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Synthesis and Characterization of Heterobimetallic Ru/Pd, Ru/Pt, Ru/Au, and Ru/Cu Complexes and Their Application for Electrooxidation of Methanol

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Title:
Synthesis and Characterization of Heterobimetallic Ru/Pd, Ru/Pt, Ru/Au, and Ru/Cu Complexes and Their Application for Electrooxidation of Methanol
Creator:
YANG, YING ( Author, Primary )
Copyright Date:
2008

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Alcohols ( jstor )
Electric current ( jstor )
Electrodes ( jstor )
Electrolysis ( jstor )
Flasks ( jstor )
Ligands ( jstor )
Oxidation ( jstor )
Phosphines ( jstor )
Product distribution ( jstor )
Room temperature ( jstor )

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University of Florida
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University of Florida
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Copyright Ying Yang. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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12/31/2014
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656216717 ( OCLC )

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SYNTHESIS AND CHARACTERIZATION OF HETEROBIMETALLIC Ru/Pd, Ru/Pt, Ru/Au, AND Ru/Cu COMPLEXES AND THEIR APPLICATION FOR ELECTROOXIDATION OF METHANOL By YING YANG A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2004

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Copyright 2004 by Ying Yang

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Dedicated to my family for their love and support

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ACKNOWLEDGMENTS I am very grateful to many individuals for their help and encouragement in my four-and-a-half years of graduate studies. First and foremost, I would like to thank my advisor, Dr. Lisa McElwee-White. Without her help, I would not be a graduate student again in a new country. This unusual and special experience makes me a chemist with more academic background and intellectual breadth. I thank my committee members, Dr. Kirk S. Schanze, Dr. William R. Dolbier, Dr. Timothy J. Anderson , Dr. Yun Cao , and Dr. James Boncella, for their valuable advice, expertise, insight, and time spent. I thank all those that directly collaborated with me on my thesis project. I especially thank Dr. Khalil Abboud, who conducted X-ray characterization for several heterobimetallic complexes and provided valuable data information and helpful discussions. I need to thank all the members in Dr. Lisa McElwee-White’s group. They have been great coworkers and friends during these years. Particular praise goes to Dr. Gilbert Matare for introducing me to the project and instructing me in the initial techniques. Daniel Serra and Corey Anthony, who are involved in the same project, have provided numerous helpful discussions and suggestions. Yue Zhang has been my great friend, who provided endless help, comfort, and gossip. In addition, I need to thank Dr. Ben Brooks, Dr. Chatu Sirimanne, Keisha-Gay Hylton, Laurel Reitfort, and Corey Wilder. iv

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Special thanks must go to my parents. They are always there no matter what happens to me. Their constant and unconditional love has sustained me through all these long years. Last, but not least, I thank my husband, Youqing, and my baby, Jimmy. They brought all the colors and happiness into my life. Without them, none of this would have a meaning. v

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TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES...........................................................................................................viii LIST OF FIGURES.............................................................................................................x ABSTRACT.......................................................................................................................xi CHAPTER 1 LITERATURE REVIEW.............................................................................................1 Methanol as the Anodic Reactant in Fuel Cell Models................................................1 Oxidation of Alcohols by Ruthenium Complexes........................................................3 Product Detection and Analysis....................................................................................6 Cooperative Interaction in Bimetallic Catalysts...........................................................8 Preliminary Results.....................................................................................................11 2 HETEROBIMETALLIC COMPLEXES WITH DPPM-BRIDGED Ru/Pd, Ru/Pt, Ru/Au, AND Ru/Cu CENTERS.................................................................................16 Synthesis.....................................................................................................................18 NMR Data...................................................................................................................22 X-ray Crystallography................................................................................................25 Cyclic Voltammetry....................................................................................................31 UV/vis Spectroscopy..................................................................................................36 Conclusions.................................................................................................................37 3 ELECTROCHEMICAL OXIDATION OF ALCOHOLS USING DPPM-BRIDGED Ru/Pd, Ru/Pt, AND Ru/Au CATALYSTS.................................................................39 Electrochemical Oxidation of Methanol.....................................................................40 Electrochemical Oxidation of Isopropanol.................................................................50 Electrochemical Oxidation of Benzyl Alcohol...........................................................50 Conclusions.................................................................................................................52 4 SYNTHESIS AND ELECTROCHEMISTRY OF BIPYRIDINE COMPLEXES....54 vi

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Synthesis.....................................................................................................................55 NMR Data...................................................................................................................57 Cyclic Voltammetry....................................................................................................58 Electrochemical Oxidation of Methanol.....................................................................59 UV/vis Spectroscopy..................................................................................................64 Conclusions.................................................................................................................64 5 SYNTHESIS AND ELECTROCHEMISTRY OF OTHER HETEROBIMETALLIC COMPLEXES.............................................................................................................68 6 EXPERIMENTAL......................................................................................................74 General........................................................................................................................74 Electrochemistry.........................................................................................................75 Synthesis.....................................................................................................................76 Crystallographic Structure Determination..................................................................93 LIST OF REFERENCES...................................................................................................96 BIOGRAPHICAL SKETCH...........................................................................................106 vii

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LIST OF TABLES Table page 1-1 Formal potentials of complexes 1-3.........................................................................13 1-2 Product distributions and current efficiencies for the electrochemical oxidation of dry methanol by 1, 2, and 3......................................................................................14 1-3 Product distributions and current efficiencies for the electrochemical oxidation of wet methanol by 1, 2, and 3.....................................................................................14 2-1 NMR data for complexes 1-20.................................................................................24 2-2 Crystal data and structure refinement for complexes 4, 5, 11, and 13.....................26 2-3 Selected bond distances () and angles (deg) for Cp(PPh 3 )Ru(-I)(-dppm)PdCl 2 (4).............................................................................................................................27 2-4 Selected bond distances () and angles (deg) for Cp(PPh 3 )Ru(-Cl)(-dppm)Pd(CH 3 )Cl (5)................................................................................................28 2-5 Selected bond distances () and angles (deg) for Cp(PPh 3 )RuCl[-PPh 2 (CH 2 ) 4 PPh 2 ]AuCl (11)......................................................................................29 2-6 Selected bond distances () and angles (deg) for and Cp(PPh 3 )Ru(-I)(-dppm)CuI (13)..........................................................................................................30 2-7 Formal potentials for complexes 1-20......................................................................35 2-8 Absorption data for complexes 1-20........................................................................37 3-1 Product distributions and current efficiencies for dry methanol oxidation by 4-12...........................................................................................................................44 3-2 Product distributions and current efficiencies for wet methanol oxidation by 4 and 5......................................................................................................................47 3-3 Product distributions and current efficiencies for methanol oxidation at the Pt (II/IV) wave of 6 or 7...............................................................................................48 3-4 Electrooxidation of DMM by 4-5, 10, and 12..........................................................50 viii

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3-5 Current efficiencies for the oxidation of isopropanol to acetone by 1-4, 6-7, 11, and 13..............................................................................................................................51 3-6 Current efficiencies for the oxidation of benzyl alcohol to benzaldehyde by 1 and 2......................................................................................................................52 4-1 NMR data for bpy complexes 21-26........................................................................57 4-2 Formal potentials for bpy complexes 21-26.............................................................59 4-3 Product distributions and current efficiencies for methanol oxidation by 21-24 in DCE..........................................................................................................................63 4-4 Product distributions and current efficiencies for methanol oxidation by 21-24 in methanol...................................................................................................................63 4-5 Absorption data for complexes 21-26......................................................................64 ix

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LIST OF FIGURES Figure page 1-1 Preparation of complexes 1-3...................................................................................11 2-1 Structures of compounds 1-13..................................................................................17 2-2 Thermal ellipsoids drawing of the molecular structure of complex 4......................25 2-3 Thermal ellipsoids drawing of the molecular structure of complex 5......................28 2-4 Thermal ellipsoids drawing of the molecular structure of complex 11....................29 2-5 Thermal ellipsoids drawing of the molecular structure of complex 13....................30 2-6 UV/vis absorption spectra of compounds 1 and 3....................................................38 3-1 Cyclic voltammograms of 4.....................................................................................41 3-2 Cyclic voltammograms of 6.....................................................................................41 3-3 Cyclic voltammograms of 7.....................................................................................42 3-4 Cyclic voltammograms of 10...................................................................................43 3-5 Cyclic voltammograms of 4.....................................................................................49 4-1 Structures of compounds 21-26................................................................................55 4-2 Cyclic voltammograms of 21...................................................................................60 4-3 Cyclic voltammograms of 22...................................................................................60 4-4 Cyclic voltammograms of 23...................................................................................61 4-5 Cyclic voltammograms of 24...................................................................................61 4-6 UV-vis spectra of compounds 21-23 and 25............................................................65 4-7 UV-vis spectra of compounds 24 and 26.................................................................66 5-1 Thermal ellipsoids drawing of the molecular structure of complex 30a..................71 x

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Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy SYNTHESIS AND CHARACTERIZATION OF HETEROBIMETALLIC Ru/Pd, Ru/Pt, Ru/Au, and Ru/Cu COMPLEXES AND THEIR APPLICATION FOR ELECTROOXIDATION OF METHANOL By Ying Yang December 2004 Chair: Lisa McElwee-White Major Department: Chemistry This dissertation describes the synthesis, electrochemistry, and electrocatalytic activity of the heterobimetallic Ru/Pd, Ru/Pt, Ru/Au and Ru/Cu complexes Cp(PPh 3 )Ru(-I)(-dppm)PdCl 2 (4), Cp(PPh 3 )Ru(-Cl)(-dppm)Pd(CH 3 )Cl (5), Cp(PPh 3 )Ru(-I)(-dppm)PtCl 2 (6), Cp(PPh 3 )Ru(-I)(-dppm)PtI 2 (7), Cp(PPh 3 )Ru(-Cl)(-dppm)Pt(CH 3 )Cl (8), Cp(PPh 3 )RuI(-dppm)AuI (9), Cp(PPh 3 )RuBr(-dppm)AuCl (10), Cp(PPh 3 )RuCl[-PPh 2 (CH 2 ) 4 PPh 2 ]AuCl (11), Cp(PPh 3 )RuCl(-Ph 2 PNHPPh 2 )AuCl (12), Cp(PPh 3 )Ru(-I)(-dppm)CuI (13), [cis-(bpy) 2 Ru(-dppm)(-Cl)PdCl 2 ] + ClO 4 (21), [cis-(bpy) 2 Ru(-dppm)(-Cl)PtMeCl] + ClO 4 (22), [cis-(bpy) 2 RuCl(-dppm) AuCl] + ClO 4 (23), and [cis-(bpy) 2 RuCl(-dppb)AuCl] + ClO 4 (24). The structures of compounds 4, 5, 11, and 13 were determined by X-ray crystallography. Cyclic voltammetry of the halide-bridged complexes revealed shifts in the redox potentials of the metals, as xi

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compared to mononuclear model compounds. The shifts are consistent with electron donation between the metals through the halide bridge. Ru/Au complexes 9-12, 23-24, which are bridged only by the bidentate phosphine, exhibited minimal electronic effects between the metal centers. This limited interaction between the metal centers is corroborated by UV/vis spectroscopy. The electrochemical oxidation of methanol was carried out using heterobimetallic complexes as catalysts. The major oxidation products were formaldehyde dimethylacetal (dimethoxymethane, DMM) and methyl formate (MF). The Ru/Pd and Ru/Pt bimetallic catalysts generally afforded lower product ratios of DMM/MF and higher current efficiencies than the Ru/Au catalysts. The Ru/Au bimetallics exhibited higher product ratios of DMM/MF and lower current efficiencies similar to those obtained from the Ru mononuclear compound CpRu(PPh 3 ) 2 Cl. Increasing the methanol concentration afforded higher current efficiencies, while the addition of water to the samples shifted the product distribution toward the more highly oxidized product, MF. xii

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CHAPTER 1 LITERATURE REVIEW Methanol as the Anodic Reactant in Fuel Cell Models The promising features of a direct methanol fuel cell (DMFC) as a distributed or portable power source have stimulated much recent interest in the use of methanol as an anodic reactant. 1 Due to its ease of handling and processing, relatively non-toxic nature, availability, and good solubility in both acidic and basic solutions, methanol is considered to be a favorable fuel candidate. 2 However, the 6e oxidation of methanol to CO 2 (Eq 1.1) involves a complicated multi-step mechanism and therefore inherently slow kinetics. 3 (1. 1) CH 3 OH + H2O CO2+6H++6eMethanol adsorbed on the electrode surface can dehydrogenate successively to form a series of intermediates (Eq 1.2-1.5). Adsorbed CO has been well identified as a key reaction intermediate. 4-9 Other adsorbed species, though difficult to detect on electrodes, are evidenced in some in situ spectroscopic methods. 6,10-12 Water also can undergo successive dehydrogenation when adsorbed on the electrode surface, as indicated in Eq 1.6 and 1.7. (1. 2) (CH 3 OH) a d s (CH 3 O) a d s +H++e((1. 5) 1. 3) (C H 3 O) a d s (C H 2 O) a d s + H ++e(1. 4) (CH 2 O) a d s (CHO) a d s +H++e) a d s (CO) a d s +H++e(CHO 1

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2 (1. 6) ( H 2 O) a d s (O H ) a d s + H ++e(1. 7) (OH) a d s (O) a d s +H++e(CO) ads is then removed from the electrode surface by reaction with (O) ads to form CO 2 . The above reaction steps show a complete oxidation of methanol; however, it is possible that the partially dehydrogenated species combine with each other and then undergo dehydrogenation reactions to form the final CO 2 . For example, (CHO) ads combines with (OH) ads to form (HCOOH) ads , which dehydrates to give CO 2 . Some stable intermediates, especially CO adsorbed strongly on the electrode surface can act as a poison because their slow oxidation to CO 2 leads to a very high overpotential at the electrode. Although platinum anodes exhibit the best performances among the pure metal electrode materials, the intermediate CO poisons the electrode surface and reduces the electrode lifetime. 2,13 Much research shows that the presence of one or more oxophilic metals can greatly improve the Pt electrode performance since the oxophilic metals can easily adsorb and dehydrogenate water at much lower potential than pure Pt. Pt/Ru systems show the highest activity among the binary catalysts. A bifunctional mechanism of activity enhancement was proposed on the basis of both theoretical calculations 14 and experimental results. 15,16 In this bifunctional mechanism, the platinum sites engage in the methanol binding and dehydrogenation while the second oxophilic metal (usually Ru) adsorbs and activates H 2 O to provide the activated oxygen to oxidize the adsorbed intermediate (CO) ads on Pt into CO 2 (Eq 1.8-1.10). (1. 8) (1. 9) (1. 10) Pt(CH3OH)ads Pt(CO)ads + 4H+ + eRu( H 2 O) a d s Ru(O H ) a d s + H ++ePt(CO) a d s + R u(OH) a d s Pt+ R u+CO 2 +H++e

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3 It was demonstrated that the practical Pt/Ru catalysts are not single phase materials, but inrface shed 6 systemIr,42 The oxidation of al as an important r the cohol (bipy)2stead mainly consist of the bulk mixture of Pt metal and hydrous Ru oxides,17-19 the latter of which have been widely used as oxidation catalysts for alcohols. Many mechanistic studies further supported the postulate. Studies on the influence of sustructure and Pt-Ru atom distribution on PtRu electrodes for methanol oxidation indicated that the most probable rate-determining step is the reaction between theadsorbed CO and Ru oxide.20 In situ reflectance spectroscopy study results establithat the rate-determining step is the formation of adsorbed OH on the ruthenium surface.In addition to Pt/Ru systems,21-27 Pt/Sn,28-30 Pt/Mo,31-33 Pt/Re,34 Pt/Ni,35 Pt/Os36 etc. s also show higher activity than pure Pt electrodes. Some ternary Pt/Ru/Sn,3 4 Pt/Ru/Os,37 Pt/Ru/Mo,38,39 Pt/Ru/W,40 and Pt/Ru/Ni41 as well as quaternary Pt/Ru/O s /Pt/Ru/Sn/W,43 and Pt/Ru/Rh/Ni44 systems were clai m ed to possess better activity. Oxidation o f Alcohols by Ruthenium Complexes cohols into carbonyl compounds is well documented process.45,46 Among a variety of transition-metal compounds as the oxidizing agents, oxocomplexes of the platinum group metals, especially ruthenium oxo complexes, have received particular attention due to their diversity in oxidation states and excellent selectivity.47,48 Usually, one or more equivalents of oxidizing agents are required fooxidation reaction. The presence of a second oxidant such as molecular oxygen, an amine N-oxide, an iodosobenzene derivative, or a peroxide can make the oxidation process catalytic. Many ruthenium complexes have been reported as catalysts for aloxidation, including not only high-valent oxo compounds such as RuO449,50 and RuO4-,51 but also complexes with O-, N-donor, halide, and phosphine ligands, such as [Ru(OH)2O3]2-,52 [RuO3Cl2]-,53 [RuO2(py)2Cl]-, [RuO2(bipy)2Cl2],54 and [RuO

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4 (py)2]2+.55,56 S o m e sup p or t e d R u catalysts also show high activi t ie s for alcohol oxid a tiin the presence of molecular oxygen.57-60 The mechanistic details usually involve a two electron hydride transfer (Scheme 1-1 on ).55 ,61 However, O-insertion62 (Scheme 1-2) and H-atom abstraction63 (Scheme 1-3) mechanisms were also proposed. 2+ RuIV=O2+ + H-C-OHCH3 CH3 Ru-O H C-OHCH3CH3 RuII-OH+ + CCH3 CH3 OH+ RuII-OH22+ + CCH3 CH3 O rapid Scheme 1-1 RuIV=O2+ + PhCH2OH Ru O H C H Ph OH 2 + HRuIII-OC OH H Ph 2+ RuII+ PhCH(OH)22+ RuII-OH22+ + PhCHO Scheme 1-2 RuIV=O2+ + Ph CH2OH RuIII-OH2+ + PhCHOH RuII-OH22+ + PhCHO r ap i d Scheme 1-3 henium-catalyzed electrooxidation of alcohols has also been extensively studieto Nafion s of [Ru(4,4-Me2bpy)2-(PPh3)(H2O)](ClO4)269 and trans-[Ru(TMC)O(X)]ClO4 (TMC = 1,4,8,11–tetramethylThe rut d.63-69 Since the oxidative species can be generated on the electrode surface at certain p ote ntials, the oxidation reactions are usually catalytic processes. In addition serving as homogenous catalysts to oxidize alcohols in solution, some ruthenium complexes were incorporated into carbon paste electrodes69 or immobilized insidefilms64,68 which were applied to the oxidation of alcohols. As examples, cyclic voltammetry of alcohol solution

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5 1,4,8,ctrode on of al of the py = 2, 2, -e was bpy)2(PPh3)(H2O)](ClO4)69 and [Ru(bpy)2(O){P(p-C6H4X)}3] (where X = OCH3, CH3, H, F, CF3)63 were found to be electrocatalysts for oxidizing benzyl alcohols 11-tetraazacyclotetradecane, X= Cl-, NCO-)66 at a glassy carbon wor k ing eleexhibits great enhancements of anodic oxidation currents, indicating catalytic processesfor alcohol oxidation. Constant potential bulk elec tr olyses of benzyl alcohol by the catalysts [Ru(4,4-Me2bpy)2(PPh3)(H2O)](ClO4)2 and trans-[Ru(TMC)O(X)]ClO4 were conducted to generate sufficient quantities of products for identification and evaluatithe activity and stability of t he ca t alysts. Then, bulk electrolyses of the solution containing benzyl alcohols and catalyst were carried out with large area platinum or glassy carbon electrodes held at a potential 100 mV positive of the formal potenticatalyst. Analysis of the oxidation products by gas chromatography and mass spectrometry showed that the oxidation produced benzaldehyde with over 90% current efficiency. Other ruthenium complexes including [Ru(terpy)(bpz)(H2O)]2+ (ter2-terpyridine, bpz = 2, 2-bipyrazine),67 [Ru(terpy)(Me2dppi)(O)]2+ (R2dppi = 3,6-bis(6methylpyrid-2-yl)pyridazine),70 and [Ru(L)(O)]2+ (LH = bis(2-(2-pyr i dyl) e thyl)(2-hydroxy-2-(2-pyridyl)ethyl)amine)68 were also demonstrated to be catalysts for the electrolysis of benzyl alcohol. Usually, only the 2eoxidation product benzaldehydfound. cis-[Ru(L)(Cl)(O)]2+ (L = N , N-dimethyl-N,N-bis(2-pyridylmethyl)-ethylenediamine) was shown to be an active catalyst for the electrooxidation of methanol in aqueous medium, and the controlled potential electrolysis with excess methanol in the presence of the catalyst afforded formaldehyde as the product with over 85% current efficiency.64 In cases relevant to this dissertation, the phosphine-coordinated Ru complexes [Ru(4,4-M e 2

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6 to benth , y [(bpy)2(O)RuIVORuV(O)(bpy)2].72 Related binuclear Ru complexes such as [Run to xidation licated -1.13). (1. 13) d in solth homogeneous catalysts, HCOOH and the reactions in Eq 1.12 and (1. 14) H zaldehydes. In these cases, no oxidation of phosphine ligand was observed. Bothe electronic and steric effects on the catalytic rates of oxidation h ave be e n investigatedand it was demonstrated by several examples that the steric factor plays a more importantrole.64,68,70,71 Oxo-bridged Ru dimers can also serve as catalysts for alcohol oxidation. The Meyer group reported rapid oxidation of a variety of alcohols, aldehydes, and carb oxylates b 2(napy)2(H2O)4Cl(OH)][ClO4] (napy = 1,8-naphthyridine) have also been showbe catalysts for the oxidation of primary and secondary alcohols, although the ochemistry was complicated by the in s tability o f t he com plexes.73 The binuclear Ru complex (LOM e )(HO)RuIV(-O)2RuIV(OH)(LOMe) where LOMe = [CpCo{P(O)(OMe)2}3]also serves to oxidize alcohols, with a further electrooxidation of formaldehyde to formate also accessible.74 Product Detection and Analysis The six-electron oxidation of methanol on the anode surface involves a compmultistep process (Eq 1 .1 1 (1. 11) 2H++2e(1. 12) CHO CO + 2H+ + 2eCO + H 2 O CO 2 + 2H++2 CH 3 OH HCHO + ution wi When the reaction is conducte is formed as the 4eoxidation product instead of CO, 1.13 are replaced by the reactions in Eq 1.14 and 1.15. eHCHO + H 2 O HCOOH+2H++2e

