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Activation of dihydrogen by ruthenium complexes containing chelating phosphines 1990

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ACTIVATION OF DIHYDROGEN BY RUTHENIUM COMPLEXES CONTAINING CHELATING PHOSPHINES By AJEY MADHAV JOSHI B.Sc. (Hons.), University of Poona, 1980 M.Sc, Indian Institute of Technology, Bombay, 1983 M.Sc, University of British Columbia, Vancouver, 1986 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November 1990 © Ajey M. Joshi, 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of CLH £ m 1 1 The University of British Columbia Vancouver, Canada Date 3)ee£«T18G^ <X^\ \<3C)0 DE-6 (2/88) ABSTRACT The previously reported synthesis of dinuclear mixed-valence ruthenium complexes of general formula Ru2Cl5(P-P)2, P-P = DPPP, DPPB, 5,5-CHIRAPHOS, or R.R-DIOP, has been extended to include other diphosphines: P-P = DPPN, DPPH, rac- DPPCP, rac-DPCYCP, 5,5-BDPP, R- and 5-BINAP, or 5-PHENOP. The complexes are prepared by the reaction of RuCl3P2(DMA)-DMA, P = PPh3 or P(p-tolyl)3, with one equivalent of the appropriate diphosphine. The H2-reduction of Ru2Cl5(P-P)2 complexes in DMA, or in toluene in the presence of an added base, affords the corresponding dimeric Ru(II) complexes [RuCl(P-P)(u-Cl)]2, P-P = DPPN, R- or 5-BINAP, or 5,5-BDPP, which have been characterised by NMR spectroscopy. The [RuCl(P-P)(u,-Cl)]2 complexes (Structure I) show a great propensity to form trichloro-bridged dinuclear species (Structure II) in the presence of neutral coordinating ligands (L). A series of trichloro-bridged complexes of the type [(L)(P-P)Ru- (u-Cl)3RuCl(P-P)] (e.g. P-P = DPPB; L = NEt3, NHBu 2, CO, DMA, PhCN, Mel) have been isolated or studied in situ and characterised spectroscopically. The molecular structure of the DMSO analogue shows an S-bonded DMSO ligand with an unsymmetrical arrangement of the chelating DPPB ligand (cf. Structure II). The reaction of [RuCl(DPPB)(u,-Cl)]2 with H2 has been investigated. In benzene or toluene, in the absence of an added base, dihydrogen adds reversibly to the ruthenium I II ii dimer to give the remarkably simple molecular hydrogen complex (L = T]2-H2; Structure II); the rj2-H2 ligand (with an H-H distance of 0.86 A as estimated by *H NMR variable temperature spin-lattice relaxation data; Tj(min) - 12 ms at 300 MHz) is replaceable by N 2 . The reaction of [RuCl(P-P)(u-Cl)]2, P-P = DPPB or 5,5-CHIRAPHOS, with H 2 in the presence of NEt3 as the added base yields the corresponding trinuclear Ru(II) hydride complex, [RuHCl(P-P)]3, along with [(NEt3)(P-P)Ru(u-Cl)3RuCl(P-P)]. The hydride complexes had been synthesised previously, albeit in low yields (<10%), and the crystal structure of the CHIRAPHOS derivative obtained. During the present work the original synthetic procedure has been modified to obtain the desired [RuHCl(P-P)]3 complexes in -50% yield. In addition, these species have been characterised completely by NMR spectroscopy. The conversion of [RuCl(P-P)-((j.-Cl)]2 to the corresponding hydride derivative likely proceeds via deprotonation by NEt3 of the initially formed molecular hydrogen species. Under hydrogen atmosphere, [RuHClQDPPB)]3 breaks down to form the dinuclear derivative [(Ti2-H2)(DPPB)Ru(p-H)(u-Cl)2RuH(DPPB)] containing a molecular hydrogen ligand, which has been identified by *H NMR Tj measurements; sirnilar complexes, but with a nitrile ligand (MeCN or PhCN) in place of the rt2-H2, have also been observed. Alternative routes to ruthenium complexes containing only one diphosphine per Ru ("Run(P-P)") have been investigated. Some of the trichloro-bridged derivatives (e.g. L = amine, CO; Structure II, see above) are also accessible through reactions of the mixed- phosphine complex RuCl2(DPPB)(PPh3) with amines and aldehydes, respectively. Studies on the reactions of RuCl2(DMSO)4 or [RuCl(p-cymene)-(u,-Cl)]2 with one equivalent of diphosphines show that the nature and the distribution of product(s) (i.e. RuCl2(P-P)2 V J . "RuCl2(P-P)") are greatly influenced by the chelate size of the diphosphine. The "RuCl2(P-P)" species is observed only for those phosphines which form at least a six-membered ring upon coordination to the metal. iii Solid-state 3 1 P NMR studies indicate that the structure of RuCl2(DPPB)(PPh3) is similar to that of RuCl2(PPh3)3, which has been characterised previously by X-ray crystallography. Reactions of RuCl2(DPPB)(PPh3) with chelating ligands afford six- coordinate complexes of the type RuCl2(DPPB)(L-L), L - L = PPh2Py, DPPM, or norbornadiene; the corresponding hydridochloro derivatives are obtained when the reactions are conducted under an atmosphere of H2 in the presence of Proton Sponge®. The dimeric [RuCl(P-P)(u-Cl)]2 and the trinuclear [RuHCl(P-P)]3 complexes described in this study are effective catalyst precursors for the hydrogenation of various alkene, ketone, imine, and nitrile substrates under relatively mild conditions (30-100 °C, 1-12 atm of H2). A detailed kinetic study on the hydrogenation of styrene catalysed by [RuCl(DPPB)(|i-Cl)]2 shows a first-order dependence of the maximum rate on catalyst concentration, a first- to zero-order dependence on styrene concentration and a zero- to first-order dependence on the H 2 pressure. A mechanism involving formation of the molecular hydrogen (r)2-H2) complex (see above) followed by hydrogen transfer to the substrate is proposed to account for the observations, and the rate constants at 30 "C for the various steps have been determined. Preliminary data on acetophenone and benzonitrile hydrogenation shows that the trinuclear hydride complexes are an order of magnitude more effective than the corresponding dimeric precursors. iv TABLE OF CONTENTS Page ABSTRACT ii TABLE OF CONTENTS v LIST OF TABLES .....xii LIST OF FIGURES xiv LIST OF ABBREVIATIONS xx ACKNOWLEDGEMENTS xxv CHAPTER 1 I N T R O D U C T I O N 1 1.1 General Introduction 1 1.2 Homogeneous Hydrogenation 3 1.2.1 Asymmetric Homogeneous Hydrogenation 4 1.2.2 Hydrogenation of Carbonyl Compounds 8 1.2.3 Homogeneous Hydrogenation of Nitriles and Imines 15 1.2.4 Transfer Hydrogenation 19 1.3 Dihydrogen Activation 23 1.4 Scope of This Thesis 26 1.5 References - Chapter 1 29 CHAPTER 2 Experimental Procedures 39 2.1 Materials 39 2.1.1 Solvents 39 2.1.2 Gases 40 2.1.3 Phosphines 40 2.1.4 Substrates 41 2.1.5 Other Materials 41 2.2 Instrumentation 42 v 2.3 Catalytic Hydrogenation of Unsaturated Organic Substrates 43 2.3.1 Work-up of Reaction Mixtures 44 2.4 Analysis of the Hydrogenation Products 45 2.4.1 Gas Chromatographic Analysis 46 2.4.2 Optical Rotation Measurements 47 2.4.3 Gas Chromatographic Separation of Enantiomers of Chiral Alcohol and Amine Products Using a Chiral Column 48 2.5 Synthesis and Characterisation of Ruthenium Complexes 49 2.5.1 Ruthenium Precursors 49 2.5.1.1 Ci5-RuCl2(DMSO)4 49 2.5.1.2 [RuCl(r|6-p-cymene)(u.-Cl)]2 50 2.5.1.3 RuCl3(PPh3)2(DMA)-DMA solvate 50 2.5.1.4 RuCl3(P(p-tolyl)3)2(DMA)-DMA solvate 51 2.5.1.5 RuCl2(PPh3)3 • 51 2.5.1.6 RuHCl(PPh3)3C6H6 solvate 51 2.5.1.7 7>a>tf-RuHCl(nbd)(PPh3)2, 34 52 2.5.2 Mixed-Phosphine Complexes, RuCl2(P-P)(PPh3) 52 2.5.2.1 Dichloro(l,4-bis(diphenylphosphino)butane)- (m ĥenylphosphme)rutheniumQI), RuCl2(DPPB)(PPh3), 23 52 2.5.2.2 Dichloro((i?)-2,2'-bis-(diphenylphosphino)- 1, r-binaphthyl)(triphenylphosphine)- ruthenium(n), RuCl2(#-BINAP)(PPh3), 21 53 2.5.3 rran -̂Chlorohydrido-(r|2,r|2--norbomadiene) [(1,4-bis(diphenylphosphino)butane)]rutheniumOH), RuHCl(nbd)(DPPB), 36 53 2.5.4 Dichloro-tri-u.-chloro-bis(bidentate phosphine)diruthenium(II,in) Complexes, [(P-P)ClRu(u.-Cl)3RuCl(P-P)] or Ru2Cl5(P-P)2 54 2.5.4.1 P-P = DPPP: Ru2Cl5(DPPP)2,1 55 2.5.4.2 P-P = DPPB: Ru2Cl5(DPPB)2,2 55 2.5.4.3 P-P = #,#-DIOP: Ru2Cl5(DIOP)2, 3 55 2.5.4.4 P-P = 5,5-CHIRAPHOS: Ru2Cl5(CHIRAPHOS)2,4 56 2.5.4.5 P-P = DPPN: Ru2Cl5(DPPN)2, 5 56 2.5.4.6 P-P = DPPH: Ru2Cl5(DPPH)2,6 56 vi 2.5.4.7 P-P = rac-DPPCP: Ru2Cl5(DPPCP)2, 7 56 2.5.4.8 P-P = rac-DPCYCP: Ru2Cl5(DPCYCP)2,8 56 2.5.4.9 P-P = 5,5-BDPP: Ru2Cl5(BDPP)2,9 57 2.5.4.10 P-P=/?-BINAP: Ru2Cl5(/?-BINAP)2,10 57 2.5.4.11 P-P = 5-BINAP: Ru2Cl5(5-BINAP)2,11 57 2.5.4.12 P-P = PHENOP: Ru2Cl5(PHENOP)2,12 57 2.5.5 DicMoro-di-p.-chloro-bis(bidentate phosphine)- dmathenium(n,II) Complexes, [RuCl(P-P)(p-Cl)]2 57 2.5.5.1 P-P = DPPP: Ru2Cl4(DPPP)2,13 58 2.5.5.2 P-P = DPPB: Ru2Cl4(DPPB)2,14 58 2.5.5.3 P-P = DPPN: Ru2Cl4(DPPN)2,17 59 2.5.5.4 P-P=tf,tf-DIOP: Ru2Cl4(DIOP)2,15 59 2.5.5.5 P-P = 5,5-CHIRAPHOS: Ru2Cl4(CHIRAPHOS)2,16 59 2.5.5.6 P-P=i?-BINAP: Ru2Cl4(^-BINAP)2,18 59 2.5.5.7 P-P = 5-BINAP: Ru2Cl4(5-BINAP)2,19 60 2.5.5.8 P-P = 5,5-BDPP: Ru2Cl4(BDPP)2, 20 60 2.5.6 Chloro-m^u.-cWoro-(ligand)bis(l,4-bis(diphenyl- phospMno)butane)curatheniumQT,n) Complexes, [(L)(DPPB)Ru(u-Cl)3RuCl(DPPB)] 60 2.5.6.1 L = NEt3: [(NEt3)(DPPB)Ru- (p-Cl)3RuCl(DPPB)], 14b 60 2.5.6.2 L = NHBun2: [(NHBun2)(DPPB)Ru- (u-Cl)3RuCl(DPPB)], 14c 61 2.5.6.3 L = CO: [(CO)(DPPB)Ru- (u.-Cl)3RuCl(DPPB)], 14d 61 2.5.6.4 L = Me2SO (DMSO): [(Me2SO)(DPPB)Ru- (u.-Cl)3RuCl(DPPB)], 14e 62 2.5.7 Reactions of Cw-RuCl2(DMSO)4 with Other Bidentate Phosphines 63 2.5.8 Chloro(p-cymene)(bidentate phosphine)ruthenium(II) chloride, [RuCl(p-cymene)(P-P)]Cl 63 2.5.8.1 P-P = #-BINAP: [RuCl(p-cymene)- (fl-BINAP)]Cl 64 2.5.8.2 P-P = 5-BINAP: [RuCl(p-cymene)- (5-BINAP)]Cl 64 vii 2.5.8.3 P-P = 5,5-BDPP: 64 2.5.9 Reactions of RuCl2(DPPB)(PPh3) with Chelating Ligands (L-L); Formation of RuCl2(DPPB)(L-L) 65 2.5.9.1 L-L = PPh2(2-Py):RuCl2(DPPB)(PPh2 -Py) 65 2.5.9.2 L-L = DPPM: rra^-RuCl2(DPPB)- (DPPM),27 66 2.5.10 Synthesis of Chlorohydrido(bidentate phosphine)- ruthenium(n) Trimers, [RuHCl(P-P)]3 66 2.5.10.1 P-P = DPPB: [RuHCl(DPPB)]3, 29 66 2.5.10.2 P-P = 5,5-CHIRAPHOS: [RuHCl(5,5-CHIRAPHOS)]3,30 67 2.5.11 Synthesis of Diphosphine-Bridged Dinuclear Ruthenium(II) Complexes, [(P-P)Cl2Ru(u,2-(P-P))RuCl2(P-P)] 68 2.5.11.1 P-P = DPPB 69 2.5.11.2 P-P = DPPN 69 2.5.11.3 P-P = DPPH 69 2.5.12 u.-Acetatohydrido(l,4-bis(diphenylphosphino)butane) (tripheny l-phosphine)rutheniumOT), Ru(C02Me)(H)(DPPB)(PPh3) 70 2.6 References - Chapter 2 71 CHAPTER 3 Chloro-Bridged Diruthenium(ILII) Complexes Containing Chelating Ditertiary Phosphines 74 3.1 Introduction 74 3.2 Synthesis and Characterisation of [RuCl20?-P)]2 Complexes - A Brief Review 77 3.3 Present Work 81 3.3.1 Ru2Cl5(P-P)2 Complexes 82 3.3.2 [RuCl2(P-P)]2 Complexes 87 3.4 Other Synthetic Routes to "Run(P-P)M Complexes 91 3.4.1 Reactions of RuCl2(DPPB)(PPh3), 23 93 3.4.2 Reactions of Non-phosphine Precursors with One Equivalent of P-P 94 viii 3.5 Attempted Removal of PPh3 from RuCl2(DPPB)(PPh3), 23: Reaction of RuCl2(DPPB)(PPh3) with Methyl Iodide 95 3.6 Synthesis of Trichloro-bridged Diruthenium(n,13) Complexes, [(L)(DPPB)Ru(u.-Cl)3RuCl(DPPB)] 97 3.6.1 Synthesis of [(Amine)(DPPB)Ru(u,-Cl)3RuCl(DPPB)], (Amine = NEt3,14b; NHBu2,14c) 97 3.6.2 Synthesis of [(CO)(DPPB)Ru(u-Cl)3RuCl(DPPB)], 14d 100 3.6.3 Synthesis of [(DMS£>)(DPPB)Ru(|i-Cl)3Ru(Cl)(DPPB)], 14e 101 3.6.4. Molecular S tructure of [(DM£0)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)] 102 3.6.5 Other [(L)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)] Complexes... 106 3.7 NMR Studies on [(L)(DPPB)Ru(n-Cl)3Ru(Cl)(DPPB)] Complexes 110 3.7.1 3l P{lH} Solution NMR Studies 110 3.8 Reactions of Cw-RuCl2(DMSO)4 with Other Bidentate Phosphines 116 3.9 Reactions of [RuCl(p-cymene)(u,-Cl)]2 with Bidentate Phosphines 119 3.10 References - Chapter 3 124 CHAPTER 4 Reactions of RuCl2(DPPB)(PPh3) with Chelating Ligands 131 4.1 Introduction 131 4.2 Solid-State 3 1 P NMR Studies on RuCl2(DPPB)(PPh3) and RuCl2(PPh3)3 133 4.2.1 Comparison of Solid-State and Solution 3 1 P NMR Data 135 4.2.2 Comparison of the 3 lP CP/MAS NMR Data for RuCl2(PPh3)3 and RuCl2(DPPB)(PPh3) Complexes 143 4.3 Reaction of RuCl2(DPPB)(PPh3), 23, with H 2 146 4.4 Synthesis of RuChCDPPB^Ph^Py) 153 4.5 Synthesis of Tra/w-RuCl2(DPPB)(DPPM) 168 4.6 Characterisation of RuCl2(/?-BINAP)(PPh3), 21 179 ix 4.7 References - Chapter 4 181 CHAPTER 5 Activation of Dihydrogen by Chloro-Bridged Diruthenium(II,II) Complexes Containing Chelating Ditertiary Phosphines 187 5.1 Introduction . 187 5.2 Molecular Hydrogen Complexes: A Brief Review 191 5.3 Interaction of [RuCl(DPPB)(u-Cl)]2,14, with H 2 and N 2 in the Absence of an Added Base 196 5.3.1 Interaction with H 2 : Formation of a Molecular Hydrogen Complex 196 5.3.2 Gas-Uptake Studies 205 5.3.3 Interaction of Other [RuCl(P-P)(u-Cl)]2 Complexes withH2 206 5.3.4 Interaction of 1 4 with N 2: Formation of a Dinitrogen Complex 206 5.4. Reaction of [RuCl(P-P)(|i-Cl)]2 Dimers with H 2 in the Presence of Triethylamine: Synthesis of [RuHCl(P-P)]3 Complexes 210 5.4.1 Improved Synthesis of [RuHCl(P-P)]3 211 5.5 Characterisation of [RuHCl(P-P)]3 Complexes 212 5.5.1 Molecular Structure of [RuHCl(S,S-CHIRAPHOS)]3, 30 212 5.5.2 *H and 3*P NMR Studies 215 5.6 Interaction of [RuHCl(P-P)]3 with H 2 and Nitriles 224 5.7 Suggested Mechanism for Formation of [RuHCl(P-P)]3 Complexes 228 5.8 References - Chapter 5 231 CHAPTER 6 Ruthenium(II) Hydrido-Diene Complexes Containing Bidentate Phosphines 238 6.1 Introduction 238 6.2 Synthesis and Characterisation of Tra/w-RuHCl(nbd)(DPPB), 36 242 6.3 Discussion 247 x 6.4 Reactivity of 7Va,tt-RuHCl(nbd)(DPPB), 36, toward H 2 and CO 251 6.5 References - Chapter 6 254 CHAPTER 7 Catalytic Hydrogenation Studies 257 7.1 Introduction 257 7.2 Hydrogenation of Styrene Catalysed by [RuCl(DPPB)(u-Cl)]2,14. : 257 7.2.1 Solubility of Hydrogen in DMA 258 7.2.2 Rate Measurements 260 7.2.3 Analysis of the Kinetic Data and Discussion 265 7.2.3.1 Dependence of the Rate on Catalyst Concentration 266 7.2.3.2 Dependence of the Rate on Styrene Concentration 267 7.2.3.3 Dependence of the Maximum Rate on Hydrogen Concentration 268 7.3 Hydrogenation of Ketones and lmines Catalysed by [RuCl(P-P)(u-Cl)]2 and [RuHCl(P-P)]3 Complexes 271 7.3.1 Transfer Hydrogenation of Acetophenone 272 7.3.2 H2-Hydrogenation of Ketones and lmines 276 7.3.3 H2-Hydrogenation of Nitriles 278 7.4 References - Chapter 7 280 CHAPTER 8 General Conclusions and Suggestions for Future Work 282 APPENDIX 285 A-1 Temperature and Concentration Dependence of the Optical Rotation of (/?)-(+)- 1-Phenylethanol 286 A-2 X-ray Crystallographic Analyses 290 > xi LIST O F T A B L E S Table Title Page 2.1 Retention Times and Response Factors 47 3.1 Magnetic moment data for Ru2Cls(P-P)2 complexes (CDCI3,20 *C) 83 3.2 Visible Spectroscopic Data for the Ru2Cls(P-P)2 Complexes 85 3.3 31P{ 1H} NMR Data (121.42 MHz, 20 °C) for [RuCl(P-P)(p>Cl)h Complexes 89 3.4 Selected Bond Lengths (A) for [(DM£0)(DPPB)Ru- (u-Cl)3Ru(Cl)(DPPB)] with Estimated Standard Deviations in Parentheses 103 3.5 Selected Bond Angles (deg) for [(DM£0)(DPPB)Ru- (u.-Cl)3Ru(Cl)(DPPB)] with Estimated Standard Deviations in Parentheses 104 3.6 31P{  lH} NMR Data (121.42 MHz, 20 °C) for the Trichloro-Bridged Dinuclear Complexes, [(L)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)] Ill 3.7 31P{ !H} NMR Data (121.42 MHz, C6D6,20 °C) for the Complexes Obtained by the Reaction of Cw-Ru(Cl)2Q3MSO)4 with One Equivalent of Bidentate Phosphines 119 4.1 Literature 31P{  lH) NMR Spectral Data for a) RuCl2(PPh3)3 at -97 °C and b) RuCl2(DPPB)(PPh3) at -63 °C in CD2CI2 Solution 138 4.2 Solid-State 3 1 P CP/MAS NMR Spectral Data for a) RuCl2(PPh3)3 andb) RuCl2(DPPB)(PPh3) 138 4.3 31P{  lH) NMR Spectral Data for RuXCl(DPPB)(PPh2Py) Complexes 24-26 (X = Cl, H) 168 4.4 3 1 P NMR Spectral Parameters (121.42 MHz) Used to Obtain the Simulated Spectrum for 7Va/w-RuCl2(DPPB)(DPPM), 27 173 5.1 Transition Elements Found in Molecular Hydrogen (rj2-H2) Complexes 193 5.2 Temperature Dependence of the *H NMR Ti Relaxation Time Data (300 MHz, toluene-̂ ) for the (ri2-H2) resonance of 31a at 8-11.0 ppm 200 xii 5.3 31P{ lR) NMR Data (121.42 MHz, C6D6 or toluene-4°, 20 'Q for the Complexes [(L)(DPPB)Ru(u-Cl)3RuCl(DPPB)] (L = T]2-H2,31a; a-N2,31b) 201 5.4 Selected Bond Lengths (A) for [RuHCl(5,5-CHIRAPHOS)]3,30, with Estimated Standard Deviations in Parentheses 214 5.5 Selected Bond Angles (deg) for [RuHCl(S,S-CHIRAPHOS)]3,30, with Estimated Standard Deviations in Parentheses 214 5.6 Results of a Selective {3 !P}-Decoupled lH NMR Spectral Study of [RuHCl(DPPB)]3, 29, in C6D6 Solution 221 5.7 lH and 3 JP{!H} NMR Data for[(RCN)(DPPB)Ru(u.-H)- (p.-Cl)2RuH(DPPB)] Complexes, R = Me, 33a; Ph, 33b 229 7.1 Solubility of H2 in 7V,N-Dimethylacetamide 259 7.2 Kinetic Data for Hydrogenation of Styrene Catalysed by [RuCl(DPPB)(u-Cl)]2 in DMA at 30 °C 262 7.3 Data for Transfer Hydrogenation of Acetophenone in 2-Propanol/KOHCatalysed by [RuCl(P-P)(u-Cl)]2 Complexes 273 7.4 Data for H2-Hydrogenation of Acetophenone Catalysed by [RuCl(DPPB)(u-Cl)]2 and Related Complexes 277 xiii LIST OF FIGURES Figure Title Page 1.1 Selected chiral diphosphines used in asymmetric catalysis 6 1.2 The chiral diphosphine BINAP 6 1.3 A possible mechanism for the chiral diphosphine rhodium-catalysed asymmetric hydrogenation of prochiral olefins 9 1.4 Mechanism proposed by Schrock and Osborn for the rhodium- phosphine catalysed homogeneous hydrogenation of ketones 12 1.5 Suggested role of water in rhodium-phosphine catalysed homogeneous hydrogenation of ketones 13 1.6 Structure of the chiral diphosphine CYCPHOS 18 1.7 Structure of the irnine substrate 18 1.8 Poly-ra- sulphonated derivatives of the bidentate chiral phosphine 2,4-bis-(diphenylphosphino)pentane 19 1.9 The chiral Schiff base PPEI 22 1.10 The unsaturate route in transfer hydrogenation from an alcohol donor 22 1.11 The saturate route for transition metal hydride-catalysed hydrogen transfer from an alcohol donor 23 1.12 Proposed transition states during a) heterolytic and, b) homolytic activation of dihydrogen by transition metal complexes 25 1.13 First reported examples of complexes containing the bound molecular hydrogen (r|2-H2) ligand 25 2.1 Kugelrohr type apparatus.... 