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Synthesis and Characterization of Heterobimetallic Complexes for Application in Homogeneous Electrocatalytic Oxidation of Methanol

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Title:
Synthesis and Characterization of Heterobimetallic Complexes for Application in Homogeneous Electrocatalytic Oxidation of Methanol
Creator:
SERRA, DANIEL ( Author, Primary )
Copyright Date:
2008

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Subjects / Keywords:
Alcohols ( jstor )
Catalysts ( jstor )
Electric current ( jstor )
Electrodes ( jstor )
Electrolysis ( jstor )
Ligands ( jstor )
Oxidation ( jstor )
Ruthenium ( jstor )
Solvents ( jstor )
Voltammetry ( jstor )

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University of Florida
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University of Florida
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Copyright Daniel Serra. 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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5/31/2012
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660020699 ( OCLC )

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SYNTHESIS AND CHARACTERIZAT ION OF HETEROBIMETALLIC COMPLEXES FOR APPLICATION IN HOMOGENEOUS ELECTROCATALYTIC OXIDATION OF METHANOL By DANIEL SERRA 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 2007

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Copyright 2007 by Daniel Serra

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iii To my parents, sister and brot her for their love and support.

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iv ACKNOWLEDGMENTS First of all, I would like to acknowledge Prof. Lisa McElwee-White for giving me an opportunity to carry out my study in her gr oup and for introducing me to the field of heterobimetallic electrocatalysis. I am d eeply thankful for her help, advice and encouragement. I thank my committee members: Dr. Susan Percival, Dr. Daniel R. Talham, Dr. Michael J. Scott and Dr. Randy Duran for their time and contributions. I also thank the McElwee-White group members past and present. Special acknowledgment goes to Dr. Gilbert Matare who passed away recently. He was the one who introduced me to the project during my REU program. I would like to thank Dr. Ying Yang, Dr. Corey R. Anthony, Dr. Corey W ilder, Dr. Keisha-Gay Hylton, Dr. Chatu Sirimanne and Seth Dumbris. I thank Dr. Kh alil Abboud for solving th e crystal structures of the compounds presented in my thesis. Of course I cannot forget, my good friend Christophe R. G. Grenier for his help, advice and coffee moments in my lab. Special thanks go to Dr. Jean Claude Daran, Dr. Eric Manour y, and Dr. Marise Gouygou from the Laboratoire de Chimie de C oordination in Toulou se for giving me solid basis in organic and organometallic s ynthesis and the first taste for research. I would like to thank my loving kobieta Magdalena Alicja Swiderska for her love and support. She has been my strength when ti mes were hard and my greatest fan when I had success.

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v Finally, I thank the persons who are always there behind the screen, with their unending support and tolerance, always there when I needed them: my parents, my sister and my brother who have always wanted to s ee me what I am today. I am lucky to have you.

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vi TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES ..............................................................................................................x LIST OF FIGURES .........................................................................................................xii ABSTRACT....................................................................................................................... xv CHAPTER 1 LITERATURE REVIEW..............................................................................................1 Oxidation of Alcohols...................................................................................................1 Anodic Oxidation of Methanol in Fuel Cells...............................................................1 Mechanism of Methanol Electrooxi dation on Heterogeneous Systems ...............4 On Pure Platinum...........................................................................................5 On Pt/Ru Alloy...............................................................................................7 Other Alloy Systems......................................................................................9 Ruthenium Catalysts for the Oxidation of Alcohols.....................................................9 Chemical Oxidation ..............................................................................................9 Electrochemical Oxidation .................................................................................12 Cooperative Interaction in He terobimetallic Catalysts ..............................................14 Heterobimetallic Catalysts for th e Electrooxidation of Methanol .............................16 Product Detection ...............................................................................................18 Bulk Electrolysis with Complexes 1 3 ................................................................21 2 WATER SOLUBLE H ETEROBIMETALLIC COMPLEXES...................................24 Introduction.................................................................................................................24 Electrochemical Oxidation of Methanol in Aqueous Media .....................................25 Water-Soluble Catalysts.............................................................................................25 Amino-Substituted Cyclopentadienyl Complexes......................................................27 Synthesis .............................................................................................................28 Synthesis of the Ru Complexes 5 8 ............................................................28 Synthesis of the Ru/Pt Complexes 8 and 9 ..................................................29 Synthesis of the Ru/Pd Complexes 10 and 11 .............................................30 NMR Data ..........................................................................................................31 X-Ray Structures ................................................................................................34

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vii Cyclic Voltammetry............................................................................................34 Voltammetry of Complexes 8 11 .................................................................38 Attempted Synthesis of Ruthenium Complexes Including Water-Soluble Phosphines..............................................................................................................40 Synthesis of TPPMS and TPPTS........................................................................40 Synthesis of the Sulfonato Complexes 13 and 14 ..............................................41 Attempted Synthesis of Heterobimeta llic Complexes Incorporating TPPMS and TPPTS Ligands.........................................................................................43 Synthesis of Complex CpRu(PTA)2I ( 17 ) ..........................................................44 Attempted Synthesis of CpRu(PTA)( 1-dppm)I ................................................44 Attempted Synthesis of Sulfonate d Bis-(diphenylphosphino)methane...............45 Conclusion..................................................................................................................45 3 ELECTROCHEMICAL OXIDATI ON OF METHANOL WITH AMINOSUBSTITUTED CYCLOPENTADIENYL COMPLEXES......................................46 Introduction.................................................................................................................46 Electrochemical Oxidation of Meth anol with the Ru/Pt Complexes 8 and 9 and with the Ru/Pd Complexes 10 and 11 ....................................................................47 Conclusion .................................................................................................................55 4 SYNTHESIS OF ISOELEC TRONIC IRON AND RUTHENIUM HETEROBIMETALLIC COMPLEXES....................................................................61 Introduction ................................................................................................................61 Iron and Ruthenium Heterobimetallic Complexes.....................................................62 Synthesis .............................................................................................................62 Synthesis of Complexes 23 28 ....................................................................62 Synthesis of Complex 30 ..............................................................................63 NMR Data ..........................................................................................................64 IR Spectroscopy...................................................................................................65 X-Ray Analysis...................................................................................................67 Cyclic Voltammetry............................................................................................73 UV-Vis Spectroscopy .........................................................................................76 Conclusion .................................................................................................................82 5 ELECTROCHEMICAL OXIDATI ON OF METHANOL WITH ANALOGOUS RUTHENIUM AND IRON HETEROBIMETALLIC COMPLEXES: A COMPARISON STUDY............................................................................................83 Introduction ................................................................................................................83 Electrochemical Oxidation of Methanol with Ru and Fe Heterobimetallic Compounds.............................................................................................................84 Experiments on CO2 Evolution................................................................................101 Isotopic Labeling Study.....................................................................................107 Synthesis of the 13CO-Ru/Pt Complex 23-13C .............................................110 Synthesis of the 13CO-Fe/Pt Complex 24-13C .............................................111

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viii Isotopic Labeling Experiments...................................................................111 Conclusion ...............................................................................................................112 6 EXPERIMENTAL SECTION...................................................................................116 General Procedures ..................................................................................................116 Electrochemistry ......................................................................................................117 Product Analysis ......................................................................................................117 Synthesis ..................................................................................................................118 CpCH2CH2N(CH3)2 ...................................................................................118 [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)2Cl ( 5 ) ..............................................118 [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)2I ( 6 ) ...........................................119 [ 5-C5H4CH2CH2NH(CH3)2]Ru(PPh3)2I ( 6' ).............................................119 [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( 1-dppm)I ( 7 ) ............................119 [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)( 1-dppm)I ( 7' ).................................120 [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PtCl2 ( 8 )................120 [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)( µ -I)( µ -dppm)PtCl2 ( 8' ) ...................120 [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PtI2 ( 9 ) .................120 [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)( µ -I)( µ -dppm)PtI2 ( 9' )......................121 [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PdCl2 ( 10 ) ............121 [ 5-C5H4CH2CH2N(CH3)]Ru(PPh3)( µ -I)( µ -dppm)PdCl2 ( 10' )..................121 [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PdI2 ( 11 ) ..............122 [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)( µ -I)( µ -dppm)PdI2 ( 11' ) ...................122 Sodium 3-(diphenylphosphino)be nzenesulfonate (TPPMS•H2O) ( 12 )......122 Tris(3-sulfonatophenyl)phos phine sodium (TPPTS•3H2O) ( 13 ) ..............123 CpRu(TPPMS)2Cl ( 14 )..............................................................................123 CpRu(TPPTS)2Cl ( 15 ) ...............................................................................124 CpRu(TPA)2Cl ( 17 ) ...................................................................................124 CpRu(CO)2I ( 20 ) .......................................................................................124 CpRu(CO)( 1-dppm)I ( 21 ) ........................................................................124 CpRu(CO)( µ -I)( µ -dppm)PtI2 ( 23 ) .............................................................125 CpFe(CO)( µ -I)( µ -dppm)PtI2 ( 24 ) .............................................................125 CpRu(CO)( µ -I)( µ -dppm)PdI2 ( 25 ) ............................................................125 CpFe(CO)( µ -I)( µ -dppm)PdI2 ( 26 ) ............................................................126 CpRu(CO)I( µ -dppm)AuI ( 27 ) ...................................................................126 CpFe(CO)I( µ -dppm)AuI ( 28 ) ...................................................................127 CpRu(PPh3)( µ -I)( µ -dppm)PdI2 ( 30 )...........................................................127 CpRu( 3-allyl)Cl2 ( 34 )...............................................................................127 CpRu(13CO)2Cl ( 35 ) ..................................................................................128 [CpFe(13CO)2]2 ( 36 ) ..................................................................................128 CpFe(13CO)2I ( 37 ) .....................................................................................128 Crystallographic Struct ure Determination ...............................................................129 Complex 8' .................................................................................................129 Complex 22 ................................................................................................129 Complex 23 ................................................................................................130 Complex 24 ................................................................................................130 Complex 25 ................................................................................................130

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ix APPENDIX: FTIR SPECTRA OF CARBONYL COMPLEXES.................................131 LIST OF REFERENCES ................................................................................................140 BIOGRAPHICAL SKETCH ..........................................................................................150

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x LIST OF TABLES Table page 1-1 Formal potentials of complexes 1-3 ...........................................................................19 1-2 Product distributions and current e fficiencies for methanol oxidation by 1-3 ............22 2-1 NMR (1H, 31P{H}) data for complexes 5-11 .............................................................36 2-2 Selected bond distances and angles for [ 5-C5H5CH2CH2N(CH3)2]Ru (PPh3)( µ -I)( µ -dppm)PtCl2 ( 8' ).................................................................................37 2-3 Crystal data and struct ure refinement for complex 8' ................................................37 2-4 Formal potentials for complexes 5-11 .......................................................................42 3-1 Bulk electrolysis data for the oxidation of methanol by complexes 8-11 and 6 .......56 3-2 Bulk electrolysis data for the oxidation of methanol in “wet methanol” by complexes 8-11 ........................................................................................................59 4-1 Selected spectroscopic data for complexes 21-28 .....................................................66 4-2 Selected bond distances and angles for CpRu(CO)( µ -I)( µ -dppm)PtI2 ( 23 )...............68 4-3 Selected bond distances and angles for CpFe(CO)( µ -I)( µ -dppm)PtI2 ( 24 ) ...............69 4-4 Selected bond distances and angles for CpRu(CO)( µ -I)( µ -ppm)PdI2 ( 25 ) ..............70 4-5 Selected bond distances and angles for CpFe(CO)( µ -I)( µ -ppm)PdI2 ( 26 ) ................71 4-6 Crystal data and struct ure refinement for complexes 23 , 24 , 25 and 26 ....................72 4-7 Formal potentials for complexes 21-32 .....................................................................77 4-8 UV-vis spectral data of complexes 21-28 ...................................................................81 5-1 Bulk electrolysis data for the ox idation of methanol in “dry methanol” with complexes 23-26 , 32 and 33 ..................................................................................100 5-2 Bulk electrolysis data for the oxidation of metha nol in “dry methanol” with monomeric complexes ...........................................................................................102

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xi 5-3 Bulk electrolysis data for the oxidation of methanol in “wet methanol” with complexes 23-26, 32 and 33 ..................................................................................104 5-4 Predicted and experimental carb onyl stretching frequencies for CpRu(CO)2I, CpFe(CO)2I , 21 , 22 , 23 and 24 ..............................................................................110

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xii LIST OF FIGURES Figure page 1-1 Schematic representation of a fuel cell ........................................................................2 1-2 Ruthenium/TEMPO catalyzed ae robic oxidation of alcohols ...................................13 1-3 Thermal ellipsoid drawings of th e molecular structures of complexes 1 , 2 and 3 .....17 1-4 Cyclic voltammograms of complex 1 in DCE............................................................19 1-5 Cyclic voltammograms of complex 2 in DCE............................................................20 1-6 Cyclic voltammograms of complex 3 in DCE ...........................................................20 2-1 Schematic representation of the stra tegies used for preparing water-soluble derivatives of complex 1 .........................................................................................27 2-2 Structures of compounds 8-11 ...................................................................................27 2-3 Synthetic pathway to Ru complexes 5-7 ....................................................................29 2-5 ORTEP drawing of the molecular structure of [ 5-C5H5CH2CH2N(CH3)2] Ru(PPh3)( µ -I)( µ -dppm)PtCl2 ( 8' ).............................................................................35 3-1 Cyclic voltammograms of complex 8 .........................................................................48 3-2 Cyclic voltammograms of complex 9 .........................................................................48 3-3 Cyclic voltammograms of complex 10 .......................................................................49 3-4 Cyclic voltammograms of complex 11 .......................................................................49 3-5 Strutures of heterobimetallic complexes 9-11 ............................................................50 3-6 Product evolution for the electrolysis of Ru/Pt complex 8 in MeOH........................53 3-7 Product evolution for the electrolysis of Ru/Pd complex 10 in MeOH......................53 3-8 Product evolution for the electrolysis of Ru/Pd complex 11 in MeOH......................54 3-9 Product evolution for the electrolysis of Ru/Pt complex 9 in MeOH........................54

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xiii 3-10 Product evolution for the electrolysis of Ru/Pt complex 8 in wet MeOH................57 3-11 Product evolution for the electrolysis of Ru/Pt complex 9 in wet MeOH................57 3-12 Product evolution for the electrolysis of Ru/Pt complex 10 in wet MeOH..............58 3-13 Product evolution for the electrolysis of Ru/Pt complex 11 in wet MeOH..............58 4-1 Heterobimetallic complexes 23-31 ............................................................................63 4-2 ORTEP drawing of the mol ecular structure of Cp(CO)Ru( µ -I)( µ -dppm)PtI2 ( 23 )....68 4-3 ORTEP drawing of the mol ecular structure of Cp(CO)Fe( µ -I)( µ -dppm)PtI2 ( 24 ) ...69 4-4 ORTEP drawing of the mol ecular structure of Cp(CO)Ru( µ -I)( µ -dppm)PdI2 ( 25 ) ..70 4-5 ORTEP drawing of the mol ecular structure of Cp(CO)Fe( µ -I)( µ -dppm)PdI2 ( 26 ) ..71 5-1 Cyclic voltammograms of complex 23 .......................................................................86 5-2 Cyclic voltammograms of complex 24 .......................................................................86 5-3 Cyclic voltammograms of complex 25 .......................................................................87 5-4 Cyclic voltammograms of complex 26 .......................................................................87 5-5 Cyclic voltammograms of complex 27 .......................................................................88 5-6 Cyclic voltammograms of complex 28 .......................................................................88 5-7 Cyclic voltammograms of complex 23 in DCE, effect of adding PPh3 ....................90 5-8 Cyclic voltammograms of complex 24 in DCE, effect of adding PPh3 ....................90 5-9 Evolution of the products from the elect rooxidation of methanol in DCE for the Ru/Pt complex 23 , effect of adding PPh3 ................................................................92 5-10 Cyclic voltammetry of complex 25 in acetonitrile ..................................................92 5-11 Cyclic voltammetry of complex 26 in acetonitrile ..................................................93 5-12 Product evolution for th e electrooxidation of metha nol in pure methanol using the Fe/Pt complex 24 ...............................................................................................96 5-13 Product evolution for th e electrooxidation of metha nol in pure methanol using the Ru/Pt complex 23 ...............................................................................................96 5-14 Product evolution for th e electrooxidation of methanol in pure methanol for the Ru/Pd complex 26 ....................................................................................................97

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xiv 5-15 Product evolution for the electrolysis of Ru/Pt complex 23 in wet MeOH............101 5-16 Product evolution for the electrolysis of Ru/Pt complex 25 in wet MeOH............103 5-17 Product evolution for the electrolysis of Ru/Pt complex 24 in wet MeOH............103 5-18 Schematic of the gas cell setup fo r FTIR detection of gaseous products ..............106 5-19 Photograph of the setup used fo r the electrooxidation of methanol ......................106 5-20 FTIR spectrum of the headspace gases during the el ectrooxidation of methanol with Ru/Pt complex 23 ..........................................................................................108 5-21 FTIR spectrum of the headspace gase s during the electrooxi dation of methanol with Fe/Pt complex 24 ...........................................................................................109 5-22 Isotopic labeling experiments. FTIR spectra .........................................................114 A-1 FTIR spectra of complexes 21 and 21-13C ..............................................................131 A-2 FTIR spectrum of complex 22 ................................................................................132 A-3 FTIR spectrum of complex 22-13C ........................................................................133 A-4 FTIR spectrum of complex 24 ................................................................................134 A-5 FTIR spectrum of complex 23-13C ........................................................................135 A-6 FTIR spectrum of complex 25 ................................................................................136 A-7 FTIR spectrum of complex 26 ...............................................................................137 A-8 FTIR spectrum of complex 27 ................................................................................138 A-9 FTIR spectrum of complex 28 ................................................................................139

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xv Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy SYNTHESIS AND CHARACTERIZAT ION OF HETEROBIMETALLIC COMPLEXES FOR APPLICATION IN HOMOGENEOUS ELECTROCATALYTIC OXIDATION OF METHANOL By Daniel Serra May 2007 Chair: Dr. Lisa McElwee-White, Major Department: Chemistry This dissertation describe s the synthesis, electroc hemistry and activity in electrooxidation of methanol for the series of hetero bimetallic Ru/Pt and Ru/Pd complexes [ 5-C5H5CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PtCl2 ( 8 ), [ 5-C5H5CH2 CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PtI2 ( 9 ), [ 5-C5H5CH2CH2N(CH3)2•HI]Ru(PPh3) ( µ -I)( µ -dppm)PdCl2 ( 10 ) and [ 5-C5H5CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PtCl2 ( 11 ). Initially synthesized for application in aqueous media, these complexes were found to have poor solubility in water, but are soluble in methanol. The electrocatalytic properties of these complexes were investigated during the electrooxidation of methanol performed in pure methanol. The oxidati on products observed are dimethoxymethane (DMM) and methyl formate (MF). The result s showed that the ch loride substituted complexes 8 and 10 exhibit higher activity compared to iodide complexes 9 and 11 as

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xvi described by the current effi ciencies (CE%) and turnover numbers (TON) (65% and 13.8 for 8 and 63% and 13.6 for 10 vs. 20% and 4 for 9 and 29% and 6 for 11 ). A series of iron-containing heterobimetallic complexes Cp(CO)Fe( µ -I)( µ -dppm) PtI2 ( 24 ), Cp(CO)Fe( µ -I)( µ -dppm)PdI2 ( 26 ) and Cp(CO)Fe(I)( µ -dppm)AuI ( 28 ), as well as the isoelectronic ruthenium analogues Cp(CO)Ru( µ -I)( µ -dppm)PtI2 ( 23 ), Cp(CO)Ru( µ -I)( µ -dppm)PdI2 ( 25 ) and Cp(CO)Ru(I)( µ -dppm)AuI ( 27 ) were also synthesized. All six complexes were charac terized by elemental analysis, IR, UV and NMR (1H and 31P) spectroscopy, and cyclic voltammet ry. The structure of compounds 23 , 24 , 25 and 26 were determined by X-ray crystallography and were found to be similar to those of halide-bridged complexes previous ly reported. The selected heterobimetallic 23-26 complexes also illustrate the effect of an I-bridged ligand in mediating the electronic interactions between the two metals as can be seen by comparison of the redox potentials, carbonyl stretching frequencies a nd UV-vis transitions of heterobimetallic complexes 23-26 with those of the monome tallic compounds Cp(CO)Ru(I)( 1-dppm) and Cp(CO)Fe(I)( 1-dppm) and also with the solely dppm-bridged complexes 27 and 28 . The electrochemical oxidation of methanol wa s carried out using the heterobimetallic complexes as catalysts. The Ru/Pt and Ru/Pd complexes 23 and 25 were found to be more active than their Fe/Pt and Fe/Pd analogues 24 and 26 . Ru/Au and Fe/Au complexes 27 and 28 are not active for electro catalytic oxidation of meth anol due to a stability problem.

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1 CHAPTER 1 LITERATURE REVIEW Oxidation of Alcohols The oxidation of alcohols to the co rresponding carbonyl compounds is a key reaction in organi c transformations.1,2 The huge number of r eagents available to accomplish this reaction is a te stimony to its importance, bot h in large scale processes and in the manufacture of fine chemicals.3-6 Unfortunately, standard organic methods still require classical oxidation procedures using stoichiometric amounts of strong oxidizing reagents, notably chromium (VI) reagents,7 ruthenium,8 or manganese salts,9 which are highly toxic and pose environmental problems. To avoid these problems, a number of catalytic oxidation processes using the combination of a metal salt, such as V,10 Mo,11,12 W,11 Zr,13 Ru,14 and Co15 derivatives and stoichiometr ic oxidants such as NMO, tBuOOH, PhIO, NaOCl, H2O2 and N-hydroxyphthalimide are now usually used. 1,2,16 The current state-of-the-art in al cohol oxidations is far better because numerous catalytic methods are now known which can be used to oxidize alcohols using either O2 or H2O2 as the oxidant. These oxidants are to be preferre d because they are inexpensive and produce water as the sole byproduct. Anodic Oxidation of Methanol in Fuel Cells Although fuel cells were invent ed in the middle of the 19th century, they didnÂ’t find the first application until sp ace exploration in the 1960s. Si nce then, the development of fuel cell technology has gone through several cy cles of intense activity, each followed by a period of reduced interest. However during the past two decades, a significant

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2 world-wide effort to develop fuel cell materials and fuel ce ll systems has been driven by the demand for efficient energy systems fo r transportation, the desire to reduce CO2 emissions and other negative environmenta l impacts, and the demand for high energy density power sources for portable electronic applications. Fuel cells are electrochemical devices that convert the chemical energy of a reaction directly into electrical energy. The ba sic building block of a fuel cell consists of two electrodes sandwiched around an electrolyte layer in contact with a porous anode and cathode on either side. Reactants (oxygen/air, hydrogen, methanol, etc.) are consumed on the electrodes generating elect ricity, heat and products of the reactions. A schematic representation of a fuel ce ll is shown in Figure 1-1. Catalyst Layers (10 µm) Diffusion Layers (100 µm) Air / H2O CH3OH / H2O CH3OH / H2O / CO2O2-reduced Air / H2O / CO2CH3OH H2O CO2CO2H2O O2PEM (200 µm) Anode Cathode H2O CO2CH3OH e-eFigure 1-1. Adapted from ref 17 Among many types of fuel cells, the Direct Methanol Fuel Cell (DMFC) has been the subject of intense study due to its numerous advantages, such as relatively low cost, high abundance, easy handling and storage of the feeds (methanol and oxygen/air) and low operating temperatures. The need to develo p DMFC is thus recognized, particularly

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3 as a primary power source for application in mobile technologies and also for portable electronic devices (for example in laptops, mp3 players, mob ile phones, etc.). Fuel cells are attractive because they work at low temperatures, do not produce much heat eliminating the need for extra cooling device, can be easily refilled, have a short start up period, have low polluting emissions (ideally CO2 and water). To be competitive, the DMFC has to operate at low temperature (close to room temperature) and has to be able to deliver a high power density at low cost. Many obstacles need to be overcome, like fuel crossing over from the anode to the cathode without producing electricity and a complicated multi-step mechanism resulting in a low rate of methanol oxidation kinetics on the anode. Another problem is that ther e are often chemical compounds formed during the process that poison the catalysts. The electrochemical oxidation of methanol to CO2 can be described by the following equation: CH3OH+H2O CO2+6H++6e-E ° =0.02V(1.1) Thermodynamically this reaction is favorable and lies very close to the equilibrium potential of hydrogen. In fact, the overpotenti al of methanol oxidation is higher than hydrogen oxidation. The difference in kinetics between these two reactions is due to the fact that hydrogen oxidation i nvolves the transfer of only tw o electrons while methanol involves the transfer of six electrons with a complicated multi-step process involving many adsorbed intermediates and formation of side products. In principle, methanol oxidation can be presented as follows:

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4 CH3OH adsorbedintermediates onheterogeneous systems COadHCHO,HCOOH CO2 Both of these pathways require a catalyst, which should be able to (a) dissociate the C-H bond and (b) facilitate the reaction of th e resulting residue with some O-containing species to form CO2 (or HCOOH). The first process invo lves adsorption of the methanol molecule and necessitates several neighbori ng sites at the surface. The second process requires dissociation of water, which is th e oxygen donor for the reaction. So far it has been found that platinum is very active in the first step (methanol dehydrogenation) but not very active in the second. If platinum is alloyed with a less noble metal like Ru, Sn etc., its activity towards meth anol oxidation will increase.18,19 Many other combinations were tested but to date a platinum-rutheniu m alloy has proven to be the best choice. Mechanism of Methanol Electrooxidat ion on Heterogeneous Systems The literature data about the electrooxidati on of methanol on heterogeneous system material are numerous. The reaction has been widely investigated during the last four decades and continues to be one of the most studied reactions.20-25 The mechanism was studied on platinum prepared in several ways (polycrystalline, single crystal platinum electrodes, dispersed platinum)26,27 and also with different t ype of PtRu catalysts (well defined alloys, ruthenium deposition on Pt, carbon supported PtRu clusters, etc).18,19,28-31 Due to the considerable progress in analyt ical instrumentation, identification of the final products and intermediates of electro oxidation of methanol was possible. A diversity of electrochemical and spectroscopic methods have been used such as cyclic voltammetry, chronoamperometry, gas chro matography coupled with mass spectral

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5 mesurements, in-situ FTIR reflectance spectroscopy methods,32,33 differential electrochemical mass spectrometry (DEMS),18,34 isotopic labeling35 combined with mass spectroscopy,36 etc. On pure platinum In 1977, Bagotzky and co-workers were th e first to propose a complete reaction scheme for the methanol oxidation on platinum which is still regarded as valid today.37 The proposed mechanism for oxidation of meth anol occurs following three major steps: a) successive dehydrogenations of meth anol upon adsorption on platinum surface, b) water dissociative adsorption and c) su rface reaction between the species formed during steps a) and b) . (indexes x, xx, and xxx denote on e, two and thr ee valence bonds with the platinum surface, respectively). a) Methanol adsorption and dehydrogenations: CH3OHCH2OH+H++e-x (1.2) CHOH+H++e-CH2OHx xx (1.3) CHOHxxC OH+H++exxx (1.4) b) Water dissociative adsorption H2O OH+H++e-x (1.5) c) Surface reactions between the species HCHO+H2O CH2OH+OHx x (1.6) CHOH+2OHxxHCOOH+H2O x (1.7) C OH+3OHxxxCO2+2H2O x (1.8)

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6 C=O+H2O C OH+OHxxx xx x (1.9) C=O+OHxx xCOOHx (1.10) COOH+OHx CO2+H2Ox (1.11) This mechanism was recently reviewed by Leger38 and completed by several other pathways where the dehydrogenation was also considered occuring at the OH group in methanol. a) Methanol dehydrogenation xCHO is also considered to be an active in termediate and can reac t further with hydroxyl adsorbed species. CHO+OHxCOOH+H++ex x (1.17) Methanol adsorbed at the surface of plat inum can electrochemically dehydrogenate successively to form a series of adsorbed intermediate (Eq. 1.2 to 1.4 and 1.12 to 1.17). In the heterogeneous chemical step c) (Eq. 1.6 to 1.11), dissociative adsorption of water (Eq. 1.5) is required to convert methanol to formic acid or CO2. However, on a pure platinum electrode, the dissociative adsorption of water is only possible at high potentials CH3OHCH3O+H++e-x (1.12) H2CO+H++e-CH3Ox x (1.13) H2COxCHO+H++ex (1.14) CH OHxCHO+H++ex (1.15) CHOxC=O+H++exx (1.16)

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7 (above 0.7 V vs. RHE) which limits the conv ersion. As a consequence (CO)ads is the only species resulting from the dehydrogenation of methanol at low poten tial since it can not be further oxidized to CO2. This was confirmed by electro-modulated infrared reflectance spectroscopy (EMIRS).39 It is generally accepted that the adsorbed CO species poisons the platinum anode since its slow oxidation to CO2 leads to a very hi gh overpotential at the electrode. As a matter of fact even if platinum exhibits the higher activity in electrooxidation of methanol, the formation of CO during the process rapidly impedes its catalytic performance. On Pt/Ru alloy Platinum is the only single component catal yst that shows a significant activity for methanol oxidation. However due to the rapid poisoning of its surface there has been only moderate success for commercial appl ications in DMFC. There has been an intensive search for more active materials. Improved activity has been observed in multicomponent catalysts incorporating oxophilic me tals such a Pt/Ru system. The oxidation of methanol was extensively studied on Pt/R u in order to clarify the nature of the ruthenium promotion on platinum. It is we ll know now that the enhancement of the methanol oxidation on Pt/Ru catalysts in compar ison to Pt catalysts is attributed to the ability of Ru to adsorb and dehydrogenate wa ter at less positive potentials than Pt. These Ru oxygenated species then minimize the effect of the poisonous CO species by converting them to CO2. In 1975, Watanabe and Motoo gave the first explanation of the enhancement of the methanol oxidation at Pt/Ru alloys.40,41 They introduced the so-called concept of “bi-functional mech anism” where the two metals are acting cooperatively for a fast conve rsion of methanol to CO2. According to this mechanism, Pt is responsible for the methanol dehydrogena tion giving adsorbed CO species while the

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8 more oxophilic Ru is responsible for th e adsorption and dehydrogenation of water molecules giving the adsorbed OH species. As a result, the species adsorbed on platinum and ruthenium combine together forming CO2. The following mechanism was proposed: Pt CH3OHa d s Pt COa d s +4H++4e-CH3OH (1.18) Pt+H2O Pt OHa d s+H++e(1.19) Ru+H2O Ru OHa d s+H++e(1.20) Pt COads+Pt OHadsCO2+H++e(1.21) Pt COads+Ru OHadsCO2+H++e(1.22) Studies on Pt/Ru alloys concerning the ro le of Ru in promoting the methanol oxidation reveal that the electroni c effect of Ru on Pt is an important factor that favors the conversion of adsorbed CO to CO2. From FTIR studies42 it was observed that the coverage by COads on a Pt/Ru alloy is reduced compared to pure platinum. An increase of the stretching frequency of bound CO is also observed. The effect is that CO is less strongly adsorbed on a Pt/Ru alloy because the -back donation from Pt to the * orbital of CO is reduced compared to pure Pt. So co ncerning the mechan ism above, reaction (1.22) is faster than (1.21) because the Pt-CO bond is weaker which forms nucleophilic attacks by OHads. Another important factor comes from the fact that Ru is oxidized at far lower potential than Pt. Pure pl atinum decomposes water at 0.7 V vs. RHE (1.19), while on pure ruthenium the water di ssociation occurs at 0.2 V vs. RHE (1.20). The evidence that Pt/Ru alloys do form Ru oxo or Ru-OHads species at significantly lower potential than on pure platinum was proved by X-ra y photoelectron spectroscopy studies (XPS).43 The Ru-OHads formed can then promote the oxidation of COads to CO2.