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7 (1. 15) During the homogeneous electrooxidation reaction, both HCHO and HCOOH undergo condensation reactions with excess methanol toHCOOH CO 2 +2H++2eform formaldehyde dimnd 1.17). It was found that both reactions are fats and the e for these reactions are shifted to the the o in Eq , the reactions in Eq 1.16 and 1.17 produce a small amount of termediates generated by methanol oxidation have received much interest since they could provide mechanistic information. It was determined that heterogeneous methanol oxidation in aqueous electrolytes at room temperature produces either formaldehyde, formaldehyde dimethylacetal or methyl formate as the major product depending on different conditions, while CO2 was only a minor product. A real-time mass spectrometric investigation of methanol oxidation in a DMFC demonstrated that formaldehyde dimethylacetal was the main product from a pure methanol feed, while an excess of water led to CO2 as the major product, indicating more complete oxidation. A sensitive fluorescence assay detected a significant amount of formaldehyde (30% of the total electrolysis charge) for ethylacetal and methyl formate (Eq 1.16 a quilibria st in the presence of acid catalys right in the presence of excess methanol.75,76 Therefore, it is possible to followformation of formaldehyde and formic acid indirectly by quantifying these twcondensation products. (1. 16) (1. 17) The presence of water as a source of oxygen is necessary for the reactions 1.13 and 1.14. However H C H O + 2 C H 3O H H 2C ( OC H 3)2+ H 2O H COO H + C H 3O H H COOC H 3+ H 2 O water which can be used for the reactions in Eq 1.13 and 1.14. In addition to the adsorbed species, the soluble in 77-7980

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8 the oxidation at low potential (0.2-0.3 V vs. Ag/AgCl).81 Formic acid and methyl formatwere also detected as the major products.10,76 Overall, the product distributions depenon different reaction conditions which include cell potentials, methanol/water ratios, temperatures, and anode materials. Cooperative Interaction in Bimet e d s recognized that two metals can cooperate with each other and show diff.82,83 The reason couldr one lyzed ts s, ityt the main catalytic Rh cente a llic Catalysts In addition to the beneficial effects observed with the bimetallic anodes, cooperative bimetallic reactivities have received considerable interest in homogeneoucatalytic reactions. It has long been erent reactivities from their mononuclear analogues be either the different catalytic functions provided by two metal centers, omain catalytic metal center whose properties are mediated by another metal. The efficiency of the intramolecular electronic communication usually depends on several factors including the nature of the metals, their oxidation state, the ancillary ligands and the structural features of the bridging ligands. The cooperative bimetallic beneficial effect has been demonstrated by many examples from various transition metal-catareactions, and the extent of electronic interaction has been evaluated based on the resulfrom spectroscopy, crystallography, and theoretical models.84-88 One example is the hydroformylation-active Rh/Ti and Rh/Zr bimetallic speciesuch as [Cp2M(CH2PPh2)2Rh(COD)]+ (M = Zr or Ti),89 Rh2(-t-BuS)2[(-Ph2PCH2)2-Zr(5-C5H5)2](CO)2,90 and Cp2Zr(CH2PPh2)2Rh(H)(PPh3).91 It was proposed that the second metal, Ti or Zr, was able to mediate the electron dens a r during the catalytic cycle, so significantly higher reactivity and enhanced selectivity were achieved . Another h eterobimetallic complex, [H(CO)(PPh3) 2 Ru(

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9 bim) M ( c od) ] (bim = 2, 2-bisimidazolate, cod = 1, 5-cycl o o c tadiene, M = Rh, Ir),92 wasreported to exhibit approximately 30 times higher reactivity in the hydrogenation reactionof cyclohexene than the parent mononuclear compounds [RuH(Hbim)(CO)(PPh3[M(Hbim)(cod)]. As an example related to this dissertation, the heterobimetallic Ruand Ru/W compounds (5-C5R5)Ru(CO)(-dppm)M(CO)2(5-C5H5) (R = H, CH )2] and /Mo of another metal nearby show strong evidence for a metal-metal interaction. 3; M = Mo, W) were reported to show catalytic activity for the reversible reaction of formic acid to CO2 and H2.93 The Nocera group94,95 reported the two-electron mixed valence di-iridium compound, which showed cooperative bimetallic reactivity for H2 activation according to the experimental results and nonlocal density-functional calculations. A heterobimetallic Rh/Ru catalyst, Ru[(CH3)2CO](PPh3)2(-Cl)3Rh(4-C4Ph4CO), was found t o be a b l e to oxidize both prim ary and secondary alcohols to corresponding aldehydes and ketones when using acetone as oxidation agent. The heterobimetallic beneficial effect was prominent since the homobimetallic Ru or Rh complexes are not catalytically active at all.96 The supported Ru(IV)/C e O2/CoO(OH) acted as a highly efficient heterogeneous catalyst for the oxidation of various alcohols into the corresponding carbonyls, in the presence of molecular oxygen under mild reaction conditions.97 It seems that each metal species works cooperatively in the above aerobicoxidation. One way to probe the interaction between two metal centers in heterobimetallic complexes is to study their redox processes, since it is easy to compare the results tothose of mo n onuclear model systems. The shifts of the redox potentials due to the introduction

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10 Previous work in the McElwee-White group has involved the oxidative electrochemistry of a series of Mo/Pt and Ru/Pt heterobimetallic complexes.98 The potentials of the metal redox couples were determined by cyclic voltammetry and correlated to those of the analogous monomers. The shifts in the oxidation potentials reflec the F6 tical )= munication have been l system t the ability of the metal centers to communicate with each other throughbridging ligands. As an example, the cationic complex [Mo(CO)3(-dppm)2 P t(H)]Pand the neutral heterobimetallic complex Mo(CO)3(-dppm)2Pt(H)Cl have an idencoordination sphere at the molybdenum center; however, there is an approximately 400mV positive shift for both Mo(II/III) and Pt(II/IV) waves in the cationic compound.Since the only change in the compounds occurs at Pt, it demonstrated the electronic interaction between the metal centers through the bridging ligand. The electronic interaction between heterobimetallic metals was also evidenced by cyclic voltammetry in the heterobimetallic transition metal complexes, [(R3P)Ag-(NNCu(PR3)]X2 (R = C6H4CH2NMe2-2; NN = NC5H4CN-4, 1,4-(CN)2C6H4, 4, 4-bipy; XClO4, OTf, PF6).99 Various extents of intramolecular electronic com identified according to the shift of the redox potentials of the metal centers. The goal of this dissertation is to probe the cooperative interactions between two different m e tal centers and to investigate the bimetallic effects in homogenous alcohol oxid a tion reac ti o n s. Due to the beneficial effects observed on bimetallic anodes in fuecells, it would be interesting to see if such effects can be realized in homogeneous s. Therefore, a series of heterobimetallic complexes was constructed by modifying both metals and ancillary ligands and their electrochemical properties and behaviors were examined. The application of these compounds as electrochemical

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11 catalysts for alcohol oxidation is expected to give improved catalytic efficiencies anmay provide information for understanding the bifunctional mechanism proposebimetallic anodes and designing more effective catalysts. Preliminary Results Preparation of complexes 1-3. The Ru/Pd complex 1, Ru/Pt complex 2, and Ru/Au complex 3 were synthesized at room temperature from the reaction of CpRu-(Cl)(PPh3)(1-dppm) with Pd(COD)Cl2, Pt(COD)Cl2, and d d for Au(PPh3)Cl, respectively100 (Figure 1-3). The complex 3 exhibits no interaction between the Ru and Au centers beyonetal d what could be transmitted via through bond interactions involving the dppm ligand. This situation differs from that in 1 and 2, in which the Cl bridge links the matoms more closely. Ru Ph2P PPh2 Pd Cl Pd(COD)Cl2 Ru Ph3PPh2PCl PPh2 Ph3PCl Cl Ru Ph3PPh2PCl PPh2 Pt Cl Cl Ru Ph3PPh2PCl PPh2 AuCl Au(PPh3)Cl12 Pt(COD)Cl2 3 Figure 1-1. Preparation of complexes 1-3

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12 Cyclic voltammetry of complexes 1-3. Cyclic voltammetry of the Ru/Pd system 1 in DCE/TBAT (DCE = 1,2-dichloroethane, TBAT = tetrabutylammoniumtrifluoro-methanesulfonate) exhibits a pair of irreversible couples at 1.29 V and 1.45 V vs. NHE (Table 1-1). The wave at 1.29 V is assigned to the Ru(II/III) couple. In comparison, the Ru(II/III) wave of the mononuclear compound CpRu(Cl)(PPh3)(1-dppm) is observed at 0.56 V.98 The nearly 700 mV shift positive in the redox potential of 1 indicates a significant loss in electron density at the Ru metal via the chloride bridge to the coordinatively unsaturated Pd center. The irreversible wave at 1.45 V is assigned to the Pd(II/IV) oxidation based on comparisons with the cyclic voltammogram of PdCl2(2-dppm). Cyclic voltammetry of 2 in CH2Cl2/TBAH (TBAH = tetrabutylammoniumhexavs. NHE and an irreversible oxidation wave at 1.78 Vtive When can be ble oxidation wave at 1.40 V in DCE/TBAT. The 0.86 V wave is assigned to the Ru(II/III) couple, while the wave at 1.40 V is assigned to the Au(I/III) oxidation. This flurophosphate) exhibits a couple at 1.13 V . The 1.13 V wave is fully reversible if the switching potential of the scan is < 1.6 V, and is assigned to the Ru(II/III) couple. This wave is shifted about 160 mV negacompared to that of the Ru/Pd complex 1. The shift is consistent with electron donationthrough the Cl bridge to the less electron-deficient Pt center of 2 (the first oxidation waveof the model compound PdCl2(2-dppm) is approximately 200 mV positive of its Pt analogue). The irreversible wave at 1.78 V is assigned to the Pt(II/IV) oxidation. the voltammetry is performed in DCE/TBAT, another irreversible wave at 1.87 Vdetected. This additional wave is assigned to the Ru(III/IV) couple. The Ru/Au complex 3 exhibits a reversible couple at 0.86 V vs. NHE and an irreversi

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13 wave a a is similar to that of the starting ma te rial, Au(PPh3)Cl, which has been reported tooxidize at 1.68 V vs. NHE in CH2Cl2.101 Table 1-1. Formal potentials of complexes 1-3 Complex Couple E1/2 (V)Couple E1/2 (V) Ru/Pt (2) Ru(II/III) 1.13b Pt(II/IV) 1.78c Ru/Au (3) Ru(II/III) 0.86 Au(I/III) 1.40c Ru Ru(II/III) 0.61 d Ru'e Ru(II/III) 0.56b aAll potentials obtained in DCE/TBAT and reported vs. NHE. bPerformed in CHCl/TBAH. Irreversible wave, Epa reported. Ru = CpRuCl(-dppm). Ru' = CpRu(PPh3)Cl(-dppm) Ru/Pd (1) Ru(II/III) 1.29 Pd(II/IV) 1.45c 22cd2e1Catalytic electrooxidation of methanol by complexes 1-3. The cyclic voltammograms of complexes 1 and 2 show dramatic increases at the Pd(II/IV) and Pt(II/IV) waves in the presence of methanol. In contrast, methanol oxidation with the Ru/Au complex 3 occurs at the Ru(III/IV) wave, which is similar to alcohol oxidation with simple mononuclear Ru complexes. Differences among the behavior of 1, 2, and 3 can be seen in the evolution of product distributions shown in Tables 1-2 and 1-3, which present the average product ratios of formaldehyde dimethyl acDMM) toormate (d during bulk electrolysis of dry and wet. The pe of water consistently shifts the product ratios toward the four-electron oxidation product, MF. Trend is reflec the comes and can b seen both in the initial product ratios for wet vs. dry samples and in the tendency toward production of more MF in the y sampnsation of tion et al (dimethoxym ethane, m e thy l f MF) forme methanol resenc his t ted by all plex e d ry samples as the reaction progresses. The time evolu t ion of product ratios i n the dr les presumably arises from water that is generated in situ during the condeformaldehyde80 and formic acid with excess methanol. It is consistent with participa

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14 of Ru oxo species formed by oxidation of complexes 1-3 with water as the oxygen source. Table 1-2. Product distributions and curre nt efficiencies for the electrochemical oxidation of dry methanol by 1, 2, and 3 Product ratio (moles of CH2(OCH3)2 / HCOOCH3) a,b Ru/Pd (1) Ru/Pt (2) Ru/Au (3) Ruc 25 3.18 2.45 1.44 n.o.d 50 2.41 2.35 1.23 n.o. 100 0.94 1.23 0.59 n.o.d 130 0.87 1.20 0.46 e Current efficiencyf 24.6 18.6 25.4 3.2 Methanol concentration was 0.35 M. bDetermined by GC with n-heptane as an internal standaobserved. eOnly CH2(OCH3)2 observed. fCurrent efficiencies after 75-130 C of charge passed. Table 1-3. Product distributions and current efficiencies for the electrochemical Product ratio (moles of CH2(OCH3)2 / HCOOCH3)a,b Charge / C d75 1.54 1.51 0.98 n.o.d aElectrolyses were performed at 1.7 V vs. NHE. A catalyst concentration of 10 mM was used. rd. Each ratio is reported as an average of 2-5 experiments. cRu = CpRuCl(2-dppm). dNo products oxidation of wet methanol by 1, 2, and 3 Charge / C Ru/Pd (1) Ru/Pt (2) Ru/Au (3) Ruc 25 1.38 1.68 1.26 n. 0 0.98 1.34 o.d 51.05 n.o.d 75 0..d 100 Current efficiencye 84 1.17 0 . 9 7 n. o 0.70 0.67 0.41 n.o .d 130 0.54 0.41 0.34 0.33 20.6 19.5 26.1 7.2 s are the same as in Table 1-2 except for the addition of L o cel l . pm). nt Current effici e e also d in T nd 1lues aCondition 5f water to thebDetermined by GC with respect to n-heptane as an internal standard. Each ratio is reported as an average of 2-5 experiments. cRu = CpRuCl(2-dp dNo products observed. eCurreefficiencies after 75-130 C of charge passed. ncies ar summarizeables 1-2 a3. These vaare the ratio of the charge necessary to p roduce the observed yields of CH2(OCH3)2 and

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15 HCOOCH3 to the total charge passed during bulk electrolysis. Although the current efficiencies for heterobinuclear complexes 1-3 were moderate (19 to 26%), they are significantlficiencies obtained from the monoel compound CpRuCl(-dppm) under both dry and wet conditions, respectively. Although the nature of the metal-metal interaction varies in comp 1-3, in each case the presence of the second metalr apparentllts in enhancatalytic activity. y higher than the 3.2 and 7.2% current ef nuclear mod 2 lex e s cente y resu ced

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CHAPTER 2 HETEROBIMETALLIC COMPLEXES WITH DPPM-BRIDGED Ru/Pd, Ru/Pt, Ru/Au, AND Ru/Cu CENTERS Heterobimetallic systems have been of interest in the context of homogeneous catalysis due to the possibility that the different metal centers could exhibit cooperative behavior. 84-86,102-105 Each metal could play a unique mechanistic role 106 or such effects could be the result of one metal center mediating the reactivity of another. 107,108 Due to the interest in the possibility of such cooperative effects between metal centers during homogenous electrooxidation of alcohols, the heterobimetallic complexes Cp(PPh 3 )Ru(-Cl)(-dppm)PdCl 2 (1), 100 Cp(PPh 3 )Ru(-Cl)(-dppm)PtCl 2 (2), 98 and Cp(PPh 3 )RuCl(-dppm)AuCl (3) 100 were prepared. Cyclic voltammetry of complexes 1-3 in the presence of methanol led to significant enhancement of oxidative currents, consistent with a catalytic process. 98,100,109 Bulk electrolysis of methanol in the presence of the heterobimetallic complexes resulted in much higher current efficiencies than those obtained from the mononuclear model compound CpRu( 2 -dppm)Cl (14), suggesting that the second metal center enhances catalytic activity. Although all three bimetallic complexes (1-3) show enhanced activity as compared to Ru, Pd, Pt, and Au model compounds, the metal-metal interactions differ. Complexes 1 and 2 both possess a bridging chloride that links the metal centers in a distorted six-membered ring. Cyclic voltammetry of 1-2 demonstrated shifts in the formal potentials of the Ru(II/III), Pd(II/IV) and Pt(II/IV) redox couples relative to the model compounds, indicating significant electron donation through the chloride bridge from Ru to the 16

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17 electron deficient Pd and Pt centers. In contrast, the redox potentials of the Ru(II/III) and Au(I/III) couples in 3 resemble those of their mononuclear model compounds, suggesting a minimal interaction between the two metal centers via the bridging dppm ligand. In order to further explore these metal-metal interactions and the resulting catalytic activity, an extended series of compounds with ligands of varying electronic character has now been prepared (Figure 2-1). Ph3P Ph2P Ru Q PPh2 M X1 X2 X3 Compound M X 1 X 2 X 3 Q 1 Pd Cl Cl Cl CH 2 2 Pt Cl Cl Cl CH 2 4 Pd I Cl Cl CH 2 5 Pd Cl Cl Me CH 2 6 Pt I Cl Cl CH 2 7 Pt I I I CH 2 8 Pt Cl Cl Me CH 2 Ph3P Ph2P Ru Q PPh2 Au X1 X2 Compound X 1 X 2 Q 3 Cl Cl CH 2 9 I I CH 2 10 Br Cl CH 2 11 Cl Cl (CH 2 ) 4 12 Cl Cl NH Ph3P Ph2P Ru PPh2 Cu I I 13 Figure 2-1. Structures of compounds 1-13

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18 In this chapter, the synthesis and characterization of additional Ru/Pd, Ru/Pt, Ru/Au, and Ru/Cu heterobimetallic complexes are reported. These new compounds are similar to compounds 1-3, but exhibit systematic perturbations in the ancillary ligands. They provide a series of related species for study of cooperative effects between the two metal centers. Synthesis Synthesis of Ru/Pd complexes 4 and 5. Ru/Pd complex 1 was previously prepared by reaction of CpRu(PPh 3 )( 1 -dppm)Cl (15) with Pd(COD)Cl 2 in CH 2 Cl 2 at room temperature. 100 The I-bridged Ru/Pd complex 4 was prepared as a red powder in an analogous manner from CpRu(PPh 3 )( 1 -dppm)I (17) and Pd(COD)Cl 2 (Eq 2.1). In contrast, reaction of CpRu(PPh 3 )( 1 -dppm)Me (18) with Pd(COD)Cl 2 in benzene at room temperature afforded the Pd-Me complex 5 in 90% yield (Eq 2.2). Transfer of the methyl group from Ru to Pd resulted in formation of the Cl-bridged core structure seen in heterobinuclear complex 1. Complexes 4 and 5 are air stable in their solid states and do not show signs of decomposition in solution even when exposed to air for days. Ru Ph3PPh2PI PPh2 Pd Cl Cl 4 Ru Ph3P I Ph2P PPh2 17+ Pd(COD)Cl2 CH2Cl2rt (2. 1) Ru Ph3PPh2PCl PPh2 Pd Cl Me 5 Ru Ph3P Me Ph2P PPh2 18 CH2Cl2rt+ Pd(COD)Cl2 (2. 2)

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19 Synthesis of Ru/Pt complexes 6, 7, and 8. The reactions of Ru complex 17 with Pt(COD)Cl 2 and Pt(COD)I 2 in CH 2 Cl 2 at room temperature afforded the I-bridged Ru/Pt complexes 6 and 7, respectively (Eq 2.3 and 2.4). Although a significant amount of Pt( 2 -dppm)Cl 2 was formed by dppm transfer in the similar reaction of CpRu(PPh 3 )( 1 -dppm)Cl (15) with Pt(COD)Cl 2 to make heterobimetallic complex 2, no phosphine transfer to produce Pt( 2 -dppm)Cl 2 or Pt( 2 -dppm)I 2 occurred during preparation of 6 and 7. The Pt-Me complex Cp(PPh 3 )Ru(-Cl)(-dppm)Pt(CH 3 )Cl (8) was obtained from the reaction of CpRu(PPh 3 )( 1 -dppm)Cl (15) and Pt(COD)(CH 3 )Cl (Eq 2.5) instead by the method used for preparation of the Pd-Me complex 5, due to the difficulty of removing the by-product Pt( 2 -dppm)Cl 2 . The stabilities of complexes 6, 7, and 8 are very similar to those of the Ru/Pd complexes 4 and 5 both in the solid state and in solution. Ru Ph3PPh2PI PPh2 Pt Cl Cl 6 Ru Ph3P I Ph2P PPh2 17 Ru Ph3PPh2PI PPh2 Pt I I 7 Pt(COD)Cl2Pt(COD)I2 (2. 3) (2. 4) Ru Ph3P (2. 5) Ru Ph3PPh2PCl PPh2 Pt Cl Me 8 CH2Cl2rt Cl Ph2P PPh2 15 + Pt(COD)MeCl

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20 S ynthesis of Ru/Au complexes 9-12. An equimolar ratio of the Ru complex 17 and A nown ducts uI were reacted in CH2Cl2 at room temperature to afford the Ru/Au complex 9 as an orange powder in 97% yield (Eq 2.6). Complex 9 has a structure similar to that of complex 3 but with the chlorides replaced by iodides. Complex 10 was prepared in the same manner as 3 starting from CpRu(PPh3)(1-dppm)Br (16) and Au(PPh3)Cl (Eq 2.7).The attempt to prepare complex 10 by the reaction of 16 and AuCl in CH2Cl2 at room temperature formed a mixture of products due to halide exchange between Br and Cl. The reaction of CpRu(PPh3)(1-dppb)Cl (19) with AuCl in CH2Cl2 at room temperatureresulted in the formation o f the heterobimetallic Ru/Au complex 11 (Eq 2.8), in which thetwo metal centers are linked by a bridging dppb ligand. The Ru/Au complex 12, in which the two metal centers are linked by a bridging Ph2PNHPPh2 ligand, was synthesized in an analogous manner from CpRu(PPh3)(1-Ph2PNHPPh2)Cl ( 2 0) and AuCl (Eq 2.9). When Au(PPh3)Cl was used as the starting materi a l for the syntheses of complexes 11 and 12, a broad peak for the Au-bound phosphines was usually observed, possibly due to a coordination equilibrium at the Au center because of the association of the releasedtriphenyl phosphine in solution. Gold(I) complexes with one to four coordinated phosphine ligands have been detected in solution,110-112 and these complexes are kto undergo facile ligand exchange.111-113 Clean sa mple s of complexes 11 and 12 with normal linewidths in their 31P NMR spectra can be obtained from the reactions of Au(PPh3)Cl with 16 and 1 9, respectively, but multiple recrystallizations of the proare necessary.

