Polyhedron 28 (2009) 3654–3658

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Polyhedron

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Preparation and characterization of diruthenium(II,III) compounds containingterminal olefin groups

Yang Fan, Phillip E. Fanwick, Tong Ren *

Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA

a r t i c l e i n f o

Article history:Received 9 June 2009Accepted 28 July 2009Available online 3 August 2009

Keywords:Terminal olefinDirutheniumStructure

0277-5387/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.poly.2009.07.052

* Corresponding author. Tel.: +1 765 494 5466; faxE-mail address: tren@purdue.edu (T. Ren).

a b s t r a c t

4-Vinylbenzoic acid reacted with Ru2(D(3,5-Cl2Ph)F)3(OAc)Cl and cis-Ru2(D(3,5-Cl2Ph)F)2(OAc)2Cl (D(3,5-Cl2Ph)F is N,N0-bis(3,5-dichlorophenyl)formamidinate) to yield Ru2(D(3,5-Cl2Ph)F)3(4-vinylbenzoate)Cl(1) and cis-Ru2(D(3,5-Cl2Ph)F)2(4-vinylbenzoate)2Cl (2), respectively. Ru2(D(3,5-Cl2Ph)F)3(OAc)Cl reactedwith 5-hexenoic acid and 6-heptenoic acid to afford Ru2(D(3,5-Cl2Ph)F)3(5-hexenoate)Cl (3) andRu2(D(3,5-Cl2Ph)F)3(6-heptenoate)Cl (4), respectively. All new compounds were characterized using vol-tammetric and Vis–NIR spectroscopic techniques, and the structures of 1 and 2 were also establishedthrough X-ray single crystal diffractions.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Organic molecules containing terminal olefin functionality areversatile building blocks that may undergo many useful transfor-mations including the Heck type reactions [1] and olefin metath-esis reactions [2]. One can easily imagine that metal compoundscontaining terminal olefin on the ligand periphery may undergosimilar reactions [3]. Indeed, many elegant examples have beendisclosed by the laboratory of Gladysz, where the olefin pen-dants of metal-bound phosphine ligands undergo both ring-clos-ing and cross metathesis reactions [4]. Metal compoundscontaining peripheral olefin have been used as the substratesof Heck cross coupling reactions, leading to the formation ofmetallo supramolecules and metallo-conjugated polymers [3].The other interesting utility of terminal olefin is its reaction witha hydride terminated silicon surface (Si–H) under photolytic con-ditions that results in the formation of a Si–C bond (Scheme 1).This type of reactions has been become an important tool for themodification of silicon surface with a molecular monolayer, asignificant step toward the realization of CMOS-molecule hybriddevices [5,6].

Recent efforts from several laboratories including ours demon-strated the modular nature of bimetallic paddlewheel species withsuitable peripheral functional groups, based on which dimeric,oligomeric and dendritic assemblies can be achieved [3,7–9].Among previously reported studies are a series of dirutheniumspecies containing one or two terminal olefins, namely

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: +1 765 494 0239.

Ru2(D(3,5-Cl2Ph)F)3(l-O2C(CH2)nCH@CH2)Cl (n = 1 and 2) and cis-Ru2(D(3,5-Cl2Ph)F)2(l-O2C(CH2)mCH@CH2)2Cl (m = 1–3), whereD(3,5-Cl2Ph)F is N,N0-bis(3,5-dichlorophenyl)formamidinate, andtheir cross metathesis and ring-closing metathesis reactions[10,11]. These diruthenium species are interesting from the deviceperspective because of both their rich redox characteristics and netmolecular spin [6,12,13]. In order to modify Si surfaces with thistype of diruthenium species, compounds with either rigid or ex-tended hydrocarbon spacers are necessitated due to the size ofRu2 head group. Reported in this contribution are the preparationand structural study of Ru2(D(3,5-Cl2Ph)F)3(l-O2CC6H4-4-CH@CH2)Cl (1, Scheme 2), cis-Ru2(D(3,5-Cl2Ph)F)2(l-O2CC6H4-4-CH@CH2)2Cl (2), and Ru2(D(3,5-Cl2Ph)F)3 (l-O2C(CH2)nCH@CH2)Cl(n = 3 (3) and 4 (4)).