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9 It appears also that the rate determin ing step of the mechanism is strongly influenced by the Pt:Ru ratio. This was supported by infrared studies.42 For a Pt/Ru alloy containing a 1:1 ratio of Pt:Ru, th e rate determining step is postulated to be the formation of the Ru-OHads species (1.20). The low coverage of the COads at the Pt/Ru alloy surface indicates that all COads produced in reaction (1.7) is consumed in reaction (1.22). However at low Ru content, IR data indicating high COads coverage of the surface of the alloy (almost the same as pure Pt) is consista nt with the rate determining step being now the removal of the COads in reactions (1.21) and (1.22). Other alloy systems Increased activity has been also observed with several other binary alloy systems such as Pt/Sn,44,45 Pt/Re,46 Pt/Ni47 and Pt/Rh.48 More complicated ternary systems such as Pt/Ru/Ni,47 Pt/Ru/Os,49 Pt/Ru/Rh48 and also quaternary systems like Pt/Ru/Mo/W50 and Pt/Ru/Os/Ir51 were found to be only sl ightly more efficient th an Ru/Pt in catalyzing methanol oxidation. Ruthenium Catalysts for the Oxidation of Alcohols Chemical Oxidation Since the early 1980s there have been exciting developments in ruthenium chemistry. Ruthenium complexes have a great potential for oxidation reactions of various compounds since ruthenium is one of the few am ong all the elements that displays a wide range of oxidation states in its complexes: from Ru(VIII) (d0) as in ruthenium tetroxide to Ru(-II) (d10). It is well documented that alcohols can be oxidized to the corresponding carbonyl compound by a variety of high oxidati on state oxo-ruthenate complexes. The highest valent ruthenium complex is ruthenium (VIII) tetroxide (RuO4),52 which is known as a powerful oxidant, that can oxidize stoichiometrically a va riety of organic substrates

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10 including primary and secondary alcohols to the corresponding ca rboxylic acids and ketones. RuO4 is rather non-selective often ca using multiple bond or aromatic ring rupture. The tetrahedral perruthenate ion [RuO4]is the only well-defined Ru(VII) complex. In aqueous solution [RuO4]oxidizes alcohols and aldehydes to ketones and carboxylic acids. The most im portant application of [RuO4]is the use of the organic soluble salt of perruthenate (NBun 4)[RuO4](TBAP) which is a remarkably gentle and selective oxidant for alcohols without competing reaction at a double bond. This oxidation can also be made catalytic by using N -methylmorpholine Noxide (NMO) as co-oxidant.53 A number of ruthenium (VI) oxidants have been studied for the oxidation of alcohols. Complexes with O-, Clor Ndonor ligands such as the hydroxo trans[RuO3(OH)2]2anion,54 the periodato trans-[RuO2{IO5(OH)}2]6-,55 the carboxylato trans[RuO2(OCOR)Cl2](R= Me, Et, Pr, CHF2),56,57 (Ph4P)[RuO2Cl3]58 or [Ru2O6 (py)4],59 can stoichiometrically or catalytically convert primary alcohols to aldehydes or secondary alcohols to ketones in the pres ence of excess persulfate, exce ss periodate or NMO as cooxidant. A series of -hydroxy carboxylate rutheniu m (V) species, (NPrn 4)[Ru(O) (O2COCRR'2)2] (RR'= Me2, MeEt, PhMe)60 has been synthesized and functions as a mild oxidant capable of slowly oxidizing alcohols to aldehydes or ketones. There have been many studies on ruth enium (IV) complexes, most of them concerning mono-oxo species containi ng polypyridyl ligands such as cis[RuO(py)(bipy)2]2+(py = pyridine). This complex wa s widely studed by Meyer et al.61,62 in the stoichiometric oxidation of primary and secondary alcohols. A detailed mechanism

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11 has been reported and it was shown that the reaction of cis-[RuO(py)(bipy)2]2+ and related complexes involves an in itial pre-association step be tween the reactants (Eq. 1.23) followed by a two electron hydride transfer mechanism with large C-H isotope effects ranging from 9 (CD3OH) to 50 (C6H5CD2OH) (Eq. 1.24), which is then followed by separation and rapid prot on equilibration (Eq. 1.25). (py)(bipy)2RuIV(=O)2++R2R1CHOH (py)(bipy)2RuIV(=O)2+,HC(OH)R1R2(py)(bipy)2RuIV(=O)2+,HC(OH)R1R2 [(py)(bipy)2Ru O H C(OH)R1R2]2+ (py)(bipy)2RuIIOH + ,R2R1COH+(py)(bipy)2RuIIOH + ,R2R1COH+ (py)(bipy)2RuIIOH2 2++R2R1C=O(1.23) (1.24) (1.25)fast Other mechanisms have been proposed involving hydrogen atom abstraction63 or oxygen insertion.64 Hydrogen abstraction was proposed for the oxo(phosphine)ruthenium (IV) complex [Ru(bpy)2(O)PPh3]2+ and was attributed to the electronic effect of the phosphine ligand in the oxo-ruthenium complex. The mechanism involves a partial hydrogen atom abstraction in the transiti on state leading to a hydroxoruthenium (III) complex and a benzyl alcohol radical fo llowed by a rapid step to form an aquoruthenium (II) complex and benzaldehyde (Eq.1.26). (PPh3)(bipy)2RuIV(=O)2++PhCH2OH (PPh3)(bipy)2RuIIOH2 2++PhCHO(1.26)fast(PPh3)(bipy)2RuIIIOH 2++PhCHOH. The oxygen insertion mechanism was obs erved with the oxo-ruthenium (VI) complex trans-[RuVI(tpy)(O)2(CH3CN)]2+ and was evidenced by 18O labeling studies and

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12 a large isotope effect which again implicates C-H bond involvement in the transition state. The mechanism is described by Eq. (1.27), (1.28) and (1.29). [RuVI(tpy)(18O)2(CH3CN)]2++PhCH2OH [RuVI(tpy)(18O)2(CH3CN)]2+,PhCH2OH (tpy)(CH3CN)(18O)Ru O H H Ph OH 2+ (tpy)(CH3CN)(18O)Ru O H Ph OH H 2+ [RuIV(tpy)(18O)(CH3CN)]2++PhCH(OH)(18OH) PhCHO+H2O(½18Oproducts)(1.27) (1.28) (1.29)IV 18 18 Low-valent ruthenium complexes can also be used for catalyzing the aerobic oxidation of alcohols to afford the corres ponding aldehyde or ketone and a ruthenium hydride complex. A number of catal ytic systems have been used.65 For example, RuCl2(PPh3)3 in combination with the st able nitroxyl radical, 2,2’,6,6’tetramethylpiperidine-N-oxyl (TEMPO)65 is a remarkably effective catalyst for aerobic oxidation acting as hydrogen transfer mediat or by promoting the regeneration of the ruthenium catalyst via oxidati on of the ruthenium hydride, resulting in the formation of the corresponding hydroxylamine derivative of TEMPO. The late r undergoes rapid reoxidation to TEMPO by mol ecular oxygen (Figure 1-2). Electrochemical Oxidation Many high oxidation state catalysts used in synthetic organic transformations have also been utilized in electrochemical transf ormation. The electrode replaces oxidants to generate selectively high-valent metal species needed for the selective oxidation of the alcohols and other organic substrates . Among the metal complexes used in

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13 electrocatalytic ox idation of alcohols, the pol ypyridyl oxo-ruthenium complexes previously mentioned, have attracted special attention,66-74 as for example R1R2CHOH R1R2CHO "Ru" RuH2 N OH N O .2 2 1/2O2H2O Figure 1-2. Ruthenium/TEMPO cataly zed aerobic oxidation of alcohols. [RuIV(trpy)(bpy)(O)]2+, [RuIV(bpy)2(py)(O)]2+, or [RuIV(trpy)(phen)(O)]2+ (phen = 1,10phenanthroline). These high oxidation st ate complexes are reached from the corresponding RuII-aqua complexes by sequential oxidatio n and loss of protons to give the corresponding ruthenium (IV)-oxo complex75 as described in (1.30) and (1.31) for [RuIV(trpy)(bpy)(O)]2+.76 [(trpy)(bpy)RuII(OH2)]2+[(trpy)(bpy)RuIII(OH)]2++H++e[(trpy)(bpy)RuIII(OH)]2+[(trpy)(bpy)RuIV(=O)]2++H++e(1.30) (1.31) In general, cyclic voltammograms of th e complexes in presence of the alcohol substrates show enhancement of the oxidati on current indicative of a catalytic process.67 For example cis-[Ru(L)(Cl)(H2O)][ClO4]2•2H2O77 [L = N,N’-dimethyl-N,N’-bis(2-pyridylmethyl)ethylene diamine] and trans-[RuIV(tmc)(Cl)(O)](ClO4)78 (tmc = 1,4,8,11tetramethyl-1,4,8,11-tetra-azcyclotetradecane) were found to be very active catalysts for oxidation of benzyl alcohol after electro-generation of the active species [RuV=O]. In

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14 addition cis -[RuV(L)(Cl)(O)]2+ [L = N,N’-dimethyl-N,N’-bis(2-pyridylmethyl)ethylene diamine] was found to be also an active catalyst for the elect ro-oxidation of methanol in aqueous solution.79 It has been demonstrated that these electrocatalytic systems are capable of providing a genera l and selective me thod for the oxidation of alcohols and diols by varying the experimental conditions such as pH, number of coulombs passed through the solution and temperature.67 In addition to the homogeneous systems, a number of techniques for attaching such electrocatalysts to the electrode surface have been also developed, as an approach to the modified electrode devices. This includes in corporation of the cat alysts in carbon paste electrodes,80-82 immobilization of the complex inside a Nafion film,82-86 grafting to a high surface graphite felt electrode87-89 or formation of anodic polymerized film of pyrroleligated Ru complexes.90,91 Cooperative Interaction in Heterobimetallic Catalysts Homogeneous catalysis with heterobime tallic complexes continues to draw considerable attention. This is largely due to the possibility of combining the different reactivities of the two metals in chemical transformations.92-98 The importance of heterobimetallic catalysts for catalysis is based on the following reasons. The close proximity of the two adjacent me tal centers offers the possibility of cooperative reactivity and different mechanistic roles of the metal centers can be expected.93,99-105 The cooperative bimetallic effect has been demonstrated in many examples of heterobimetallic complexes with unsaturated hydrocarbon bridges,106 complexes based on bridging ligands containing bi pyridine, phenanthroline and terpridine chelating units,107 as well as complexes containing µ-P-(CH2)n-Y (Y = P,S),108-110 µ-thiolate,111 µ-oxo112 or µ-halide113,114 bridged ligands. It ha s been shown that the cooperative effect in

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15 heterobimetallic complexes can enhance catalyt ic activities or can result in unique properties not observed in monomeric models.115-120 As an example, the heterobimetallic Rh/Ru catalyst [( 4-C4Ph4CO)Rh(µ-Cl)3Ru(PPh3)2(acetone)] was found to be very active in the Openauer-type oxidation of alcohol s showing turnover numbers up to 500 while the related homobimetallic complexes [( 4-C4Ph4CO)Rh(µ-Cl)2Rh( 4-C4Ph4CO)], [(PPh3)2(Cl)Ru(µ-Cl)3Ru(PPh3)2(acetone)] or [(PPh3)2(Cl)Ru(µ-Cl)2(µ-O=CH(NHPh)Ru (Cl)(PPh3)2)] are not active at all in the same reaction.121 This behavior has been also observed for the W-Rh heterobimetallic complex [(CO)4(PEtPh2)W(µ-PPh2)Rh (PPh3)(CO)],122 which shows higher activity and selectivity for hydroformylation of monosubstituted al kenes when compared to [RhH(CO)(PPh3)3], which is considered to be one of the more efficient catalysts. In contrast, the dimer [Rh(µ-PPh2)(cod)]2 only induces isomerization of alkenes. Another example is the selective oxidation of alc ohols catalyzed by the Os/Cr and Ru/Cr complexes [N(nBu)4][M(N)(CH2SiMe3)2(µ-O)2Cl2] (M = Ru,Os).112 Again these heterobimetallic systems exhibit improved reac tivity and selectivity for th e oxidation of primary and secondary alcohols to the corresponding carbonyl compound using molecular oxygen since the mononuclear complex is not selective at all and cannot use O2 in the catalytic process. Understanding the effects of changes in the ancillary ligands has led to great improvements in catalyst properties. Many of the techniques employed to study the different phenomena associated with the electr onic interaction between the metal centers have been already applied to homobimetallic mixed-valence complexes.123 Electrochemical techniques, in particular cyclic voltammetry106,124,125 have been among

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16 the most widely used to investigate metal-me tal interactions in heterobimetallic systems since the results can be compared with the mononuclear model systems.124 Several examples were observed in previous studi es on the heterobimetallic Mo/Pt complex [Mo(CO)3( µ -dppm)2Pt(H)]PF6,126 and the series of ruthenium-containing heterobimetallic complexes Cp(PPh3)Ru( µ -I)( µ -dppm)PtI2, Cp(PPh3)Ru( µ -I)( µ -dppm) PdCl2, Cp(PPh3)RuI( µ -dppm)AuI and Cp(PPh3)Ru( µ -I)( µ -dppm)CuI.124 The shifts of the redox potentials are usually c onsistent with electronic in teractions between the two metals through the bridging ligand. For exam ple, the cyclic voltammogram of complex Cp(PPh3)Ru( µ -I)( µ -dppm)PtI2 124 shows a 460 mV shift positiv e shift for the Ru(II/III) waves compared to the monomeric compound Cp(PPh3)Ru(I)( 1-dppm) as a result of electron donation from the Ru to Pt through the iodide bridge. Other specific techniques such as NMR, IR spectroscopy and X -ray crystallography are useful to study the structural informa tion in solution and solid state while UV-vis spectra and theoretical investig ations are valuable to classify the extent of interaction between the two metals.96,106,124,125,127-129 Heterobimetallic Catalysts for th e Electrooxidation of Methanol The development of heterobimetallic catalys ts for electrooxidation of methanol was initially motivated by literature results of introducing a second metal into bulk metal anodes,130-133 and also by the possibility that each metal center could exhibit cooperative activity or a unique mechan istic function. The choice of bis(diphenylphosphino)methane (dppm) as a brid ging ligand was directed by the fact that metal-phosphorus bonds are often very strong and two metals can be lo cked together in close proximity by a bidentate phosphine. Th e first generation of heterobimetallic complexes Cp(PPh3)Ru( µ -Cl)( µ -dppm)PtCl2 ( 1 ),134 Cp(PPh3)Ru( µ -Cl)( µ -dppm)PdCl2

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17 1 2 3 Figure 1-3. Thermal ellipsoid drawings of the molecular structures of complexes 1 ,134 2135 and 3 .135 Thermal ellipsoids are plotted at 50% probability. Phenyl rings and most hydrogen atoms are omitted for clarity.

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18 ( 2 ),135 and Cp(PPh3)RuCl( µ -dppm) AuCl( 3 )135 was prepared by the reaction of CpRu(PPh3)( 1-dppm)Cl ( 4 ) with Pt(COD)Cl2, Pd(COD)Cl2 and Au(PPh3)Cl, respectively. All of them possess a dppm linkage between Ru and the second metal center with a three-legged piano stool geometry at Ru (Figure 1-3). Complexes 1 and 2 possess a bridging chloride that links Ru centers and the quasi square planar Pt or Pd, in a distorted six-membered ri ng. In contrast, complex 3 is linked only via dppm in a pendant fashion with a linear configuration at the Au center. Cyclic voltammetry can be used to establish the metal-metal interactions in the heterobimetallic complexes (Table 1-1). Cyclic voltammetry of 1 and 2 demonstrates shifts in the formal potentials of Ru(II/III), Pt(II/IV) and Pd (II/IV) redox couples relative to the monomeric Ru, Pt, and Pd models, indicative of signifi cant electron donation through the chloride bridge from the Ru to th e electron deficient Pt or Pd centers. In contrast, the redox potentials of th e Ru(II/III) and Au(I/ III) couples in 3 are very similar to mononuclear complexes suggesting minimal interaction between the two metals via the dppm bridge. Cyclic voltammetry of complexes 1 3 in the presence of me thanol led to significant enhancement of oxidative current, consistent with a catalytic process (Figures 1-4, 1-5 and 1-6).126,134,135 Product Detection The electrooxidation of methanol has been investigated since the 1960’s and several reviews on methanol oxidation have been published.26,130 As previously described by Parson and Iwasita for oxidation on an a node surface, the si x-electron oxidation process involves a complicated multistep mechanism (Eq. 1.321.34), where methanol is converted to CO2 via formation of formaldehyde and CO. However, when the process is

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19 performed in solution in presence of homogeneous catalysts, formic acid is formed as the 4eoxidation product instead of carbon monoxide (Eq. 1.35, 1.36). Table 1-1. Formal Potentials of Complexes 1-3 . Complex Couple E1/2 (V)a Couple E1/2 (V)a Ru/Pt ( 1 )135 Ru(II/III) 1.13b Pt(II/IV) 1.78c Ru/Pd ( 2 )126 Ru(II/III) 1.29 Pd(II/IV) 1.45c Ru/Au ( 3 ) 135 Ru(II/III) 0.89 Au(I/III) 1.42c Rud Ru(II/III) 0.61 Ru e Ru(II/III) 0.87b Pt( 2-dppm)Cl2 136 Pt(II/IV) 2.21c Au(PPh3)Cl2 137 Au(I/III) 1.68b a All potentials obtained in DCE/TBAT (tetrabutylammonium triflate) and reported vs . NHE. b Performed in CH2Cl2/TBAH. c Irreversible wave, Epa reported. d Ru = CpRuCl(2-dppm). e Ru = CpRu(PPh3)2Cl. Figure 1-4. Cyclic voltammograms of 1134 under nitrogen in 2.5 mL of DCE/0.7 M TBAT (tetrabutylammonium triflate); glassy carbon working electrode; Ag/Ag + reference electrode.

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20 Figure 1-5. Cyclic voltammograms of 2135 under nitrogen in 2.5 mL of DCE/0.7 M TBAT (tetrabutylammonium triflate); glassy carbon working electrode; Ag/Ag+ reference electrode. Figure 1-6. Cyclic voltammograms of 3135 under nitrogen in 2.5 mL of DCE/0.7 M TBAT (tetrabutylammonium triflate); glassy carbon working electrode; Ag/Ag+ reference electrode.

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21 When methanol is used in excess during the homogeneous electrooxidation reaction, both formaldehyde and formic acid undergo condensation reactions with methanol to form dimethoxymethane and methyl formate as the 2eand 4eoxidation products, respectively (Eq. 1.37, 1.38). It is impor tant to point out th at the equilibria for these reactions are shifted to the right in the presence of an excess of methanol. As highlighted by Rand138 and Sermon,139 these reactions are also favored by the presence of acid catalysts. It is possible to follow the oxidation pro cess by analysis of the products. For example, a direct FTIR inves tigation of the methanol oxid ation in a prototype direct methanol fuel cell (DMFC)140 demonstrated that dimethoxym ethane, methyl formate and CO2 were the products of the electrooxidation process with pure meth anol in the anode feed. However, the product distribution is dependent on different factors including the activity of the catalyst, the methanol/water ratio, and the temperature of operation. Bulk Electrolysis with Complexes 1-3 Electrolyses with complexes 1-3 were performed for pr oduct identification and quantification. A potential of 1.7 V vs. NHE for the bulk was chosen in earlier studies, CH3OHHCHO+2H++2e-HCHO CO+2H++2e-CO+H2OCO2+2H++2e-(1.32) (1.33) (1.34) HCHO+H2O HCOOH+2H++2e-CO2+2H++2e-(1.35) (1.36) HCOOH HCHO+2CH3OH HCOOH+CH3OH H2C(OCH3)2+H2O HCOOCH3+H2O (1.37) (1.38)

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22 coincident with the redox of the second meta l. As previously mentioned, the oxidation products observed during the bulk electrolysis are dimethoxymethane (DMM) and methyl formate (MF) as the 2eand 4eoxidation products, respect ively. Methanol undergoes oxidation to formaldehyde and formic acid during the process, however, neither was observed in the reaction mixtures. Acid cat alyzed condensation of these products with excess methanol yields D MM and MF (Eq. 1.35, 1.37, 1.38) . The evolution of the product distributions as th e reaction progresses is s hown in Table 1.2. At low conversion, all of the hetero bimetallic catalysts afforded a much higher proportion of DMM. As the reaction progresses, the same tendency toward production of the more highly oxidized product (MF) can be observed fo r all the heterobimetallic catalysts. This is presumably due to the water formed in situ during the condensation of formaldehyde and formic acid with excess methanol. The presence of water during the experiments (wet conditions) shifts the product ratio toward the formation of MF, the four electron oxidation product. Table 1-2. Product Distributions and Current Efficiencies for Methanol Oxidation by 1-3 . Product ratios (DMM/MF)a,b Dry conditions Wet conditionsd Charge/ C 1 2 3 1 2 3 25 2.45 3.18 1.44 1.68 1.38 1.26 50 2.35 2.41 1.23 1.34 0.98 1.05 75 1.51 1.54 0.98 1.17 0.84 0.97 100 1.23 0.94 0.59 0.67 0.70 0.41 130 1.20 0.87 0.46 0.41 0.54 0.34 Current Efficiency (%)c 18.6 24.6 25.5 19.5 20.6 26.1 aElectrolyses were performed at 1.7V vs. NHE. A catalyst concentration of 10 mM was used. Methanol concentration was 0.35 M. bDetermination by GC with respect to n -heptane as internal standard. Each ratio is reported as an average of 2-5 experiments. cAverage current efficiencies after 75-130 C of charge passed.d Addition of 5µL of water.

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23 -12 x DMMmol 4 x MF(mol) ) Total Charge passed(C)Current Efficiency (%) x 96500 (C.mol x 100 (1.39) The current efficiencies (Eq. 1.39) for the oxidation processes are also summarized in Table 1-2. These values are the ratio of the charge necessary to produce the observed yield of DMM and MF to the total charge passed during the bulk electrolysis. Although the current efficiencies for the electrochemical oxidation of methanol are modest (18.6-26.1%), they are significantly higher compared to the monomeric Ru model compounds CpRu( 2-dppm)Cl113 showing low 3.2% and 7.2% current efficiencies in dry and wet condition, respectively. Complexes 1 , 2 and 3 were found to be effective cat alysts for electrooxidation of methanol, resulting in much higher current effi ciencies compared to those obtained with the monomeric model compound CpRu( 2-dppm)2Cl.113 Clearly, the significant enhancement of the catalytic ac tivity is due to the presence of the second metal. As a continuation, this dissertation will descri be the synthesis of new generations of heterobimetallic complexes for application in electrocatalytic oxi dation of methanol.

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24 CHAPTER 2 WATER SOLUBLE HETEROBIMETALLIC COMPLEXES Introduction Application of bimetallic catalysts to organic transformations has emerged dramatically in the last few years and huge progress has been made in research and development of such systems. Compounds wh ich contain two different metal centers have attracted particular interest due to the possibility of exploiting the different reactivities of the two metal centers in chemical transformations.92-98 It has been long recognized that interesting char acteristics such as cooperative behavior and/or different mechanistic roles of the metal centers can be expected when the two metals are in close proximity.93,99-105 The interest in the possibility of a su ch cooperative effect between the two differerent metal centers in homogeneous el ectrochemical oxidation of alcohols led to preparation and investigation of the electrochemical propert ies of the heterobimetallic complexes Cp(PPh3)Ru( µ -Cl)( µ -dppm)PtCl2 ( 1 ),134 Cp(PPh3)Ru( µ -Cl)( µ -dppm)PdCl2 ( 2 )135 and Cp(PPh3)RuCl( µ -dppm)AuCl ( 3 ).135 Electrooxidation of methanol with complexes 1 3 proved to be successful since the results with these catalysts showed significant increases in the current efficien cies compared to those of the mononuclear model compounds CpRu( 2-dppm)Cl,113 or CpRu(PPh3)2Cl.141 Clearly the significant enhancement of the catalytic activity is due to the pres ence of the second metal.