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21 Ru Ph3P I Ph2P PPh2 17+ AuI CH2Cl2rt Ru Ph3PPh2PI PPh2 Au 9 I Ru Ph3P I Ph2P PPh2 17+ CuI (excess) CH2Cl2rt Ru Ph3PPh2P PPh2 Cu 13 (2. 6) (2. 7) (2. 9) plex 13 was prepa (2. 10) Ru Ph3P Br Ph2P PPh2 16+ Au(PPh3)Cl CH2Cl2rt Ru Ph3PPh2PBr PPh2 Au 10 (2. 8) Synthesis of Ru/Cu complex 13. The heterobimetallic Ru/Cu com Ru Ph3P Cl Ph2P NH PPh2 20+ AuCl CH2Cl2rt red as a deep red powder by the reaction of 17 with excess CuI in CH2Cl2 at roomtemperature (Eq 2.10). The compound is moderately stable in its solid state but decomposes slowly in solution when stored outside of a glove box. I I Ru Ph3PPh2PCl NHPPh2 AuCl 12 Cl Ru Ph3PPh2PCl PPh2 AuCl 11 Ru Ph3P Cl 2P 19 PPh2 + AuCl CH2Cl2rt Ph

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22 NMR Data The 31P NMR spectrum of 5 (Table 2-1) exhibits the expected three resonances. The d ted (Tablite t. e 2.85 ppm as a result of coupling to the adjacent phosphorus atoms. ownf ie ld resonances (45.6 and 39.3 ppm) correspond to the Ru-bound phosphineswhile the upfield doublet is assigned to the Pd-bound phosphorus of the bridging dppm. In the 1H NMR spectrum of 5, the Cp signal appears as a singlet at 4.58 ppm while the methyl group gives rise to a doublet at 0.39 ppm. The diastereotopic methylene protonsof the bridging dppm are observed as a multiplet at 2.86 ppm as a result of coupling to the adjacent phosphorus atoms. The spectra of 4 are similar, with the exception that an additional JPP between the Pd-bound dppm phosphorus and Ru-PPh3 can be observed in the 31P{1H} NMR spectrum, and the chemical shifts of the diastereotopic methylene protons differ significantly, with two multiplets appearing at 3.48 and 2.72 ppm. The 31P{1H} NMR spectra of 6 and 7 both exhibit three resonances as expec e 2-1 ). T h e downfield Ru-bound phosphorus signals of the two complexes are qusimilar, while the upfield ones assigned to the Pt-bound phosphorus atoms exhibit a chemical shift difference of 5.6 ppm due to the different halide ligands (Cl vs. I) on PThe Cp signals for 6 and 7 appear in their 1H NMR spectra as singlets at approximately 4.6 ppm. The diastereotopic methylene protons of dppm for each complex display two multiplets with chemical shift differences of about 0.5 ppm. The 31P{1H} NMR spectrumof 8 exhibits the expected three resonances. The downfield resonances (46.2 and 38.7 ppm) correspond to the Ru-bound phosphines while the upfield doublet is assigned to thPt-bound phosphorus of the bridging dppm. In the 1H NMR spectrum of 8, the Cp signal appears as a singlet at 4.46 ppm with the methyl group giving rise to a triplet at 0.15 ppm. The diastereotopic methylene protons of the bridging dppm are observed as a multiplet at

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23 The spectral data for 9-12 are listed in Table 2-1. Complexes 9 and 10 both exhibit spectra similar to those of complex 3. In their 31P{1H} NMR spectr a, two downfield resona ances ng let, which was assigned to Ru-bound PPh3, appears at a normg ances (a doublet and a doublet of doublets) were ascribed to Ru-bound phosphines and one upfield doublet was assigned to Au-bound phosphines. Their 1H NMR spectrshow large differences in the chemical shifts of the diastereotopic methylene protons (3.44 and 3.43 ppm, respectively), indicating the absence of a halide br i dge between the two metal centers. The 31P{1H} NMR spectrum of complex 11 exhibits two downfielddoublets for Ru-bound phosphines and one upfield singlet for Au-bound phosphorus. Asexpected, the chemical shifts and coupling constants of the Ru-bound phosphorus resonances of 11 are similar to those of the starting material 19, due to the significant distance between the Ru and Au metal centers. Complex 12 also shows three resonin the 31P{1H} NMR spectrum. All of the phosphorus resonances (Ru-bound and Au-bound) were shifted significantly downfield due to the presence of the Ph2PNHPPh2 ligand. The N-H proton appears as a multiplet in the 1H NMR spectrum due to couplito the adjacent phosphorus atoms. As expected, three resonances were observed in the 31P{1H} NMR spectra of compound 13. The downfield doub al chemical shift position (40.3 ppm). The resonan ce o f the Ru-bound bridgindppm phosphorus appears as a doublet of doublets shifted upfield to 26.7 ppm. The furthest upfield broad peak (-18.5 ppm) was assigned to Cu-bound phosphorus.

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Table 2-1. NMR data for complexes 1-20 1 H NMR () a 31 P NMR () a Cp Q Ru-PPh 3 Ru-PPh 2 M-PPh 2 Reference 1 4.72 2.67 (m) 37.5 (d, 35 Hz) 52.2 (dd, 28, 35 Hz) 19.7 (d, 28 Hz) 100 2 4.67 2.78 (m) 37.8 (d, 36 Hz) 49.1 (dd, 21, 36 Hz) -2.9 (d, 20 Hz) 98,109 3 4.09 4.74 (m), 1.33 (m) 42.8 (d, 43 Hz) 36.3 (dd, 28, 43 Hz) 20.8 (d, 28 Hz) 100 4 4.65 3.48 (m), 2.72 (m) 40.1 (dd, 7, 35 Hz) 49.5 (dd, 20, 35 Hz) 10.5 (dd, 7, 20 Hz) b 5 4.58 2.86 (m) 39.3 (d, 36 Hz) 45.6 (dd, 36, 27 Hz) 25.5 (d, 27 Hz) b 6 4.63 3.45 (m), 2.94 (m) 40.5 (dd, 3, 35 Hz) 46.4 (dd, 11, 35 Hz) -7.7 (dd, 3, 11 Hz) b 7 4.65 3.52 (m), 3.12 (m) 40.4 (dd, 3, 35 Hz) 45.8 (dd, 12, 35 Hz) -2.1 (dd, 3, 12 Hz) b 8 4.46 2.85 (m) 38.7 (d, 36 Hz) 46.2 (dd, 20, 36 Hz) 6.1 (d, 20 Hz) b 9 4.16 5.04 (m), 1.60 (m) 41.7 (d, 42 Hz) 31.4 (dd, 25, 42 Hz) 27.9 (d, 25 Hz) b 10 4.12 4.86 (m), 1.43 (m) 42.5 (d, 42 Hz) 34.2 (dd, 27.5, 42 Hz) 22.0 (d, 27.5 Hz) b 11 4.11 2.21-0.55 (m) 44.8 (d, 42 Hz) 37.0 (d, 42 Hz) 31.6 (s) b 12 4.12 5.93 (m, NH) 54.0 (d, 38 Hz) 87.7 (dd, 46, 38 Hz) 40.4 (d, 46 Hz) b 13 4.34 2.89 (m), 2.51 (m) 40.3 (d, 40 Hz) 26.7 (dd, 40, 20 Hz) -18.5 (s(br)) b 14 4.70 5.08 (m), 4.36 (m) 13.41 (s) 114 15 4.10 3.84 (m), 1.11 (m) 43.4 (d, 41 Hz) 37.5 (dd, 41, 20 Hz) -28.4 (d, 20 Hz) 115 16 4.13 3.94 (m), 1.15 ( m) 43.2 (d, 42 Hz) 35.8 (dd, 42, 20 Hz) -27.5 (d, 20 Hz) b 17 4.18 4.12 (m), 1.24 (m) 42.9 (d, 41 Hz) 33.5 (dd, 41, 20 Hz) -27.0 (d, 20 Hz) b 18 4.19 2.82 (m), 1.15 (m) 59.3 (dd, 3, 37 Hz) 48.2 (dd, 16, 37 Hz) -27.8 (dd, 3, 16 Hz) b 19 4.09 2.30-0.50 (m) 44.7 (d, 42 Hz) 37.3 (d, 42 Hz) -14.4 (s) b 20 4.11 4.82 (m, NH) 42.0 (d, 46 Hz) 85.5 (dd, 46, 12 Hz) 24.3 (d, 12 Hz) b 24 a Spectra measured in CDCl 3 at room temperature. b This work.

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25 X-ray Crystallography Crystallographic details for complexes 4, 5, 11, and 13 are provided in Table 2-2. Crystal structure of complex 4. Complex 4 exhibits a bridging iodide (Figure 2-2), with the remaining structure similar to those of its Cl-bridged Ru/Pd and Ru/Pt analogues 1 100 and 2. 109 The six central atoms in 4 (Ru1, P2, C6, P3, Pd1, I1) form a distorted six-membered ring with a pseudotetrahedral geometry at Ru and square planar structure at Pd. The Ru-I distance in 4, 2.6749(5) , is comparable to the shorter value of 2.685(1) reported for [Ru 2 I(CO) 4 (C 7 H 6 Ph)], in which the iodide bridges asymmetrically between the two Ru centers. 116 The Pd-I bond length, 2.5822(5) , is shorter than the 2.665(1) and 2.723(1) distances found in [(-I)-PdP(o-tol) 2 -o-C 6 H 4 CH 2 ] 2 , in which the Pd-I bond is trans to P and C, respectively. 117 The Pd-Cl1 bond of 4 [2.3528(12) ] is longer than the analogous distance in 1 [2.2842(8) ] due to the higher trans influence of I as compared to Cl (Table 2-3). Figure 2-2. Thermal ellipsoids drawing of the molecular structure of complex 4. Thermal ellipsoids are plotted at 50 % probability. Phenyl rings and most hydrogen atoms are omitted for clarity.

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26 Table 2-2. Crystal data and structure refinement for complexes 4, 5, 11, and 13 Complex 4 5 11 13 Empirical formula C 52 H 46 Cl 14 IP 3 PdRu C 55 H 57 Cl 8 P 3 PdRu C 51 H 48 AuCl 2 P 3 Ru C 50 H 46 Cl 4 CuI 2 P 3 Ru Formula weight 1594.47 1301.99 1122.74 1299.99 T (K) 173(2) 173(2) 193(2) 193(2) () 0.71073 0.71073 0.71073 0.71073 Cryst syst Triclinic Monoclinic Monoclinic Monoclinic Space group P-1 P2(1)/n P2(1)/n P2(1)/n a () 11.4480(13) 13.8306(6) 13.7910(6) 20.2849(8) b () 12.2567(14) 22.8974(9) 18.5416(8) 11.3392(5) c () 22.402(3) 18.4161(7) 18.4876(8) 20.9410(9) (deg) 98.508(2) 90 90 90 (deg) 96.142(2) 108.070(2) 109.800(2) 91.758(2) (deg) 90.895(2) 90 90 90 Volume ( 3 ) 3089.2(6) 5544.4(4) 4447.9(3) 4814.5(4) Z 2 4 4 4 cacld (Mg/m 3 ) 1.714 1.560 1.677 1.793 (mm -1 ) 1.753 1.105 3.898 2.395 F 000 1568 2520 2224 2552 Cryst size (mm 3 ) 0.17 x 0.15 x 0.10 0.36 x 0.24 x 0.23 0.23 x 0.23 x 0.07 0.19 x 0.17 x 0.11 range (deg) 0.92 to 27.50 1.78 to 27.50 1.92 to 27.50 1.38 to 27.49 Index ranges -14h14 -13h17 -17h17 -26h26 -15k15 -29k28 -23k24 -14k14 -28l29 -23l23 -24l23 -27l26 Reflections collected 26139 36509 39309 42538 Independent reflections 13243 [R(int) = 0.0389] 12593 [R(int) = 0.0352] 10148 [R(int) = 0.0551] 11042 [R(int) = 0.0392] Completeness to = 27.49 93.5 % 98.9 % 99.5 % 99.8 % Absorption correction Integration Integration Analytical Integration Max. / min. transmission 0.8572 / 0.7580 0.8300 / 0.6953 0.7741 / 0.3779 0.7944 / 0.6136 Data / restraints / parameters 13243 / 30 / 689 12593 / 0 / 505 10148 / 0 / 538 11042 / 0 / 553 GOF on F 2 1.072 1.007 1.051 1.041 R1 a 0.0582 0.0381 0.0386 0.0325 wR2 b 0.1298 0.0794 0.0747 0.0784 Largest diff. peak / hole (e. -3 ) 1.827 and -2.275 0.882 / -1.874 1.572 / -0.509 0.756 / -0.473 a R1 = (||Fo| |Fc||) / |Fo|; b wR2 = [[w(Fo 2 Fc 2 ) 2 ] / [w(Fo 2 ) 2 ]] 1/2 ; S = [w(Fo 2 Fc 2 ) 2 ] / (n-p)] 1/2 ; w= 1/[ 2 (Fo 2 )+(0.0337*p) 2 +1.24*p]; p = [max(Fo 2 ,0)+ 2* Fc 2 ]/3

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27 Table 2-3. Selected bond distances () and angles (deg) for Cp(PPh 3 )Ru(-I)(-dppm)PdCl 2 (4) Ru1-P2 2.3212(12) Pd1-Cl1 2.3528(12) Ru1-P1 2.3325(12) Pd1-I1 2.5822(5) Ru1-I1 2.6749(5) Pd1-Cl2 2.3710(12) Pd1-P3 2.2333(12) P2-Ru1-I1 90.70(3) Cl1-Pd1-I1 174.85(3) P1-Ru1-I1 91.31(3) C6-P3-Pd1 115.38(14) P2-Ru1-P1 98.19(4) P3-Pd1-Cl1 93.88(4) C6-P2-Ru1 120.29(15) P3-Pd1-Cl2 174.26(5) Pd1-I1-Ru1 101.408(16) Cl2-Pd1-I1 89.96(3) Cl1-Pd1-Cl2 90.61(4) P3-C6-P2 121.7(2) P3-Pd1-I1 85.88(3) Crystal structure of complex 5. Complex 5 (Figure 2-3) is formally the result of replacement of one Pd-bound Cl of 1 with a methyl group trans to the chloride bridge. As expected, complexes 1 and 5 exhibit nearly identical structures. The exception is the Pd-Cl1 bond of 5, 2.4479(5) (Table 2-4), which is significantly longer than the analogous bond in 1 [2.3256(7) ] due to the higher trans influence of CH 3 as compared to Cl. Crystal structure of complex 11. As shown in Figure 2-4, complex 11 possesses a dppb linkage between Ru and Au with the three-legged piano stool geometry at Ru and linear configuration at Au that were previously reported for the related complex 3. 100 Due to the long distance between the two metals, their only interactions would be the insignificant perturbations transmitted through the phosphine.

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28 Figure 2-3. Thermal ellipsoids drawing of the molecular structure of complex 5. Thermal ellipsoids are plotted at 50 % probability. Phenyl rings and most hydrogen atoms are omitted for clarity. Table 2-4. Selected bond distances () and angles (deg) for Cp(PPh 3 )Ru(-Cl)(-dppm)Pd(CH 3 )Cl (5) Ru-P1 2.3282(6) Pd-P3 2.2208(6) Ru-Cl1 2.4436(5) Pd-Cl1 2.4479(5) Ru-P2 2.3039(6) Pd-C7 2.081(2) Pd-Cl2 2.3843(6) P2-Ru-Cl1 90.33(2) C6-P2-Ru 120.39(7) P1-Ru-Cl1 88.314(19) Ru-Cl1-Pd 104.82(2) P2-Ru-P1 98.33(2) C7-Pd-Cl1 175.00(7) P2-C6-P3 119.58(12) Cl2-Pd-Cl1 91.90(2) C7-Pd-P3 90.09(7) C6-P3-Pd 113.97(7) C7-Pd-Cl2 90.75(7) P3-Pd-Cl2 177.51(2) P3-Pd-Cl1 87.44(2)

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29 Figure 2-4. Thermal ellipsoids drawing of the molecular structure of complex 11. Thermal ellipsoids are plotted at 50 % probability. Phenyl rings and most hydrogen atoms are omitted for clarity. Table 2-5. Selected bond distances () and angles (deg) for Cp(PPh 3 )RuCl[-PPh 2 (CH 2 ) 4 PPh 2 ]AuCl (11) Ru-P3 2.3000(8) Au-P1 2.2337(9) Ru-P2 2.3123(8) Au-Cl2 2.2759(10) Ru-Cl1 2.4645(9) P3-Ru-P2 96.63(3) C7-C8-C9 115.7(3) P1-Au-Cl2 176.47(4) P3-Ru-Cl1 95.12(3) C8-C7-C6 111.0(3) C6-P2-Ru 117.96(11) C7-C6-P2 118.1(2) C8-C9-P1 113.8(2) P2-Ru-Cl1 88.42(3) C9-P1-Au 113.06(11) Crystal structure of complex 13. Complex 13 (Figure 2-5) exhibits a bridging iodide and a distorted six-membered ring formed by the six central atoms (Cu, P1, C6, P2, Ru, I1). The disordered I2 was found in two alternative positions (I2 and I2) with a I2-Ru-I2 angle of 0.88 o and a bond length difference of 0.052 between Ru-I2 and Ru-I2. The standard pseudotetrahedral geometry is observed at Ru while the Cu site exhibits a distorted trigonal planar geometry with Cu lying slightly out of the I 2 P plane (0.075

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30 from the I1P1I2 plane and -0.059 from the I1P1I2 plane). The I-Cu-P angles of 102.23(2) o and 136.63(10) o (Table 2-6) result from an angular distortion which also occurs in Cu 2 I 2 (PPh 3 ) 3 118 and [CuI(PPh 3 )] 4 . 119 The Cu-P and Cu-I bond distances of 13 are typical of those found in three-coordinate Cu(I) complexes. 118-121 Figure 2-5. Thermal ellipsoids drawing of the molecular structure of complex 13. Thermal ellipsoids are plotted at 50 % probability. Phenyl rings and most hydrogen atoms are omitted for clarity. Table 2-6. Selected bond distances () and angles (deg) for and Cp(PPh 3 )Ru(-I)(-dppm)CuI (13) Ru-P2 2.3197(6) Cu-P1 2.2113(8) Cu-I2 2.499(3) Ru-P3 2.3254(6) Cu-I1 2.6244(4) Cu-I2' 2.446(4) a Ru-I1 2.7403(2) P2-Ru-P3 99.05(2) P2-Ru-I1 94.607(16) P3-Ru-I1 91.974(15) P1-Cu-I2 136.63(10) I2-Cu-I1 120.83(9) P1-Cu-I1 102.23(2) P1-Cu-I2' 137.62(10) I2'-Cu-I1 119.95(9) I2'-Cu-I2 8.28(19) C6-P1-Cu 113.84(8) P1-C6-P2 116.09(14) C6-P2-Ru 122.69(8) Cu-I1-Ru 99.374(10) a I2' refers to the alternative position of the disordered I.

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31 Cyclic Voltammetry Voltammetry of complexes 1-13. Cyclic voltammograms of the heterobimetallic complexes 1-13 generally exhibit three redox waves within the solvent window. The first and the third wave are assigned to the Ru(II/III) and Ru(III/IV) couples respectively, while the middle one is ascribed to a redox couple of the second metal. The exception is Ru/Cu complex 13, for which the Cu(I/II) couple at 0.88 V occurs at a less positive potential than the Ru(II/III) wave (vide infra). The potentials of the Ru(III/IV) waves vary little among the binuclear complexes but the first oxidation potential of each metal center is dependent on the amount of electron donation from Ru to the second metal center through the bridging ligands. For cyclic voltammograms of Ru/Pt bimetallics 6, 7, and 8, the two-electron Pt(II/IV) wave is relatively small compared to the one-electron redox wave of Ru(II/III). It is probably due to the slow interconversion between square planar Pt(II) and octahedral Pt(IV) by outer sphere electron transfer, which is usually characterized by irreversible electrochemistry due to the accompanying large molecular reorganization. 122,123 It was reported that the interconversion can be facilitated by high concentrations of coordinating anions, and a two-electron wave was apparent in cyclic voltammograms. 124 Therefore, the cyclic voltammograms of 6 and 7 were investigated in the presence of Bu 4 NCl as an anion source. Although a well-shaped reversible Pt(II/IV) wave was not observed, probably due to the complicated bimetallic structure and electronic interaction between Ru and Pt centers, the Pt(II/IV) wave became more apparent for both 6 and 7 in the presence of excess chloride anions. Significant electron donation from Ru to Pd or Pt through the halide bridge can be seen in all of the Ru/Pd and Ru/Pt bimetallics (1, 2, 4-8) by comparison of their Ru(II/III)

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32 redox potentials to those of the model compounds CpRu(PPh 3 )( 1 -dppm)Cl (15) and CpRu(PPh 3 )( 1 -dppm)I (17). All of the bimetallics show significant positive shifts of the Ru(II/III) wave upon introduction of the halide bridge to the second metal. However, the identity of the halide is less critical. Comparison of the I-bridged complexes 4 and 6 with their Cl-bridged analogues 1 and 2 reveals negligible perturbations in the Ru(II/III) or Ru(III/IV) potentials as the bridging halide is changed. More substantial effects can be seen in the Pd(II/IV) and Pt(II/IV) couples. Although these waves are irreversible in Cl-bridged complexes 1 and 2, compounds 4 and 6 exhibit reversible Pd(II/IV) and Pt(II/IV) waves, respectively, implying greater stability for the oxidized I-bridged complexes. While I-bridged Ru/Pd complex 4 exhibits a positive shift of about 60 mV for the Pd(II/IV) potential as compared to the same wave in 1, the Pt center of 6 is approximately 150 mV easier to oxidize than the analogous Pt site in 2. Interestingly, changing the identity of the ligands on Pd or Pt has its largest effect on the Ru(II/III) redox potentials of analogous complexes. Substituting an electron donating methyl group for a chloride in Ru/Pd complex 1 and Ru/Pt complex 2 to yield the Pd-Me species 5 and Pt-Me species 8 shifts the anodic peak potentials of the Ru(II/III) waves 170 mV and 110 mV negative of those in 1 and 2. A similar effect is noted for the I-bridged Ru/Pt compound 6 and its Pt-I analogue 7. In this case, iodide 7 exhibits an approximately 200 mV negative shift for the anodic wave of the Ru(II/III) couple with respect to 6. For both related pairs (1 and 5, 8; 6 and 7), the Pd or Pt(II/IV) and Ru(III/IV) couples occur at similar potentials. The Ru/Cu compound 13 exhibits a complex cyclic voltammogram. Two major irreversible waves at 1.12 and 1.80 V were ascribed to the Ru(II/III) and Ru(III/IV) redox

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33 couples respectively. A small wave at 0.88 V, partially overlapping with the Ru(II/III) couple, was assigned as the Cu(I/II) redox couple. This assignment is consistent with the cyclic voltammetry of cyano-bridged Cu(I)-Ru(II) complexes, for which it was reported that Cu(I) was oxidized at less positive potentials than Ru(II). 125,126 The assigned Cu(I/II) redox potential for 13 is also similar to the value of 0.82 V vs. NHE (reported as 0.58 V vs. SCE) for the model compound [Cu(dppm)I] 2. 127 Subsequent scans resulted in the presence of an additional small shoulder peak at 1.25 V, which can be attributed to halide dissociation and formation of a solvent-coordinated species, as has previously been observed in cyclic voltammograms of Cu(I) iodide complexes. 128 The dppm-bridged Ru/Au bimetallic complexes 3, 9, 10 exhibit reversible waves for the Ru(II/III) couple and irreversible waves for the Au(I/III) couple. The redox potentials for both the Ru(II/III) and Au(I/III) couples are close to those of their mononuclear model compounds, indicating minimal electronic communication between the two metal centers through the dppm bridge. Interestingly, changing the halides from Cl to Br to I on the Ru center did not affect the formal potential of the Ru(II/III) couple (0.89 V for all three complexes 3, 9, 10), while the anodic peak potentials of the Au(I/III) couple were shifted slightly positive as the halide went from Cl to Br to I. The dppb-bridged Ru/Au compound 11 exhibits a reversible couple at 0.75 V and an irreversible couple at 1.76 V vs. NHE, which were attributed to the Ru(II/III) and Ru(III/IV) couples respectively. Under the original conditions of the cyclic voltammetry experiment, the Au(I/III) couple could not be observed. In comparison, the Au (I/III) wave of the dppm-bridged analogue 3 can be observed at 1.40 V. 100 It was possible that the Au(I/III) wave was obscured by the Ru(III/IV) couple at 1.76 V, since the starting

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34 material, Au(PPh 3 )Cl, has been reported to oxidize at 1.68 V vs. NHE in CH 2 Cl 2 . 101 Another possibility was that the Au(I/III) wave was not evident due to a lack of suitable ligands in the electrolyte solution for the incipient Au(III) complex. The electrochemistry of Au(PR 3 )Cl complexes is complicated by substitutional equilibria involving phosphine and halide ligands. 129,130 In order to investigate this possibility, the cyclic voltammetry of 11 was investigated in the presence of Bu 4 NCl as a chloride source. Under these conditions, a broad shoulder peak was observed on the less positive side of the Ru(III/IV) wave. Although the peak potential could not be accurately determined, the appearance of this wave in the presence of Cl is consistent with the need for a ligand in solution for the peak to be observed. The neglible interaction between the Ru and Au centers in 11 is evidenced by the lack of a shift in the Ru(II/III) couple between the starting material CpRu(PPh 3 )( 1 -dppb)Cl (19) and Ru/Au complex 11 [0.75 V for both]. Note that the Ru/Au compound 3, in which the centers are bridged by the smaller dppm ligand, exhibits a 100 mV shift in the anodic Ru(II/III) wave when the Au center is coordinated to the starting material CpRu(PPh 3 )( 1 -dppm)Cl. 100 Overall, the Ru(II/III) and Ru(III/IV) redox couples of complex 11 more closely resemble the mononuclear model compound due to the longer bridge between the two metal centers. The cyclic voltammogram of the Ru/Au complex 12 shows a reversible Ru(II/III) couple shifted 210 mV positive as compared to the same wave in the mononuclear complex 20, providing evidence of electron donation from Ru through the Ph 2 PNHPPh 2 bridge.