44 3.1 Coordinatively unsaturated rutliemiim(n)-diphospnine complexes prepared by phosphine displacement reactions 75 3.2 Geometry of Ru2Cl5(CHIRAPHOS)2 77 3.3 Suggested geometry for [RuCl2(P-P)]2 complexes 79 3.4 Diphosphines used in the preparation of Ru- (P-P) complexes 81 3.6 Visible spectra of the Ru2Cls(P-P)2 complexes (5, 7,8,10,12) in C H 2 C l 2 a t 25°C 84 xiv 3.7 31P{1H} NMR spectrum (121.42 MHz, 20°C) of [RuCl2(S-BINAP)] 2, 19, in C 6 D 6 88 3.8 Suggested geometry of [RuCl(BINAP)(u-Cl)]2 90 3.9 lH NMR spectrum of (NHBu2)(DPPB)Ru(p,-Cl)3RuCl(DPPB), 14c, in CDC13 (300 MHz, 20°C) .99 3.10 An ORTEP stereoview of [(DMSJD)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)] showing the atom numbering scheme used. The thermal ellipsoids for non-hydrogen atoms are drawn at 50% probability 103 3.11 Geometry of a) [Ru2CU(DPPB)2(DMSO)],14e and, b) [Ru2Cl5(CHIRAPHOS)2], 4 105 3.12 Geometry of [(CS)(PPh3)2Ru(u,-Cl)3RuCl(PPh3)2] 106 3.13 The'non-nucleophilic* bases (a) Proton Sponge® and (b) DBU 107 3.14 31P{ lH) NMR spectrum of [RuCl2(DPPB)(PhCN)]2 in CDC13 109 3.15 *H NMR spectrum of [RuCl2(DPPB)(PhCN)]2 in CDC13 109 3.16 Proposed structure for Ru2Cl4(DPPB)2Q )̂ complexes 110 3.17 A symmetric dinuclear structure for Ru2Cl4(DPPB)2Ql) complexes 112 3.18 31P{!H} NMR spectra (121.42 MHz, 20°C) of [(L)(DPPB)Ru(u.-Cl)3Ru(Cl)(DPPB)] complexes 113 3.19 3 *P {*H} NMR spectrum of the mixture of products isolated from the reaction of c«-Ru(Cl)2(DMSO)4 with one equivalent of S.S-BDPP 118 3.20 ! H NMR spectrum (300 MHz, 20°C) of [RuCl(p-cymene)- (/?-BINAP)]+Cl- in CDC13 121 3.21 Geometry of [RuX(arene)(BINAP)]+X- complexes 122 4.1 The 80.99 MHz CP/MAS 3 1 P NMR spectra of the complexes a) RuCl2(PPh3)3 and b) RuCl2(DPPB)(PPh3), at a MA spinning frequency of 3.5 kHz 134 4.2 a) A simulated solution NMR spectrum of RuCl2(PPh3)3 obtained using the literature data given in Table 4.1. b) A CP/MAS 3 1 P NMR (TOSS ) spectrum of RuCl2(PPh3)3 136 4.3 a) A simulated solution NMR spectrum of RuCl2(DPPB)(PPh3) obtained using the literature data given in Table 4.1. b) A CP/MAS 3 1 P NMR (TOSS) spectrum of RuCl2(DPPB)(PPh3)... 137 4.4 Geometry of RuCl20?Ph3)3 as determined by an X-ray diffraction study 139 4.5 31P{ NMR spectrum (121.42 MHz, 20 °C) of RuCl2(DPPB)(PPh3) in CDC13 140 xv 4.6 The CP/MAS 3*P NMR spectra of RuCl2(DPPB)(PPh3) showing (a) Non-Quaternary Suppression (NQS) with a dipolar dephasing delay of 303 u,s. The corresponding TOSS spectrum (b) is shown for comparison 142 4.7 Proposed solid-state geometry of RuCl2(DPPB)Q?Ph3) based on the present 31P-CP/MAS NMR studies 144 4.8 3lp{lH} NMR spectrum (121.42 MHz, C6D6 lock, 20 °C) of the H2-uptake solution of 23 in DMA 147 4.9 31P{ lH} NMR spectrum (121.42 MHz, 20 °C) of the reaction mixture obtained after stirring 23 in C6D6 solution under 1 atm H2 for 18 h in the presence of Proton Sponge® (~1 equiv./Ru) 149 4.10 *H NMR spectrum (300 MHz, 20 °C) of the reaction mixture obtained after stirring 23 in C6D6 solution under 1 atm H2 for 18 h in the presence of Proton Sponge® (~1 equiv./Ru) 150 4.11 Possible structures for Ru-hydrides formed from RuCl2(DPPB)(PPh3) 152 4.12 7>a/iJ-RuCl2(DPPB)(PPh2Py), 24 153 4.13 3lp{lH} NMR spectrum (121.42 MHz, C6D6, 20 *C) of rra/w-RuCl2(DPPB)(PPh2Py) 155 4.14 *H NMR spectrum (300 MHz, C6D6. 20 °C) of rrans-RuCl2(DPPB)(PPh2Py) 156 4.15 3lP{lH) NMR spectrum (121.42 MHz, CDCI3, 20 °C) of cw-RuCl2(DPPB)(PPh2Py) 158 4.16 *H NMR spectrum (300 MHz, C D C I 3 , 20 °C) of cw-RuCl2(DPPB)(PPh2Py) 159 4.17 Cw-RuCl2(DPPB)(PPh2Py), 25 160 4.18 Enantiomeric forms of cw-(/ac)-RuCl20DPPB)(PPh2Py), 25 163 4.19 3 1 P NMR spectrum (121.42 MHz, C6D6. 20 °C) of the orange-brown solid obtained from the reaction of PPh2Py with hydrides formed in situ from the reaction of 23 with H2 in the presence of Proton Sponge® 165 4.20 *H NMR spectrum (300 MHz, C s D ^ 20 °C) of the orange-brown solid obtained from the reaction of PPh2Py with hydrides formed in situ from the reaction of 23 with H2 in the presence of Proton Sponge® 166 4.21 7>a,™-RuHCl(DPPB)(PPh2Py), 26 167 4.22 Tra^-RuCl2(DPPB)(DPPM), 27 169 xvi 4.23 ! H NMR spectrum (300 MHz, 20 'C) of rra^-RuCl2(DPPB)(DPPM), 27, in CeD6 solution 170 4.24 31p{lH) NMR spectrum (121.42 MHz, 20 °C) of f/ww-RuCl2(DPPB)(DPPM), 27, in solution 171 4.25 31p_31P homonuclear COSY contour plot (121.42 MHz, 20 °C) of fra«5-RuCl2(DPPB)(DPPM), 27, in C6D6 solution 172 4.26 A simulated 3 1 P NMR spectrum (121.42 MHz, AA'BB' spin-system) for rra/w-RuCl2(DPPB)(DPPM), 27, obtained using the parameters listed in Table 4.4 ..174 4.27 ! H NMR spectrum (300 MHz, CsD^ 20 °C) of the yellow solid obtained from the reaction of DPPM (1 equiv./Ru) with hydrides formed in situ from the reaction of 23 with H 2 in the presence of Proton Sponge® 176 4.28 3 1P{ ]H) NMR spectrum (121.42 MHz, C6D6,20 °C) of the yellow solid obtained from the reaction of DPPM with hydrides formed in situ from the reaction of 23 with H 2 in the presence of Proton Sponge® 177 4.29 3lP{ 1H) NMR spectrum (121.42 MHz, C6D 6 ) 20 °C) of RuCl2(/?-BINAP)(PPh3), 21, in CeD6 180 5.1 Some early examples of molecular hydrogen complexes 192 5.2 A bonding scheme for M-(ri 2-H2) moiety; the shaded areas represent occupied orbitals 194 5.3 ! H NMR spectrum (300 MHz, toluene-^, 292 K) of the complex [RuCl(DPPB)(|i-Cl)]2,14, sealed under ~1 atm H 2 pressure 198 5.4 31P{1H} NMR spectrum (121.42 MHz, toluene-cfe, 292 K) of a sample of [RuCl(DPPB)(u-Cl)]2,14, sealed under ~1 atm H 2 pressure 199 5.5 Temperature dependence of Tj for the molecular hydrogen (Tj2-H2) moiety in [(ri2-H2)(DPPB)Ru(u-Cl)3RuCl(DPPB)], 31a 200 5.6 ! H NMR spectrum (300 MHz, C ^ , 20 °C) of [(r]2-HD)(DPPB)Ru- Qi-Cl)3RuCl(DPPB)], formed in situ by leaving 14 under 1.2 atm of H2andl.8atmofD2 203 5.7 Possible intermediates in 14-catalysed H 2 / D 2 HD isotope exchange 205 5.8 Suggested geometry for the dinitrogen complex, 31b 206 xvii 5.9 *H NMR spectrum (300 MHz, CfsDfr 20 °C) of the dinitrogen complex 31b formed in situ from [RuCl(DPPB)(u.-Cl)]2,14, under ~1 atm N2 pressure 208 5.10 31P{ lK] NMR spectrum (121.42 MHz, C6D6.20 °C) of the dinitrogen complex 31b formed in situ from [RuCl(DPPB)(u-Cl)]2,14, under ~1 atm N2 pressure 209 5.11 Infra-red spectrum of a CH2CI2 solution of 14 sealed under N2 atmosphere 210 5.12 Molecular structure of [RuHCl(S,S-CHIRAPHOS)]3,30, showing the atom numbering scheme used 213 5.13 *H NMR spectrum of [RuHCl(DPPB)]3,29, in 0^6 solution (300 MHz, 20 °C) 216 5.14 31P{ !H} NMR spectrum of [RuHCl(DPPB)]3,29, in Q D 6 solution (121.42 MHz, 20 °C) 217 5.15 iHpiP} high-field NMR spectra of [RuHCl(DPPB)]3,29, in C6D6 solution (500.13 MHz for iH, 202.46 MHz for 3 1 P, 23 °C) with selective phosphorus decoupling at: (a) 71.8; (b) 69.5; (c) 61.9; (d) 59.7; (e) 57.6; (f) 48.9 ppm; and(g) with broad-band decoupling 219 5.16 Schematic structural representation of [RuHClQ?-P)]3 complexes 221 5.17 *H NMR spectrum (hydride region, 300 MHz, C^D6> 20 °C) of [RuHCl(5,S-CHIRAPHOS)]3, 30 222 5.18 ^P^H) NMR spectrum (121.42 MHz, C6D6, 20 °C) of a crude reaction mixture showing resonances of the hydridochloro trimer [RuHCl(CHIRAPHOS)]3,30, and the dinuclear coproduct [(Et3N)(CHIRAPHOS)Ru(tt-Cl)3RuCl(CHIRAPHOS)], 16b 223 5.19 Suggested geometry for [RuHCl(DPPB)]2(ri2-H2) complex, 32 225 5.20 Variable temperature *H NMR spectra of the dinuclear T|2-H2 complex [RuHCl(DPPB)]2(r|2-H2), 32, generated in situ from the reaction of [RuHCl(DPPB)]3 with H 2 227 6.1 *H NMR (300 MHz, C6D6,20 °C) hydride region for rra^-RuHCl(nbd)(DPPB), 36 243 6.2 *H NMR 2D-COSY spectrum (300 MHz, C6D6,20 °C, aliphatic proton region) of rra/«-RuHCl(nbd)(DPPB), 36 244 6.3 *H NMR NOEDIFF spectra (400 MHz, C6D6,20 °C) of rranj-RuHCl(nbd)(DPPB), 36 245 xviii 6.4 Proposed geometry for RuHCl(nbd)(DPPB), 36, deluding the proton assignment, based on analysis of the solution NMR spectral data 246 7.1 Thevan't Hoff plot for the temperature dependence of H2-solubility in DMA 259 7.2 A typical H2-uptake plot for the hydrogenation of styrene catalysed by [RuCl(DPPB)(u-Cl)]2,14, in DMA at 3 0 °C and 785 Ton- pressure of H 2 260 7.3 Rate plots for styrene hydrogenation catalysed by 14 in DMA, at 30 °C, at various [RU]T 263 7.4 Dependence of the rnaximum hydrogenation rate on [RU]T at 3 0 "C 263 7.5 Dependence of the maximum hydrogenation rate on [Styrene] at 30 °C 264 7.6 Dependence of the maximum hydrogenation rate on [H2] at 30 °C 264 7.7 Plot of ./(Maximum Rate) against l/[Styrene] 268 7.8 Plot of l/(Maximum Rate) against 1/[H2] 269 7.9 iH NMR spectrum (hydride region, 300 MHz, 20 °C, toluene-fife) of the residue obtained from transfer hydrogenation of acetophenone using the CHIRAPHOS system 274 7 . 1 0 An imine substrate tested for asymmetric H2-hydrogenation using [RuHCl(CHIRAPHOS)]3 as catalyst 278 xix L I S T O F A B B R E V I A T I O N S The following list of abbreviations, most of which are commonly used in the chemical literature, will be employed in this thesis: At absorbance at time t (UV-Vis) A angstrom, 10"8 centimeter APT attached proton test (NMR) atm atmosphere; 1 atm = 760 mm Hg (5,5)-BDPP (25,45)-bis(diphenylphosphino)pentane; also called Skewphos BINAP (/?)- or (5)-2,2'-bis(diphenylphosphino)-l,l'-binaphthyl bipy 2,2'-bipyridine BMPP (/?)-(+)-benzylmethylphenylphosphine BPPFA 1, l'-bis(diphenylphosphino)-2,-(l-N,N-a-dmiethylaminoethyl) ferrocene BPPM (25,45)-N-(r-butoxycarbonyl)-4-diphenylphosphino-2- diphenylphosphinomethylpyrolidine br broad Bu butyl, CH2(CH2)2CH3 c concentration (in g/100 mL) 1 3 C carbon-13 °C degree Celsius cat. catalyst CD circular dichroism 5,5-CHIRAPHOS (25,35)-bis(diphenylphosphino)butane cm centimeter xx cod cyclooctadiene CP cross polarisation (NMR) Cp cyclopentadienyl, TjS-CsHs COSY homonuclear correlation spectroscopy Cp* pentamethylcyclopentadienyl, ri5-C5Me5 C YCPHOS 1 -cyclohexyl-1,2-bis (diphenylphosphino)ethane D configuration relative to D-glyceraldehyde °C degree Celsius d doublet (NMR) d dextrorotatory DBU l,8-diazabicyclo[5.4.0]undec-7-ene DIOP (2R3R) or (2S,3S)-0-isopropylidene-2,3-dihydroxy-1,4- bis(diphenylphosphino)butane DIPAMP 1,2-bis(orr/w-anisylphenylphosphino)ethane DMA N,N-dimethylacetamide, CH3C(=0)N(CH3)2 DMSO dimethylsulphoxide DPCYCP rac-(±)-1,2-bis(dicyclohexylphosphino)cyclopentane DPPB 1,4-bis(diphenylphosphino)butane DPPCP rac-(±)-1,2-bis(diphenylphosphino)cyclopentane DPPE 1,2-bis(diphenylphosphino)ethane DPPH 1,6-bis(diphenylphosphino)hexane DPPM 1,1 -bis(diphenylphosphino)methane DPPN 1,5-bis(diphenylphosphino)pentane DPPP 1,3-bis(diphenylphosphino)propane EAC ethyl-(Z)-a-acetarridc<:innamate e. e. enantiomeric excess fac facial xxi FID flame-ionisation detector GC gas chromatography gem geminal lH proton-1 Hz Hertz, cycles per second HETCOR heteronuclear correlation (NMR) IR infra-red iPr iso-propyl, (CH3)2CH J coupling constant, in Hz k rate constant L ligand litre L configuration relative to L-glyceraldehyde 1 path length / levorotatory M central metal atom in a complex molarity, moles L"1 m multiplet (NMR) moderate intensity (IR) [M]D T molar rotation, [M]D T = [CX]DT X molecular weight /100 MA magic angle (NMR) MAC methyl-(Z)-a-acetamidccinnamate Me methyl, CH3 mer meridional min minute(s) mL millilitre mmol rriillimole(s) xxii mol mole(s) nm nanometer(s) nbd 2,5-norbornadiene NMR nuclear magnetic resonance NOEDIFF nuclear Overhauser effect difference o ortho obs observed o.y. optical yield p para 3 1 P phosphorus-31 P-P ditertiary phosphine Ph phenyl, C6H5 phen 1,10-phenanthroline PHENOP the chiral aminophosphinephosphinite ligand: Ph2PN(Et)CH(CH2Ph)CH2OPPh2 PPh2Py diphenyl(2-pyridyl)phosphine ppm parts per million PROPHOS 1,2-bis(diphenylphosphino)propane py pyridine q quartet (R)- absolute configuration (latin: rectus; right) RT room temperature S solvent or substrate (5)- absolute configuration (latin: sinister, left) s singlet (NMR), strong (IR) Tj spin-lattice (or longitudinal) relaxation time (NMR) t triplet xxiii TCD mermal-conductivity detector tert tertiary TMS tetramethylsilane tol tolyl, -C6H4CH3 UV-vis ultraviolet-visible w weak intensity (JR) wj 12 linewidth at half height a observed rotation [a]oT specific or absolute rotation (measured as the sodium D line) at temperature T A heat e extinction coefficient (in M _ 1 cm-1) X wave length 8 chemical shift (in ppm downfield from TMS) v frequency (cm-1) Tj descriptor for hapticity u. descriptor for bridging * chiral centre xxiv ACKNOWLEDGEMENTS I would like to thank Professor B. R. James for his guidance, encouragement, and patience throughout the duration of this work. I am also indebted to members of the James group (past and present) for their friendship and support. I wish to express my gratitude to the proof-readers for their excellent criticism. Special thanks are due to Mr. Ken MacFarlane for allowing the use of his personal computer equipment The assistance of the various departmental services is gratefully acknowledged Finally, I would like to thank my family for their encouragement and support over the years. \ xxv CIHAIPTriElR a Introduction 1.1 General Introduction The past three decades have witnessed enormous advances in the field of homogeneous catalysis. The use of soluble organometallic complexes, particularly those containing transition metals, is fast becoming an important tool in effecting a variety of stoichiometric and catalytic organic reactions. The ever-increasing demand for synthetic specialty fine chemicals, including pharmaceuticals, food additives, and pesticides, whose syntheses often consist of highly specific and selective organic transformations, has provided impetus for further development in this area.1 Transition metal complexes catalyse a wide range of important chemical reactions (e.g. references 1-6); these include hydrogenation, hydrosilylation, and hydrocyanation of unsaturated organic substrates, olefin isomerisation, dehydration of tertiary alcohols, and various hydroformylation, epoxidation, and polymerisation reactions. The relative advantages and disadvantages of homogeneous and heterogeneous catalysts, particularly from an industrial point of view, have been widely discussed.7"9 The generally higher activity of homogeneous catalysts compared to the industrially more prevalent heterogeneous catalysts allows for the use of relatively mild reaction conditions. Greater specificity, selectivity and reproducibility exhibited by the homogeneous systems, and the ability to vary systematically their catalytic properties by simply changing the ligand environment around the metal centre, are strongly desirable for industrial processes. 1 Moreover the ease of monitoring homogeneous catalytic reactions by conventional spectroscopic and other kinetic techniques makes them amenable to detailed mechanistic investigations.2 The difficulty in separating the often expensive soluble catalysts from reaction products and, to a lesser extent, the oxygen- and moisture-sensitivity and low thermal stability of the catalysts, remain the principal hurdles toward a more widespread use of homogeneous systems in large scale industrial processes.7 Considerable efforts have been made to circumvent the separation problem by anchoring homogeneous catalysts on insoluble inorganic supports (e.g. silica, alurnina and zeolites), or on organic cross-linked (e.g. polystyrene-divinylbenzene)7> 8 » 1 0 as well as noncross-linked (e.g. polyamides)11 polymer supports. Phase-transfer catalysis offers another promising approach.12 The Wacker and the Oxo processes, methanol carbonylation, oligomerisation of dienes, some Ziegler-Natta systems, and the adiponitrile synthesis, are some notable examples from the forty-odd industrial processes515 currently using homogeneous catalysts.3-5 In recent years, a major thrust in research on homogeneous catalysis has been directed at designing catalysts containing chiral ligands for asymmetric synthesis of optically active compounds, whereby enantiomeric products are obtained in unequal amounts. A number of comprehensive reviews have been published.13*19 Because specific biological activity of organic compounds is often associated with only one of the enantiomers or diastereomers, it is highly desirable and in some cases even necessary to obtain such compounds in pure form. l a- 2u> 2 1 Asymmetric synthesis through enantioselective catalysis offers the most plausible alternative to the costly and tedious process of resolution of a racemic mixture. Biosynthetic pathways, while highly specific and efficient, may not always be available or suitable for such transformations.14'21 • 2 2 Monsanto's introduction of a Wilkinson-type rhodium(I) catalyst with a chiral diphosphine ligand (P*—*P) for large scale commercial production of the amino acid drug 2 S-Dopa (Equation 1.1), which is used for treating Parkinson's disease, was one of the most significant developments.15 y C 0 2 R SNHCOR 1) [Rh(P*-*P)(S)2J+ + :* H 3 N — C — H H 2 , S = MeOH 2 ) H 3 0 + C H 2 (1.1) HO f ^ O H 5-Dopa Similar chiral catalyst systems are being employed elsewhere for the asymmetric synthesis of other amino acids,13"15 for example, in the production of constituents of the popular sugar substitute aspartame (Nutrasweet™) which is a methyl ester of the dipeptide S-aspartyl-S-phenylalanine.23 Of note, none of the other three diastereomers of aspartame is sweet. 1.2 Homogeneous Hydrogenation Hydrogenation of unsaturated organic substrates is by far the most extensively studied area of homogeneous catalysis, as evidenced by the vast amount of literature available on this topic. A number of excellent comprehensive reviews,8*24"27 specialised texts and books have been published.28"31 Partly because of historical reasons and partly because of obvious potential commercial applications, a major portion of the literature on homogeneous hydrogenation deals with the more easily reduced and more commonly available substrates containing carbon-carbon multiple bonds.32 A number of systems have been studied in considerable detail and their mechanisms deduced. However, work 3 on the reduction of carbon-nitrogen and carbon-oxygen double bonds has gained momentum in recent years. 