2. Results and discussion

2.1. Synthesis

Preparative chemistry of compounds 1–4 is based on the Ru2-(DArF)4�x(l-O2CMe)xCl (x = 1 and 2) type synthons that have beendeveloped by several laboratories [8,9,14]. As illustrated in Scheme2, gentle reflux of Ru2(D(3,5-Cl2Ph)F)3(l-O2CMe)Cl with 4-vinyl-benzonic acid in excess afforded compound 1 in excellent yield.Carboxylate exchange reaction between Ru2(D(3,5-Cl2Ph)F)2-(l-O2CMe)2Cl and 4-vinylbenzonic acid required more rigorousconditions and the synthesis of 2 was achieved through reflux intoluene using a setup involving a micro Soxhlet extractor as de-scribed previously [15]. Preparations of compounds 3 and 4 aresimilar to that of 1 and both were obtained in good yields.Compounds 1–4 are all purple crystalline materials and yielded

hυ (254 nm)

hydride terminated Si(111)

SiSi

SiSi

SiSi

Si

H H

Si Si Si

Scheme 1. Functionalization of Si surface with olefin-capped molecule (solid ballrepresent the head group).

Y. Fan et al. / Polyhedron 28 (2009) 3654–3658 3655

satisfactory combustion analysis results. All four compounds areparamagnetic with the room temperature effective magnetic mo-ments in a narrow range of 3.81–3.93 Bohr magneton, which isconsistent with the presence of three unpaired electrons [12,16].

2.2. Molecular structures

Both compounds 1 and 2 crystallize in the space group P�1, andthe asymmetric unit contains a complete diruthenium molecule ineach case. The structural plot of 1, Fig. 1, reveals the presence ofthree D(3,5-Cl2Ph)F ligands and one 4-vinylbenzoate around thediruthenium core. The coordination sphere of the Ru2 unit is com-pleted with a chloro and a water ligand in the axial positions,which were disordered over both axial sites and refined with 50%occupancy each for Cl and O (labeled as Cl0 in Fig. 1). Hence, theRu–Cl0 distance is shorter than the Ru1–Cl1 bond in 2 but longerthan the Ru–O(OH2) distance in Ru2(D(3,5-Cl2Ph)F)2(l-O2CMe)2Cl(H2O) (2.362 Å) [9]. It is clear from the structural plotof 2 (Fig. 2) that the coordination sphere of the Ru2 unit consists

N

Ru

Ru

O

O

N

N

N

N

N

Cl

Ar

Ar

Ar

Ar

Ar

Ar

Ar

Ar

N

Ru

Ru

O

O

N

N

O

O

N

Cl

Ar

Ar

Ar

Ar

Ar

Ar

OHO

OHO

THF / CH3OH

toluene

Scheme 2. Preparation of dirutheniu

of two D(3,5-Cl2Ph)F and two 4-vinylbenzoate bridging bidentateligands in a cis-arrangement, and a chloro and an ethanol axialligands.

Listed in Table 1 are the selected bond lengths and angles datafor compounds 1 and 2. The Ru–Ru bond length in 1 (2.3381(4) Å)is slightly longer than that in the precursor Ru2(D(3,5-Cl2Ph)F)3(l-O2CMe)Cl (2.3220(7) Å), and the shortness of Ru–Ru bond in thelatter is attributed to the absence of axial water ligand [9]. TheRu–Ru bond length in 2 (2.319(2) Å) is slightly shorter than thatof and Ru2(D(3,5-Cl2Ph)F)2(l-O2CMe)2Cl(H2O) (2.327 Å) [9],reflecting the weak ligating ability of ethanol in comparison withwater. The equatorial Ru–O and Ru–N bond lengths are all in goodagreement with those of related compounds reported earlier[9,11].