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Table 2-7. Formal potentials for complexes 1-20 35 Complex Couple E pa (V) a E 1/2 (V) a, b Couple E pa (V) a E 1/2 (V) a, b Couple E pa (V) a Reference 1 Ru(II/III) 1.30 Pd(II/IV) 1.49 Ru(III/IV) 1.92 c 1 Ru(II/III) 1.29 Pd(II/IV) 1.45 100 2 Ru(II/III) 1.25 1.21 Pt(II/IV) 1.69 Ru(III/IV) 1.91 c 2 Ru(II/III) 1.13 d Pt(II/IV) 1.78 d 98 3 Ru(II/III) 0.95 0.89 Au(I/III) 1.42 Ru(III/IV) 1.81 c 3 Ru(II/III) 0.86 Au(I/III) 1.40 100 4 Ru(II/III) 1.29 Pd(II/IV) 1.55 1.50 Ru(III/IV) 1.98 c 5 Ru(II/III) 1.13 1.10 Pd(II/IV) 1.50 1.43 Ru(III/IV) 1.95 c 6 Ru(II/III) 1.29 1.25 Pt(II/IV) 1.54 1.47 Ru(III/IV) 1.90 c 7 Ru(II/III) 1.10 Pt(II/IV) 1.49 1.43 Ru(III/IV) 1.98 c 8 Ru(II/III) 1.14 1.08 Pt(II/IV) 1.53 1.40 Ru(III/IV) 1.95 c 9 Ru(II/III) 0.97 0.89 Au(I/III) 1.54 Ru(III/IV) 1.80 c 10 Ru(II/III) 0.95 0.89 Au(I/III) 1.48 Ru(III/IV) 1.85 c 11 Ru(II/III) 0.80 0.75 Au(I/III) Ru(III/IV) 1.76 c 12 Ru(II/III) 1.02 0.97 Au(I/III) 1.41 Ru(III/IV) 1.78 c 13 Ru(II/III) 1.12 Cu(I/II) 0.88 Ru(III/IV) 1.80 c 14 Ru(II/III) 0.61 Ru(III/IV) 1.29 100 14 Ru(II/III) 0.56 c 98 15 Ru(II/III) 0.85 0.72 c 16 Ru(II/III) 0.85 0.73 c 17 Ru(II/III) 0.83 c 18 Ru(II/III) 0.53 c 19 Ru(II/III) 0.80 0.75 c 20 Ru(II/III) 0.87 0.76 c a All potentials obtained in DCE/TBAT unless otherwise specified and reported vs. NHE. b E 1/2 reported for reversible waves. c This work. d Potential obtained in CH 2 Cl 2 /TBAH and reported vs. NHE.

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36 UV/vis Spectroscopy In order to investigate the effects of changes in the metal and ancillary ligands on the electronic structure of the bimetallic complexes, the absorption spectra of complexes 1-20 were measured in methylene chloride solution (Table 2-8). For the mononuclear complexes 14-17, 19-20, and the Ru/Au bimetallics 3, 9-12, a weak low energy band at 440 470 nm (Band I, Figure 2-6) is accompanied by a pair of overlapping bands at higher energy (Bands II and III, Figure 2-6). By analogy to the known compounds Cp*(PMe 3 ) 2 RuX, 131 we have assigned these transitions as Ru d-d bands. The relatively low extinction coefficients and lack of solvatochromism as the solvent polarity varies from benzene to DMSO support this assignment. Note also the red shift in Band III as the halide goes from Cl to Br to I in the series 15-17. An analogous effect was seen as the ligand field strength of X decreased in the series Cp*(PMe 3 ) 2 RuX. 131 The nearly identical absorption spectra of Ru complexes 14-20 and the Ru/Au bimetallics 3, 9-12 suggest negligible electronic interaction between the metal centers, a conclusion consistent with the results of cyclic voltammetry. The Ru/Pd, Ru/Pt, and Ru/Cu bimetallic complexes (with the exception of 5) tend to exhibit a simpler band structure with two absorptions of roughly equal intensity (Figure 2-6, Table 2-8). The general similarity of the spectral features of the bimetallic complexes to those of their mononuclear Ru counterparts 14-20 imply that the transitions are primarily localized at the Ru center, with the differences in absorption attributed to electronic interactions between Ru and the second metal in the bimetallics.

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37 Table 2-8. Absorption data for complexes 1-20 max /nm (/M -1 cm -1 ) a Complex III II I 1 365 (3620) 470 (2080) 2 331 (3340) 365 (2750) 3 336 (2720) 380 (1990) 437 (960) 4 373 (4550) 453 (5030) 5 320 (3940) 372 (1850) 430 (830) 6 354 (6050) 7 373 (6100) 424 (4030) 8 375 (2430) 435 (870) 9 350 (2670) 380 (2220) 440 (890) 10 343 (2660) 380 (2100) 439 (850) 11 336 (2370) 380 (1730) 436 (830) 12 343 (2460) 370 (1990) 435 (740) 13 380 (2120) 448 (700) 14 321 (2460) 395 (1530) 460 (890) 15 336 (2620) 380 (1990) 436 (930) 16 343 (2606) 380 (2105) 438 (890) 17 350 (2580) 380 (2240) 440 (810) 18 358 (2450) 19 336 (2310) 380 (1680) 436 (760) 20 338 (2230) 370 (2005) 435 (780) a UV/vis spectra were measured in CH 2 Cl 2 at room temperature. Conclusions A series of Ru/Pd, Ru/Pt, Ru/Au and Ru/Cu heterobimetallic complexes with bidentate phosphine bridges has been synthesized and characterized. In addition to the phosphine linker, the Ru/Pd, Ru/Pt and Ru/Cu complexes contain halide bridges that facilitate electronic interactions between the metal centers. The solid state structures of

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38 four of these complexes were determined by X-ray crystallography and were found to be similar to those of previously synthesized related Ru/Pd, Ru/Pt and Ru/Au heterobimetallic complexes. 100,109 Cyclic voltammetry of the halide-bridged complexes revealed shifted redox potentials for the Ru(II/III) couples and the first oxidative wave of the second metal, as compared to mononuclear model compounds. The shifts are consistent with electron donation between the metals through the halide bridge. The Ru/Au complexes 3, 9-12, which are bridged only by the bidentate phosphine, exhibited minimal electronic effects between the metal centers. The limited interaction between the Ru and Au centers is corroborated by UV/vis spectroscopy, where 3, 9-12 exhibited the band structure characteristic of the Ru mononuclear model compounds 14-20. Figure 2-6. UV/vis absorption spectra of compounds 1 and 3 obtained in CH 2 Cl 2 at room temperature. 1: () 3: ().

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CHAPTER 3 ELECTROCHEMICAL OXIDATION OF ALCOHOLS USING DPPM-BRIDGED Ru/Pd, Ru/Pt, AND Ru/Au CATALYSTS Cooperative interactions between metals have been a topic of interest during the development of electrooxidation catalysts for direct methanol fuel cells. Studies on Pt anodes have established that the presence of one or more additional metals can decrease the overpotential and greatly improve the anode performance. 132-135 The effect of the second metal has generally been ascribed to a bifunctional oxidation mechanism, 18,132,136 in which Pt sites engage in methanol binding and dehydrogenation while the second metal is involved in water activation and oxo transfer. In addition, interest in potential catalytic applications has led to extensive investigation of bimetallic complexes. 86,137,138 Heterobimetallic complexes have been of particular interest, due to the possibility of exploiting the different reactivities of the two metals in chemical transformations. 84,103,139,140 It has been long recognized that two metals in close proximity may exhibit new reactivities which are different from their parent mononuclear compounds. The reason could be either the different catalytic functions provided by two metal centers, 106 or one main catalytic center whose properties are mediated by another metal. 107,108 Previously, the electrochemical oxidation of methanol catalyzed by the heterobimetallic complexes CpRu(PPh 3 )(-Cl)(-dppm)PdCl 2 (1), CpRu(PPh 3 )(-Cl)(-dppm)PtCl 2 (2) and CpRu(PPh 3 )Cl(-dppm)AuCl (3) has been reported. 100 The presence 39

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40 of a second metal was found to result in enhanced catalytic activity as compared to the ruthenium mononuclear model compounds CpRu(PPh 3 ) 2 Cl 141 and CpRu( 2 -dppm)Cl. In the previous chapter, synthesis and electrochemistry of an extended series of Ru/Pd, Ru/Pt, Ru/Au, and Ru/Cu heterobimetallic compounds that are structurally related to compounds 1-3 were described. 142 The metal-metal interactions and the cooperative effects between the metal centers were investigated through spectroscopic studies and cyclic voltammetry. In this chapter, the catalytic activities of these heterobimetallic complexes for the electrochemical oxidation of methanol are further explored. Electrochemical Oxidation of Methanol Cyclic voltammograms of the heterobimetallic complexes 1-12 142 generally exhibit three redox waves within the solvent window. The first and the third wave are assigned to the Ru(II/III) and Ru(III/IV) couples, respectively, while the middle one is ascribed to a redox couple of the second metal. The potentials of the Ru(III/IV) waves vary little among the binuclear complexes but the first oxidation potential of each metal center is dependent on the amount of electron donation from Ru to the second metal center through the bridging ligands. The formal potentials for the Ru(II/III) and Ru(III/IV) couples are in the ranges 0.75-1.30 V and 1.76-1.98 V, respectively, while the formal potential for the redox couple of the second metal is 1.41-1.69 V. The cyclic voltammograms of Ru/Pd complex 4 (Figure 3-1) and Ru/Pt complex 6 (Figure 3-2) after addition of methanol show a significant current increase at the Pd(II/IV) and Pt(II/IV) waves, indicating a catalytic process of methanol oxidation coinciding with the oxidation of the Pd(II) and Pt(II) centers, respectively.

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41 Figure 3-1. Cyclic voltammograms of 4 under nitrogen in 3.5 mL of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag + reference electrode; 50 mV/s; solutions as specified. Figure 3-2. Cyclic voltammograms of 6 under nitrogen in 3.5 mL of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag + reference electrode; 50 mV/s; solutions as specified.

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42 Figure 3-3. Cyclic voltammograms of 7 under nitrogen in 3.5 mL of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag + reference electrode; 50 mV/s; solutions as specified. In contrast, the cyclic voltammograms of Ru/Pd complex 5 and Ru/Pt complexes 7 (Figure 3-3) and 8 only exhibit small current increases at the Pd(II/IV) and Pt(II/IV) waves in the presence of methanol. For Ru/Au complexes 9-12, onset of methanol oxidation generally occurs at the Ru(III/IV) wave (Figure 3-4). The dppb-bridged Ru/Au complex 11 shows a current increase after the Ru(III/IV) wave in the cyclic voltammogram after addition of methanol, which is the same as the case of the mononuclear model compound CpRu(PPh 3 ) 2 Cl. This is consistent with the compound structure in which a long bridge between Ru and Au results in minimal interaction between the two metal centers. For all heterobimetallic complexes, little or no current increase was observed at the Ru(II/III) wave in the presence of methanol. Electrochemical oxidation of methanol in the presence of complexes 4-12 leads to considerable enhancement of the oxidative currents at the

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43 second metal’s redox wave or the Ru(III/IV) wave, indicating catalytic activities of complexes 4-12 for methanol oxidation. Figure 3-4. Cyclic voltammograms of 10 under nitrogen in 3.5 mL of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag + reference electrode; 50 mV/s; solutions as specified. Bulk electrolyses of methanol with complexes 4-12 were carried out for product identification and quantification. The potential for bulk electrolyses (1.7 V vs. NHE) was chosen during earlier studies with the Ru/Pt complex 2, 109 which exhibits its rise in catalytic current at that potential, coincident with the Pt(II/IV) wave. For comparison purposes, bulk electrolyses of methanol with complexes 4-12 were performed at the same potential. Therefore, oxidations of these complexes were performed at potentials positive of both the Ru(II/III) couple and the first oxidative wave of the second metal but before the Ru(III/IV) wave.

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Table 3-1. Product distributions and current efficiencies for dry methanol oxidation by 4-12 Product ratios (DMM/MF) a,b Ru/Pd (4) Ru/Pd (5) Ru/Pt (6) Ru/Pt (7) Ru/Pt (8) Ru/Au (9) Ru/Au (10) Ru/Au (11) Ru/Au (12) CpRu(PPh 3 ) 2 Cl + Pd(COD)Cl 2 CpRu(PPh 3 ) 2 Cl 25 1.85 4.25 2.27 2.23 6.08 3.78 3.86 3.88 3.85 4.20 50 1.56 3.62 1.68 1.66 4.50 3.25 3.04 3.56 2.89 2.95 4.00 75 1.21 3.19 1.24 1.40 3.53 2.74 2.60 2.94 2.55 2.58 3.73 100 0.91 2.94 0.98 1.26 3.02 2.10 2.35 2.32 2.32 1.97 2.87 Current Efficiency (%) c 42 23 43 39 32 16 20 12 19 18 12 Charge / C 3.43 44 a Electrolyses were performed at 1.7 V vs. NHE. A catalyst concentration of 10 mM was used. Methanol concentration was 0.35 M. b Determined by GC with respect to n-heptane as an internal standard. Each ratio is reported as an average of 2-5 experiments. c Average current efficiencies after 75-100 C of charge passed.

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45 The oxidation products observed during the bulk electrolysis are formaldehyde dimethylacetal (dimethoxymethane, DMM) and methyl formate (MF). Methanol can undergo both two-electron oxidation and four-electron oxidation to afford formaldehyde and formic acid, respectively, 6,7,10,81,143 but neither is observed in the reaction mixtures. Acid-catalyzed condensation of these products with excess methanol yields DMM and MF, along with water. 75,76,78,144 The evolution of product distributions as the reactions progress is shown in Table 3-1. At low conversion, all of the heterobimetallic catalysts afford much higher proportions of DMM. As the reactions progress, the same tendency toward production of more highly oxidized product, MF, can be seen for all the bimetallic catalysts. The time evolution of product ratios presumably arises from water that is generated in situ during the condensation of formaldehyde and formic acid with excess methanol. This behavior is consistent with the catalytic performance of complexes 1-3 observed previously. 100 The differences among the behaviors of complexes 4-12 are apparent in the product ratios of the methanol oxidation products. The oxidation with I-bridged complexes 4, 6, and 7 afforded relatively more of the four-electron oxidation product, MF, especially at the late stage of the reactions as compared to the Cl-bridged methyl complexes 5 and 8. Interestingly, 5 and 8 favored the production of the two-electron oxidation product throughout the entire bulk electrolysis process. The Ru/Au complexes 9-12 exhibited very similar behaviors for their product distributions as the reaction progressed, with all of them resembling the Ru mononuclear compound, CpRu(PPh 3 ) 2 Cl. The current efficiencies for the oxidation processes are also summarized in Table 3-1. These values are the ratio of the charge necessary to produce the observed

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46 yields of DMM and MF to the total charge passed during bulk electrolyses. The I-bridged Ru/Pd complex 4 and Ru/Pt complex 6 gave moderately higher current efficiencies (42 and 43%) as compared to the previously reported Cl-bridged complexes 1 and 2 (24.6 and 18.6%), 100 probably due to the higher stability of the I-bridged complexes. It was found that the irreversible Pd(II/IV) and Pt(II/IV) waves in Cl-bridged compounds 1 and 2 became reversible in I-bridged compounds 4 and 6, implying greater stabilities for the oxidized I-bridged complexes. 142 The methyl substituted complexes 5 and 8 afforded somewhat lower current efficiencies. The Ru/Au complexes 9-12 produced moderately low current efficiencies (12-20%), similar to the value for the mononuclear Ru compound, CpRu(PPh 3 ) 2 Cl. The behavior of Ru/Au complexes 9-12 is consistent with their structure with no halide bridge and minimal interaction between the Ru and Au centers. In order to probe whether the reaction involves both metal centers in close proximity, a mixture of CpRu(PPh 3 ) 2 Cl and Pd(COD)Cl 2 was used as a model for the binuclear Ru/Pd catalysts with PdCl 2 moieties (1 and 4). The product distribution for electrooxidation of methanol by the mixture was similar to that of the mononuclear Ru compound, though a somewhat higher current efficiency was afforded (Table 3-1). Given the differences in product distribution and current efficiency between the mixture and Ru/Pd complex 4, the bimetallic structure appears to be significant. Similar control experiments were previously carried out with a mixture of CpRu( 2 -dppm)Cl and Pt( 2 -dppm)Cl 2 as a model system for Ru/Pt catalyst 2. 109 Because of the apparent effect of increasing water concentration on product ratios during the electrooxidation of methanol with 4-12, the electrooxidation of wet methanol

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47 was also carried out with Ru/Pd bimetallic complexes 4 and 5 as catalysts (Table 3-2). The presence of water decreased the product ratios of DMM/MF for both catalysts as compared to the dry methanol oxidation. This demonstrated that the additional water consistently shifts the product distributions toward the more highly oxidized product, MF, which is consistent with paticipation of Ru oxo species formed by oxidation of bimetallic complexes in the presence of water. Table 3-2. Product distributions and current efficiencies for wet methanol oxidation by 4 and 5 Product ratios (DMM/MF) a Ru/Pd (4) Ru/Pd (5) Charge / C Wet b Dry c Wet b Dry c 25 1.26 1.85 3.55 4.25 50 1.06 1.56 3.07 3.62 75 0.72 1.21 2.58 3.19 100 0.58 0.91 2.14 2.94 Current Efficiency (%) d 41 42 27 23 a Electrolyses were performed at 1.7 V vs. NHE. A catalyst concentration of 10 mM was used. Methanol concentration was 0.35 M. Product ratios were determined by GC with respect to n-heptane as an internal standard. Each ratio is reported as an average of 2-5 experiments. b 5 L water added. c No water added. d Average current efficiencies after 75-100 C of charge passed. Since the oxidation waves of the non-Ru metals of catalysts 4-12 occur at different potentials, and the magnitudes of methanol-induced current increases in the cyclic voltammograms are potential dependent, methanol oxidation experiments were also carried out at the redox potential of the second metal. Table 3-3 summarizes the methanol oxidations with Ru/Pt complex 7 at 1.49 V and Ru/Pt complex 6 at 1.54 V, which were the anodic peak potentials of the Pt(II/IV) redox waves. Oxidations at the lower potentials still produced both DMM and MF, although Ru/Pt complex 7 exhibited very little current increase at the Pt(II/IV) wave. However, the product ratios at lower

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48 potentials indicated formation of more DMM than obtained at higher potentials. In addition, the current efficiencies were somewhat lower and it required more time to pass the same amount of charge. Table 3-3. Product distributions and current efficiencies for methanol oxidation at the Pt (II/IV) wave of 6 or 7 Product ratios (DMM/MF) a,b Ru/Pt (7) Ru/Pt (6) Charge / C 1.70 V 1.49 V 1.70 V 1.54 V 25 2.23 2.95 2.27 2.48 50 1.66 2.48 1.68 1.84 75 1.40 2.29 1.24 1.51 100 1.26 1.95 0.98 1.27 Current efficiency (%) c 39 33 43 33 Time / h 4.0 6.7 4.4 5.8 a A catalyst concentration of 10 mM was used. Methanol concentration was 0.35 M. b Determined by GC with respect to n-heptane as an internal standard. Each ratio is reported as an average of 2-5 experiments. c Average current efficiencies after 75-100 C of charge passed. The initial methanol concentrations (0.35 M) were the same as in the previous experiments with catalysts 1-3 100,109 in order to facilitate comparison. However, it was found that oxidation current increases in the cyclic voltammograms were dependent on methanol concentration (Figure 3-5). Therefore, bulk electrolyses of Ru/Pd complex 4 and Ru/Pt complex 6 in the presence of 1.41 M methanol were carried out, and much higher current efficiencies for both catalysts (73% and 75%, respectively) were obtained. These effects are attributed to the improved electron transfer kinetics and to the higher concentration of substrate when methanol is present in greater quantities.

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49 Figure 3-5. Cyclic voltammograms of 4 under nitrogen in 3.5 mL of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag + reference electrode; 50 mV/s; solutions as specified. Electrochemical oxidation of DMM. In order to determine if DMM could be an intermediate on the pathway to MF, the electrooxidation of DMM was carried out in the presence of complexes 4, 5, 6, 10, and 12. Methyl formate was the sole oxidation product detected in these experiments. The oxidation in the presence of I-bridged Ru/Pd complex 4 and Ru/Pt complex 6 resulted in higher current efficiencies (18%) than those observed for both methyl-substituted Ru/Pd complex 5 and Ru/Au complexes 10 and 12 (Table 3-4). These data are consistent with the methanol oxidation results in which I-bridged Ru/Pd complex 4 and Ru/Pt complex 6 provided a greater proportion of MF than catalysts 5, 10, and 12. Given these results, it is possible that DMM could be an intermediate during the electrooxidation of methanol to MF. However, we cannot rule out participation of small amounts of free formaldehyde as an intermediate.