1 3- 3 1 - 3 4 Based on the mechanistic studies, hydrogenation of alkenes mediated by a transition metal complex may be seen generally as consisting of four fundamental processes:25-29 a) activation of molecular hydrogen b) substrate activation c) hydrogen transfer to the substrate d) release of the product and, in case of a catalytic reaction, regeneration of the catalyst. 1.2.1 Asymmetric Homogeneous Hydrogenation The earliest attempts at asymmetric hydrogenation of organic substrates, in fact, employed a heterogeneous palladium catalyst absorbed on silk, but gave poor results.35 Attention soon turned to the use of transition metal complexes modified with chiral auxiliary ligands. Chiral monophosphines of the type P*PhR1R2, which have a centre of asymmetry at the phosphorus atom, were first reported in 1968.36 Kagan's group reported the synthesis of the first chiral diphosphine viz. DIOP (Figure 1.1), from naturally occurring tartaric acid;37 in DIOP the chirality resides in the carbon skeleton joining the two phosphorus atoms. Successful use of transition metal complexes with these phosphines as catalysts for asymmetric hydrogenation of several prochiral alkenes triggered a rapid development. The progress in asymmetric homogeneous hydrogenation of organic substrates is well-documented.13'19,33,38-40 A quantitative measure of the effectiveness of chiral induction via enantioselective catalysis is provided by the enantiomeric excess (e.e.) or the optical yield (o.y.), which are usually considered to be equivalent (Equations 1.2 and 1.3). 4 o.y.(%) = observed specific rotation [a]pT x 100 (1.2) specific rotation of pure enantiomer [CC]DT e.e.(%) = I [R] - [S] I [R] + [S] x 100 (1.3) Catalyst systems incorporating rhodium and chiral diphosphines were first proved to be the most effective for asymmetric hydrogenation of a variety of olefinic acids and related derivatives, under relatively mild conditions (20-100 *C, 1-10 atm of H2).41 Until recently, chiral catalyst systems consisting of group 8-10 transition metals other than rhodium remained largely underdeveloped. In the last few years, however, some ruthenium-chiral diphosphine systems have emerged as effective enantioselective hydrogenation catalysts for a much wider range of organic substrates, including the olefinic acids, allylic alcohols, dienes, and functionalised ketones.13'33,42 At best, only moderate optical yields (-50%) have been obtained using non- phosphine chiral ligands such as Schiff bases, amines, amides, and sulphoxides.26, 3 3 A large number of chiral phosphines have been synthesised and tested as ligands in the past fifteen years.14, 1 6 b Some prominent representative examples of such phosphines are: PROPHOS and BPPM, derived from lactic acid and the amino acid proline, respectively; CHLRAPHOS, which contains two asymmetric centres in the carbon backbone; ferrocene- based BPPFA, which exhibits planar as well as carbon chirality; and DiPAMP, which is used in the Monsanto S-DOPA process15,43 0?igure 1.1). 5 DIOP CHIRAPHOS BPPM Figure 1.1: Selected chiral diphosphines used in asymmetric catalysis. Of particular interest is the diphosphine BINAP (Figure 1.2) which exhibits solely a planar or axial chirality.13- 4 4 The steric bulk of the naphthyl rings and the attached diphenylphosphine substituents prevents free rotation about the carbon-carbon single bond joining the naphthyl groups, essentially locking the ligand in one of the two configurations. Figure 1.2: The chiral diphosphine BINAP. Rhodium- and ruthenium-BINAP systems have been reported to give consistently high optical yields (90-100%) for hydrogenation of not only dehydroamino acids and dicarboxylic acids, 1 3 - 4 4 1 4 5 but perhaps more significantly, for reduction of a variety of 6 functionalised carbonyl substrates13-42- 4 6 (e.g. P-ketoesters and substituted aceto- phenones). A large amount of e.e. data has accumulated over the years on hydrogenation of a wide range of substrates using various chiral ligand-metal combinations as catalyst precursors. Enantiomeric excesses of close to 100% have been achieved for hydrogenation of several alkenes.1 6 b-4 1 Attempts to correlate the observed e.e. with the nature of the ligand, the metal, the substrate, and also with the absolute configurations of the ligand and the metal compound, highlight the complexity of the enantioselection process. 1 7- 4 1- 4 7. While no general correlations are forthcoming, some useful trends have emerged. Chelating ligands are more effective than monodentate ones. 1 4- 1 7> 4 1 Ligands such as CHIRAPHOS that form rigid five-membered chelates are more likely to show higher enantioselectivity than those which form more flexible, six- or seven-membered rings. A rigid chiral array of phenyl rings in the five-membered chelates presumably helps discriminate the enantiotopic faces of the prochiral substrate in the binding step.17 Nature of the substrate also plays an important role in determining the extent of asymmetric induction. High optical yields are often realised for functionalised substrates with the ability to bind the metal in a bidentate fashion which presumably provides a degree of rigidity in the configuration determining step. For example, enamides such as methyl-(Z)- a-acetamido-cinnamate (MAC) consistently give high e.e. (up to 100%) compared to simple prochiral alkenes such as a-ethylstyrene (< 20%).16b Using an ingenious combination of kinetic, X-ray, and NMR studies, Halpern and coworkers have elucidated a possible mechanism for asymmetric hydrogenation of prochiral alkenes catalysed by the extremely effective Rh-CHLRAPHOS and Rh-DiPAMP systems (Figure 1.3).48 Addition of methyl- or ethyl-(Z)-a-acetamidocinnamate (R = methyl, MAC; R = ethyl, EAC; see Figure 1.3) substrate to the catalyst precursor [Rh(P- P)(MeOH)n]+, generated in situ (P-P = CHIRAPHOS, DiPAMP), affords two diastereomers (A' and A") which differ only in the olefinic faces coordinated. The two 7 diastereomers could be distinguished in solution by 3 1 P NMR spectroscopy. Examination of the major diastereomer (A') of [Rh(S,S-CHIRAPHOS)(EAC)]+C104-, which was isolated and characterised by X-ray crystallography, revealed that the major diastereomer was not the one expected to lead to the principal product. Earlier, the enantioselectivity of the reduction was thought to be governed by the initial diastereomeric ratio (A'/A") of the catalyst-substrate adduct. However, detailed kinetic studies showed that it was the relative reactivity of the diastereomers with H2 that determined the observed optical yield. For example, in the related [Rh(/?,/?-DiPAMP)]+ system using MAC as the substrate, the minor species, A", reacted with H2 ~580 times faster than did the major diastereomer, A' (k" = 6.4 x 102 and k' * 1.1 M-^s-1, respectively, at 25 °C, 1 atm H2), yielding the corresponding S-enantiomer in over 95% e.e. The mechanism illustrated in Figure 1.3 also explains the observed decrease in e.e. with increasing H2 pressure. Increase in H2 pressure increases rates of both the pathways (k' and k"). This can lead to depletion of the minor diastereomer A" faster than the equilibrium between A' and A" can be re-established, consequently producing more of the /?-isomer, and hence lower optical yields. 1.2.2 Hydrogenation of Carbonyl Compounds As mentioned in Section 1.2, work on reduction of substrates other than alkenes has lagged behind considerably. This is evident from the relatively few literature reports on homogeneous hydrogenation of aldehydes, ketones, esters, imines, nitriles, anhydrides, and nitro compounds.29* 3 1> 3 2 There appears to be a certain degree of correlation between the ease of reduction of these substrates and the volume of work done on them. Amongst the non-olefinic substrates, those containing a carbonyl functionality are the most easily reduced and have probably received the most attention. 8 Figure 1.3: A possible mechanism for the chiral diphosphine rhodium-catalysed asymmetric hydrogenation of prochiral olefins. 9 Except in a Umited number of documented systems,25 substrate activation by coordination to the metal centre is usually essential for a metal-catalysed transformation to take place. Carbonyl groups exhibit a much lower binding ability (compared to alkenes) toward transition metals, and very few late transition metal coordination complexes containing carbonyl compounds are known.49* 5 0 Also, unlike in the case of olefin substrates and their reduction product alkanes, the non-olefinic substrates and their hydrogenation products show very similar affinity toward the metal catalyst (for example, carbonyl compounds and the corresponding product alcohols).32 In many cases the hydrogenation products of non-olefinic substrates exhibit even higher affinity toward the metal catalyst when compared to that of the parent substrates (for example, amines vs. imines). Such product coordination can result in a competitive inhibition of further reduction. Aldehydes are the most easily reduced of the carbonyl compounds (followed by ketones and esters); however, aldehydes are prone to facile and usually irreversible decarbonylation by the hydrogenation catalysts. This in turn results in a progressive loss of catalytic activity by CO poisoning of the catalyst; 3 l b- 3 2 the presence of a CO ligand is known to lessen the catalytic hydrogenation activity of most group 8 and 9 transition metal catalysts.51 The anionic hydrido(phosphine)ruthenate complexes reported by Grey et al. are perhaps the only effective catalysts known for H2-hydrogenation of esters to the corresponding alcohols (Equation 1.4) under relatively mild conditions. 5 2 , 5 3 Stoichiometric reduction by hydride reagents such as NaBR* and LiAUij is still the method of choice for reduction of ester substrates.32 10 o II C H 3 C - O C H 3 10 atm H 2 , 90 °C, toluene CH3CH2OH + CH3OH O II + CH 3C-OCH 2CH 3 (1.4) Ph3 P H, Ru Ph3P PPh2 H Work on hydrogenation of ketones has gathered momentum in recent years, and a number of reviews have appeared.3 lb> 32> 3 3 > 4 9 The increase in activity in this area stems mainly from the interest in asymmetric synthesis of chiral alcohols. The chiral secondary alcohols, obtained by hydrogenation of prochiral ketones (R^OR 2 ) , are important intermediates in the fine chemicals and pharmaceutical industries and in natural product synthesis.54 Stoichiometric borohydride and organoborane reagents modified by chiral auxiliaries have been shown to hydrogenate simple prochiral ketones in high e.e. (up to 100%).55 In one interesting case, propiophenone was reduced with 78% e.e. by achiral NaBH4 in the presence of bovine serum albumin as the chiral template.56 However, these reagents lack diversity and are often much less effective for reduction of functionalised ketones, such as aryl diketones and a-dicarbonyl compounds. As in the case of olefin hydrogenation, phosphine complexes of group 8 and 9 metals constitute the largest and the most effective class of homogeneous catalysts for ketone hydrogenation. Schrock and Osborn57 investigated H2-hydrogenation of simple ketones (e.g. acetone, acetophenone) under relatively mild conditions catalysed by canonic rhodium catalysts Q3quation 1.5) 0 f the type [RhH2(PR3)2(solv)2l+ which are easily prepared in situ from [Rh(diene)(PR3)2]+X~ precursors.32 Use of relatively more basic 11 phosphines, such as PBU3, resulted in turnovers of ca. 1000 or more, notably in the presence of added water (~ 1%), at 60-80 °C and ~ 7 atm H 2 . 5 8 O -R R2 [Rh(diene)P2]+X- 1% H zO P = PArxR3_x X = PC16, BF4, CIO4 OH I CH 1 / \ 0 -R R 2 (1.5) Based on their studies, Schrock and Osborn proposed the following mechanism Qrigure 1.4) for the hydrogenation of ketones. H— Rh-S R2C=0 + H 2 -R2CHOH S .CHR2 S—Rh-O P ' H H,0 T , P . C R 2 H—Rh —1 I + I x r H— Rh — OCHR? P = PAr^Rj., S = solvent Figure 1.4: Mechanism proposed by Schrock and Osborn57 for the rhodium-phosphine catalysed homogeneous hydrogenation of ketones. The initial cis-hydride migration to the carbonyl carbon of the bound ketone is followed by a water-promoted proton transfer to the carbonyl oxygen. Dissociation of the product 12 alcohol and subsequent oxidative addition of H2 then regenerate the catalyst. The observed incorporation of deuterium exclusively at the carbonyl carbon of acetone, when D2 is used for the reduction, supports the above mechanism and also rules out participation of the enol tautomer in the catalytic cycle.57 The proposed role of water in the proton transfer step is illustrated below (Figure 1.5). There is no clear evidence as to whether the proton abstraction by OH~ from the rhodium dihydride, and the proton transfer from a water molecule to the bound alkoxy moiety, occur in a concerted fashion or in a stepwise manner. Figure 1.5: Suggested role of water in rhodium-phosphine catalysed homogeneous hydrogenation of ketones (also see Figure 1.4). As in the case of alkene hydrogenation, phosphine complexes of group 8 and 9 metals have proved to be the most effective for ketone hydrogenation. Recently, however, rhodium and iridium complexes containing nitrogen-based donor ligands such as 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen) and related ligands have been reported to be highly active for H2- and transfer hydrogenation (Section 1.2.4) of ketones.59-60 The use of such non-phosphine catalyst systems may become important in light of the problems of degradation and ligand loss sometimes associated with phosphine ligands (under hydrogenation conditions).61 The asymmetric hydrogenation of prochiral ketones is not as well understood as that of alkenes.33 Attempts at using heterogeneous catalysts, notably Raney nickel, modified by chiral auxiliaries have been only moderately successful at best.35b> c 13 However, 3-hydroxybutanoate has been obtained in ~85% e.e. by hydrogenation of methyl acetoacetate using a Raney nickel catalyst modified by tartaric acid and NaBr.14 High optical yields have been obtained for hydrogenation of acetylacetone to 2,4-pentanediol, using a similar catalyst system.62 Asymmetric homogeneous hydrogenation of unsubstituted ketones under mild conditions (30 *C, 1 atm H2), using the Schrock-Osborn type cationic [RhH2P2(solvent)2]+ systems containing chiral phosphines, gave poor optical yields (e.g. < 10% for acetophenone) at low rates.63 Of the several chiral phosphines studied only a few exhibit good activity and enantioselectivity. Higher e.e.'s are generally observed for aryl alkyl ketones than for dialkyl ketones. Addition of small amounts of triethylamine to the neutral [Rh(nbd)Cl]2/DIOP catalyst system resulted in a dramatic increase in the observed e.e. (from 51% to ~ 80%) for hydrogenation of acetophenone at 50 °C and 70 atm H2 pressure Q̂ quation 1.6).54-64 ° 1/2 [Rh(nbd)Cl]2, (+)-DIOP C + H 2 M g / \ p h NEt3, benzene 50°C, 70 atm QH Me—C-Ph 1 H 80% e.e. (1.6) Results of H2-reduction of functionalised ketones have been generally more encouraging. Improved optical yields have been attributed to the increased rigidity of the catalyst-substrate adduct due to the chelating effect of the secondary functional group (hydroxy, alkoxy, carboxy, halo etc.).17- 4 6« 5 4 Close to 100% optical (and chemical) yields have been realised for the reduction of a wide range of substituted ketones using Ru- chiral phosphine systems, particularly with BINAP. 1 3- 4 6 Hydrosilylation of prochiral ketones in the presence of appropriate chiral transition metal catalysts, followed by hydrolysis, provides an indirect alternative route to enantioselective synthesis of chiral secondary alcohols.1 4-1 6-1 7-3 8-6 5 Optical yields of up 14 to 85% with rhodium chiral phosphine catalysts have been reported.4 9*6 5 Non-phosphine chiral ligands have also proved effective in asymmetric synthesis of chiral secondary alcohols via ketone hydrosilylation. Acetophenone is converted to 1-phenylethanol in 98% e.e. and quantitative yield using a rhodium catalyst prepared in situ from [Rh(cod)Cl]2 and a pyridine thiazolidine derivative (shown in Equation 1.7);14 the thiazolidine ligand can be synthesised by a one-step condensation of 2-pyridinealdehyde with an L-cysteine ester. O i. [Rh(cod)Cl]2:L(l:13) H A + H-SiHPh 2 ^20_C ^ Me—<?—Ph (1.7) M / \ p h i i . H 2 0 L OH 98% e.e. C - O C 2 H 5 o Asymmetric reduction of prochiral ketones can also be achieved by hydrogen transfer from an appropriate donor (e.g. alcohols, amines) in a chiral environment. Transfer hydrogenation is discussed in Section 1.2.4. 