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nsition metal organometallic compounds & Cataly Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French Chemist L. C. Cadet 1760 As 2 Me 4 dicacodyl Re R 3 P CO P R 3 CH 3 CO Mo P R 2 R 2 P Cl C C Mo Cl R 2 P P R 2 C C O O O O

Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

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Page 1: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Transition metal organometallic compounds & Catalysis

Metal-carbon bond: a few from many?

Which one is organometallic? Ni(CO)4 or NaCN ?

French Chemist L. C. Cadet 1760 As2Me4 dicacodyl

ReR3P CO

PR3

CH3

CO

MoPR2

R2P Cl

C

C

MoCl

R2P

PR2

C

C

O O

OO

Page 2: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Ligand Name Bonding Type

Molecular Hydrogen: H2

Hydride H- M-H

Phosphine: PR3 M-PR3

Carbonyl: CO

Alkyl , Aryl M-CR M-Ph

Alkene

MH

H

CM O

CH2H2C

M

Organometallic Compound: Looking closer

Page 3: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

18 en rule

Organic compounds – Octet rule

Organometallic – 18 electron rule

* 18 valance electron – inert gas configuration

1920 British Chemist Sidgwick

Page 4: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL
Page 5: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

To determine the electron count for a metal complex:

Determine the oxidation state of the transition metal center(s) and

the metal centers resulting d-electron count. To do this one must:

a) note any overall charge on the metal complex

b) know the charges of the ligands bound to the metal

center

c) know the number of electrons being donated to the metal

center from each ligand

2) Add up the electron counts for the metal center and ligands

Counting the number of electronsCounting the number of electrons

Page 6: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Ligand Name Bonding Type Formal Charge

Electrons donated

Molecular Hydrogen: H2

0 2

Hydride H- M-H -1 2

Halide X- M-X -1 2

Amine, phosphine, arsine: NR3, PR3, AsR3

M-NR3 M-PR3 0 2

Carbonyl: CO 0 2

Alkyl , Aryl M-CR M-Ph -1 2

Alkene -1 2

MH

H

CM O

CH2H2C

M

Counting the number of electronsCounting the number of electrons

Page 7: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Fe

OC

OCCO

CO

CO

Fe is 4s23d6 = 8e

each Co is neutral so Fe0

each CO donates 2 e = 10e

8e + 10e = 18ecoordinately saturated

RhPh3P Cl

Ph3P PPh3 Rh is s1d8 = 9e

since Cl is -1, Rh is +1 (the complex is neutral)

4 ligands x 2e each = 8e9e - 1e + 8e = 16e

therefore coordinately unsaturated

Page 8: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL
Page 9: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Catalysis

Reaction Coordinate

G

GReactants

Products

Ea

E acatalyzed

Catalyzed rxn proceeding through

an interm ediateA + B CA + B C

Catalyst

HeterogeneousHeterogeneous HomogeneousHomogeneous

A catalyst lowers the activation barrier for a transformation, by introducing a new reaction pathway.

It does not change the thermodynamics!!It does not change the thermodynamics!!

Page 10: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Synthesis of chemicals… pharmaceutical, agricultural

Catalytic converter … environmental

Biological system – efficient catalyst

Catalysis : Why?

Organometallic compounds, metals etc.

Page 11: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

How to select an efficient catalyst?

Activity: related to rate of reaction (also called turnover)

efficient catalyst: good activity

Turnover frequency (N) N = N = /[Q]/[Q]Large turnover frequency – efficient catalyst

Selectivity: Byproducts should be minimized

Lifetime: It is costly to replace the catalyst frequently

Cost: The acceptable cost depends upon the catalyst lifetime, product value lifetime and product value

Poisoning: decomposition of catalyst, adsorption of reactant/product

Page 12: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Coordination compounds in catalysis Nobel Prizes

2005 Yves Chauvin,Robert H. Grubbs

and Richard R. Schrock.

2001 KNOWLES, NOYORI, SHARPLESS

1973 WILKINSON

1963 ZIEGLER, NATTA

1918 HABER

1909 OSTWALD

Page 13: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Hydrogenation of Unsaturated Hydrocarbons

The most common catalyst

Wilkinson’s Catalyst, [RhCl(PPh3)3]

-CH=CH- + H2 -CH-CH-

H H

NOBEL : 2001

Page 14: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Wilkinson’s Catalyst (WC)

Rh

Ph3P PPh3

PPh3ClChlorotris(triphenylphosphine)rhodium(I)

square planar dsquare planar d88 configuration configuration

Page 15: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Geoffrey Wilkinson

• Born July 14, 1921, Yorkshire, England

• Ph.D from Cal Berkeley studying with Glenn Seaborg

• First published compound in 1965 in Journal of the Chemical Society - Chemical Communications

•Nobel Prize in Chemistry 1973 (shared with Ernst Otto Fischer) for their pioneering work, performed independently, on the chemistry of the organometallic, so called sandwich compounds.

Organometallic compounds prepared by Wilkinson in display at Harvard Univ.

Page 16: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Synthesis of WC

Rh

Ph3P PPh3

PPh3Cl

+EtOH

78 oC

+ Ph3PORhCl3 3 H2O + >4 PPh3

Commercially available

Page 17: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Catalytic steps

(a) Ligand coordination and dissociation

Facile coordination of the reactant and facile loss of products.