2.3. Voltammetry

Similar to other Ru2(DArF)4�x(carboxylate)x type compounds,compounds 1–4 display cyclic voltammograms (CV, Fig. 3) withrich features. Common to all compounds are three Ru2-centeredone-electron events: the quasi-reversible oxidation (A), quasi-reversible reduction (B), and subsequent irreversible reduction(D) as illustrated in Scheme 3. It is clear from Table 2 that themono-carboxylate species 1, 3 and 4 have nearly identical elec-trode potentials. Interestingly, the voltammetric characteristic ofthe dicarboxylate species 2 is comparable to those of the otherthree compounds, except that the couple D of 2 is anodicallyshifted. Additional features such as peaks C and E are related tothe dissociation/association of the chloro ligand (Scheme 3), as dis-cussed in our prior study of related species [11]. Peaks F and G arealso prevalent and could be related to the dissociation/associationof axially bound solvent molecule, although there is no concreteevidence supporting this speculation.

N

Ru

Ru

O

O

N

N

N

N

N

Cl

Ar

Ar

Ar

Ar

N

Ru

Ru

O

O

N

N

O

O

N

Cl

Ar

Ar

1

2

m-4-vinylbenzoate compounds.

Fig. 2. Structural plot of molecule 2.(HOEt). Hydrogen atoms were omitted forclarity.

Table 1Selected bond lengths (Å) and angles (�) for compounds 1 and 2.

1 2

Ru1�Ru2 2.3381(4) Ru1�Ru2 2.319(2)Ru1�N1 2.085(3) Ru1�N5 2.03(1)Ru1�N3 2.069(3) Ru1�N7 2.03(1)Ru1�N5 2.073(3) Ru2�N6 2.03(1)Ru2�N2 2.059(3) Ru2�N8 2.04(1)Ru2�N4 2.058(3) Ru1�O1 2.075(8)Ru2�N6 2.087(3) Ru1�O3 2.064(8)Ru1�O1 2.067(3) Ru2�O2 2.063(8)Ru2�O2 2.080(3) Ru2�O4 2.048(9)Ru1�Cl01 2.437(2) Ru1�Cl1 2.501(4)Ru2�Cl02 2.435(2) Ru2�O21 2.35(1)C8–C9 1.307(8) C17–C18 1.32(2)

C37–C38 1.28(2)Ru2�Ru1�Cl1 174.54(4) Ru2�Ru1�Cl1 171.13(9)

Ru1�Ru2�O21 169.7(2)

1 A B

D

C

GF

E

AB

DG

F

E

2

3 AB

DG

C

-2-1.5-1-0.500.511.5

E/V, vs. Ag/AgCl

A B

DC

GF

4

Fig. 3. Cyclic voltammograms of compounds 1–4 recorded in 0.20 M THF solutionof Bu4NPF6 at a scan rate of 0.10 V/s.

Fig. 1. Structural plot of molecule 1. Hydrogen atoms were omitted for clarity.

3656 Y. Fan et al. / Polyhedron 28 (2009) 3654–3658

3. Conclusion

We have successfully prepared several diruthenium specieswith terminal olefin that may be suitable for photolytic immobili-zation on Si surfaces, and are currently exploring and optimizingconditions for the immobilization of these novel Ru2 compoundson various Si surfaces.