1.2.3 Homogeneous Hydrogenation of Nitriles and lmines There are very few reports in the literature dealing with transition metal catalysed hydrogenation of carbon-nitrogen multiple bonds ( O N , C=N).3 1* 3 3 * 4 9 Relatively severe temperatures (100-200 *C) and pressures (40-200 atm H2) are generally required in order to obtain reasonably fast rates.3 2 Catalytic hydrogenation (both homogeneous and heterogeneous) of nitriles often results in the formation of a mixture of primary, secondary and tertiary amines as well as ammonia ̂ Equation 1.8). Selectivity for only one product is usually the prime consideration in the choice of a catalyst. For example, the complex 15 RuHCl(PPh.3)3 catalyses hydrogenation of acetonitrile in toluene at 90 "C and 7 atm H2; at 15% conversion (20 h) of the nitrile, a mixture of ethylamine (34%), diethylamine (58%), methylamine (8%) and ammonia was obtained OBquation 1.8).52 CH 3CN 7 atm H2,90 *C, toluene CH 3CH 2NH 2 + (CH3CH2)2NH 34% 58% (1.8) RuHCl(PPh3)3 + (CH3CH2)3N + NH3 8% Interestingly, under the same reaction conditions the anionic hydrido(phosphine)ruthenate complex (shown in Equation 1.4), which is derived from the neutral RuHCl(PPn3)3 precursor, hydrogenated acetonitrile to ethylamine with 98% selectivity and at a faster rate (38% conversion); the rate of hydrogenation could be further increased by addition of 18-crown-6 to this system (60% conversion in 20 h).52 The rhodium hydride complex RhH(PPr'3)3 is an extremely effective nitrile hydrogenation catalyst; a number of alkyl and aryl nitriles have been reduced selectively to the corresponding primary amines Êquation 1.9) under very mild conditions (20 °C, 1 atm H2).3l, 66 of note, this rhodium complex also catalyses the reverse reaction, viz. dehydrogenation of primary amines OBquation 1.10), in the absence of H2 and at high temperatures (110 °C). -R-C=N 1 atm H 2 , 20 °C, THF -R-CH 2NH 2 (1.9) R = Bun, Bu1 RhH(PPr'3)3 a', W, Bz, CH2=CHCH2, Ph 110 *C, 0.05 torr PhC=N + 2H 2 PhCH2NH2 (1.10) RhH(PPr'3)3 16 lmines are intermediates in the reduction of nitriles to amines. They are also easily accessible synthetically via simple condensation reactions of carbonyl compounds such as aldehydes and ketones with primary amines (Equation 1.1l).67 Several rhodium and ruthenium phosphine complexes are active catalysts for the reduction of imines using molecular hydrogen;31"33' 4 9 « 6 3 relatively severe conditions are often required. Moreover, catalyst poisoning by the amine products sonietirnes results in reduced catalytic activity. l R \ cat l R \ C=0 + 3 R-NH 2 ^J^l " C=N—R3 + H 2 0 (1.11) 2 R X 2 R X Reduction of imines provides an easy route to substituted amines; in particular, there is considerable interest in the asymmetric synthesis of chiral amines (Equation 1.12).33> 6 8> 6 9 For example, some chiral amine derivatives are used as herbicides,68-69 in which one enantiomer is found to be far more potent than the other. Asymmetric synthesis of the more active enantiomer in high e.e. is desirable for environmental reasons because it would allow for the use of smaller doses of these herbicides. ]R ^ \ > I W R3 2? ^ H — ^ C - N ~ , R3 (1.12) 2 R / cat*. 2 R / H (-R * 2R) Attempts at asymmetric hydrogenation of prochiral imines, until recently,68'69 have been generally much less successful (typical e.e.'s < 40%) when compared to the relatively high e.e.'s (90-100%) achieved for enantioselective hydrogenation of several functionalised alkene and ketone substrates.33 However, the recently reported rhodium catalyst generated in situ from [Rh(nbd)Cl]2 and (i-?)-(+)-CYCPHOS (Figure 1.6) gives 17 high e.e.'s for hydrogenation of several prochiral imines in the presence of added iodide cocatalyst at low temperatures 25 °C) and high H 2 pressures (70 atm).6 8-6 9 Ph2P H 3 PPh 2 Figure 1.6: Structure of the chiral diphosphine CYCPHOS. For example, the imine shown in Figure 1.7 was hydrogenated with 91% e.e.; interestingly, in the absence of iodide only 71% e.e. was observed.68-69 Other workers70 have also reported increased optical yields upon the addition of halide cocatalysts, iodide being the most effective of Cl~, Br - and I~. Recently, Sinou and coworkers71 have reported > 95% e.e. for hydrogenation (70 atm H 2 , 20 *C) of the imine obtained from acetophenone and benzylamine, using as catalysts water-soluble rhodium complexes containing poly-m-sulphonated derivatives of the chiral chelating phosphine 2,4-bis(diphenylphosphino)pentane (Figure 1.8). The reductions were carried out in an aqueous/organic two-phase solvent system (e.g. H 20/AcOEt). Interestingly, the best optical yields were obtained when a mixture of mono-, di- and tri-sulphonated phosphines was used as opposed to the pure tetra- sulphonated phosphine. Me Figure 1.7: Structure of the imine substrate. 18 Figure 1.8: Poly-m- sulphonated derivatives of the bidentate chiral phosphine 2,4-bis- (cbphenylphosphino)pentane. The mechanism for the H2-hydrogenation of imines is thought to be very similar to that of ketone hydrogenation, although few kinetic and mechanistic studies are available. Several workers have noted the requirement for an alcohol co-solvent for effective imine hydrogenation,68' 6 9 « 7 2 and hydrogen-bonding between the alcohol -OH proton and the imine nitrogen during the substrate binding step has been invoked as a possible explanation.68- 7 2 Based on the limited literature data available for asymmetric hydrogenation of imines, neutral and anionic (in situ) catalysts appear to be relatively more enantioselective than cationic ones, at least for the rhodium-based systems.69' 7 0 The nature of the chiral induction step(s) remains unclear. 1.2.4 Transfer Hydrogenation Catalytic hydrogen transfer from an appropriate donor organic molecule (DH2) to an unsaturated acceptor substrate (A) provides an alternative to direct H2-hydrogenation (Equation 1.13). Transfer hydrogenation reactions can be carried out under mild conditions (1 atm pressure) usually at the boiling point of the solvent; also, the use of relatively expensive H2 and the high pressure equipment often required for H2- hydrogenation reactions is avoided. C3.t D H 2 + A " D + A H 2 (1.13) 19 The extensive literature on transfer hydrogenation has been reviewed periodically.73'74 Alcohols, glycols, aldehydes, amides, amines, ethers and alkylbenzenes are some of the compounds which have been used as a source of hydrogen.26 Alcohols are the most commonly used donors, 2-propanol being the prime choice. 2-Propanol is inexpensive, and its dehydrogenation product, acetone, can be easily distilled off from the reaction mixture. Secondary alcohols are more reactive than primary, but the latter are generally more selective.3115 Complexes of cobalt, rhodium, iridium and ruthenium are sometimes efficient catalysts for hydrogen transfer reactions;26*75 a variety of ligands including phosphines, phosphites, sulphoxides, Schiff bases and other nitrogenous compounds (e.g. bipy, substituted phenanthrolines, and alkaloids) has been employed successfully.26- 3 2 The presence of a base cocatalyst such as KOH or NE13 is often essential.76'77 Small amounts of added water (-0.1% by volume) is also known to improve the catalytic activity of many systems.77* 7 8 The roles of the base and the added water are not well understood. It should be noted that base by itself is capable of catalysing the hydrogen transfer by a different mechanism,76'77 albeit rather slowly compared to the transition metal-mediated reaction 7 6 Generally speaking, the best catalytic activity for the reduction of ketones and imines is achieved by transfer hydrogenation. For example, under the same conditions (82 *C), the time required for complete RhCl(PPh3)3-catalysed hydrogenation of benzylidene aniline (C6HsCH-=NC6H5) is reduced from 6 h to a few minutes when 2-propanol is used instead of H2 (70 atm).32 As depicted in Equations 1.13 and 1.14, transfer hydrogenation reactions are often reversible. The reduction products of carbonyl and irriine substrates (viz. alcohols and amines, respectively) themselves can act as hydrogen donors toward the concomitantly formed oxidation product of the original donor (e.g. acetone formed from 2-propanol).49 The extent of transfer hydrogenation is therefore determined by thermodynamic parameters. 20 The equilibrium can be shifted to the right by continual distillation of the dehydrogenated product, R 3OOR 4, from the reaction mixture (Equation 1.14). O H o»t X-H 9 c + I c a t > I + c d- 1 4 ) R i / S R 2 R 3 - C H - R 4 — R 1 - C H - R 2 R 3 / X R 4 X = O or N—R Of particular interest are the unusual selectivities sometimes observed for reduction by transfer hydrogenation as opposed to direct H2-hydrogenation. For example, the IrHCl2(DMSO)3-catalysed transfer hydrogenation of ct,P-unsaturated aldehydes in 2-propanol selectively affords the corresponding a,P-unsaturated alcohols (Equation 1.15), whereas H.2-hydrogenation invariably results in the formation of saturated aldehydes and, under more severe conditions, the saturated alcohols.79 H v .CHO \ / IrHCl2(DMSO)3 R / C " ~ C \ H (CH3)2CH(OH) R = CgHj, C H 3 H ^ ^ C H 2 O H C = C (1.15) H Only low to moderate optical yields have been observed for the asymmetric transfer hydrogenation of simple aryl alkyl ketones.80 The best e.e.'s to date (~50%) have been realised for the reduction of t-butyl phenyl ketone and benzyl phenyl ketone by hydrogen transfer from 2-propanol using fIr(cod)(PPEI)]+C104- as catalyst, where PPEI is a chiral Schiff base (Figure 1.9).81 Propiophenone is reduced with 33% e.e. using the same system.81 Optical yields of 30-50% have been achieved for hydrogen transfer to acetophenone and propiophenone using chiral sulphoxide complexes of rhodium as catalyst precursors.33 ,78 • 8 2 -S4 21 Figure 1.9: The chiral Schiff base PPEI. Kinetic and mechanistic investigation of transfer hydrogenation reactions is made difficult by the complex nature of these systems; a large number of species is often present in solution during the course of the reaction.3115 Two pathways, which are formally, equivalent to the saturate and the unsaturate routes encountered in H2-hydrogenation, have been suggested.25 Transfer of the (3-hydrogen from the alkoxide is thought to be the rate determining step in both these mechanisms (see below). The unsaturate route (Figure 1.10) involves initial coordination of the substrate, then that of the alcohol donor. Formation of an alkoxide, which may be base-assisted, is followed by transfer of the p-hydrogen of the alkoxide to the bound substrate. Finally, protonolysis liberates the product and regenerates the catalyst.25 R - R 2 C H ( O H ) M(S) M + substrate(S) . M(S) — I - H + O C H R ^ 2 0  H + M - S H C + S H 2 + M - - I R l ' R2 O - S C R ^ 2 Figure 1.10: The unsaturate route in transfer hydrogenation from an alcohol donor. 22 In the saturate (hydride) route (Figure 1.11), initial reaction of the metal complex and the alcohol donor yields a hydridoalkoxide species.25 P-Hydrogen transfer from the alkoxide and coordination of the substrate result in a dihydride species which can transfer both hydrides to the substrate either in a single step or in a stepwise, hydride transfer - protonolysis sequence.25 MHC1P, R-R2CHOH MHPn(OCHR*R2) HCl MHPn(SH) Figure 1.11: The saturate route for transition metal hydride-catalysed hydrogen transfer from an alcohol donor. 1 . 3 Dihydrogen Activation As mentioned earlier (Section 1.2), activation of dihydrogen by a metal complex is a key step in both stoichiometric and catalytic hydrogenation. For a metal complex to be able to activate hydrogen (or the substrate), coordinative unsaturation at the metal centre is usually essential.25' 2 9« 8 5> 8 6 Coordinatively saturated complexes, which are generally unreactive toward hydrogen for lack of a vacant site, may become active in solution through dissociation of a labile ligand. Not surprisingly, group 8-10 metal complexes, which are often coordinatively unsaturated, or which can easily become so by loss of a ligand, constitute the largest group of hydrogenation catalysts. The nature of the interaction 23 between molecular hydrogen and a metal complex is also dictated by the electronic and steric properties of the surrounding ligands.85'86 The energetics of hydrogen activation have important consequences for the catalytic activity of the metal complex. While too strong a metal-hydrogen (M-H) bond may retard or even prevent hydrogen transfer to the coordinated substrate, too weak an interaction may result in a concentration of the M-H species too small to achieve an appreciable reaction rate. As summarised by Halpern,87 activation of dihydrogen may involve (a) base- promoted overall heterolytic splitting of the H-H bond to form a hydride and a proton (Equation 1.16), or (b) oxidative addition resulting in homolytic cleavage of the H-H bond (Equations 1.17a-c). Further, hydrogenolysis of a metal-metalloid bond2 5-8 8 such as M - Ge, M-Si, but most commonly M-C (Equation 1.18), can be considered a special case of heterolytic activation, wherein the leaving group itself plays the role of a base (denoted by B in Equation 1.16). These different processes of H2-activation have been discussed in detail in a number of review articles on hydrogenation.25' ̂  8 6 a M n + H 2 + B - H~Mn + BH + Heterolytic splitting (1.16) 2M n + H 2 2HM n + 1 Homolytic splitting (1.17a) M 2 n + H 2 *- 2HM" + 1 - " - (1.17b) M n + H 2 (H) 2M n + 2 - » - (1.17c) R-M n + H 2 - H~Mn + R-H Hydrogenolysis (1.18) Heterolytic splitting of H 2 (Equation 1.16) is thought to involve a four-centre transition state (Figure 1.12a). Oxidative addition of H 2 at a metal centre (Equation 1.17c) is thought to proceed via initial coordination of the dihydrogen molecule; a subsequently formed three-centre, two-electron transition state is often invoked (Figure 1.12b). 24 H H M a b Figure 1.12: Proposed transition states during a) heterolytic and, b) homolytic activation of dihydrogen by transition metal complexes. The latest development concerning the various modes of H2-activation came with Kubas' discovery in 1984 of the first isolable molecular hydrogen complexes89 M(CO)3(PPr'3)2(T)2-H2), M = Mo or W, which contain an H2 ligand bonded side-on (Figure 1.13) as in the transition state shown in Figure 1.12b. PR 3 M = Mo, W R = Pr\ Cy PR 3 Figure 1.13: First reported examples of complexes containing the bound molecular hydrogen (ri2-H2) ligand.89 A growing number of new complexes containing one or more bound molecular hydrogen Cn2-H2) ligands has been reported since in the literature.90'91 The formation of molecular hydrogen complexes, and their role in catalytic processes, are of particular relevance to the topic of this thesis. More detailed background information encompassing various aspects of these novel complexes is given in a later chapter (Chapter 5). 25 1.4 Scope of This Thesis Much effort has been directed at developing chiral rhodium catalysts for asymmetric hydrogenation. Chiral hydrogenation catalysts involving metals other than rhodium have received relatively little attention. The recent success of the chiral Ru-BINAP catalysts in asymmetric hydrogenation of several functionalised prochiral substrates has highlighted the potential of non-rhodium catalyst systems.13'42 Previous work from this laboratory on RuHCl(DIOP)2-catalysed asymmetric hydrogenation of alkenes revealed that the active species contained one DIOP per Ru(II) centre ["RuHCl(DIOP)"].83, 9 2 > 9 3 This provided the impetus for devising a general, synthetic approach toward complexes containing a single bidentate phosphine (P-P) per Ru. Thorburn et al. in 1985 successfully developed such a synthetic strategy and isolated several such derivatives as dichloro-bridged, dimeric complexes of the type Ru2Cl4 (P-P )2 . 3 3 , 9 4 " 9 6 While the development of other potential synthetic routes to such complexes remained one of the objectives, the main objective of the current work was to investigate in detail the interaction of the Ru2CU(P-P)2 species with H2. Because of the high cost of chiral phosphines, much of the general chemistry was performed on complexes containing the nonchiral bidentate phosphine analogues, Ph2P(CH2)nPPh2 (n = 1-6). The nonchiral ligand l,4-bis(diphenylphosphino)butane, (DPPB, n = 4), which forms a seven-membered chelate similar to the chiral DIOP and BINAP ligands (see Figures 1.1 and 1.2), was used extensively. Chapter 3 deals with alternative synthetic routes to dichloro-bridged ruthenium(II)- diphosphine complexes of the type Ru2CU(P-P)2- These complexes readily coordinate simple organic ligands (L) to give trichloro-bridged species of the general formula Ru2Cl4(P-P)2(L)- The previously known ruthenium complexes RuCl2(DPPB)(PPh3)97 and c/j-RuCl2(Me2SO)498 were found to be useful as precursors to such trichloro-bridged 26 dinuclear species. Phosphorus-31 and proton-1 NMR spectral studies in solution were used to characterise the trichloro-bridged complexes. An X-ray diffraction study of [(Me2SO)(DPPB)Ru(u-Cl)3RuCl(DPPB)] confirmed the trichloro-bridged dinuclear structure. Attempts to use the mixed-phosphine complex, RuCl2(DPPB)(PPh3), as a precursor to Ru2Cl4(DPPB)2 and related derivatives led to the study of its reactivity with a variety of ligands. Reactions of RuCl2(DPPB)(PPh3) with chelating ligands (L-L) gave six-coordinate complexes of the type RuCl2(DPPB)(L-L) by a simple substitution of the PPh3 ligand. Characterisation of such complexes and their reactivity with H 2 , as well as a solid-state CP/MAS 3 1 P NMR spectral study of the complexes RuCl2(DPPB)(PPh3) and RuCl2(PPh3)3, are presented in Chapter 4. Reactivity of the chloro-bridged, dinuclear Ru(II) complexes with H 2 was investigated as a means of preparing hydride complexes (Chapter 5). Solution NMR studies (*£!, 3 1 P and Tj-measurements) on the DPPB complex in the presence of H 2 , without and with an added base, established the in situ formation of a molecular hydrogen complex, [(n2-H2)(DPPB)Ru(u-Cl)3RuCl(DPPB)],99 en route to the trinuclear ruthenium(II)-hydride cluster, [RuHCl(DPPB)]3.33.96 The corresponding CHIRAPHOS trimer had been characterised earlier by X-ray crystallography.33* 9 6 The temperature dependence of the *H NMR longitudinal relaxation times (Tj) of the T|2-H2 moiety was used to estimate the H-H internuclear distance. Interestingly, the trinuclear hydridochloro complex, [RuHCl(DPPB)]3, breaks down under hydrogen atmosphere to give dinuclear complexes of the type [(Ti2-H2)(P-P)ClRu(u-Cl)2(u-H)RuH(P-P)]. Hydridodiene complexes containing bidentate phosphines were of interest as potential precursors to "RuHCl(P-P)" species (by hydrogenation of the diene moiety) and to acyl complexes "Ru(COR)Cl(P-P)M (by carbonylation). Chapter 6 describes the synthesis and properties of RuHCl(nbd)(DPPB) (nbd = 2,5-norbornadiene) and its reactivity with H 2 and C O . 