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25 Electrochemical Oxidation of Methanol in Aqueous Media The oxo-ruthenium complexes have received a lot of attention in view of their potential as catalysts for th e electrooxidation of alcohols.66-78 Many monomeric Rupolypyridine based complexes such as [RuIV(bpy)2(py)(O)]2+ have been developed and were found to be very efficient in catalyz ing the electrooxidation of alcohols to the corresponding carbonyl compounds in aqueous media. Previous studies in the McElwee-White group have been carried out in nonaqueous media (1,2-dichloromethane) due to th e solubility of the previously synthesized catalysts in non-polar solvents. Of course in order to compare the behavior of these compounds with those well know n ruthenium-oxo catalysts already published in the literature, a switch to aqueous media would be more informative because the complexes could be studied under the same conditions. Additionally, since the mechanism of the electrooxidation of methanol involves the formation of a Ru-oxo intermediate by activation of a water molecule, the poor sol ubility of the compounds in aqueous media could be a limitation during the catalysis in organic media. In this chapter several attempts to synthesize water soluble heterobimetallic complexes have been carried out by modification of the ancillary ligands of the first generation complexes. Water-Soluble Catalysts Since complexes 1-3 and related species exhibit poor solubility in water, several modification strategies can be propose d. Moving to aqueous systems can be accomplished by synthesizing heterobimetallic compounds using water soluble versions of the ancillary ligands. This technique has been already used in the past with success. The possible strategies for wa ter soluble modifications are depicted in Figure 2-1. A possible strategy to enhance the solubility in aqueous media is to functionalize the

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26 cyclopentadienyl ligand with an am ino group or by its quaternization.142-144 Several examples have been published with applications for biological activity145,146 such as the titanocene dichloride [ 5-C5H4CH2CH2NMe2•HCl]2TiCl2 used against human lung cancer and ovarian cancer.147 Another possible approach i nvolves the use of water solu ble phosphines such as (3sulfonatophenyl)phosphine (TPPM S) or tris(3-sulfonatoph enyl)phosphine (TPPTS). In general both are used as their sodium salts a nd their solubilities in water are respectively, 80 g.dm-3 and 1100 g.dm-3. The monosulfonated triphe nylphosphine, TPPMS, was initially synthesized in 1958148 and is used as a ligand for a large variety of biphasic metal catalyzed reactions such as hydroge nation of cyclohexene or styrene using [Ru(H)Cl(CO)(TPPMS)3]•2H2O in water/decalin solutions149 or hydrogenation of aldehydes with [RuCl2(TPPMS)2] to give the corresponding alcohol.150 The use of trisulfonated TPPTS as a ligand has been stud ied when high solubility in aqueous media was required. It has been efficiently used as a ligand in transition metal complexes for the hydroformylation reaction in water/organic systems using [Rh(acac)(CO)2]/TPPTS.151 Another alternative can be the 1,3,5-triaza-7-phosphaadamantane (PTA). This ligand was found to have similar solubility to the TPPM S sulfonated ligand and was also applied to biphasic homogeneous catalysis. An example is the complex [RhCl(PTA)3] which is an active catalyst for hydrogenation of various ol efinic acids and ally lic alcohols in water.152 The use of water soluble derivatives of the bidentate phosphine dppm has been considered as a possible candidate since the dppm ligand is strongly bonded to the metals in the heterobimetallic complexes. A lthough syntheses of sulfonated compounds containing longer carbon chains between th e two phosphorus atoms have been reported

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27 [e.g. dppets: tetra-sulfonated -bis(diphenylphosphino)ethane , dpppts: tetra-sulfonatedbis(diphenylphosphino)propane, dppbts: tetra-sulfonated-bi s-(diphenylphosphino)butane ],153 the synthesis of the sulfonated water soluble dppm analogue is not found in the literature. Attempts to sulf onate dppm in the same manner as described for dppets, dpppts and dppbts will be described. N Ru Ph3P Cl Ph2P PPh2 Pt Cl Cl Ph2P SO3Na P SO3Na 3 or P P SO3Na NaO3S 2 2 NHMe2 P N N orTPPMS TPPTS PTA Figure 2-1. Schematic representation of the strategies used for preparing water-soluble derivatives of complex 1 . Amino-Substituted Cyclopentadienyl Complexes Compound M X 8 Pt Cl 9 Pt I 10 Pd Cl Ru Ph3P I Ph2P PPh2 M X X NHMe2 11 Pd I Figure 2-2. Struct ures of compounds 8-11 .

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28 Synthesis The synthesis of the cyclopentadienyl derivative 4 (Figure 2-3) can be accomplished following a known procedure by direct reaction of sodium cyclopentadienide with freshly distilled 2-chloroN , N -dimethylethanamine. After fractional distillation under vacuum, compound 4 was isolated in 60% yield as a yellow oil containing a mixture of two regioisomers . This compound is temperature sensitive and rapidly undergoes Diels-Alder di merization if stored at room temperature. Degradation can be avoided by storing freshly prep ared samples at -30ºC under nitrogen. Synthesis of the Ru Complexes 5-8. Following the procedure previously reported for CpRu(PPh3)2Cl, Ru complex 5 was prepared by reacting RuCl3•xH2O, PPh3 and Cpamine compound 4 in refluxing ethanol. Depending on th e scale of the reaction (usually 1 gram), the hydrated RuCl3 starting material can be conve rted in approximately 2-3 days to the bright brown-orange products (84% yield) (Figure 2-3). This complex is moderately stable in the solid state and need s to be stored under an inert atmosphere of nitrogen. Solution of 5 slowly degrades if manipulated outside a glove box as observed by the change of color from orange to dark brown. As previously observed for related complexes,113 the substitution of Cl by I usually conf ers an increase in the stability of the compounds. The chloride intermediate 5 can be converted to th e more stable complex 6 by protonation of the amine mo iety in the presence of 1 M degassed hydrochloric acid followed by halide substitution with 10 equivalents of NaI in dichloromethane. The iodide complex 6 can be obtained in 85 % yield afte r these two successive steps as a bright orange solid (Figure 2-3). The last step to the intermediate 7 is a direct reaction of the iodide compound 6 with bis(diphenylphosphino)methane (dppm) in tetrahydrofuran (Figur e 2-3). This step

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29 requires several days of reaction at room temperature since the substitution is slow. Increase of the temperature does speed up the substitution but also decreases the yield of the reaction due to the formation of the unwanted [ 5-C5H4CH2CH2NMe2•HI] (PPh3)Ru( 2-dppm)I. Crude product from room temperature reaction requires only several recrystallizations using dichlorome thane/hexane to obtai n a clean pure product (92% yield). However, impur e material can be purified by column chromatography. The red-orange solid 7 complex is air stable but a soluti on of the complex slowly degrades after several hours exposure to air. Ru Ph3P I Ph2P PPh2 NHMe2 Ru Ph3P I PPh3 NHMe2 Ru Ph3P Cl PPh3 NMe2 Na+ Cl NMe2 THF,reflux NMe2 RuCl3-xH2O,PPh3Ethanol,reflux 4 5 Ru Ph3P Cl PPh3 NMe2 5 61)1MHCl 2)NaI/CH2Cl2 dppm THF,RT7 Figure 2-3. Synthetic pathway to Ru complexes 5-7 . Synthesis of the Ru/Pt Complexes 8 and 9. The reaction of Ru complex 7 with Pt(COD)Cl2 or Pt(COD)I2 at room temperature afforded the resulting heterobimetallic complexes 8 and 9 as a yellow and a red-orange pow der, respectively (Eq 2.1 and 2.2). The formation of complex 8 is usually accompanied by a small amount of Pt( 2dppm)Cl2 formed by dppm transfer from the [ 5-C5H4CH2CH2NMe2•HI](PPh3)Ru( 1dppm)I ( 7 ) to the Pt center. Complexes 8 and 9 are air stable in their solid state but show signs of decomposition when expos ed to air for several days.

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30 Synthesis of the Ru/Pd Complexes 10 and 11. The Ru/Pd complex 10 was prepared in a similar manner to complexes 8 and 9 by reaction of [ 5C5H4CH2CH2NMe2•HI](PPh3)Ru( 1-dppm)I ( 7 ) with Pd(COD)Cl2 in dichloromethane at Ru Ph3P I Ph2P PPh2 Pt Cl Cl NHMe2 Ru Ph3P I Ph2P PPh2 NHMe2 7 I-IPt(COD)Cl28 Ru Ph3P I Ph2P PPh2 Pt I I NHMe2 I-9 Pt(COD)I2 (2.1) (2.2) room temperature (Eq. 2.3). The I-bridged co mplex can be obtained as a yellow powder after several successive recrystallizations us ing dichloromethane/hexanes as solvent (66% yield). The synthesis of complex 11 requires an additional step since Pd(COD)I2 is not commercially available. Instead, 11 was synthesized by generating complex 10 in-situ in dichloromethane, followed by 48 hours reac tion at room temperature with five equivalents of NaI. The resulting compound can be purified by filtration and successive recrystallizations (CH2Cl2/Hexane) yielding a dark purple solid in 65% yield. Complexes 10 and 11 show very similar st abilities as compared to the Ru/Pt analogues 8 and 9 . As seen above, the ammonium substituted cyclopentadienyl complexes 8-11 were synthesized successfully. Unfortunately, the a mmonium moiety did not confer sufficient solubility in aqueous solution for the electrochemical experime nts. However, in contrast

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31 to the original compounds 1-3 , these compounds show solubility in polar solvents such as methanol. The electrolysis results will be presented in the next chapter. Additionally, the Ru Ph3P I Ph2P PPh2 Pd Cl Cl NHMe2 Ru Ph3P I Ph2P PPh2 NHMe2 7 I-IPd(COD)Cl210 Ru Ph3P I Ph2P PPh2 Pd I I NHMe2 I-11 1)Pd(COD)Cl2 (2.3) (2.4)2)NaInon-protonated amino-complexes of 8-11 were also successfully obtained ( 8' 11' , respectively) (Figure 2-4). These complexe s can be synthesized following the route described in Figure 2-3 but omitting the HCl st ep. After successive treatments with NaI and with dppm complexes 8'-11' were obtained in a simila r manner to the protonated analogues. NMR Data 1H and 31P {1H} NMR were the major tools for the characterization of the complexes (Table 2-1). The 31P NMR spectra of complexes 5 and 6 were recorded in CDCl3. Both compounds exhibit a singlet at 39.20 ppm and 37.85 ppm, respectively, suggesting that the two triphenylphosphines c oordinated to the Ru center are in the same environment. The 1H NMR spectra of the monometallic Ru complexes 5 and 6 also show similar features, which are two broad singlets fo r the olefinic protons from the Cp ring at 3.80 and 3.51 ppm for complex 5 and at 4.19 and 3.61 ppm for 6 . Each complex also

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32 Ru Ph3P I Ph2P PPh2 Pt Cl Cl NMe2 8' Ru Ph3P I Ph2P PPh2 Pt I I NMe2 9' Ru Ph3P I Ph2P PPh2 Pd Cl Cl NMe2 10' Ru Ph3P I Ph2P PPh2 Pd I I NMe2 11'Figure 24. Struct ures of compounds 8'-11' . exhibits a singlet at 2.82 ppm for 5 and 2.76 ppm and 6 , assigned to the six methyl protons from the amino moiety. As expect ed, three resonances are observed in the 31P {1H} NMR spectra of [ 5-C5H4CH2CH2NMe2•HI](PPh3)Ru( 1-dppm)I ( 7 ). An upfield doublet of doublets at -26.64 ppm is assigned to the non coordinated phosphine moiety of dppm while two downfield doublets of doublets are observed at 43.85 ppm and 33.89 ppm which were assigned to the Ru-coor dinated triphenylphosphine and the Rucoordinated diphenylphosphine from dppm, respectively. 1H NMR of complex 7 shows features similar to thos e of the monomeric compound 6 . Two broad doublets are observed at 4.36 ppm and 4.22 ppm for the Cp protons an d one singlet is observed at 2.19 ppm for the methyl protons of the dimethylamine group. Additional signals can be detected for the diastereotopic methylene protons of dppm a ppearing as two multiplets at 3.47 and 3.11 ppm. The 31P NMR spectra of complexes 8-11 showed signals for the phosphine ligands similar to those previously reported for complexes 1134 and 2 .135 Three doublets of doublets are always observed, the two downfie ld resonances corresponding to the Rubound phosphorus (Ru-PPh3 and Ru-PPh2-) while the upfield doublet of doublets is assigned to phosphorus coordinated to the seco nd metal. A downfield shift is observed for the phosphorus signal after coordi nation of the second metal with the diphenylphosphine moiety of dppm. The 31P NMR spectrum of complex 8 exhibits three

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33 signals, two downfield doublet s of doublets at 40.98 and 47.37 ppm, assigned to the Rubound phosphorus of PPh3 and to the Ru-bound phosphorus of dppm, respectively. The more upfield signal, appearing also as a doubl et of doublets at -7.21 ppm, can be easily assigned to the Pt-bound phosphor us of the bridged dppm. The 1H NMR spectrum of 8 exhibits two broad singlets fo r the four protons of the Cp ring appearing slightly shifted downfield at 4.44 ppm and 4.26 ppm when co mpared to the monometallic complex 7 . Complex 9 also shows the same features observed for 8 in the 31P {1H} NMR spectrum. The two downfield doublets of doubl ets are assigned to the Ru-bound PPh3 and dppm at 39.36 ppm and 46.65 ppm while the upfield double t of doublets at 1.84 ppm is assigned to the Pt-bound phosphorus of the dppm bridge. As expected, the Ru/Pd analogues 10 and 11 show similar resonances compared to the Ru/Pt complexes 8 and 9 , with slight differences due to the electronic change from Pt to Pd. Complexes 10 and 11 also exhibit two downfield doublets of doublets at 41.26 ppm and 51.22 ppm for complex 10 and 39.38 ppm and 49.45 ppm for complex 11 . Additionally the Pd bound phosphor us appears also as a doublet of doublets in the upfield section of the spectrum at 11.73 ppm for complex 10 and at 13.83 ppm for 11 . The 1H NMR spectra of 10 and 11 do not show significant changes in the chemical shifts when compared to the Pt analogues 8 and 9 . The Cp protons, the di astereotopic methylene protons of dppm as well as the dimethylamin e protons can be observed at approximately similar chemical shifts. The effect observed after coordination of the second metal at the PPh2-dppm affects the 31P NMR shifts of the Ru-bound phosphorus. The 31P NMR for Ru-PPh2 bound phosphorus shows a significant downfie ld shift of about 14 ppm in all compounds 8-11 when compared to the one from complex 7. As a result, the phosphorus

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34 resonance of the Ph3P-Ru is observed more upfield compared to the one for Ru-PPh2in all the heterobimetallic complexes 8-11 . Similar effects were observed in the original compound bearing a regular cyclopentadienyl ring.124,134,135 The non-protonated amine compounds 8'-11' show similar chemical shifts in 1H and 31P NMR. The removal of this proton does not seem to affect the complexes since no changes are observed. X-Ray Structures Many attempts were performed in order to obtain suitable crystals for X-ray analysis of complexes 8-11 . The resulting crystals were not good enough (too small or not single crystal) for stru cture determination. From all of the complexes only the nonprotonated complex 8' gave satisfactory results. Crystallographic details for the I-bridged complex 8' are provided in Table 2-2. The structure is similar to thos e of I-bridged complexes pr eviously reported, where the coordination about the ruthenium atoms reta ined a piano-stool c onfiguration and the coordination about the Pt atom is a distorte d square planar. Shown in Figure 2-5 is the ORTEP drawing of the Ru/Pt complex 8' . Selected bond distances and bond angles for complex 8' appear in Table 2-2. The M-IM´ angle and bo nd distances in 8' fall within the range of expected values, with asymmetric Ru-I (2.6694(5) Å) and Pt-I (2.5732(4) Å) distances. The Ru-I distance for 8' is comparable to the value of 2.6749(5) Å reported for CpRu(PPh3)( µ -I)( µ -dppm)PdCl2 ( 2 ).135 As expected the amino group from the Cp ring is pendant and does not seem to interact with the rest of the molecule. Cyclic Voltammetry The CV data for complexes 5-11 are listed in Table 2.4. The cyclic voltammetry of the monometallic ruthenium complexes generally exhibits two waves. The first one is

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35 assigned to the Ru(II/III) redox c ouple while the sec ond one is assigned to the Ru(III/IV) couple. In the case of the amino-substituted compounds a third wave is also observed due to the oxidation of the amino moiety. This el ectrochemical process has been previously described for aliphatic amines.154,155 Tertiary aliphatic amin es can be oxidized to a radical cation (Eq. 2.5) which can depr otonate to give a radical (Eq. 2.6). Figure 2-5. ORTEP drawing of the molecular structure of [ 5-C5H5CH2CH2N(CH3)2] Ru(PPh3)( µ -I)( µ -dppm)PtCl2 ( 8' ). Thermal ellipsoids are plotted at 50% probability. Phenyl rings and hydrog en atoms are omitted for clarity.

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36 Table 2-1. NMR (1H, 31P{H}) data for complexes 5-11 . 1H NMR ( )a 31P {1H} NMR ( )a Cp -C H2-NH(C H3)2 Ph3P-Ru Ru-PPh2PPh2 or Ph2P-M 5 3.80 (br s), 3.51 (br s) 2.82 (s) 39.20 6 4.19 (br s), 3.61 (br s) 2.76 (s) 37.85 7 4.36 (br s), 4.22 (br s) 3.47 (m), 3.11 (m) 2.19 (s) 43.85 (dd, JPP = 41 Hz) 33.89 (dd, JPP = 21, 41 Hz) 26.64 (dd, JPP = 3, 21 Hz) 8 4.44 (br s), 4.26 (br s) 3.50 (br s), 3,05 (br s) 2.39 (s) 40.98 (dd, JPP = 3, 35 Hz) 47.37 (dd, JPP = 13, 35 Hz) 7.21 (dd, JPP = 3, 13 Hz) 9 5.75 (br s), 4.47 (br s) 5.29 (br s), 2.66 (br s) 3.07 (s) 39.36 (dd, JPP = 34 Hz) 46.65 (dd, JPP = 12, 35 Hz) 1.84 (dd, JPP = 3, 12 Hz, ) 10 5.26 (br s), 4.40 (br s) 4.31 (br s), 3.72 (br s) 2.42 (s) 41.26 (dd, JPP = 35 Hz) 51.22 (dd, JPP = 23, 34 Hz) 11.73 (dd, JPP = 22 Hz) 11 5.73 (br s), 4.44 (br s) 5.27 (br s), 2.60 (br s) 3.08 (s) 39.38 (dd, JPP = 6, 35 Hz) 49.45 (dd, JPP = 22, 35 Hz) 13.83 (dd, JPP = 6, 22 Hz) a Spectra measured in CDCl3 at room temperature.

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37 Table 2-2. Selected bond distan ces (Å) and angles (º) for [ 5-C5H5CH2CH2N(CH3)2]Ru (PPh3)( µ -I)( µ -dppm)PtCl2 ( 8' ). Pt-P3 2.2170(13) Pt-Cl2 2.3284(13) Pt-Cl1 2.4071(14) Pt-I 2.5732(4) Ru-C3 2.178(5) Ru-C4 2.194(5) Ru-C2 2.225(5) Ru-C5 2.229(5) Ru-C1 2.266(5) Ru-P2 2.3070(13) Ru-P1 2.3407(12) Ru-I 2.6694(5) P1-C16 1.831(5) P1-C10 1.842(5) P1-C22 1.844(5) P2-C28 1.839(5) P2-C34 1.845(5) P2-C52 1.868(5) P3-C46 1.823(5) P3-C40 1.830(6) P3-C52 1.857(5) N1-C8 1.423(11) N1-C7 1.443(8) N1-C9 1.474(9) P3-Pt-Cl2 94.53(5) P3-Pt-Cl1 175.78(5) Cl2-Pt-Cl1 89.37(5) P3-Pt-I 87.68(4) Cl2-Pt-I 176.63(4) Cl1-Pt-I 88.50(3) P2-Ru-P1 98.34(5) P2-Ru-I 89.98(3) P1-Ru-I 91.17(3) Pt-I-Ru 102.754(14) C8-N1-C7 110.7(7) C8-N1-C9 111.0(7) C7-N1-C9 109.9(6) P3-C52-P2 120.9(3) Table 2-3. Crystal data and st ructure refinement for complex 8'. Empirical formula C54 H53 Cl8 I N P3 Pt Ru Mr 1515.54 T/K 173(2) /Å 0.71073 Crystal system Monoclinic Space group P2(1)/n a /Å 14.1702 (8) b /Å 23.3127 (12) c /Å 18.167 (2) / 90 / 107.566 (2) / 90 V /Å3 5721.7 (5) Z 4 Dc/Mg.m-3 1.759 µ /mm-1 3.740 F000 2960 Crystal size/mm3 0.12 × 0.06 × 0.05 Range/ 1.46 to 27.50 Index ranges -18 h 18 -30 k 30 -23 l 23 Reflection collected 50597 Independent reflections (Rint) 13068 (0.0477) Completeness to = 27.49 (%) 99.3 Absorption correction Integration

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38Max./min. transmission 0.8603/0.5805 Data/restraints/parameters 13068 / 0 / 625 GOF on F2 1.163 R 1a 0.0454 wR 2b 0.0819 Largest diff. peak, hole/e Å-3 1.531, 1.080 a R 1 = (|| Fo| | Fc||)/ | Fo|, b wR 2 = [ [ w ( Fo 2Fc 2)2]/ [ w ( Fo 2)2]1/2, S = [ w ( Fo 2Fc 2)2]/( n – p )]1/2; w = 1/[ 2( Fo 2) + 0.0337 p )2 + 1.24p]; p = [max( Fo 2, 0) + 2 Fc 2]/3. (RCH2)3N (RCH2)3N -e-+.(RCH2)3N +. -H + (RCH2)2NCHR+H.+ (2.5) (2.6) Protonation of the amine moiety should gi ve electrochemically inactive ammonium ions that exhibit the regular waves obs erved for the mono and heterobimetallic complexes. However, it appears that the cyclic voltammetry of all the ammonium complexes performed in DCE always exhibits a small wave due to the oxidation of the amine moiety. This phenomenon is probably due to the presence of small amount of non-protonated amine in the samples. The cy clic voltammetry performed in methanol does not show this wave. Voltammetry of Complexes 8-11 Electronic interactions between the two metals in the I-bridged heterobimetallic complexes 8-11 are evidenced by significant redox potenti al shifts compared to those of the monometallic model compound 7 . The cyclic voltammograms of the Ru/Pt complexes 8 and 9 performed in DCE exhibit four redox waves each. The second and fourth waves are due to the Ru(II/III) and Ru(III/IV) couples , while the third wave is assigned to the Pt(II/IV) redox couple of platinum. A small fi rst redox wave is also observed and has been assigned to the oxidation of the re sidual non-protonated amines. As expected, electronic interactions between the metal cente rs are observed for those complexes due to

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39 the presence of the iodide bridge. This behavior has already been described for complexes 1134 and 2135 and also for analogue compounds.124 Other examples will be described in Chapter 4. The potentials for th e Ru(III/IV) waves are not affected by the changes of the ligands around the Pt center for 8 and 9 . In contrast, comparison of the Pt substituted chloride 8 with the iodide complex analogue 9 reveals a significant 430 mV negative shift of the Ru(II/III) redox potential as a result of an increase of the electron density at the Pt center. A similar effect is al so observed at the Pt center with the Pt(II/IV) redox couple found to be easier to oxidize by 160 mV, as the chlorides are replaced by iodide ligands. It is very interesting that changing the halides in the ancillar y ligand of platinum affects not only the Ru(II/III) and Pt(II/IV) redox waves but also affects the redox potentials of the amine oxidation waves of the cyclopentadienyl ring. A considerable 610 mV negative shift is observe d for the oxidation of the amine when the electron density is increa sed at the Pt center. It is not surprising to observe the sa me behavior for the palladium analogue complexes 10 and 11 . The cyclic voltammograms for the Ru/Pd compounds 10 and 11 each exhibit irreversible oxidations at 1.35 V and 1.00 V vs. NHE, respectively, assigned to the Ru(II/III) couples. As for 8 and 9 an important 350 mV ne gative shift is observed when the chlorides are substituted by iodides at the Pd centers of 10 and 11 . Complexes 10 and 11 exhibit also a quasi reversible Pd(II/IV) redox wave at 1.67 V and 1.57 V vs. NHE, respectively. The same behavior is also observed for the Pd(II/IV) redox wave of the Ru/Pd complexes 10 and 11 . The Pd(II/IV) couple for the iodide compound 11 is found to be easier to oxidize by 100 mV when compared to the Pd(II/IV) couple for the chloride compound 10 . Again the residual non protonated amine complexes show the

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40 effect of increasing the elec tronic density at the Pd center since the amine oxidation is shifted by 480 mV negative when chlorides ar e substituted by iodides at the Pd center. Comparisons of the heterobimetallic complexes 8-11 with the mononuclear complex 7 exhibit shifts that are attributed to the electron donati on through the iodide bridges. In fact significant el ectron donation is always obser ved from the Ru center to the more electron poor Pt or Pd in chloride complexes 8 and 10 . The Ru(II/III) couples are found to be higher in potential when compared to the monomeric complex 7 (1.36 V, 1.35 V and 1.05 V for 8 , 10 and 7 , respectively). In contrast, the presence of the iodide ligands at the Pt or Pd centers of 9 and 11 disfavors the electron donation from the Ru to the second metal (Pt or Pd) through the iodide bridge. As a result th e Ru(II/III) oxidation waves are shifted to lower potential due to a more electron-rich ruthenium center for complexes 9 and 11 . Attempted Synthesis of Ruthenium Comple xes Including Water-Soluble Phosphines Synthesis of TPPMS and TPPTS In order to provide greater solubility in aqueous media, the use of water soluble phosphine ligands was investig ated. All the triphenylphosphin e analogs (n = 1,3) were synthesized using the known procedures156 described in Eq 2.5. However, only the mono(3-sulfonatophenyl)phosphine (TPPMS) and tr is(3-sulfonatophenyl)phosphine (TPPTS) were used for coordination with ruthenium. TPPMS ( 12 ) and TPPTS ( 13 ) can be selectively obtained using similar experiment al procedures but using a longer reaction time for the latter one. Reaction of triphenyl phosphine with fuming sulfuric acid followed by treatment of 5% NaOH afforded TPPMS ( 12 ) after two hours and TPPTS ( 13 ) after 24hrs. Usually the crude products contain poly -sulfonatophenyl mixtur es. Purification of these compounds can be carried out via co lumn chromatography using Sephadex G15 as

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41 support and degassed water as eluent. TPPMS and TPPTS, respectively, were obtained as white solids in 30% and 22.5% yield. The 31P {1H} NMR spetrum of the TPPMS in D2O shows a unique singlet at – 5.61 ppm (4.03 ppm in CD3OD), while the tris-substituted analog shows a singlet at -5.18 ppm in D2O. Ph(3-n)P SO3Na n •xH2O PPh3 1)Oleum 2)toluene/triisooctylamine 3)5%NaOH Oleum=fumingsulfuricacid,30%wtSO 3 free12 n=1"TPPMS" 13 n=3"TPPTS" (2.5) Synthesis of the Sulfonato Complexes 13 and 14 Formation of the ruthenium complexes w ith these sulfonated phosphines was found to be a challenging task. Direct reaction of RuCl3•xH2O, cyclopentadienyl and TPPMS in refluxing ethanol does not afford the expect ed complex. Better results were obtained by displacement of PPh3 by TPPMS or TPPTS from CpRu(PPh3)2Cl. When exactly two equivalents of TPPMS or TPPTS ar e refluxed in THF with CpRu(PPh3)2Cl, the reaction leads to a clean formation of complexes 13 (96% yield) or 14 ( 63% yield) (Eq. 2.6). These complexes can be obtained as yellow-orange solids, both exhibiting a unique singlet in the 31P {1H} NMR spectrum at 40.19 ppm a nd 40.60 ppm, respectively. The mono-substituted product was not observed wh en the reaction was performed with one equivalent of TPPMS or TPPTS, resu lting in formation of mixtures of 13 or 14 together with starting material. The use of excess of sulfonated phosphorus ligands results in purification problems caused by the low air stability of 13 or 14 . Attempts to purify complexes 13 and 14 by column chromatography results in degradation of the complexes.

