyda-Grubbs type catalysts it causes catalyst decomposition.


5.2.1 Reactivity with One Equivalent of BCl3

In the mechanism for a Grubbs type olefin metathesis reaction, the active species is a four

coordinate Ru alkylidene complex. In an effort to increase the activity of the previously reported

five coordinate, Ru alkylidene species bearing tridentate ligands, an investigation into the

reactivity of these species with Lewis acids was pursued. The motivation was based on previous

reports of Lewis acid activation and the potential for working against the chelate effect in

creating a four coordinate complex.

As a starting point, BCl3 was used as the Lewis acid due to its cost and commercial availability.

Thus, when a 1 M BCl3 solution in hexanes was added to a CD2Cl2 solution of 3-1, a color

change from red to green immediately occurred as 5-1 was formed (Scheme 5.2.1). A downfield

shift of the alkylidene proton signal is observed in the 1H NMR spectrum from 13.48 to

82

17.96 ppm. Ligand backbone signals which appear as four multiplets in 3-1 now display eight

multiplets suggesting loss of symmetry. The signal for the alkylidene carbon also shifts

downfield from 235.2 to 275.3 ppm in the 13

C NMR. The 31

P{1H} NMR has a new resonance at

34.9 ppm with complete disappearance of the signal from 3-1. In the 11

B NMR a resonance at 9.9

ppm as a sharp singlet is observed suggesting four-coordinate boron.


Similar chemistry was observed in the reaction of 3-2 with BCl3, and similar NMR changes were

seen. However, the presence of two isomers was observed based on spectroscopic data. The

isolated green solid displays two downfield shifted resonances for the alkylidene protons in the

1H NMR at 17.20 and 16.30 ppm. There are two sharp singlets at 12.0 and 9.9 ppm in the

11B NMR suggesting the presence of two four-coordinate boron environments. X-ray quality

crystals of one of the isomers of 5-2 were grown and an X-ray crystallographic study confirmed

its formulation as (SIMes)Ru(CHPh)Cl[S(CH2CH2S)2BCl2] (Figure. 5.2.1). The dithiolates

which are trans in 3-2 are now cis in 5-2 and bridge between the Ru and B centers. The Ru-S

thiolate bond lengths are 2.3557(5) and 2.5027(5) Å with a S-Ru-S angle of 78.21(2)º. The B-S

bond lengths are 1.950(2) and 1.960(2) Å with as S-B-S angle of 103.28(11)º. A chloride from

the BCl3 has been transferred to Ru making it six coordinate with a geometry best described as

distorted octahedral. The Ru-Cl bond length is 2.4350(5) Å and the two Cl remaining on the B

are 1.844(3) and 1.850(2) Å from B. The tridentate ligand has flipped and the thioether which

was trans to the NHC in 3-2 is now trans to the alkylidene and has a Ru-S bond distance of

2.4919(5) Å. The Ru-C(alkylidene) and Ru-C(NHC) distances are 1.909(2) and 2.081(2) Å

respectively. All other angles around Ru range from 81.42(2)º to 94.54(2)º giving the distorted

octahedral geometry. The reason for this ligand rearrangement can be explained by the trans

effect. The BCl2 fragment which bridges the two thiolates forces them to be cis and the transfer

83

of a chloride to Ru creates a six coordinate species. In a distorted octahedral geometry there must

be a ligand trans to the strongly donating alkylidene ligand. Although similar, the thioether has a

slightly weaker trans effect than the boron-ruthenium bridged thiolate in 5-2. The two carbene

ligands (NHC and alkylidene) also have similar trans effects however the alkylidene is slightly

stronger. This difference in trans effects results in the weaker thioether donor being trans to the

stronger alkylidene donor as observed in the molecular structure. However, since the trans

effects are so similar, both isomers with and without ligand rearrangement are formed.

(Scheme 5.2.2).

Scheme 5.2.2. Synthesis 5-2

Figure 5.2.1. POV-ray depiction of 5-2a; B: pink, C: black, N: blue-green, S: yellow, Cl:

green, Ru: teal

84

Analogous to the reaction of 3-2 with BCl3, an isomeric mixture was obtained from the reaction

of 3-3 with BCl3 (Scheme 5.2.3). The presence of two phosphine NMR handles provides more

evidence to support the identity of the isomeric structures. The 31

P{1H} NMR shows two sets of

two doublets (Figure 5.2.2a). One set occurs at 81.5 and 26.9 ppm with a coupling constant of

226 Hz suggesting trans-phosphines. The other set occurs at 75.8 and 29.6 ppm with a coupling

constant of 26 Hz which is indicative of cis-phosphines. The alkylidene region of the 1H NMR

spectrum also displays two signals (Figure 5.2.2b). One signal is at 18.2 ppm and appears as a

doublet with a coupling constant of 6.8 Hz and the other is at 17.4 ppm and is a doublet of

doublets with coupling constants of 17.4 and 10.6 Hz. The 11

B NMR shows a sharp singlet at

10.7 ppm. This data suggests the formation of two isomers in a ratio of 9:1 with the formulation

(PCy3)RuCl(CHPh)[Cl2B(SCH2CH2)2PPh]. 5-3a is the product of the analogous rearrangement

seen for 5-1 where the tridentate ligand has rearranged to have the central phosphine donor trans

to the alkylidene. In the second isomer, 5-3b, the ligand has not rearranged on the ruthenium

centre and the central phosphine donor remains trans to the PCy3.

85

(a)

(b)

Figure 5.2.2. (a) 31

P{1H} NMR spectrum and (b) alkylidene region of

1H NMR spectrum of

5-3 in CD2Cl2

86

In 5-3 the central PPh is a much stronger donor than the central thioether in 5-1. The stronger

donating ability and trans effect of the central phosphine results in an isomeric mixture in which

one isomer has the PPh trans to the strongly donating alkylidene ligand and the other has the PPh

trans to the PCy3. Attempting to force the reaction towards one of the isomers with heating or

cooling was unsuccessful.

Scheme 5.2.3. Synthesis of 5-3a and 5-3b

3-4 and 3-5 reacted with BCl3 in an analogous fashion (Scheme 5.2.4). The red CH2Cl2 solution

of 3-4 turned green with the addition of BCl3 to give 5-4. The doublet for the alkylidene proton

shifts downfield from 13.68 in 3-4 to 18.93 in 5-4. There is an obvious loss in symmetry based

on the eight multiplets present in the alkyl region (Figure 5.2.3). The alkylidene carbon resonates

at 277.4 ppm in the 13

C{1H} NMR spectrum and the PCy3 signal in the

31P{

1H} NMR spectrum

has shifted upfield to 35.5 ppm. Four coordinate boron can be observed in the 11

B NMR

spectrum at 11.1 ppm as a sharp singlet.

87

(a)

(b)

Figure 5.2.3. (a) 1H NMR Spectrum of 5-4. (b) Expansion of Ligand Backbone Region of

1H NMR Spectrum of 5-4

Based on these data and a X-ray crystallographic study 5-4 was determined to be

(PCy3)Ru(CHPh)Cl[O(CH2CH2S)2BCl2] (Figure 5.2.4). 5-4 adopts a disordered octahedral

geometry about Ru. A chloride has been transferred from BCl3 to Ru and has a Ru-Cl distance of

2.3982(4) Å. The remaining BCl2 fragment (B-Cl distances 1.8304(18) and 1.8367(17) Å)

bridges the two thiolates arising to B-S distances of 1.8228(14) and 1.9472(17) Å. The S-B-S

88

angle is 104.04(8)º. The Ru-S distances for the axial and equatorial S are 2.4622(4) and

2.3702(4) Å respectively and produce a S-Ru-S angle of 78.889(13)º. The central ether of the

tridentate ligand is trans to the alkylidene with a Ru-O bond distance of 2.3554(9) Å. The Ru-C

and Ru-P distances are 1.8679(13) and 2.3666(4) Å, respectively. All remaining angles around

Ru range from 75.90(3)º to 98.82(4)º which are consistent with the distorted octahedral

geometry.


Figure 5.2.4. POV-ray depiction of 5-4; B: pink, C: black, O: red, P: orange, S: yellow, Cl:

green, Ru: teal

The NMR data for the reaction of 3-5 with one equivalent of BCl3 displays the characteristic

shifts seen for the identical reaction of 3-1 through 3-4 leading to 5-5 in 92% yield. The signal

89

attributed to the proton of the alkylidene shifts downfield to 17.68 ppm. The 13

C spectrum has a

resonance at 308.9 ppm from the alkylidene carbon and a sharp singlet is observed in the

11B NMR at 11.5 ppm. An X-ray crystallographic study confirmed the formulation of 5-5 as

(SIMes)Ru(CHPh)Cl[O(CH2CH2S)2BCl2] (Figure 5.2.5). Similar to the crystallographically

studied isomer of 5-2, this complex adopts a geometry in which the NHC ligand is trans to S,

alkylidene is trans to the ether O atom and the remaining S atom is trans to a Cl which was

transferred from BCl3 to Ru. The trans C(NHC)-Ru-S, CCHPh-Ru-O, S-Ru-Cl angles in 5-5 of

175.64(9)º, 161.79(9)º and 167.22(3)º are consistent with a distorted octahedral geometry. The

Ru-C(NHC), Ru-CCHPh, Ru-O and the two Ru-S distances in 5-5 were determined to be 2.056(3),

1.864(3), 2.300(2), 2.3444(7) and 2.4105(7) Å, respectively, all slightly longer than those seen in

3-5. Bridging the two S atoms is a BCl2 fragment with S-B distances of 1.951(3) and 1.929(3) Å

and B-Cl bond lengths of 1.831(3) and 1.845(3) Å. The S-Ru-S and S-B-S angles were found to

be 79.07(2)º and 104.62(15)º, respectively.

Figure 5.2.5. POV-ray depiction of 5-5; B: pink, C: black, N: blue-green O: red, S: yellow,

Cl: green, Ru: teal

90

Compounds 3-6 and 3-7 displayed identical reactivity to that previously discussed giving only

one isomer (Scheme 5.2.5). Compound 3-6 reacted to give (PCy3)RuCl(CHPh)[Cl2B(SC6H4)2O],

5-6 which displays a downfield shifted alkylidene signal in the 1H NMR at 18.9 ppm

(d, 3JPH = 11.6 Hz) and an upfield phosphorus shift at 36.5 ppm. 3-7 gives the analogous product

(SIMes)RuCl(CHPh)[Cl2B(SC6H4)2O], 5-7 which is characterized by its downfield alkylidene

signal at 17.75 ppm in the 1H NMR. The characteristic

11B shift can be observed for 5-6 and 5-7

at 12.1 and 14.7 ppm, respectively.


Complexes 3-8 and 3-9 reacted with one equivalent of BCl3 to give 5-8 and 5-9, respectively

(Scheme 5.2.6). These complexes proved difficult to isolate cleanly but the evidence for their

formation could be observed in situ via NMR spectroscopy. In the 1H NMR, the characteristic

downfield shift of the alkylidene can be seen for 5-8 and 5-9 to 20.13 and 16.83 ppm,

respectively. The PCy3 signal in the 31

P NMR spectra shifts from 64.76 ppm in 3-8 to 28.8 ppm

in 5-8. Four coordinate boron can be seen at 23.4 and 18.2 for 5-8 and 5-9 respectively in the

11B NMR. Based on these data 5-8 and 5-9 are formulated as

(PCy3)Ru(CHPh)Cl[O(CH2CH2O)2BCl2] and (SIMes)Ru(CHPh)Cl[O(CH2CH2O)2BCl2]

respectively.


91

5.2.2 Reactivity with Two Equivalents of BCl3

The addition of one equivalent of BCl3 to the Ru alkylidene complexes 3-1 through 3-9 results in

the formation of a 6-coordinate complex. Although this reaction is interesting, the formation of a

6-coordinate species from a catalytic point of view is undesirable. As discussed in Section 1.2.3

the active species in the mechanism of Grubbs Catalyst is a four-coordinate species. There have

been reports of 5-coordinate complexes being catalytically active, but it is very unlikely that a

coordinatively saturated Ru alkylidene would be active for olefin metathesis. In an effort to form

a coordinatively unsaturated species, the effect of an additional equivalent of BCl3 on 5-1

through 5-9 was investigated.