4. Experimental

4.1. General

4-Vinylbenzoic acid, 5-hexenoic acid, and 6-heptenoic acidwere purchased from Aldrich. Ru2(D(3,5-Cl2Ph)F)3(OAc)Cl and cis-Ru2(D(3,5-Cl2Ph)F)2(OAc)2Cl were prepared using a literature pro-cedure [9]. Vis–NIR spectra in THF were obtained with a JASCO V-670 UV–Vis–NIR spectrophotometer. Magnetic susceptibility wasmeasured at 294 K with a Johnson Matthey Mark-I magnetic sus-ceptibility balance. Cyclic voltammograms were recorded in0.2 M n-Bu4NPF6 solution (THF, N2-degassed) on a CHI620A vol-tammetric analyzer with a glassy carbon working electrode (diam-

{Ru2(III,III)Cl}+ Ru2(II,III)Cl {Ru2(II,II)Cl}- {Ru2(II,I)Cl}2-DBA

+ e- + e-+ e-

- Cl-

{Ru2(II,III)}+ Ru2(II,II) {Ru2(II,I)}-

- Cl-

C+ e-

E+ e-

+ Cl-

Scheme 3. Assignments of observed Ru2-based redox couples in compounds 1–4.

Table 2Electrode potentials of compounds 1–4.

Compounds E1/2(A) (V) E1/2(B) (V) Epc(D) (V)

1 1.09 �0.20 �1.412 1.17 �0.27 �1.293 1.11 �0.22 �1.504 1.10 �0.23 �1.48

Table 3Crystal data for compounds 1 and 2.

1�3THF (2.HOC2H5)�4EtOH

Formula C60H52Cl13N6O6Ru2 C54H58Cl9N4O9Ru2

Formula weight 1616.15 1428.30Space group P�1 P�1a (Å) 12.1831(4) 11.479(4)b (Å) 12.4481(4) 13.119(3)c (Å) 25.6312(8) 20.330(5)a (�) 85.369(2) 78.384(6)b (�) 85.490(2) 86.27(1)c (�) 64.326(2) 83.97(2)V (Å3) 3487.8(2) 2979(1)Z 2 2T (K) 150 150k (Mo Ka) (Å) 0.71073 0.71073q (g cm�3) 1.539 1.592Goodness-of-fit (GOF) on F2 1.094 1.200R1, wR2 0.049, 0.143 0.101, 0.207

Y. Fan et al. / Polyhedron 28 (2009) 3654–3658 3657

eter = 2 mm), a Pt-wire auxiliary electrode, and a Ag/AgCl referenceelectrode. The concentration of diruthenium species is always1.0 mM. The ferrocenium/ferrocene couple was observed at0.606 V (versus Ag/AgCl) under the experimental conditions.

4.2. Preparation of Ru2(D(3,5-Cl2Ph)F)3(l-O2CC6H4-4-CH@CH2)Cl (1)

A mixture of Ru2(D(3,5-Cl2Ph)F)3(OAc)Cl (200 mg, 0.15 mmol),4-vinylbenzoic acid (222 mg, 1.5 mmol), THF (20 mL), and metha-nol (20 mL) was refluxed in air overnight. After the solvent re-moval, the residue was washed with H2O, ethanol and hexanesto yield a purple solid. Further purification was carried out byrecrystallization from a mixed solvent of THF/ethanol (1:5, v:v)to yield a purple solid (172 mg, 83% based on Ru). Vis, kmax (nm,e(M�1 cm�1)): 520(5000). Anal. Calc. for C48H31N6O2Cl13Ru2�H2O:C, 41.04; H, 2.37; N, 5.98. Found: C, 40.85; H, 2.36; N, 5.78%.leff = 3.93lB.