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42 Table 2-4. Formal potentials for complexes 5-11 . Complexes solvent Couple Epa/V Couple Epa/V E1/2 b/V Couple Epa/V E1/2 b/V Couple Epa/V N,Ndimethylphenethylamine DCE amine 1.35 Ru(II/III) Ru(III/IV) 5 DCE amine 1.11 Ru(II/III) 0.85 0.78 Ru(III/IV) DCE aminea 0.60 Ru(II/III) 0.83 0.76 Ru(III/IV) 1.64 6 MeOH amine Ru(II/III) 0.82 0.76 Ru(III/IV) c DCE aminea 0.78 Ru(II/III) 1.05 0.96 Ru(III/IV) 1.95 7 MeOH amine Ru(II/III) 1.00 0.94 Ru(III/IV) c DCE aminea 1.26 Ru(II/III) 1.36 Pt(II/IV) 1.72 Ru(III/IV) 1.98 8 MeOH amine Ru(II/III) 1.32 Pt(II/IV) c Ru(III/IV) c DCE aminea 0.65 Ru(II/III) 0.93 0.82 Pt(II/IV ) 1.56 1.45 Ru(III/IV) 2.01 9 MeOH amine Ru(II/III) 0.83 Pt(II/IV) 1.55 Ru(III/IV) c DCE aminea 1.12 Ru(II/III) 1.35 Pd(II/IV) 1.67 1.52 Ru(III/IV) 2.04 10 MeOH amine Ru(II/III) 1.33 Pd(II/IV) c Ru(III/IV) c DCE aminea 0.64 Ru(II/III) 1.00 Pd(II/IV) 1.57 1.47 Ru(III/IV) 2.09 11 MeOH amine Ru(II/III) 0.93 Pd(II/IV) 1.46 Ru(III/IV) c All potentials obtained in 0.1 M DCE/TBAT (tetrabutylammonium triflate)or in 0.1 M MeOH/TBABF4 (tetrabutylammonium te trafluoroborate), reported vs. NHE and referenced to Ag/Ag+.a presence of non protonated amine in samples. b E1/2 reported for reversible waves. c oxidation wave covered by the solvent current.

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43 Complexes 13 and 14 were both reacted with dppm in THF. The reaction proceeds slowly and requires 14 days for comp letion at 40-43 ºC to obtain complex 15 and 16 , respectively. Below this temperature, no r eaction occurs and at higher temperature the major major product is [CpRu( 2-dppm)(L)]I (L=TPPMS, TP PTS). During the reaction one equivalent of TPPMS or TPPTS is released. Although complexes 15 and 16 were successfully formed in the reaction, it was very difficult to separate the TPPMS or TPPTS free ligands from the expected compound due to the low stability of 15 and 16 . These complexes easily convert to [CpRu( 2-dppm)(L)]I, (L=TPPMS, TPPTS) during the purification on a Sephadex G15 column. Ot her attempts to purify the complexes were not successful such as alumina or silica gel column as well as recrystallizations using different solvent mixtures. Ru Ph3P Cl PPh3 TPPMS(orTPPTS) THF,reflux Ru Ph2P Cl Ph2P NaO3S Ru Ph2P Cl PPh2 NaO3S SO3Na PPh2 dppm THF,40-43°C 14days13(14) 15(16)(2.6) Attempted Synthesis of Heterobimetal lic Complexes Incorporating TPPMS and TPPTS Ligands Several attempts to form heterobimetallic complexes from 13 and 14 gave only negative results. When 14 or 15 was reacted with Pt(COD)Cl2 or Pd(COD)Cl2, no identifiable heterobimetallic product was obtained. The major products formed were Pd( 2-dppm)Cl2 or Pt( 2-dppm)Cl2, along with bis-phosphino-sulfonated platinum or palladium compounds. This is without doubt due to the presence of re sidual free ligand in the mixture. When analyzing the results, it seems obvious th at a decoordination of dppm from the ruthenium center occurs, and is followe d by transfer of the dppm to the Pt or Pd.

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44 Several tests were performed to see if ruthenium complexes of TPPMS and TPPTS were stable in aqueous media. The dissolu tion of these comple xes in degassed water showed good solubility, however after several hours, degradation of the solutions was observed. This was confirmed by a 31P {1H} NMR experiment in D2O . Synthesis of Complex CpRu(PTA)2I (17) 1,3,5-Triaza-7-phosphaadamantane157 (PTA) has been used to make a variety of water-soluble metal complexes, which have s hown moderate to good ac tivities for a large range of catalytic reactions such as hydrogenation of CO2,158 aldehydes,159,160 olefins159,160 and allyl alcohols160 or hydrohalogenation of organic halides162 in aqueous biphasic systems. Synthesis of th e water-soluble complex CpRu(PTA)2I has been performed using the literatu re preparation for the s ynthesis of the CpRu(PTA)2Cl complex.163 Reaction of CpRu(PPh3)2I with two equivalents of PTA ligand in refluxing toluene led to the formation of the PTA complex 17 in 73 % yield after workup. The compound exhibits a characteristi c singlet at 29 ppm in its 31P {1H} spectrum. Ru Ph3P I PPh3 Toluene,reflux Ru I (2.7)P N N N P N N N P N N N 17 Attempted Synthesis of CpRu(PTA)( 1-dppm)I Substitution of one of the PTA ligand by dppm in complex 17 proved to be very difficult. It appears that both PTA ligands are strongly bonded to the ruthenium center

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45 and substitution of one PTA by dppm was not observed even using strong conditions such as high pressure reactions. No furthe r investigation was attempted in that case. Attempted Synthesis of Sulfonated Bi s-(diphenylphosphino)methane (dppm) The direct sulfonation of dppm was atte mpted since this method was for bis(diphenyphosphino)ethane, ( dppe), bis-(diphenyphosphino)p ropane (dppp) and bis(diphenyphosphino)butane (dppb). This reactio n does not offer much control over the degree of sulfonation and, since fuming sulfuric acid is a str ong oxidant the formation of phosphine oxide cannot be avoided. No identif iable product could be obtained in this way. Conclusion New Ru/Pt and Ru/Pd heterobimetallic co mplexes bearing tethered amino groups on the cyclopentadienyl ligands were synthesized and characterized. Besides the substitution at the cyclopentadi enyl ring, these complexes are ve ry similar in structure to the original heterobimetallic complexes previously synthesized.124,134,135 Initially synthesized for application in aqueous solu tion, these amino complexes were found to have poor solubility in water. However, in contrast to the original catalysts, these compounds are soluble in methanol. This allo ws the use of methanol as solvent for the electrolysis. Cyclic voltammetry of the comple xes revealed shifts in the redox potentials for the Ru(II/III) and the first oxidation wa ve of the second metal, Pt(II/IV) and Pd(II/IV), respectively. The shif ts are consistent with an electron donation between the two metals through the iodide bridge. Another feature of these complexes is the presence of the amino moiety in the cy clopentadienyl ring. Oxidation of the amine can be observed at a lower potential than the Ru(II/III) couple. Shifts in the oxidation of the amine moiety are also dependent on the electronic interaction between the two metals.

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46 CHAPTER 3 ELECTROCHEMICAL OXIDATION OF METHANOL WITH AMINOSUBSTITUTED CYCLOPEN TADIENYL COMPLEXES Introduction Interest in potential catalytic applications has led to extensive research concerning heterobimetallic complexes. The major reason is due to the possibili ty of exploiting the different reactivity of the two meta ls in chemical transformations.92-98 A similar effect has been noted for the electrooxidation of meth anol using various electrode materials, initially Pt anodes and then more complex alloys. Surface studies on Pt anodes showed that Pt is poisoned by CO-adsorbed interm ediates formed during the electrooxidation process, which leads to a decrease in ca talytic activity. Additi on of a second metal improved the anode behavior, with RuPt systems proving to be particular ly effective. In the “bi-functional mechanism” initially proposed by Watanabe and Motoo, the Pt sites are responsible for the binding and dehydroge nation of methanol while the Ru sites activate water through forma tion of Ru-oxo intermediate s, which are involved in conversion of surface-bound CO to CO2. The possibility of cooperative interactions in heterobinuclear systems led to preparation of the heterobimetallic complexes Cp(PPh3)Ru( µ -Cl)( µ -dppm)PtCl2 ( 1 ),134 Cp(PPh3)Ru( µ -Cl)( µ -dppm)PtCl2 ( 2 ),135 Cp(PPh3)RuCl( µ -dppm)AuCl ( 3 )135 as catalysts for the electrochemical oxidation of alcohols. This chapter discusses investigation of electrochemical oxidation of methanol by the Ru/Pt complexes [ 5-C5H4CH2CH2NMe2•HI](PPh3)Ru( µ -I)( µ -dppm)PtCl2 ( 8 ) and

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47 [ 5-C5H4CH2CH2NMe2•HI](PPh3)Ru( µ -I)( µ -dppm)PtI2 ( 9 ), and the Ru/Pd complexes [ 5-C5H4CH2CH2NMe2•HI](PPh3)Ru( µ -I)( µ -dppm)PdCl2 ( 10 ) and [ 5-C5H4CH2CH2 NMe2 •HI](PPh3)Ru( µ -I)( µ -dppm)PdI2 ( 11 ). Electrochemical Oxidation of Methanol wi th the Ru/Pt Complexe s 8 and 9 and with the Ru/Pd Complexes 10 and 11 The cyclic voltammograms of the heterobimetallic complexes were obtained in 1,2dicloroethane (DCE) using 0.1 M tetrabutylamm onium triflate (TBAT) as electrolyte and also in methanol using 0.1 M tetra butylammonium tetrafluoroborate (TBABF4) as electrolyte. Besides the wave attributed to the oxidation of the residual amine in the samples, the cyclic voltammograms of the heterobimetallic complexes 8-11 exhibit three major redox couples in the 0.93-2.09 V range assi gned to the Ru(II/III), M(II/IV) (M = Pt or Pd), and Ru(III/IV) couples. One way to determine if these com pounds are active catalysts for the electrooxidation of methanol is to observe th e effect of addition of methanol during the cyclic voltammetry experiments.124,134,135 The cyclic voltammograms of the heterobimetallic chloride Ru/Pt complex 8 , and the Ru/Pd complexes 10 and 11 show current increases starting at the oxidation wave of the second metal center (Pt(II/IV) and Pd(II/IV) couples, respectively) indicating that a catalytic process of methanol oxidation is occurring at this point (Figures 3-1, 3-2 and 3-3). On the other hand, the cyclic voltammogram of the iodide heterobimetallic Ru/Pt complex 9 shows only a smaller increase of the current at the Pt(II/IV) wave (Figure 3-4). Previous bulk electrolysis experime nts with heterobimetallic complexes 1 ,134 2135 and 3135 and related complexes were performed in the non-polar solvents 1,2-dichloromethane or dichloromethane due to poor solubility of complexes 1 , 2 and 3

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48 E vs. NHE (V) 0.81.01.21.41.61.82.02.22.4 I ( A) 0 20 40 60 80 100 120 140 160 180 5 mM catalyst 50 L MeOH Ru Ph3P I Ph2P PPh2 Pt Cl Cl NHMe2 Ru(II/III) Pt(II/IV) Ru(III/IV) CH2NMe2+0.1M TBAT/DCE sr = 20 mV/s . . Figure 3-1. Cyclic vol tammograms of complex 8 ; glassy carbon working electrode; Ag/Ag+ reference electrode. E vs. NHE (V) -0.50.00.51.01.52.02.5 I ( A) -20 0 20 40 60 80 100 120 140 160 180 5 mM catalyst 50 L MeOH Ru Ph3P I Ph2P PPh2 Pt I I NHMe2 Ru(II/III) Pt(II/IV) Ru(III/IV) CH2NMe2+0.1M TBAT/DCE sr = 20 mV/s . Figure 3-2. Cyclic vol tammograms of complex 9 ; glassy carbon working electrode; Ag/Ag+ reference electrode.

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49 E vs. NHE (V) 0.00.51.01.52.02.5 I ( A) -50 0 50 100 150 200 250 5 mM catalyst 50 L of methanol 0.1M TBAT/DCE sr = 20 mV/s Ru Ph3P I Ph2P PPh2 Pd Cl Cl NHMe2 Ru(II/III) Pd(II/IV) Ru(III/IV) CH2NMe2+ . Figure 3-3. Cyclic vol tammograms of complex 10 ; glassy carbon working electrode; Ag/Ag+ reference electrode. E vs. NHE(V) -0.50.00.51.01.52.02.5 I ( A) -50 0 50 100 150 200 250 5 mM catalyst 50 L MeOH Ru(II/III) Pd(II/IV) Ru(III/IV) CH2NMe2+0.1M TBAT/DCE sr = 20 mV/s Ru Ph3P I Ph2P PPh2 Pd I I NHMe2 . Figure 3-4. Cyclic vol tammograms of complex 11 ; glassy carbon working electrode; Ag/Ag+ reference electrode.

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50 in polar media. The use of a chlorinated solvent is a limiting factor during the catalysis since high concentration of supporting electr olyte (0.7M DCE/TBAT) is necessary to reach an acceptable conductivity and electr on transfer rate during the electrolysis processes. One of the goals is to switch to a more polar solvent or, best, water in order to improve the electron transfer prope rties during the electrolysis. Ru Ph3P I Ph2P PPh2 Pt Cl Cl NMe2 8 Ru Ph3P I Ph2P PPh2 Pt I I NMe2 9 Ru Ph3P I Ph2P PPh2 Pd Cl Cl NMe2 10 Ru Ph3P I Ph2P PPh2 Pd I I NMe2 11 + + ++ Figure 3-5. Strutures of heterobimetallic complexes 9-11. Although they were initially synthesized for application in aqueous solution, the amino-substituted complexes 8-11 (Figure 3-5) were found to have poor solubility in water. However, in contrast to the origin al catalysts, these co mpounds are soluble in methanol. This allows the use of methanol as both reactant and solvent for the electrolysis experiments. In the case of the amino-substituted complexes 8-11, using a high potential of 1.7 V vs. NHE as necessary in DCE proved to be impractical since methanol is limited by the anodic potential ra nge. In this case an advantageous lower fixed potential of 1.5 V vs. NHE was used in 0.1M TBABF4 in methanol. Control experiments without catalysts did not show evidence of meth anol oxidized products at that potential. As already described,124,134,135 the homogeneous electr ochemical oxidation of methanol involves formation of formalde hyde, formic acid, dimethoxymethane (DMM), methyl formate (MF) and CO2 as oxidation products. Form aldehyde and formic acid are

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51 the initial two-electron and four-electron oxidation prod ucts from the oxidation of methanol; however in the presence of excess methanol those two undergo fast condensation leading to the formation of DMM, MF and water. The product ratios, current efficiencies and turnover numbers (T ON) for the electrooxid ation of methanol by catalysts 8-11 are summarized in Table 3-1. For comparison purposes, results for the monomeric model complex 6 are also presented. The current efficiencies are the ratio of the charge necessary to produce the observed yi elds of DMM and MF to the total charge passed during the bulk electrolysis (Eq 1.39). The chloride Ru/Pt complex 8 and Ru/Pd complex 10 gave moderately higher current efficiencies, (51.0% and 43.6%, re spectively) when compared to compounds 1 , 2 and 3 synthesized in the McElwee-White group. Experiments in pure methanol have demonstrated that this solvent is more favorable for the catalysis since the electron transfer kinetics are improved in more polar solvent and the high concentration of substrate can only be beneficial even if a d ecrease of the potential to 1.5 V is necessary due to the anodic limitation of the solvent. The product ratios a nd product evolutions (Figures 3-6 and 3-7) from complexes 8 and 10 show also that the partitioning of oxidation products for those two complexes is di fferent. In the early stage of the catalysis, complex 8 forms the four-electr on oxidation product MF in higher concentration. However at a late stage of th e process it appears that the production of the two-electron oxidation product DMM becomes more favored. The overall process shows formation of the two oxidation products in about same concentration. Complex 11 shows similar behavior compared to 8 but with a lower activity ( 23.36 % CE and 4 TON for complex 11 versus 51.04% CE and 11 TON for 8 ) (Figure 3-8). For Ru/Pd complex 10 , the

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52 behavior is different as obser ved in Figure 3-6. From the early stage of the catalysis until the end, the two-electron oxidation product DMM is favored as described by the increase of the product ratio from 1.66 to 3.82. This behavior seem s to be similar to the monomeric model complex 6 but with better current effi ciency for heterobimetallic complex 10 . Complex 9 was found to be the least active catalyst with only 15.79 % current efficiency. Close observation of the da ta shows fast increases of the product ratios from 0.41 to 12.99 until 300 C of charge are pa ssed. In fact this complex selectively favors the formation of the two-electron oxi dation product DMM while the concentration of MF stagnates during the process (Figure 3-9). The resu lts observed for those four compounds show that the chlorides substituted Pt or Pd complexes 8 and 10 exhibit better electrocatalytic results as observed by the higher current efficiencies and TON. In contrast the iodide complexes 9 and 11 prove to be less active. The electrochemical oxidation of methanol by complexes 8-11 was also performed under “wet conditions” by adding 10 µL of water into the system before electrolysis. The previous results in the McElwee-White group s howed that the presen ce of water at an earlier stage of the electrolys is (before it is generated by co ndensation) usually favors the formation of the more oxidized product MF. The presence of water for the Ru/Pt complexes 8 and 9 (Table 3-2) decreases the product ra tios when compared to those from the “dry conditions” (Table 3-1). Obviously for those two compounds, water favors the formation of MF in higher c oncentration (Figures 3-10 and 311). Increases of the current efficiencies and TON are also observed for complexes 8 and 9 when the electrolysis is performed under “wet conditions”. Again comparison of complex 8 with compound 9 shows that chloride substitution at the Pt cen ter highly enhances the activity for electro-

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53 Charge(C) 050100150200250300350 Oxidation Products ( mol) 0 50 100 150 200 250 300 350 DMM MF Ru Ph3P I Ph2P PPh2 Pt Cl Cl NHMe2 Figure 3-6. Product evolution for th e electrolysis of Ru/Pt complex 8 in 0.1M MeOH/TBABF4. Charge(C) 050100150200250 Oxidation Products ( mol) 0 50 100 150 200 250 300 350 DMM MF Ru Ph3P I Ph2P PPh2 Pd Cl Cl NHMe2 Figure 3-7. Product evolution for th e electrolysis of Ru/Pd complex 10 in 0.1M MeOH/TBABF4.

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54 Charge(C) 050100150200250300 Oxidation Products ( mol) 0 20 40 60 80 100 120 140 DMM MF Ru Ph3P I Ph2P PPh2 Pd I I NHMe2 Figure 3-8. Product evolution for th e electrolysis of Ru/Pd complex 11 in 0.1M MeOH/TBABF4. Charge(C) 050100150200250300350 Oxidation Products ( mol) 0 50 100 150 200 250 300 350 DMM MF Ru Ph3P I Ph2P PPh2 Pt I I NHMe2 Figure 3-9. Product evolution for th e electrolysis of Ru/Pt complex 9 in 0.1M MeOH/TBABF4.

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55 catalytic oxidation of methanol (65.18% CE and 13 TON for 8 versus 20.58% CE and 4 TON for 9 ). In the case of the Ru/Pd complexes 10 and 11, the same behavior is observed (Figures 3-12 and 3-13). About twice current efficiency and twice TON are obtained with the chloride substituted comp lex (63.63 % CE and 13 TON for 10 and 29.80% CE and 6 TON for 11 ). Among the catalysts, complex 8 is again more active followed closely by the analogous Ru/Pd chloride complex 10 . One interesting experiment was to see how long the catalysis could hold without losing its activity and how much product co uld be formed during the process. Two compounds, 9 and 10 were used for the experiments (Table 3-2). For complex 9 , 800 C of charge were passed in about 26 hours. In this case 41 turnovers were obtained, forming about 100 µL of DMM (1.127 mmol), 21 µL of MF (0.3 mmol) with an efficiency of 43.3% (GC determination) (Figure 3-11). For complex 10 only 555C of charge could be passed into the system in about the same time but with superior results. About 98 % current efficiency and 58 TON were reached with complex 10 (24 hours), forming about 167 µL of DMM (1.897 mmol) and 28 µL of MF (0.46 mmol) (Figure 3-12). Usually deactivation of the catalysts can be detected during the electr olysis by the color change of the solution to a colorless solution in the reaction side of the cell. Conclusion The catalytic activities for the electroch emical oxidation of methanol were investigated for a series of heterobimetallic Ru/Pt and Ru/Pd complexes bearing aminosubstituted Cp rings. Although these com pounds were initially synthesized for application in aqueous media, theywere found to have poor solubility in water. However, in contrast to the original catalysts 1 , 2 and 3 , compounds 8-11 are soluble in methanol.

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56 Table 3-1. Bulk electrolysis data for the oxidation of methanol by complexes 8-11 and 6 . Product ratios (DMM/MF)a,b Complex Ru/Pt ( 8 ) Ru/Pt (9 ) Ru/Pd (10 ) Ru/Pd ( 11 ) Ru (6 ) Charge (C) 25 50 0.25 0.41 1.66 0.13 1.59 75 0.48 1.18 1.76 0.45 2.09 100 0.69 1.89 2.34 0.64 2.44 150 0.94 4.39 3.17 0.86 3.80 200 1.08 6.27 3.82 1.01 4.50 (at charge X) 1.16 (300C) 12.99 (300C) 1.02 (250C) Current efficiencies (%) after 200C 51.04 15.79 43.65 23.36 9.73 TON after 200C 11 4 9 4 2 Current efficiencies (%) (at charge X) 56.87 (300C) 23.24 (300C) 26.94 (250C) TON (at charge X) 19 (300C) 9 (300C) 6 (250C) a Electrolysis were performed at 1.5 V vs. NHE in pure methanol. A 10 mM catalyst concentration was used for each experiment. b Determined by GC with respect to n-heptane as an internal stan dard. Each ratio is reported as an average of 2-3 experiments.

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57 Charge(C) 050100150200250300350 Oxidation Products ( mol) 0 100 200 300 400 500 DMM MF Ru Ph3P I Ph2P PPh2 Pt Cl Cl NHMe2 Figure 3-10. Product evolution for th e electrolysis of Ru/Pt complex 8 in 0.1M MeOH/TBABF4 in wet methanol. Charge(C) 02004006008001000 Oxidation Products ( mol) 0 200 400 600 800 1000 1200 DMM MF Ru Ph3P I Ph2P PPh2 Pt I I NHMe2 Figure 3-11. Product evolution for th e electrolysis of Ru/Pt complex 9 in 0.1M MeOH/TBABF4 in wet methanol.

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58 Charge(C) 0100200300400500600 Oxidation Products ( mol) 0 500 1000 1500 2000 DMM MF Ru Ph3P I Ph2P PPh2 Pd Cl Cl NHMe2 Figure 3-12. Product evolution for th e electrolysis of Ru/Pt complex 10 in 0.1M MeOH/TBABF4 in wet methanol. Charge(C) 050100150200250300 Oxidation Products ( mol) 0 50 100 150 200 250 DMM MF Ru Ph3P I Ph2P PPh2 Pd I I NHMe2 Figure 3-13. Product evolution for th e electrolysis of Ru/Pt complex 11 in 0.1M MeOH/TBABF4 in wet methanol.

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59 Table 3-2. Bulk electrolysis data for the oxidation of methanol in “wet methanol” c by complexes 8-11. Product ratios (DMM/MF)a, b, c Complex Ru/Pt ( 8 ) Ru/Pt (9 ) Ru/Pd (10 ) Ru/Pd ( 11 ) Ru (6 ) Charge (C) 25 50 0.16 1.53 75 0.28 0.45 2.53 0.27 100 0.40 0.71 3.50 0.44 150 0.63 1.18 4.07 0.86 200 0.78 1.73 4.24 1.26 (at charge X) 0.92 (300C) 3.37 (800C) 4.11 (555C) 1.79 (250C) Current efficiencies (%) after 200C 65.18 20.58 63.63 29.80 TON after 200C 13 4 13 6 Current efficiencies (%) (at charge X) 75.62 (300C) 43.30 (800C) 98.05 (555C) 33.91 (250C) TON (at charge X) 24 (300C) 41 (800C) 58 (555C) 9 (250C) a Electrolysis were performed at 1.5 V vs. NHE in pure methanol . 10 mM catalyst concentration was used for each experiment. b Determined by GC with respect to n-heptane as an internal stan dard. Each ration is reported as an average of 2-3 experiments. c Addition of 10µL of water was added in to the system before electrolysis.

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60 Addition of methanol during cyclic vol tammetry experiments in 0.1 M TBAT/ DCE with 8-11 showed an enhancement of the current typical of catalytic activity for the electrooxidation of methanol. As previously described124,134,135 DMM and MF are the oxidation products detected during bulk electr olyses in pure methanol. The differences among the complexes can be observed in th e product ratios, current efficiencies and TON. The chloride substituted Pt or Pt complexes 8 and 10 are the most active catalysts having the highest TON and current e fficiencies (51.04% CE and 11 TON for 8 and 43.65 % CE and 9 TON for 10 ). The iodide substituted complexes 9 and 11 are less active but still more active than the mononuclear model complex [ 5-C5H4CH2CH2NMe2•HI]Ru(PPh3)2 I ( 6) . Increasing the electr onic density at the nonRu metal appears to deactivate the catalyst as demonstrated by the lower results from complexes 9 and 11 (15.79% CE and 4 TON for 9 and 23.36% CE and 4 TON for 11 ). Experiments in which water is added at th e beginning of the catalysis show that the formation of the more oxidized product MF is favored in the presence of water along with higher current efficiencies and TON.

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61 CHAPTER 4 SYNTHESIS OF ISOELECTRONIC IRON AND RUTHENIUM HETEROBIMETALLIC COMPLEXES Introduction The chemistry of heterobimetallic complexes has attracted great attention due to the possibility of combining the different reac tivities of the two metals in chemical transformations.92-98 It has been long recognized that interesting characteristics such as cooperative behavior and/or different mechan istic roles of the me tal centers can be expected when two metals are in close proximity.93,99-105 It has also been shown that the cooperative effect in heterobimetallic comple xes can enhance catalytic activities or can result in unique properties not observed in monomeric models.115-120 Cooperative interactions in he terobinuclear systems have been the primary target in the development of the catalysts for the electrooxidation of alcohols and led to preparation of the heterobimetallic complexes Cp(PPh3)Ru( µ -Cl)( µ -dppm)PtCl2 ( 1 ),134 Cp(PPh3)Ru( µ -Cl)( µ -dppm)PtCl2 ( 2 ),135 Cp(PPh3)RuCl( µ -dppm)AuCl ( 3 ).135 These complexes were found to be effective catalysts for electrooxidation of methanol, resulting in much higher current efficiencies compar ed to those obtained with the monomeric model compounds CpRu( 2-dppm)Cl,113 or CpRu(PPh3)2Cl.141 Clearly, the significant enhancement of the catalytic ac tivity is due to the presence of the second metal. As a continuation, the replacement of ruthen ium by its congener iron was investigated. Catalysis by iron complexes has been of recen t interest due to th eir reactivity and the possibility of replacing expensive precious meta ls with the more readily available first

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62 row metals.164-172 In this chapter are reported the s ynthesis and characterization of new carbonyl-containing Ru/Pt, Ru/Pd, and Ru/Au derivatives of 1-3 , as well as their isoelectronic Fe/Pt, Fe/Pd and Fe/Au analogue s. X-ray analysis, cyclic voltammetry, IR, UV-vis, and NMR (1H and 31P) spectroscopy were used to examine the electronic interaction between the two metal centers. Iron and Ruthenium Heterobimetallic Complexes Synthesis Preparation and spectroscopic data for CpFe(CO)( 1-dppm)I173 ( 22 ) have been reported. The ruthenium analogue was synthe sized following a similar procedure. Reaction of CpRu(CO)2I174 with dppm in refluxing benzene afford CpRu(CO)( 1-dppm)I ( 21 ) in greater than 70% yield. Synthesis of complexes 23-28. Reactions of CpRu(CO)( 1-dppm)I ( 21 ) or CpFe(CO)( 1-dppm)I ( 22 ) with Pt(COD)I2 in CH2Cl2 afford the I-bridged Ru/Pt complex 23 (57% yield) and Fe/Pt complex 24 (62% yield), respectively (Eq. 4.1). During the reactions, small amounts of Pt( 2-dppm)I2 were formed by dppm transfer to Pt(COD)I2. This byproduct can be detected by 31P NMR as a singlet with Pt sa tellites at ca. -70 ppm. Complexes 23 and 24 were obtained as a bright ora nge solid and a pale green solid respectively. These complexes are moderately stable in the solid state but decompose slowly in solution if stored outside a glove box. Since Pd(COD)I2 could not be isolated, the I-bridged Ru/Pd complex 25 (83% yield) and Fe/Pd complex 26 (65% yield) were prepared by reacting the precursors 21 and 22 with Pd(COD)Cl2 in CH2Cl2, followed by reaction with 10 equivalents of NaI (Eq. 4.2). The Ru/Au complex 27 (78% yield) and Fe/Au complex 28 (64% yield), in which the two me tal centers are linked only via the dppm bridge, were prepared by di rect reaction of the precursors 21 and 22 with AuI.