Although the addition of a second equivalent of BCl3 to 5-1 and 5-2 showed no reaction, an

obvious reaction occurred with the addition of BCl3 to 5-4 and 5-5 (Scheme 5.3.7). When a

second equivalent of BCl3 was added to a CH2Cl2 solution of 5-4 the reaction mixture became

darker green. Preliminary 11

B NMR data suggested the formation of the BCl4- anion presumably

via halide abstraction and generation of salt 5-10. In the 1H NMR a broadening of the peaks

occurs. In an attempt to isolate this salt, a small excess of CH3CN was added which resulted in

an immediate color change to red as 5-11 formed. Ultimately a red solid was isolated in 87%

yield. The resonance attributed to the alkylidene proton in the 1H NMR shifts from 18.93 ppm

for 5-4 to 18.66 ppm for 5-11. A small shift in the 31

P NMR is observed with a new signal at

36.14 ppm. There are two peaks in the 11

B NMR at 11.8 and 7.0 ppm with the later attributed to

the BCl4- anion. An X-ray crystallographic study confirmed the structure of 5-11 as

[(PCy3)Ru(CHPh)CH3CN(O(CH2CH2S)2BCl2)][BCl4] (Figure 5.2.6). The geometry remains a

distorted octahedral about Ru, similar to 5-4. The Ru-P bond lengthens slightly from 2.3666(4)

in 5-4 to 2.4080(9) Å in 5-11. The Ru-S bonds shorten from 2.4622(4) and 2.3702(4) Å to

2.4405(10) and 2.3596(9) Å with a S-Ru-S angle of 79.55(3)º. The Ru-O and Ru-C bonds are

2.292(2) and 1.874(3) Å respectively. The Ru-N bond length is 2.053(3) Å and the N-Ru-C and

N-Ru-O angles are 98.18(14) and 89.66(10)º, respectively. The B-S bond lengths are 1.967(5)

and 1.950(4) Å and the S-B-S angle is 103.3(2)º. The B-Cl bond length of the coordinated borate

are 1.841(4) and 1.811(5) Å with a Cl-B-Cl angle of 112.0(2)º.

92

Scheme 5.2.7. Synthesis of 5-10 - 5-13

Figure 5.2.6. POV-ray depiction of 5-11; B: pink, C: black, N: blue-green, O: red, P:

orange, S: yellow, Cl: green, Ru: teal

The addition of a second equivalent of BCl3 to 5-5 also resulted in the green solution darkening

as 5-12 formed. Assuming salt formation by halide abstraction, an excess of CH3CN was added

to trap it. The solution immediately turned red and the red compound, 5-13 was isolated. The

11B NMR shows the presence of a BCl4

- anion with a resonance at 6.92 ppm with the coordinated

93

borate giving a signal at 11.39 ppm. The proton resonance from the alkylidene shifts from 17.68

in 5-5 to 17.26 ppm in 5-13. The remaining 1H NMR data were consistent with the NHC,

dithiolate and CH3CN ligands. An X-ray crystallographic study confirmed the formation of the

salt [(SIMes)Ru(CHPh)CH3CN(O(CH2CH2S)2BCl2)][BCl4] 5-13 (Figure 5.2.7). The cation of

5-13 adopts a pseudo-octahedral geometry similar to that of 5-5. The Ru-C(NHC) bond length has

lengthened from 2.056(3) Å in 5-5 to 2.099(2) Å. The Ru-C(CHPh) distance has also slightly

lengthened from 1.864(3) to 1.872(2) Å. The Ru-O, and Ru-S bonds have remained very similar

in length with bonding distances of 2.2960(15), 2.3607(5) and 2.4475(5) Å respectively. The

new Ru-N bond is 2.0407(18) Å which is similar to 5-11. The trans C(NHC)-Ru-S, C(CHPh)-Ru-O

and S-Ru-N angles are 167.50(6), 166.21(7) and 169.81(5)º respectively, displaying the pseudo-

octahedral geometry. The B-S bond distances are 1.948(3) and 1.943(3) Å and form a S-B-S

angle of 105.20(11)º. The B-Cl lengths of the coordinated borate are 1.828(3) and 1.854(3) Å

with a Cl-B-Cl angle of 111.42(13)º.

Figure 5.2.7. POV-ray depiction of 5-13; B: pink, C: black, N: blue-green, O: red, S:

yellow, Cl: green, Ru: teal. Anion omitted for clarity

94

Complexes 5-6 - 5-9 display analogous reactivity with a second equivalent of BCl3 to give

complexes 5-14 - 5-17 (Figure 5.2.8). The formation of the BCl4- anion can be observed in the

11B NMR spectrum and a small shift and broadening of the signals in the

1H and

31P{

1H} NMR

spectrums occurs. While the formation of the analogous 5-coordinate cationic ruthenium species

is observed via halide abstraction, attempts to trap these species with a Lewis base failed.

Figure 5.2.8. Complexes 5-14 - 5-17

5.2.3 Reactivity with Bronsted Acid

Since Lewis acids react with these Ru alkylidene complexes, the reactivity with Bronsted acid

was investigated. Potentially, the acid could protonate a coordinated thiolate ligand causing it to

be more labile and possibly activate the catalyst. In order to prevent coordinatively saturating the

metal centre, a non-coordinating anion must be used which would create a formally cationic Ru

species. This motivated the use of [Et2O•H][BF4] which when combined with 3-4 in CH2Cl2

resulted in a lightening of the brown solution as 5-18 formed. Preliminary 1H NMR data shows

the loss of the alkylidene signal and the appearance of a new singlet at 4.20 ppm that integrates

to two protons (Figure 5.2.9). All other peaks can be assigned to the PCy3, the tridentate ligand

backbone, and the phenyl group. The presence of the BF4 anion can be observed in the 11

B and

19F NMR spectra of the product with resonance at -1.2 and -151.8 ppm respectively. A new

resonance in the 31

P{1H} NMR is observed at 53.2 ppm, which is shifted upfield from the

starting material 3-4 (65.6 ppm). Based on this data, 5-18 is formulated to be

[(PCy3)Ru(CH2Ph)(SCH2CH2)2O][BF4] where protonation of the alkylidene carbon has occurred

with the formation of a formally cationic Ru(IV) species (Scheme 5.2.8). To test this conclusion,

PtBu3 was added to 5-18 which resulted in the precipitation of a white solid which was identified

as [HPtBu3][BF4]. All the NMR data of the resulting compound matched that of 3-4. This type of

95

reactivity has been seen for earlier transition metal alkylidene complexes but is rare for Ru

alkylidenes.21-22

Reacting 3-5 with [Et2O•H][BF4] resulted in the observation of the analogous

compound. However, it quickly decomposed as the formation of protonated SIMes is observed.

Figure 5.2.9. 1H NMR spectra of 3-4 (Top) and 5-18 (Bottom)


96

5.2.4 Reversibility of Lewis Acid Reactivity

Due to the reversibility of the Bronsted acid reactivity, the reversibility of the Lewis acid

reactivity was probed. The addition of PtBu3 to 5-4 in CH2Cl2 resulted in the green solution

becoming red. A white precipitate formed and preliminary 31

P and 11

B NMR data showed the

presence of the tBu3PBCl3 adduct. The

31P{

1H} NMR displays a singlet at 65.60 ppm suggesting

the recovery of 3-4 (Scheme 5.2.9). The 1H NMR spectrum confirms the formation of 3-4 with

the reappearance of the alkylidene resonance at 13.68 ppm and all other peaks corresponding to

3-4. This reversibility where PtBu3 abstracts the BCl3 moiety from the complex resulting in the

reformation of the parent Ru alkylidene complex is observed for complexes 5-1 through 5-9.

Compounds 5-10 and 5-12 also display reversible BCl3 reactivity. Addition of 1 equivalent of

PtBu3 to these complexes resulted in the recovery of 5-4 and 5-5, respectively with the

elimination of the tBu3PBCl3 adduct.

Scheme 5.2.9. Reversibility of Lewis Acid Reactivity

5.3 Conclusion

The Ru alkylidene complexes with tridentate, dianionic ligands were shown to react sequentially

with 2 equivalents of BCl3. The first equivalent results in a chloride being transferred to the

metal centre and the remaining BCl2 fragment bridges the two anionic donors. Due to the trans

effect this causes a rearrangement of the tridentate ligand on the metal centre. However, in some

cases due to similarities in donor strength two isomers are formed. One isomer with the

rearranged ligand and the other isomer has the original ligand binding mode. The second

equivalent of BCl3 abstracts the chloride from the metal centre resulting in a cationic ruthenium

species. In some cases this cation can be trapped with the addition of a small donor such as

CH3CN. This step-wise reactivity is reversed in a step-wise manner with the sequential addition

97

of 2 equivalents of PtBu3 with the elimination of the Lewis acid-base adduct

tBu3PBCl3. By

contrast, these Ru complexes react with Bronsted acids via protonation of the alkylidene carbon.

This creates a cationic Ru benzyl species. This reactivity is also reversible and with the addition

of PtBu3 the benzyl carbon is deprotonated resulting in the formation of the original starting

material.







Teflon valve stopcocks. Acetonitrile was dried over CaH2 and distilled. Dichloromethane-d2 was

dried over CaH2 and benzene-d6 was dried over Na metal and vacuum-transferred into a Young

bomb. All solvents were thoroughly degassed after purification (three freeze-pump-thaw cycles).

1H,

13C, and

31P NMR spectra were recorded at 25 °C on Varian 300 and 400 MHz and Bruker

400 MHz spectrometers. Commercially available substrates were obtained from Sigma-Aldrich

and used without further purification. Chemical shifts are given relative to SiMe4 and referenced

to the residual solvent signal (1H,

13C) or relative to an external standard (

31P: 85% H3PO4). In

some instances, signal and/or coupling assignment was derived from two-dimensional NMR

experiments. Chemical shifts are reported in ppm and coupling constants as scalar values in Hz.

Combustion analyses were performed in house employing a Perkin-Elmer CHN Analyzer.


Synthesis of 5-1: To a CH2Cl2 solution (1 mL) of 3-1 (0.020 g, 0.032

mmol) was added BCl3 in hexanes (1 M, 32 µL, 0.032 mmol). The red

solution immediately turned green. All volatiles were removed, and the

resulting dark solid was washed with CH3CN (2 mL) and dried to yield a

green solid. (0.022 g, 93%). 1H NMR (CD2Cl2): 17.96 (d,

3JPH = 15.1 Hz,

1H, Ru=CH), 8.34 (d, 3JHH = 8.81 Hz, 2H, o-H of C6H5), 7.65 (t,

3JHH =

7.73 Hz, 1H, p-H of C6H5), 7.40 (t, 3JHH = 7.83Hz, 2H, m-H of C6H5), 3.66, 3.13, 2.95 (all m,

1H, CH2), 2.55 (m, 5H, 5 CH2), 2.05, 1.88, 1.75-1.45, and 1.18 (all m, P(C6H11)3). 11

B NMR

98

(CD2Cl2): 9.94 (s). 13

C{1H} NMR (CD2Cl2): 275.25 (Ru=CH), 154.83 (ipso-C, Ph), 132.15 (CH,

Ph), 131.84 (2 CH, Ph), 128.77 (2 CH, Ph), 39.32, 38.98 (2 CH2), 36.73 (d, 1JPC = 19.32

Hz, ipso-C of P(C6H11)3), 30.24, 30.03 (2 CH2), 27.79 (m-C of P(C6H11)3), 27.55 (o-C of

P(C6H11)3), 26.56 (p-C of P(C6H11)3). 31

P{1H} NMR (CD2Cl2): 34.92. Analysis calculated for

C29H47BCl3PRuS3: C, 47.00; H, 6.39. Found: C, 46.89 H, 6.46.

Synthesis of 5-2: To a CH2Cl2 solution (1 mL) of

3-2 (0.020 g, 0.031 mmol) was added BCl3 in

hexanes (1 M, 31 µL, 0.031 mmol). The brown

solution immediately turned dark green. All

volatiles were removed, and the resulting dark

solid was washed with CH3CN (2 mL) and dried

to yield a blue-green solid. (0.022 g, 93%). X-Ray quality crystals were grown from a

CH2Cl2/CH3CN solution.1H NMR (CD2Cl2): 17.20 (Ru=CH, 5-2a), 16.30 (Ru=CH, 5-2b), 7.61

(m, 2H, o-H of C6H5) 7.43 (m, 1H, p-H, Ph), 7.34 (m, 2H, m-H of C6H5), 7.12 (s, 2H, 2 CH,

Mes), 7.04 (s, 1H, CH, Mes) 6.58 (s, 1H, CH, Mes), 3.90 (m, 2H, CH2, Im), 3.77 (m, 2H, CH2,

Im), 3.51, 3.31, 3.20 (all m, 1H, CH2), 2.97 (m, 2H, CH2) 2.65, 2.60, 2.49, 2.40, 2.33, 2.28 (all s,

3 H, 6 CH3, Mes), 2.06 (m, 1H, CH2), 1,85 (m, 2H, CH2). 13

C{1H} NMR (CD2Cl2): 152.7,

150.4, 138.7, 138.6, 137.7,137.3, 131.7, 131.2, 129.6,129.5, 128.3 (all Ph, Mes), 65.6 (2 CH2,

Im), 52.1, 51.9, 42.2, 40.5, 39.4, 35.4, 31.5, 31.2, 28.5, 26.8, 25.5 (all CH2), 20.8, 20.6, 19.3,

19.0, 18.8, 18.7 (CH3, Mes). 11

B NMR (CD2Cl2): 11.95, 9.89. Analysis calculated for

C32H40BCl3N2RuS3: C, 50.10; H, 5.26; N, 3.65. Found: C, 49.46 H, 5.14; N, 3.39.