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50 Table 3-4. Electrooxidation of DMM by 4-5, 10, and 12 Catalyst Current Efficiency (%) a,b Ru/Pd (4) 18 Ru/Pt (6) 18 Ru/Pd (5) 8 Ru/Au (10) 5 Ru/Au (12) 7 a Electrolyses were performed at 1.7 V vs. NHE. A catalyst concentration of 10 mM was used. DMM concentration was 0.16 M. b Average current efficiencies after 75-100 C of charge passed. Electrochemical Oxidation of Isopropanol The cyclic voltammograms of the heterobimetallic complexes 1-4, 6-7, 11 and 13 after addition of isopropanol exhibit current increases at the same potentials previously observed in the methanol cases, indicating similar catalytic behavior of the heterobimetallic complexes for the oxidation of isopropanol. Bulk electrolyses of isopropanol were conducted at the same potential (1.7 V vs. NHE) as those of methanol. Only the 2e oxidation product, acetone, was generated and quantitatively analyzed by GC. The current efficiencies are summarized in Table 3-5. These values are relatively higher than those of methanol electrooxidation. In addition, the presence of water resulted in higher current efficiencies, indicating the facilitation of the electrooxidation of alcohols by water. Electrochemical Oxidation of Benzyl Alcohol Benzyl alcohol can undergo both 2e and 4e oxidation to form benzaldehyde and benzoic acid, respectively. Hence comparison of its electrooxidation catalyzed by heterobimetallic complexes with methanol oxidation could provide useful information. The cyclic voltammograms of the heterobimetallic complexes after addition of benzyl alcohol exhibit current increases, implying catalytic activity of the complexes for

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51 benzyl alcohol oxidation. However, in all the cases investigated so far, only the 2e oxidation product, benzaldehyde, was detected. No benzoic acid was found under any conditions. Neither adding water into the system nor increasing the oxidation potential resulted in the formation of the carboxylic acid. Significantly higher current efficiencies were obtained for the heterobimetallic complexes 1 and 2 (22.8% and 20.8%) than for the mononuclear Ru model compound CpRuCl( 2 -dppm) (8.4%) (Table 3-6). Table 3-5. Current efficiencies for the oxidation of isopropanol to acetone by 1-4, 6-7, 11, and 13 Catalyst Concentration of H 2 O (M) Current Efficiency (%) a,b 0 54.6 Ru/Pd (1) 0.079 67.8 0 56.5 Ru/Pt (2) 0.079 63.2 0 46.5 Ru/Au (3) 0.079 63.2 Ru/Pd (4) 0 55.7 Ru/Pt (6) 0 46.8 Ru/Pt (7) 0 35.5 Ru/Au (11) 0 53.3 Ru/Cu (13) 0 18.2 0 37.5 CpRu( 2 -dppm)Cl 0.079 50.3 a Electrolyses were performed at 1.7 V vs. NHE. A catalyst concentration of 10 mM was used. Isopropanol concentration was 0.37 M. b The amounts of acetone were determined by GC with n-heptane as an internal standard.

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52 Table 3-6. Current efficiencies for the oxidation of benzyl alcohol to benzaldehyde by 1 and 2 PhCHO / mol a,b Ru/Pt (2) Charge / C CpRuCl( 2 -dppm) Ru/Pd (1) Dry Wet d Dry / 2.1 V 25 8.90 31.25 26.88 24.42 25.21 50 23.20 42.45 56.91 68.49 57.50 75 46.15 73.40 76.25 103.14 79.00 100 86.70 118.2 110.32 138.40 115.18 130 139.8 198.75 170.08 Current Efficiency (%) c 8.4 22.8 20.8 26.5 21.2 a Electrolyses were performed at 1.7 V vs. NHE unless otherwise specified. A catalyst concentration of 10 mM was used. Benzyl alcohol concentration was 0.27 M. b Determined by GC with respect to n-dodecane as an internal standard. c Current efficiency after 100-130 C of charge passed. d 5 L of water was added. Conclusions The catalytic activities for the electrooxidation of methanol were investigated for a series of dppm-bridged Ru/Pd, Ru/Pt, and Ru/Au heterobimetallic complexes. The Ru/Pd and Ru/Pt complexes, which contain both a phosphine linker and a halide bridge between metal centers, exhibited much higher current efficiencies than the Ru mononuclear compound, CpRu(PPh 3 ) 2 Cl. The Ru/Au complexes, which are bridged between the Ru and Au centers only by the bidentate phosphine, dppm, showed lower current efficiencies which resemble those of CpRu(PPh 3 ) 2 Cl. The differences among the behaviors of these complexes were also apparent in the relative proportions of the methanol oxidation products. Although the I-bridged Ru/Pd and Ru/Pt complexes afforded low ratios of DMM to MF, the methyl-substituted Ru/Pd and Ru/Pt complexes favored the production of more DMM. All Ru/Au catalysts afforded product ratios similar to those from the Ru

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53 mononuclear compound, CpRu(PPh 3 ) 2 Cl. The presence of water consistently shifted the product distribution toward the highly oxidized product, MF. Higher methanol concentrations resulted in higher current efficiencies. The electrooxidation of DMM afforded MF as the sole oxidation product, indicating DMM could be an intermediate on the pathway to MF. The heterobimetallic catalysts afforded much higher current efficiencies than that of the model compound CpRu(PPh 3 ) 2 Cl, suggesting that the second metal center enhances the catalytic activities. Electrooxidation of isopropanol and benzyl alcohol were carried out for comparison to methanol electrooxidation. The 2e oxidation product, acetone, was obtained for isopropanol oxidation. Benzyl alcohol oxidation afforded the 2e oxidation product benzaldehyde as the only product. Significantly higher current efficiencies were observed for all bimetallic compounds than the mononuclear Ru model compound.

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CHAPTER 4 SYNTHESIS AND ELECTROCHEMISTRY OF BIPYRIDINE COMPLEXES Bimetallic complexes 1-13 exhibit limited solubility in water. Several attempts have been made to prepare water-soluble derivatives of 1-13 by introducing water-soluble ligands, such as sulfonated phospines, amine-substituted Cp or phosphines. So far, a limited number of such bimetallic compounds have been made. 145 However, they are either not sufficiently water soluble or unstable in the presence of water for methanol electrooxidation. As an adaptation of our heterobimetallic complexes, a series of 2, 2'-bipyridine (bpy) complexes was synthesized (Figure 4-1). The pyridine-type ligands and the positive charge increase their solubility in polar solvents, even water. Meanwhile, the -acidic aromatic ligands make it possible to run catalyzed electrolyses at higher potentials with these bpy complexes, which may switch the organic products to predominantly the more highly oxidized products. As a literature example, the oxidation of formate ion to CO 2 was obtained using the catalysts [Ru IV (bpy) 2 (py)(O)] 2+ and [Ru III (bpy) 2 (py)-(OH)] 2+ . 61 In this chapter, the synthesis and electrochemistry of the bpy-coordinated heterobimetallic complexes 21-24 (Figure 4-1) were reported. The electrooxidation of methanol with these compounds as catalysts was investigated and the results were compared to those obtained using compounds 1-13. 54

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55 Ru N N N N Cl Ph2P PPh2 +Ru N N N N Cl Ph2P PPh2 +Pd ClCl ClO4-ClO4-Ru N N N N Cl Ph2P PPh2 +Au Cl ClO4-Ru N N N N Cl Ph2P PPh2 +Pt ClMe ClO4-Ru N N N N Cl Ph2P PPh2 +ClO4Ru N N N N Cl Ph2P PPh2 +ClO4Au Cl 232422212625 Figure 4-1. Structures of compounds 21-26 Synthesis Synthesis of 2,2'-bipyridine substituted Ru/Pd complex 21 and Ru/Pt complex 22. The reaction of the Ru complex [cis-(bpy) 2 Ru( 1 -dppm)Cl] + ClO 4 (25) with Pd(COD)Cl 2 in acetonitrile at room temperature afforded the Cl-bridged Ru/Pd complex [cis-(bpy) 2 Ru(-dppm)(-Cl)PdCl 2 ] + ClO 4 (21) as a red powder in 94% yield (Eq 4.1). The Ru/Pt complex [cis-(bpy) 2 Ru(-dppm)(-Cl)PtMeCl] + ClO 4 (22) was obtained in an analogous manner from Ru complex 25 and Pt(COD)MeCl in 90% yield (Eq 4.2). Complexes 21 and 22 have a similar bridging structure to compounds 1-13 except that bpy ligands replace the Cp and triphenylphosphine ligands. They are air stable in the solid state and their NMR samples do not show signs of decomposition even when exposed to air for weeks.

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56 Ru N N N N Cl Ph2P PPh2 ++ Pd(COD)Cl2 CH3CNrtRu N N N N Cl Ph2P PPh2 +Pd ClCl ClO4-ClO4-2521 N N Ph2P PPh2 rt N N Ph2P PPh2 2523 (4.(4. 2) An equimlar ratio of Ru complex 25 and AuCl were reacted in acetonitrile at room tempe) as a ge is ate (4. 3) 1) Synthesis of 2,2'-bipyridine substituted Ru/Au complexes 23 and 24. Ru N N N N Cl Ph2P PPh2 + Pt(COD)ClMe CH3CNrtRu N N N N Cl Ph2P PPh2 Pt Me 2522 + + Cl ClO4-ClO4o rature to afford the Ru/Au complex [cis-(bpy)2RuCl(-dppm)AuCl]+ClO4(23red solid in 85% yield (Eq 4.3). The dark red Ru/Au compound [cis-(bpy)2RuCl(dppb)AuCl]+ClO4(24) was prepared in the same m a nner as 23 starting from [cis-(bpy)2Ru(1-dppb)Cl]+ClO4(26) and AuCl (Eq 4.4). Complexes 23 and 24 possesssimilar structures to those Cp-coordinated Ru/Au complexes in which a halide bridabsen t . They have ver y sim i l ar stabilities to complexes 21 and 22 both in the solid stand in solution. N N + ClO+ AuCl CH3CNRu N N Cl +Au Cl ClO4-4 Ru Cl

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57 (4. 4)hbridging dppm. The downfield double to the Ru-bound phosphorus while the uptrum 1a31a NMR Data The NMR spectral data for bpy compounds 21-26 appear in Table 4-1. T31P{1H} NMR spectrum of complex 21 exhibits the expected two resonances for the N N Ph2P PPh2 Au rt2624 N N Ph2P PPh2 e t corresponds field doublet is assigned to the phosphorus bound to Pd. In the 1H NMR spec of 21, the chemical shifts of the two diastereotopic methylene protons of the bridgingdppm differ significantly, with two multiplets appearing at 3.80 ppm and 3.35 ppm. Table 4-1. NMR data for bpy complexes 21-26 H NMR () P NMR () Compound P-(CH2)n-P (n = 1 or 4) Ru-PPh2 M-PPh2 21 3.80 (m), 3.35 (m) 39.9 (d, 15 Hz) 17.6 (d, 15 Hz) 22 3.68 (m), 3.48 (m) 38.1 ( d, 9 Hz) 6.4 (d, 9 Hz) 4.9) 41.2 (d, 21 Hz) 4 (d, 21 Hz) 24 23 0 (m), 2.50 (m 20. 2.6 0 – 1.21 (m) 36.8 (s) 32.6 (s) 25 3.72 (m), 2.10 (m) 4.09 (d, 36 Hz) -28.3 (d, 36 Hz) 26 2.42 – 1.20 (m) 37.8 (s) -15.8 (s) n CD3CN at room re. Tw re also expected } NMR mplex 22 aSpectra measured itemperatuo doublets a for the 31P{1H spectrum of co; the downfield Ru-bound phosphorus signal appears at 38.1 ppm and the upfield Pt-bound rum of 22, the methyl signal appears as a tr+ AuCl Ru N N Cl Cl CH3CNRu N Cl N +ClO4p hosphorus signal at 6.4 p pm. In the 1H NMR spect iplet at 0.37 ppm as a result of coupling to Pt. The two diastereotopic methylene protons of the bridging dppm appear at 3.68 and 3.48 ppm.

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58 The spectral data for the Ru/Au complex 23 are listed in Table 4-1. In the 31P{1H} NMR spectrum, one downfield doublet was ascribed to Ru-bound phosphorus and one upfield doublet was assigned to Au-bound phosphorus. The 1H NMR spectrum of comphe glets. . bit the solvent window. The first wave is assigned to the Ru(II/III) couple, while the second one is ase of the second metal. The Ru(II .34 ), Pt(II/IV), and Ru(III) V lex 23 shows a large difference in the chemical shifts of the diastereotopic methylene protons ( = 2.40 ppm), indicating the absence of a halide bridge between ttwo metal centers.142 The 31P{1H} NMR spectrum of compound 24 exhibits the expected two sinThe absence of the coupling between the two phosphines is consistent with the long distance between t he m Cyclic Voltammetry Cyclic voltammograms of the heterobimetallic complexes 21-24 generally exhitwo redox waves within cribed to a redox coupl I/IV) wave, which usually appears in the cyclic voltammograms of heterobimetalliccompounds 1-13 is not observed here except for the Ru/Pt compound 22. Heterobimetallic Ru/Pd compound 21 exhibits a reversible Ru(II/III) wave at 1V and an irreversible Pd(II/IV) wave at 1.60 V, while the Ru/Pt compound 22 shows three quasireversible waves at 1.32 V, 1.55 V, and 1.77 V for the Ru(II/III I/IV) redox couples, respectively. Electron donation from Ru to Pd or Pt through the halide bridge can be seen in compounds 21 and 22 by comparison of their Ru(II/IIredox potentials to that of the model compound [cis-(bpy)2Ru(1-dppm)Cl]+ClO4(25). The bimetallics 21 and 22 show significant positive shifts of the Ru(II/III) wave (190 mand 220 mV) upon introduction of the halide bridge to the second metal. The Ru/Au

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59 bimetallic compound 23 only exhibits one reversible wave at 1.24 V which w as a s signedto the Ru(II/III) couple. There is only an 80 mV positive shift of the Ru(II/III) wave due to the absence of the halide bridge. The lack of a shift in the Ru(II/III) couple betweenthe starting material [cis-(bpy)2RuCl(-dppb)AuCl]+ClO4(24) and Ru/Au complex 26 (1.15 V for both) demonstrated the negligible interaction between the Ru and Au centers in 26. The Au(I/III) wave is not evident for either Ru/Au compound 23 or 24, possibly due to a lack of suitable ligands in the electrolyte so Complex Couple E (V)a E(V)a Couple E (V)a E(V)a l utio n for the incipient Au(III) complex. A similar situation was also observed for the dppb-bridged Ru/Au compound 11.142 Table 4-2. Formal potentials for bpy complexes 21-26 pa1/2 pa1/2 21 Ru(II/III) 1.40 1.34 Pd(II/IV) 1.60 22 Ru(II/III) 1.43 1.32 Pt(II/IV) 1.59 1.55 (I/III) Ru(II/III) 1.20 [Ru4b Ru(II/III) [R6b Ru(II/III) 23 Ru(II/III) 1.29 1.24 Au 24 1. 15 Au(I/III) 25 Ru(II/III) 1.21 26 Ru(II/III) 1.21 1.15 ]ClO 1.24 1.19 u]PF 1.25 1.19 2 T h e clic voltam rams obim pounds 4 aAll potentials obtained in 0.7 M TBAT/DCE and reported vs. NHE. b[Ru] = [cis-(bpy)Ru(PPh3)Cl]+. Electrochemical Oxidation of Methanol cymog of heteretallic com21-2 exhibit small d 4-5), indicating catalytic activities of complexes 21-24 for methanol oxidation. c urrent increases in the preenc e o sf methanol (Figure 4-2, 4-3, 4-4, an

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60 Figure 4-2. Cyclic voltammograms of 21 under nitrogen in 3.5 mL of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag+ reference electrode; 50 mV s; solutions are as specified. Figure 4-3. Cyclic voltammograms of 22 under nitrogen in 3.5 mL of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag+ reference electrode; 50 mV s; solutions are as specified.

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61 Figure 4-4. Cyclic voltammograms of 23 under nitrogen in 3.5 mL of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag+ reference electrode; 50 mV s; solutions are as specified. Figure 4-5. Cyclic voltammograms of 24 under nitrogen in 3.5 mL of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag+ reference electrode; 50 mV s; solutions are as specified. uct identificatintial for bulk electrolyses (1.7 V vs. NHE) was Bulk electrolyses of methanol with complexes 21-24 were carried out for prodon and quantification. The pote

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62 choseive e dimetf ese ll the fts urrent efficith catalyol the Ru n during earlier studies with the Ru/Pt complex 2.109 For comparison purposes, bulk electrolyses of methanol with complexes 21-24 were performed at the same potential. Therefore, oxidations of these complexes were performed at potentials positof both the Ru(II/III) couple and the first oxidative wave of the second metal. The oxidation products observed during bulk electrolyses are the same as those found in the methanol oxidation with compounds 1-12, which are formaldehyd hylacetal (dimethoxymethane, DMM) and methyl formate (MF). The evolution oproduct distributions as the reactions progress is shown in Table 4-3. For all of thbpy-coordinated heterobimetallic catalysts 21-24, the same tendency to produce more 2e-oxidation product (DMM) was observed as the reactions progress. This behavior is different from the methanol oxidation with compounds 1-12, in which the tendency toward production of more highly oxidized product, MF, over time can be seen for abimetallic catalysts. Moreover, it was shown that the presence of a second metal shithe product distribution to the less highly oxidized product, DMM, as compounds 21-24 produced higher DMM/MF ratios than the Ru mononuclear compound. The current efficiencies for the oxidation processes are also summarized in Table 4-3. When the same methanol concentration was used, the c encies obtained from catalysts 21-24 were much lower than those obtained wi sts 1-12. Comparable current efficiencies were obtained when the methanconcentration was increased by a factor of four. The Ru/Pd complex 21 and Ru/Pt complex 22 gave moderately higher current efficiencies (21.1%) by comparison to mononuclear compound [cis-(bpy)2RuCl(PPh3)]+ClO4-. The Ru/Au complex 23 produced moderately low current efficiency (14.6%). Surprisingly, much lower current

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63 efficiency than that of the Ru mononuclear compound was obtained with Ru/Au c24. Table 4-3. Product distributions and current efficiencies for methanol oxidation by 21-24 omplex in DCE Product ratios (DMM/MF)a, b 21 22 23 24 [Ru]ClO4e Charge / C MeOH 0.35 M MeOH 1.41 M MeOH MeOH MeOH .41 M MeOH 1.41 M 1.41 M 1.41 M 1 2.53 1.68 1.83 2.42 0.78 1.31 3.39 2.48 2.26 4.65 1.64 1.41 100 3.57 2.72 2.39 4.72 1.44 lyse form ation mM w Dete GC w espec eptan inter arge passed. O MF o ed. e[Ru [cis-( . 25 1.17 0.90 1.48 0.76 -d 0.97 50 75 2.37 Current Efficiency (%)c 12.8 21.1 21.1 14.6 4.5 9.3 aElectros were pered at 1.7 V vs. NHE. A catalyst concentr of 10 as used. brmined byith rt to n-he as annal standard. Each ratio is reported as an average of 2 experiments. cAverage current efficiencies after 75-100 C of chdnly bserv] = bpy)2Ru(PPh3)Cl]+ b Table 4-4. Product distributions and current efficiencies for methanol oxidation by 21-24 in methanol Product ratios (DMM/MF)a, Charge / C 21 22 23 24 [Ru]ClO4e 25 0.23 0.67 0.42 -d -d 50 0.62 10.11 75 1.03 1.73 3.08 0.30 0.42 0.43 Current Efficiency (%)c 27.5 .38 1.37 0.13 0.26 100 1.45 2.25 4.99 32.8 24.6 10.0 18.5 HE. talyst ntrati mM was rmin respecriments. heptaverag an intrent e standard. Each ratio is cies a -100 C arge passed. dOnly MF ved. e [cisRu(P l]+. aElectrolyses were performed at 1.7 V vs. N A caconceon of 5used. bDeteed by GC with t to n-ne as ernal reported as an average of 2 expecAe curfficienfter 75 of ch obser[Ru] =(bpy)2Ph3)C was carried out. Table 4-4 summarizes the product distributions and current efficiencies for methanol The pyridine-type ligands and the positive charge render the compounds 21-24 very soluble in polar solvents. Therefore, bulk electrolysis in pure m e thanol

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64 oxidass phosphine ligands whiche the heterobimetallic compounds. ar complexes 25-26 and the bimet-1-1a tion in neat methanol. While the product distributions are similar to those obtained in DCE, the current efficiencies are almost doubled (Table 4-4). Overall, the bpy-coordinated heterobimetallic catalysts 21-24 turned out to be leefficient catalysts than compounds 1-12. The reason may be the high stabilities of the bpy-coordinated structures of 21-24, while compounds 1-12 have can dissociate to form catalytically active unsaturated species during the reaction. UV/vis Spectroscopy The absorption spectra of compounds 21-26 were investigated in order to see theffects of the second metal center and the ancillary ligands on the electronic properties of For both the mononucle allics 21-24, two major absorption bands are observed (bands I-II in order of increasing energy) (Table 4-5). Table 4-5. Absorption data for complexes 21-26 max/nm (/Mcm) Complex II I 21 -c 425 (7940) 22 -c 435 (6641) 331 (5740) 448 (6950) 24 333 (5210) 460 (6010) 25 333 (7440) 458 (8440) 26 334 (5080) 460 (6900) [Ru]ClO4b 333 (6650) 452 (7180) 23 pect n acetonitril re. is-( aUV/vis sra were measured ie at room temperatub[Ru] = [cbpy)2Ru(PPh3)Cl]+. cPosition cannot be determined.

