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Redox Active Binuclear Complexes of Ruthenium

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Redox Active Binuclear Complexes of Ruthenium REDOX ACTIVE BINUCLEAR COMPLEXES OF RUTHENIUM AND OSMIUM Alan J. Lindsay Ph. D. Thesis University of Edinburgh 1982 DECLARATION Except where specific reference is made to other sources, the work presented in this thesis is the original work of the author. It has not been submitted, in whole or in part, for any other degree. Certain of the results presented have already been published. Alan J. Lindsay. To my Mother, Father and Sister ACKNOWLEDGEMENTS I wish to thank Dr. T.A. Stephenson and Dr. G.A. Heath for their help, encouragement and enthusiasm throughout this work. I also wish to express my gratitude to Dr. D.K. Vattis of the University of PAtras, Greece, for his invaluable contribution to this study. In addition, I am grateful to Dr. D. Reed, Mr. L.H. Bell 13 and Mr. J.A.A. Millar for recording 31 P, C and 1H n.m.r. spectra, Dr. S.F. Watkins of Louisiana State University, U.S.A., for carrying out X-ray work and Mr. N. Grunbaum for performing microanalytical measurements. I am deeply indebted to the S.E.R.C. for their financial support and the University of Edinburgh for the use of facilities. Finally, my thanks to Miss A. Erskine for typing this thesis. ABSTRACT Chapter 1 gives a brief account of some of the general aspects of ruthenium and osmium chemistry. Chapter 2 describes efforts to extend the range of triple chioro bridged binuclear ruthenium (11/11) complexes in an orderly fashion by application of two alternative synthetic strategies: assembly from appropriate monomers such as RuC1 2 L4 (L = py, 4-Mepy, MeCN and Me 2 SO) and by terminal ligand displacement from existing triple chioro bridged complexes e.g. Ru 2 Cl 4 (PEt 2 Ø) 5 . Chapter 3 discusses the formation of new non-chloro triple bridged binuclear ruthenium(II/II) complexes. This can be achieved through the action of weak acids such as H 2 0 or HSEt on basic ruthenium hydrido species such as [RuH(cod) (PMe 2 Ø) 3 1PF6 . The product of the former reaction is the hydroxo bridged complex [Ru 2 (OH) 3 (PMe 2 Ø) 6 ]PF6, which may then be converted to [Ru 2 X3 (PMe 2 Ø) 6 ]PF 6 (X = Cl, Br, I) through treatment with the appropriate acid HX. The synthesis, characterisation and isomerisation of the neutral complex Ru2 Br 4 (CO)(P0 3 ) 4 is also discussed. The related chloro bridged complexes Ru 2 C1 4Y(P03)4 (Y = CO, CS) are shown to react with aqueous NaOH in CH 2 C1 2 to produce Ru 2 C1(OH) 3 Y(P0 3 ) 4 . In the absence of excess OH ion this compound rearranges to form [RuCl(OH) 2Y 2 (P 3 ) 4 JCl and [Ru(OH) 2 (PØ 3 ) 2 1 2 . Chapter 4 attempts to account for the stereospecific formation of neutral "asymmetric" mixed-valence Ru 2 (II/III) triple chloro bridged complexes of type (PR 3 ) 2YRuC1 3 RUC12 (PR 3 ) (Y = CO, CS, PR 3 ) from the reaction between their related Ru2 (II/II) precursors, (PR 3 ) 2YRUC1 3 RUC1(PR3 ) 2 , and concentrated HC1. In addition attempts are made to devise a method of synthesis of neutral "symmetric" mixed-valence Ru 2 (II/III) and Os (il/Ill) complexes. Chapter 5 discusses the influences, such as metal ion identity and terminal and bridging ligand characteristics, affecting the redox potentials of M 2 (II/II), M2 (II/III) (M = Ru, Os) and Ru 2.(III/III) triple bridged complexes discussed in Chapters 1-4. It will be shown that, by comparing the redox potentials of these compounds with those of their related monomers, simple, but highly effective structure/ redox potential correlations can be derived. Chapter 6 describes how variable temperature magnetic measurements in solid and solution states of triple chioro bridged Ru 2 (III/III) compounds, and the detection and analysis of the characteristic intervalence charge transfer (IT) bands in the near-infrared absorption spectrum of the correspoLding Ru 2 (II/III) compounds reveal that the degree of metal-metal interaction in these confacial bioctahedral systems decreases as the molecular asymmetry increases. Appendix I deals with the formation of some monomeric tertiary phosphine complexes from the hydrido compound [RuH(cod) (NH 2NMe 2 ) 3 }B0 4 . Appendix II describes the thermodynamic relationship between the optical transition energy of an intervalence charge band and the measured and inferred E½ values. CONTENTS Page CHAPTER 