Synthesis of isomeric 5-3: To a CH2Cl2

solution (1 mL) of 3-3 (0.020 g, 0.029 mmol)

was added BCl3 in hexanes (1 M, 29 µL,

0.029 mmol). The brown solution

immediately turned dark green. All volatiles

were removed, and the resulting dark solid

was washed with CH3CN (2 mL) and dried to

yield a dark green solid. (0.022 g, 93%). The compound exists as a mixture of isomers (12a,

12b). With the addition of one more equivalent of BCl3 the compound becomes an active olefin

metathesis catalyst. 1H NMR (CD2Cl2): 18.06 (d,

3JPH = 6.78 Hz, Ru=CH, 5-5b), 17.32 (dd,

3JPH

99

= 17.4 Hz, 3JPH = 10.6 Hz, Ru=CH, 5-5a), 7.80 (m, Ph), 7.76 (m, Ph), 7.64 (m, Ph), 7.59 (m, Ph),

7.55 (m, Ph), 7.43 (m, Ph), 7.35 (m, Ph), 7.26 (m, Ph), 7.17 (m, Ph), 7.11 (m, Ph), 6.99 (m, Ph),

4.63 (m, CH2, 5-3a), 4.39 (m, CH2, 5-3a), 4.19 (m, CH2, 5-3a), 4.05 (m, CH2, 5-3a), 3.61 (m,

CH2, 5-3b), 3.17 (m, CH2, 5-3b), 2.89 (m, CH2, 5-3b), 2.82 (m, CH2, 5-3b), 2.49 (m, PCy3), 2.16

(m, PCy3), 1.87 (m, PCy3), 1.68 (m, PCy3), 1.32 (m, PCy3). 13

C{1H} NMR (CD2Cl2): 153.3 (Ph),

151.1 (Ph), 137.3 (Ph), 134.9 (Ph), 133.3 (Ph), 131.9 (Ph), 131.5 (Ph), 130.6 (Ph), 130.2 (Ph),

129.7 (Ph), 129.2 (Ph), 128.8 (Ph), 128.6 (Ph), 128.4 (Ph), 128.1 (Ph), 128.0 (Ph), 127.9 (Ph),

127.6 (Ph), 127.1 (Ph), 126.4 (Ph), 37.6 (CH2), 35.8 (CH2), 35.7 (CH2), 34.1 (CH2), 31.3 (d, 1JPC

= 29.9 Hz, PCy3), 30.9 (CH2), 30.6 (CH2), 30.1 (CH2), 29.7 (CH2), 29.5 (CH2), 27.7 (d, 3JPP = 4.2

Hz, PCy3), 27.2 (d, 2JPP = 10.5 Hz, PCy3), 26.5 (CH2), 25.7(CH2).

11B NMR (CD2Cl2): 10.67.

31P{

1H} NMR (CD2Cl2): 81.54 (d,

2JPP = 255.2 Hz, PPh, 5-5b), 75.76 (d,

2JPP = 25.8 Hz, PPh, 5-

5a), 29.64 (d, 2JPP = 25.9 Hz, PCy3, 5-5a), 26.87 (d,

2JPP = 256.6 Hz, PCy3, 5-5b).

Synthesis of 5-4: To a CH2Cl2 solution (1 mL) of 3-4 (0.020 g, 0.033 mmol)

was added BCl3 in hexanes (1 M, 33 µL, 0.033 mmol). The red solution

immediately turned green. All volatiles were removed, and the resulting

dark solid was washed with CH3CN (2 mL) and dried to yield a green solid.

(0.021 g, 89%). X-Ray quality crystals were grown from a CH2Cl2/CH3CN

solution. 1H NMR (CD2Cl2): 18.93 (d,

3JPH = 11.7 Hz, 1H, Ru=CH), 8.87

(d, 3JHH = 8.27 Hz, 2H, o-H of C6H5), 7.74 (t,

3JHH = 7.98 Hz, 1H, p-H of C6H5), 7.51 (t,

3JHH =

8.17 Hz, 2H, m-H of C6H5), 5.05, 4.56, 4.19, 3.82, 3.13, 3.00, 2.89, 2.78 (all m, 1H, CH2), 2.12,

1.88, 1.82-1.64, 1.52, and 1.21-1.13 (all m, P(C6H11)3). 11

B NMR (CD2Cl2): 11.08 (s). 13

C{1H}

NMR (CD2Cl2): 277.37 (Ru=CH), 153.05 (ipso-C, Ph), 132.67 (2 CH, Ph), 131.81 (CH, Ph),

128.36 (2 CH, Ph), 71.15, 68.58 (2 CH2), 36.20 (d, 1JPC = 19.21 Hz, ipso-C of P(C6H11)3),

33.24, 30.57 (2 CH2), 29.54 (m-C of P(C6H11)3), 27.93 (o-C of P(C6H11)3), 26.43 (p-C of

P(C6H11)3). 31

P{1H} NMR (CD2Cl2): 35.54. Analysis calculated for C29H47BCl3OPRuS2: C,

48.04; H, 6.53. Found: C, 47.83 H, 6.62.

100


mmol) was added BCl3 in hexanes (1 M, 32 µL, 0.032 mmol). The

brown solution immediately turned dark green. All volatiles were

removed, and the resulting dark solid was washed with CH3CN (2 mL)

and dried to yield a blue-green solid. (0.022 g, 92%). X-Ray quality

crystals were grown from a CH2Cl2/CH3CN solution.1H NMR (CD2Cl2):

17.68 (s, 1H, Ru=CH), 8.09 (br, 2H, o-H of C6H5) 7.56 (t, 3JHH = 7.54

Hz, 1H, p-H, Ph), 7.24 (t, 3JHH = 7.54 Hz, 2H, m-H of C6H5), 7.03 (s, 2H, 2 CH, Mes), 6.56 (s,

2H, 2 CH, Mes), 4.84 (m, 1H, CH2), 3.84 (m, 2H, CH2, Im), 3.74 (m, 1H, CH2), 3.64 (m, 2H,

CH2, Im), 3.01, 2.80, 2.62 (all m, 1H, CH2), 2.52 (s, 6 H, 2 CH3, Mes), 2.34 (m, 2H, CH2), 2.25

(s, 6 H, 2 CH3, Mes), 2.20 (s, 6 H, 2 CH3, Mes), 2.17 (m, 1H, CH2). 13

C{1H} NMR

(CD2Cl2): 308.91 (Ru=CH), 214.62 (ipso-C, Ph), 152.04 (ipso-C, NCN), 138.54 (CMe, Mes),

137.59 (ipso-C, Mes), 137.39 (ipso-C, Mes), 132.65 (2 o-CH, Ph), 130.65 (p-CH, Ph), 129.64,

129.25 (4 CH, Mes), 126.96 (2 m-CH, Ph), 70.30, 68.12 (2 CH2), 52.16, 53.83 (2 CH2,

Im), 30.56, 26.53 (2 CH2), 20.70 (2 CH3, Mes), 19.05 (2 CH3, Mes), 18.73 (2 CH3, Mes).

11B NMR (CD2Cl2): 11.46. Analysis calculated for C32H40BCl3N2ORuS2•CH2Cl2: C, 47.41; H,

5.06; N, 3.35. Found: C, 48.05 H, 5.36; N, 3.78.



solution immediately turned green and a blue-green precipitate began to

form. All volatiles were removed, and the resulting dark solid was

washed with CH3CN (2 mL) and dried to yield a blue-green solid. (0.020

g, 87%). 1H NMR (CD2Cl2): 18.85 (d,

3JPH = 11.6 Hz, 1H, Ru=CH), 8.54 (d,

3JHH = 7.9 Hz, 2H,

Ph), 7.74 (m, 3H, Ph), 7.57-7.37 (m, 6H, Ph), 7.20 (m, 2H, Ph), 2.40, 2.07, 1.80, 1.62, 1.43 (all

m, P(C6H11)3. 13

C{1H} NMR (Partial) (CD2Cl2): 154.6, 131.9, 131.2, 130.9, 128.7, 126.7, 123.1,

122.2, 121.2, 118.1, 116.3, 35.3, 31.6, 29.7, 29.1, 27.8, 27.7, 27.5 27.2 26.9, 26.3. 31

P{1H} NMR

(CD2Cl2): 36.51. 11

B NMR (CD2Cl2): 12.11. Analysis calculated for C37H47BCl3OPRuS2: C,

54.12; H, 5.77. Found: C, 53.94 H, 5.62.

101



solution immediately turned green and a blue-green precipitate began

to form. All volatiles were removed, and the resulting dark solid was

washed with CH3CN (2 mL) and dried to yield a green solid. (0.019 g,

83%). 1H NMR (CD2Cl2): 17.75 (s, 1H, Ru=CH), 7.60 (t, 1H, Ph), 7.40

(m, 5H, Ph), 7.31 (m, 2H, Ph), 7.13 (m, 3H, Ph), 7.06 (m, 3H, Ph, Mes), 6.82 (m, 1H, Ph), 6.04

(s, 2H, Mes), 3.83 (m, 1H, CH2, Im), 3.68 (m, 1H, CH2, Im), 3.48 (m, 2H, CH2, Im), 2.59 (s, 6 H,

2 CH3, Mes), 2.18 (s, 6H, 2 CH3, Mes), 2.05 (s, 6H, 2 CH3, Mes).13

C{1H} NMR (CD2Cl2):

289.9 (Ru=CH), 212.4, 183.7, 161.4, 160.4, 151.3, 138.6, 137.6, 137.3, 136.6, 134.1, 131.3,

130.2, 129.6, 129.4, 129.1, 128.5, 128.3, 126.8, 126.1, 125.7, 125.0, 123.0, 120.2, 52.2 (2 CH2,

Im), 20.8 (2 CH3, Mes), 19.0 (2 CH3, Mes), 18.5 (2 CH3, Mes). 11

B NMR (CD2Cl2): 14.7.

In situ synthesis of 5-8: To a CH2Cl2 solution (1 mL) of 3-8 (0.020 g, 0.035

mmol) was added BCl3 in hexanes (1 M, 35 µL, 0.035 mmol). The red solution

immediately turned green.

In situ synthesis of 5-9: To a CH2Cl2 solution (1 mL) of 3-9 (0.020 g,

0.033 mmol) was added BCl3 in hexanes (1 M, 33 µL, 0.033 mmol). The

brown solution immediately turned dark green.

102

Synthesis of 5-11: To a CH2Cl2 solution (1 mL) of 5-3 (0.050 g,

0.069 mmol) was added BCl3 in hexanes (1 M, 69 µL, 0.069

mmol). The green solution immediately turned darker green. To

this, CH3CN (0.30 mL) was added and the solution turned dark

red. All volatiles were removed and the dark red solid was

dissolved in CH2Cl2 (1 mL) and filtered. Pentane (5 mL) was

added and a dark red precipitate formed. The solid was collected, washed with pentane

(2 x 2 mL) and dried in vacuo to yield a dark red solid. (0.053 g, 87%). X-Ray quality crystals

were grown from a CH2Cl2 solution layered with pentane. 1H NMR (CD2Cl2): 18.66

(d, 3JPH = 9.3 Hz, 1H, Ru=CH), 8.36 (d,

3JHH = 7.9 Hz, 2H, o-H of C6H5), 7.91 (t,

3JHH = 7.4 Hz,

1H, p-H of C6H5), 7.71 (t, 3JHH = 7.6 Hz, 2H, m-H of C6H5), 4.66 (m, 2H, CH2), 4.50 (m. 1H,

CH2), 4.37 (m, 2H, CH2), 4.25 (m, 1H, CH2), 3.95 (m, 2H, CH2), 2.65 (s, 3H CH3CN) 2.09, 1.95,

1.89-1.77, and 1.26-1.15 (all m, P(C6H11)3). 11

B NMR (CD2Cl2): 11.74 (s, S2BCl2), 6.98 (s,

BCl4). 13

C{1H} NMR (CD2Cl2): 152.0 (ipso-C, Ph), 134.7 (2 CH, Ph), 131.9 (CH, Ph), 129. 6

(2 CH, Ph), 75.2, 70.5 (2 CH2), 36.7 (d, 1JPC = 18.9 Hz, ipso-C of P(C6H11)3), 33.4, 31.6

(2 CH2), 29.5 (m-C of P(C6H11)3), 27.7 (o-C of P(C6H11)3), 26.0 (p-C of P(C6H11)3), 13.9

(CH3, CH3CN). 31

P{1H} NMR (CD2Cl2): 36.12. Analysis calculated for C31H50B2Cl6NOPRuS2:

C, 42.15; H, 5.71; N, 1.59. Found: C, 42.28 H, 5.51; N, 1.10.