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65 By analogy to the previous assignments in the related bpy-Ru( II) compounds,146 we ) d (Ru) transition. A blue shift was observed when a second metal center was introduced (compounds 21-23), with less shift for Ru/Au complexes than for Ru/Pd and Ru/Pt complexes, which is consistent with the bimetallic structure (Figure 4-6, Table 4-5). Figure 4-6. UV-vis spectra of compounds 21-23 and 25 in acetonitrile at room temperature. Band II is partially obscured because it is weak and overlaps with the high energy to the assignment in some [(bpy)Ru(L)Cl]+ (L = phosphine ligand) compounds.146 In compounds 21 and 22, band II blue shifts so that it becomes a tail of the high energy band, and the position is difficult to determine. The nearly identical UV-vis spectra of Ru mononuclear compound 24 and Ru/Au bimetallic compound 26 indicate that there is negligible electronic perturbation at Ru h ave assigned band I as a * (bpy Wavelength (nm) 300350400450500550 Ab sor b ance -0.50.00.51.01.52.0 25 21 22 23 III 2.5 band. It is assigned as a 2* (bpy) d (Ru) charge transfer process, referring 2

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66 center from the Au center due to the long dppb bridge (Figure 4-7). This is consistentwith the results from NMR spectroscopy and cy clic voltammetry. Figure 4-7. UV-vis spectra of compounds 24 and 26 in acetonitrile at room temperature. Conclusions A series of bpy-coordinated Ru/Pd, Ru/Pt, and Ru/Au heterobimetallic complexes with bidentate phosphine bridges has been synthesized and characterized. With the compounds 1-12. Cyclic voltammetry of the halide-bridged Ru/Pd and Ru/Pt complexes revea The Wavelength (nm) 300350400450500550 Ab sor b ance -0.50.00.5 24 III 1.01.5 26 exception of the bpy ligands, these compounds have a very similar structure to led shifted redox potentials for the Ru(II/III) couples and the first oxidative wave ofthe second metal, as compared to mononuclear model compounds. The shifts are consistent with electron donation between the metals through the halide bridge. Ru/Au complexes, which are bridged only by the bidentate phosphine, exhibited minimal electronic effects between the metal centers. The limited interaction between the Ru and

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67 Au centers is corroborated by UV/vis spectroscopy, where 23 and 24 exhibited the bastructure characteristic of the Ru mononuclear model compounds. Lower catalytic activities were obtained for the electrooxidation of methanol of compounds 21-24 by comparison to those obtained for compounds 1-12, probably due to the strong coordination of bipyridine ligands, which are difficult to nd dissociate to form cataly tically active intermediates. For the product evolution as reactions progress, the same tendency to produce more two-electron oxidation product, DMM, was observed for all of the bipyridine compound catalysts. This is different from catalysts 1-12 which always shift the product distribution to the more highly oxidized product, MF, as the reaction progresses. The heterobimetallic catalysts are more selective for the less oxidized product, DMM, than the Ru mononuclear catalyst.

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CHAPTER 5 SYNTHESIS AND ELECTROCHEMISTRY OF OTHER HETEROBIMETALLIC COMPLEXES In addition to the heterobimetallic complexes described in the previous chapters, several additional attempts have been made to modify the compound structure and properties by varying the ancillary ligands and the second metals. However, for these cases, either the heterobimetallic compound was obtained successfully while its electrochemistry was unpromising or the synthesis itself was a failure. In this chapter, these synthesis and electrochemistry results will be discussed in detail. Ru/Au heterobimetallic complex 27. Treatment of {[ 5 -C 5 H 4 (CH 2 ) 2 NH(CH 3 ) 2 ]-Ru(PPh 3 )Cl( 1 -dppm)}Cl with one equivalent of Au(PPh 3 )Cl in methylene chloride at room temperature resulted in the formation of {[ 5 -C 5 H 4 (CH 2 ) 2 NH(CH 3 ) 2 ]Ru(PPh 3 )Cl(-dppm)AuCl}Cl (27) in 94% yield (Eq 5.1). When starting from the unprotonated Ru compound [ 5 -C 5 H 4 (CH 2 ) 2 N(CH 3 ) 2 ]Ru(PPh 3 )Cl( 1 -dppm), the 31 P{ 1 H} NMR spectrum of the reaction mixture indicates that two compounds were obtained. Neither compound resembled the spectrum of protonated product 27. N(CH3)2 HCl Ru Ph3P Ph2P Cl PPh2 N(CH3)2 HCl Ru Ph3P Ph2P Cl PPh2 + Au(PPh3)ClAu Cl CH2Cl2rt ..27 (5. 1) 68

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69 The goal of preparing the Ru/Au complex 27 with a protonated amine group was to obtain a water soluble derivative. The related complexes [{ 5 -C 5 H 4 (CH 2 ) 2 N(H)Me 2 } 2 -Co III ] 3+ (Cl ) 3 147 and [{ 5 -C 5 H 4 (CH 2 ) 2 N(H)Me 2 } 2 Rh III ] 3+ (Cl)(PF 6 ) 2 , 148 which contain the same Cp amine ligand, were found to be water soluble. However, compound 27 is only very slightly soluble in water due to the small amine group as compared to the big bimetallic structure. The cyclic voltammetry of 27 in DCE exhibits a reversible wave at 0.89 V and one quasireversible wave at 1.48 V vs. NHE. The wave at 0.89 V was assigned to the Ru(II/III) couple, while the wave at 1.48 V was ascribed to the Au(I/III) couple. The introduction of the alkylamine substituent on Cp does not shift the oxidation potential of the Ru(II/III) couple, as the analogous wave in Ru/Au compound 3 also appears at 0.89 V. The bulk electrolysis of methanol with complex 27 gave results similar to those from Ru/Au complex 3. Ru/Pd heterobimetallic complex 28. The I-bridged Ru/Pd heterobimetallic complex ( 5 -indenyl)Ru(PPh 3 )(-I)(-dppm)PdCl 2 (28) was prepared by the reaction of ( 5 -indenyl)Ru(PPh 3 )I( 1 -dppm) and Pd(COD)Cl 2 in CH 2 Cl 2 at room temperature as a dark red powder in 95 % yield (Eq 5. 2). The Cl-bridged analogue could not be obtained because the attempted synthesis of ( 5 -indenyl)Ru(PPh 3 )Cl( 1 -dppm) from ( 5 -indenyl)-Ru(PPh 3 ) 2 Cl and dppm leads to the formation of clean [( 5 -indenyl)Ru(PPh 3 )( 2 -dppm)] + Cl . 149 (5. 2) CH2Cl2rt Ru Ph3P Ph2P I PPh2 Ru Ph3P Ph2P I PPh2 Pd Cl Cl + Pd(COD)Cl228

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70 C yclic voltammetry of 28 shows a reversible wave at 1.19 V and a quasireversible waveue 4 nt lex 29. The Ru mononuclear compound (5-NC4Hture to -pared to the . 3) N at 1.45 V vs. NHE. The wave at 1.19 V was assigned to the Ru(II/III) couple while the wave at 1.45 V was ascribed to the Pd(II/IV) couple. The anodic wave of the Ru(II/III) couple is shifted 100 mV negative compared to that of Ru/Pd Cp analogwhich shows an irreversible wave at 1.29 V. This shift is consistent with the replacemeof the Cp ligand of 4 by the more electron-rich indenyl ligand in 28. Bulk electrolysis of methanol with complex 28 under the same condition used with catalysts 1-12 afforded a moderate current efficiency of 27%. Ru/Pd heterobimetallic comp 4)Ru(PPh3)Cl(1-dppm) reacts with Pd(COD)Cl2 in CH2Cl2 at room temperaafford the Ru/Pd heterobimetallic complex (5-NC4H4 ) Ru(PP h 3) ( -Cl)(-dppm)PdCl2 (29) as a yellow powder in 83% yield (Eq 5.3). Cyclic voltammetry of complex 29 exhibits only one irreversible wave at 1.56 V. Cyclic voltammetry of (5-NC4H4)Ru(PPh3)2Cl150 exhibits a reversible wave at 1.06 V, suggesting that the 5-coordinated pyrrole is stable in the p resence of electrolyte, and the replacement of Cp by pyrrole leads to a 260 mV positive shift of Ru(II/III) wave compared to the same wave of CpRu(PPh3)2Cl. If the Ru(II/III) wave of 29 also shifts 260 mV positive comsame wave of Cp analogue 1, then it would overlap with the Pd(II/IV) wave which appears at 1.45 V in compound 1. Ru Ph3P Ph2P Cl PPh2 CH2Cl2rt Ru Ph3P Ph2P PPh2 Pd Cl + Pd(COD)Cl2 29 Cl Cl N (5

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71 R u/Pd heterobimetallic complex 30. The reaction of CpRu(PPh3)Cl(1-dppb) with Pile nsd(COD)Cl2 in methylene chloride at room temperature generated the dimeric Ru/Pd bimetallic complex [CpRu(PPh3)Cl(-dppb)PdCl2]2 (30) with dppb linkages between the Ru and Pd centers (Eq 5.4). In the 31P{1H} NMR spectrum of 30, two downfield doublets (44.9 and 37.3 ppm) were as s ign e d to Ru-bound phosphines, whthe Pd-bound phosphorus signal exhibits two singlets (32.0 and 31.9 ppm), probably dueto the mixture of trans(30a) and cis(30b) isomers. Crystals were grown by diffusion of pentane into the chloroform solution of 30, and the structure of the trans-isomer (30b)has been determined (Figure 5-1). The similar situation was found for the dimeric square-planar Pd complex [Pd{PPh2(C16H15)}Cl2]2, which exhibited isomerization between pseudo-transand cis-conf i rm a tions in its NMR spectrum, while only the traisomer was observed by single crystal X-ray diffraction.151 Figure 5-1. Thermal ellipsoids drawing of the molecular structure of complex 30a. Thermal ellipsoids are plotted at 50 % probability. Phenyl rings and mot s hydrogen atoms are omitted for clarity.

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72 + Pd(COD)Cl2 Ru Ph3PPh2PCl Pd PPh2 Cl Cl Cl Pd Ph2P Cl PPh2 Ru Cl PPh3 Ru Ph3PPPh2(CH2)4PPh2Cl CH2Cl2rt30b Ru Ph3PPh2PCl Pd PPh2 Cl Cl Cl Pd Ru ClPPh2PPh3 PPh2 Cl +30a (5. 4) Cyclic voltammetry of 30 shows a reversible wave for the Ru(II/III) couple at 0.75 V, which is the same as in complexes 10 and 11. Bulk electrolysis of methanol with 30 occurred with a low current efficiency of 7.5%. These results are consistent with the compound structure, which has a long distance and negligible interaction between the two metal centers. Some failed synthesis examples. An interesting question is whether the role of the non-Ru metal centers in these heterobimetallic complexes is to provide an additional electron-deficient site for use as a Lewis acid. One approach to this issue is to prepare derivatives containing metals, such as Zn 2+ , Cd 2+ , Hg 2+ , and Ni 2+ that are not redox active within the solvent window. However, reactions of CpRu(PPh 3 )( 1 -dppm)X (X = Cl or I) with ZnCl 2 , ZnI 2 , CdCl 2 , or CdI 2 resulted in the abstraction of Cl and the clean formation of [CpRu(PPh 3 )( 2 -dppm)] + , while no reaction occurred for NiCl 2 , NiI 2 , or Ni(PPh 3 ) 2 Cl 2 . The Ru/Hg complex CpRu(PPh 3 )(-Cl)(-dppm)HgCl 2 was prepared by the reaction of CpRuCl(PPh 3 )( 1 -dppm) with Hg(OAc) 2 followed by acetyl chloride. 152 However, the bimetallic complex decomposes in the presence of electrolyte. In order to change both the steric and electronic properties of heterobimetallic complexes, the attempts to replace the Cp ligand of compound CpRu(PPh 3 ) 2 Cl with Tp or

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73 Cp* groups were made. However, the reaction of TpRu(PPh 3 ) 2 Cl or Cp*Ru(PPh 3 ) 2 Cl with dppm afforded TpRu( 2 -dppm)Cl or Cp*Ru( 2 -dppm)Cl exclusively. This could be the result of facilitation of PPh 3 loss by the more bulky and electron-rich Tp or Cp* ligand. 1,2-Bis(diphenylphosphino)ethane (dppe) was tried to replace the bis(diphenyl-phosphino)methane (dppm) bridge in order to change the distance of the two metal centers. However, the reaction of CpRu(PPh 3 ) 2 Cl with dppe forms CpRu(PPh 3 )( 1 -dppe)Cl along with a significant amount of CpRu( 2 -dppe)Cl. Though pure CpRu(PPh 3 )( 1 -dppe)Cl was obtained by chromatography, its reaction with Pd(COD)Cl 2 , Pt(COD)Cl 2 or Au(PPh 3 )Cl afforded a small amount of the expected bimetallic compounds, along with a large amount of CpRu( 2 -dppe)Cl. cis-1,2-Bis(diphenylphosphino)ethylene (dppee) was also tried as a replacement for the dppm bridging ligand. However, the reaction of CpRu(PPh 3 ) 2 Cl with dppee affords CpRu( 2 -dppee)Cl exclusively.

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CHAPTER 6 EXPERIMENTAL General Standard Schlenk/vacuum techniques were used throughout. 1,2-Dichloroethane and acetonitrile were distilled from CaH 2 . Pentane and toluene were distilled from Na/benzophenone. Methanol and ethanol were distilled from Mg. Hexanes, benzene, methylene chloride, diethyl ether, and tetrahydrofuran were purged with nitrogen and dried by passing the degassed solvent through a column packed with activated alumina. 153 All NMR solvents were degassed via freeze-pump-thaw cycles and stored over molecular sieves. 1 H and 31 P NMR spectra were recorded on a Varian VXR 300 or a Varian Mercury 300 NMR spectrometer. 1 H and 31 P NMR spectra are referenced to the residual proton in the deuterated solvent and to 85% H 3 PO 4 , respectively. The 31 P NMR spectra were proton-decoupled. High-resolution mass spectrometry was performed by the University of Florida analytical service. Elemental analyses were performed by Robertson Microlit Laboratories, Madison, NJ. UV-visible absorption spectra were recorded on a UV-2501PC-Shimadzu spectrophotometer. CpRu(PPh 3 ) 2 Cl, 154,155 CpRu(PPh 3 ) 2 Me, 156,157 Cp*Ru(PPh 3 ) 2 Cl, 158,159 CpRu( 2 -dppm)Cl (14), 114 Cp(PPh 3 )Ru( 1 -dppm)Cl (15), 115 Cp(PPh 3 )Ru(-Cl)(-dppm)PdCl 2 (1), 100 Cp(PPh 3 )Ru(-Cl)(-dppm)PtCl 2 (2), 109 Cp(PPh 3 )RuCl(-dppm)AuCl (3), 100 cis-(bpy) 2 RuCl 2 2H 2 O, 146 and [cis-(bpy) 2 RuCl(PPh 3 )] + ClO 4 -146 were prepared as previously described. All other starting materials were purchased in reagent grade purity and used without further purification. 74

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75 Electrochemistry Electrochemical experiments were performed under nitrogen using an EG&G PAR model 263A potentiostat/galvanostat. Cyclic voltammograms (scan rate = 50 mV/s) were recorded in 3.5 mL of DCE/0.7 M TBAT with a highly polished glassy-carbon working electrode (3 mm diameter) at ambient temperature under nitrogen. All potentials are reported vs. NHE and referenced to Ag/Ag + . For electrolyses in DCE, the reference electrode consisted of a silver wire immersed in an acetonitrile solution containing freshly prepared 0.01 M AgNO 3 and 0.1 M TBAT. The Ag + solution and silver wire were contained in a 75 mm glass tube fitted at the bottom with a Vycor tip. The bottom part of the glass tube was immersed in a solution of 0.1 M TBAT/DCE, which was contained in a glass tube fitted at the bottom with a Vycor tip. E 1/2 for the couple Cp 2 Fe II/III was 0.25 V vs. Ag/Ag + under these conditions. For electrolysis in methanol, the reference electrode consisted of a silver wire immersed in a methanol solution containing freshly prepared 0.01 M AgNO 3 and 0.1 M TBAT, which was contained in a glass tube fitted at the bottom with a Vycor tip. Bulk electrolysis was performed in an H-cell in 3.5 mL of DCE/0.7 M TBAT at room temperature under nitrogen using a vitreous carbon working electrode, a platinum foil counter electrode, and an Ag/Ag + reference electrode. All electrochemical measurements were performed inside a glove box. Electrolysis products were analyzed by gas chromatography on a Shimadzu GC-17A chromatograph. For methanol and 2-propanol oxidation, a 15 m 0.32 mm column of AT-WAX (Alltech, 0.5 m film) on fused silica which was attached to the injection port with a neutral 5 m 0.32 mm AT-Wax deactivated guard column was used, while for benzyl alcohol oxidation, a 5 m

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76 0.53 mm 2.65 m of HP-1 (J&W) with a neutral 5 m 0.53 mm AT-WAX deactivated guard column was applied. The products produced during electrolysis of methanol and isopropanol were quantitatively determined with the use of a known amount of n-heptane as an internal standard, while that of benzyl alcohol were determined with n-dodecane as an internal standard. Product identity was confirmed by comparing retention times of the oxidation products with authentic samples. Synthesis CpRu(PPh 3 ) 2 I. In a 100 mL Schlenk flask, CpRu(PPh 3 ) 2 Cl (0.725 g, 1.00 mmol) and NaI (3.00 g, 20.0 mmol) were dissolved in 60 mL of degassed methanol. The cloudy mixture was stirred at room temperature for 3 days. The red precipitate was filtered out and dissolved in 20 mL of CH 2 Cl 2 . The solution was washed with water (20 mL 2) and dried over anhydrous MgSO 4 . Removal of the solvent afforded the red product. Yield: 0.776 g (95 %). The compound was identified by comparison to literature data. 156 CpRu(PPh 3 ) 2 Br. The reaction was performed similarly as for CpRu(PPh 3 ) 2 I starting from CpRu(PPh 3 ) 2 Cl (0.725 g, 1.00 mmol) and LiBr (1.30 g, 15.0 mmol). Yield: 0.724 g (94 %). The compound was identified by comparison to literature data. 160 Pt(COD)(CH 3 )Cl. In a 25 mL Schlenk flask, Pt(COD)Me 2 (0.553 g, 1.66 mmol) was dissolved in methylene chloride (6 mL) and MeOH (4 mL). Acetyl chloride (0.130 g, 0.120 mL, 1.66 mmol) was introduced by a syringe, during which effervescence was immediately observed and heat was released. The solution was stirred for 10 minutes. Then the solvent was removed under vacuum and MeOH (1 mL) was added. The Schlenk was cooled to 0 for 30 min. The product was filtered through a medium frit,

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77 washed with cold methanol and hexanes, and dried in vacuo to afford white crystals. Yield: 0.52 g, 88.6%. The compound was identified by comparison to literature data. 161 CpRu(PPh 3 )( 1 -dppm)Br (16). In a 50 mL Schlenk flask, CpRu(PPh 3 ) 2 Br (0.500 g, 0.649 mmol) and dppm (0.264 g, 0.688 mmol) were dissolved in 30 mL of benzene. The yellow solution was heated to 65 o C and stirred for 6 h, during which an orange precipitate formed. The mixture was cooled to room temperature and filtered to afford 16 as an orange powder. Yield: 0.527 g (91%). 1 H NMR (CDCl 3 ): 7.82-6.95 (m, 35H, Ph 2 PCH 2 PPh 2 + PPh 3 ), 4.13 (s, 5H, Cp), 3.94 (m, 1H, Ph 2 PCHHPPh 2 ), 1.15 (m, 1H, Ph 2 PCHHPPh 2 ). 31 P NMR (CDCl 3 ): 43.2 (d, Ru-PPh 3 , J PP = 42 Hz), 35.8 (dd, Ru-Ph 2 PCH 2 PPh 2 , J PP = 42, 20 Hz), -27.5 (d, Ru-Ph 2 PCH 2 PPh 2 , J PP = 20 Hz). HRMS (FAB): calcd for C 48 H 42 P 3 Ru 813.1549 (M-I) + , found 813.1545. CpRu(PPh 3 )( 1 -dppm)I (17). The reaction was performed similarly as for 16 starting from CpRu(PPh 3 ) 2 I (0.500 g, 0.612 mmol) and dppm (0.250 g, 0.650 mmol). Yield: 0.518 g (90%). 1 H NMR (CDCl 3 ): 7.86-6.94 (m, 35H, Ph 2 PCH 2 PPh 2 + PPh 3 ), 4.18 (s, 5H, Cp), 4.12 (m, 1H, Ph 2 PCHHPPh 2 ), 1.24 (m, 1H, Ph 2 PCHHPPh 2 ). 31 P NMR (CDCl 3 ): 42.9 (d, Ru-PPh 3 , J PP = 41 Hz), 33.5 (dd, Ru-Ph 2 PCH 2 PPh 2 , J PP = 41, 20 Hz), -27.0 (d, Ru-Ph 2 PCH 2 PPh 2 , J PP = 20 Hz). HRMS (FAB): calcd for C 48 H 42 P 3 Ru 813.1549 (M-I) + , found 813.1541. CpRu(PPh 3 )( 1 -dppm)Me (18). In a 100 mL Schlenk flask, CpRu(PPh 3 ) 2 Me (0.500 g, 0.709 mmol) and dppm (0.544 g, 1.42 mmol) were dissolved in 50 mL of benzene. The orange brown solution was heated to 80 o C and stirred for 5 days. The mixture was cooled to room temperature and the solvent was removed under vacuum to produce a brown residue which was recrystallized in CH 2 Cl 2 /pentane to afford the yellow

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78 product. Yield: 0.381 g (65%). 1 H NMR (CDCl 3 ): 7.40-6.85 (m, 35H, Ph 2 PCH 2 PPh 2 + PPh 3 ), 4.19 (s, 5H, Cp), 2.82 (m, 1H, Ph 2 PCHHPPh 2 ), 1.15 (m, 1H, Ph 2 PCHHPPh 2 ), 0.37 (t, 3H, CH 3 , J PH = 6 Hz). 31 P NMR (CDCl 3 ): 59.3 (d, Ru-PPh 3 , J PP = 3, 37 Hz), 48.2 (dd, Ru-Ph 2 PCH 2 PPh 2 , J PP = 16, 37 Hz), -27.8 (d, Ru-Ph 2 PCH 2 PPh 2 , J PP = 3, 16 Hz). HRMS (FAB): calcd for C 48 H 42 P 3 Ru 813.1549 (M-CH 3 ) + , found 813.1537. CpRu(PPh 3 )( 1 -dppb)Cl (19). In a 50 mL Schlenk flask, CpRu(PPh 3 ) 2 Cl (1.00 g, 1.38 mmol) and dppb (0.705 g, 1.65 mmol) were dissolved in 30 mL of CH 2 Cl 2 . The yellow solution was kept refluxing for 3 days. The mixture was cooled to room temperature and condensed to a small volume (~5 mL). Pentane (30 mL) was added to precipitate the yellow powder, which was filtered and dried under vacuum. The resulting solid was purified by chromatography on Al 2 O 3 (2.5 10 cm) with 1:3 hexane/ether as eluent. Yield: 0.74 g (60%). 1 H NMR (CDCl 3 ): 7.88-6.98 (m, 35H, Ph 2 P(CH 2 ) 4 PPh 2 + PPh 3 ), 4.09 (s, 5H, Cp), 2.30-0.50 (m, 8H, Ph 2 P(CH 2 ) 4 PPh 2 ). 31 P NMR (CDCl 3 ): 44.7 (d, PPh 3 -Ru, J PP = 42 Hz), 37.3 (d, Ru-Ph 2 P(CH 2 ) 4 PPh 2 , J PP = 42 Hz), -14.4 (s, Ru-Ph 2 P(CH 2 ) 4 PPh 2 ). HRMS (FAB): calcd for C 51 H 48 P 3 ClRu 890.1704 (M + ), found 890.1716. CpRu(PPh 3 )( 1 -Ph 2 PNHPPh 2 )Cl (20). The reaction was performed similarly as for 15 starting from CpRu(PPh 3 ) 2 Cl (0.500 g, 0.689 mmol) and Ph 2 PNHPPh 2 (0.278 g, 0.724 mmol). Yield: 0.538 g (92%). 1 H NMR (CDCl 3 ): 7.82-6.97 (m, 35H, Ph 2 PNHPPh 2 + PPh 3 ), 4.82 (m, 1H, Ph 2 PNHPPh 2 ), 4.11 (s, 5H, Cp). 31 P NMR (CDCl 3 ): 85.5 (dd, Ru-Ph 2 PNHPPh 2 , J PP = 46, 12 Hz), 42.0 (d, Ru-PPh 3 , J PP = 46 Hz), 24.3 (d, Ru-Ph 2 PNHPPh 2 , J PP = 12 Hz). HRMS (FAB): calcd for C 47 H 41 NClP 3 Ru 814.1489 (M-Cl) + , found 814.1465.