1 A General Survey of the Oxidation States Exhibited by Ruthenium 1.1 Preamble 1 1.2 Introduction 1 Ru(VIII)d0 , Ru(VII)d 1 and Ru(VI)d 2 3 Ru(V)d3 6 Ru(IV)d4 6 Ru(III)d5 11 Ru(II)d6 19 Ru(I)d7 27 Ru(0)d8 29 Ru(-I)d 9 , Ru(-II)d1° 31 CHAPTER 2 Synthesis and Characterisation of New Triple Chioro Bridged Rutheriiuln(II/II) Binuclear Complexes 2.1 Preamble 32 2.2 Introduction 33 2.3 Results and Discussion (a) Dimerisation of Ru(II) monomers of type RuC1 2 L 4 L = Me2SO 47 L = MeCN, pyridine and 64 4-methylpyridine (b) Specific nucleophilic substitution at terminal sites in existing triple chioro bridged complexes Attempted replacement of neutral 66 diazadiene ligands Terminal chloride substitution 67 69 2.4 Conclusions 71 2.5 Experimental CHAPTER 3 Synthesis and Characterisation of New Non- Chioro Triple Bridged Ruthenium(II/II) Binuclear Complexes 77 3.1 Preamble 77 3.2 Introduction 3.3 Results and Discussion (a) Dimerisation of Ru(II) Monomers Reactions of the weak acids 0 and HSEt with [RuH(cod)- H 2 84 (NH 2NMe 2 ) 3 ]X (X=BØ4, PF 6 ) and excess PMe 2 Ø Preparation and reactions 86 of pure RuBr2(P03)3 (b) Nucleophilic attack at bridging sites of triple chloro bridged Ru2 (II/II) binuclear complexes (bridging group replacement) Attack of hydroxide ion on 96 Ru2 C1 4Y (P03) 4(YCO,CS) Reactions of [Ru2(OH)3 111 (PMe 2 Ø) 6 1PF6 with acids HX 3.4 Conclusions 114 3.5 Experimental 115 CHAPTER 4 PreparatiOn and Characterisation of Mixed- Valence Triple Bridged Binuclear Ru 2 (il/Ill) Complexes 4.1 Preamble 122 4.2 Introduction 124 4.3 Results and Discussion Chemical oxidation of neutral triple chloro Ru2 (II/II) binuclear 128 complexes in acidic media ff Direct reactions between "RuC13HO 137 or Na2 OsCl 6 and various ligands L 4.4 Conclusions 142 4.5 Experimental 143 CHAPTER 5 Electrochemical Studies on Some Triple Bridged Ruthenium and Osmium Binuclear Complexes 5.1 Preamble 147 5.2 Introduction 148 Cyclic Voltammetry (C.V.) 148 Stirred Linear Sweep Voltainmetry 153 Linear Sweep a.c. Voltainmetry 155 Electrosyntheses 159 5.3 Results and Discussion (a) [(PR ) MCi M(PR ) 3 ] and related 162 M2 (II/II) cations (b) Ru 2 C1 4 (PR 3 ) 5 and related Ru 2 (II/II) 167 neutral compounds (c) Ru 2 X4 Y(PR3 ) 4 and related complexes 169 (d) M2 C1 5 (LR3 ) 4 and related neutral mixed-valence Ru2 (Il/Ill) complexes "Asymmetric." mixed-valence 170 complexes "Symmetric" mixed-valence 172 complexes (e) Ru2 C1 6 (A5R3 ) 3 173 (f) Structure/redox potential 176 correlations 5.4 Conclusions 180 5.5 Experimental 182 CHAPTER 6 Spectroscopic and Magnetic Studies on Electrogenerated Mixed-Valence Ruthenium Complexes 6.1 Preamble 186 6.2 Introduction 187 6.3 Results and Discussion Factors influencing the degree of metal-metal interaction in triple chioro bridged binuclear ruthenium 192 complexes at the Ru 2 (II/III) and Ru2 (III/III) oxidation levels Using intervalence charge-transfer bands to explore the tendency to partial charge delocalisatiOn in 194 the IIRuClRu2+ht core of binuclear Ru2 (II/III) complexes Using magnetic studies to explore the degree of metal-metal interaction 201 in the URuC13Ru3+u core of binuclear Ru2 (ill/Ill) complexes 202 6.4 Conclusions 206 6.5 Experimental APPENDIX I Some Monomeric Tertiary Phosphine Complexes Derived from the Hydrido Compound [RuH (cod) (NH 2NMe 2 ) 3j 4 214 A.1 Preamble. 214 A.2 Introduction A.3 Results and Discussion Reaction of [RuH(cod) (NH NMe 2 ) ]BØ4 2 215 with a four-fold excess of PMe 2 0 Reaction of [RuH(cod) (NH 2NMe 2 ) 3 1B04 with NaOMe and a three-fold excess 226 of PE t02 22.7 A.4 Conclusions 231 A.5 Experimental APPENDIX II The Thermodynamic Relationship Between the Optical Transition Energy and the Measured 234 and Inferred E values 236 APPENDIX III Abbreviations 238 References FIGURES Triple chioro bridged structural reformulation 2.1 49 of Ru 2 C1 4 (Me 2 SO) 5 C1 4 (Me 2 2.2a,b, 1 H and 13 C— H }n.m.r. spectra of RU 2 SO) 5 50 in CD2 C1 2 at 303 K ' 2.3a,b,c n.m.r. spectra of [RuCln(Me2SO)6_ n 55. (BF 4)2_n (n = 0,1,2) in CD 3NO 2 at 303 K 2 C1 4 (Me 2 SO) 5 and 2.4 infrared spectrum of Ru 59 Ru 2 C1 4 (d -Me 2 SO) 5 31 P-{ 1 H} n.in.r. spectrum of RuBr2(P03)3 in 3.1 88 6 CH 2 C1 2 /d -acetone in 183 K H} n.m.r. spectrum of Ru 2Br 4 (CO(P0) 4 3.2 31P-{ 1 91 in CD 3 C 6 D5 at 183 K 93 3.3 Isomerisatiofl of Ru2X4(CO)(P03)4 spectrum of RU2 C1 4 (CS) (P03)4 3.4 31P-{ 1H} n.m.r.
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