1 0 0 27 The dinuclear Ru2CU(P-P)2 complexes and their trinuclear hydride derivatives, [RuHCl(P-P)]3, were found to be effective catalysts for hydrogenation of a variety of substrates including alkenes, ketones, imines and nitriles (Chapter 7). Results of preliminary investigations into certain alkene-, ketone- and nitrile-hydrogenations are presented. 28 1.5 References - Chapter 1 Sheldon, R. Chemistry and Industry 1990, 212. Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987. Jennings, J. R. Selected Developments in Catalysis; Blackwell Scientific Publications: Oxford, Vol. 12,1985. Masters, C. Homogeneous Transition-metal Catalysis- a Gentle Art, Chapman and Hall: London, 1981. (a) Parshall, G. W. Homogeneous Catalysis; Wiley-Interscience: New York, 1980. (b) ibid.; 2nd Edn., in press. Nakamura, A.; Tsutsui, M. Principles and Applications of Homogeneous Catalysis; Wiley-Interscience: New York, 1980. (a) Hartley, F. R. in Supported Metal Complexes, Catalysis by Metal Complexes Ser.; James, B. R., Ugo, R., Eds.; D. Reidel Publishing Co.: Boston, 1985. (b) Iwasawa, Y., Ed.; Tailored Metal Catalysts, Catalysis by Metal Complexes Ser.; D. Reidel Publishing Co.: Boston, 1986. Dolcetti, G.; Hoffman, N. W. Inorg. Chim. Acta 1974, 9, 269; and references therein. (a) Bayer, E.; Shurig, V. Chemtech. 1976, 212. (b) Skinner, K. J. Chem. & Eng. News 1977, Feb. 7, 18. (a) Hartley, F. R.; Vezey, P. N. Adv. Organomet. Chem. 1977,15, 189. (b) Haggin, J. Chem. & Eng. News 1982, Nov. 15, 11. (c) Manassen, J. Plat. Met. Rev. 1971,15, 142; and references therein. 29 11. Michalska, Z. M.; Ostaszewski, B. / . Organomet. Chem. 1986,299, 259. 12. Alper, H. Adv. Organomet. Chem. 1981,19, 183. 13. (a) Noyori, R. Science 1990,248,1194; and references therein. (b) Noyori, R.; Kitamura, M. in Modern Synthetic Methods, Scheffold R., Ed.; Springer-Verlag: Berlin, 1989; p 115. 14. (a) Brunner, H. Synthesis 1988, 645. (b) Brunner, H. J. Organomet. Chem. 1986,300, 39. 15. Knowles, W. S. Acc. Chem. Res. 1983,16, 106. 16. (a) Kagan, H. B. in Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon Press: Oxford, 1982; Vol. 8, Chapter 53. (b) Caplar, V.; Comisso, G.; Sunjic, V. Synthesis 1981, 85. 17. Bosnich, B.; Fryzuk, M. D. in Topics in Inorganic and Organometallic Stereo- chemistry; Geoffrey, G. L., Ed.; Wiley-Interscience: New York, 1981, p 119. 18. (a) Pino, P.; Consiglio, G. in Fundamental Research in Homogeneous Catalysis; Tsutsui, M., Ed.; Plenum: New York, 1979; Vol. 3, p 519. (b) ibid.; Tsutsui, M., Ugo, R., Eds.; 1977; Vol. 1, p 147. 19. (a) Blystone, S. L. Chem. Rev. 1989,59, 1663. (b) Brown, J. M.; Chaloner, P. A.; Murrer, B. A.; Parker, D. ACS Symposium Series, 1980,119, 169. (c) Valentine, D.; Scott, J. W. Synthesis 1978, 329. 20. For example, (a) Emsley, J. New Scientist 1990, March 31, 32. (b) Larsen, R. D.; Corley, E. G.; Davis, P.; Reider, P. J.; Grabowski, E. J. J. /. Am. Chem. Soc. 1990, 111, 7650. 21. Lehninger, A. L. Principles of Biochemistry; Worth Publishers: New York, 1982; Chapters 3 and 30. 30 \ 22. (a) Bednarski, M. D. in Catalysis of Organic Reactions; Blackwell, D. W., Ed; Marcel Dekker: New York, 1990; Vol. 40, Chapter 5; and references therein. (b) Yamada, K.; Kinoshita, S.; Tsunoda, T.; Aida, K. The Microbial Production of Amino Acids; Wiley: New York, 1972. 23. Hatada, M.; Jancarik, J.; Graves, B.; Kim, S. / . Am. Chem. Soc. 1985,107, 4279. 24. Brown, J. M. Angew. Chem., Int. Ed. Engl. 1987,26, 190. 25. James, B.R. in Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon Press: Oxford, 1982; Vol. 8, Chapter 51. 26. James, B. R. Adv. Organomet. Chem. 1979,17, 319. 27. Crabtree, R. H. Acc. Chem. Res. 1979, 72, 331. 28. Rylander, P. N. Catalytic Hydrogenation in Organic Syntheses; Academic Press: New York, 1979. 29. James, B. R. Homogeneous Hydrogenation; Wiley: New York, 1973. 30. Freifelder, M. Practical Catalytic Hydrogenation; Wiley-Interscience: New York, 1971. 31. (a) Ref. 2, Chapter 10. (b) Chaloner, P. Handbook of Coordination Catalysis in Organic Chemistry; Butterworths: Toronto, 1986: Chapter 2. (c) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; Wiley- Interscience: New York, 4th Edn., 1980; Chapter 30. 32. Mestroni, G.; Camus, A.; Zassinovich, G. in Aspects of Homogeneous Catalysis; Ugo, R., Ed.; D. Reidel Publishing Co.: Dordrecht, 1981; Vol. 4, p 71. 31 33. James, B. R.; Joshi, A. M.; Kvintovics, P.; Morris, R. H.; Thorburn, I. S. in Catalysis of Organic Reactions; Blackburn, D. W., Ed.; Marcel Dekker: New York, 1990; Chapter 2; and references therein. 34. (a) Eleveld, M. B.; Hogeveen, H.; Schudde, E. P. / . Org. Chem. 1986,57, 3635. 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G.; Prescher, G.; Schaefer, A.; Nagel, U. in Catalysis of Organic Reactions; Blackburn, D. W., Ed.; Marcel Dekker. New York, 1990; Chapter 3. (b) Noyori, R.; Takaya, H. Acc Chem. Res. 1990, 23, 345. 32 41. (a) Koenig, K. E. in Catalysis of Organic Reactions; Kosak, J. R., Ed.; Marcel Dekker: New York, 1984; Chapter 3. (b) Marko, L.; Bakos, J. in Aspects of Homogeneous Catalysis; Ugo, R., Ed.; D. Reidel Publishing Co.: Dordrecht, 1981; Vol. 4, p 145. 42. Noyori, R. Chem. Soc. Rev. 1989, 75, 187; and references therein. 43. Vineyard, B. D.; Knowles, W. S.; Sabacky, M. J.; Bachman, G. L.; Weinkauff, D. J. / . Am. Chem. Soc. 1977, 99, 5946. 44. (a) Miyashita, A.; Yasuda, A.; Takaya, H.; Toriumi, K.; Ito, T.; Souchi, T.; Noyori, R. J. Am. Chem. Soc. 1980,102, 7932. (b) Miyashita, A.; Takaya, H.; Souchi, T.; Noyori, R. Tetrahedron 1984,40, 1245. (c) Takaya, H.; Mashima, K.; Koyano, K.; Yagi, M.; Kumobayashi, H.; Taketomi, T.; Akutagawa, S.; Noyori, R. J. Org. Chem. 1986,57, 629. 45. (a) Kawano, H.; Ishii, Y.; Ikariya, T.; Saburi, M.; Yoshikawa, S.; Uchida, Y.; Kumobayashi, H. Tetrahedron Lett. 1987,25, 1905. (b) Ikariya, T.; Ishii, Y.; Kawano, H.; Aral, T.; Saburi, M.; Yoshikawa, S.; Akutagawa, S. / . Chem. Soc, Chem. Commun. 1985, 922. 46. (a) Mashima, K.; Kusano, K.; Ohta, T.; Noyori, R.; Takaya, H. J. Chem. Soc, Chem. Commun. 1989, 1208. (b) Kitamura, M.; Ohkuma, T.; Inoue, S.; Sayo, N.; Kumobayashi, H.; Akutagawa, S.; Ohta, T.; Takaya, H.; Noyori, R. J. Am. Chem. Soc. 1988, 770, 629. (c) Noyori, R.; Ohkuma, T.; Kitamura, M.; Takaya, H.; Sayo, N.; Kumobayashi, H.; Akutagawa, S. / . Am. Chem. Soc. 1988, 709, 5856. 47. (a) Slack, D. A.; Greveling, J.; Baird, M. C. Inorg. Chem. 1979, 75, 3125. (b) Bosnich, B.; Roberts, N. K. Adv. Chem. Ser. 1982, 796, 337. (c) Knowles, W. S.; Christophel, W. C; Koenig, K. E.; Hobbs, C. F. Adv. Chem. Ser. 1982, 796, 325. 33 48. (a) Chan, A. S. C; Pluth, J. J.; Halpem, J. J. Am. Chem. Soc. 1980,702, 5952. (b) Halpern, J. Science 1982,217, 401. (c) Halpem, J. in Ref. 39, Chapter 2. 49. Heil, B.; Marko, L.; Toros, S. in Homogeneous Catalysis with Metal Phosphine Complexes; Pignolet, L. H., Ed.; Plenum Press: New York, 1983; p. 317. 50. Huang, Y-H.; Gladysz, J. A. / . Chem. Ed. 1988, 65, 298. 51. James, B. R. Inorg. Chim. Acta Rev. 1970,4, 73. 52. (a) Pez, G. P.; Grey, R. A.; Corsi, J. J. Am. Chem. Soc. 1981,103, 7528. (b) Grey, R. A.; Pez, G. P.; Wallo, A. J. Am. Chem. Soc. 1981,103, 7536. 53. Pez, G. P.; Grey, R. A. in Fundamental Research in Homogeneous Catalysis; Graziani, M. and Giongo, M., Eds.; Plenum: New York, 1982; Vol. 4, p. 97. 54. Chan, A. S. C; Landis, C. R. / . Mol. Catal. 1989,49, 165. 55. (a) Midland, M. M. Chem. Rev. 1989, 89, 1553. (b) Aldrichimica Acta, 1987,20(1); and references therein. 56. Sugimoto, T.; Matsumura, Y.; Tanimoto, S.; Okano, M. J. Chem. Soc, Chem. Commun. 1978, 926. 57. Schrock, R. R.; Osborn, J. A. J. Chem. Soc, Chem. Commun. 1970, 567. 58. Solodar, J. Chemtech. 1975, 421. 59. Mestroni, G.; Spogliarich, R; Camus, A.; Martinelli, F.; Zassinovich, G. 7. Organomet. Chem. 1978, 757, 345. 34 60. (a) Mestroni, G.; Zassinovich, G.; Alessio, E.; Tornatore, M. J. Mol. Catal. 1989,49, 175. (b) Zassinovich, G.; Mestroni, G. J. Mol Catal 1987,42, 81. (c) Mestroni, G.; Zassinovich, G.; Camus, A.; Martinelli, F. / . Organomet. Chem. 1980,198, 87. 61. Garrou, P. E. Chem. Rev. 1985, 85, 171. 62. (a) Ito, K.; Harada, T.; Tai, A.; Izumi, Y. Chem. Lett. 1979, 1049. (b) Bakos, J.; Toth, I.; Marko, L. / . Org. Chem. 1981,46, 5427. 63. Levi, A.; Modena, G.; Scorrano, G. / . Chem. Soc, Chem. Commun. 1975, 6. 64. Heil, B.; Toros, S.; Bakos, J.; Marko, L. J'. Organomet. Chem. 1979, 775, 229. 65. (a) Brunner, H. in Catalysis of Organic Reactions; Blackburn, D. W., Ed.; Marcel Dekker: New York, 1990; Chapter 1. (b) Ojima, I.; Yamamoto, K.; Kumada, M. in Aspects of Homogeneous Catalysis; Ugo, R., Ed.; Reidel: Dordrecht, 1977; Vol. 3, p. 185. (c) Karim, A.; Mortreux, A.; Petit, F.; Buono, G.; Peiffer, G.; Siv, C. J. Organomet. Chem. 1986,577, 93. (d) in Reference 39, Chapter 3. 66. Yoshida, T.; Okano, T.; Otsuka, S. J. Chem. Soc, Chem. Commun. 1979, 870. 67. Dayagi, S.; Degani, Y. in The Chemistry of Carbon-Nitrogen Double Bond; Patai, S., Ed.; Interscience: New York, 1970; Chapter 2. 68. Kang, G.; Cullen, W. R.; Fryzuk, M. D.; James, B. R.; Kutney, J. P. J. Chem. Soc, Chem. Commun. 1988, 1466. 69. Cullen, W. R.; Fryzuk, M. D.; James, B. R.; Kutney, J. P.; Kang, G.-J.; Herb, G.; Thorburn, I. S.; Spogliarch, R. J. Mol. Catal. 1990; in press. 35 70. Vastag, S.; Bakos, J.; Toros, S.; Takach, N. E.; King, R. B.; Heil, B.; Marko, L. J. Mol. Catal. 1984,22, 283. 71. (a) Bakos, J.; Heil, B.; Lecompte, L.; Sinou, D. 5 t h IUPAC Symposium on Organometallic Chemistry directed towards Organic Synthesis (OMCOS-V), Florence, Italy, October 1989; Abstract # PSl-36. 7 1 b (b) Amrani, Y.; Lecompte, L.; Sinou, D.; Bakos, J.; Toth, I.; Heil, B. Organometallics 1989,8, 542. 72. Longley, C. J.; Goodwin, T. J.; Wilkinson, G. Polyhedron 1986,5, 1625. 73. Brieger, G.; Nestrick, T. J. Chem. Rev. 1974, 74, 567. 74. Kolomnikov, I. S.; Kukolev, V. P.; Volpin, M. E. Russ. Chem. Rev. (Engl. Transl.) 1974,43, 399. 75. Imai, H.; Nishiguchi, T.; Fukuzumi, K. / . Org. Chem. 1976,41, 665. 76. Spogliarich, R.; Kaspar, J.; Graziani, M. J. Catal. 1985, 94, 292. 11. Sasson, Y.; Blum, J. J. Org. Chem. 1915,40, 1887. 78. Kvintovics, P.; James, B. R.; Heil, B. / . Chem. Soc, Chem. Commun. 1986, 1810. 79. James, B. R.; Morris, R. H. J. Chem. Soc, Chem. Commun. 1978, 929. 80. Toros, S.; Heil, B.; Kollar, L.; Marko, L. J. Organomet. Chem. 1980,197, 85. 81. Zassinovich, G.; Bianco, C. 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Chem. 1988,28, 299; and references therein. (b) Crabtree, R. H. Acc. Chem. Res. 1990,23, 95; and references therein. 92. James, B. R.; Wang, D. K. W. Can. J. Chem. 1980,58, 245. 93. Wang, D. K. W., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1978. 94. Thorburn, I. S., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1985. 95. Thorburn, I. S.; Rettig, S. J.; James, B. R. Inorg. Chem. 1986,25, 234. 37 96. James, B. R.; Pacheco, A.; Rettig, S. J.; Thorburn, I. S.; Ball, R. G.; Ibers, J.A. / . Mol. Catal. 1987,4/, 147. 97. Jung, C. W.; Garrou, P. E.; Hoffman, P. R.; Caulton, K. G. Inorg. Chem. 1984, 23, 726. 98. (a) James, B. R.; Ochiai, E.; Rempel, G. I. Inorg. Nucl. Chem. Lett. 1971, 7, 781. (b) Evans, I. P.; Spencer, A.; Wilkinson, G. J. Chem. Soc, Dalton Trans. 1973, 204. 99. Joshi, A. M.; James, B. R. / . Chem. Soc, Chem. Commun. 1989, 1785. 100. Dekleva, T. W.; Joshi, A. M.; Thorburn, I. S.; James, B. R.; Evans, S. V.; Trotter, J. Isr. J. Chem. 1990,30(4); in press. 38 CffilAIPTOIR 2 Experimental Procedures 2.1 Materials 2.1.1 Solvents Spectral or reagent grade solvents were obtained from MCB, BDH, Mallinckrodt, Fisher, Eastman or Aldrich Chemical Co. Benzene, toluene, hexanes, tetrahydrofuran (THF) and diethyl ether were refluxed with, and distilled from, sodium metal/benzo- phenone under a nitrogen atmosphere. N,N-cnmethylacetamide (DMA) was stirred with CaH2 for at least 24 h, vacuum distilled at 35-40 "C, and stored under argon in the dark. Dichloromethane, acetone, methanol, ethanol and 2-propanol were distilled after refiuxing with the appropriate drying agents (P2O5 for CH2CI2, anhydrous K 2 C O 3 for acetone, and Mg/I2 for the alcohols).1 All solvents were deoxygenated by freeze-pump-thaw cycles prior to use. The deuterated solvents (CDCI3, CD2CI2, C6D6, toluene-̂ 8, acetone-G?6> CD3CN, DMSO-^6. methanol-* ,̂ 2-propanol-<i8 and D 20), used in NMR spectroscopy, were obtained from Merck Frosst Canada Ltd. and Aldrich Chemical Co. All deuterated solvents (with the exception of D2O!) were dried if necessary over activated molecular sieves (Fisher: Type 4 A, 4-8 mesh), and stored under argon. 39 2.1.2 Gases Purified argon (H.P.), nitrogen (U.S.P.), carbon monoxide (CP.) and hydrogen (U.S.P.) were obtained from Union Carbide Canada Ltd.; all except hydrogen were used without further purification. Hydrogen was passed through an Engelhard Deoxo catalytic hydrogen purifier to remove traces of oxygen. 2.1.3 Phosphines Reagent grade triphenylphosphine (PPh3), tri(p-tolyl)phosphine (P(p-tol)3), methyltriphenylphosphonium iodide (MePh3P+I~), and the chelating phosphines Ph 2P(CH 2) nPPh2 (n = 1, DPPM; 2, DPPE; 3, DPPP; 4, DPPB; 5, DPPN; 6, DPPH) were used as supplied (all from Strem Chemicals, Inc.). The chiral phosphines: (2S,3S)- bis(diphenylphosphino)butane (5,5-CHIRAPHOS), (25,4S)-bis(diphenylphosphino)- pentane (S.5-BDPP), (2/?,37?)-2,3,-0-isopropylidene-2,3-dihydroxy-l,4-bis(diphenyl- phosphino)butane (R,R-DlOP), and (R)- and (S)-2,2'-bis-(diphenylphosphino)-l,l'- binaphthyl (R- and 5-BINAP, respectively), were also obtained from Strem Chemicals and used as received. The chiral aminophosphinephosphinite ligand, S-Ph2PN(Et)CH(CH2Ph)CH2OPPh2 (5-PRENOP), was prepared from 5-phenylalanine using a literature method.2 The phosphines, rac-(±)-l ,2-bis(diphenylphosphino)- cyclopentane (DPPCP) and rac-(±)-l,2-bis(dicyclohexylphosphino)cyclopentane (DPCYCP), were synthesised by a reported method and used as such without resolution.3 Diphenyl(2-pyridyl)phosphine (PPh2Py) was prepared by L. Xie in this laboratory using a published procedure.4 Purity of all the phosphines was ascertained by 3 1P{ 1H) and *H NMR spectroscopy. 40 2.1.4 Substrates The alkene substrates: 1-hexene, styrene, a-methylstyrene, 2,5-norbornadiene, 1,3-cyclohexadiene and 1,4-cyclohexadiene (all Eastman or Aldrich) were purified prior to use by passing through a column of activated alumina (Fisher, A-950 neutral chromatographic grade, 80-200 mesh). Itaconic acid Q3astman), (Z)-a-acetamidocinnamic and (Z)-a-methylcinnamic acids (Aldrich) were recrystallised from hot ethanol to yield colourless crystals. The ketone substrates acetophenone and propiophenone (Aldrich) were dried over anhydrous CaSC«4, purified by vacuum distillation, and stored under argon. The nitrile substrates acetonitrile and benzonitrile (BDH) were distilled from CaH2, and then stored under argon. N-Benzylideneaniline and 7V-benzylidenebenzylamine were synthesised by P. Kvintovics and G. Kang of this department; both imines were used without further purification. The imine, (C^H3(CH3)2N=C(CH3)(CH20CH3), formed by condensation of 1-methoxyacetone and 2,6-dimethylaniline, was used as supplied by Ciba-Geigy. Purity of all the substrates used in this study was confirmed by *H NMR spectroscopy. Authentic samples of the hydrogenation products corresponding to the above mentioned substrates were purchased from appropriate sources (mostly Aldrich), and used as supplied for comparison. 2.1.5 Other Materials Triethylamine, di-n-butylamine and tri-n-butylamine (all from MCB) were stirred over KOH and purified by distillation. Polyvinylpyridine Q?VP) and the non-nucleophilic base, l,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU), were used as supplied by Aldrich. Proton Sponge®, l,8-bis(dimethylamino)naphthalene, from Aldrich, was purified by passing an n-pentane solution of the base through an alumina column. Concentration of the 41 solution yielded Proton Sponge as a white solid. The reagents LiAlH4, NaBH4, and KO'Bu were used as received. The ruthenium, supplied on loan by Johnson Matthey Ltd., was obtained as hydrated R.UCI3; depending upon the batch, the ruthenium content varied from 38 to 42%. 2.2 Instrumentation Infrared spectra were recorded on a Nicolet 5DX FT-IR spectrophotometer as KBr pellets, or Nujol mulls between Csl plates, unless specified otherwise. UV-visible spectra were recorded on a Perkin Elmer 552A spectrophotometer with thermostatted cell compartments, using spectral cells (path length = 0.1 or 1.0 cm) attached to Schlenk flasks.5 The solution nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AC200 (200.1 MHz for iH, 50.3 MHz for 13c, 81.0 MHz for 3lp), a Varian XL300 (300.0 MHz for lH, 75.0 MHz for 13c, 121.4 MHz for 31p), or a Bruker WH400 (400.0 MHz for lH) FT-NMR spectrometers, using tetramethylsilane (TMS) and PPh3 (ca. -6 ppm w.r.t. 85% H3PO4) 6 as external standards. All 3lp NMR shifts are reported relative to 85% H 3 P O 4 , with downfield shifts taken as positive. Variable temperature NMR spectral studies and various ID- and 2D-NMR experiments (e.g. selective decoupling studies, NOEDIFF, and COSY experiments) were conducted on the Varian XL300, the Bruker WH400 or the Bruker AMX500 spectrometer. lH NMR longitudinal relaxation time (Tj) measurements were performed on the Varian XL300 spectrometer, using a standard (180°-t-90°) pulse sequence. The 31p NMR spectral simulations were performed on a Varian ADS4000 work station using Varian NMR spectral spin simulation software. The 31p{lH) solid state cross polarization, magic angle spinning (CP/MAS) FT- NMR spectra were recorded (with kind help from Dr. Andy Root of this department) on a 42 Bruker MSL400 or a Bruker CXP200 instrument (161.97 and 80.99 MHz for 3 1 P , respectively). Optical rotation values were measured on a Perkin Elmer 141 polarimeter at the sodium-D line (589 nm) at ambient temperature, using a thermostatted glass optical cell (~1.0 mL capacity) with a pathlength of 1.000 dm (also see Section 2.4.2). Gas chromatographic analyses (also see Sections 2.4.1 and 2.4.3) were performed on a temperature programmable Hewlett Packard 5890A instrument equipped with a thermal conductivity detector (TCD) and a flame ionisation detector (HD), using helium as the carrier gas (flow rate -40 mL/min). Carbowax 20M on Chromosorb W 80/100 (3 m, packed), or HP1 (15 m, 0.2 mm I.D. capillary, crosslinked methyl silicone) columns were used for qualitative and quantitative analyses of alkene/alkane, ketone/alcohol, and nitrile/ imine/amine mixtures. A 25 m x 0.25 mm I.D. capillary chiral column, Chirasil-Val III (Alltech), was used for separating enantiomers of chiral alcohol and amine products (Section 2.4.3). Gas uptakes for stoichiometric or kinetic studies and gas solubility measurements were performed on a conventional constant-pressure, constant-temperature gas-uptake apparatus. The general procedure employed for gas-uptake measurements is described elsewhere.5-7 Elemental analyses were performed by Mr. Peter Borda of this department. Single crystal X-ray diffraction studies were carried out by Dr. Steven Rettig of the departmental crystallographic service. 