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79 Cp(PPh 3 )Ru(-I)(-dppm)PdCl 2 (4). In a 25 mL Schlenk flask, CpRu(PPh 3 )( 1 -dppm)I (0.200 g, 0.213 mmol) and Pd(COD)Cl 2 (0.061 g, 0.21 mmol) were dissolved in 10 mL of CH 2 Cl 2 . The red-orange solution was stirred at room temperature overnight. The solution was condensed under vacuum to a small volume (~3 mL), and pentane (15 mL) was transferred through a syringe to precipitate a red solid. The solid was filtered with a medium swivel frit, washed with hexanes, and dried under vacuum. The product was recrystallized from CH 2 Cl 2 /pentane to yield 0.202 g (84.9%). Single crystals suitable for X-ray diffraction were grown by slow solvent diffusion of pentane into a solution of 4 in chloroform. 1 H NMR (CDCl 3 ): 8.08-6.16 (m, 35H, Ph 2 PCH 2 PPh 2 + PPh 3 ), 4.65 (s, 5H, Cp), 3.48 (m, 1H, Ph 2 PCHHPPh 2 ), 2.72 (m, 1H, Ph 2 PCHHPPh 2 ). 31 P NMR (CDCl 3 ): 49.5 (dd, Ru-Ph 2 PCH 2 PPh 2 , J PP = 20 Hz, 35 Hz), 40.1 (dd, Ru-PPh 3 , J PP = 7, 35 Hz), 10.5 (dd, Ph 2 PCH 2 PPh 2 -Pd, J PP = 7, 20 Hz). HRMS (FAB): calcd for C 48 H 42 IClP 3 PdRu 1080.9312 (M-Cl) + , found 1080.9304. Anal. Calcd for C 48 H 42 Cl 2 IP 3 PdRu: C, 51.66; H, 3.70. Found: C, 51.36; H, 3.52. Cp(PPh 3 )Ru(-Cl)(-dppm)Pd(CH 3 )Cl (5). In a 25 mL Schlenk flask, CpRu(PPh 3 )( 1 -dppm)Me (0.200 g, 0.242 mmol) and Pd(COD)Cl 2 (0.069 g, 0.24 mmol) were dissolved in 10 mL of benzene. The clear solution was stirred at room temperature for 4 h, during which a precipitate formed. The solid was filtered with a frit, washed with pentane, and dried under vacuum. Yield: 0.224 g (92%). Single crystals suitable for X-ray diffraction were grown by slow diffusion of pentane into a solution of the orange product 5 in 1, 2-dichloroethane. 1 H NMR (CDCl 3 ): 8.06-5.90 (m, 35H, Ph 2 PCH 2 PPh 2 + PPh 3 ), 4.58 (s, 5H, Cp), 2.86 (m, 2H, Ph 2 PCH 2 PPh 2 ), 0.39 (d, 3H, CH 3 , J PH = 3 Hz). 31 P NMR (CDCl 3 ): 45.6 (dd, Ru-Ph 2 PCH 2 PPh 2 , J PP = 36, 27 Hz), 39.3 (d, Ru-PPh 3 , J PP

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80 = 36 Hz), 25.5 (d, Ph 2 PCH 2 PPh 2 -Pd, J PP = 27 Hz). HRMS(FAB): calcd for C 49 H 45 P 3 ClRuPd 969.0501 (M-Cl) + , found 969.0494. Anal. Calcd for C 49 H 45 Cl 2 P 3 PdRu: C, 58.57; H, 4.42. Found: C, 57.86; H, 3.94. Cp(PPh 3 )Ru(-I)(-dppm)PtCl 2 (6). The reaction was performed similarly as for 4 starting from CpRu(PPh 3 )( 1 -dppm)I (0.20 g, 0.21 mmol) and Pt(COD)Cl 2 (0.08 g, 0.21 mmol). Yield: 0.188 g (73%). 1 H NMR (CDCl 3 ): 8.04-6.12 (m, 35H, Ph 2 PCH 2 PPh 2 + PPh 3 ), 4.63 (s, 5H, Cp), 3.45 (m, 1H, Ph 2 PCHHPPh 2 ), 2.94 (m, 1H, Ph 2 PCHHPPh 2 ). 31 P NMR (CDCl 3 ): 46.4 (dd, Ru-Ph 2 P-CH 2 PPh 2 , J PP = 11, 35 Hz), 40.5 (d, Ru-PPh 3 , J PP = 3, 35 Hz), -7.7 (d, Ph 2 PCH 2 PPh 2 -Pt, J PP = 3, 11 Hz). HRMS (FAB): calcd for C 48 H 42 IClP 3 PtRu 1169.9924 (M-Cl) + , found 1169.9916. Anal. Calcd for C 48 H 42 Cl 2 IP 3 PtRu: C, 47.82; H, 3.51. Found: C, 47.60; H, 3.36. Cp(PPh 3 )Ru(-I)(-dppm)PtI 2 (7). The reaction was performed similarly as for 4 starting from CpRu(PPh 3 )( 1 -dppm)I (0.200 g, 0.213 mmol) and Pt(COD)I 2 (0.119 g, 0.213 mmol). Yield: 0.266 g (90%). 1 H NMR (CDCl 3 ): 8.12-5.76 (m, 35H, Ph 2 PCH 2 PPh 2 + PPh 3 ), 4.65 (s, 5H, Cp), 3.52 (m, 1H, Ph 2 PCHHPPh 2 ), 3.12 (m, 1H, Ph 2 PCHHPPh 2 ). 31 P NMR (CDCl 3 ): 45.8 (dd, Ru-Ph 2 P-CH 2 PPh 2 , J PP = 12 Hz, 35 Hz), 40.4 (dd, Ru-PPh 3 , J PP = 3, 35 Hz), -2.1 (dd, Ph 2 PCH 2 PPh 2 -Pt, J PP = 3, 12 Hz). HRMS (FAB): calcd for C 48 H 42 I 3 P 3 PtRu 1261.9280 (M-I) + , found 1261.9274. Anal. Calcd for C 48 H 42 I 3 P 3 PtRu: C, 41.52; H, 3.05. Found: C, 41.24; H, 2.79. CpRu(PPh 3 )(-Cl)(-dppm)Pt(CH 3 )Cl (8). In a 25 mL Schlenk flask, CpRuCl(PPh 3 )( 1 -dppm) (0.203 g, 0.240 mmol) and Pt(COD)(CH 3 )Cl (0.080 g, 0.240 mmol) were dissolved in methylene chloride (10 mL). The resulting clear yellow solution was stirred at room temperature under N 2 overnight. The solvent was removed

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81 under vacuum to yield a yellow solid residue which was recrystallized in methylene chloride/hexanes to afford a yellow powdery product. Yield: 0.254 g (97%). 31 P NMR (CDCl 3 ): 46.2 (dd, Ru-PPh 2 CH 2 PPh 2 , J PP = 36, 20 Hz), 38.7 (d, Ru-PPh 3 , J PP = 36 Hz), 6.1 (d, PPh 2 CH 2 PPh 2 -Pt, J PP = 20 Hz, J Pt-P = 2430 Hz). 1 H NMR (CDCl 3 ): 7.93-5.81 (m, 35H, PPh 2 CH 2 PPh 2 + PPh 3 ), 4.46 (s, 5H, Cp), 2.85 (m, 2H, Ph 2 PCH 2 PPh 2 ), 0.15 (t, 3H, CH 3 , J Pt-H = 42 Hz). HRMS (FAB): calc. for C 49 H 45 Cl 2 P 3 RuPt m/z 1058.1122 (M-Cl) + , found 1058.1112. Anal. Calc. for C 49 H 45 Cl 2 P 3 RuPt: C, 53.80; H, 4.15. Found: C, 53.86; H, 3.91. Cp(PPh 3 )RuI(-dppm)AuI (9). In a 20 mL Schlenk flask, CpRu(PPh 3 )( 1 -dppm)I (0.20 g, 0.21 mmol) and AuI (0.069 g, 0.21 mmol) were slurried in 10 mL of CH 2 Cl 2 . The mixture was stirred at room temperature for 5 h, during which the solid AuI dissolved to afford a clear orange red solution. The solution was condensed under vacuum to a small volume (~3 mL), and hexane (15 mL) was transferred through a syringe to precipitate a red solid. The solid was filtered with a medium swivel frit, washed with hexanes, and dried under vacuum. Yield: 0.260 g (97%). 1 H NMR (CDCl 3 ): 8.07-6.13 (m, 35H, Ph 2 PCH 2 PPh 2 + PPh 3 ), 5.04 (m, 1H, Ph 2 PCHHPPh 2 ), 4.16 (s, 5H, Cp), 1.60 (m, 1H, Ph 2 PCHHPPh 2 ). 31 P NMR(CDCl 3 ): 41.7 (d, Ru-PPh 3 , J PP = 42 Hz), 31.4 (dd, Ru-Ph 2 PCH 2 PPh 2 , J PP = 42, 25 Hz), 27.9 (d, Ph 2 PCH 2 PPh 2 -Au, J PP = 25 Hz ). HRMS calcd for C 48 H 42 P 3 I 2 RuAu 1137.0255 (M-I) + , found 1137.0246. Anal. Calcd for C 48 H 42 P 3 I 2 RuAu: C, 45.63; H, 3.35. Found: C, 45.70; H, 3.36. Cp(PPh 3 )RuBr(-dppm)AuCl (10). The reaction was performed similarly as for 3 100 starting from CpRu(PPh 3 )( 1 -dppm)Br (0.200 g, 0.224 mmol) and Au(PPh 3 )Cl (0.111 g, 0.224 mmol). Yield: 0.179 g (71.0%). 1 H NMR (CDCl 3 ): 7.96-6.86 (m, 35H,

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82 Ph 2 PCH 2 PPh 2 + PPh 3 ), 4.86 (m, 1H, Ph 2 PCHHPPh 2 ), 4.12 (s, 5H, Cp), 1.43 (m, 1H, Ph 2 PCHHPPh 2 ). 31 P NMR(CDCl 3 ): 42.5 (d, PPh 3 -Ru, J PP = 42 Hz), 34.2 (dd, Ru-Ph 2 PCH 2 PPh 2 , J PP = 42, 28 Hz), 22.0 (d, Ph 2 PCH 2 PPh 2 -Au, J PP = 28 Hz). HRMS calcd for C 48 H 42 P 3 BrClRuAu 1089.0392 (M-Cl) + , found 1089.0398. Anal. Calcd for C 48 H 42 P 3 BrClRuAu: C, 51.24; H, 3.76. Found: C, 51.49; H, 3.67. Cp(PPh 3 )RuCl[-PPh 2 (CH 2 ) 4 PPh 2 ]AuCl (11). The reaction was performed similarly as for 9 starting from CpRu(PPh 3 )( 1 -dppb)Cl (0.20 g, 0.22 mmol) and AuCl (0.052 g, 0.22 mmol). Yield: 0.202 g (94%). Single crystals suitable for X-ray diffraction were grown by slow diffusion of pentane into a solution of the yellow product 11 in dichloromethane. 1 H NMR (CDCl 3 ): 7.84-7.00 (m, 35H, Ph 2 P(CH 2 ) 4 PPh 2 + PPh 3 ), 4.11 (s, 5H, Cp), 2.12 (m, 3H, dppb), 1.18 (m, 3H, dppb), 0.58 (m, 2H, dppb). 31 P NMR(CDCl 3 ): 44.8 (d, PPh 3 -Ru, J PP = 42 Hz), 37.0 (d, Ru-Ph 2 P(CH 2 ) 4 PPh 2 , J PP = 42 Hz), 31.6 (s, Ph 2 P(CH 2 ) 4 PPh 2 -Au). HRMS calcd for C 51 H 48 P 3 Cl 2 RuAu 1122.1055 (M + ), found 1122.1055. Anal. Calcd for C 51 H 48 P 3 Cl 2 RuAu: C, 54.56; H, 4.31. Found: C, 54.30; H, 4.02. Cp(PPh 3 )RuCl(-Ph 2 PNHPPh 2 )AuCl (12). The reaction was performed similarly as for 9 starting from CpRu(PPh 3 )( 1 -Ph 2 PNHPPh 2 )Cl (0.200 g, 0.235 mmol) and AuCl (0.0546 g, 0.235 mmol). Yield: 0.208 g (81.6%). 1 H NMR (CDCl 3 ): 7.93-6.91 (m, 35H, Ph 2 PCH 2 PPh 2 + PPh 3 ), 5.93 (m, 1H, Ph 2 PNHPPh 2 ), 4.12 (s, 5H, Cp). 31 P NMR(CDCl 3 ): 87.7 (dd, Ru-Ph 2 PNHPPh 2 , J PP = 46, 38 Hz), 54.0 (d, PPh 3 -Ru, J PP = 38 Hz), 40.4 (d, Ph 2 PNHPPh 2 -Au, J PP = 46 Hz ). HRMS calcd for C 47 H 41 NCl 2 P 3 RuAu 1046.0850 (M-Cl) + , found 1046.0876. Anal. Calcd for C 47 H 41 NCl 2 P 3 RuAu: C, 52.19; H, 3.82; N, 1.29. Found: C, 51.71; H, 3.52; N 1.21.

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83 Cp(PPh 3 )Ru(-I)(-dppm)CuI (13). In a 25 mL flask, CpRu(PPh 3 )( 1 -dppm)I (0.200 g, 0.213 mmol) and CuI (0.203 g, 1.07 mmol) were dissolved in 10 mL of CH 2 Cl 2 . The red cloudy mixture was stirred at room temperature overnight. After the solids settled, the clear red supernatant was transferred to another 25 mL Schlenk flask under N 2 by means of a filter cannula. The filtrate was condensed under vacuum to a small volume (~2 mL), and pentane (15 mL) was added through a syringe to precipitate a red solid. The solid was filtered with a medium swivel frit, washed with pentane (10 mL 3), and dried under vacuum. Yield: 0.216 g (90%). Single crystals suitable for X-ray diffraction were grown by slow diffusion of pentane into a solution of the red product 13 in dichloromethane. 1 H NMR (CDCl 3 ): 7.63-6.92 (m, 35H, 7Ph), 4.34 (s, 5H, Cp), 2.89 (m, 1H, Ph 2 PCHHPPh 2 ), 2.51 (m, 1H, Ph 2 PCHHPPh 2 ). 31 P NMR (CDCl 3 ): 40.3 (d, Ru-PPh 3 J PP = 40 Hz), 26.7 (dd, RuPh 2 PCH 2 PPh 2 , J PP = 40, 20 Hz), -18.5 (s(br), Ph 2 PCH 2 PPh 2 -Cu). HRMS calcd for C 48 H 42 P 3 I 2 RuCu 1129.8928 (M + ) found 1129.8922. Anal. Calcd for C 48 H 42 P 3 I 2 RuCu: C, 51.01; H, 3.75. Found: C, 51.25; H, 3.54. [cis-(bpy) 2 RuCl( 1 -dppm)] + ClO 4 (25). To a 100 mL Schlenk flask with acetone (50 mL, degassed) were added cis-(bpy) 2 RuCl 2 2H 2 O (0.52 g, 1.00 mmol) and AgClO 4 (0.21 g, 1.00 mmol). The resulting deep purple brown suspension was stirred under N 2 for 1.5 h. The solution was filtered by gravity in the air, then the deep brown filtrate was returned to the Schlenk flask. The solution was deareated, dppm (577 mg, 1.5 mmol) was added, and the mixture was stirred at room temperature under N 2 for 24 h. The volume of the solution was reduced under vacuum to about 20 mL. Ether (60 mL) was introduced to precipitate out the dark red solid which was filtered in the air, washed with ether (15 mL 2), and then dried under vacuum. A 31 P NMR spectrum of the reaction

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84 mixture indicated it to be a mixture of [cis-(bpy) 2 RuCl( 1 -dppm)] + ClO 4 and [cis-(bpy) 2 Ru( 2 -dppm)](ClO 4 ) 2 (ratio 1:1). The mixture was separated by chromatography on Al 2 O 3 (2.5 6 cm) with acetone/hexane (3:1) as eluent to afford 25 in 40% yield. 31 P NMR (CD 3 CN): 40.9 (d, Ru-PPh 2 CH 2 PPh 2 , J PP = 36 Hz), -28.3 (d, Ru-PPh 2 CH 2 PPh 2 , J PP = 36 Hz). 1 H NMR (CD 3 CN): 9.61-6.64 (m, 36H, 2bpy + 4Ph), 3.53 (m, 1H, Ru-PPh 2 CHHPPh 2 ), 2.10 (m, 1H, Ru-Ph 2 PCHHPPh 2 ). HRMS (FAB): calcd for C 45 H 38 N 4 ClP 2 Ru 833.1297 (M) + , found 833.1320. [cis-(bpy) 2 RuCl( 1 -dppb)] + ClO 4 (26). To a 500 mL Schlenk flask with acetone (400 mL, degassed) were added cis-(bpy) 2 RuCl 2 2H 2 O (2.31 g, 4.44 mmol) and AgClO 4 (0.920 g, 4.44 mmol). The resulting deep purple brown suspension was stirred under N 2 for 3.0 h. The mixture was filtered by gravity in the air, and the deep brown filtrate solution was returned to the Schlenk and deareated. Then dppb (2.70 g, 6.33 mmol) was added. The mixture was stirred at room temperature under N 2 for 24 h. The volume of the solution was reduced to ~50 mL, then ether (200 mL) was added to precipitate out the solid product. Filtration afforded a black powdery solid and a light red solution. The solid product was purified by chromatography on Al 2 O 3 (2.5 6 cm) with acetone/hexane (3:1) as eluent. A 31 P NMR spectrum of the chromatographed material indicated that the product still contained a large amount of free dppb. Recrystallization in acetone/hexane yielded the clean product. Yield: 2.16 g (50%). 31 P NMR (acetone-d 6 ): 37.8 (s, Ru-PPh 2 (CH 2 ) 4 PPh 2 ), -28.3 (s, Ru-PPh 2 (CH 2 ) 4 PPh 2 ). 1 H NMR (acetone-d 6 ): 9.67-7.00 (m, 36H, 2bpy + 4Ph), 2.43-1.20 (m, 8H, PPh 2 (CH 2 ) 4 PPh 2 ). [cis-(bpy) 2 Ru(-Cl)(-dppm)PdCl 2 ] + ClO 4 (21). In a 25 mL Schlenk flask, [cis-(bpy) 2 RuCl( 1 -dppm)] + ClO 4 (0.12 g, 0.13 mmol) and Pd(COD)Cl 2 (0.037 g, 0.13 mmol)

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85 were dissolved in acetonitrile (10 mL). The resulting clear red solution was stirred under N 2 at room temperature for 4 h, then solvent was removed under vacuum to give a red powdery solid product. Yield: 135 mg (94%). 31 P NMR (CD 3 CN): 39.9 (d, Ru-PPh 2 CH 2 PPh 2 , J PP = 15 Hz), 17.6 (d, Ru-PPh 2 CH 2 PPh 2 , J PP = 15 Hz). 1 H NMR (CD 3 CN): 10.2-6.0 (m, 36 H, 4Ph + 2bpy), 3.8 (m, 1H, Ru-PPh 2 CHHPPh 2 ), 3.35 (m, 1H, Ru-Ph 2 PCHHPPh 2 ). HRMS (FAB): calcd for C 45 H 38 N 4 Cl 3 P 2 PdRu 1008.9703 (M) + , found 1008.9708. Anal. Calcd for C 45 H 38 N 4 Cl 3 P 2 PdRu: C, 48.69; H, 3.45; N, 5.05. Found: C, 48.61; H, 3.20; N, 4.89. [cis-(bpy) 2 RuCl(-dppm)AuCl] + ClO 4 (23). In a Schlenk flask, [cis-(bpy) 2 RuCl( 1 -dppm)] + ClO 4 (100 mg, 0.110 mmol) and AuCl (25 mg, 0.11 mmol) were suspended in acetonitrile (15 mL). The resulting mixture was stirred under N 2 at room temperature for 4 h during which the solid dissolved. The solvent was removed under vacuum to give a red powdery solid product. The product was washed with a limited amount of methanol to get rid of the impurities. Yield: 106 mg (85%). 31 P NMR (CD 3 CN): 41.2 (d, Ru-PPh 2 CH 2 PPh 2 , J PP = 21 Hz), 20.4 (d, PPh 2 CH 2 PPh 2 -Au, J PP = 21 Hz). 1 H NMR (CD 3 CN): 9.94-6.75 (m, 36H, 2bpy + 4Ph), 4.90 (m, 1H, Ru-PPh 2 CHHPPh 2 ), 2.50 (m, 1H, Ru-Ph 2 PCHHPPh 2 ). HRMS (FAB): calcd for C 45 H 38 N 4 Cl 2 P 2 AuRu 1065.0658 (M) + , found 1065.0650. [cis-(bpy) 2 Ru(-Cl)(-dppm)PtMeCl] + ClO 4 (22). In a 25 mL Schlenk flask, [cis-(bpy) 2 RuCl( 1 -dppm)] + ClO 4 (100 mg, 0.105 mmol) and Pt(COD)MeCl (35 mg, 0.11 mmol) were dissolved in acetonitrile (20 mL). The resulting clear red solution was stirred under N 2 at room temperature overnight. The solvent was removed under vacuum to afford a red solid residue. Yield: 111 mg (90%). 31 P NMR (CD 3 CN): 38.1 (d, Ru