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63 Figure 4-1. Heterobimetallic complexes 23-31 . I M OC I Ph2P PPh2 M OC I Ph2P PPh2 Pd I I M OC I Ph2P PPh2 Pt I I M OC I Ph2P PPh2 Au Pt(COD)I2Pd(COD)Cl3NaI AuI 21 :M=Ru 22 :M=Fe 23 :M=Ru 24 :M=Fe 25 :M=Ru 26 :M=Fe 27 :M=Ru 28 :M=Fe(4.1) (4.2) (4.3) Although pure samples of the Ru/Au complex 27 could be isolat ed, it was found to be the most sensitive of all heterobimetallic complexes. Degradation of 27 could be observed in solid state ev en stored under nitrogen. Synthesis of complex 30. The heterobimetallic Ru/Pd complex 30 was prepared in a similar manner than 25 and obtained as a dark brow n solid in 63% yield. The M L I Ph2P PPh2 M I I Complex M M´ L 23 Ru Pt CO 24 Fe Pt CO 25 Ru Pd CO 26 Fe Pd CO 29 Ru Pt PPh3 30 Ru Pd PPh3 I M L I Ph2P PPh2 Au Complex M L 27 Ru CO 28 Fe CO 31 Ru PPh3

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64 stability of complex 30 was also found to be similar to the I-bridged complexes synthesized in this work. NMR data The 31P NMR spectra of the iron complexes 24 , 26 , and 28 showed features for the phosphine ligands similar to those prev iously reported for CpFe(CO)(µ-I)(µdppm)M(CO)4 (M = Cr, Mo, W).175 A pair of doublets is always observed, the downfield resonance corresponding to the Fe-bound ph osphorus while the upfield doublet is assigned to phosphorus coordinated to the second metal (Pt, Pd, or Au). The spectra of the ruthenium complexes 23 , 25 , and 27 are similar and can be assigned in an analogous fash ion. Chemical shifts ( ) as well as coupling constants are reported in Table 4-1. It has been noted th at, for the metal phosphine complexes of the same structure and oxidation state, one generally observes shift of the 31P resonance to higher field as one descends in a given group.176 Accordingly, we clearly see a decrease in P as one descends from Fe to Ru. Intera ction between Fe or Ru and the second metal can be evidenced by careful examination of the M-bound phosphorus (M = Fe, Ru). Although the resonances of the Fe-bound phosphorus atoms are essentially identical, we again see a decrease in P from 69.2 ppm to 65.3 ppm as on e descends from Pd to Pt in compounds 24 and 26 . Variation in P also follows this trend for the Ru series. When the M´-bound (M´ = Pt, Pd) phosphorus sh ifts are compared, we can clearly see a decrease in P from 46.7 ppm to 43.5 ppm when the meta l goes from Pd to Pt for compounds 23 and 25 , respectively. Although a similar trend in the phosphorus shifts from Fe (62.0 ppm) to Ru (40.6 ppm) can be observed for the Ru/Au and Fe/Au complexes 27 and 28 , no further comparison with the I-bridged compounds can be made due to the differences in structures and oxidation states comp ared to the I-bridged complexes.

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65 The 1H NMR data for 21-28 are reported in Table 4-1. The spectra for the iron derivatives 24 , 26 , and 28 , show chemical shifts values similar to those previously published.175 A sharp singlet in the range 4.36-4.51 ppm is observed for the Cp protons and the diastereotopic methylene protons of the bridging dppm appear as two sets of doublet of doublet of doublets centered in the range 3.19-4.46 ppm as a result of the coupling to each other and to the two adjace nt phosphorus atoms. The spectra for the ruthenium analogues 23 , 25 and 27 are similar, with a sharp singlet for the Cp protons observed in the range 4.82-5.07 ppm and the two sets of multiplets for the diastereotopic methylene protons centered in the range 3.63-4.70 ppm. IR spectroscopy The IR data for compounds 21-28 are reporte d in Table 4-1. The infrared spectra of all the complexes displayed a single carbonyl stretching frequenc y in the range 19451969 cm-1, characteristic of termin al CO ligands. Examination of CO provides a powerful tool to probe the overall electronic de localization in the bimetallic complexes. As electron donation from metal d orbitals to *CO increases, there is a concomitant decrease in CO. On this basis the infrared data ar e consistent with an increase of the electron density at the carbonyl along the compound series: Ru/Pt ( 23 ) ~ Ru/Pd ( 25 ) < Fe/Pt ( 24 ) < Fe/Pd ( 26 ) < Ru monomer ( 21 ) ~ Ru/Au ( 27 ) < Fe/Au ( 28 )~ Fe monomer ( 22 ). This confirms that the bridging i odide is an important conduit for donation from the Ru or Fe center to Pd or Pt since the values of the CO stretching frequencies are greater than those of the monomeric models 21 and 22 . As expected, negligible interaction between the metals is observed for the Ru/Au complex 27 and Fe/Au complex 28 since the two metals are linked only by the saturated three atom bridge of the dppm

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66 Table 4-1. Selected spectroscopic data for complexes 21-28 . 1H NMR ( ) a 31P NMR ( )a IR (cm-1)b Cp -CH2Ru-PPh2Fe-PPh2M-PPh2 CO` 21 4.85 3.81-3.56 (m) 44.3 (d, 70 Hz) 23.8 (70 Hz) 1952 22 4.38 3.59 (m), 3.16 (m) 63.3 (d, 51.3 Hz) 24.0 (51.3 Hz) 1946 23 5.02 4.10 (m), 3.73 (m) 43.5 (d, 10 Hz) 3.3 (d, 10 Hz) 1969 24 4.51 3.72 (m) 65.3 (d, 8.5 Hz) 4.3 (d, 8.5 Hz) 1963 25 5.07 4.01 (m), 3.64 (m) 46.7 (d, 19.5 Hz) 12.6 (d, 19.5 Hz) 1968 26 4.56 3.72 (m), 3.44 (m) 69.2 (d, 17.7 Hz) 12.2 (d, 17.7 Hz) 1960 27 4.82 4.70 (m), 3.63 (m) 40.6 (d, 18.2 Hz) 26.9 (d, 18.2 Hz) 1952 28 4.36 4.46 (m), 3.19 (m) 62.0 (d, 22.2 Hz) 27.6 (d, 22.2 Hz) 1945 a Spectra measured in CDCl3, at room temperature. b neat film.

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67 ligand. These compounds exhibit CO resonances similar to the monomeric compounds, Ru complex 21 and Fe precursor 22 . X-Ray analysis X-ray structures were obtained for the I-bridged complexes 23 , 24 , 25 and 26 . Crystallographic details are provided in Table 4-6. All of these complexes show structures similar to those of I-bri dged complexes previously reported,124,135,175 where the coordination about the iron and ruthenium atoms retained a pi ano-stool configuration and the coordination about the Pt and Pd atoms is distorted square planar . Shown in Figures 4-1, 4-2, 4-3 and 4-4 are the ORTEP drawings of the Ru/Pt, Fe/Pt, Ru/Pd and Fe/Pd compounds 23 , 24 , 25 and 26 , respectively. Selected bond distances and bond angles for compounds 23-26 appear in Tables 4-2, 4-3, 4-4 a nd 4-5, respectively. In each complex, the two metals are linked by the dppm ligand and iodine atom to form a distorted sixmembered ring. Consistent with the IR data (Table 4-1), the carbonyl ligands for 23-26 are terminal. As previously noted for heterobimetallic iron complexes,175 the cyclopentadienyl ring is bound asym metrically to Ru or Fe, with the Ru-C(Cp) distances range from 2.156(7) Å through 2.248(8) Å ( 23 and 25 ), while the Fe-C(Cp) distances ranging from 2.071(8) Å through 2.102(8) Å ( 24 and 26 ). The shortest metal-carbon bond lengths (Ru-C5, Fe-C5, Ru-C1 and Fe-C5, for 23 to 26 , respectively) are definitely due to the trans influence from the iodide ligand (C5-Ru-I1 = 148º ( 23 ), C5-Ru-I1 = 150º ( 25 ), C5-Fe-I1 = 150º ( 24 ) and C5-Fe-I1 = 149.68 º ( 26 )) The M-I-M´ angles and bond distances in 23-26 fall within the range of expected values, with asymmetric M-I and M´I distances varying between 2.5944(4) Å an d 2.6962(5) Å. The Ru-I distance for the Ru/Pt complex 23 , 2.6620(6) Å and for the Ru/Pd complex 25 , 2.6962(5) are comparable to the value of 2.6749(5) Å reported for CpRu(PPh3)( µ -I)( µ -dppm)PdCl2,124 in which the

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68 Figure 4-2. ORTEP drawing of the molecular structure of Cp(CO)Ru( µ -I)( µ -dppm)PtI2 ( 23) . Thermal ellipsoids are plotted at 50% probability. Hydrogen atoms are omitted for clarity. Table 4-2. Selected bo nd distances (Å) and angles (deg) for CpRu(CO)( µ -I) ( µ -dppm)PtI2 ( 23 ). Ru1-P1 Ru1-I1 Pt1-P2 Pt1-I1 Pt1-I2 Pt1-I3 Ru1-C1 C1-O1 2.3030(12) 2.6620(6) 2.2420(11) 2.5944(4) 2.645(4) 2.5987(4) 1.864(6) 1.147(7) P1-C19 P2-C19 Ru1-C2 Ru1-C3 Ru1-C4 Ru1-C5 Ru1-C6 1.846(4) 1.850(4) 2.248(8) 2.227(7) 2.168(7) 2.156(10) 2.190(10) P1-Ru1-I1 Pt1-I1-Ru1 P2-Pt1-I1 P2-Pt1-I2 P2-Pt1-I3 90.15(3) 108.233(15) 94.88(3) 176.34(11) 89.55(3) I1-Pt1-I3 I1-Pt1-I2 I3-Pt1-I2 O1-C1-Ru1 C5-Ru1-I1 173.163(12) 88.38(9) 87.06(10) 174.6(5) 148.6(4)

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69 Figure 4-3. ORTEP drawing of the molecular structure of Cp(CO)Fe( µ -I)( µ -dppm)PtI2 ( 24) . Thermal ellipsoids are plotted at 50% probability. Hydrogen atoms are omitted for clarity. Table 4-3. Selected bo nd distances (Å) and angles (deg) for CpFe(CO)( µ -I) ( µ -dppm)PtI2 ( 24 ). Fe-P1 Fe-I1 Pt-P2 Pt-I1 Pt-I2 Pt-I3 Fe-C7 C7-O1 2.217(2) 2.6001(12) 2.2338(17) 2.6071(5) 2.6518(6) 2.6078(5) 1.783(8) 1.138(8) P1-C6 P2-C6 Fe-C1 Fe-C2 Fe-C3 Fe-C4 Fe-C5 1.857(6) 1.846(6) 2.102(8) 2.100(7) 2.088(6) 2.073(7) 2.071(8) P1-Fe-I1 Fe-I1-Pt P2-Pt-I1 P2-Pt-I2 P2-Pt-I3 92.13(6) 108.46(3) 95.35(4) 173..28(5) 87.65(4) I1-Pt-I3 I1-Pt-I2 I3-Pt-I2 O1-C7-Fe C5-Fe-I1 176.86(2) 87.399(17) 89.715(18) 173.3(7) 150.1(2)

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70 Figure 4-4. ORTEP drawing of the molecular structure of Cp(CO)Ru( µ -I)( µ -dppm)PdI2 ( 25) . Thermal ellipsoids are plotted at 50% probability. Hydrogen atoms are omitted for clarity. Table 4-4. Selected bo nd distances (Å) and angles (deg) for CpRu(CO)( µ -I) ( µ -ppm)PdI2 ( 25 ). Ru-P1 Ru-I1 Pd-P2 Pd-I1 Pd-I2 Pd-I3 Ru-C15’ C15’-O1 2.2988(12) 2.6962(5) 2.2702(12) 2.6155(5) 2.6433(5) 2.6042(4) 1.893(5) 1.102(5) Ru-C1 Ru-C2 Ru-C3 Ru-C4 Ru-C5 P1-C6 P2-C6 2.184(4) 2.224(4) 2.237(5) 2.240(5) 2.198(4) 1.850(6) 1.841(4) P1-Ru-I1 Pd-I1-Ru P2-Pd-I1 P2-Pd-I2 P2-Pd-I3 90.63(3) 108.293(15) 95.19(3) 172.46(3) 87.05(3) I3-Pd-I1 I1-Pd-I2 I3-Pd-I2 O1-C15’-Ru C5-Ru-I1 177.347(19) 87.899(15) 90.050(15) 172.2(4) 150.16(14)

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71 Figure 4-5. ORTEP drawing of the molecular structure of Cp(CO)Fe( µ -I)( µ -dppm)PdI2 ( 26) . Thermal ellipsoids are plotted at 50% probability. Hydrogen atoms are omitted for clarity. Table 4-5. Selected bo nd distances (Å) and angles (deg) for CpFe(CO)( µ -I) ( µ -ppm)PdI2 ( 26 ). Fe-P1 Fe-I1 Pd-P2 Pd-I1 Pd-I3 Pd-I2 Fe-C7 C7-O1 2.2161(17) 2.5966(10) 2.2682(15) 2.6186(6) 2.6432(6) 2.6060(6) 1.765(7) 1.156(8) Fe-C1 Fe-C2 Fe-C3 Fe-C4 Fe-C5 P1-C6 P2-C6 2.092(6) 2.097(6) 2.098(6) 2.076(7) 2.065(7) 1.871(6) 1.841(6) P1-Fe-I1 Fe-I1-Pd P2-Pd-I1 P2-Pd-I3 P2-Pd-I2 92.43(5) 108.70(2) 94.99(4) 172.39(5) 86.80(4) I2-Pd-I1 I1-Pd-I3 I2-Pd-I3 O1-C7-Fe C5-Fe-I1 177.63(3) 88.072(19) 90.35(2) 172.6(6) 149.68(19)

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72 Table 4-6. Crystal data and stru cture refinement for complexes 23 , 24 , 25 and 26 . Complex 23 24 25 26 Empirical formula C33H31Cl2I3OP2PtRu C33H31Cl2I3OP2PtFe C33H31Cl2I3OP2PdRu C33H31Cl2I3OP2PdFe Mr 1253.28 1278.96 1235.49 1190.27 T/K 173(2) 173(2) 173(2) 173(2) /Å 0.71073 0.71073 0.71073 0.71073 Crystal system Monoclinic M onoclinic Monoclinic Monoclinic Space group P2(1)2(1)2(1) P2(1)2(1)2(1) P2(1)2(1)2(1) P2(1)2(1)2(1) a /Å 11.8206(8) 13.7053(9) 13.7041(7) 13.7016(12) b /Å 12.9648(9) 14.9673(9) 14.9191(7) 14.9761(13) c /Å 24.4701(17) 18.7364(12) 18.9157(9) 18.7778(16) / 90 90 90 90 / 90 99.6020 (10) 97.9240(10) 99.7360(10) / 90 90 90 90 V /Å3 3750.1(4) 3789.6(4) 3830.4(3) 3797.6(6) Z 4 4 4 4 Dc/Mg.m-3 2.220 2.242 2.142 2.082 µ /mm-1 6.852 6.908 3.671 3.687 F000 2328 2392 2336 2264 Crystal size/mm 0.28 × 0.21 × 0.10 0.18 × 0.09 × 0.03 0.21 × 0.17 × 0.03 0.17 × 0.09 × 0.05 Range/ 1.66 to 27.50 1.71 to 27.50 1.73 to 27.50 1.71 to 27.50 Index ranges 13 h 15, 14 k 16, 28 l 31 17 h 15, 19 k 12, 20 l 24 17 h 17, 14 k 19, 24 l 20 17 h 15, 19 k 12, 20 l 24 Reflection collected 22870 24440 24746 24319 Independent reflections (Rint) 8433(0.0462) 8580(0.0909) 8711(0.0607) 8603(0.0954) Completeness to = 27.49 (%) 99.4 98.4 99.0 98.5 Absorption correction Integration In tegration Integration Integration Max./min. transmission 0.5224/0. 2130 0.8179/0.3668 0.8848/ 0.5465 0.8600/0.5741 Data/restraints/paramete rs 8433/0/399 8580/0/352 8711/0/352 8603/0/352 GOF on F2 1.054 0.899 0.796 0.979 R 1a 0.0264 0.0732 0.0634 0.0812 wR 2b 0.0587 0.1035 0.0638 0.1308 Largest diff. peak, hole/e Å-3 1.134, 1.043 2.911, 1.983 1.189, 1.175 1.682, 1.291 a R 1 = (|| Fo| | Fc||)/ | Fo|, b wR 2 = [ [ w ( Fo 2Fc 2)2]/ [ w ( Fo 2)2]1/2, S = [ w ( Fo 2Fc 2)2]/( n – p )]1/2; w = 1/[ 2( Fo 2) + 0.0337 p )2 + 1.24p]; p = [max( Fo 2, 0) + 2 Fc 2]/3.

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73 carbonyl is replaced by a PPh3 ligand. Cyclic Voltammetry Cyclic voltammetry was performed on heterobimetallic complexes 23 28 as well as the monometallic complexes 21 and 22 . In addition to these complexes, electrochemical experiments were also performed on ruthenium triphenylphosphine complexes 29 and 31 ,124 as well as for Ru/Pd complex 30 , which was prepared for comparison purposes. The CV data for complexes 21-31 are listed in Table 4-7. The cyclic voltammograms for the heterobimetallic complexes 23 28 each display three waves in the 1.00-2.25 V range. These redox processes have been previously described for several Ru heterobimetallic complexes having similar structures.134,135,124 For ruthenium complexes 23 , 24 and 27 , the first and third waves are assigned to the Ru(II/III) and Ru(III/IV) couples, respectively, while the second wave is assigne d to the redox couple of the second metal. For iron complexes 24 , 26 and 28 , the trend is very simila r to the ruthenium analogue with the first and third waves assigned to the Fe(II/III) and Fe(III/IV) couples, respectively and the middle one assigned to the redox couple of the second metal. Electronic interactions between the two metals in the I-bridged heterobimetallic complexes 23 28 are evidenced by significant redox poten tial shifts compared to those of the monometallic model compounds CpRu(CO)(1-dppm)I ( 21 ) and CpFe(CO)(1dppm)I ( 22 ). The cyclic voltammograms of the Ru/Pt complex 23 and Fe/Pt complex 24 exhibit irreversible oxidation at 1.21 V vs. NHE, assigned to Ru(II/III) and at 1.19 V for the Fe(II/III) couple. Ru/Pt complex 23 exhibits a second wave a ssigned to the Pt(II/IV) couple, overlapping with an irreversible oxidation wave at 2.02 V assigned to the Ru(III/IV) couple. Using TBAH (Tetran -butylammonium hexafluorophosphate) as

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74 electrolyte allows better resolution of the Pt(II/IV) oxidation as a quasireversible redox wave at 1.82 V vs. NHE. For the Fe/Pt analogue 24 , the quasireversible Pt(II/IV) wave is shifted about 370 mV (E1/2 = 1.45 V) negative compared to the one from complex 23 and the irreversible Fe(III/IV) wave is f ound to be easier to oxidize by 290 mV (Epa = 1.96 V) than the Ru(III/IV) wave for 23 . Surprisingly, a more si gnificant electron donation from Fe to Pt through the I-bridge is observed for the Fe/Pt complex 24 compared to the Ru/Pt analog 23 resulting in a significant shift to lower potentials for Pt(II/ IV) couple. Since ruthenium is more electron-rich than iron th e opposite behavior should be expected. IR data for complexes 23 and 24 do not show a significan t break out in the carbonyl stretching frequencies which could reflect a direct effect of th e carbonyl ligand. The difference between CO(Ru) and CO(Fe) for all the congeneric pairs of complexes including monomers 21 and 22 is about 6-8 cm-1 which is roughly the difference observed for the terminal carbonyl ligand on heterobimetallic complexes [MCl(CO)( µ -CO)( µ -dppm)2PtCl, M = Fe,177 Ru178] reported in the lit erature (about 10 cm-1). Hence, the difference in the potential shifts may be relate d to a better energy match between Fe and Pt which would favor the electronic interactions. The lower interactions in the Ru/Pt analog 23 could be due to larger ga ps between the Ru and Pt energy levels. However, further investigation is necessary to determine if a correlation between measured redox potentials and elec tronic interactions is justifiable. Additional studies on the CpRu(PPh3)( µ -I)( µ -dppm)PtI2 complex 29 , show that the more electron-donating ligand triphenylphosphine exhibits ne gative shifts for all the redox waves of the Ru/Pt complex 29 , compared to the carbonyl compound 23 . On the other hand, the iron complex 24 shows very similar behavior compared to the

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75 heterobimetallic complex 29 . It seems that the combination Fe-carbonyl/Pt in complex 24 exhibits equivalent elect ronic interactions compared to the combination Ru-PPh3/Pt in complex 29 as described by the identical redox pote ntials between those two complexes. The cyclic voltammograms for the Ru/Pd complex 25 and the Fe/Pd complex 26 exhibit irreversible oxida tions at 1.02 V and 1.07 V vs . NHE assigned to the Ru(II/III) and Fe(II/III) couples, re spectively. Ru/Pd complex 25 exhibits a Pd(II/IV) redox wave around 1.91 V vs. NHE, (in TBAH) which appears as a shoulder on the irreversible Ru(III/IV) wave (Epa = 2.12 V). As for the Fe/Pt complex 24 , significant electron donation through the I-bridge is also observed for the Fe/Pd complex 26, with a quasireversible Pd(II/IV) redox wave of 26 easier to oxidize by 440 mV (E1/2 = 1.47 V) compared to the Ru/Pd complex 25 . Comparison of complexes 25 and 26 with the triphenylphosphine Ru/Pd compound 30 shows a slightly different trend. The more electron donating triphenylphosphine ligand doe s not induce a significant negative shift of the potential of the Ru(II/III) center for 30 as observed for the Ru/Pt complex 29 analog. The Ru(II/III) wave of 30 is actually observed shifte d to higher potential by 270 mV compared to 29, resulting probably from re latively stronger electron donation through the iodide bridge. It appears as for complex 29 that the Pd(II/IV) wave is shifted to lower potential which is consistent with the electron donation from Ru to the more electron deficient Pd through th e iodide bridge. Again as observed for the analogous Pt complexes 24 and 29 a very similar behavior is observed between the Ru-PPh3/Pd compound 30 and the Fe-carbonyl/Pd compound 26 . Besides the first Fe(II/III) redox wave from 26 which is 220 mV easier to oxidi zed than the Ru(II/III) couple of 30, the rest of the redox potential show very visible resemblance.

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76 Ru/Au complex 27 exhibits irreversible wa ves at 1.13 V, 1.69 V and 2.00 V vs. NHE for the Ru(II/III), Au(I/III) and Ru(III/IV ) couples, respectively. This compound was found to be the least stable heterobimetallic complex under the conditions of cyclic voltammetry, with degradation evident afte r several successive cycles. The cyclic voltammogram of the Fe/Au analogue 28 also displays three redox waves, two quasireversible at 0.96 V and 1.57 V vs. NHE assigned to the Fe(II/III) and Au(I/III) redox couples, respectively and an irreversible wave at 2.04 V for the Fe(III/IV) couple. As previously observed for CpRu(PPh3)I( µ -dppm)AuI (31) , the waves for the non-iodide bridged Ru/Au and Fe/Au complexes 27 and 28 are very similar to those of the mononuclear compounds CpRu(CO)(1-dppm)I ( 21 ), CpFe(CO)(1-dppm)I ( 22 ) and PPh3AuI ( 32 ). This is consistent with the IR data, which suggest limited interactions between the two metals of 27 and 28 through the dppm bridge. UV-vis spectroscopy In order to gain further insight into th e electronic structure of these bimetallic complexes, we investigated their absorp tion spectra. The UV-vis spectra of the heterobimetallic complexes 23 28 were recorded in acetonitrile, THF, dichloromethane, and benzene solutions (Table 4-8) and co mpared with those of the corresponding monometallic derivatives 21 and 22 . All the compounds exhib it intense absorptions in the UV range below 270 nm. Similar high energy bands in half-sandwich complexes bearing phosphine ligands have b een assigned to ligand centered * electronic transitions.179 The spectrum for the mononuclear Ru complex 21 possesses two major features, a low energy band in the visible region at 437 nm (band I, = 428-472 M-1cm-1), and a

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77 Table 4-7. Formal potentials for complexes 21-32 .a Complexes Couple Epa/V E1/2 b/V Couple Epa/V E1/2 b/V Couple Epa/V Ref 21c Ru(II/III) 0.93 Ru(III/IV) 2.02 i 22c Fe(II/III) 1.01 0.90 Fe(III/IV) 2.16 i 23 Ru(II/III) 1.21 Pt(II/IV) e Ru(III/IV) 2.02 i 23c Ru(II/III) 1.19 Pt(II/IV) 1.91 1.82 Ru(III/IV) 2.25 i 24 Fe(II/III) 1.19 Pt(II/IV) 1.54 1.45 Fe(III/IV) 1.96 i 29d Ru(II/III) 1.10 Pt(II/IV) 1.49 1.43 Ru(III/IV) 1.98 124 29d Ru(II/III) 1.17 Pt(II/IV) 1.51 1.44 Ru(III/IV) 1.88 i 25 Ru(II/III) 1.02 Pd(II/IV) e Ru(III/IV) 2.17 i 25c Ru(II/III) 1.00 Pd(II/IV) 1.91 Ru(III/IV) 2.12 i 26 Fe(II/III) 1.07 Pd(II/IV) 1.56 1.47 Fe(III/IV) 1.96 i 30f Ru(II/III) 1.29 Pd(II/IV) 1.55 1.50 Ru(III/IV) 1.98 i 27 Ru(II/III) 1.13 Au(I/III) 1.54 Ru(III/IV) 2.00 i 28 Fe(II/III) 1.05 0.96 Au(I/III) 1.71 1.57 Fe(III/IV) 2.05 i 31g Ru(II/III) 0.95 0.85 Au(I/III) 1.48 Ru(III/IV) 1.87 i 32h Au(I/III) 1.64 i a All potentials obtained in 0.1 M DCE/TBAT (tetrabuty lammonium triflate) unless otherwise specified, reported vs. NHE and referenced to Ag/Ag+. b E1/2 reported for reversible waves. c Potentials obtained in 0.1 DCE/TBAH (tetrabutylammonium hexafluorophosphate). d CpRu(PPh3)( µ -I)( µ -dppm)PtI2. e Oxidation wave overlapping with Ru(III/IV). f CpRu(PPh3)( µ -I)( µ dppm)PdI2.g CpRu(PPh3)I( µ -dppm)AuI. h PPh3AuI. i This work.