2.3 Catalytic Hydrogenation of Unsaturated Organic Substrates Catalytic hydrogenation of various alkene, ketone, nitrile and imine substrates (0.05 to 2.0 M) was typically carried out in 5-10 mL solvent, using 0.5-5.0 mM catalyst (precursor), in the temperature range 20-100 °C. The gas-uptake apparatus was used to 43 monitor the course of catalytic hydrogenation at < 1 atm H 2 pressure. Specially designed, thick walled Schlenk tubes (~60 mL capacity) fitted with Kontes valves were used for hydrogenation reactions between 1-12 atm H 2 pressures, and also for transfer hydrogenation experiments. Reactions at up to 80 atm H 2 pressures were conducted in glass-lined, high-pressure steel vessels. 2.3.1 Work-up of Reaction Mixtures At the end of each hydrogenation run, the reaction mixture was transferred with a syringe to a Kugelrohr type apparatus (Figure 2.1) under a stream of argon. A typical procedure used for isolation of substrate and product(s) is described below. septum Figure 2.1: Kugelrohr type apparatus. The reaction mixture was frozen in bulb 3 by immersing this bulb in a Dewar of liquid nitrogen. The Kugelrohr apparatus was then removed from liquid N 2 . Whenever the solvent used was relatively low boiling compared to both substrate and product(s), for example, toluene solution containing acetophenone and 1-phenylethanol, the solvent was pumped off under vacuum until the third bulb had returned to room temperature. At this point, most of the solvent had been removed. The mixture of substrate and product(s), and also the solvent, in case of relatively high boiling solvents such as DMA, was then isolated by bulb-to-bulb vacuum distillation in the Kugelrohr apparatus, leaving behind the metal complex residue and any solid products (see below). This was achieved by gradually 44 heating under vacuum the second and third bulbs of the apparatus up to -100 °C in a small oven, while the first bulb was cooled with liquid N 2 in order to collect the product- substrate (and solvent) mixture. Solid products resulting from the hydrogenation experiments were isolated from the residue as follows: Typically the residue was dissolved in dichloromethane, or an appropriate solvent (5-10 mL), and the solution was passed through a -5 cm long column of neutral alumina in a Pasteur pipet to remove the metal complex and any insoluble material. The column was further eluted with -5 mL of the solvent. The mixture of solid substrate/product(s) was then isolated from the eluate by evaporating the solvent. The product(s) could be further purified, if necessary, by recrystallisation or sublimation and analysed by ] H NMR spectroscopy or GLC and, in case of chiral products, also by optical rotation measurements. 2.4 Analysis of the Hydrogenation Products The separated product mixture was analysed by gas chromatography (Section 2.4.1) , or examined by *H NMR spectroscopy, to determine the conversion (%) of the substrate to product(s). The optical purity of a chiral product (% e.e.) was determined either by: (a) measuring the optical rotation of the solution using a polarimeter (Section 2.4.2) ; or (b) injecting a derivative of the product onto a chiral column (Section 2.4.3). Finally, the catalyst residue in bulb 3 (Section 2.3) was dissolved in an appropriate deuterated solvent and transferred under a stream of argon for examination by NMR spectroscopy. 45 2.4.1 Gas Chromatographic Analysis The extent of hydrogenation was determined by gas chromatographic analysis of the product mixture using an HP1 capillary column (for alkenes/alkanes, nitriles, imines/ amines), or a Carbowax 20M packed column (ketones/alcohols). Benzonitrile hydrogenation products (benzonitrile/benzyl amine/dibenzylidene aniline/dibenzylamine mixtures) were analysed in the temperature programme mode (80 °C, 5 min-30 °C/min- 230 °C, 10 min), with injector and detector (FED) temperatures of 325 °C. Analyses of the undiluted and the diluted (10 uL of product mixture in 1.0 mL of 2-propanol, diethyl ether or hexane) ketone/alcohol product mixtures, e.g. acetophenone/l-phenylethanol, were performed isothermally at 150 °C with injector and detector (TCD) temperatures of 250 °C. The conversion of substrate to product was taken as an average value obtained from 3-4 injections of each substrate-product solution. Retention times (min) and the relative detector response factors (peak area per unit volume or unit weight) of all components under the conditions used were determined by injection of authentic samples. The response factors were then used to calculate the product concentration (g/mL). As an illustration, the retention times and normalised response factors under the conditions specified above for the substrate (acetophenone), the corresponding hydrogenated product (1-phenylethanol) and the 2-propanol solvent are shown in Table 2.1. The concentration of the product alcohol was determined by dividing the areas obtained from the GC integrator by the appropriate response factor and using the density (g/mL) of the alcohol. Determination of the concentration was necessary for calculation of the specific rotation from the observed rotation (Equation 2.1, see below). 46 Table 2.1: Retention Times and Response Factors. Compound Retention time (min) Response factor 2-propanol 0.7 1.0 acetophenone 5.8 4.0 1-phenylethanol 9.6 4.0 2.4.2 Optical Rotation Measurements Optical rotations were measured on mixtures of the chiral products and substrates (e.g. 1-phenylethanol and acetophenone). The rotations were corrected for the presence of substrate using calibration curves (see Appendix A-l), knowing the amount of substrate present from GC analysis. The corrected observed rotation, a, was used to calculate the specific rotation [OC]D t according to the equation: where [OC]D t = specific rotation at temperaiure T, measured at the sodium-D line; a = observed rotation; 1 = pathlength of the cell in decimeters; and C = concentration of solution in g/mL. The optical purity of a reaction product in terms of the enantiomeric excess (% e.e.) can be determined knowing the specific rotation of a pure enantiomer (Eqs. 1.2 and 1.3, see Section 1.2.1). [a]D T = a (2.1) 1 x C 47 2.4.3 Gas Chromatographic Separation of Enantiomers of Chiral Alcohol and Amine Products Using a Chiral Column In order to separate effectively the enantiomers of chiral alcohols it is essential to first derivatise the alcohol.8*9 Enantiomer separation of alcohols was achieved using their isopropyl urethane derivatives (Equation 2.2) which were conveniently prepared by dissolving the product alcohol mixture (1-20 uL, depending on the conversion of the substrate to the product) in dichloromethane (200 uL), followed by addition of isopropyl isocyanate (-100 uL, <100 fold excess). The mixture was heated in a screw-capped vial at 100 "C for 20 min. The solvent and excess isopropyl isocyanate were removed with a stream of nitrogen, and the urethane derivatives were dissolved in diethyl ether (-0.5 mL) for injection onto the chiral column, Chirasil-Val III. O H u /~« R O *i H 3 K C H 2 C I 2 i* II A " 3 CH + CH-N=C=0 - H - C - O - C - N H - C H (2.2) R N R H 3 C ' 100'C I ^ R Gas chromatographic analysis was performed isothermally at 145 °C with injector and detector (FLD) temperatures of 250 and 300 °C, respectively. The e.e. was taken as the average of 3-4 injections. Enantiomers of chiral amines can also be separated using this isocyanate method.10 No racemisation was observed when this procedure was performed on pure enantiomers, consistent with previous reports.11 Injection of derivatives of known enantiomeric composition showed.a good correlation with the observed e.e., with an estimated error of ± 1%.12 48 2.5 Synthesis and Characterisation of Ruthenium Complexes All synthetic reactions, unless specified otherwise, were carried out under an atmosphere of argon, employing Schlenk techniques,13 as most of the ruthenium complexes prepared in the course of this work were susceptible to oxidation by air, at least in solution. The yields reported for synthetic reactions are generally the average of several preparations. 2.5.1 Ruthenium Precursors The following ruthenium complexes, used as starting materials for the synthesis of ruthenium- chelating ditertiary phosphine complexes described in this study, were prepared by literature methods: m-RuCl2(DMSO) 4; 1 4- 1 5 [RuCl(n6-p-Cymene)(u-Cl)]2;16 RuCl3(PAr3)2(DMA)-DMA solvate (Ar = phenyl or p-tolyl);17"19 RuCl 2(PPh 3)3; 1 9- 2 1 RuHCl(PPh 3 ) 3 -C 6 H 6 solvate;22- 2 3 and -rans-RuHCl(nbd)(PPh 3) 2. 2 3 All these complexes were analytically pure (see below); the spectroscopic data (NMR, IR, UV-VIS) agreed with those reported previously in the literature.14-23 2.5.1.1 Cw-RuCl2(DMSO)4:14 The complex was prepared by refiuxing a DMSO solution (10 mL) of RuCl3-3H20 (2.0 g, 7.65 mmol) under N2 atmosphere followed by precipitation with acetone (-40 mL), according to the procedure described by Wilkinson and coworkers.1415 This method is sensitive to the reaction conditions (temperature, duration of heating, quality of DMSO used- it works better with 'bad' DMSO), and often gives inconsistent results, sometimes leading to other undesired products.15-24a Yield of this bright yellow complex varied from 50-90%. The method reported by our group (using H2 to reduce the Ru to the divalent state143), or simply refiuxing the RuCl3'3H20/DMSO solution in air instead of under 49 nitrogen,24b gives more consistent, albeit lower, yields (50-60%). Anal. Calcd for C8H24O4S4CI2RU: C, 19.83; H, 4.99; S, 26.47. Found: C, 19.8; H, 4.9; S, 26.5. IR (Nujol, cm-1): V(s=o) at 1115, 1089 (s, Seconded DMSO; reported: 1125 and 1095 cirr l); V( S = 0) at 932 (s, O-bonded DMSO; reported: 925 cm-1). 2.5.1.2 [RuCl(ri6-p-cymene)(u-Cl)]2:16 The Ru(n)-r|6-p-cymene complex was prepared by refiuxing an ethanolic solution (100 mL) of RUCI33H2O (2.0 g, 7.65 mmol) with 5-isopropyl-2-methylcyclohexa-l,3- diene (10 mL), according to the procedure reported by Bennett and Smith.16 Yield of the dark red-brown solid: 1.45 g (62%). Anal. Calcd for C20H28CI4RU2: C, 39.23; H, 4.61. Found: C, 39.4; H, 4.6. 2.5.1.3 RuCl3(PPh3)2(DMA)DMA solvate: 1 7 ~ 1 9 This Ru(III) complex was synthesised by stirring a DMA solution (30 mL) of RuCl3 .3H 20 (2.0 g, 7.65 mmol) with two equivalents of PPh3 (4.0 g, 15.3 mmol) for 24 h at room temperature.17-18 The green product was filtered, washed with DMA (2x5 mL) and hexane (10 mL), and vacuum dried. Yield: 5.2 g (75%). Anal. Calcd for C44H48N2O2CI3P2RU: C, 58.32; H, 5.34; N, 3.09; Cl, 11.74. Found: C, 58.3; H, 5.3; N, 3.0; Cl, 12.0. IR (Nujol, cm"1): V(c=0) at 1632 (m, uncoordinated DMA); V(c=0) at 1598 (m, coordinated DMA). A small amount of a previously unknown, crystalline dark red complex (-0.5 g) was isolated from the DMA filtrate after -4 weeks. A single crystal X-ray diffraction study by Dr. S. Rettig of this department established the identity of the new compound to be the related Ru(III) complex, mer-RuCl3(PPh3)(DMA)2-DMA solvate, in which one of the PPh3 ligands has been replaced by DMA. Attempts to make this complex on purpose by stirring only one equivalent PPh3 (0.546 g, 2.1 mmol) with RUCI33H2O (0.5 g, 2.1 mmol) in DMA (5 mL) were not successful; a dark red-brown solution was obtained after 50 ~24 h but no solid could be isolated on work-up. Anal. Calcd for C30H42N3O3CI3PRU: C, 49.29; H, 5.79; N, 5.75. Found: C, 49.1; H, 5.9; N, 5.8. IR (Nujol, cm"1): V(c=0) at 1635 (m, uncoordinated DMA); V(c=0) at 1593, 1572 (m, coordinated DMA). The crystal structure data, including tables of bond lengths and bond angles, and the ORTEP stereoview of the molecular structure, are presented in the Appendix (A-2.1). 2.5.1.4 RuCl3(P(p-tolyl)3)2(DMA)-DMA solvate: 1 7 b > 1 8 The title complex was prepared in exacdy the same manner as its PPh3 analogue, but using two equivalents of P(p-tolyl)3 (4.7 g, 15.3 mmol).17b' 1 8 Yield of the bright green solid: 4.47 g (59%). Anal. Calcd for C5oH6oN202Cl3P2Ru: C, 60.64; H, 6.11; N, 2.83; Cl, 10.74. Found: C, 60.4; H, 6.1; N, 2.6; Cl, 10.6. IR (Nujol, cm-1): V(c=0) at 1646 (m, uncoordinated DMA); V(c=0) at 1598 (m, coordinated DMA). 2.5.1.5 RuCl 2(PPh 3) 3: 1 9- 2 1 The Ru(II) complex was prepared by refiuxing a methanol solution (300 mL) of RuCl3-3H20 (2.0 g, 7.65 mmol) and PPh3 (12.1 g, 46.1 mmol) under N 2 . 1 9 - 2 0 Yield of the dark brown product: 7.2 g (98%). Anal. Calcd for C 5 4 H 4 5 C l 2 P 3 R u : C, 67.64; H, 4.73; Cl.7.39. Found: C, 67.6; H, 4.7; Cl, 7.4. 2.5.1.6 RuHCl(PPh3)3-C6H6 solvate:22'23 This complex was synthesised by stirring a benzene suspension (200 mL) of RuCl2(PPh3)3 (4.5 g, 4.7 mmol) with triethylamine (0.07 mL, 5 mmol) under 1 atm H2 at room temperature.22' 2 3 Yield of the dark violet solid: 4.1 g (87%). Anal. Calcd for C60H52CIP3RU: C, 71.89; H, 5.23; Cl, 3.54. Found: C, 71.9; H, 5.2; Cl, 3.4. IR (Nujol, cm-1): V(RU_H) at 2028 (w). lH NMR (CDCI3, 20 °C): 8 -17.75 ppm (q, 2 7 P . H = 26 Hz, Ru-H). 51 2.5.1.7 7ra«5-RuHCl(nbd)(PPh3)2,34:23 The hydridochloro derivative was prepared by stirring a benzene suspension (50 mL) of RuHCl(PPh3)3-C6H6 solvate (1.9 g, 1.9 mmol) with 2,5-norbornadiene (2 mL) at room temperature.23 Yield of the pale brown solid: 1.0 g (70%). Anal. Calcd for C43H38CIP2RU: C, 68.57; H, 5.08; Cl, 4.71. Found: C, 68.4; H, 5.2; Cl, 4.6. IR (Nujol, cm-l): V(RU_H) at 2082 (w). !H NMR (CD2C12, 20 °C): 8 -8.90 ppm (t, 2 / P H = 24 Hz, Ru-H). 2.5.2 Mixed-Phosphine Complexes, RuCl2(P-P)(PPh 3 ) 2.5.2.1 Dichloro(l,4-bis(diphenyIphosphino)butane)(triphenyIphosphine)- ruthenium(II), R u C l 2 ( D P P B ) ( P P h 3 ) , 22 The title complex was prepared according to the method reported by Caulton and coworkers 2 5 DPPB (0.445 g, 1.04 mmol) was added to a CH2C12 (20 mL) solution of RuCl2(PPh3)3 (1.0 g, 1.04 mmol) at room temperature; the dark brown solution turned green immediately. The solution was stirred under argon for 2 h, and concentrated to ~5 mL by pumping off the solvent under vacuum. Addition of dry ethanol (40 rnL) caused precipitation of the green product, which was filtered, washed with ethanol (2 x 10 mL) and hexanes (2 x 10 mL), and dried in vacuo. The concentration step prior to the addition of ethanol (not reported in the original procedure25) improved the yield of the complex dramatically, to essentially quantitative as compared to the ~66% reported by Caulton et al. Yield: 0.86 g (96%); Anal. Calcd for RuCl2(DPPB)(PPh3), C46H43Cl2P3Ru: C, 64.19; H, 5.04. Found: C, 63.6; H, 5.0. The complex sometimes contained small amounts (<2-3%) of the known dinuclear Ru(II) complex with a bridging DPPB ligand, (DPPB)Cl2Ru(|i-DPPB)RuCl2(DPPB) 2 6 as evidenced by 3 lP NMR spectroscopy and elemental analysis (see Section 2.5.11.1); this CH^l^insoluble impurity can be removed 52 by filtration of the CH2CI2 solution of RuCl2(DPPB)(PPh3) at the pre-concentration stage. Details of further characterisation of the mixed-phosphine complex are described in Chapter 4, Section 4.2. 2.5.2.2 Dichloro((^)-2,2'-bis-(diphenylphosphino)-l,l'-binaphthyl)- (triphenylphosphine)ruthenium(II), RuCl2(R-BINAP)(PPh3), 21 The /?-BINAP analogue was prepared by stirring RuCl2(PPh3)3 (0.12 g, 0.125 mmol) with one equivalent of the diphosphine in dichloromethane solution (15 mL) for 10 h under argon. There was no perceptible change in the initial brown colour of the solution. Addition of diethyl ether (15 mL) following concentration of the solution to ~2 mL resulted in precipitation of an orange-brown solid. The mixture was stirred for 4 h, and the product was separated by filtration, washed with diethyl ether and hexane (5 mL each), and dried under vacuum. Yield: 0.13 g (81%); Anal. Calcd for RuCl2(BINAP)(PPh3), C62H47CI2P3RU: C, 70.46; H, 4.48; Cl, 6.71. Found: C, 70.2; H, 4.6; Cl, 6.5. Spectroscopic characterisation of this complex is presented in Section 4.6. 2.5.3 rra«s-Chlorohydrido(ri2,ri2-norbornadiene)[(l,4-bis(diphenylphos- phino)butane)]ruthenium(II), RuHCl(nbd)(DPPB),27 3Ji (a) One equivalent of DPPB (0.227 g, 0.53 mmol) was added to a benzene solution (25 mL) of RuHCl(nbd)(PPh3)2, (0.40 g, 0.53 mmol), and the solution stirred at 20 °C for 20 h under argon. The resulting yellow solution was concentrated to -10 mL, hexane (30 mL) added, and the mixture stirred for 2 h. The yellow-brown solid that precipitated was filtered, washed with hexane (2 x 10 mL), and dried under vacuum (yield: 0.10 g); this solid contained substantial amount of unreacted starting complex, RuHCl(nbd)(PPh3)2, along with the desired product ( 3 1P NMR evidence, see below). 