Synthesis of 5-13: To a CH2Cl2 solution (1 mL) of 4 (0.030 g,

0.040 mmol) was added BCl3 in hexanes (1 M, 40 µL, 0.040

mmol). The green-blue solution immediately turned darker

green. To this, CH3CN (0.100 mL) was added and the solution

turned red. All volatiles were removed and the red solid was

dissolved in CH2Cl2 (1 mL) and filtered. Pentane (5 mL) was

added and a red precipitate formed. The solid was collected,

washed with pentane (2 x 2 mL) and dried in vacuo to yield a red solid. (0.034 g, 94%). X-Ray

quality crystals were grown from a CH2Cl2 solution layered with pentane.1H NMR (CD2Cl2):

17.26 (s, 1H, Ru=CH), 7.64 (m, 3H, o-H and p-H of C6H5) 7.38 (t, 3JHH = 7.99 Hz, 2H, m-H of

C6H5), 7.00 (s, 2H, 2 CH, Mes), 6.77 (s, 2H, 2 CH, Mes), 4.02 (m, 1H, CH2), 3.83 (br, 5H,

1H, CH2 and 2 CH2, Im), 3.46 (m, 2H, CH2, Im), 3.21 (m, 1H, CH2), 2.66 (m, 3H, 3 CH,

103

CH2), 2.53 (s, 6 H, 2 CH3, Mes), 2.47 (s, 3H, CH3CN), 2.27 (s, 6 H, 2 CH3, Mes), 2.25 (s, 6

H, 2 CH3, Mes). 13

C{1H} NMR (CD2Cl2): 208.50 (ipso-C, Ph), 151.65 (ipso-C, NCN), 140.05

(CMe, Mes), 137.53 (ipso-C, Mes), 136.85 (Mes), 136.43 (Mes), 134.08 (2 o-CH, Ph), 131.79

(p-CH, Ph) 130.33, 129.92 (4 CH, Mes), 129.06 (2 m-CH, Ph), 70.35, 69.45 (2 CH2),

54.10, 53.14 (2 CH2, Im), 34.52, 33.92 (2 CH2), 22.76 (2 CH3, Mes), 19.03 (2 CH3,

Mes), 18.79 (2 CH3, Mes), 14.20 (CH3, CH3CN). 11

B NMR (CD2Cl2): 11.39 (BS2Cl2), 6.92

(BCl4). Analysis calculated for C34H43B2Cl6N3ORuS2: C, 44.91; H, 4.77; N, 4.62. Found: C,

44.52 H, 4.60; N, 4.27.

Synthesis of 5-18: To a CH2Cl2 solution of 3-4 (0.050 g,

0.082 mmol) was added [Et2O•H][BF4] (0.011 mL, 0.082 mmol).

The solution immediately became lighter. The solvent was

removed under vacuum and the resulting brown solid was washed

with hexanes (5 mL) and dried in vacuo. (0.052 g, 91 %). 1H

NMR (CD2Cl2): 7.40 (t, 3JHH = 7.7 Hz, 1H, p-H of C6H5), 7.32 (t,

3JHH = 7.7 Hz, 2H, m-H of

C6H5), 7.20 (d, 3JHH = 7.7 Hz, 2H, m-H of C6H5), 4.23 (s, 2H, CH2Ph), 4.64 (m, 2H, CH2), 4.49

(m. 2H, CH2), 4.43 (m, 2H, CH2), 2.74 (m, 2H, CH2), 2.40, 2.11, 1.94, 1.81, 1.68 and 1.44-1.23

(all m, P(C6H11)3). 11

B NMR (CD2Cl2): -1.2. 19

F NMR (CD2Cl2): -151.8. 13

C{1H} NMR

(CD2Cl2): 142.7 (ipso-C, Ph), 130.4 (2 CH, Ph), 129.0 (2 CH, Ph), 127.7 (CH, Ph), 71.2

(2 CH2), 52.1 (CH2Ph), 39.3 (2 CH2), 36.4 (d, 1JPC = 23.9 Hz, ipso-C of P(C6H11)3), 29.4

(m-C of P(C6H11)3), 27.5 (d, 2JPC = 11.3 Hz, o-C of P(C6H11)3), 25.9 (p-C of P(C6H11)3).

31P{

1H}

NMR (CD2Cl2): 53.2. Analysis calculated for C29H48BF4OPRuS2: C, 50.07; H, 6.95. Found:

C, 50.21 H, 6.85.








104






The heavy





2) and Fo










105


(5-2) (5-4) (5-5)

Formula 2(C32H40BCl3N2RuS3)

CH2Cl2

C29H47BCl3OPRuS2 2(C32H40BCl3N2ORuS2)

CH2Cl2

Formula weight 1619.13 725.01 1586.99

Crystal System Monoclinic Monoclinic Monoclinic

Space group C2/c P21/n C2/c

a(Å) 34.498 17.7135(6) 34.706(4)

b(Å) 10.716 10.0800(3) 10.5082(13)

c(Å) 23.057 19.4358(7) 28.072(4)

α(deg) 90 90 90

β(deg) 124.73 109.048(2) 138.090(9)

γ(deg) 90 90 90

V(Å3) 7005.187 3280.29(19) 6838.5(19)

Z 4 4 4

d(calc)gcm-3

1.535 1.468 1.541

R(int) 0.0440 0.0413

Abs coeff,μ,mm-1

0.959 0.921 0.923


>2(FO2) 9427 10021 5575


R(>2) 0.0369 0.0318 0.0389

Rw 0.0962 0.0524 0.0623

GOF 1.023 1.370 1.249

106

Table 5.4.2. Select Crystallographic Data for 5-11 and 5-13.

(5-11) (5-13)

Formula C31H50B2Cl6NOPRuS2 C34H40B2Cl6N3ORuS2

CH2Cl2

Formula weight 883.22 991.15

Crystal System Monoclinic Monoclinic

Space group P21/n P21/n

a(Å) 10.5984(5) 11.8055(2)

b(Å) 13.8097(7) 21.9531(3)

c(Å) 27.2535(15) 17.1265(2)

α(deg) 90 90

β(deg) 100.467(3) 96.030(1)

γ(deg) 90 90

V(Å3) 3922.5(3) 4414.07(11)

Z 4 4

d(calc)gcm-3

1.496 1.492

R(int) 0.0778 0.0337

Abs coeff,μ,mm-1

0.983 0.966

Data collected 9330 13981

>2(FO2) 6104 11002

Variables 411 469

R(>2) 0.0454 0.0367

Rw 0.1022 0.0935

GOF 1.006 0.967

107


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5288-5290.



109

Chapter 6 Catalytic Olefin Metathesis

6.1 Introduction

6.1.1 Types of Olefin Metathesis Reactions

The power of carbon-carbon bond redistribution offered by catalytic olefin metathesis has been

harnessed in a variety of ways and used for a number of applications.1-7

The most common

reactions are categorized into a few specific types (Figure 6.1.1). This includes ring closing

metathesis (RCM) where two olefinic functionalities are contained within the same molecule and

the catalytic transformation links these olefins together creating a cyclic product with the

liberation of ethylene or another byproduct.8 This can be used to form heterocycles, bicycles and

cycloalkenes.9-11

The equilibrium of this reaction can be driven to the cyclic product by the

removal of ethylene from the system. The reverse reaction can be accomplished by pressurizing

the system with ethylene driving the equilibrium to the ring opened product in a process called

ring opening metathesis (ROM).

Olefin metathesis can be used to synthesize polymers by ring opening metathesis polymerization

(ROMP).12-14

This is accomplished by the continuous opening of cyclic olefinic monomers

resulting in a growing polymer attached to the metal centre. The driving force for this reaction is

typically from the relief of ring strain in the monomer. This can be used to synthesize a number

of interesting polymers including polydicyclopentadiene15

and polynorbornene16-17

which are

used for body panels of vehicles and anti-vibration, anti-impact and grip improvement

respectively.

By combining two olefinic substrates in the presence of an olefin metathesis catalyst, cross

metathesis (CM) of the two substrates can occur resulting in a coupled product with the

liberation of ethylene or another byproduct.18-20

Similar to RCM, this equilibrium is driven to the

coupled product by the liberation of ethylene. CM is synthetically equivalent to, and has

replaced, performing ozonolysis on an olefinic substrates to give a carbonyl functionality

followed by a reaction with a Wittig reagent. The reverse reaction can be accomplished by

applying an ethylene pressure resulting in ethenolysis and cleavage of the carbon-carbon double

110

bond resulting in two terminal olefinic products.21-22

This process is used for the production of

biodiesel from unsaturated fatty acids.23

Figure 6.1.1. Common Olefin Metathesis Reactions

6.1.2 Catalyst Screening

6.1.2.1 Standard Test Reactions

Due to the lack of a set of standard reaction conditions and substrates, the process of screening

new olefin metathesis catalysts and being able to compare their activities to existing catalysts

was highly inconsistent. This was the motivation for Grubbs and coworkers to develop a series of

standard transformations to serve as a useful and easily applicable platform for catalyst

comparison.24

These standard tests and conditions give researchers the ability to easily and

accurately assess the impact of structural changes made to catalyst frameworks thus leading to

more effective rational catalyst design. The three standard tests provide insight into a catalysts

ability to perform the three common reactions described above (RCM, ROMP and CM).

The standard test for RCM is the ring closing of diethyl diallylmalonate (Scheme. 6.1.1). The

reaction takes place at 30 ºC in CD2Cl2 at a concentration of 0.1 M with 1 mol% of metathesis

catalyst.

111

Scheme 6.1.1. Standard Test Reaction for RCM

To investigate the effectiveness of a catalyst to accomplish ROMP, 1,5-cyclooctadiene is

polymerized using 0.1 mol% catalyst loading (Scheme 6.1.2). This is done with a 0.5 M solution

of 1,5-cyclooctadiene at 30 ºC in CD2Cl2.

Scheme 6.1.2. Standard Test Reaction for ROMP

The standard metathesis test for CM involves the coupling of 5-hexenyl acetate and methyl

acrylate with the test reaction taking place at a concentration of 0.4 M and 2.5 mol % catalyst at

room temperature in CD2Cl2 (Scheme 6.1.3). This reaction can give the desired heterocoupled

product as shown in Scheme 6.1.3 and also the homocoupled 5-hexenyl acetate product.

Scheme 6.1.3. Standard Test Reaction for CM

6.1.2.2 Activity of Common Catalysts

As a comparison for the results discussed in this chapter, the activity of some common olefin

metathesis catalysts are presented in Table 6.1.1.24

1st Generation Grubbs Catalyst (Grubbs 1)

can convert diethyl diallylmalonate to the ring closed product in 66 % yield after 30 min. 2nd

Generation Grubbs Catalyst (Grubbs 2), 1st Generation Hoveyda-Grubbs Catalyst (HG 1), and

2nd

Generation Hoveyda-Grubbs Catalyst (HG 2) can accomplish RCM of diethyl

diallylmalonate to over 90% in 30 min with HG 2 being the most active. For ROMP, Grubbs 2

and HG 2 are the most active achieving 99% conversion in 6 and 5 min respectively. After

112

90 min Grubbs 1 achieves 40% conversion and after 100 min HG 1 achieves 4% conversion. For

CM Grubbs 2 and HG 2 achieve 90% conversion after 70 min with 97 and 99% consumption of

5-hexenyl acetate respectively. Grubbs 1 achieves 8% conversion to the heterocoupled product

with 87% consumption of 5-hexenyl acetate and HG 1 achieves 3% conversion with 73%

consumption of 5-hexenyl acetate. The consumption of 5-hexenyl acetate in these reactions is

due to both the formation of the heterocoupled product and the homocoupled 5-hexenyl acetate

product.