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78 higher energy band at 324 nm (band II, = 3110-3480 M-1cm-1). A third band (band III) is also observed around 276 nm, appearing as a shoulder on the hi gher energy feature. The iron complex 22 shows features similar to those of Ru complex 21 . Complex 22 exhibits a low energy ab sorption (band I, 612-620 nm, = 161-206 M-1cm-1) and two absorptions at higher energy (band II, 438-442 nm, = 802-950 M-1cm-1 and band III, 381-396 nm, = 800-1130 M-1cm-1). These transitions are red shifted by approximately 173, 114 and 105 nm, respectively, from Ru complex 21 and their extinction coefficients are 2-5 times lower. An analogous e ffect has been reported for Cp*M(PMe3)2X (M = Fe, Ru).180 An additional absorption (band IV, 2900 M-1cm-1) is also observed for 22, in the high energy side, appear ing as a shoulder around 330 nm. The relatively weak intensities of these bands, low solvent depende nce and band shifts to higher energy in the series Fe < Ru,180,181 allow assignment of bands I, II, III and IV as d-d transitions. As expected, the absorption spectra of the bimetallic Ru/Au complex 27 are very similar to those of Ru complex 21 and a similar relationship is observed for Fe complex 22 and Fe/Au complex 28 . These results are consistent with those obtained in IR and cyclic voltammetry, once again confirming that that the electronic interactions between the two metals through the dppm bridge are negligible. Previous studies with the PPh3-substituted compounds Cp(PPh3)Ru ( µ -X)( µ -dppm)MX2 (M = Pt, Pd),124 have shown that the heterobimetallic complexes tend to exhibit band structures comparable to those of the corre sponding monometallic Ru complexes. These results suggest that th e low energy transitions are localized at the Ru center with the differences in absorption attributed to the electronic interactions between the two metals. Spectra of the Ru/Pt and Fe/Pt heterobimetallic complexes 23

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79 and 24 are similar to those of 21 and 22 , respectively. Three transitions are observed for the Ru/Pt complex 23 . The first band (band I, 423-432 nm, = 2300-3620 M-1cm-1) appears as a shoulder and has an extinction co efficient 5 times that of the monometallic Ru complex 21 . This is probably resulting from some charge transfer character due to the iodide bridge. Transitions II and III are si milar in intensity to those from the Ru monometallic 21 but slightly red shifted. The UV-vis spectrum for complex 24 is complicated by the overlapping of the bands which make them appearing as shoulders that are not well resolved. As for the monometallic Fe complex 22 , the Fe/Pt complex 24 exhibits four transitions. Band I appears as a tail around 571 nm with a rela tively low extinction coefficient ( 270 M-1cm-1 ) while band II ( 404-438 nm, = 3610-5670 M-1cm-1), band III ( 326-391 nm, = 5970-7430 M-1cm-1) and band IV ( 288-324 nm, = 9024-12120 M-1cm-1) are similar to the ones from complex 21 but exhibiting higher intensities (3-7 times higher). Usually, a blue shift of the dd transitions is expect ed for isostructural compounds when the metal is changed from Fe to Ru, due to increas ed electronic density at the more electron rich Ru metal center.180 Comparison of the transitions between the two platinum complexes 23 and 24 reveals the expected blue shift of all the transitions. However (except for band I) th e intensities are similar between the Ru/Pt complex 23 and the Fe/Pt complex 24 which suggests some charge transf er character associated with the d-d transitions. Since most of the transitions appear as shoulders no further rationalization can be made about the nature of these charge transfers. The spectrum for the Fe/Pd complex 26 shows features similar to of Fe complex 22 but the transitions are slightly red shifted and 5-11 times more intense. Three transitions

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80 are observed in the visible region of the spectrum for complex 26 . Band I appears as a shoulder around 613-647 nm, with an extincti on coefficient difficult to resolve ( 946-1840 M-1cm-1), followed by two bands with highe r intensities (band II, 495-520 nm, = 3220-5160 M-1cm-1 and band III 421-430 nm, = 3950-4930 M-1cm-1), while a more intense absorption is also observed in th e near UV region at 329-352 nm (band IV, = 11790-14500 M-1cm-1). A significant difference is observed for Ru/Pd complex 25 as compared to the monometallic Ru complex 21 and the heterobimetallic complexes 23 and 27. The spectrum is dominated by two transitions, band II in the visible region (482-524 nm, = 2050-4720 M-1cm-1) and band IV, showing at higher energy (327-330 nm, = 13910-18300 M-1cm-1). Two shoulders difficult to locate accurately are also observed in the lower energy sides of ba nd II (band I, 618625 nm, = 816-1050 M-1cm-1) and band IV (band III, 389-397 nm, 6320 M-1cm-1). First of all, the expected blue shift of the bands observed for the heterobimetallic Ru/Pt and Fe/Pt pair 23 and 24 as well as for the heterobimetallic Ru/Au and Fe/Au pair 27 and 28 is not observed for the two heterobimetallic complexes 25 and 26 . In fact the transitions for Ru/Pd complex 25 are red shifted with respec t to the model compound 21 and Ru/Pt complex 23, which make them more similar to those from the Fe/Pd complex 26 . These spectral characteristics for complex 25 are consistent with a charge transfer process. The presence of the solvatochromic effect182,183 observed for band II of complexes 25 and 26 is consistent with MLCT since a blue shift of the maximu m absorption is observed when the polarity of the solvent increases. Already from these results, we can see that the iodide bridge is responsible for the electronic changes in th e spectra of the compounds since the non-

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81 iodide bridge complexes 27 and 28 do not exhibit a significant difference compared to monometallic complexes 21 and 22 . Table 4-8. UV-vis spectr al data of complexes 21-28. abs, max/nm ( /M-1.cm-1) Complex Medium IV III II I Benzene 279 (7830) sh 324 (3480) 436 (472) THF 276 (8490) sh 325 (3110) 438 (432) CH2Cl2 275 (9780) sh 324 (3140) 436 (428) 21 Acetonitrile 276 (9720) sh 324 (3250) 439 (438) Benzene 328 (2850) sh 388 (920) sh 439 (860) 612 (193) THF 332 (2940) 396 (1130) sh 442 (950) 620 (206) CH2Cl2 324 (2700) sh 385 (800) sh 438 (802) 612 (191) 22 Acetonitrile 323 (2430) sh 381 (720) sh 438 (770) 612 (161) Benzene 334 (3860) sh 388 (3140) sh 431 (2720) THF 328 (8620) sh 387 (4350) 428 (3620) sh CH2Cl2 335 (7510) sh 388 (4300) 432 (3010) sh 23 Acetonitrile 331 (5580) sh 384 (3170) 423 (2300) sh Benzene 288 (12120) sh 354 (6190) 438 (3611) sh tail THF 324 sh 391 (5970) 423 (5670) sh tail CH2Cl2 321 (9025) sh 350 (6450) sh 417 (4690) tail 24 Acetonitrile 326 (7430) sh 404 (3911) 571 (270) Benzene 324 (8830) 524 (2050) 624 (660) sh THF 327 (14100) 397 sh 520 (3480) 641 (885) sh CH2Cl2 330 (18330) 396 sh 495 (4720) 622 (985) sh 25 Acetonitrile 329 (17380) 389 (6320) sh 482 (4300) 618 (816) sh Benzene 329 (14250) 430 (3950) sh 520 (3220) 647 (946) sh THF 337 (14570) sh 424 (4780) sh 513 (4370) 643 (1280) sh CH2Cl2 351 (11790) sh 424 (4700) sh 499 (4540) 618 sh 26 Acetonitrile 352 (12570) sh 421 (4930) sh 495 (5160) 613 (1840) sh Benzene 280 (6600) 308 (3820) sh 414 (215) THF 274 (7680) sh 304 (3650) sh 418 (248) CH2Cl2 274 (8950) sh 304 (3760) sh 418 (245) 27 Acetonitrile 274 (7920) sh 306 (3350) sh 420 (197) sh Benzene 326 (2950) sh 386 (996) sh 442 (741) 607 (182) THF 325 (2950) 375 (1660) sh 437 (724) 610 (149) CH2Cl2 325 (3340) sh 375 (1160) sh 441(814) 611 (199) 28 Acetonitrile 327 (1430) sh 377 (869) sh 440 (697) 612 (158)

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82 Conclusion In summary, this chapter describes the synthesis and characterization of a new series of heterobimetallic Ru/Pt, Ru/Pd and Ru/Au complexes as well as their isoelectronic Fe/Pt, Fe/Pd and Fe/Au an alogues. The structur es of compounds 23-26 were determined by X-ray crystallography and were found similar to those of halide-bridged complexes previously reported.124,134,135 The heterobimetallic complexes 23-28 also illustrate the effect of an I-bridged ligand in mediating the electronic interactions between the two metals as can be seen by comparison of the redox potentials, carbonyl stretching frequencies and UV-vis transitions of heterobimetallic complexes 23-26 with those of the monometallic compounds 21 and 22 and also with the dppm-bridged complexes 27 and 28 . Investigations on methanol oxi dation studies using these comp lexes will be presented in Chapter 5.

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83 CHAPTER 5 ELECTROCHEMICAL OXIDATION OF METHANOL WITH ANALOGOUS RUTHENIUM AND IRON HETEROBIMETALLIC COMPLEXES: A COMPARISON STUDY Introduction Heterobinuclear complexes have long been recognized to have reactivity different from that of their mononuclear analogues.115-120 The interest in such species is due to the fact that the two different metals can work cooperativel y and/or each metal center can perform a different task to lead to an increase in activity.93,99-105 Such an effect has been noted for the el ectrooxidation of meth anol using various electrode materials, initially Pt anodes26-27 and then more complex alloys.18,19,28-31,44-51 Surface studies on Pt anodes showed that Pt is poisoned by adsorbed CO which is formed as an intermediate during the electrooxidation process.39 Addition of a second metal improved the anode behavior, with RuPt systems proving to be particularly effective.18,19,28-31 In the “bi-functional mechanism” initially proposed by Watanabe and Motoo, the Pt sites are responsible for th e binding and dehydrogenation of methanol while the Ru sites activate wa ter through formation of Ru-oxo intermediates, which are involved in conversion of surface-bound CO to CO2.37,38,40,41 Previous studies of electrochemical oxidation of methanol using the heterobimetallic catalysts Cp(PPh3)Ru( µ -Cl)( µ -dppm)PtCl2 ( 1 ),134 Cp(PPh3)Ru( µ -Cl) ( µ -dppm) PtCl2 ( 2 ),135 and Cp(PPh3)RuCl( µ -dppm)AuCl ( 3 )135 proved that the presence of the second metal is beneficial since an enhancement of the catalytic activity is

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84 observed when compared to the monomeric model compounds CpRu( 2-dppm)Cl,113 or CpRu(PPh3)2Cl.141 In this chapter the heterobimetallic Ru complexes Cp(CO)Ru( µ -I)( µ -dppm)PtI2 ( 23 ), Cp(CO)Ru( µ -I)( µ -dppm)PdI2 ( 25 ), and Cp(CO)RuI( µ -dppm)AuI ( 27 ) and their isoelectronic Fe analogues Cp(CO)Fe( µ -I)( µ -dppm)PtI2 ( 24 ), Cp(CO)Fe( µ -I) ( µ -dppm)PdI2 ( 26 ), and Cp(CO)FeI( µ -dppm)AuI ( 28) were investigated as catalysts for the electrochemical oxidation of methanol. Electrochemical Oxidation of Methanol with Ru and Fe Heterobimetallic Compounds The cyclic voltammograms of the heterobimetallic complexes were obtained in 1,2dicloroethane (DCE) using 0.1 M tetrabutylamm onium triflate (TBAT) as electrolyte. Some of the experiments were performed with tetrabutylammonium hexafluorophosphate (TBAH) as electrolyte in order to re solve overlapping redox waves (complexes 23 and 25 ). The cyclic voltammograms for the heterobimetallic complexes 23 28 each display three waves in the 1.00-2.25 V range. These redox processes have been previously described for several Ru heterobimetallic complexes having similar structures. For ruthenium complexes 23 , 24 and 27 , the first and third waves are assigned to the Ru(II/III) and Ru(III/IV) couples, respectively, while the second wave is assigned to the redox couple of the second metal. For iron complexes 24 , 26 and 28 , the trend is very similar to their ruthenium analogues with the first and third waves assigned to the Fe(II/III) and Fe(III/IV) couples , respectively and the middle one assigned to the redox couple of the second metal. The cyclic voltammograms of the Ru/Pt complex 23 (Figure 5-1), Ru/Pd compound 25 (Figure 5-3) and Fe/Pd complex 26 (Figure 5-4) show significant increases of the

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85 current after addition of 50 µL of methanol to the system. These current increases usually coincide with the redox potential of the sec ond metal and indicate that a catalytic process for methanol oxidation is occu rring at this point. The cyclic voltammogram for the isoelectronic Fe/Pt complex 24 (Figure 5-2) was also obtai ned. Again the same behavior is observed after addition of methanol , but in contrast to the complexes 23 , 25 or 26 smaller increases are observed at the Pt(II/IV) redox waves of 24 . Ru/Au complex 27 was found to be the least stable of all the complexes since decomposition of the solid state compound was observed after several weeks in the dry box and also under the conditions of cyclic voltammetry. The cyclic voltammogram of complex 27 could be obtained, howe ver rapid degradation of the heterobimetallic structure to the fragment [CpRu(CO)( 2dppm)]I is evidenced after several cycles (Figure 5-5) (compared with the original sample). In the beginning, there is an irreversible Ru(II/III) redox wave which rapidly becomes reversible with a slight shift to lower potential. The dppm-bridged Fe/Au complex 28 was more stable and the cyclic voltammetry could be performed without any problems (Fi gure 5-6). After additi on of methanol, the typical increases in the current are observed for both Ru/Au complex 27 and for the Fe/Au complex 28 that coincides with the oxidation wa ves of Au(I/III) couples and Ru or Fe(III/IV) redox waves, indicati ng catalytic activity for meth anol oxidation. This process was previously observed for the analogous CpRu(PPh3)I( µ -dppm)AuI ( 31 ).113 In order to determine the catalytic behavior of complexes 23-28 , bulk electrolyses of methanol were carried out for product identification and quantification. The in itial electrooxidation experiments using complexes 23-28 were performed in 0.7 M TBAT/DCE at a potential

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86 E vs. NHE (V) 0.00.51.01.52.02.5 I ( A) -50 0 50 100 150 200 250 5 mM catalyst addition of 50 L of MeOH Ru OC I Ph2P PPh2 Pt I I 0.1 M TBAT/ DCE sr= 50 mV/sRu(II/III) Pt(II/IV) Ru(III/IV) Figure 5-1. Cyclic vol tammograms of complex 23 ; glassy carbon working electrode; Ag/Ag+ reference electrode. E vs. NHE (V) 0.20.40.60.81.01.21.41.61.82.02.22.4 I ( A) -20 0 20 40 60 80 100 120 5 mM catalyst addition of 50 L of MeOH Fe OC I Ph2P PPh2 Pt I I 0.1 M TBAT/ DCE sr= 50 mV/sFe(II/III) Pt(II/IV) Fe(III/IV) Figure 5-2. Cyclic vol tammograms of complex 24 ; glassy carbon working electrode; Ag/Ag+ reference electrode.

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87 E vs. NHE (V) 0.00.51.01.52.02.5 I ( -20 0 20 40 60 80 100 120 140 160 180 200 5 mM catalyst addition of 50 mL of MeOH Ru(II/III) Pt(II/IV) Ru(III/IV)0.1 M TBAH/ DCE sr = 50 mV/s Ru OC I Ph2P PPh2 Pd I I Figure 5-3. Cyclic vol tammograms of complex 25 ; glassy carbon working electrode; Ag/Ag+ reference electrode. E vs . NHE (V) 0.00.51.01.52.02.5 I ( A) -20 0 20 40 60 80 100 120 140 5 mM catalyst addition of 50 L of MeOH 0.1 M TBAT/ DCE sr= 50 mV/sFe(II/III) Pd(II/IV) Fe(III/IV) Fe OC I Ph2P PPh2 Pd I I Figure 5-4. Cyclic vol tammograms of complex 26 ; glassy carbon working electrode; Ag/Ag+ reference electrode.

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88 E vs. NHE (V) 0.20.40.60.81.01.21.41.61.82.02.2 I ( A) -50 0 50 100 150 200 5 mM catalyst addition of 50 mL of MeOH Ru OC I Ph2P PPh2 Au I 0.1 M TBAT/ DCE sr= 50 mV/sRu(II/III) Au(I/III) Ru(III/IV) E vs. NHE (V) 0.20.40.60.81.01.21.4I ( A) -60 -40 -20 0 20 40 60 After 2 cycles After 5 cycles Figure 5-5. Cyclic vol tammograms of complex 27 ; glassy carbon working electrode; Ag/Ag+ reference electrode. E vs. NHE (V) 0.20.40.60.81.01.21.41.61.82.02.22.4 I ( A) -20 0 20 40 60 80 100 5 mM catalyst addition of 50 mL of MeOH Fe OC I Ph2P PPh2 Au I 0.1 M TBAT/ DCE sr= 50mV/sFe(II/III) Au(I/III) Fe(III/IV) Figure 5-6. Cyclic vol tammograms of complex 28 ; glassy carbon working electrode; Ag/Ag+ reference electrode.

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89 of 1.7 V vs. NHE as done in previous studies.113,134,135 Under these conditions very poor results were obtained due to the degradation of the catalysts and/or side reactions with the chlorinated solvent, resulting in inhibition of the catalysis. Control reactions using Ru/Pt complex 23 and Fe/Pt complex 24 showed that reaction of 1,2-dichloroethane or dichloromethane solutions of the complexes led to side reactions with the solvent after several days. Evidence could be seen in the 31P{1H} NMR spectra, which showed the presence of additional small peaks along with formation of Pt( 2-dppm)I2. Also, mass spectrometry of the vacuum-transferred solutions showed the presence of chlorinated compounds not present in the solvent in such high concentration before the reaction. In order to stabilize the catalysts, several solutions were attempted such as adding PPh3 to the system (1:1, catalyst: PPh3) and changing the solvent. The results obtained when PPh3 was added showed small improvements due to substitution of the carbonyl ligand by PPh3. The substitution can be detected by cyclic voltammetry (CV). For the Ru/Pt complex 23, addition of 1 equiv. of triphenylphosphine results in the splitting of the Ru(II/III) redox wave of 23 (Figure 5-7). Addition of methanol to the catalyst/PPh3 solution seems to favor the substitution of the carbonyl ligand by PPh3 since stabilization is now observe d and the resulti ng complex shows identical redox potentials with the PPh3 complex 29. The isoelectronic Fe/Pt complex 24 (Figure 5-8) exhibited behavior simi lar to that of the Ru/Pt complex 23. When PPh3 (1 equiv) is added to the system, a small shift to lower potential is observed for all the waves which would be expected if the CO ligand is substituted by the more electrons donating PPh3. An additional wave is also observed at lower potential after addition of methanol into the system. No comparison could be made with Cp(PPh3)Fe( µ -I)( µ -dppm)

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90 E vs. NHE (V) 0.40.60.81.01.21.41.61.82.02.22.4 I ( A) -100 0 100 200 300 400 Cp(PPh 3 )Ru( -I)( -dppm)PtI 2 ( 29 ) 5 mM Cp(CO)Ru( -I)( -dppm)PtI 2 ( 23 ) 10mM 1 eq. PPh 3 50 L MeOH 50 L MeOH 0.1 M TBAT /DCE sr= 50 mV/S Figure 5-7. Cyclic vol tammograms of complex 23 in 0.1 M TBAT/ DCE effect of adding PPh3 ; glassy carbon working electrode; Ag/Ag+ reference electrode. E vs. NHE (V) 0.20.40.60.81.01.21.41.61.82.02.22.4 I ( A) -100 0 100 200 300 400 500 Cp(CO)Fe( -I)( -dppm)PtI2 ( 24 ) 10mM 1 eq. PPh3 50 L MeOH 50 L MeOH 0.1 M TBAT /DCE sr= 100 mV/S Figure 5-8. Cyclic vol tammograms of complex 24 in 0.1 M TBAT/ DCE effect of adding PPh3 ; glassy carbon working electrode; Ag/Ag+ reference electrode.

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91 PtI2 complex since an authentic samp le could not be prepared. Electrolyses in the presence of one equivalent of PPh3 were also carried out for the Ru/Pt complex 23 and for the Fe/Pt complex 24, resulting in an improvement of the catalysis only for the ruthenium heterobimetallic complex 23 (Figure 5-9). The experiments were performed at 1.9 V vs. NHE in 0.7 M TBAT/ DCE solution with the potential corresponding to the Pt (II/IV) redox couple of complex 23 (at 1.7 V vs. NHE only traces of oxidation products were detected). Adding PPh3 allowed improvement of the current efficiencies of 23 to a maximum value of 19.9 % obtained at 75 C (11.2 % without PPh3). The efficiecy decreased upon passage of further charge probably due to the degradation or deactivation of the catalyst. For the iron complex 24, only traces of dimethoxymethane as the 2-electron oxida tion product could be detected during the process. The use of acetonitrile as solvent for the cyclic voltammetry as a replacement for 1,2-dichoroethane showed that the complexes react with coordinating solvents, resulting in additional waves and shifts of the poten tials. Examples are shown in Figure 5-10 (CH3CN) and Figure 5-3 (DCE) for the heterobimetallic Ru/Pd complex 25 ; and also in Figure 5-11 (CH3CN) and Figure 5-4 (DCE) for the Fe/Pd complex 26 . Similar observations have been made with all of th e heterobimetallic complexes incorporating a CO ligand ( 23 28 ). Surprisingly, methanol proved to be th e best choice as solvent since carbonyl compounds 23-28 are more soluble in methanol th an the initial triphenylphosphine complexes 1 3 . Again, the experiments in neat metha nol demonstrated that the solvent is more favorable for the catalysis, as evidenced by improvement in the current efficiencies

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92 Charge (C) 020406080100120140 Oxidation Product ( mol) 0 20 40 60 80 100 DMM Ru/Pt ( 23 ) MF Ru/Pt ( 23 ) DMM (Ru/Pt + PPh3) MF (Ru/Pt + PPh 3 ) Figure 5-9. Evolution of the products from the electrooxidation of methanol in 0.7 M TBAT/DCE at 1.9 V vs. NHE for the Ru/Pt complex 23 . Effect of adding one equivalent of PPh3. E vs. NHE (V) 0.40.60.81.01.21.41.61.82.02.22.4 I ( A) -10 0 10 20 30 40 50 60 5 mM catalyst Ru OC I Ph2P PPh2 Pd I I 0.1 M TBAT/ Acetonitrile sr= 50mV/s0.99 V 1.24 V1.55 V 1.74 V 1.85 V Figure 5-10. Cyclic voltammetry of complex 25 in 0.1 M TBAT/ acetonitrile; glassy carbon working electrode; Ag/Ag+ reference electrode.

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93 E vs. NHE (V) 0.00.51.01.52.02.5 I ( A) -50 0 50 100 150 200 5 mM catalyst 0.1 M TBAT/ Acetonitrile sr= 50mV/s1.03 V 1.29 V 1.59 V 1.91 V Fe OC I Ph2P PPh2 Pd I I Figure 5-11. Cyclic voltammetry of complex 26 in 0.1 M TBAT/ acetonitrile; glassy carbon working electrode; Ag/Ag+ reference electrode. and turnover numbers. Due to the more limited anodic range for methanol, bulk electrolysis in methanol was performed at 1.5 V vs. NHE in 0.1 M tetrabutylammonium tetrafluoroborate (TBABF4), as previously described for the amino-substituted cyclopentadienyl complexes 8-11 , in Chapter 3. The oxidation products observed during the electrolyses are the same as those detected in the methanol oxidation with compounds 8-11 , which are dimethoxymethane (DMM) and methyl formate (MF). Carbon dioxide (CO2) formation was also detected by FTIR analysis of the headspace gases duri ng the electrooxidation of methanol using heterobimetallic complexes 23 and 24 . The product ratios, current efficiencies and turnover numbers (TON) for the electrochemi cal oxidation of me thanol by catalysts 23-26 as well as by the monomeric compounds CpRu(CO)(PPh3)I ( 32 ) and CpFe(CO)(PPh3)I ( 33 ) are summarized in Table 5-1. Results for the other monomeric

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94 model compounds, CpRu(CO)2I, CpFe(CO)2I, and Pt(COD)I2 as well as those from the combination of monomeric complexes 33 or 34 with Pt(COD)I2 are presented in Table 5-2. Pd(COD)I2 could not be used as a model compound because attempts to synthesize it led to undefined mixtures due of to the low stability of the compound. Attempts to perform electrolyses with the heterobimetallic Ru/Au and Fe/Au complexes 27 and 28 , respectively, proved to be very diffi cult due to the poor stability of the complexes under the condition of the electroly ses. In fact, traces of the two and four electron oxidation products DMM and MF were observed in the case of complex 27 but rapid degradation was observed after about 50C of charge was passed in the system as the color changed from pale yellow to colorless. No more charge could be passed after the color change was observed. Attempts to iden tify degradation products from the residual solid (after vacuum transfer of solvent) by 31P {1H} NMR or FTIR spectroscopy were unsuccessful because of the pres ence of the electrolyte in high concentration. The same decoloration could be observed upon elec trolysis of solution of Fe/Au complex 28, but no traces of DMM or MF could be de tected by GC or FTIR analysis. The ruthenium-containing complexes we re found to have superior activity compared to the isoelectronic iron complexes. Most of the time, no activity (complexes 26 and 28 ) or poor activities (complex 24 ) were observed for the iron-containing compounds in electrooxidation of methanol. No detectable product could be observed by GC analysis for the Fe/Pd or Fe/Au complexes 26 and 28 , respectively. Although for the Fe/Pt complex 24, the two-electron oxidation product DM M was formed selectively, only 4.86 % current efficiency could be achieved with about 1 TON after 200 C of charge was passed (Figure 5-12 and Table 5-1 ) .

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95 The Ru/Pt complex 23 was the most active catalyst among all the carbonyl compounds, reaching 63% current efficiency an d 13 TON, after 200 C of charge passed. The product evolutions (Figure 5-13) and product ratios (Table 5-1) for complex 24 show that DMM and MF are the oxi dation products from the elec trooxidation of methanol. In the early stage of the catalysis MF is pres ent in higher concentration than DMM (ratio: 0.35 at 20 C to 0.83 at 60 C). However, at th e end of the experiment, the 2-electron oxidation product DMM is observed in highe r concentration (ratio: 2.5 at 200 C). The Ru/Pd carbonyl complex 25 gave lower current efficiency and turnover number (22.78 % and 4) when co mpared to the Ru/Pt complex 23 . The product ratios and product evolution for 25 (Figure 5-14 and Table 5.1) also show a partitioning of the oxidation products different from that of 23 . In the beginning of the catalysis the 4-electron oxidation product is favored, then at the end of the experiment roughly 1:1 ratio of DMM and MF is detected. Control reactions with two monomeric mode l compounds were performed in order to compare their activities with those of the heterobimetallic complexes in electrooxidation of methanol (Table 5-2). Neither of them CpFe(CO)2I or CpFe(CO)(PPh3)I ( 33) showed any activity in oxidizing methanol. This is not surprising since the heterobimetallic complexes show poor (Fe/Pt complex 24 ) or no activity (complexes 26 and 28 ) for the process. A 1:1 mixture of 33 and Pt(COD)I2 complexes was also considered as a possible candidate for catalysis since the Fe/Pt complex 24 showed some activ ity (4.86% current efficiency and 1 TON). However only traces of DMM could be detected after 200 C of charge was passed into th e system. Although th e results from the Fe/Pt complex 24 are poor compared to the ones from the Ru -containing heterobimetallic complexes, the

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96 Charge (C) 050100150200250 Oxidation Products ( mol) 0 10 20 30 40 50 60 DMM Fe OC I Ph2P PPh2 Pt I I Figure 5-12. Product evolution for the electrooxidation of methanol in pure methanol using the Fe/Pt complex 24 . Charge (C) 050100150200250300350 Oxidation Products ( mol) 0 100 200 300 400 500 600 700 DMM MF Ru OC I Ph2P PPh2 Pt I I Figure 5-13. Product evolution for the electrooxidation of methanol in pure methanol using the Ru/Pt complex 23 .