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86 PPh 2 CH 2 PPh 2 , J PP = 9 Hz), 6.4 (d, PPh 2 CH 2 PPh 2 -Pt, J PP = 9 Hz, J Pt-P = 2328 Hz). 1 H NMR (CD 3 CN): 10.08-5.54 (m, 36 H, 4Ph + 2bPy), 3.68 (m, 1H, Ru-PPh 2 CHHPPh 2 ), 3.48 (m, 1H, Ru-Ph 2 PCHHPPh 2 ), 0.37 (t, 3H, CH 3 , J Pt-H = 40 Hz). HRMS (FAB): calcd for C 46 H 41 N 4 Cl 2 P 2 PtRu 1078.0875 (M) + , found 1078.0872. Synthesis of [cis-(bpy) 2 RuCl(-dppb)AuCl] + ClO 4 (24). In a 20 mL vial, [cis-(bpy) 2 RuCl( 1 -dppb)] + ClO 4 (84 mg, 0.086 mmol) and AuCl (20 mg, 0.086 mmol) were dissolved in acetonitrile (10 mL), and the resulting red clear solution was stirred under N 2 for 5 h. The solvent was removed under vacuum to afford a red solid residue.Yield: 91 mg (88%). 31 P NMR (acetone-d 6 ): 36.8 (s, Ru-PPh 2 (CH 2 ) 4 PPh 2 ), 32.6 (s, PPh 2 (CH 2 ) 4 PPh 2 -Au). 1 H NMR (acetone-d 6 ): 9.62-7.00 (m, 36H, 2bpy + 4Ph), 3.02-1.40 (m, 8H, dppb). HRMS (FAB): calcd for C 48 H 44 Cl 2 N 4 AuRu 1107.1127 (M + ), found 1107.1109. (Dimethylaminoethyl)cyclopentadiene. To a 100 mL Schlenk flask under N 2 were added CpLi (3.10 g, 43.0 mmol) and (dimethylamino)ethyl chloride hydrochloride (2.31 g, 16.0 mmol). Addition of THF (50 mL) resulted in a light yellow solution. The mixture was cooled to 0 o C with an ice bath. HMPA (10 mL) was added. The mixture was stirred for about 1 h to give a brown solution. The cooling bath was removed and the mixture was heated to reflux for 24 h. Water (40 mL) was added. The solution was extracted with pentane (20 mL 2). The organic layer was separated, and concentrated on a rotovap. The residue was distilled under vacuum at room temperature and collected at -78 o C. The product was obtained as a light yellow oil which was a mixture of isomers. Yield: 1.10 g (50%). 1 H NMR (CDCl 3 ): 6.45-6.03 (m, 3H, Cp), 2.94-2.89 (m, 2H, Cp),

PAGE 99

87 2.60-2.43 (m, 4H, CH 2 CH 2 N(CH 3 ) 2 ), 2.26 (s, 6H, N(CH 3 ) 2 , major), 2.25 (s, 6H, N(CH 3 ) 2 , minor). [ 5 -C 5 H 4 (CH 2 ) 2 N(CH 3 ) 2 ]Ru(PPh 3 ) 2 Cl. In a three-necked 100 mL flask, a solution of hydrated ruthenium trichloride (1.00 g, 4.82 mmol) in dry ethanol (30 mL) was added to a rapidly stirred solution of triphenyl phosphine (5.05 g, 19.3 mmol) in refluxing ethanol (60 mL), followed by adding a solution of freshly distilled dimethylaminoethyl cyclopentadiene (1.32 g, 9.64 mmol) in dry ethanol (20 mL). The resulting brown solution was then refluxed for 24 hours until an orange red solution was formed. The solution was concentrated to a small volume until an orange precipitate began to form. The mixture was filtered in the air to isolate an orange solid, which was washed with hexanes (20 mL 3) to remove excess triphenyl phosphine and then dried under vacuum. Yield: 3.42 g (89%). 1 H NMR (CDCl 3 ): 7.37-7.08 (m, 30H, 2PPh 3 ), 3.97 (s, 2H, Cp), 3.32 (s, 2H, Cp), 2.50 (m, 4H, CH 2 CH 2 N(CH 3 ) 2 ), 2.265 (s, 6H, N(CH 3 ) 2 ). 31 P NMR (CDCl 3 ): 40.8 (s, PPh 3 ). [ 5 -C 5 H 4 (CH 2 ) 2 N(CH 3 ) 2 ]Ru( 1 -dppm)(PPh 3 )Cl. In a 50 mL Schlenk flask, [ 5 -C 5 H 4 (CH 2 ) 2 N(CH 3 ) 2 ]Ru(PPh 3 ) 2 Cl (0.160 g, 0.200 mmol) and dppm (0.115 g, 0.300 mmol) were dissolved in methylene chloride (30 mL). The mixture was stirred under N 2 at room temperature for 3 days. The mixture was concentrated under vacuum to a small volume (~5 mL), then pentane (30 mL) was added to precipitate a yellow solid. The solid was filtered with a medium swivel frit, washed with pentane (10 mL 3), and dried under vacuum. The resulting solid was purified by chromatography on Al 2 O 3 (2.5 10 cm) with a mixture of ether/ethanol (1/0.05) with triethylamine (0.1%)as eluent. Yield: 0.092 g (50%). 1 H NMR(CDCl 3 ): 7.74-6.98 (m, 35H, PPh 2 CH 2 PPh 2 + PPh 3 ), 4.20 (s,

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88 2H, Cp), 4.02 (s, 2H, Cp), 3.74 (m, 1H, PPh 2 CHHPPh 2 ), 3.20 (m, 2H, CH 2 CH 2 N(CH 3 ) 2 ), 2.93 (m, 2H, CH 2 CH 2 N(CH 3 ) 2 ), 2.82 (s, 6H, N(CH 3 ) 2 ), 1.21 (m, 1H, PPh 2 CHHPPh 2 ). 31 P NMR (CDCl 3 ): 44.1 (dd, RuPPh 3 , J pp = 3 Hz, 42 Hz), 38.8 (dd, Ru-PPh 2 -CH 2 PPh 2 , J pp = 20 Hz, 42 Hz), -27.3 (dd, Ru-PPh 2 -CH 2 PPh 2 , J pp = 3 Hz, 20 Hz). {[ 5 -C 5 H 4 (CH 2 ) 2 NH(CH 3 ) 2 ]Ru( 1 -dppm)(PPh 3 )Cl}Cl. The orange powder [ 5 -C 5 H 4 (CH 2 ) 2 N(CH 3 ) 2 ]Ru( 1 -dppm)(PPh 3 )Cl (1.0 g, 1.1 mmol) was dissolved in CH 2 Cl 2 (50 mL). The solution was acidified with 1 M HCl (20 mL). The organic layer was washed with saturated NaCl solution and dried over anhydrous MgSO 4 . The solvent was removed to afford an orange red solid. Yield: 0.94 g (90%). 1 H NMR(CDCl 3 ): 12.50 (s(br), 1H, + NH(CH 3 ) 2 ), 7.78-6.81 (m, 35H, PPh 2 CH 2 PPh 2 + PPh 3 ), 4.29 (s, 2H, Cp), 4.01 (s, 2H, Cp), 3.76 (m, 1H, PPh 2 CHHPPh 2 ), 3.20 (m, 2H, CH 2 CH 2 N(CH 3 ) 2 ), 2.93 (m, 2H, CH 2 CH 2 N(CH 3 ) 2 ), 2.82 (s, 6H, N(CH 3 ) 2 ), 1.21 (m, 1H, PPh 2 CHHPPh 2 ). 31 P NMR(CDCl 3 ): 43.8 (dd, RuPPh 3 , J pp = 3 Hz, 42 Hz), 38.1 (dd, Ru-PPh 2 -CH 2 PPh 2 , J pp = 20 Hz, 42 Hz), -27.2 (dd, Ru-PPh 2 -CH 2 PPh 2 , J pp = 3 Hz, 20 Hz). {[ 5 -C 5 H 4 (CH 2 ) 2 NH(CH 3 ) 2 ](PPh 3 )RuCl(-dppm)AuCl}Cl (27). In a 50 mL Schlenk flask, {[ 5 -C 5 H 4 (CH 2 ) 2 NH(CH 3 ) 2 ]Ru( 1 -dppm)(PPh 3 )Cl}Cl (0.383 g, 0.400 mmol) and Au(PPh 3 )Cl(0.198 g, 0.400 mmol) were dissolved in CH 2 Cl 2 (10 mL). The resulting red-orange solution was stirred at room temperature for 24 h. The solvent was removed under vacuum. Methylene chloride (2 mL) was added to dissolve the solid residue, and then pentane (10 mL) was added to precipitate a yellow solid. The mixture was filtered with a medium frit, washed with pentane (10 mL 2), and dried under vacuum to afford a light yellow powder. Yield: 0.45 g (94%). 1 H NMR(CDCl 3 ): 12.39 (s(br), 1H, + NH(CH 3 ) 2 ), 7.78-6.81 (m, 35H, PPh 2 CH 2 PPh 2 + PPh 3 ), 4.30 (s, 2H, Cp),

PAGE 101

89 4.01 (s, 2H, Cp), 3.76 (m, 1H, PPh 2 CHHPPh 2 ), 3.20 (m, 2H, CH 2 CH 2 N(CH 3 ) 2 ), 2.90 (m, 2H, CH 2 CH 2 N(CH 3 ) 2 ), 2.84 (s, 6H, N(CH 3 ) 2 ), 1.21 (m, 1H, PPh 2 CHHPPh 2 ). 31 P NMR (CDCl 3 ): 41.9 (d, RuPPh 3 , J pp = 43 Hz), 36.6 (dd, Ru-PPh 2 -CH 2 -PPh 2 , J pp = 19 Hz, 43 Hz), 28.6 (s(br), Au-PPh 2 -CH 2 PPh 2 ). ( 5 -Indenyl)Ru(PPh 3 ) 2 I. In a 100 mL Schlenk flask, ( 5 -indenyl)Ru(PPh 3 ) 2 Cl (0.426 g, 0.550 mmol) and HI (55% aq) (10.0 mL, 133 mmol) were added to methanol (50 mL). The resulting red suspension was heated to reflux and stirred for 3 h. The mixture was filtered to give a dark red solid, which was washed with methanol (10 mL 3), and dried under vacuum to afford 0.35 g of product. 162 Yield: 74%. 31 P NMR (CDCl 3 ): 46.4 (s). 1 H NMR (CDCl 3 ): 7.24-6.90 (m, 34 H, 6Ph + phenyl ring of indenyl), 4.71 (m, 2H, Cp ring of indenyl), 4.24 (m, 2H, Cp ring of indenyl). ( 5 -Indenyl)Ru(PPh 3 )( 1 -dppm)I. In a 50 mL Schlenk, ( 5 -indenyl)Ru(PPh 3 ) 2 I (0.500 g, 0.577 mmol) and dppm (0.444 g, 1.15 mmol) were dissolved in methylene chloride (20 mL). The resulting red brown solution was stirred for one week. The mixture was evaporated to dryness under vacuum, and the solid residue was recrystallized in CH 2 Cl 2 /pentane to afford the product as a red powder. Yield: 0.522 g (91.4 %). 31 P NMR (CDCl 3 ): 48.6 (dd, J PP = 42, 26 Hz, Ru-PPh 2 CH 2 PPh 2 ), 44.0 (d, J PP = 42 Hz, Ru-PPh 3 ), -25.7 (d, J PP = 26 Hz, Ru-PPh 2 CH 2 PPh 2 ). 1 H NMR (CDCl 3 ): 7.88-6.30 (m, 39 H, phenyl), 4.75 (m, 2H, Cp ring of indenyl), 4.20 (m, 1H, Ph 2 PCHHPPh 2 ), 3.25 (m, 2H, Cp ring of indenyl), 1.25 (m, 1H, Ph 2 PCHHPPh 2 ). ( 5 -Indenyl)Ru(PPh 3 )(-I)(-dppm)PdCl 2 (28). In a 25 mL Schlenk flask, ( 5 -indenyl)Ru(PPh 3 )( 1 -dppm)I (0.100 g, 0.100 mmol), Pd(COD)Cl 2 (28.8 mg, 0.100 mmol) was dissolved in methylene chloride (10 mL). The resulting deep red solution

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90 was stirred at room temperature overnight. The reaction mixture was condensed to a small volume (~5 mL), and pentane (15 mL) was added to precipitate the product as a solid, which was filtered through a medium frit, washed with pentane, and dried under vacuum to afford a deep red powdery product. Yield: 0.11 g (95%). 31 P NMR (CDCl 3 ): 61.7 (dd, Ru-PPh 2 , J PP = 32, 18 Hz,), 40.8 (dd, Ru-PPh 3 , J PP = 32, 7 Hz), 11.6 (dd, Pd-PPh 2 , J PP = 18, 7 Hz). 1 H NMR (CDCl 3 ): 8.30-5.81 (m, 39 H, phenyl), 4.88 (m, 2H, Cp ring of indenyl), 3.60 (m, 1H, Ph 2 PCHHPPh 2 ), 3.52 (m, 2H, Cp ring of indenyl), 2.79 (m, 1H, Ph 2 PCHHPPh 2 ). HRMS(FAB): calcd for C 52 H 44 Cl 2 P 3 IRuPd (M-Cl) + 1130.9468, found 1130.9460. RuCl 2 (PPh 3 ) 2 . In a 250 mL Schlenk flask, RuCl 3 H 2 O (1.00 g, 3.82 mmol) was dissolved in methanol (250 mL, degassed). The solution was heated to reflux for 5 min. After cooling, triphenylphosphine (6.01 g, 22.9 mmol) was added. The brown solution was again heated to reflux and stirred for 4 h. After the heat was removed and the solution settled, a clear green supernatant solution and a deep brown powdery solid were seen. The solid was isolated by filtration, washed with diethyl ether, and dried under vacuum to afford 3.55 g of product. 163 Yield: 96%. 31 P NMR (CDCl 3 ): 42.2 (m(br)) (some small impurity peaks at 52, 48, 30, -5 ppm). 1 H NMR (CDCl 3 ): 7.33-6.96 (m, Ph). ( 5 -C 4 H 4 N)Ru(PPh 3 ) 2 Cl. In a 250 mL Schlenk flask, RuCl 2 (PPh 3 ) 3 (1.00 g, 1.04 mmol) and pyrrolyllithium (0.120 g, 1.67 mmol) were dissolved in benzene (100 mL). The resulting brown solution was heated to 40 o C in an oil bath and stirred for 3 h, during which the solution became clear orange. After cooling to room temperature, the solution was filtered through a Celite bed (prepared freshly from a Celite/benzene suspension).

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91 The orange filtrate was condensed under vacuum to afford a brown residue, which was purified by chromatography on Al 2 O 3 (2.5 10 cm) with 15:1 (toluene/acetonitrile) as an eluent to afford 0.44 g of the yellow product. Yield: 58%. 31 P NMR (CDCl 3 ): 42.0 (s) Lit. 41.4 (s). 150 1 H NMR (CDCl 3 ): 7.38-7.14 (m, 30 H, 6 Ph), 5.65 (s, 2H, pyr), 4.24 (s, 2H, pyr). ( 5 -C 4 H 4 N)Ru(PPh 3 )( 1 -dppm)Cl. In a 25 mL Schlenk flask, ( 5 -C 4 H 4 N)Ru-(PPh 3 ) 2 Cl (0.20 g, 0.28 mmol) and dppm (0.16 g, 0.42 mmol) were dissolved in benzene (15 mL). The solution was heated to 55-60 o C in an oil bath and stirred overnight, during which a precipitate formed. After the solution was allowed to cool down, the solid obtained upon filtration was washed with 50 mL benzene to yield product B. The benzene solution was evaporated to dryness to yield product A (A:B 1:3). RuPPh2 PPh2 Ph2P Ph2P Cl +Cl-B N Ru Ph3P Ph2P Cl PPh2 A Product A: 31 P NMR (CDCl 3 ): 46.0 (dd, Ru-PPh 3 , J PP = 43, 2.4 Hz), 40.8 (dd, Ru-PPh 2 , J PP = 43, 22 Hz), -22.0 (dd, CH 2 PPh 2 , J PP = 22, 2.4 Hz). 1 H NMR (CDCl 3 ): 7.88-6.98 (m, 35 H, 7Ph), 5.86 (s, 1H, pyr), 5.45 (s, 1H, pyr), 4.15 (s, 1H, pyr), 4.00 (s, 1H, pyr), 3.71 (m, 1H, Ph 2 PCHHPPh 2 ), 0.96 (m, 1H, Ph 2 PCHHPPh 2 ). Product B: 31 P NMR (CDCl 3 ): 0.22 (t, J PP = 36 Hz), -26.0 (t, J PP = 36 Hz). 1 H NMR (CDCl 3 ): 8.23-6.55 (m, 40H, 8Ph), 4.91 (m, 2H, dppm), 4.65 (m, 2H, dppm). HRMS(FAB): calcd for C 50 H 44 ClP 4 Ru (M-Cl) + 905.1125, found 905.1140.

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92 ( 5 -C 4 H 4 N)Ru(PPh 3 )(-dppm)(-Cl)PdCl 2 (29). In a 25 mL Schlenk flask, ( 5 -C 4 H 4 N)Ru(PPh 3 )( 1 -dppm)Cl (50 mg, 0.059 mmol) and Pd(COD)Cl 2 (17 mg, 0.059 mmol) were dissolved in methylene chloride (10 mL). The resulting solution was stirred at room temperature for 4 h, during which a yellow precipitate formed. The solid was filtered, washed with pentane, dried under vacuum to afford 0.50 g product. Yield: 83.3 %. 31 P NMR (CDCl 3 ): 42.7 (d, Ru-PPh 3 , J PP = 43 Hz,), 41.0 (dd, Ru-PPh 2 , J PP = 43, 14 Hz), 22.7 (d, Pd-PPh 2 , J PP = 14 Hz). 1 H NMR (CDCl 3 ): 8.00-6.60 (m, 35H, 7Ph), 5.75 (s, 1H, pyr), 5.38 (s, 1H, pyr), 5.31 (s, 1H, pyr), 4.22 (m, 1H, Ph 2 PCHHPPh 2 ), 3.46 (s, 1H, pyr), 2.56 (m, 1H, Ph 2 PCHHPPh 2 ). HRMS(FAB): calcd for C 47 H 41 NCl 3 P 3 RuPd (M-Cl) + 989.9907, found 989.9900. {CpRu(PPh 3 )Cl[-PPh 2 (CH 2 ) 4 PPh 2 ]PdCl 2 } 2 (30). In a 25 mL Schlenk flask, CpRu(PPh 3 )( 1 -dppb)Cl (0.20 g, 0.22 mmol) and Pd(COD)Cl 2 (0.064 g, 0.22 mmol) were dissolved in methylene chloride (10 mL). The resulting solution was stirred at room temperature for 4 h, during which a yellow precipitate formed. The solid was filtered, washed with pentane, and dried under vacuum to afford 0.23 g product. Yield: 96.2 %. Single crystals suitable for X-ray diffraction were grown by slow diffusion of pentane into a solution of the yellow product 30 in chloroform. 31 P NMR (CDCl 3 ): 44.8 (d, Ru-PPh 3 , J PP = 42 Hz), 37.1 (d, Ru-PPh 2 , J PP = 42 Hz), 32.0, 31.9 (s, Pd-PPh 2 , cis and trans). 1 H NMR (CDCl 3 ): 7.80-6.99 (m, 35H, 7Ph), 4.08 (s, 5H, Cp), 2.16-0.45 (m, 8H, Ph 2 P(CH 2 ) 4 PPh 2 ). HRMS(FAB): calcd for C 102 H 96 Cl 6 P 6 Ru 2 Pd 2 (M-Cl) + 2132.0225, found 2132.0210. TpRu(PPh 3 ) 2 Cl. RuCl 2 (PPh 3 ) 3 (0.500 g, 0.516 mmol) and K[HB(pz) 3 ] (0.140 g, 0.516 mmol) were dissolved in methylene chloride (30 mL) to give a yellow solution,

PAGE 105

93 which was stirred overnight to form a green solution. The mixture was condensed to a small volume and hexane (20 mL) was added to precipitate a green-white solid. The product was isolated by filtration and dried under vacuum. Yield: 0.41 g (90%). 31 P NMR (CDCl 3 ): 42.5 (Lit. 42.9 ppm). 164 Crystallographic Structure Determination Data for all complexes were collected at 173 K on a Siemens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters for each structure were refined using up to 8192 reflections. A full sphere of data (1850 frames) was collected using the -scan method (0.3 frame width). The first 50 frames were remeasured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The structures were solved by the Direct Methods in SHELXTL6, 165 and refined using full-matrix least squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. All software and sources of the scattering factors are contained in the SHELXTL program library. For 4: The asymmetric unit consists of the metal complex and four chloroform molecules. Two of the latter were disordered. For one of these, the whole molecule was refined in two parts with their site occupation factors dependently refined (0.53(1) and 0.47(1)) for the major and minor parts, respectively. The second chloroform molecule has its chlorine atoms disordered and was refined in two sets of three (0.57(1) and

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94 0.43(1), respectively). A total of 689 parameters were refined in the final cycle of refinement using 26139 reflections with I > 2(I) to yield R 1 and wR 2 of 4.62% and 12.33%, respectively. Refinement was done using F 2 . For 5: The asymmetric unit consists of the complex and three dichloroethane molecules of crystallization. The latter were significantly disordered and could not be fully modeled. Thus the program SQUEEZE, 166 a part of the PLATON 167 package of crystallographic software, was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. A total of 505 parameters were refined in the final cycle of refinement using 9978 reflections with I > 2(I) to yield R 1 and wR 2 of 2.99% and 7.74%, respectively. Refinement was done using F 2 . For 11: The AuCl and the two phenyl rings are positionally disordered. Only the AuCl moiety was resolved and was refined in three parts. Their site occupation factors were dependently refined to 0.960(1) for the major part and 0.030(1) for each of the other two parts. A total of 538 parameters were refined in the final cycle of refinement using 8550 reflections with I > 2(I) to yield R 1 and wR 2 of 2.81% and 7.01%, respectively. Refinement was done using F 2 . For 13: The asymmetric unit consists of the complex and two molecules of dichloromethane disordered around a center of inversion. The latter could not be fully resolved. Thus the program SQUEEZE, 166 a part of the PLATON 167 a part of the PLATON 167 package of crystallographic software, was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. A total of 553 parameters were refined in the final cycle of refinement using 9283 reflections

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95 with(I) to yield R 1 and wR 2 of 2.62% and 7.64%, respectively. Refinement was done using F 2 . For 29: The asymmetric unit consists of a half dimer and three chloroform molecules of crystallization. Two of the chloroform molecules were disordered and could not be modeled properly, thus program SQUEEZE, a part of the PLATON package of crystallographic software, was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. A total of 570 parameters were refined in the final cycle of refinement using 7097 reflections with I > 2(I) to yield R 1 and wR 2 of 3.86% and 8.62%, respectively. Refinement was done using F 2 .

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BIOGRAPHICAL SKETCH Ying Yang was born on December 24, 1970, in Jiangsu, China. She graduated from Nanjing Normal University in July of 1993 where she received a Bachelor of Science degree in chemistry. She was then accepted as a graduate student by Dalian Institute of Chemical Physics, Chinese Academy of Sciences (DICP, CAS) with the exemption of an entrance examination. Ying received a Master of Science degree in July of 1996 and a PhD degree in July of 1999 in organic chemistry under the supervision of Prof. Shiwei Lu. Several months before her graduation, she was appointed as a group director of medicine, pesticide and intermediate synthesis by Dalian High-Tech Developing Center, DICP, CAS in March 1999. Ying continued her graduate study in University of Florida in August 2000. She joined Dr. Lisa McElwee-white’s group and started research in organic and organometallic chemistry. She graduated in December of 2004 with a second Ph.D. degree. 106