Coordinatively unsaturated - 16-electron complexes

(b) Oxidative addition

Metal must possess a non-bonding electron pair

Coordinatively unsaturated

Oxidation of metal by two units – Mn to Mn+2

-occurs when a complex behaves simultaneously as a Lewis base and a Lewis acid

Page 18: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

IrCO

Ph3P

Ph3P

Cl+ H2 Ir

CO

Ph3P

Ph3P

ClH

H

Oxidative addition…

LnMn + X-YLnMn

X-Y

LnMn+2

X

Y

Page 19: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

(c) Insertion or migrationMigration of alkyl and hydride ligands

L + M CO

R

M C

L

O

R

M

H CH2

CH2

M CH2CH3

Page 20: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

LnM

R

CO

LnM

S

CR

O

LnM CR

O

S

LnM

RC

O

LnM

L'

CR

O

L'

Page 21: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

(d) Nucleophilic attack(d) Nucleophilic attack

C

C

R R

H R

L3Pd OH2C

R

H

C OH

R

R

2+

L3Pd

+

L5M CO + OH- L5M C

O

OH L5M H

-

-

+CO2

Page 22: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

(d) Reductive elimination

Involves decrease in the oxidation and coordination number

Rh

COPh3P

Ph3P Me

COR

Cl RhCOPh3P

Ph3P Cl

RCOMe

+

Page 23: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Hydrogenation of Unsaturated Hydrocarbons

-CH=CH- + H2 -CH-CH-

H H

G0 = -101 kJ/mol

Page 24: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

RhPh3P Cl

Ph3P PPh3

+ H2 RhPh3P

Cl

Ph3P PPh3

H

HRh+1

Rh3+

RhPh3P

Cl

Ph3P PPh3

H

HRh

Ph3PCl

Ph3PH

H + PPh3

(1) Oxidative addition(1) Oxidative addition

(2) Ligand Dissociation(2) Ligand Dissociation

WC in alkene Hydrogenation: Catalytic Steps

Page 25: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

(3) Ligand Association(3) Ligand Association

(4) Migration/Insertion(4) Migration/Insertion

RhPh3P

Cl

Ph3PH

HCH2

CH2Rh

Ph3PCl

Ph3PH

H

CH2

CH2+Rh

Cl PPh3

Ph3PH

H

CH2H2C

RhPh3P

Cl

Ph3PH

H

CH2

CH2

RhPh3P

Cl

Ph3PCH2

H

CH2H

Rh

Cl PPh3

Ph3PH

H

CH2H2C

WC in alkene Hydrogenation: Catalytic Steps

Page 26: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

+ PPh3RhPh3P

Cl

Ph3PCH2

H

CH2H

RhPh3P

Cl

Ph3PCH2

H

CH2H

PPh3

(5) Ligand association(5) Ligand association

WC in alkene Hydrogenation: Catalytic Steps

Page 27: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

RhPh3P Cl

Ph3P PPh3RhPh3P

Cl

Ph3PCH2

H

CH2H

PPh3

+ CH3 CH3

(note: regeneration of the catalyst)

(6) Reductive elimination(6) Reductive elimination

WC in alkene Hydrogenation: Catalytic Steps

Page 28: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

WC

IN

A

C

T

I

O

N

Page 29: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Rate of the reaction decreases as the alkyl substitution increases

Highly sensitive to the nature of the phosphine ligand

Analogous complexes with alkylphosphine ligands are inactive

Highly selective for C=C over C=O

WC in alkene Hydrogenation: Additional Notes

* Laboratory scale organic synthesis* Production of fine chemicals

Applications

Page 30: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Chiral phosphine ligands have been developed to synthesize optically

active products.

Synthesis of L-DOPA (Used in the treatment of Parkinson’s diseases)

Synthetic route was developed by Knowles & co-workers at Monsanto

Dr. William S. Knowles received Nobel prize in chemistry 2001 Dr. William S. Knowles received Nobel prize in chemistry 2001 along with other two scientists.along with other two scientists.

Alkene Hydrogenation & Chirality & Nobel

Page 31: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

This reaction, developed by Knowles, Vineyard, and Sabacky, was used at Monsanto as a commercial route to the Parkinson's drug L-DOPA.

Alkene Hydrogenation, Chirality & Nobel

Page 32: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL
Page 33: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Non-superimposable mirror image

Enantiomeric excess = (moles of major enantiomer - moles of other enantiomer / Total moles of both enantiomers) 100

Page 34: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

phenylanisylmethylphosphine (PAMP)

Dimeric product is DiPAMP

Page 35: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL
Page 36: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

Additional notes For interested students

(a) Ligand coordination and dissociation

Facile coordination of the reactant and facile loss of products.

Coordinatively unsaturated - 16-electron complexes

(b) Oxidative addition

Metal must possess a non-bonding electron pair

Coordinatively unsaturated

Oxidation of metal by two units – Mn to Mn+2

-occurs when a complex behaves simultaneously as a Lewis base and a Lewis acid

Page 37: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

IrCO

Ph3P

Ph3P

Cl+ H2 Ir

CO

Ph3P

Ph3P

ClH

H

Oxidative addition…

LnMn + X-YLnMn

X-Y

LnMn+2

X

Y

Page 38: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

(c) Insertion or migrationMigration of alkyl and hydride ligands

L + M CO

R

M C

L

O

R

LnM

R

CO

LnM

S

CR

O

LnM CR

O

S

LnM

RC

O

LnM

L'

CR

O

L'

Page 39: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

M

H CH2

CH2

M CH2CH3

Page 40: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

(d) Nucleophilic attack(d) Nucleophilic attack

C

C

R R

H R

L3Pd OH2C

R

H

C OH

R

R

2+

L3Pd

+

L5M CO + OH- L5M C

O

OH L5M H

-

-

+CO2

Page 41: Transition metal organometallic compounds & Catalysis Metal-carbon bond: a few from many? Which one is organometallic? Ni(CO) 4 or NaCN ? French ChemistL

(e) Reductive elimination

Involves decrease in the oxidation and coordination number

Rh

COPh3P

Ph3P Me

COR

Cl RhCOPh3P

Ph3P Cl

RCOMe

+