53 Concentration of the filtrate to ca. 10 mL followed by stirring for 10 h precipitated the pure RuHCl(nbd)(DPPB) complex as an off-white solid. Yield: 0.14 g (40%). (b) A benzene (30 mL) solution of RuCl2(DPPB)(PPh3) (0.40 g, 0.47 mmol) was stirred with 2,5-norbomadiene (3.5 mL, 34 mmol) at 60 °C for 18 h under argon; the initially green solution turned into a greenish yellow suspension. Proton Sponge (0.234 g, 1.1 mmol) was added and the mixture stirred under 1 atm H 2 for 24 h. The resulting yellow suspension was then allowed to cool to 20 *C and filtered to remove the white Proton Sponge hydrochloride (PSH+C1-, confirmed by *H NMR, quantitative yield). The yellow filtrate was concentrated to 10 mL; addition of hexane (50 mL) precipitated the off- white product which was filtered, washed with hexane (2 x 10 mL) to remove any traces of PPh3 and Proton Sponge, and dried in vacuo. Yield: 0.19 g (62%). Anal. Calcd for RuHCl(nbd)(DPPB), C 3 5 H 3 7 ClP 2 Ru: C, 64.05; H, 5.68; Cl, 5.41. Found: C, 64.2; H , 5.8; Cl, 5.6. IR (Nujol, cm"1): v ( R u . H ) 2045 (w). *H NMR (C 6D 6, 20 °C), ppm: 8 8.25, 7.33 (4 H each, m, ortho-phenyl, DPPB), 5 7.3-6.9 (12 H, br m, meta-,para- phenyl, DPPB), 6 3.89, 2.84 (2 H each, br m, olefinic, nbd), 5 3.75, 2.07, 1.22 and 0.98 (2 H each, br m, methylene, DPPB), 5 3.67, 3.36 (1 H each, br m, methine, nbd), 8 0.90 (2 H, s, bridgehead methylene, nbd); 8 -9.69 (-10.38 in CDC13; 1 H, t, Ru-H, Vm = 20.7 Hz); 3 1 p { l H ) NMR: 43.2 ppm, s. 2.5.4 DichIoro-tri-u-chIoro-bis(bidentate phosphine)diruthenium(II,III) Complexes, [(P-P)ClRu(u-Cl)3RuCl(P-P)] or Ru 2 Cl 5 (P-P) 2 P-P = DPPP, DPPB, fl,/?-DIOP, 5,5-CHIRAPHOS, DPPN, DPPH, rac-DPPCP, rac-DPCYCP, 5,5-BDPP, R-BINAP, and 5-BINAP, 5-PHENOP: The procedure described by Thorburn et al. for the preparation of Ru2Cl5(P-P)2 complexes, containing P-P = DPPP, DPPB, DIOP, CHIRAPHOS and NORPHOS,2 8-2 9 54 was employed for the preparation of similar complexes containing other bidentate phosphines. A suspension of RuCl3(PAr3)2(DMA)-DMA solvate (1.0 g) in hexanes (150 mL) was refluxed under a N 2 atmosphere with an equimolar amount of the appropriate bidentate phosphine (Ar = phenyl, for P-P = DPPB, DPPN, DPPH, or DIOP, 1.1 mmol; Ar = p-tolyl, for all other chelating phosphines, 1.0 mmol). The brown products were filtered, rinsed well with hexanes (4 x 20 mL) and vacuum dried. The crude product was washed down the filter as a solution with CH2CI2 (~30-60 mL) leaving behind some insoluble impurities. Analytically pure products were obtained from the filtrate after concentration to -10 mL followed by addition of diethyl ether (-40 mL). The complexes were characterised by elemental analysis, IR and UV-visible spectroscopy, and magnetic susceptibility measurements where possible (see Chapter 3, Section 3.3.1). The Ru-Cl stretch in the IR spectra of Ru2Cls(P-P)2 complexes was found in 320-340 cm - 1 (w) range. 2.5.4.1 P-P = DPPP: Ru 2Cl 5(DPPP)2, l 2 9 Yield: 0.45 g (74%). Anal. Calcd for Ru 2Cl 5(DPPP) 2, C54H52CI5P4RU2: C, 53.86; H, 4.35; Cl, 14.72. Found: C, 53.7; H, 4.5; Cl, 14.6. 2.5.4.2 P-P = DPPB: Ru 2Cl 5(DPPB)2, 2 2 9 Yield: 0.54 g (80%). Anal. Calcd for Ru2Cl 5(DPPB) 2 , C56H56CI5P4RU2: C, 54.58; H, 4.58; Cl, 14.38. Found: C, 55.0; H, 4.5; Cl, 13.7. 2.5.4.3 P-P = R,R-DIOP: Ru2Cl5(DIOP)2, 3 2 9 Yield: 0.51 g (70%). Anal. Calcd for Ru2Cl5(DIOP)2, C62H64O4CI5P4RU2: C, 54.10; H, 4.69; Cl, 12.88. Found: C, 54.1; H, 4.8; Cl, 12.8. 55 2.5.4.4 P-P = S,S-CHIRAPHOS: Ru2Cl5(CHIRAPHOS)2, 4 2 9 Yield: 0.55 g (81%). Anal. Calcd for Ru2Cl5(CHIRAPHOS)2, C56H56CI5P4RU2: C, 54.58; H, 4.58; Cl, 14.38. Found: C, 54.5; H, 4.8; Cl, 14.3. 2 .5 .4 .5 P-P = DPPN: Ru2Cl5(DPPN)2, 5 Yield: 0.40 g (58%). Anal. Calcd for Ru2Cl5(DPPN)2, C58H60CI5P4RU2: C, 55.27; H.4.80. Found: C, 55.7; H, 4.5. 2.5.4.6 P-P = DPPH: Ru2Cl5(DPPH)2, 6 Yield: 0.42 g (59%). Anal. Calcd for Ru2Cl5(DPPH)2, C60H64CI5P4RU2: C, 55.93; H, 5.01. Found: C, 55.5; H, 5.0. 2.5.4.7 P-P = rac-DPPCP: Ru 2Cl 5(DPPCP) 2 , 7 Yield: 0.44 g (69%). Anal. Calcd for Ru2Cl 5(DPPCP) 2, C 5 8 H 5 6 C l 5 P 4 R u 2 : C, 55.45; H, 4.49. Found: C, 55.1; H, 4.5. 2.5.4.8 P-P = roc-DPCYCP: Ru 2Cl 5(DPCYCP) 2, 8 Yield: 0.175 g (27%). Anal. Calcd for Ru2Cl5(DPCYCP)2, C58H104CI5P4RU2: C, 53.39; H, 8.03; Cl, 13.59. Found: C, 53.5; H, 8.0; Cl, 16.25 (14.0). § The higher than expected chloride content found for complex 8 (elemental analysis) is likely due to interference by PC»43 _ (produced as a result of combustion of the sample prior to halide-determination), which coprecipitates with AgCl during the Cl-analysis (AgNC>3 method). The interference was removed by a) maintaining a high acidic pH (<2) during halide-determination, or b) by pretreating the solution with La(NC*3)3 to remove the P O 4 3 - . The new values (given in brackets) of the Cl-content obtained by one of these modified methods are in reasonable agreement with those expected. A higher than expected Cl-content was also found for the analogous mixed-valence dinuclear complexes 10 and 11, (see the next page). 56 2.5.4.9 P-P = S,S-BDPP: Ru2Cl5(BDPP)2, 9 Yield: 0.50 g (78%). Anal. Calcd for Ru2Cl5(BDPP)2, C58H6oCl5P4Ru2: C, 55.27; H, 4.80. Found: C, 52.0; H, 4.7. 2.5.4.10 P-P = UNBINAP: Ru2CI5(/?-BINAP)2,10 (halfscale) Yield: 0.26 g (64%). Anal. Calcd for Ru2Cl5(i?-BINAP)2, C88H64Cl5P4Ru2: C, 65.05; H, 3.97; Cl, 10.91; Calcd for C88H64ClsP4Ru2H20: C, 64.34; H, 4.05; Cl, 10.79. Found: C, 64.3; H, 4.2; Cl, 17.0§. The presence of water was confirmed from the IR spectrum. 2.5.4.11 P-P = 5-BINAP: Ru2Ci 5(S-BINAP) 2,11 Yield: 0.70 g (85%). Anal. Calcd for Ru2Cl5(S-BINAP)2, C 8 8H64Cl 5 P 4 Ru 2 : C, 65.05; H, 3.97; Cl, 10.91; Calcd for C88H64Cl 5 P 4 Ru 2 H 2 0: C, 64.34; H, 4.05; Cl, 10.79. Found: C, 64.6; H, 4.3; Cl , 16.9§ (10.6). 2.5.4.12 P-P = S-PHENOP: Ru 2Cl 5(PHENOP) 2, 12 The S-PHENOP is insoluble in hexane, therefore, some benzene (~30 mL) was added to the hexane suspension in order to solubilise the ligand and facilitate the reaction. Yield: 0.41 g (56%). Anal. Calcd for Ru2Cl5(PHENOP)2, C 7 oH 7 oN 2 0 2 C l 5 P 4 R u 2 : C, 57.02; H, 4.78; N, 1.90. Found: C, 57.5; H, 5.0; N, 1.6. 2.5.5 Dichloro-di-|i-chloro-bis(bidentate phosphine)diruthenium(II) Complexes, [RuCl(P-P)(u-Cl)]2 The dinuclear complexes, [RuCl(P-P)(u.-Cl)]2, were prepared by the H2-reduction of the respective Ru(II,III)-bidentate phosphine complexes, Ru2Cl50?-P)2 (Section 2.5.4), in the presence of an appropriate base ( D M A or polyvinylpyridine), following the general 57 strategy developed by Thorburn from this laboratory.29' 3 0 The complexes were stored under argon, because they are air-sensitive to varying degrees, the initially orange-brown colour turning greenish black on exposure to air (within a few minutes in solution and in a few hours to days in the solid state). The spectroscopic characterisation (NMR, UV- visible) of the new complexes is presented in Chapter 3, Section 3.3.2. (a) P-P = DPPP, DPPB, DPPN: Typically, Ru2Cls(P-P)2 (1.0 g) was stirred in 20 mL DMA under 1 atm H2 for 24 h. The resulting dark brown solution was concentrated to 5 mL, dry methanol (40 mL) added, and the mixture stirred overnight under H2. The orange yellow product was filtered, washed with methanol (2x5 mL) and diethyl ether (10 mL) and vacuum dried. 2.5.5.1 P-P = DPPP: Ru2Cl4(DPPP)2) 13 2 9 Yield: 0.45 g (74%). Anal. Calcd for Ru2Cl4(DPPP)2-H20, C54H52CI4P4RU2- •H20: C, 54.65; H, 4.59; Cl, 11.95. Found: C, 54.7; H, 4.8; Cl, 11.9. 2.5.5.2 P-P = DPPB: Ru2Cl4(DPPB)2,14 2 9 The complex is hygroscopic even in the solid state (IR and lH NMR evidence). Yield: 0.88 g (89%). Anal. Calcd for Ru2Cl4(DPPB)2.H20, C 5 6 H 5 6 C l 4P4Ru2 . H 2 0 : C, 55.36; H, 4.81. Found: C, 55.4; H, 5.0. The DPPB complex was also obtained as its more stable acetone adduct, Ru2Cl4(DPPB)2(acetone)acetone solvate,29* 3 0 by dissolution of the product in acetone/dichloromethane (1:1,10 mL) and reprecipitation by addition of 40 mL of diethyl ether (-70% yield). Anal. Calcd for Ru2Cl4(DPPB)2(acetone) -acetone solvate, C62H68O2CI4P4RU2: C, 56.71; H,5.22; 0,2.44; Cl, 10.82. Found: C, 56.5; H, 5.1; O, 2.6; Cl, 10.6. IR (Nujol, cm-1): V(c=o) at 1705 (m, uncoordinated acetone); V(c=0) at 1645 (m, coordinated acetone). 58 2.5.5.3 P-P = DPPN: Ru2Cl4(DPPN)2,17 (halfscale) Yield: 0.38 g (79%). Anal. Calcd for Ru2Cl4(DPPN)2, C58H60CI4P4RU2: C, 56.87; H.4.94. Found: C, 57.5; H, 5.2. (b) P-P = RA-DIOP, 5,5-CHIRAPHOS, fl-BINAP, 5-BINAP, and 5,5-BDPP: The Ru2Cl5(P-P)2 (1.0 g) was added to a rigorously deoxygenated benzene or toluene suspension (30 mL) of polyvinylpyridine (PVP, 2.5 g) and the mixture stirred under 1 atm H2 for 24 h. The orange-brown solution obtained after separation of the insoluble polymer by filtration was concentrated to ~5 mL. Addition of dry hexanes (40 mL) followed by stirring for a few hours yielded the respective Ru2CU(P-P)2 products as brown solids which were filtered, washed with hexanes (20 mL) and vacuum dried. 2.5.5.4 P-P = J?,R-DIOP: Ru2Cl4(DIOP)2,15 2 9 Yield: 0.81 g (83%). Anal. Calcd for Ru2Cl4(DIOP)2, Q2H64O4CI4P4RU2: C, 55.53; H.4.81; Cl, 10.57. Found: C, 55.7; H, 5.0; Cl, 10.8. 2.5.5.5 P-P = S,S-CHIRAPHOS: Ru2Cl4(CHIRAPHOS)2,16 2 9 Yield: 0.80 g (82%). Anal. Calcd for Ru2Cl4(CHIRAPHOS)2, C 5 6H 5 6 Cl 4 P 4 Ru2: C, 56.20; H, 4.72; Cl, 11.85. Found: C, 56.2; H, 4.9; Cl, 11.6. 2.5.5.6 P-P = R-BINAP: Ru2Cl4(tf-BINAP)2,18 (1/Sth scale) Yield: 0.16 g (81%). Anal. Cdcd for Ru2CU(^BINAP)2, C 88H 6 4Cl 4P 4Ru 2: C, 66.50; H, 4.06. Found: C, 65.9; H, 4.5. 2.5.5.7 P-P = S-BINAP: Ru2Cl4(5-BINAP)2,19 (l/5th scale) Yield: 0.17 g (87%). Anal. Calcd for Ru2Cl4(fl-BINAP)2, C88H64CI4P4RU2: C, 66.50; H, 4.06; Cl, 8.92. Found: C, 66.2; H, 4.2; Cl, 8.8. 59 2.5.5.8 P-P = 5,5-BDPP: Ru2Cl4(BDPP)2, 20 No reaction could be observed, even after heating the mixture at 60 °C for 4 days under 1 atm of H 2 , as the toluene solution remained essentially colourless and the mixed- valence precursor 9 remained undissolved in the toluene solvent. After two months, the toluene solution had become yellow-orange, although much of the starting complex was still present in suspension. The mixture was filtered to separate the solids and the filtrate evaporated to dryness. The resultant orange residue was dissolved in ~2 mL of CH2C12 addition of Et 2 0 (10 mL) precipitated an orange solid which was filtered, washed with a small amount of Et 2 0 (2 mL), and dried under vacuum. Yield: 0.08 g (8%). Anal. Calcd for Ru 2Cl 4(5,5-BDPP) 2, Cs8H6oCl4P4Ru2: C, 56.87; H, 4.94. Found: C, 56.0; H, 5.2. 2.5.6 Chloro-tri-|i-chloro-(Iigand)bis(l,4-bis(diphenylphosphino)butane)- diruthenium(II) Complexes, [(L)(DPPB)Ru(u-Cl)3RuCl(DPPB)] Properties and characterisation of these complexes are discussed in Chapter 3, Sections 3.6 and 3.7. 2.5.6.1 L = NEt 3: [(NEt3)(DPPB)Ru(u-Cl)3RuCl(DPPB)], 14b 30 The triethylamine adduct was prepared by stirring [RuCl(DPPB)(u-Cl)]2 (0.20 g, 0.17 mmol Ru2) with excess NEt3 (0.5 mL, 3.6 mmol) in benzene or toluene (10 mL) for 6 h. Some orange solid precipitated; further precipitation was induced by adding hexanes (20 mL). The product was washed with ethanol and hexanes and dried under vacuum. Yield: 0.18 g (84%). Alternatively, this complex can be prepared starting with RuCl2(DPPB)(PPh3) and NEt 3, in the same manner (-90% yield). Anal. Calcd for [(NEt3)(DPPB)Ru(u-Cl)3RuCl(DPPB)], C 6 2 H 7 1 N C l 4 P 4 R u 2 : C, 57.37; H, 5.51; N, I. 08; Cl, 10.92. Found: C, 57.3; H, 5.6; N, 1.0; Cl, 10.7. ! H NMR (CDC13, 20 °C), 60 ppm: 8 3.20 (broad m, 6H, -NC// 2CH 3 of bound NEt3), 1.08 (9H, broad m, -NCH2C#3 of bound NEt3). 31P{1H} NMR: 48.3 ppm, s. This complex is also a byproduct in the synthesis of the hydridochloro-Ru(II) complex, [RuHCl(DPPB)]3 (see Section 2.5.10).30 2.5.6.2 L = NHBun2* [(NHBun2)(DPPB)Ru(u-Cl)3RuCl(DPPB)], 14c The complex, [(NHBun2)(DPPB)Ru(u-Cl)3RuCl(DPPB)], was prepared (a) from [RuCl(DPPB)(u-Cl)]2 in exactly the same manner as its NEt3 analogue, but using NHBu n 2 ; or (b) by refiuxing a benzene/hexane (1:4, 20 mL) suspension of RuCl2(DPPB)(PPh3), (0.20 g, 0.23 mmol) with either NHBun 2 or NBun 3 (2 mL) for 3 h under N 2 . In each case, the orange-brown product was filtered after concentration of the solution to ~5 mL followed by addition of hexanes (40 mL), washed with ethanol and hexanes and dried under vacuum. Yield: 0.11 g (71%). Anal. Calcd for [(NHBun2)(DPPB)Ru(u-Cl)3RuCl(DPPB)], C64H75NCI4P4RU2: C, 57.97; H, 5.70; N, 1.06. Found: C, 57.7; H, 5.5; N, 1.0. IR (Nujol, cm"1): 1572 (m, N-H bending). iH NMR (CDC13, 20 °C), ppm: 8 2.87 (4H, br m, -NC// 2 of bound NHBu2), 1.62 (4H, m, -NCH2C//2), 1.34 (4H, m, - C / / 2 C H 3 of NHBu2), and 0.97 (6H, t, -CH2C / / 3 ) . 31p{lH) NMR: 48.2 ppm, s. 2.5.6.3 L = CO: [(CO)(DPPB)Ru(u-Cl)3RuCl(DPPB)], 14d 3 1 The title complex was synthesised from [RuCl(DPPB)(u-Cl)]2 by decarbonylation of aldehydes such as formaldehyde, acetaldehyde, or benzaldehyde. Gaseous formaldehyde, generated by heating paraformaldehyde at 180 °C under a slow stream of argon, was bubbled through a CH2C12 solution (30 mL) of [RuCl(DPPB)(u-Cl)]2 (0.50 g, 0.42 mmol). After 10 min, the solution was concentrated to a red oil to which 30 mL of benzene were added; the solution was stirred for 16 h under argon and filtered through Celite® to remove some "polymeric" material. Concentration of the filtrate to ca. 10 mL 61 precipitated the orange product which was filtered, washed with hexanes and dried under vacuum. Yield: 0.29 g (57%). The carbonyl adduct can also be prepared by stirring a benzene solution of [RuCl(DPPB)(u-Cl)te,14 (0.25 g, 0.21 mmol), with excess acetaldehyde or benzaldehyde (0.5 mL) at 50 °C for 24 h; concentration of the solution to ~5 mL, followed by addition of hexanes (30 mL), gives the product in high yield. Alternatively, this complex is obtained by heating to 50 e C a benzene solution (20 mL) of RuCl2(DPPB)(PPh3), (0.20 g, 0.23 mmol), with an equimolar amount of Mo(CO)6 for 24 h under argon. Concentration of the resultant greenish yellow solution to ~5 mL followed by addition of hexane (30 mL) precipitates the orange-brown product (90% yield). Anal. Calcd for [(CO)(DPPB)Ru(u-Cl)3RuCl(DPPB)], C57H56OCI4P4RU2: C, 55.89; H, 4.61; Cl, 11.58. Found: C, 56.2; H, 4.8; Cl, 11.4. IR (Nujol, cm - 1): v (co) at 1977 (s). 3lP{lH}NMR (C 6 D 6 , 20 °C): 8 A = 53.8, 6 B = 53.3 ppm, 2 / A B = 45.2 Hz; 8C = 46.9, 8 D = 33.1 ppm, 27CD = 29.6 Hz (see Chapter 3, Table 3.6). Direct carbonylation with CO of either precursor (14 or 23) resulted in the formation of a different set of products. Details of the carbonylation reaction are discussed in Chapter 3, Section 3.6.2. 2.5.6.4 L = Me 2SO (DMSO): [(DMSO)(DPPB)Ru(u-Cl)3RuCl(DPPB)], 14e 3 1 Some DPPB (0.15 g, 0.35 mmol) was added to a solution of m-RuCl2(DMSO)4 (0.17 g, 0.35 mmol) in dichloromethane:acetone (1:1,20 mL) and the mixture stirred for 8 h under argon. The original yellow solution instantly turned orange and further changed slowly to a greenish brown suspension. The bright green solid was filtered (Ru2Cl4(DPPB)3,26 ~7 mg) and washed with dichloromethane (5 mL). The orange-yellow filtrate was reduced to ~5 mL, diethyl ether (25 mL) added and the mixture stirred for 8 h. The resulting orange suspension was filtered to remove small amounts of RuCl2(DPPB)2 (~8 mg). The bright orange filtrate was refridgerated for a week to afford dark orange-red crystals of [(DMSjD)(DPPB)Ru(u-Cl)3RuCl(DPPB)]. Yield: 0.17 g (76%). Anal. Calcd 62 for [(DMSO)(DPPB)Ru(u-Cl)3RuCl(DPPB)], CsgH^SOCL^Ri^: C, 54.63; H, 4.90; Cl, 11.12. Found: C, 54.7; H, 5.1; Cl, 11.0. The complex was characterised crystallographically (Sections 3.6.3, 3.6.4, and Appendix A-2.2). IR (Nujol, cm-1): V(S=0) at 1090 (s, S-bonded DMSO). 31P{ lH)NMR (C6D6, 20 *C): 8A = 53.6, 8B = 50.6 ppm, 2/AB = 43.8 Hz; 8c = 41.6, 8D = 28.9 ppm, 2JQD = 32.1 Hz (see Chapter 3, Table 3.6). 2.5.7 Reactions of Cis-RuCI 2(DMSO) 4 with Other Bidentate Phosphines P-P = DPPM, DPPE, and S.S-BDPP: Reactions of m-RuCl2(DMSO)4 (0.17 g, 0.35 mmol) with one equivalent of the appropriate chelating phosphine were carried out in dichloromethane:acetone solution (1:1, 20 mL) employing the procedure described for the reaction with DPPB (previous section). Characterisation of the products by NMR spectroscopy is discussed in Section 3.8 of Chapter 3. 2.5.8 Chloro(p-cymene)(bidentate phosphine)ruthenium(II) chloride, [RuCl(p-cymene)(P-P)]Cl Recently, Takaya and coworkers have reported on the synthesis of a series of complexes of general formula [RuX(arene)(S-BINAP)]+X_ (X = Cl, Br or I; arene = benzene, toluene, or p-cymene).32 The procedure used for preparation of the complexes described below is similar to that reported.32 The reactions are discussed in more detail in Chapter 3, Section 3.9. A solution of [RuCl(p-cymene)(u-Cl)]2 (0.10 g, 0.33 mmol) in methanol/CH2Cl2 (3:1,20 mL) was stirred with an equimolar amount of the appropriate bidentate phosphine, for 24 h under argon. The resultant orange-yellow solution was reduced to ~3 mL, diethyl ether (20 mL) added to precipitate the orange-yellow product, and the rnixture stirred for 63 2 h. The solid was isolated by filtration, washed with diethyl ether (5 mL) and dried under vacuum. 2.5.8.1 P-P = tf-BINAP: [RuCl(p-cymene)(fl-BINAP)]Cl Yield: 0.27 g (90%). Anal. Calcd for [RuCl(p-cymene)(BINAP)]C10.5H2O, C54H46CI2P2RUO.5H2O: C, 69.15; H, 5.05; Cl, 7.56. Found: C, 69.1; H, 5.1; Cl, 7.5. The presence of water was confirmed by IR and lH NMR spectroscopy. 3lp{ iH} NMR (CDCI3, 20 °C): 6 A = 40.0, 8 B = 23.5 ppm, 2 / A B = 62.5 Hz. 2.5.8.2 P-P = 5-BINAP: [RuCl(p-cymene)(S-BINAP)]Cl 32 Yield: 0.25 g (83%). Anal. Calcd for [RuCl(p-cymene)(BINAP)]C10.5H2O, C54H46Cl2P2Ru-0.5H2O: C, 69.15; H, 5.05. Found: C, 69.2; H, 5.4. 