Table 6.1.1. Standard Olefin Metathesis Reactions Using Common Catalysts.

Catalyst RCM1 ROMP

2 CM

3

Grubbs 1 66% 40% (90 min) 8% (87 %)

Grubbs 2 96% 99% (6 min) 90% (97%)

HG 1 90% 4% (100 min) 3% (73 %)

HG 2 99.5% 99% (5 min) 90% (99 %)

1Conversions at 30 min reaction time under standard conditions.

2Max conversions at the respective reaction times.

3Conversion to heterocoupled product at 70 min. In brackets, consumption of 5-hexenylacetate.

6.1.3 Cross Metathesis of NBR and 1-Hexene

As previously mentioned in Section 1.4, NBR can be processed by performing cross metathesis

with 1-hexene to give a polymer with a lower molecular weight.6, 25

This process is conceptually

related to ethenolysis where the internal olefins in the polymer structure are undergoing cross

metathesis with a small olefinic substrate (1-hexene) to essentially cut the polymer into shorter

chains. Industrially this is accomplished by employing 2nd

Generation Grubbs Catalyst.

Depending on the catalyst loading and reaction times, polymers of varying molecular weights

and viscosities can be obtained. The crude NBR obtained from Lanxess has an initial Mn and Mw

of 95 000 and 270 000 Da respectively resulting in a PDI of 2.8.

113

6.1.4 Hydrogenation of NBR

To reduce the susceptibility of the polymer to oxidative aging and to alter its properties to be

more oil and hydrocarbon resistant NBR is hydrogenated.26-27

This is done by Lanxess using the

rhodium based Wilkinson's Catalyst. It is important that the catalyst is selective for the

hydrogenation of the olefins and unreactive towards the nitrile functionalities present in NBR.

When the nitrile groups are reduced, the resulting amines react with olefins in the polymer

creating a cross linked structure. Reduction of the nitrile groups also alters the polymers

properties resulting in undesirable products.


With a library of ruthenium alkylidene species prepared, their activity for catalytic olefin

metathesis was probed. To do this, the standard system of characterization for olefin metathesis

catalysts was followed using the three specific reactions outlined above. From this, active

catalysts were then screened for activity in the cross metathesis of NBR with 1-hexene.

6.2.1 Comparing Catalytic Activity of BCl3 'Activated' and 'Non-Activated' Species

With each ligand set, there are three ruthenium alkylidene compounds related by the number of

equivalents of BCl3 reacted with the parent tridentate complex. Therefore, it was of interest to

compare the activities of these related species. To do this, the series of compounds 3-4, 5-4, and

5-10 and the series 3-5, 5-5, and 5-12 were tested for the three standard metathesis reactions

(Figure 6.2.1). The first standard test which was investigated was the ring closing metathesis of

diethyl diallylmalonate with 5 mol% catalyst loading (Scheme 6.1.1).

.

Figure 6.2.1. Compounds used to Compare BCl3 Activation Effects on Catalysis

114

Comparing the series containing PCy3 (3-4, 5-4, 5-10) for RCM activity, it is clear to see that

reacting the parent complex, 3-4, with 2 equivalents of BCl3 to generate cationic 5-10 gives the

most conversion to the ring closed product (Figure 6.2.2). Not surprisingly, the parent complex

3-4 shows no catalytic activity. This is similar to the related species bearing tridentate dianionic

ligands reported by Jensen and Erker.28-29

Considering the accepted mechanism of ruthenium

based olefin metathesis, the inactivity of this system can be easily explained. In order for the

olefinic substrate to coordinate to the metal centre, one of the phosphines in 1st Generation

Grubbs Catalyst must dissociate to create a 4-coordinte species.30-31

In the case of 3-4 the PCy3 is

bound too strong to dissociate. The central ether donor on the tridentate ligand could potentially

dissociate to form a 4-coordinate species but the chelate effect drives the equilibrium towards the

5-coordinate species preventing any coordination of olefin and subsequent catalysis. Complex

5-4 also shows no catalytic activity for RCM of diethyl diallylmalonate. This is also of no

surprise as there is no open coordination site for the incoming olefin to bind to the metal. 5-10

displays moderate activity achieving 42% conversion to the ring closed product in 40 min.

Figure 6.2.2. Ring Closing Metathesis of Diethyl Diallylmalonate using Complexes 3-4


Loadings at 25 ºC in CD2Cl2

115

A similar trend is observed with the SIMes series of ruthenium alkylidene complexes (3-5, 5-5,

5-12) (Figure 6.2.3). Both 3-5 and 5-5 show no catalytic activity for the RCM of diethyl

diallylmalonate. However, cationic 5-12 which is formed from the reaction of 5-5 with one

equivalent of BCl3 gives 98% conversion to the ring closed product after just 40 min.

Figure 6.2.3. Ring Closing Metathesis of Diethyl Diallylmalonate With Complexes 3-5



When tested for ROMP of COD, complexes 3-4, 5-4, and 5-10 all displayed no activity. Even

though the cationic 5-10 was active for RCM of diethyl diallylmalonate, at 0.1 mol% catalyst

loading it did not convert any COD to polymer. This is consistent with previous reports from

Dixneuf and co-workers who demonstrated that their cationic ruthenium allenylidene species

were only active for RCM.32

Examining the SIMes, series (3-5, 5-5, 5-12) for ROMP of COD gave results which follow the

trend seen previously with these compounds. The cationic species, 5-12 is the most active,

achieving 53% conversion to polymer after 44 min. However, unlike the previous results, the

parent complex 3-5 and the complex formed by the addition of one equivalent of BCl3, 5-5

116

display some catalytic activity. 3-5 and 5-5 achieve 26% and 4.8% conversion, respectively after

44 min (Figure 6.2.4). Not surprisingly, 5-coordinate 3-5 is more active for ROMP of

1,5-cyclooctadiene than 6-coordinate 5-5.

Figure 6.2.4. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene With

Complexes 3-5 (Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with

0.1 mol% Catalyst Loadings at 25 ºC in CD2Cl2

The test reaction which is most applicable to our ultimate goal of cross metathesis of NBR with

1-hexene was the CM of 5-hexenyl acetate with methyl acrylate. Similar to the ROMP of COD,

complexes 3-4, 5-4, and 5-10 were all inactive for the standard CM test. However, for the series

of compounds containing SIMes (3-5, 5-5, 5-12), a similar trend to the previous test reactions is

observed with the cationic species being most active. 3-5 and 5-5 are inactive for the CM

reaction. However, complex 5-12 is active for CM giving the heterocoupled CM product in 62%

yield 160 min (Figure 6.2.5).

117

Figure 6.2.5. Cross Metathesis of 5-Hexenyl Acetate And Methyl Acrylate With Complexes

3-5 (Green Triangles), 5-5 (Red Squares), and 5-12 (Blue Diamonds) with 5 mol% Catalyst


Based on these experiments, it is clear that the cationic species generated upon the reaction of the

parent five-coordinate species with 2 equivalents of BCl3 is the most active. In most cases the

parent species 3-4 and 3-5 are completely inactive for olefin metathesis. Similarly, the

complexes generated by reacting these parent species with 1 equivalent of BCl3 (5-4, 5-5) are

inactive for olefin metathesis.

6.2.2 Catalytic Olefin Metathesis Activity of Catalyst Derivatives

The previously mention trends (Section 6.2.1) demonstrated that the cationic alkylidene species

were the most active catalysts, with both types of neutral species displaying very limited to no

conversion. Therefore, in subsequent investigations into the influence of the dianionic, tridentate

ligand structure, only the activated cationic species will be discussed.

To determine the influence of backbone rigidity and the basicity of the thiolate ligands

complexes 5-14 and 5-15 were screened for olefin metathesis activity (Figure 6.2.6). Compounds

5-6 and 5-7 were activated with another equivalent of BCl3 to form the 5-coordinate cationic

species, and screened for RCM, ROMP and CM in an identical fashion as the compounds tested

118

above. For RCM, 5-14 reaches 38.8 % in 40 min and 5-15 is slightly less active reaching 35.9 %

in 40 min (Figure 6.2.7).

Figure 6.2.6. Compounds 5-14 and 5-15

Figure 6.2.7. Ring Closing Metathesis of Diethyl Diallylmalonate with 5-14 and 5-15 with

5 mol% Catalyst Loadings at 25 ºC in CD2Cl2

Compound 5-14 is inactive for ROMP of COD. This is expected based on the result of the

related species 5-10. However, 5-15 is active for ROMP of COD resulting in 86% conversion of

the monomer to polymer (Figure 6.2.8).

119


0.1 mol% Catalyst Loading at 25 ºC in CD2Cl2

The CM of 5-hexenyl acetate and methyl acrylate with 5-14 at 5 mol% is inactive similar to the

alkyl backbone analogue 5-10. 5-15 achieves 74% conversion after 180 min (Figure 6.2.9).


5 mol% Catalyst Loading at 25 ºC in CD2Cl2

120

When another equivalent of BCl3 is added to a solution of compounds 5-1 and 5-2 the resulting

mixtures are inactive for all of the standard olefin metathesis tests. This is because the second

equivalent of BCl3 is unable to abstract a chloride form the ruthenium centre. It is unclear why

this is the case. It is presumably a result of the central thioether donor since all other related

compounds with a different central donor undergo this type of reactivity. This includes

compound 5-3 with the central phosphine donor. However the resulting complex is only slightly

active for RCM of diethyl diallylmalonate achieving only 3% conversion after 40 min. Similar to

the previously discussed compounds containing a PCy3 ligand, it is also inactive for the standard

ROMP and CM tests.

The final complexes that were tested were the ones containing the all oxygen ligands where the

tridentate dianionic ligand consist of two alkoxy ligands and a central ether donor. Since the

intermediate complexes with the addition of one equivalent of BCl3 were difficult to isolate, for

these catalytic tests complexes 3-8 and 3-9 were activated with two equivalents of BCl3 in situ to

give 5-16 and 5-17 respectively. These solutions were used for the catalytic tests (Figure 6.2.10).

Figure 6.2.10. Complexes 5-16 and 5-17

When 5-16 was screened for catalytic activity in RCM of diethyl diallylmalonate at a 5 mol%

catalyst loading, 99% conversion to the ring closed product was achieved after 30 min

(Figure 6.2.11).

121

Figure 6.2.11. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-16 at a 5 mol%

Catalyst Loading at 25 ºC in CD2Cl2

When 5-17 was used for RCM of diethyl diallylmalonte at a 5 mol% catalyst loading conversion

to the ring closed product was 93% complete after 6 min and essentially complete after 8 min

(Table 6.2.1). When the catalyst loading was dropped to 1 mol% the catalyst was able to achieve

56% conversion to the ring closed product after 40 min (Figure 6.2.12).

Table 6.2.1. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-17 at a 5 mol%

Catalyst Loading at 25 ºC in CD2Cl2

Time (min) Conv (%)

2 24

4 67

6 93

8 >99

122

Figure 6.2.12. Ring Closing Metathesis of Diethyl Diallylmalonate Using 5-17 at a at a


Complex 5-17 was able to accomplish ROMP of COD achieving 96% conversion of monomer to

polymer after 30 min (Figure 6.2.13). Although 5-17 was more active than the previously

reported catalysts in this section for RCM and ROMP, it only achieved 31% conversion to the

heterocoupled product for the standard CM test reaction (Figure 6.2.14). However, in the

1H NMR spectrum it is evident that the 5-hexenyl acetate has been fully consumed and converted

to the homocoupled product. This has been observed with other olefin metathesis catalysts

including Grubbs 1. Grubbs and coworkers have provided an explanation for this observation.18

They categorized all olefins into 4 classes: Type 1 undergoes fast homodimerization; Type 2

undergoes slow homodimerization; Type 3 undergoes no homodimerization; and Type 4 are

spectators to olefin metathesis. 5-hexenyl acetate is considered a Type 1 olefin which rapidly

undergoes homodimerization with the release of ethylene as a byproduct. The homodimer can

then undergo secondary olefin metathesis and react with methyl acrylate resulting in the

heterocoupled CM product. The amount of secondary olefin metathesis which occurs resulting in

the heterocoupled product is dependent on catalyst used. For example, it can be seen in

Table 6.1.1. that Grubbs 1 results in only 8% conversion to the heterocoupled CM product.