4.3. Preparation of cis-Ru2(D(3,5-Cl2Ph)F)2(l-O2CC6H4-4-CH@CH2)2Cl(2)

A 100 mL round-bottom flask was charged with cis-Ru2(D(3,5-Cl2Ph)F)2(OAc)2Cl (200 mg, 0.20 mmol), 4-vinylbenzoic acid(65 mg, 0.44 mmol) and 40 mL toluene. The flask was mountedwith a MicroSoxhlet extractor containing a thimble filled withK2CO3. The reaction mixture was refluxed in air for 6 h. Solventwas removed, and the residue was washed with H2O, ethanoland hexanes to yield a dark red solid. Further purification was car-ried out by recrystallization from a mixed solvent of THF/ethanol(1:5, v:v) to yield a purple solid (182 mg, 76% based on Ru). Vis,kmax (nm, e(M�1 cm�1)): 535(3550). Anal. Calc. for C44H30N4O4Cl9-

Ru2�THF: C, 45.32; H, 3.01; N, 4.40. Found: C, 45.18; H, 3.02; N,4.38%. leff = 3.81lB.

4.4. Preparation of Ru2(D(3,5-Cl2Ph)F)3(l-O2CCH2CH2CH2CH@CH2)Cl(3)

A mixture of Ru2(D(3,5-Cl2Ph)F)3(OAc)Cl (200 mg, 0.15 mmol),5-hexenoic acid (0.18 mL, 1.5 mmol), THF (20 mL), and methanol(20 mL) was refluxed in air overnight. After the solvent removal,the resultant oily residue was dissolved in dichloromethane, andthen washed with water, brine and dried with anhydrous Na2SO4.After the solvent removal, the residue was mixed with smallamount of n-pentane, and kept at �20 �C overnight. The precipitatewas collected by filtration and washed with a mixed solvent ofTHF/n-pentane (1:10, v:v) to yield a purple solid (145 mg, 71%

based on Ru). Vis, (nm, e(M�1 cm�1)): 520 (5100). Anal. Calc. forC45H33N6O2Cl13Ru2�THF: C, 41.30; H, 2.90; N, 5.90. Found: C,41.35; H, 2.58; N, 5.87%. leff = 3.91lB.

4.5. Preparation of Ru2(D(3,5-Cl2Ph)F)3(l-O2CCH2CH2CH2CH2CH@CH2)Cl (4)

This compound was prepared using the same synthetic proce-dure as that of the above compound except that 6-heptenoic acid(0.20 mL, 1.5 mmol) was used in place of 5-hexenoic acid. Yield:150 mg (73% based on Ru). Vis, (nm, e(M�1 cm�1)): 520(5520).Anal. Calc. for C46H35N6O2Cl13Ru2�0.5THF: C, 41.10; H, 2.80; N,5.99. Found: C, 41.08; H, 2.55; N, 6.01%. leff = 3.90lB.

4.6. X-ray diffraction study of compounds 1 and 2

Single crystals of compound 1 and 2 were obtained by slow dif-fusion of hexanes into a THF solution and slow cooling of a THF/ethanol (1:5, v:v) solution in refrigerator, respectively. The X-rayintensity data were collected at 150 K on a Nonius Kappa CCD X-ray diffractometer system using Mo Ka (k = 0.71073 Å). The struc-tures were solved by direct methods using SIR2004 [17] and refinedusing the SHELX-97 in the space group P�1 for both 1 and 2 [18]. Theasymmetric unit of 1 contains one diruthenium molecule and threeTHF solvent molecules, while that of 2 contains one dirutheniummolecule, a coordinating ethanol and four interstitial ethanol mol-ecules. Relevant information on the data collection and the figuresof merit of final refinement are listed in Table 3.

Supplementary data

CCDC 735349 and 735350 contain the supplementary crystallo-graphic data for 1 and 2, respectively. These data can be obtainedfree of charge via http://www.ccdc.cam.ac.uk/conts/retriev-ing.html, or from the Cambridge Crystallographic Data Centre, 12

3658 Y. Fan et al. / Polyhedron 28 (2009) 3654–3658

Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; ore-mail: deposit@ccdc.cam.ac.uk.

Acknowledgments

We thank the support from the National Science Foundation(Grant No. CHE 0715404) and DoD DURIP (Grant No. W911 NF-07-1-0193 for the UV–Vis–NIR spectrophotometer).

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