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97 Charge (C) 050100150200250 Oxidation Products ( mol) 0 20 40 60 80 100 DMM MF Ru OC I Ph2P PPh2 Pd I I Figure 5-14. Product evolution fo r the electrooxidation of me thanol in pure methanol for the Ru/Pd complex 26 . beneficial effect of using he terobimetallic complexes can be observed in this case since the monomers are not active at all. Between all the monomeric ruthenium models used for the control reactions, only CpRu(CO)(PPh3)I ( 32 ) showed activity for electrooxi dation of methanol, having 21.42 % current efficiency with 3 TON achieved after 200 C of charge was passed. These results are similar to those from the Ru/Pd complex 25 (22.78% CE and 4 TON), however they are much lower compared to the Ru/Pt complex 23 (63.03 % CE and 12 TON) (Table 5-1). Other monomeric Ru complexes were also used for comparison. Complexes such as CpRu(CO)I2 or the cationic [Cp(CO)Ru( 2-dppm)]I exhibit limited activity for the electrooxidation of methanol sinc e only traces of the oxidation products could be detected after 200 C of charge was passed. Finally, the mixture of the monomeric complex 32 and Pt(COD)I2 was also used for quantification. In contrast to the Fe monomer 33 , complex

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98 32 when used in combination with Pt(COD)I2 exhibited slightly higher activity than the mononuclear Ru complex 32 alone (27.34% CE and 6 TON). Since Pt(COD)I2 shows only little activity (5.71% CE and 1 TON), the catalysis results from the mixture can be attributed to the combination of the activities of complex 32 and Pt(COD)I2. However, electrolysis with the heterobimetallic Ru/Pt complex 23 shows that in this case this is not the combination of the reactivit ies of each metal that is responsible for the higher activity of 23 but, in contrast to the mixt ure, it is due to an enhan cement of one metal by the close proximity of the other in the bimetallic complex 23 . In other words, the electronic interaction is important during the process which indicates that the structure of the heterobimetallic catalyst is still preserved during the electrocatalytic electrooxidation of methanol with complex 23 . As was also done for the amino-substituted complexes 8-11 from Chapter 3, the electrochemical oxida tion of methanol was performed in “wet conditions” by adding 10 µL of water into the system before starting the electrolysis experiments. The results are presented in Table 5-3 for the heterobimetallic complexes 23-26 as well as for the mononuclear compounds 32 and 33 . As mentioned, the presence of water at an early stage of the electrolysis (b efore it is generated by conde nsation) usually favors the formation of the more oxidized product MF. In contrast to the Cp-amino-substituted complexes 8-11 , the carbonyl complexes tend to exhi bit lower act ivities when water is added before the experiment. The Ru/Pt and Ru/Pd complexes 23 and 25, respectively, exhibit decreases of the current e fficiencies from 63.12% to 47.85% for 23 and from 22.78 % to 12.62% for 25 when wet conditions are used (Table 5-3). Closer observation of the product ratios and pr oduct evolutions for compound 23 shows that in the early

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99 stage of the catalysis methyl formate is favored until about 50 C of charge passed into the system (Figure 5-15). Then dimethoxymethane is formed preferentially until the end of the experiment. Degradation or /and deactivation of complex 23 is also observed under wet conditions since a decrease of the current efficiencies is det ected after 200 C of charge was passed (from 47.85% at 200 C to 40 .97% at 372 C). A decrease of the activity of 25 in wet conditions (from 22.78% to 12.62% at 200 C of charge passed), is also observed for the Ru/Pd complex 25 (Table 5-3, Figure 5.16). However, for complex 25, the partitioning of the oxidation products is slightly modified when compared to complex 23 since MF is formed as the major product until about 150 C, then DMM again becomes favored until the end of the experiment (200 C). Surprisingly, the Fe/Pt complex 24 shows small increases in the current efficiencies and TON under wet conditions (8.60% and 1 TON at 200 C). The product ratios and product evolutions for complex 24 show that under wet co nditions DMM and MF are formed in contrast to dry conditions which results in formation of the only 2-electron oxidation product (Table 5-3 and Figure 517). DMM was found to be the favored oxidation product during all the process, howev er after 100 C of charge was passed, MF could be detected in about 2:1 ratio. Additionally, a longer experiment (until 402 C) was performed for the Fe/Pt complex 24 which demonstrated that the complex did not lose its activity and a maximum of 10.35% CE and 4 TO N could be reached at the end of the electrolysis. As already observed under dry conditions , electrolyses of the heterobimetallic Fe/Pd complex 26 under wet conditions did not re sult in formation of any product detectable either in solutions by GC or in the gas phase by IR. The mononuclear Fe

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100 Table 5-1. Bulk electrolysis data for th e oxidation of methanol in “dry methanol” c by complexes 23-26 , 32 and 33 . Product ratios (DMM/MF)a,b Complex Ru/Pt ( 23 ) Fe/Pt ( 24 ) Ru/Pd ( 25 ) Fe/Pd ( 26 ) Ru ( 32 ) Fe( 33 ) Charge (C) 20 0.35 n/o 0.19 n/o 40 0.64 n/o 0.36 n/o 60 0.83 n/o 0.52 n/o 0.80 (50C) n/o (50C) 80 1.23 + 0.67 n/o 100 1.53 + 0.82 n/o 1.10 n/o 150 2.14 + 1.09 n/o 200 2.50 + 1.12 n/o 1.27 n/o (at charge X) 3.26 (302C) Current efficiencies (%) after 200C 63.12 4.86 22.78 21.42 TON after 200C 12 1 4 3 Current efficiencies (%) (at charge X) 64.05 (302C) TON (at charge X) 20 (302C) a Electrolysis were performed at 1.5 V vs. NHE in pure methanol. A 10 mM catalyst concentration was used for each experiment. b Determined by GC with respect to n-heptane as an internal standard. n/o : non observable product

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101 complex 33 exhibits very similar behavior compared to 26 , however in the case of the mononuclear Ru complex 33 , slightly lower activity was observed when water was added before the electrolysis. MF was found to be formed favorably during the experiment since the ratio decreased from 0.81 at 50 C to 0.71 at 200 C of charge passed and 20.11 % CE was obtained at 200 C with a total of 3 TON obtained at the end of the experiment. Experiments on CO2 Evolution As discussed above, the electrooxidati on of methanol in the presence of homogeneous catalysts results in the forma tion of formaldehyde and formic acid, which are the initial two and four-electron oxidation products fr om the process. In the presence of excess methanol those two undergo fast condensation leading to the formation of DMM, MF and water. The yields of liquid products DMM and MF, which can be Charge (C) 0100200300400 Oxidation Products ( mol) 0 100 200 300 400 500 600 DMM MF Ru OC I Ph2P PPh2 Pt I I Figure 5-15. Product evolution for th e electrolysis of Ru/Pt complex 23 in 0.1M MeOH/TBABF4 in wet methanol.

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102 Table 5-2. Bulk electrolysis data for th e oxidation of methanol in “dry methanol” c with monomeric complexes. Product ratios (DMM/MF)a,b Complex CpRu(CO)2I CpFe(CO)2I [CpRu( 2-dppm)(CO)]I Ru ( 32 ) + Pt(COD)I2 Fe( 33 ) + Pt(COD)I2 Pt(COD)I2 Charge (C) 50 n/o n/o n/o 100 n/o n/o n/o 8.57 n/o 150 10.76 200 n/o 4.21 14.31 4.38 (at charge X) Current efficiencies (%) after 200C 0.4 0.74 27.34 0.22 5.71 TON after 200C <1 <1 6 <1 1 Current efficiencies (%) (at charge X) TON (at charge X) a Electrolysis were performed at 1.5 V vs. NHE in pure methanol. A 10 mM catalyst concentration was used for each experiment. b Determined by GC with respect to n-heptane as an internal standard.

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103 Charge (C) 050100150200250 Oxidation Products ( mol) 0 10 20 30 40 50 60 DMM MF Ru OC I Ph2P PPh2 Pd I I Figure 5-16. Product evolution for th e electrolysis of Ru/Pt complex 25 in 0.1M MeOH/TBABF4 in wet methanol. Charge (C) 0100200300400500 Oxidation Products ( mol) 0 20 40 60 80 100 120 140 DMM MF Fe OC I Ph2P PPh2 Pt I I Figure 5-17. Product evolution for th e electrolysis of Ru/Pt complex 24 in 0.1M MeOH/TBABF4 in wet methanol.

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104 Table 5-3. Bulk electrolysis data for the oxidation of methanol in “wet methanol” c with complexes 23-26, 32 and 33 . Product ratios (DMM/MF)a,b Complex Ru/Pt ( 23 ) Fe/Pt ( 24 ) Ru/Pd ( 25 ) Fe/Pd ( 26 ) Ru ( 32 ) Fe( 33 ) Charge (C) 20 0 n/o 0 n/o n/o 40 0.64 n/o 0.13 n/o n/o 60 1.15 0.28 n/o 0.81 (50C) n/o 80 1.57 0.45 n/o n/o 100 1.90 0.60 n/o 0.78 n/o 150 2.71 2.01 1.07 n/o n/o 200 3.49 2.16 1.47 n/o 0.71 n/o (at charge X) 4.10 (372C) 2.28 (402C) Current efficiencies (%) after 200C 47.85 8.60 12.62 20.11 TON after 200C 10 1 2 3 Current efficiencies (%) (at charge X) 40.97 (372C) 10.35 (402C) TON (at charge X) 16 (372C) 4 (402C) a Electrolysis were performed at 1.5 V vs. NHE in pure methanol. A 10 mM catalyst concentration was used for each experiment. b Determined by GC with respect to n-heptane as an internal standard. n/o: non observable product.c Addition of 10 µL of water before starting the electrolyses.

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105 determine by GC analysis, have been used to follow the process. Such experiments are now standard practice for the electrochemi cal oxidation of methanol in homogeneous systems.113, 134, 135, 141 Until now, no experiments detecting any possible gaseous products have been reported. In order to detect gaseous products a gas cell system for FT IR detection of the head space gases during the electrooxidatio n of methanol has been designed and fabricated. Since the FTIR spectrometer is ou tside a glove box, the major difficulty is to avoid contamination by CO2 from the atmosphere. Ambient CO2 can be purged from the instrument sample cell compartment by N2 purge (Figure 5-18) and a blank is always analyzed before introducing the gas sample for verification. All the electrolyses have been performed in the glove box and a gas tight syringe has been used to take gas sample from the head space gases during the process, (every 20C until 200C of charge have been passed) (Figure 5-19). At the end of each expe riment a total volume collected of 60 mL of gas is always introduced in the IR gas cell in order to compare the results observed for the experiments. The FTIR analysis of the headspace ga ses has been performed for all the electrolyses using the hete robimetallic carbonyl compounds 23-26 ,as well as 32 and 33 and mixtures. However, among all the complexes, only heterobimetallic 23 and 24 showed sufficient quantity of CO2 for isotopic labeling experi ments while only traces are observed for the other compounds. As obser ved in the FTIR spectra for the Ru/Pt complex 23 (Figure 5-20) and for the Fe/Pt complex 24 (Figure 5-21), CO2 could be detected ( CO = 2361, 2338 cm-1) along with traces of MF a nd a large excess of methanol gas. For both compounds the electrolyses ha ve been performed under “dry conditions”

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106 FTIR spectrometer cage under N260 mLgas tight syringe septa NaClwindows Figure 5-18. Schematic of the gas cell set up for FTIR detection of gaseous products. Figure 5-19. Photograph of the setup used for the electrooxidation of methanol. The gas tight syringe (on the right side) is used to take samples of gas.

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107 and “wet conditions". It appeared that the pres ence of water before the electrolyses favors the formation of CO2 for both complexes. With these results in hand 13C labeling experiments have been carried out to confirm the origin of the CO2 (originally from Ru-CO or Fe-CO vs. originally from CH3OH). Isotopic Labeling Study In order to determine the origin of the CO2 formed during the electrolyses with complexes 23 and 24, two experiments needed to be performed, one using 12CH3OH and the 13CO compounds of the Ru/Pt or Fe/Pt complexes 23 or 24 , respectively, the other one using the unlabeled 12CO complexes and 13CH3OH. The theoretical values of the IR freque ncies for the labeled compounds can be calculated using the equation derive d from the Hooke’s law (Eq. 5.3).184 1/21 2c()/()xyxyf v MMMM (5.3) where = the vibrational frequency (cm-1) c = velocity of light (cm/s) f = force constant of bond (dyne/cm) Mx, My = exact masses of isotopes (g) Using the experimental values of the carbonyl stretching frequencies for 12CO2 (Figure 5-22, (CO) = 2349 cm-1) and Eq. 5.4, the theoretical value for the asymmetrical stretching frequency of 13CO2 is predicted to be at (CO) = 2296 cm-1. Using the experimental values of the carbonyl stretching frequencies of complexes 21-24 , predicted values of the stretching frequencies can be obtained in the same manner (Table 5-4).

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108 4000.03600320028002400200018001600140012001000800600450.0 cm-1 %T Ru OC I Ph2P PPh2 Pt I I methanol CO2HCOOCH3 Dry methanol Wet methanol Figure 5-20. FTIR spectrum of the headspace gases during the electrooxidation of methanol with Ru/Pt complex 23 ; In dry and wet conditions; after 200 C of charge passed.

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109 Fe OC I Ph2P PPh2 Pt I I CO2HCOOCH3CO2 Dry methanol Wet methanol methanol 4000.03600320028002400200018001600140012001000800600450.0 cm-1 %T Figure 5-21. FTIR spectrum of the headspace gases during the electrooxidation of methanol with Fe/Pt complex 24 ; In dry and wet conditions; fter 200 C of charge passed

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110 1313 12121/2 12 13()/() () ()()/()OO CC OO CCMMMM vCO vCOMMMM (5.4) where 12 13-23 -23 -23161.9926 x 10 2.1592 x 10 2.6560 x 10 ()C C OMg Mg M gO Table 5-4. Predicted and experimental carbonyl stretching frequencies for CpRu(CO)2I, CpFe(CO)2I , 21 , 22 , 23 and 24 . Complex (CO) exp (13CO) theo (13CO) exp CpRu(CO)2I 2040, 1966 cm-1 1994, 1922 cm-1 1998, 1918 cm-1 Cp(CO)Ru( 1-dppm)I ( 21 ) 1952 cm-1 1908 cm-1 1907 cm-1 Ru/Pt ( 23 ) 1969 cm-1 1925 cm-1 1924 cm-1 CpFe(CO)2I 2039, 1968 cm-1 2044, 2000 cm-1 (lit) 1993, 1924 cm-1 1998, 1955 cm-1 1986, 1941 cm-1 Cp(CO)Fe( 1-dppm)I ( 22 ) 1946 cm-1 1902 cm-1 1900 cm-1 Fe/Pt ( 24 ) 1963 cm-1 1919 cm-1 1914 cm-1 Synthesis of the 13CO-Ru/Pt complex 23-13C The 13CO-Ru/Pt complex 23-13C was synthesized from the monomeric CpRu(PPh3)2Cl. Using a known procedure,185 incorporation of the 13CO was achieved by formation of the RuIV-( 3-allyl) complex 34 by oxidative addition of allyl chloride to CpRu(PPh3)2Cl (45% yield) followed by reductive elim ination in presence of 13CO which leads to CpRu(13CO)2Cl (80% yield) (Eq. 5.1). Subsequent steps to 23-13C have already been described in Chapter 3 for the unlabeled compound.

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111 Ru Ph3P Cl PPh3 Cl Ru Cl Cl decane 120°C 13CO(1atm) decane 140°C Ru O13C Cl C13O (5.1)3435 Synthesis of the 13CO-Fe/Pt complex 24-13C The synthesis of the 13CO-Fe/Pt complex 24-13C needed to follow a different way than that in Eq. 5.1 due to the diffi culties with the isolation of CpFe( 3-allyl)Cl2. In order to incorporate the carbonyl ligands, CpFeII(benzene)PF6 has been chosen as a possible intermediate. Since reduction of the com pound by Na/Hg leads to the very reactive intermediate CpFeI(benzene), substitution of the benzene by ligand such as CO can be carried out. This strategy ha s been applied to synthesize 13C labeled [CpFe(CO)2]2 dimer (Eq. 5.2)185 which led to the formation of the CpFe(13CO)2I precursor after reaction with iodine in refluxing chloroform (Eq.5.3). Again subsequent steps to 24-13C have already been described in Chapter 3 for the unlabeled compound. Fe (5.2) PF6Na/Hg(5%) THF -20°C Fe 13CO THF [CpFe(13CO)2]2 36 (5.3)[CpFe(13CO)2]2 Fe I2CHCl3O13C O13C I 37 Isotopic labeling experiments Bulk electrolyses have been performed in the presence of a 1:1 mixture of 12CH3OH and 13CH3OH (about 2 mL of 13CH3OH was used for each experiment) for both (12CO)-Ru/Pt complex 23 and (12CO)-Fe/Pt complex 24 . If the 13C labeled CO2 were

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112 formed from the electrooxidation of 13CH3OH, it would be observe d at the theoretical stretching frequency value of 2296 cm-1. However for both complexes 23 and 24, no 13CO2 has been detected (Figure 5-22) wh ich indicates that the origin of CO2 during the electrolysis is exclusively from th e conversion of the CO ligand to CO2. The 13C Ru/Pt complex 23-13C has been synthesized a nd the electrooxidation of methanol has been carried out. In that case, traces of 13CO2 could be detected by FTIR along with the presence of 12CO2. Since the amounts of CO2 formed for the Ru/Pt complex 23 are minor compared to the Fe/Pt complex 24 , the 12CO2 could be from some of CO2 present in the needle, even if a small amount of the gas sample from the syringe is always used to purge the needle before injection. However traces of 13CO2 are also detected when the electrolysis is performed with the 13C Ru/Pt complex 23-13C which confirms that the 13CO ligand is oxidized to 13CO2 during the process. It has been also observed that the formation of CO2 is favored by the presen ce of water since the concentration of CO2 is higher in wet conditions for both complexes. The Fe/Pt complex 24-13C has been synthesized as well and the results showed that compound 24 is a better candidate for the labeling experiments since the concentration of CO2 formed during the process is much higher than in the case of the Ru/Pt analogue 23 . Again the results confirme d without doubt that the CO2 is originally coming from the oxidation of the CO ligand by water pr esent during the process since only 13CO2 could be observed when the labeled Fe/Pt complex 24-13C was used for the electrolysis (Figure 5-22) Conclusion The catalytic activities for the electrooxidati on of methanol were investigated for a series of heterobimetallic Ru/Pt, Ru/Pd and Ru/Au as well as for their isoelectronic Fe/Pt,

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113 Fe/Pd and Fe/Au complexes incorporating a ca rbonyl ligand at the Ru or Fe centers. These complexes showed an enhancement of the current after a ddition of methanol during the CV which is typical for electrooxidation of meth anol. Similar behavior had been previously reported for related complexes.124,134,134 Electrolyses with complexes 23-28 have been performed in the presence of methanol and the product mixtures were analyzed for DMM and MF only. The carbo nyl complexes Ru/Au, Fe/Au and Fe/Pd complexes 27 , 28 , and 26, respectively, did not show ev idence of methanol oxidation products during the process since DMM, MF or CO2 could not be dete cted by GC or by FTIR. In contrast Ru/Pt Ru/Pd complexes 23 and 25, respectively are active catalysts for the electrochemical oxidation of methanol showing good (63.12% CE and 12 TON for 23 ) to moderate activity for the pr ocess (22.78% CE and 4 TON for 25 ). The results showed that water does not enhance the catalysis as observed for other systems (Chapter 3) but instead deactivation and/or degradation of the catalysts were observed resulting in lower current effici encies (47.85% CE and 10 TON for 23 and 12.62% CE and 2 TON for 25 ). The Fe/Pt complex 24 was found to be the only Fe-containing heterobimetallic demonstrating some activity for the electrooxidation of methanol with 4.86% CE and 1 TON in dry methanol and 8.60% CE and 1 TON in wet methanol. FTIR detection of the headspace gases during the electrochemical processes using heterobimetallic Ru/Pt and Fe/Pt complexes 23 and 24 showed formation of the possible 6e-oxidation product of methanol, CO2. The concentration of CO2 was found to be enhanced by the presence of water. Isotopic labeling experiments using 13CH3OH reveled that CO2 is not formed from the oxidation of methanol since no 13CO2 could be detected during the process for both Ru/Pt and Fe/Pt complexes 23 and 24 , respectively, in

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114 3538.932002800240020001800160014001200980.7 cm-1 %T 2361.42 2338.61 2295.81 2271.55 12CO2 13CO2 (13CO)Ru/Pt -12CH3OH (12CO)Ru/Pt -13CH3OH (13CO)Fe/Pt -12CH3OH (12CO)Fe/Pt -13CH3OH Wet conditions Figure 5-22. Isotopic labeling experiments. FTIR spectra of the headspace gases during the electrooxidation of methanol

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115 presence of 13CH3OH. Experiments in wet cond itions (addition of 10 µ L of water into the system before electrolyses) using the 13CO-Ru/Pt complex 23-13C in presence of 12CH3OH showed formation of traces of 13CO2 which confirms that the origin of the CO2 is from the catalyst and not from the oxidation of methanol. The experiment using 13CO-Fe/Pt complex 24-13C proved to be particularly effici ent in showing the origin of carbon dioxide when compared to the isoelectronic 13CO-Ru/Pt complex 23-13C s ince CO2 was observed in higher concentration. From the results, it is clear that the origin of carbon dioxide is again from the oxidation of the carbonyl ligand present in the complexes.

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116 CHAPTER 6 EXPERIMENTAL SECTION General Procedures All reactions and manipulations were pe rformed under an argon atmosphere using standard Schlenk techniques. Pentane and ethyl ether were dried by distillation from Na/Ph2CO. 1,2-Dichloroethane and acetonitrile were dried by distillation from CaH2. Benzene and dichloromethane were dried on an MBRAUN solvent purification system using a double 4.8 L activated alumina columns type A2 for dichloromethane and a 4.8 L activated alumina type A2 couple with a 4.8 L column of cupper catalyst. All solvents were saturated with argon prior to use. Al l deuterated solvents for NMR measurements (Cambridge Isotope Labora tories) were degassed via freeze-pump-thaw cycles and stored over molecular sieves (4Å). 1H, 13C{1H} and 31P{1H} NMR spectra were recorded at room temperature on a Varian Mercury 300 spectrometer opera ting at 300, 75 and 121 MHz respectively, with chemical shifts ( , ppm) reported relative to tetramethylsilane (1H NMR), residual solvent (13C NMR) or 85% H3PO4 (31P NMR). High-resolution mass spectrometry was performed by the University of Florida analytical service. IR spectra were obtained as neat films on NaCl us ing a Perkin-Elmer Spectrum One FT-IR spectrophotometer. UV-vis spectra were recorded on Shimadzu UV-1650PC spectrophotometer using silica qua rtz cells (1 cm path length). Elemental analyses (C, H) were performed by Robertson Microlit Laboratories, Madison, NJ. CpRu(PPh3)( µ -I)( µ -dppm)PtI2 ( 29 ),124 CpRu(PPh3)I(1-dppm),134,135 CpRu(PPh3)I( µ dppm)AuI ( 31 ),124 CpFe(CO)(1-dppm)I ( 22 ),173 PPh3AuI ( 32 ), CpRu(CO)2I,174 1,3,5-

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117 Triaza-7-phosphaadamantane157 (PTA), CpRu(PTA)2Cl,163 and CpFe(benzene)BF4 186 were prepared as previously described. Al l other starting materials were purchased in reagent grade purity and used w ithout further purification. Electrochemistry Electrochemical experiments were perfor med at ambient temperature in a glove box using an EG&G PAR model 263A potentiost at/galvanostat. Cyclic voltammograms (CV) were recorded in 3.5 mL of DCE/0.1 M tetrabutylammonium trifluoromethanesulfonate (TBAT) at ambient temperature under nitrog en. All potentials are reported versus NHE and referenced to Ag/Ag+. The reference electrode consisted of a silver wire immersed in an acetonitrile solution containing freshly prepared 0.01 M AgNO3 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. Cyclic voltammetry was performed in a three-compartment H-cell separated by a medium -porosity sintered gl ass frit in 2.5-3.5 mL of DCE/0.1 M TBAT at room temperature under nitrogen. A gl assy carbon electrode (diameter 3 mm) was the working electrode and a platinum flag was used as the counter electrode. All electrochemical measurements were performed inside the glove box. The constant potential electrolysis was performed in similar equipment except that the glassy carbon working electrode was replaced by a vitreous carbon electrode Product Analysis The analysis of the remaining methanol and the oxidation products from the bulk electrolysis was performed via gas chromatography on a Shimadzu GC-17A chromatograph using a 15 m x 0.32 mm colu mn of AT™-WAX (Alltech®, 0.5µm film) on fused silica. The column was attached to the injection port with a neutral 5 m x 0.32 mm AT™-WAX deactivated guard column. The products produced during the

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118 electrolysis of methanol were quantitativel y determined with the use of a known amount of n-heptane as an internal standard. Produc t identification was c onfirmed by comparison of the retention times of the oxidation product with authentic samples. Synthesis CpCH2CH2N(CH3)2. In a 500 mL Schlenck flask, a solution of 1-chloro-2dimethylaminoethane (24.44 g, 0.227 mol) in 50 mL of THF was added dropwise to a cold (-20°C) stirred solution of CpNa ( 20 g, 0.227 mol) in 200 mL of THF. After the addition was completed, the reaction mixture wa s stirred at ambient temperature for 1 hr and subsequently refluxed for 24 hr s. To the mixture, 150 mL of Et2O were added and extraction was performed with H2O (3 x 100 mL). The organic layer was dried (MgSO4), filtered and concentrated at ambient temperature on a rotary evaporator. The residue remaining in the flask was fractionally distilled under vacuum (0.01mmHg, 30°C) to yield 18.5 g of a mixture of two olef inic regioisomers (60 % yield). 1H NMR (CDCl3): 2.22 (s, 6H, N(C H3)2 major), 2.23 (s, 6H, N(C H3)2 minor), 2.86-2.93 (m, 2H, C5H5 methylene), 6.01-6.41 (m, 3H, C5H5 vinyl). [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)2Cl (5). A solution of hydrated ruthenium trichloride (1.00 g, 4.82 mmol) in dry ethano l (50 mL) was added to a solution of triphenylphosphine (5.00 g, 19.28 mmol) in refl uxing ethanol (150 mL). Freshly distilled dimethylaminomethyl cyclopentadiene (1.31 g, 9.64 mmol) was dissolved in 50 mL of ethanol and added to the br own refluxing solution. The mi xture was refluxed for 48 hrs until an orange solution is formed. When th e solution was then concentrated to a small volume, an orange precipitate began to form. The orange solid was filtered through a swivel medium frit, dried and crystallized fr om methylene chloride and hexanes. Yield: 3.84 g (84%). 1H NMR (CDCl3): 2.82 (s, 6H, N(C H3)2), 2.80-2.85 (m, 2H,

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119 C H2CH2N(CH3)2), 3.21-3.36 (m, 2H, CH2C H2N(CH3)2), 3.51 (br s, 2H, C5H4), 3.80 (br s, 2H, C5H4), 7.09-7.31 (m, 30H, P(C6H5)3). 31P{1H} NMR (CDCl3): 39.2. [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)2I (6). A solution of 5 (1.52 g, 1.905 mmol) in methylene chloride (100mL) was washed with 150 mL solution of degazed 1M HCl. The organic layer was dried under MgSO4 and the solvent was evaporated. The resulting orange solid, after drying, was re acted with sodium i odide (2.85 g, 19.05 mmol) in degassed dichloromethane at room temperat ure. After 48 hrs, the resulting mixture was was washed with 3 x 50 mL of H2O. After drying the organic layer, evaporation of the solvent and recrystallization with CH2Cl2/hexanes, 1.68 g of a re d brown solid were obtained (85.5% yield). 1H NMR (CDCl3): 2.76 (s, 6H, NH+(C H3)2), 2.70-2.80 (m, 2H, C H2CH2NH+(CH3)2), 3.10-3.20 (m, 2H, CH2C H2NH+(CH3)2), 3.61 (br s, 2H, C5H4), 4.19 (br s, 2H, C5H4), 7.13-7.33 (m, 30H, P(C6H5)3). 31P{1H} NMR (CDCl3): 37.85. [ 5-C5H4CH2CH2NH(CH3)2]Ru(PPh3)2I (6'). The reaction was performed as for 6 , omitting the protonation step with 1 M HCl. [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( 1-dppm)I (7). A 500 mL Schlenk flask was charged with 6 (1.68 g, 1.63 mmol), dppm (1.25 g, 3.2 5 mmol) and 250 mL of THF. The orange mixture was stirred for 7 days at ambient temperature and the solvent was evaporated on vacuum pump line. The resulting crude mixture contained 1-dppm compound 7 , excess dppm and PPh3. After evaporation of the solvent on a rotary evaporator, purification was ach ieved by recrystallization us ing dichloromethane/hexane. 1.10 g of red-orange solid was obtained (59.3% yield). 1H NMR (CDCl3): 2.19 (s, 6H, NH+(C H3)2), 2.34-2.82 (m, 2H, C H2CH2NH+(CH3)2), 3.10-3.35 (m, 2H, CH2C H2NH+(CH3)2), 3.11 (m, 2H, Ph2PCH H PPh2), 3.47 (m, 2H, Ph2PCH H PPh2), 4.22