123

However, 87% of the 5-hexenyl acetate is consumed. Using Grubbs 2 as the catalyst results in

90% conversion to the heterocoupled product with 97% of the 5-hexenyl acetate being

consumed.

Figure 6.2.13. Ring Opening Metathesis Polymerization of 1,5-Cyclooctadiene with 5-17 at

a 5 mol% Catalyst Loading at 25 ºC in CD2Cl2



124

6.2.3 Comparisons of Active Catalysts

In general, the SIMes versions of the catalysts are more active than the PCy3 containing

catalysts. This is especially evident for ROMP and CM test reaction since the PCy3 containing

catalysts are inactive for these reactions. For RCM of diethyl diallylmalonate, it is obvious that

the SIMes analogue 5-12 is more active than the PCy3 analogue 5-10 (Figure 6.2.15). 5-12

reached 98% completion after 40 min whereas 5-10 only achieved 42% conversion after 40 min.


for RCM of Diethyl Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2

Interestingly, when 5-14 and 5-15 are compared for RCM activity, the PCy3 containing catalyst

is slightly more active than the SIMes containing catalyst (Figure 6.2.16). Complex 5-14

achieved 39% conversion to the ring closed product after 40 min. The SIMes derivative, 5-15

accomplished slightly less conversion reaching 36% after 40 min.

125



The trend of the catalyst containing the SIMes ligand being more active than the PCy3 analogues

was observed again when looking at complexes 5-16 and 5-17. At 5 mol% both 5-16 and 5-17

accomplish 100 % conversion to the ring closed product of diethyl diallylmalonate. However, the

reaction was complete after 30 min using 5-16 while it took 5-17 only 8 min (Figure 6.2.17).

This demonstrates once again that keeping everything else about the catalyst structure constant

and changing PCy3 to SIMes results in increased activity.

126

Figure 6.2.17. Comparing the Activity of PCy3 Containing 5-16 and SIMes Containing 5-17


Of the three catalysts containing a PCy3 ligand, the catalyst with the dialkoxy ether ligand (5-16)

is the most active for RCM of diethyl diallylmalonate (Figure 6.2.18). After 30 min this catalyst

accomplished nearly 100% conversion to the ring closed product. After 40 min, complexes 5-10

and 5-14 accomplished nearly the same conversion reaching 41 and 39% completion,

respectively.


Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2

127

When comparing the activities of the SIMes derivatives of the catalysts for the RCM of diethyl

diallylmalonate it is evident that complex 5-17 with the all oxygen ligand was the most active

accomplishing complete conversion after 8 min. The alkyl backbone derivative (5-12) of the

dithiolate complexes was second best achieving near complete conversion after 34 min. While

5-15 which achieved only 36 % conversion to the ring closed product after 40 min was the worst

(Figure 6.2.19).


Diallylmalonate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2

Similar to the trend observed for the standard RCM test, complex 5-17 was more active than

5-15 and 5-12 for ROMP of 1,5-cyclooctadiene (Figure 6.2.20). After 30 min 5-17 achieved 96%

conversion to the polymer. Catalyst 5-15 was second best achieving 86% conversion after 40

min and 5-12 was the least effective catalyst achieving 53% conversion.

128

Figure 6.2.20. Comparing Activities of 5-12, 5-15 and 5-17 for ROMP of 1,5-Cyclooctadiene

at 0.1 mol% Catalyst Loadings at 25 ºC in CD2Cl2

The trend of catalyst 5-17 being most active was not observed for the standard CM test

(Figure 6.2.21). Catalyst 5-15 was the most active accomplishing 74% conversion to the

heterocoupled product in 180 min. 5-12 was second best achieving 62% conversion and the

alkoxide containing catalyst, 5-17 was the least effective achieving only 32% conversion to the

heterocoupled product. However, when the consumption of 5-hexenyl acetate was tracked by

1H NMR catalyst 5-17 showed nearly complete consumption of the starting material. As

discussed, this is due to the formation of the homocoupled product. When considering activity to

produce the heterocoupled product, 5-17 was the worst of the three catalysts tested. However in

terms of overall metathesis, 5-17 was the most active catalyst.

129

Figure 6.2.21. Comparing Activities of 5-12, 5-15 and 5-17 for CM of 5-hexenyl Acetate and

Methyl Acrylate at 5 mol% Catalyst Loadings at 25 ºC in CD2Cl2

6.2.4 Cross Metathesis of NBR and 1-hexene

The ultimate goal of this thesis was to develop olefin metathesis catalyst which were active for

the cross metathesis of NBR and 1-hexene to achieve a decreased molecular weight and PDI of

the polymer. The NBR had an initial Mw of 270 000 Da and a Mn of 95 000 Da with a PDI of

2.8. For comparison purposes, a benchmark was set using 2nd

Generation Grubbs Catalyst at the

currently industrially used loading of 0.007 phr with 5 phr of 1-hexene. In polymer science phr

stands for parts per hundred. This is used as a measurement of the amount of additives in a

mixture per one hundred parts polymer. In this example, this equates to 5 mg of catalyst and 4 g

of 1-hexene for 75 g of NBR in 425 g of chlorobenzene. After 1 h the Mw and Mn were slightly

reduced to 208 000 and 79 000 Da respectively. After 24 h the Mw and Mn were reduced to

164 000 and 69 000 Da respectively (Figure 6.2.22). This results in a PDI of 2.4.

130

Figure 6.2.22. Mw (Blue Diamonds) and Mn (Red Squares) Over Time of NBR Cross

Metathesis with 1-hexene Using 2nd

Gen. Grubbs Catalyst at a 0.007 phr Catalyst Loading

at 25 ºC in Chlorobenzene

Only catalysts which displayed activity for CM of 5-hexenyl acetate and methyl acrylate were

tested for CM of NBR and 1-hexene. Using 5-12 at the same loading as Grubbs catalyst resulted

in an initial decrease in Mw and Mn after 1 h but after 24 h the NBR was essentially at the initial

molecular weight (Figure 6.2.23). The catalyst was then tested at loadings of 0.014, 0.028, 0.05

and 0.10 phr. It was found that to achieve the same degree of CM as Grubbs Catalyst, 0.05 phr of

5-12 was required. After 24 h the Mw and Mn of the NBR were 155 000 and 67 000 Da

respectively. At a catalyst loading of 0.10 phr 5-12 reduces the Mw and Mn to 97 000 and

48 000 Da respectively.

131


Loadings of 5-12 at 25 ºC in Chlorobenzene

Catalyst 5-15 was also not as active as Grubbs catalyst for the cross metathesis of NBR and

1-hexene. It was also less active than 5-12. At 0.007, 0.014 and 0.028 phr catalyst loading it

essentially accomplished no metathesis (Figure 6.2.24). At the higher loading of 0.050 phr after

24 h it had reduced the Mw and Mn slightly to 240 000 and 60 000 respectively.

132



Complex 5-17 was the most active for the standard metathesis tests. Similar to the metathesis of

NBR and 1-hexene using catalyst 5-12, this species required higher catalyst loadings to achieve

the same conversion as Grubbs Catalyst. However, the metathesis occurs much faster than with

Grubbs Catalyst (Figure 6.2.25). After 15 min at a catalyst loading of 0.05 phr the Mw and Mn of

the NBR were reduced to 157 000 and 64 000 Da respectively. After 24 h the Mw increased

slightly to 160 000 Da while the Mn stayed the same. This result was similar to using Grubbs

Catalyst at a loading of 0.007 phr.

133



6.2.5 Hydrogenation of NBR

The second goal of the Lanxess funded project was to develop new hydrogenation catalysts for

the hydrogenation of NBR. There are a number of examples of ruthenium based complexes

being active olefin hydrogenation catalysts including ruthenium alkylidene complexes. This was

the motivation for testing these complexes for hydrogenation of NBR. The series of compounds

3-5, 5-5 and 5-12 were therefore also tested for catalytic hydrogenation of NBR. Using 10 µmol

of catalyst for 2 mL of a 5 wt% NBR solution in chlorobenzene at 50 bar hydrogen pressure and

80 ºC for 20 h, compound 3-5 was able to achieve 82% hydrogenation (Table 6.2.2). The degree

of hydrogenation was determined from the FTIR spectrum of the polymer (Figure 6.2.26). The

olefinic stretch at 973 cm-1

disappears upon hydrogenation. However, the reaction became more

viscous indicating that cross linking had occurred. This occurs when the catalyst is not selective

for the hydrogenation of the olefin and also hydrogenates the nitrile groups within the polymer.

These amines can then react with olefins within the polymer creating a cross linked structure. In

an attempt to prevent this the catalyst loading was reduced to 5 µmol for 2 mL of a 5 wt% NBR

solution. The pressure was increased to 82 bar in an attempt to push the hydrogenation to

134

completion. This resulted in 71% hydrogenation of the olefins in the NBR but still with some

minor cross linking. At both pressures compounds 5-5 and 5-12 are inactive for hydrogenation of

NBR.

Table 6.2.2. Hydrogenation of NBR with 3-5, 5-5 and 5-12

Compound

Catalyst

Loading

(µmol)

Pressure

(bar)

Degree of

Hydrogenation

3-5 10 50 82%1

5 82 71%1

5-5 10 50 0%

10 82 0%

5-12 10 50 0%

10 82 0% Conditions: 80 ºC for 20 h. 2 mL of a 5 wt% NBR solution in chlorobenzene

1Minor cross linking observed

Compound 3-9 was screened for hydrogenation of NBR by itself and with the addition of 1 and 2

equivalents of BCl3 to generate 5-9 and 5-17, respectively. They were all found to be active for

hydrogenation with 3-9 resulting in such a cross linked polymer that the 2 mL, 5 wt% NBR

solution became a solid (Table 6.2.3). This occurred at a lower catalyst loading as well.

Complexes 5-9 and 5-17 were able to accomplished 74 and 36% hydrogenation respectively at

50 bar hydrogen pressure. Increasing the hydrogen pressure to 82 bar resulted in 99 and 96%

hydrogenation for 5-9 and 5-17 respectively.

Table 6.2.3. Hydrogenation of NBR using 3-9, 5-9 and 5-17

Compound

Catalyst

Loading

(µmol)

Pressure

(bar)

Degree of

Hydrogenation

3-9 10 50 Major Cross Linking

5 82 Major Cross Linking

5-9 10 50 74%

10 82 99%

5-18 10 50 36%

10 82 96% Conditions: 80 ºC for 20 h. 2 mL of a 5 wt% NBR solution in chlorobenzene

135

Figure 6.2.26. FTIR Spectrum of NBR (top) and Hydrogenated NBR (bottom)

6.3 Conclusion

Ruthenium alkylidene complexes bearing tridentate dianionic ligands 3-1 - 3-9 were inactive for

RCM, ROMP and CM. The complexes generated by the addition of one equivalent of BCl3

136

(5-1 - 5-9) were also inactive for RCM, ROMP and CM. Conversely, the cationic complexes

generated by the addition of a second equivalent of BCl3 (5-10, 5-12, 5-14 - 5-17) were active for

RCM, ROMP and CM achieving near complete conversion for certain cases. The complexes

containing the (SCH2CH2)2PPh and (SCH2CH2)2S ligands (3-1 - 3-3) were inactive for catalytic

olefin metathesis even with the addition of 2 equivalents of BCl3. In general the catalysts which

contain a SIMes ligand were more active than the catalysts containing a PCy3 ligand. The

catalysts with the (OCH2CH2)2O ligand (5-16 and 5-17) are most active compared to the

catalysts with the same L (SIMes or PCy3) ligand. The catalysts with the aryl backbone dithiolate

ligand (5-14 and 5-15) are the second best and the alkyl dithiolate complexes (5-10, 5-12) are the

least active. These complexes were shown to be active for cross metathesis of NBR and 1-

hexene. However, higher catalyst loadings were required to achieve the similar conversions as

Grubbs 2 Catalyst. Complexes 3-5, 3-9¸ 5-9 and 5-17 are active for hydrogenation of NBR.

However, catalyst 3-5 and 3-9 both resulted in crosslinking of the polymer.







Teflon valve stopcocks. Dichloromethane-d2 was dried over CaH2 and benzene-d6 was dried over

Na metal and vacuum-transferred into a Young bomb. All solvents were thoroughly degassed

after purification (three freeze-pump-thaw cycles). 1H,

13C, and

31P NMR spectra were recorded

at 25 °C on Varian 300 and 400 MHz and Bruker 400 MHz spectrometers. Commercially

available substrates were obtained from Sigma-Aldrich and used without further purification.

NBR was obtained from Lanxess and stored at -40 ºC. Chemical shifts are given relative to

SiMe4 and referenced to the residual solvent signal (1H,

13C) or relative to an external standard

(31

P: 85% H3PO4). In some instances, signal and/or coupling assignment was derived from two-

dimensional NMR experiments. Chemical shifts are reported in ppm and coupling constants as

scalar values in Hz. FTIR spectrum were collected on a Perkin Elmer Spectrum One

spectrometer. GPC data was collected using Styragel HR 5E-THF columns at 45 ºC using a

137

Waters 2414 RI Detector. Data was processed using Empower Pro software and Mw and Mn data

were determined against a polystyrene calibration curve.


6.4.2.1 Standard Metathesis Reaction Tests

All standard metathesis reaction tests were performed employing a modified procedure of

Grubbs et al.24

A standard procedure for the ring closing metathesis of diethyl diallylmalonate is as follows. The

required amount of catalyst (5 or 1 mol%) was weighed out and dissolved in CD2Cl2.

Compounds 5-10, 5-12, 5-14 and 5-15 were generated by the addition of 1 equiv. of a 1 M BCl3

in hexanes solution to solutions of 5-4, 5-5, 5-6 and 5-7 respectively. For compounds 5-16 and

5-17, 2 equiv. of a 1 M BCl3 in hexanes solution were added to solutions of 3-8 and 3-9

respectively. The solutions were placed in an NMR tube equipped with a septa. Diethyl

diallylmalonate (40 μL, 0.165 mmol) was added via the septum and solution was mixed.

Reaction progress was monitored by 1H NMR every 2 min. Reaction progress was determined by

integration of the olefinic peaks of the starting material versus the product.

A standard procedure for the ring opening polymerization of 1,5-cyclooctadiene is as follows.

Standard solutions in CD2Cl2 were prepared and the appropriate volumes (0.1 mol%) were

diluted for the tests. Compounds 5-10, 5-12, 5-14 and 5-15 were generated by the addition of

1 equiv. of a 1 M BCl3 in hexanes solution to solutions of 5-4, 5-5, 5-6 and 5-7 respectively. For

compounds 5-16 and 5-17, 2 equiv. of a 1 M BCl3 in hexanes solution were added to solutions of

3-8 and 3-9 respectively. The solutions were placed in an NMR tube equipped with a septa.

1,5-cyclooctadiene (50 μL, 0.40 mmol) was added via the septum and solution was mixed.

Reaction progress was monitored by 1H NMR every 2 min. Reaction progress was determined by

integration of the peaks of the starting material versus the product.

A standard procedure for cross metathesis of 5-hexenyl acetate and methyl acrylate is as follows.

The required amount of catalyst (5 mol%) was weighed out and dissolved in CD2Cl2.

Compounds 5-10, 5-12, 5-14 and 5-15 were generated by the addition of 1 equiv. of a 1 M BCl3

in hexanes solution to solutions of 5-4, 5-5, 5-6 and 5-7 respectively. For compounds 5-16 and

5-17, 2 equiv. of a 1 M BCl3 in hexanes solution were added to solutions of 3-8 and 3-9

138

respectively. The solutions were placed in an NMR tube equipped with a septa. A mixture of

5-hexenyl acetate (20 μL, 0.12 mmol) and methyl acrylate (10 μL, 0.11 mmol) was added via the

septum and solution was mixed. Reaction progress was monitored by 1H NMR every 2 min.

Reaction progress was determined by integration of the olefinic peaks of the starting material

versus the product.

Table 6.4.1. RCM of Diethyl Diallylmalonate with 3-4, 5-4 and 5-10

3-4 5-3 5-10

Time (min) Conv (%) Time (min) Conv (%) Time (min) Conv (%)

1 2 0 1 2 0 1 2 1.6

2 4 0 2 4 0 2 4 3.7

3 6 0 3 6 0 3 6 5.4

4 8 0 4 8 0 4 8 7.3

5 10 0.1 5 10 0 5 10 9.1

6 12 0.1 6 12 0 6 12 10.7

7 14 0.1 7 14 0 7 14 13.0

8 16 0.1 8 16 0 8 16 14.5

9 18 0.1 9 18 0 9 18 16.7

10 20 0.2 10 20 0 10 20 18.0

11 22 0.2 11 22 0 11 22 20.6

12 24 0.2 12 24 0 12 24 22.5

13 26 0.2 13 26 0 13 26 23.7

14 28 0.2 14 28 0 14 28 26.5

15 30 0.3 15 30 0 15 30 28.6

16 32 0.3 16 32 0 16 32 31.0

17 34 0.3 17 34 0 17 34 33.3

18 36 0.3 18 36 0 18 36 35.9

19 38 0.3 19 38 0 19 38 38.7

20 40 0.4 20 40 0 20 40 41.5

Table 6.4.2. RCM of Diethyl Diallylmalonate with 3-5, 5-5 and 5-12

3-5 5-5 5-12

Time (min) Conv (%) Time (min)

(min(min) Conv (%) Time (min) Conv (%)

1 5 0 1 5 0 1 5 55.8

2 7 0 2 7 0 2 7 67.5

3 9 0 3 9 0 3 9 75.4

4 11 0.1 4 11 0 4 11 81.1

5 13 0.1 5 13 0.3 5 13 85.1

6 15 0.1 6 15 0.4 6 15 88.2

139

7 17 0.2 7 17 0.5 7 17 90.7

8 19 0.2 8 19 0.6 8 19 92.4

9 21 0.2 9 21 0.6 9 21 93.7

10 23 0.3 10 23 0.7 10 23 94.8

11 25 0.3 11 25 0.7 11 25 95.9

12 27 0.3 12 27 0.8 12 27 96.4

13 29 0.4 13 29 0.9 13 29 97

14 31 0.4 14 31 0.9 14 31 97.4

15 33 0.4 15 33 1 15 33 97.8

16 35 0.5 16 35 1.1 16 35 98.1

17 37 0.5 17 37 1.2 17 37 98.2

18 39 0.6 18 39 1.3 18 39 98.4

19 41 0.7 19 41 1.4 19 41 98.6

20 43 0.7 20 43 1.4 20 43 98.6

Table 6.4.3. ROMP of 1,5-cyclooctadiene with 3-5, 5-5 and 5-12

3-5 5-5 5-12


1 2 1.1 1 2 1.1 1 2 17.3

2 4 2.4 2 4 1.6 2 4 30.9

3 6 3.5 3 6 2 3 6 36.5

4 8 4.6 4 8 2.3 4 8 39.8

5 10 5.7 5 10 2.5 5 10 41.7

6 12 6.8 6 12 2.7 6 12 43.4

7 14 7.9 7 14 2.9 7 14 44.7

8 16 8.9 8 16 3.1 8 16 45.7

9 18 10 9 18 3.2 9 18 46.7

10 20 11.4 10 20 3.3 10 20 47.4

11 22 12.4 11 22 3.6 11 22 48.2

12 24 13.6 12 24 3.8 12 24 48.9

13 26 14.8 13 26 3.8 13 26 49.4

14 28 16.1 14 28 3.9 14 28 49.9

15 30 17.3 15 30 4.1 15 30 50.4

16 32 18.5 16 32 4.2 16 32 50.8

17 34 19.7 17 34 4.4 17 34 51.1

18 36 21 18 36 4.5 18 36 51.5

19 38 22.1 19 38 4.6 19 38 52

20 40 23.5 20 40 4.7 20 40 52.3

21 42 24.7 21 42 4.8 21 42 52.8

22 44 25.9 22 44 4.8 22 44 53.1

140

Table 6.4.4. CM of 5-hexenyl Acetate and Methyl Acrylate with 3-5, 5-5 and 5-12

3-5 5-5 5-12


1 2 0 1 2 0 1 2 30.9

2 4 0 2 4 0 2 4 40.4

3 6 0 3 6 0 3 6 45.6

4 8 0 4 8 0 4 8 48.2

5 10 0 5 10 0 5 10 50.2

6 12 0 6 12 0 6 12 51.9

7 14 0 7 14 0 7 14 52.4

8 16 0 8 16 0 8 16 53.7

9 18 0 9 18 0 9 18 53.7

10 20 0 10 20 0 10 20 54.2

11 22 0 11 22 0 11 22 54.9

12 24 0 12 24 0 12 24 55.2

13 26 0 13 26 0 13 26 55.6

14 28 0 14 28 0 14 28 56.7

15 30 0 15 30 0 15 30 56.8

16 32 0 16 32 0 16 32 57.4

17 34 0 17 34 0 17 34 57.5

18 36 0 18 36 0 18 36 57.8

19 38 0 19 38 0 19 38 57.9

20 40 0 20 40 0 20 40 58.1

30 60 0 30 60 0 30 60 59.2

40 80 0 40 80 0 40 80 60.4

50 100 0 50 100 0 50 100 60.7

60 120 0 60 120 0 60 120 60.9

70 140 0 70 140 0 70 140 61.7

80 160 0 80 160 0 80 160 62

90 180 0 90 180 0 90 180 62.3

Table 6.4.5. RCM of Diethyl Diallylmalonate with 5-14

5-14

Time (min) Conv (%)

1 2 3.8

2 4 14

3 6 19.4

4 8 23.1

5 10 25.4

6 12 27.5

141

7 14 29.1

8 16 30.1

9 18 31.5

10 20 32

11 22 33.3

12 24 33.8

13 26 34.6

14 28 35.9

15 30 36.5

16 32 37.5

17 34 38.3

18 36 38.4

19 38 38.7

20 40 38.8


5-15

Time (min) Conv (%)

1 2 5.7

2 4 12.6

3 6 15.3

4 8 17.5

5 10 19.7

6 12 21.2

7 14 23.4

8 16 25.3

9 18 26.7

10 20 27.5

11 22 29.3

12 24 30.4

13 26 31.3

14 28 32.2

15 30 32.8

16 32 33.6

17 34 33.8

18 36 34.6

19 38 35.2

20 40 35.9

142

Table 6.4.7. ROMP of 1,5-cyclooctadiene with 5-15

5-15

Time (min) Conv (%)

1 2 52.2

2 4 66.6

3 6 71.3

4 8 74.4

5 10 77.7

6 12 78.4

7 14 79.2

8 16 80.3

9 18 81.1

10 20 81.7

11 22 82.1

12 24 82.4

13 26 82.5

14 28 83.2

15 30 83.8

16 32 84.1

17 34 84.9

18 36 85.4

19 38 85.7

20 40 86.3

Table 6.4.8. CM of 5-hexenyl Acetate and Methyl Acrylate with 5-15

5-15

Time (min) Conv (%)

1 2 9.0

2 4 13.0

3 6 18.0

4 8 23.1

5 10 25.4

6 12 30.1

7 14 33.3

8 16 36.7

9 18 39.8

10 20 42.9

11 22 45.1

12 24 46.8

13 26 49.5

143

14 28 52.8

15 30 53.9

16 32 54.8

17 34 57.1

18 36 58.3

19 38 60.2

20 40 60.6

30 60 68.2

40 80 70.8

50 100 71.7

60 120 72.6

70 140 73.1

80 160 73.7

90 180 74.4


5-16

Time (min) Conv (%)

1 2 8.7

2 4 23.1

3 6 35.9

4 8 47.9

5 10 58.3

6 12 66.7

7 14 74.4

8 16 80.8

9 18 85.3

10 20 89.5

11 22 92.2

12 24 94.5

13 26 96.6

14 28 98.5

15 30 99.6

16 32 99.6

17 34 99.6

18 36 99.6

19 38 99.6

20 40 99.6

144

Table 6.4.10. RCM of Diethyl Diallylmalonate with 5-17 with 5 mol% Catalyst Loading

5-17, 5 mol%

Time (min) Conv (%)

1 2 24

2 4 67

3 6 93

4 8 100

5 10 100

Table 6.4.11. RCM of Diethyl Diallylmalonate with 5-17 with 1 mol% Catalyst Loading

5-17, 1 mol%

Time (min) Conv (%)

1 2 3.7

2 4 10.3

3 6 15.7

4 8 20.3

5 10 24.1

6 12 28.0

7 14 31.2

8 16 34.1

9 18 36.8

10 20 39.4

11 22 41.8

12 24 43.8

13 26 45.7

14 28 47.4

15 30 49.1

16 32 50.5

17 34 52.2

18 36 53.5

19 38 55.0

20 40 55.9

145

Table 6.4.12. ROMP of 1,5-cyclooctadiene with 5-17

5-17

Time (min) Conv (%)

1 2 11.5

2 4 56.5

3 6 74.3

4 8 82.1

5 10 86.2

6 12 87.6

7 14 88.9

8 16 90.5

9 18 91.1

10 20 92.9

11 22 93.5

12 24 94.1

13 26 94.9

14 28 95.3

15 30 95.6

16 32 95.8

Table 6.4.13. CM of 5-hexenyl Acetate and Methyl Acrylate with 5-17

5-17

Time (min) Conv (%)

5 10 19.2

10 20 22.2

15 30 26.1

20 40 27.4

30 60 28.6

40 80 29.4

50 100 30.5

60 120 30.8

70 140 31.0

80 160 31.3

90 180 31.5

6.4.2.2 Cross Metathesis of NBR and 1-hexene

A standard procedure for the cross metathesis of nitrile butadiene rubber (NBR) and 1-hexene is

as follows. 75 g of NBR was placed in 325 g of chlorobenzene and placed on a shaker for 48 hr

146

to give a 15 wt% NBR solution. 1-hexene (4 g) was added to the solution and shaken for 1 hr.