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120 (br s, 2H, C5H4), 4.36 (br s, 2H, C5H4), 6.79-7.79 (m, 35H, (C6H5)2PCH2P(C6H5)2 + P(C6H5)3). 31P{1H} NMR (CDCl3): 43.85 (dd, RuP Ph2CH2PPh2, JPP = 3, 41 Hz), 33.89 (dd, RuP Ph3, JPP = 21, 41 Hz), -26.64 (dd, Ru-PPh2CH2P Ph2, JPP = 3, 21 Hz) . [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)( 1-dppm)I (7'). The reaction was performed as for 7 , starting from the non protonated complex 6' . [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PtCl2 (8). In a 50 mL Schlenk flask, complex ( 7 ) (0.300 g, 0.263 mmol) and Pt(COD)Cl2 (98.5 mg, 0.263 mmol) were dissolved in 30 mL of benzene. The yellow solution was stirred at ambient temperature for 24 hrs then the solution was dr ied under vacuum and recrystallized from CH2Cl2/pentane to yield 0.151 g (41%) of yellow solid. 1H NMR (CDCl3): 2.39 (s, 6H, NH+(C H3)2), 2.74 (m, 2H, C H2CH2NH+(CH3)2), 3.05 (m, 1H, Ph2PC H HPPh2) 3.50 (m, 1H, Ph2PCH H PPh2), 3.70 (m, 2H, CH2C H2NH+(CH3)2), 4.26 (br s, 2H, C5H4), 4.44 (br s, 2H, C5H4), 6.03-8.07 (m, 35H, (C6H5)2PCH2P(C6H5)2 + P(C6H5)3). 31P{1H} NMR (CDCl3): 47.37 (dd, RuP Ph2CH2PPh2, JPP = 13, 35 Hz), 40.98 (dd, RuP Ph3, JPP = 3, 35 Hz), -7.21 (dd, Ru-PPh2CH2P Ph2-Pd, JPP = 3, 13 Hz, JPtP = 1872 Hz). HRMS (FAB): calcd for C52H52Cl2INP3PtRu 1277.0425 (M-I)+ , found 1277.0426. [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)( µ -I)( µ -dppm)PtCl2 (8'). The reaction was performed as for 8 , starting from the non protonated complex 7' . [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PtI2 (9). In a 50 mL Schlenk flask, complex 7 (0.200 g, 0.175 mmol) and Pt(COD)I2 (97.8 mg, 0.175 mmol) were dissolved in 30 mL of dichloromethane. The yellow-orange solution was stirred at ambient temperature for 2 hrs then the solution was dried under vacuum pump and recrystallized from CH2Cl2/pentane to yield 0.185 g ( 64.5%) of an orange solid. 1H NMR

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121 (CDCl3): 2.66 (m, 1H, Ph2PCH H PPh2), 3.07 (s, 6H, NH+(C H3)2), 3.55-3.72 (m, 4H, C H2C H2NH+(CH3)2), 4.47 (br s, 2H, C5H4), 5.29 (m, 1H, Ph2PC H HPPh2), 5.75 (br s, 2H, C5H4), 6.81-8.12 (m, 35H, (C6H5)2PCH2P(C6H5)2 + P(C6H5)3). 31P{1H} NMR (CDCl3): 46.65 (dd, RuP Ph2CH2PPh2, JPP = 12, 35 Hz), 39.36 (dd, RuP Ph3, JPP = 3, 34 Hz), -1.84 (dd, Ru-PPh2CH2P Ph2-Pd, JPP = 3, 12 Hz, JPPt = 1872 Hz). HRMS (FAB): calcd for C52H52I3NP3PtRu 1460.9137 (M-I)+ , found 1460.9116. [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)( µ -I)( µ -dppm)PtI2 (9'). The reaction was performed as for 9 , starting from the non protonated complex 7' . [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PdCl2 (10). In a 50 mL Schlenk flask, complex 7 (0.300 g, 0.263 mmol) and Pd(COD)Cl2 (75.2 mg, 0.26 mmol) were dissolved in 30 mL of dry methanol. Th e dark red solution was stirred at ambient temperature for 1 hr until formation of a red-orange precipitate. The solution was concentrated under vacuum to a small volum e (4-5 mL), filtra ted through a medium swivel frit, washed with hexanes and drie d under vacuum. The product was recrystallized from CH2Cl2/pentane to yield 0.243 g (65.9%) of a red-orange solid. 1H NMR (CDCl3): 2.42 (s, 6H, NH+(C H3)2), 2.78 (m, 2H, C H2CH2NH+(CH3)2), 3.48 (m, 2H, CH2C H2NH+(CH3)2), 3.72 (m, 1H, Ph2PC H HPPh2), 4.31 (m, 1H, Ph2PCH H PPh2), 4.40 (br s, 2H, C5H4), 5.26 (br s, 2H, C5H4), 6.06-8.07 (m, 35H, (C6H5)2PCH2P(C6H5)2 + P(C6H5)3). 31P{1H} NMR (CDCl3): 51.22 (dd, RuP Ph2CH2PPh2, JPP = 23, 35 Hz), 41.26 (dd, RuP Ph3, JPP = 7, 35 Hz), 11.73 (dd, Ru-PPh2CH2P Ph2-Pd, JPP = 7, 23 Hz). [ 5-C5H4CH2CH2N(CH3)]Ru(PPh3)( µ -I)( µ -dppm)PdCl2 (10'). The reaction was performed as for 10 , starting from the non protonated complex 7'. Single crystals suitable

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122 for X-ray diffraction were grown by slow diffu sion of hexanes into a solution of the redorange product 10' in dichloromethane. [ 5-C5H4CH2CH2N(CH3)2•HI]Ru(PPh3)( µ -I)( µ -dppm)PdI2 (11). In a 50 mL Schlenk flask , complex 7 (0.254 g, 0.223 mmol) and Pd(COD)Cl2 (63.8 mg, 0.223 mmol) were dissolved in 30 mL of dichloro methane. The yellow solution was stirred at ambient temperature for 2 hrs then 10 equiva lents of NaI were added to the solution and stirred for 24 hrs at room temperature. The solution was filtered under N2 and the filtrate was dried under vacuum a nd recrystallized from CH2Cl2/pentane to yield 0.195 g (66.4%) of a dark purple solid. 1H NMR (CDCl3): 2.60 (m, 1H, Ph2PCH H PPh2), 3.08 (s, 6H, NH+(C H3)2), 3.47-3.78 (m, 4H, C H2C H2NH+(CH3)2), 4.44 (br s, 2H, C5H4), 5.27 (m, 1H, Ph2PC H HPPh2), 5.73 (br s, 2H, C5H4), 6.76-8.08 (m, 35H, (C6H5)2PCH2P(C6H5)2 + P(C6H5)3). 31P{1H} NMR (CDCl3): 49.45 (dd, RuP Ph2CH2PPh2, JPP = 22, 35 Hz), 39.38 (dd, RuP Ph3, JPP = 6, 35 Hz), 13.83 (dd, Ru-PPh2CH2P Ph2-Pd, JPP = 6, 22 Hz). [ 5-C5H4CH2CH2N(CH3)2]Ru(PPh3)( µ -I)( µ -dppm)PdI2 (11'). The reaction was performed as for 11 , starting from the non protonated complex 7' . Sodium 3-(diphenylphosphino )benzenesulfonate (TPPMS•H2O) (12). Under N2, in a 250 mL Schlenk flask, 7 g of PPh3 were added over a period of 1 hr into 13 mL of oleum at 0°C. The solution was refluxed for 2 hrs and the mixt ure was poured into 150 mL of cold degassed water. 10 mL of tr iisooctylamine was added and the product was extracted with 200 mL of toluene. To the or ganic layer was slowly added a solution of 5% NaOH until pH = 3-4. The aqueous layer was discarded. NaOH solution was then added until pH = 6-7 where a white precipit ate formed. The aqueous layer was separated and concentrated on rotary evaporator to obtain a white solid. Washing with cold

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123 methanol (2 x 15 mL) and drying under vacuum yield a white solid. 2.67 g (30% yield). No further purification was necessary. 31P{1H} NMR (CD3OD): 4.03 (s), (D2O): 5.610 (s). Tris(3-sulfonatophenyl)phosphine sodium (TPPTS•3H2O) (13). Under N2 in a 250 mL Schlenk flask, 6 g of PPh3 were added over a period of 1 hr into 60 g of oleum at 0°C (until complete dissolution). The mi xture was stirred for 24 hr at ambient temperature and then the contents of the fl ask were poured into 150 mL of cold, degassed water. A mixture of toluene/triisooctylami ne (90 mL/24 mL) was added to the aqueous solution and extracted. To the organic layer was slowly added a so lution of 5% NaOH until pH = 5-6. The aqueous layer was discarded. NaOH solution was then added until pH = 7-8 with formation of a white precipitate. The aqueou s layer was separated and concentrated on rotary evaporator to obtain a white solid. Washing with cold methanol (2x15mL) and drying under vacuum yield to a white solid containing a mixture of di(7%) and tri-substituted (93%) sulfonated tr iphenylphosphine without oxides. Further separation was performed on a Sephadex G15 co lumn using water as eluant. Yield 4.05 g (22.5%) of TPPTS were obt ained as a white solid. 31P{1H} NMR (D2O): – 5.18 (s). CpRu(TPPMS)2Cl (14). In a 250 mL Schlenk fl ask, 1 g (1.37 mmol) of CpRu(PPh3)2Cl was dissolved in 80 mL of THF. To this solution was added via cannula a hot solution of TPPMS (1 g, 2.74 mmol) in THF. The mixture was refluxed for 2 hrs, the amount of solvent was reduced until a small volume (30 mL) and then dry ether was added until to obtain a cream y yellow-orange precipitate. After filtration and washing with ether (3 x 50 mL), 1.15 g of a yelloworange solid was obt ained (96% yield). 1H

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124 NMR (DMSO-d6): 3.34 (s, 5H, C5H5), 7.14-7.62 (m, 28H, P(C6H5)2-(C6H4SO3Na)). 31P{1H} NMR (DMSO-d6): 40.19 (s). CpRu(TPPTS)2Cl (15). The reaction was performed similarly as for 12 starting from CpRu(PPh3)2Cl (1.00 g, 1.37 mmol) and TPPTS (1.71 g, 2.74 mmol) dissolved in 200 mL of methanol. Purification was car red out on a Sephadex G15 column using degassed water as eluent. Yield: 1.2 g (63%).1H NMR (DMSO-d6): 3.33 (s, 5H, C5H5), 7.12-7.60 (m, 24H, P(C6H4SO3Na)3). 31P{1H} NMR (DMSO-d6): 40.60 (s). CpRu(TPA)2Cl (17). A 40 mL toluene solution of CpRu(PPh3)2I (1.00 g, 1.37 mmol) and PTA (0.43 g, 2.73 mmol) was refluxed for 2 hrs. After cooling the solution the resulting precipitate was f iltered and washed with hexane to yield 0.54 g (72.9%) of an orange solid. 1H NMR (300 MHz, CD2Cl2): 4.04 (m, 12H, PC H2N), 4.54 (m, 12H, NC H2N), 4.72 (s, 5H, Cp). 31P{1H} NMR (CD2Cl2): -29.30 (s). CpRu(CO)2I (20). A solution of CpRu(CO)2Cl (0.5 g, 1.94 mmol) and NaI (2.91 g, 19.42 mmol) in dichloromethane (80 mL) was stirred for 48 hrs. The solvent was evaporated and the compound was extracted with CH2Cl2 (2 x 50 mL). Evaporation of the solvent led to a red-ora nge solid. Yield: 0.57 g (84%). 1H NMR (300 MHz, CDCl3): 5.44 (s, 5H, C5H5). co = 2046, 1094 cm-1 . CpRu(CO)( 1-dppm)I (21). In a Schlenk flask a solution of CpRu(CO)2I (1.08 g, 3.10 mmol) and dppm (1.25 g, 3.25 mmol) in 150 mL of benzene was refluxed for 12 hrs. The solvent was removed under vacuum. Purification of the product was achieved by column chromatography on silica gel using CH2Cl2 as eluent to afford 1.53 g (70.1%) of 21 as an orange powder. IR (NaCl) CO 1952 cm-1. 1H NMR (CDCl3): 7.62-7.12 (m, 20H, (C6H5)), 4.85 (s, 5H, C5H5), 3.81-3.58 (m, 2H, (PC H2P). 31P{1H} NMR (CDCl3):

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125 44.32 (d, RuP Ph2CH2PPh2, JPP = 70 Hz), -23.83 (d, Ru-PPh2CH2P Ph2, JPP = 70 Hz). Anal. Calcd. for C31H27IOP2Ru: C, 52.78; H, 3.86. Found: C, 53.04; H, 3.78. CpRu(CO)( µ -I)( µ -dppm)PtI2 (23). A solution of 21 (0.400 g, 0.567 mmol) in CH2Cl2 (15 mL) was added to a suspension of Pt(COD)I2 (0.347 g, 0.625 mmol) in CH2Cl2 (5 mL). The resulting solution was stirre d for 1 hr at ambient temperature. The solvent was removed under vacuum and purification was achieved by column chromatography on silica gel using CH2Cl2 as eluent. Yield: 0.37 g, 57.6%. IR (NaCl) CO 1969 cm-1. 1H NMR (CDCl3): 7.89-6.84 (m, 20H, (C6H5)), 5.02 (s, 5H, C5H5), 4.10 (m, 1H, (PC H2P) 3.73 (m, 1H, (PC H2P). 31P{1H} NMR (CDCl3): 43.49 (d, RuP Ph2, JPP = 10 Hz, JPPt = 40 Hz), -3.28 (d, P Ph2-Pt, JPP = 10 Hz, JPPt = 1742 Hz). Anal. Calcd. for C31H27I3OP2PtRu: C, 32.25; H, 2.36. Found: C, 32.28; H, 2.26 . CpFe(CO)( µ -I)( µ -dppm)PtI2 (24). Using the same procedure as for 23 , a solution of CpFe(CO)( 1-dppm)I (0.500 g, 0.756 mmol) and Pt(COD)I2 (0.463 g, 0.831 mmol) in 20 mL of CH2Cl2 was stirred for 1 hr at ambient temperature. After purification, 24 was obtained as pale-green solid. Yield: 0.493 g, 62.3%. IR (NaCl) CO 1963 cm-1. 1H NMR (CDCl3): 7.98-7.05 (m, 20H, (C6H5)), 4.51 (s, 5H, C5H5), 3.72 (m, 2H, (PC H2P). 31P{1H} NMR (CDCl3): 65.30 (d, FeP Ph2, JPP = 8 Hz, JPPt = 35 Hz), -4.34 (d, P Ph2-Pt, JPP = 8 Hz, JPPt = 1746 Hz). Anal. Calcd. for C31H27FeI3OP2Pt: C, 33.57; H, 2.45. Found: C, 33.50; H, 2.44. CpRu(CO)( µ -I)( µ -dppm)PdI2 (25) . To a solution of 21 (0.400 g, 0.567 mmol) in CH2Cl2 (20 mL) was added a solution of Pd(COD)Cl2 (0.178 g, 0.623 mmol) in CH2Cl2 (20 mL). After stirring for 1 hr at ambien t temperature, 10 equivalents of NaI (0.85 g, 5.67 mmol) were added and the resulting su spension was stirred for 24 hrs. After

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126 evaporation of the solvent under vacuum , purification was achieved by column chromatography on silica gel (CH2Cl2) to give 25 as a dark brown powder. Yield: 0.503 g, 83.2%. IR (NaCl) CO 1968 cm-1. 1H NMR (CDCl3): 7.86-6.85 (m, 20H, (C6H5)), 5.07 (s, 5H, C5H5), 4.01 (m, 1H, (PC H2P) 3.64 (m, 1H, (PC H2P). 31P{1H} NMR (CDCl3): 46.69 (d, RuP Ph2, JPP = 19 Hz), 12.58 (d, P Ph2-Pd, JPP = 19 Hz). Anal. Calcd. for C31H27I3OP2PdRu: C, 34.94; H, 2.55. Found: C, 34.76; H, 2.34. CpFe(CO)( µ -I)( µ -dppm)PdI2 (26). A solution of CpFe(CO)(1-dppm)I (0.200 g, 0.303 mmol), Pd(COD)Cl2 (0.103 g, 0.303 mmol) and NaI (0.450 g, 3.03 mmol) in 50 mL of CH2Cl2 was reacted in a similar manner described above for 25. Similar purification afforded 26 as a dark brown solid. Yiel d: 0.203 g, 65.6%. IR (NaCl) CO 1960 cm-1. 1H NMR (CDCl3): 7.97-6.98 (m, 20H, (C6H5)), 4.56 (s, 5H, C5H5), 3.72 (m, 1H, (PC H2P) 3.44 (m, 1H, (PC H2P). 31P{1H}NMR (CDCl3): 69.17 (d, FeP Ph2, JPP = 17 Hz), 12.02 (d, P Ph2-Pd, JPP = 17 Hz). Anal. Calcd. for C31H27FeI3OP2Pd: C, 36.49; H, 2.67. Found: C, 36.56; H, 2.31. CpRu(CO)I( µ -dppm)AuI (27). A solution of 21 (0.25 g, 0.36 mmol) in CH2Cl2 (15 mL) was added at -20°C to a so lution of AuI (0.11 g, 0.36 mmol) in CH2Cl2 (15 mL). The reaction was stirred for 1 hr at ambien t temperature and afte r evaporation of the solvent, purification was achieved by extracti on with approximately 30 mL of ethyl ether leading to 27 as an orange solid. Yield: 0.29 g, 78.5%. IR (NaCl) CO 1952 cm-1. 1H NMR (CDCl3): 7.97-7.22 (m, 20H, (C6H5)), 4.82 (s, 5H, C5H5), 4.70 (m, 1H, (PC H2P) 3.63 (m, 1H, (PC H2P). 31P{1H} NMR (CDCl3): 40.61 (d, RuP Ph2, JPP = 18 Hz), 26.90 (d, P Ph2-Au, JPP = 18 Hz). Anal. Calcd. for C31H27AuI2OP2Ru: C, 36.17; H, 2.64. Found: C, 36.20; H, 2.45.

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127 CpFe(CO)I( µ -dppm)AuI (28). In the same manner described for 24, a solution of CpFe(CO)( 1-dppm)I (0.70 g, 10.58 mmol) and AuI (0.40 g, 10.58 mmol) in CH2Cl2 (50 mL) was stirred for 1 hr. After evaporation of the solvent, purifica tion was achieved by column chromatography on silica gel using CH2Cl2 as eluent to afford 28 as a dark green solid. Yield: 0.67 g, 64.3%. IR (NaCl) CO 1945 cm-1. 1H NMR (CDCl3): 8.23-7.19 (m, 20H, (C6H5)), 4.46 (m, 1H, (PC H2P)), 4.36 (s, 5H, C5H5), 3.19 (m, 1H, (PC H2P). 31P{1H} NMR (CDCl3): 62.02 (d, FeP Ph2, JPP = 22 Hz), 27.66 (d, P Ph2-Au, JPP = 22 Hz). Anal. Calcd. for C31H27AuFeI2OP2: C, 37.83; H, 2.77. Found: C, 37.53; H, 2.57 CpRu(PPh3)( µ -I)( µ -dppm)PdI2 (30). A solution of CpRu(PPh3)(1-dppm)I (0.40 g, 0.43 mmol), Pd(COD)Cl2 (0.13 g, 0.45 mmol) and NaI ( 0.32 g, 2.16 mmol) in 50 mL of CH2Cl2 were reacted in a similar manner as described above for 25 . After evaporation of the solvent the purification was achieved by recrystallization from dichloromethane/pentane to yield 30 as a dark brown powder. Yield: 0.35 g, 63.5%. 1H NMR (CDCl3): 8.09-5.81 (m, 35H, (C6H5)), 4.62 (s, 5H, C5H5), 3.49 (m, 1H, (PC H2P)), 2.94 (m, 1H, (PC H2P). 31P{1H} NMR (CDCl3): 48.23 (dd, RuP Ph2, JPP = 20, 35 Hz), 40.40 (dd, RuP Ph3, JPP = 6, 35 Hz), 12.7 (dd, PdP Ph2, JPP = 6, 20 Hz). HRMS (FAB): calcd for C48H42I2P3PdRu 1172.8667 (M-I)+ , found 1172.8758. CpRu( 3-allyl)Cl2 (34). In a 50 mL Schlenk flas k containing CpRu(PPh3)2Cl (1.00 g, 1.36 mmol) under argon were added ally l chloride (1.54 mL, 13.58 mmol) and n-decane (3 mL). The mixture was heated at 120ºC for 2 hrs. After cooling the resulting crude product was chromatographed column us ing successively as eluent hexane and ether. Finally complex 34 was obtained by eluting with dichloromethane/methanol (50:1)

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128 as red-orange solid, 0.171 g (44.8% yield). 1H NMR (CDCl3): 5.69 (s, 5H, (C6H5)), 4.99 (m, 1H, allyl), 4.46 (d, 2H, allyl), 2.73 (m, 2H, allyl). CpRu(13CO)2Cl (35). In a high pressure vessel, a suspension of complex 34 (0.150 g, 0.54 mmol) in 3 mL of n-decane was stirred for 2 hrs under 1 atm of 13CO at 140ºC. The cooled solution was passed through a silica gel column w ith hexane as eluent in order to remove n-decane, then with ether to obtain complex 35 . 0.105 g (75.5%). 1H NMR (CDCl3): 5.44 (s, 5H, (C6H5)). 13C NMR (CDCl3): 195.98 , 87.69. [CpFe(13CO)2]2 (36). A solution of CpFe(benzene)BF4 (0.650 g, 2.27 mmol) in 10 mL of THF was stirred on 15 g of sodium amalgam (1%) at -20ºC. After 1 hr, the resulting dark green solution was transferre d via cannula to another Shlenk flask and the solvent was evaporated under vacuum. The resul ting residue was then extracted with cold pentane and the filtrate was then drie d under vacuum. Finally, the crude product containing only the reduced CpFe(benzene) (without NaBF4 salt) was dissolved in cold THF (40 mL), charged in a bomb at -78ºC a nd stirred at ambient temperature under 1 atm of 13CO for 24 hrs. After evaporat ion of the THF, extraction with toluene (2 x 30 mL), and evaporation of toluene under vacuum, 0.31 g (77.1%) of a dark red solid were obtained. 1H NMR (C6D6): 4.10 (s, 5H, (C6H5)). co = 1943, 1900, 1815 cm-1 . CpFe(13CO)2I (37). A solution of 36 (0.31 g, 0.87 mmol) and I2 (0.44 g, 1.2 mmol) in chloroform (30 mL) were refluxed fo r 1 hr. After cooling to room temperature, the solution was washed with an aqueous soluti on of sodium thiosulfate (5 g in 150 mL). Evaporation of the solvent, washing the solid with pentane results in a dark brown solid (0.29 g , 55% yield). 1H NMR (CDCl3): 4.97 (s, 5H, (C6H5)). 13C NMR (CDCl3): 213.16 , 84.89. co = 1986, 1941 cm-1 .

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129 Crystallographic Structure Determination Data 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 Ã…). Cell parameters 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 structure was solved by the Direct Methods in SHELXTL6, and refined using full-matrix least squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal posit ions and were riding on their respective carbon atoms. Complex 8': The asymmetric unit consists of the complex and two chloroform molecules of crystallization. A total of 625 pa rameters were refined in the final cycle of refinement using 11858 re flections with I > 2 (I) to yield R1 and wR2 of 4.54% and 8.19%, respectively. Refinement was done using F2. Complex 22 : The complex has the Cp ring disordered due to an in plane vibrational motion as can be seen from the in-plane elongated thermal ellipsoids. A couple of phenyl rings show a similar moti on and one out of plane motion where the C atom thermal ellipsoids are pointed out of the ring plane. The refinement converged to an R value of 4.8 and a wR2 of 14. The data was treated as having a racemic twinning which led to a better refinement and R value convergence with a BASF value of 0.52. A total of 399 parameters were refined in the final cycle of re finement using 7999

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130 reflections with I > 2 (I) to yield R1 and wR2 of 2.46% and 5.82%, respectively. Refinement was done using F2. Complex 23 : The asymmetric unit consists of the complex and two dichloromethane molecules. The latter we re 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 di sorder area and remove its contribution to the overall intensity data. A total of 352 parameters were refined in the final cycle of refinement using 8580 reflections with I > 2 (I) to yield R1 and wR2 of 4.47% and 9.78%, respectively. Refinement was done using F2. Complex 24 : The asymmetric unit consists of the complex and two dichloromethane molecules. The latter we re 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 di sorder area and remove its contribution to the overall intensity data. A total of 352 parameters were refined in the final cycle of refinement using 8711 reflections with I > 2 (I) to yield R1 and wR2 of 3.18% and 6.04%, respectively. Refinement was done using F2. Complex 25 : The asymmetric unit consists of the complex and two dichloromethane molecules. The latter we re 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 di sorder area and remove its contribution to the overall intensity data. A total of 352 parameters were refined in the final cycle of refinement using 8603 reflections with I > 2 (I) to yield R1 and wR2 of 5.07% and 12.01%, respectively. Refinement was done using F2.

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131 APPENDIX FTIR SPECTRA OF CARBONYL COMPLEXES 4000.03600320028002400200018001600140012001000800600450.0 cm-1 %T CpRu(13CO)I(n1-dppm) CpRu(CO)I(n1-dppm) 1952.12 1433.35 1095.55 733.16 694.04 1907.96 1433.15 1095.26 733.38 693.89 523.32 Ru OC I Ph2P PPh2 Ru O13C I Ph2P PPh2 Solution on NaCl Figure A-1 FTIR spectra of complexes 21 and 21-13C

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132 4000.03600320028002400200018001600140012001000800600.0 17.6 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 98.9 cm-1 %T 3051.79 1946.27 1481.17 1433.20 1094.75 824.33 732.33 694.34 1265.60 Solution on NaCl Fe OC I Ph2P PPh2 Figure A-2 FTIR sp ectrum of complex 22 .

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133 4000.03600320028002400200018001600140012001000800.0 27.2 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90.0 cm-1 %T 3052.34 1900.75 1481.11 1433.38 1264.19 1094.70 Fe O13C I Ph2P PPh2 Solution on NaCl Figure A-3 FTIR spectrum of complex 22-13C .

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134 4000.03600320028002400200018001600140012001000800600.0 79.47 80.0 80.5 81.0 81.5 82.0 82.5 83.0 83.5 84.0 84.5 85.0 85.5 86.0 86.5 87.0 87.5 88.0 88.5 89.0 89.5 90.0 90.5 91.0 91.5 92.0 92.5 93.0 93.5 93.90 cm-1 %T 1969.55 693.06 735.54 1095.66 1433.52 Solution on NaCl Ru OC I Ph2P PPh2 Pt I I Figure A-4 FTIR sp ectrum of complex 24 .

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135 3974.13600320028002400200018001600140012001000800617.7 54.8 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85.0 cm-1 %T 1924.91 Ru O13C I Ph2P PPh2 Pt I I Solution on NaCl Figure A-5 FTIR spectrum of complex 23-13C .

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136 4000.03600320028002400200018001600140012001000800600.0 73.1 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 89.7 cm-1 %T 1968.74 1431.50 1093.64 735.54 689.01 Solution on NaCl Ru OC I Ph2P PPh2 Pd I I Figure A-6 FTIR sp ectrum of complex 25 .

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137 4000.03600320028002400200018001600140012001000800600.0 72.4 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 95.5 cm-1 %T 1960.76 689.01 733.52 1093.64 1433.52 Solution on NaCl Fe OC I Ph2P PPh2 Pd I I Figure A-7 FTIR spectrum of complex 26 .

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138 4000.03600320028002400200018001600140012001000800600.0 54.2 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100.4 cm-1 %T 1952.34 1435.22 1098.00 736.64 691.24 Solution on NaClI Ru OC I Ph2P PPh2 Au Figure A-8 FTIR spectrum of complex 27 .

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139 4000.03600320028002400200018001600140012001000800600.0 47.3 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96.4 cm-1 %T 1945.41 1435.51 1098.23 736.63 690.53 Solution on NaClI Fe OC I Ph2P PPh2 Au Figure A-9 FTIR sp ectrum of complex 28 .

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150 BIOGRAPHICAL SKETCH Daniel Serra was born in Moyeuvre-Gra nde (Moselle) in France on September 1st, 1974. In 1999, Daniel graduated from Univers ite Paul Sabatier in Toulouse with a Bachelor of Science, and decided to continue in the way of science. Two years later, he graduated from the same University with a Licence and Maitrise degree in applied organometallic chemistry. He then joined th e Group G in the Laboratory de Chimie de Coordination (LCC) in Toulouse under the supe rvision of Dr. Jean Claude Daran, Dr. Eric Maroury and Dr. Marise Gouygou, in the synthesis of chiral N,P phospholeferrocene ligands for palladium-catalyzed ally lic substitution with whom he got his first taste of research. Daniel enjoyed this one year of learning and good experience and decided to work in research field. In Ap ril 2001, Daniel joined the REU France-USA exchange program and spent four months in the McElwee-White research group in University of Florida in the synthesis of amino-substituted-cyclopentadienyl Ru/Pt and Ru/Pd heterobimetallic complexes for the homogeneous electrooxidation of methanol. In January 2002 Daniel moved his scientific caree r to University of Florida, joined the McElwee-White research group and began his P h.D. studies in the field of organometallic chemistry in the synthesis and application of heterobimetallic complexes for the electrochemical oxidatio n of methanol. After 5 years of research, he graduated from the University of Florida with a Doctorat e of Philosophy in inorganic chemistry