The catalysts were prepared by dissolving the required mass of precatalyst in CH2Cl2 (5 mL) in a

glove box and 1 or 2 equivalents of BCl3 was added. The solutions were stirred for 5 min before

being taken out of the glove box and added to the NBR solutions. Samples were taken at 1, 2, 3,

4, and 24 hr. The catalysts were poisoned with ethyl vinyl ether (0.5 mL) to stop the metathesis.

All volatiles were removed from the samples. GPC samples were made by preparing a 1 mg/mL

THF solution of the resulting NBR. The samples were passed through a microporous filter and

the Mn, Mw, and PDI were determined by GPC using a polystyrene calibration curve.

Table 6.4.14. GPC Data for the Metathesis of NBR and 1-hexene using 0.007 phr Grubbs 2

Time (h)

1 Mw (Da) 208500

Mn (Da) 78750

PDI 2.65

2 Mw (Da) 180000

Mn (Da) 74500

PDI 2.42

3 Mw (Da) 174000

Mn (Da) 71300

PDI 2.44

24 Mw (Da) 164000

Mn (Da) 69200

PDI 2.37

147

Table 6.4.15. GPC Data for the Metathesis of NBR and 1-hexene using 5-12

Catalyst loading (phr)

Time (h)

0.007 0.014 0.028 0.05 0.10

1 Mw (Da) 230000 235000 232500 174000 123500

Mn (Da) 83750 84950 82500 71800 57400

PDI 2.75 2.77 2.82 2.42 2.15

2 Mw (Da) 266000 246500 246500 178000 122500

Mn (Da) 91500 86850 86900 71400 56450

PDI 2.91 2.84 2.84 2.49 2.17

3 Mw (Da) 257000 251000 238500 181500 127000

Mn (Da) 91800 87600 89600 73900 59000

PDI 2.80 2.87 2.66 2.46 2.15

4 Mw (Da) 263000 253500 246500 NA NA

Mn (Da) 94750 88750 86800

PDI 2.78 2.86 2.84

24 Mw (Da) 264000 252500 246000 154500 97000

Mn (Da) 93000 88500 91000 67350 47850

PDI 2.84 2.85 2.70 2.29 2.03



Time (h)

0.007 0.014 0.028 0.05

1 Mw (Da) 256250 267000 267000 240000

Mn (Da) 66000 65000 62500 60000

PDI 3.88 4.11 4.27 4.00

2 Mw (Da) 272000 266000 263000 241500

Mn (Da) 64500 66000 63000 60000

PDI 4.22 4.03 4.17 4.03

3 Mw (Da) 279500 266000 270000 238000

Mn (Da) 67900 64500 64000 60000

PDI 4.12 4.12 4.22 3.97

4 Mw (Da) 272000 272000 268000 239000

Mn (Da) 65000 66250 64000 60000

PDI 4.18 4.11 4.19 3.98

24 Mw (Da) 271500 276000 266500 239000

Mn (Da) 64000 65000 63000 60000

PDI 4.24 4.25 4.23 3.98

148



Time (h)

0.007 0.014 0.028 0.05

0.25 Mw (Da) 267500 228500 196500 156500

Mn (Da) 81000 78000 70500 63500

PDI 3.30 2.93 2.79 2.46

1 Mw (Da) 267500 215500 192000 153000

Mn (Da) 81500 76700 71000 61750

PDI 3.28 2.81 2.70 2.48

2 Mw (Da) 220500 217000 189000 152500

Mn (Da) 71500 75600 69750 60900

PDI 3.08 2.87 2.71 2.50

3 Mw (Da) 238500 216000 194000 155000

Mn (Da) 80500 75550 70650 62150

PDI 2.96 2.86 2.75 2.49

4 Mw (Da) 243000 213500 187000 151000

Mn (Da) 79850 74850 69500 60350

PDI 3.04 2.85 2.69 2.50

24 Mw (Da) 241000 220500 198500 160000

Mn (Da) 80600 75400 71800 63400

PDI 2.99 2.92 2.76 2.52

6.4.2.3 Hydrogenation of NBR

A standard procedure for the hydrogenation of NBR is as follows. A 5 wt% solution of NBR in

chlorobenzene was prepared. In a glovebox 2 mL of the NBR solution was place in a vial with a

stirbar. The catalyst solution was prepared by dissolving the precatalyst (10 or 5 µmol) in

CH2Cl2 (0.2 mL) and if required the appropriate amount of BCl3 was added. The catalyst

solution was added to the NBR and the vials were placed in a high pressure Parr reactor. The

reactor was purged with H2 and charged to the required pressure. The reactor was heated to the

required temperature and the reaction was left for 20 hr. The degree of hydrogenation was

determined by IR spectroscopy following the procedure described by following literature

procedures.27

149

Table 6.4.18. Hydrogenation of NBR using 3-5, 5-5, 5-12

Compound

Catalyst

Loading (µmol)

Pressure

(bar)

Degree of

Hydrogenation

3-5 10 50 82%

5 82 71%

5-5 10 50 0%

10 82 0%

5-12 10 50 0%

10 82 0%

Table 6.4.19. Hydrogenation of NBR using 3-9, 5-9, 5-17

Compound

Catalyst Loading

(µmol)

Pressure

(bar)

Degree of

Hydrogenation

3-9 10 50 Major Cross Linking

5 82 Major Cross Linking

5-9 10 50 74%

10 82 99%

5-17 10 50 36%

10 82 96%

150


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152

Chapter 7 Summary and Future Work

7.1 Summary

The work presented herein was motivated by the desire to develop new olefin metathesis

catalysts for the cross metathesis of NBR and 1-hexene. Recognizing a gap in the patent

literature, the use of tridentate ligands for this new development was targeted. Specifically,

tridentate dianionic ligands were used to synthesize new ruthenium alkylidene complexes. These

complexes were inactive for olefin metathesis on their own but upon the stepwise addition of two

equivalents of BCl3 the resulting complexes were active for a variety of metathesis reactions.

Chapter 2 explores the coordination chemistry of tridentate dithiolate ligands on ruthenium. It

was found that only complexes with tridentate dithiolate ligands with a central ether donor could

be successfully isolated. These complexes were demonstrated to react with BCl3 to give new

6-coordinate ruthenium complexes. A chloride from BCl3 was transferred to ruthenium and the

remaining BCl2 fragment was bridged between the two thiolate ligands.

In Chapter 3, the ligands used in Chapter 2 were used for the synthesis of ruthenium alkylidene

complexes from Grubbs Catalysts. A library of compounds was synthesized with variations to

the central donor of the tridentate ligand including ether, thioether and phosphino. A ligand with

an aryl backbone and a tridentate dialkoxide ligand were also used. In most cases, complex

derivatives where the 5th ligand was either PCy3 or SIMes were prepared.

Due to the motivation to prepare the targeted olefin metathesis catalysts independently of Grubbs

Catalyst, Chapter 4 describes the development of a new method to prepare ruthenium

alkylidenes. Using a Ru(0) source such as Ru(cod)(cot) or Ru(PPh3)4H2 and dithioacetals derived

from the ligands used in Chapter 3, tridentate, dithiolate ruthenium alkylidene complexes could

be synthesized. This method provides a convenient route to these complexes by installing the

tridentate dithiolate ligand and the alkylidene on to ruthenium in one step.

Chapter 5 describes the reactivity of the complexes prepared in Chapters 3 and 4 with BCl3.

Similar to the reactivity observed in Chapter 2, these complexes react with 1 equivalent of BCl3

to form new 6-coordinate complexes. In the new complexes a chloride has transferred from BCl3

153

to ruthenium and the remaining BCl2 fragment is bridged between the thiolate ligands. Due to the

trans effect, the tridentate ligand rearranges on the metal centre. However, in some cases two

isomers are formed. In one isomer the ligand has rearranged and in the other it has not. With

some complexes the addition of a second equivalent of BCl3 results in abstraction of the chloride

from ruthenium to give a 5-coordinate cationic complex. In contrast, the parent complexes react

with Bronsted acids by protonation of the alkylidene carbon. The reactivity with both Lewis and

Bronsted acids is reversible by the addition of a base such as PtBu3 to give the parent tridentate

dithiolate ruthenium alkylidene complexes.

Finally, in Chapter 6 the ruthenium alkylidene complexes prepared were tested for catalytic

olefin metathesis. The tridentate dithiolate ruthenium alkylidene complexes described in

Chapters 3 and 4 were inactive for olefin metathesis. This was also the case for the complexes

formed by the addition of 1 equivalent of BCl3. The 5-coordinate cationic ruthenium alkylidenes

generated by the addition of a second equivalent of BCl3 were found to be active for a variety of

olefin metathesis reactions including ring closing metathesis (RCM), ring opening metathesis

polymerization (ROMP) and cross metathesis (CM). In general the catalysts containing SIMes

were more active than the PCy3 derivatives. The three most active catalysts were screened for

CM of NBR and 1-hexene. It was found that in order to achieve the same activity as 2nd

Generation Grubbs Catalyst, higher catalyst loadings were required. A series of these complexes

were also tested for the hydrogenation of NBR and shown to be active hydrogenation catalysts.

The successful development of new olefin metathesis catalysts presented herein has afforded a

large volume of new ruthenium chemistry. The knowledge gained from this work can be used in

the development of new, more active olefin metathesis catalysts.

7.2 Future Work

The activation of all the catalysts presented herein were done with the Lewis acid BCl3. An

obvious area of further development would be to investigate the effect of different Lewis acids.

Perhaps the use of a more electron withdrawing Lewis acid would result in a more active

catalyst. A Lewis acid activation method which is non-reversible may improve catalyst

performance also. Since the activation with BCl3 was shown to be reversible this could be a

potential path of catalyst decomposition and deactivation. Using a Lewis acid activator which

154

performs the activation in a non-reversible fashion could prevent this possible decomposition

pathway.

A rational design of precatalyst/activator could be performed if the catalyst decomposition was

better understood. This would be the motivation behind a study of catalyst deactivation and

decomposition pathways. The isolation and characterization of ruthenium species after catalytic

olefin metathesis would be of great interest. Once the decomposition products were isolated a

detailed mechanistic study of the pathway to these species would prove to be invaluable in the

design of longer living and thus more active catalysts.

Due to the easy variability of the dithioacetals used in the independent synthesis of these

complexes the scope of this reaction could be easily determined. This would provide convenient

access to a number of new catalyst variants. Modifications could be made to the ligand itself

using different tridentate dithiols in the dithioacetal synthesis. Modifications could include

different central donors and varied ligand backbones. Easy modification to the resulting

ruthenium alkylidene could be accomplished simply by using different aldehydes in the

dithioacetal preparation. The effect of electron withdrawing or donating substituents on the

phenyl ring could be investigated and alkyl variants could also be easily prepared.

The catalyst with the tridentate dialkoxide ligand was shown to be the most active for the

standard metathesis reaction. However, this catalyst could not be synthesized independently of

Grubbs Catalyst. It would therefore be beneficial if an independent synthesis of this catalyst was

developed. Developing a new method for synthesizing ruthenium alkylidenes could also allow

access to a variety of new complexes.

Finally the scope of metathesis reactions that these catalysts can perform should be broadened.

Although these catalysts were demonstrated to be active for the standard metathesis reactions

and the metathesis of NBR, knowledge of the scope of these catalysts would be useful for

developing new uses and applications for them.

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Lewis Acid Activated Olefin Metathesis Catalysts · Lewis Acid Activated Olefin Metathesis Catalysts Adam Michael McKinty Doctor of Philosophy Department of Chemistry University of