31P{1H} NMR (CDCI3, 20 °C): 6A = 41.2, 8 B = 24.5 ppm, 2 / A B = 62.6 Hz. 2.5.8.3 P-P = 5,S-BDPP: [RuCl(p-cymene)(S,S-BDPP)]Cl Reaction of [RuC10>-cymene)(u-Cl)]2 with S,S-BDPP gave a mixture of products, including the desired arene derivative (NMR spectroscopic evidence, see below); details of this reaction are given in Chapter 3, Section 3.9. One of the products, isolated as bright red crystals from the CH2Cl2/Et20 filtrate and identified as rrartS-RuC^CS.S-BDPPh by NMR spectroscopy (31p{lH) NMR, CDCI3, 20 'C: 8.7 ppm, s), has also been characterised by X-ray diffraction analysis. The molecular structure (ORTEP view), along with the various structural parameters including tables of selected bond lengths/angles are given in Appendix A-2.3. 31P{lH) NMR data (CDCI3,20 °C) for [RuCl(p-cymene)(S,S- BDPP)]C1: 8 A = 39.2, 8 B = 29.1, 2 / A B = 60.7 Hz. 64 2.5.9 Reactions of RuCl2(DPPB)(PPh3) with Chelating Ligands (L-L); Formation of RuCl2(DPPB)(L-L) A benzene solution (20 mL) of the mixed phosphine complex, RuCl2(DPPB)(PPh3) (0.10 g, 0.12 mmol), was stirred under argon with the appropriate chelating ligand (0.12 mmol). The original green solution which changed to yellow within minutes was stirred for 16 h and concentrated to ~5 mL. Addition of hexanes (30 mL) followed by stirring for 2 h precipitated the product which was fdtered, washed with hexanes and vacuum dried. The spectroscopic characterisation of the RuCl2(DPPB)(L-L) complexes is presented in Chapter 4, Sections 4.4 and 4.5. 2.5.9.1 L - L = PPh2(2-Py): RuCl2(DPPB)(PPh2(2-Py)) The pyridylphosphine ligand, PPh2(2-Py), will be referred to as PPh2Py for the sake of convenience. (a) 7Vaw-RuCl2(DPPB)(PPh2Py), 24 Orange-yellow solid. Yield: 0.08 g (80%). Anal. Calcd for trans- RuCl2(DPPB)(PPh2Py), C45H42NCI2P3RU: C, 62.72; H, 4.91; N, 1.63; Cl, 8.23. Found: C, 62.7; H, 4.9; N, 1.8; Cl, 8.1. (b) Cj5-RuCl2(DPPB)(PPh2Py), 25 The complex, m-RuCl2(DPPB)(PPh2Py), was obtained by heating a benzene solution of the trans isomer at 80 °C for 8 h. The cis isomer, being relatively insoluble in benzene, precipitated from the solution; the solid was washed carefully with a small amount of benzene followed by hexanes and dried under vacuum. Anal. Calcd for cis- RuCl2(DPPB)(PPh2Py). C 4 5 H 4 2 N C l 2 P 3 R u : C, 62.72; H, 4.91; N, 1.63; (for C45H42NCI2P3RU.O.5H2O: C, 62.07; H, 4.98; N, 1.61). Found: C, 62.0; H, 5.2; N, 1.6. The presence of water was confirmed by IR and lU NMR spectroscopy. 65 2.5.9.2 L - L = DPPM: 7>a/u-RuCl2(DPPB)(DPPM), 27 Pale brownish yellow solid. Yield: 0.10 g (87%). Anal. Calcd for trans- RuCl2(DPPB)(DPPM), C52H48Cl2P4Ru: C, 64.47; H, 4.99; Cl, 7.33. Found: C, 64.2; H, 5.0; Cl, 7.0. 2.5.10 Synthesis of Chlorohydrido(bidentate phosphine)ruthenium(II) Trimers, [RuHCl(P-P)]3 The title trinuclear ruthenium-hydride complexes containing DPPB and 5,5- CHIRAPHOS were first isolated in -5-10% yield by Thorburn in this laboratory.30 The synthetic procedure described by Thorburn30 has been modified during the present study, and the isolated yields of the trimeric Ru hydrides improved dramatically (-40-50%, see Chapter 5, Section 5.4 for details). 2.5.10.1 P-P = DPPB: [RuHCl(DPPB)]3, 29 . 3 0 A benzene or toluene (60 mL) suspension/solution of the dichloro(DPPB)- ruthenium(II) dimer, [RuCl(P-P)(u-Cl)]2 (1.0 g, 1.67 mmol monomer), was stirred under 1 atm H 2 for 1 h at room temperature. The yellow-brown suspension turned lighter brown, and deoxygenated triethylamine (0.235 mL, 1.69 mmol) was then added carefully under a blanket of hydrogen. The supension turned into a deep red solution within a couple of hours; the mixture was left stirring under H 2 for 36 h, replenishing the H 2 once after 18 h. The resulting red-brown suspension/solution was reduced to 20 mL. The precipitated NEt 3HCl salt and an orange complex, identified as the NEt3 adduct [(NEt3)(DPPB)Ru(|i-Cl)3RuCl(DPPB)] (see Section 2.5.6.1), were filtered off. The clear deep wine-red filtrate was pumped to a viscous oil. Addition of hexane (10 mL) precipitated more of the NEt3 adduct along with some of the desired Ru-hydride product. The solids were filtered and rinsed first with hexane (5 mL), followed with a 1:1 66 toluene/hexane mixture (15 mL) to wash down any precipitated hydride product. Concentration of the filtrate to ~10 mL afforded the hydride complex [RuHCl(DPPB)]3 as a brown solid (darker brown when microcrystalline) which was filtered and vacuum dried. The NEt3-HCl salt, a shiny white solid, could be separated from the NEt3 adduct by washing the mixture with ethanol and then stripping the solvent from the filtrate. The salt was identified by *H NMR spectroscopy (CDC13, 20 °C, ppm: 8 3.09, 6H, AB q of d, -NC/-/2; 8 1.6, IH, br m, -N/-/+C1-; 8 1.41, 9H, t, CH 2 C// 3 . Yield of NEt3HCl salt: 0.14 g (60%). Yield of [(NEt3)(DPPB)Ru(u-Cl)3RuCl(DPPB)]: 0.40 g (40%). Characterisation of this complex is described earlier in Section 2.5.6.1. Yield of [RuHCl(DPPB)]3: 0.50 g (53%). Anal. Calcd for (C28H29ClP2Ru)3: C, 59.63; H, 5.18. Found: C, 61.0; H, 5.5. Small amounts of the triethylamine adduct (see above) are sometimes present, which is evidenced by the presence of nitrogen in elemental analysis and a singlet at 48.3 ppm in the 3 1 P NMR spectrum. IR (Nujol, cm-1): V ( R U _ H ) at 2010 and 1995 (w). *H NMR, hydride region (C6D6, 20 °C), 8 ppm: -17.65, t, 2JPH = 31.7 Hz, terminal Ru-H; -21.1, m with 2 / P H -13-18 Hz, terminal Ru-H; -21.9 ppm, t, 2 / P H = 33.2 Hz, terminal Ru-H. The phosphorus NMR data are given in Chapter 5, Section 5.5.2. 2.5.10.2 P-P = 5^-CHIRAPHOS: [RuHCl(S,S-CHIRAPHOS)]3, 30 3 0 The CHIRAPHOS trimer analogue was prepared in exactly the same manner as die corresponding DPPB complex (see above), but using [RuCl(CHIRAPHOS)(u-Cl)]2 precursor on half the scale. The NEt3-HCl salt was again identified by *H NMR spectroscopy. The orange coloured NEt3 adduct, [(NEt3)(CHIRAPHOS)Ru(u-Cl)3RuCl(CHIRAPHOS)] similar to the corresponding DPPB complex, was isolated in -40% yield. Anal. Calcd for C62H71NCI4P4RU2: C, 57.37; H, 5.51; N, 1.08; Cl, 10.92. Found: C, 57.3; H, 5.6; 67 N, 1.0; Cl, 10.7. 3ip{ lH} NMR (C6D6, 20 °C), AB q: 8 A = 87.3, 8 B = 80.2 ppm, 2 / A B = 37.3 Hz. The trimeric hydride complex [RuHCl(CHIRAPHOS)]3, a dark red-brown solid, was recrystallised from CH2Cl2/Et20. Bright red crystals suitable for X-ray diffraction studies were isolated by Thorburn;30 results of the X-ray analysis, carried out by Dr. R. G. Ball then at the University of Alberta, are discussed in Chapter 5 (Section 5.5.1). Yield (after recrystallisation): 0.23 g (46%). Anal. Calcd for [RuHCl(CHIRAPHOS)]3, (C28H29ClP2Ru)3: C, 59.63; H, 5.18. Found: C, 60.1; H, 5.3. IR (Nujol, cm"1): V ( R u - H ) at 2025 and 2015 (w). *H NMR, hydride region (CeD6, 20 °C), ppm: -17.0 , dd, 2 / P H = 36.6 and 26.4 H z , terminal Ru-H; -19.4, m with 2Jpu in the 8-21 Hz range, bridging Ru-H; -24.8, 2Jpu = 36.3 and 31.8 Hz, terminal Ru-H. The phosphorus NMR data are given in Chapter 5, Section 5.5.2. 2.5.11 Synthesis of Diphosphine-Bridged Dinuclear Ruthenium(II) Complexes, [(P-P)Cl 2Ru(u 2-(P-P))RuCl 2(P-P)] Reaction of RuCl2(PPh 3) 3 with -1.5 mole equivalents of the diphosphines DPPB 2 6 and D I O P 1 7 a - 3 3 are known to give diphosphine-bridged complexes of the stoichiometry RuCl2(P-P)i.5. Analogous new complexes containing the chelating phosphines DPPN and D P P H were prepared by a similar route, and characterised by NMR spectroscopy and elemental analysis. In a typical procedure, RuCl2(PPh3)3 (0.1 g, 0.10 mmol) was stirred with -2 equivalents of the appropriate diphosphine in benzene (25 mL) solution for 1 h under argon. The resultant dark green solution was concentrated to -5 mL and hexanes (20 mL) added to precipitate the green product, which was then separated by filtration, washed with hexanes (2 x 10 mL) and dried under vaccum. These diphosphine-bridged complexes are essentially insoluble in most common non-aromatic organic solvents, and only sparingly soluble in aromatic solvents. 68 2.5.11.1 P-P = DPPB 2 6 Yield: 0.070 g (86%). Anal. Calcd for [RuCl2(DPPB)i.5]2, Cg^CUPeRu* C, 62.15; H, 5.22; Cl, 8.74. Found: C, 62.5; H, 5.2; Cl, 8.6. 2.5.11.2 P-P = DPPN Yield: 0.075 g (90%). Anal. Calcd for [RuCl2(DPPN)i.5]2, C87H90CI4P6RU* C, 62.74; H, 5.45; Cl, 8.51. Found: C, 62.9; H, 5.4; Cl, 7.3. 31P{!H} NMR (toluene-ds, -60 'C): 5A = 20.8, 8B = 41.5, 8X = 78.6 ppm; 2 7 AB = 306, 2/A X = 27.8, 2/ BX = 31.3Hz. The product usually contained small amounts of a related mononuclear complex, RuCl2(DPPN)(DPPN*), as evidenced by the presence of an additional 3 1 P NMR singlet resonance at -17.0 ppm due to the free end of the dangling DPPN ligand, DPPN* (cf. -15.6 ppm for free DPPN). The DIOP analogue of RuCl2(DPPN)(DPPN*) has been characterised by a previous worker in this laboratory,173 and a 3 1 P NMR shift just high- field of the free phosphine shift has been noted for the corresponding dangling phosphine (-26.3 and -24.7 ppm, respectively). 2.5.11.3 P-P = DPPH Yield: 0.075 g (84%). Anal. Calcd for [RuCl2(DPPH)i.5]2, C90H96CI4P6RU* C, 63.31; H, 5.67; Cl, 8.30. Found: C, 64.4; H, 5.8; Cl, 7.3. 3lp{lH} NMR (toluene-ds. 20 °C): 8A = 23.1, 8B = 32.0, 8X = 70.7 ppm; 2 / A B = 301, 2 / A X = 29.9, 2 / B X = 32.2Hz. Again, the presence of some RuCl2(DPPH)(DPPH*) impurity, where DPPH* represents a dangling phosphine, is apparent from a 3 1 P NMR singlet at-17.0 ppm (cf. -15.6 ppm for free DPPH), which is assigned to the dangling end of DPPH; the differences in the calculated and the found % C, H, and Cl are also explained by the 69 presence of RuCl2(DPPH)(DPPH*) impurity (Calcd for C60H64CI2P4RU: C, 66.66; H, 5.97; Cl, 6.56). 2.5.12 Acetatohydrido(l,4-bis(diphenylphosphino)butane)(triphenyI- phosphine)ruthenium(II), Ru(C02Me)(H)(DPPB)(PPh3) A suspension of RuCl2(DPPB)(PPh.3) (0.20 g, 0.23 mmol) in dry methanol/toluene (4:1, 25 mL) was stirred with sodium acetate (0.05 g, 0.61 mmol) at 60 *C for 16 h under argon. The resultant dark yellow solution was concentrated to ~5 mL. The solid that precipitated was filtered, washed with toluene (5 mL) and dried under vacuum (yield of the white solid: 0.03 g, NaCl and excess NaOAc). The filtrate was further concentrated to ~2 mL and hexane (20 mL) added to precipitate the yellow product, which was filtered, washed with diethyl ether and vacuum dried. The complex is air-sensitive even in the solid state, turning green within a few hours. Yield of the yellow solid: 0.11 g (55%). Anal. Calcd for C48H47O2P3RU: C, 67.84; H, 5.57. Found: C, 65.1; H, 5.2. IR (KBr, cm-1): 2065 (w, V ( R U .H ) ) ; 1538 (s, V(ocO). acetate, asymm.); 1481 (s, V ( O C O ) . acetate, symm.). iHNMR (C 6 D 6 , 20 °C), ppm: 6 1.1, 3H, s, -CO2C//3; -18.8, IH, dt, 2 / P H = 30.6 (d) and 24.6 (t) Hz. 31p{lH) NMR: 6 A = 43.5, 6 B = 46.7, 8 X = 78.9 ppm; 2 / A B = 292, VAX = 35.9, 2 / B X = 25.7 Hz. 70 2.6 References - Chapter 2 1. Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals; Pergamon Press: Oxford, 2nd Edn., 1980. 2. Karim, A.; Mortreux, A.; Petit, F.; Buono, G.; Peiffer, G.; Siv, C. J. Organo- met. Chem. 1986,377, 93. 3. Allen, D. L.; Gibson, V. C ; Green, M. L. H.; Skinner, J. F.; Bashkin, J.; Grebenik, P. D. / . Chem. Soc, Chem. Commun. 1983, 895. 4. Maisonnet, A.; Farr, J. P.; Olmstead, M. M.; Hunt, C. T.; Balch, A. L. Inorg. Chem. 1982,27,3961. 5. Joshi, A. M., M.Sc. Dissertation, The University of British Columbia, Vancouver, Canada, 1986; Chapter 2. 6. (a) Kosolapoff, G. M.; Maier, L. Organic Phosphorus Compounds ; Wiley-Inter- science: New York, 2nd Edn., 1972; Vol. 1, p. 130. (b) This was confirmed by recording 3 1P{ 1H) NMR spectra (300 MHz) of PPh3 in various solvents (CDC13, CD2CI2, Q5D6, and toluene-fife, 20 *C) against 85% H3PO4, which was placed in a sealed inner capillary tube. The observed 3 1 P{ ]H} chemical shift values for PPh3 ranged from -5 to -6 ppm w.r.t. 85% H3PO4. 7. (a) James, B. R.; Rempel, G. L. Discuss. Faraday Soc. 1968,46, 48. (b) Can. J. Chem. 1966, 44, 233. 8. Konig, W. A.; Francke, W.; Benecke, I. J. Chromatogr. 1982, 239, 227. 9. Slessor, K. N.; King, G. G. S.; Miller, D. R.; Winston, M. L.; Cutforth, T. L. J. Chem. Ecol, 1985, 78, 1659. 10. Konig, W. A.; Benecke, I.; Sievers, S. / . Chromatogr. 1982,238, 427. 11. Chan, A. S. C ; Landis, C. R. J. Mol. Catal. 1989,49, 165. 71 12. MacFarlane, K. S., M.Sc. Dissertation, The University of British Columbia, Vancouver, Canada, 1989; Chapter 2. 13. Shriver, D. F.; Drezdon, M . A. The Manipulation of Air-Sensitive Compounds; Wiley: New York, 2nd Edn., 1986. 14. (a) James, B. R.; Ochiai, E. ; Rempel, G. I. Inorg. Nucl. Chem. Lett. 1971, 7, 781. (b) Evans, I. P.; Spencer, A.; Wilkinson, G. J. Chem. Soc, Dalton Trans. 1973, 204. (c) Mercer, A.; Trotter, J. J. Chem. Soc, Dalton Trans. 1975, 2480. 15. Bora, T.; Singh, M . M . Transition Met. Chem. 1978, 3, 27; and references therein. 16. Bennett, M . A.; Smith, A. K. J. Chem. Soc, Dalton Trans. 1974, 233. 17. (a) Wang, D. K. W., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1978; Chapter 2. (b) Thorburn, I. S., M.Sc. Dissertation, The University of British Columbia, Vancouver, Canada, 1980; Chapter 2. 18. Dekleva, T. W.; Thorburn, I. S.; James, B. R. Inorg. Chim. Acta 1985,100, 49. 19. Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966,28, 945. 20. Hallman, P.S.; Stephenson, T. A.; Wilkinson, G. Inorg. Syntheses 1970, 12, 237. 21. Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1 9 7 5 , 9 7 , 4221. 22. Schunn, R. A.; Wonchoba, E . R.; Wilkinson, G. Inorg. Syntheses 1972,13, 131. 72 23. Hallman, P. S.; McGarvey, B. R.; Wilkinson, G. J. Chem. Soc, A 1968, 3143. 24. (a) Jaswal, J.; Rettig, S. J.; James, B. R. Can. J. Chem. 1990, in press. (b) Yapp, D. T. T., personal communication. 25. Jung, C. W.; Garrou, P. E.; Hoffman, P. R.; Caulton, K. G. Inorg. Chem. 1984, 23, 726. 26. Bressan, M ; Rigo, P. Inorg. Chem. 1975,14, 2286. 27. Dekleva, T. W.; Joshi, A. M.; Thorburn, I. S.; James, B. R.; Evans, S. V.; Trotter, J. Isr. J. Chem. 1990, 30(4); in press. 28. Thorburn, I. S.; Rettig, S. J.; James, B. R. Inorg. Chem. 1986, 25, 234. 29. Thorburn, I. S., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1985. 30. James, B. R.; Pacheco, A.; Rettig, S. J.; Thorburn, I. S.; Ball, R. C ; Ibers, J. A. J. Mol. Catal. 1987, 41, Ul. 31. Joshi A. M.; James, B. R. J. Chem. Soc, Chem. Commun. 1989, 1785. 32. Mashima, K.; Kusano, K.; Ohta, T.; Noyori, R.; Takaya, H. J. Chem. Soc, Chem. Commun. 1989, 1208. 33. James, B. R.; McMillan, R. S.; Morris, R. H.; Wang, D. K. W. Adv. Chem. Ser. 1978, 167, 122. 73 C H A P T E R 3 Chloro-Bridged Diruthenium(II,II) Complexes Containing Chelating Ditertiary Phosphines 3.1 Introduction The phenomena] success of chiral rhodium complexes, particularly those containing chiral bidentate phosphines, as homogeneous catalysts for the asymmetric hydrogenation of a variety of prochiral unsaturated substrates is evident from even a brief survey of the literature in this field (see Chapter 1). Rhodium-chiral phosphine systems have attracted much attention in the past twenty years. The high degree of enantioselectivity achieved using these catalysts (up to 100% e.e.) and their easy synthetic accessibility have played an important part in their development. Work on chiral diphosphine complexes of other transition metals which also exhibit catalytic activity, however, has been very limited. Over the years, ruthenium has developed a rich coordination and organometallic chemistry.1- 2 The literature on the synthesis, reactivity, properties and catalytic applications of tertiary phosphine complexes of ruthenium is extensive.1-5 The ruthenium(II) hydrido phosphine complex RuHCl(PPh3)3 surpasses, or is comparable to, its well-known rhodium analogue, Wilkinson's catalyst RhCl(PPh3)3, in its activity for die hydrogenation of terminal alkenes.6-8 In contrast with the chemistry of diphosphine analogues of the Wilkinson catalyst, however, the chemistry of chelating phosphine analogues of the ruthenium complex is much less established. 74 Since the early work on ruthenium(II) diphosphine complexes by Chatt and Hayter,9 a series of coordinatively saturated complexes of general formula RuX2(P-P)2 and RuXY(P-P)2 containing an extensive array of diphosphines (P-P) has been prepared.1' ^0-12 x and Y represent anionic ligands such as halides, pseudohalides, hydrides, or o-bonded alkyl or aryl groups; the complexes are largely of the trans geometry. A simple displacement of monodentate phosphines by bidentate phosphines from RunXY(PR3)3 precursors almost always yields the corresponding inherently stable six-coordinate complexes (Equation 3.1); even when only one equivalent of the diphosphine is used, -50% conversion to the bis(diphosphine) derivatives is noted. 1 3 , 1 4 RuXY(PR3)3 +2 P-P RuXY(P-P)2 + 3 PR3 (3.1) X and Y = anionic ligands PR3 = monodentate phosphine P-P = bidentate phosphine As a result, very few coordinatively unsaturated (C.N. <6) ruthenium-diphosphine compounds have been synthesised by this route. 1 3 - 1 6 Figure 3.1 summarises the five- coordinate Ru(U) complexes containing a bidentate phosphine ligand reported to date. Cl P _ p = DIOP 1 5 or Ph2P(CH2)nPPh2 n = 4, DPPB; 1 6 5, DPPN; 1 4 6, DPPH; 1 4 P—P = DIOP1 5 or DPPB 1 3 P = PPh3 Figure 3.1: Coordinatively unsaturated mthenium(II)-diphosphine complexes prepared by phosphine displacement reactions. 75 Coordinative unsaturation at some stage in a catalytic cycle is usually essential for a transition metal complex to be catalytically active.17 Previous work from this laboratory on Ru(II)-diphosphine complexes has clearly highlighted this unsaturation requirement. Mechanistic studies on the coordinatively saturated Ru(II)-hydride complex, rran5-RuHCl(DIOP)2, which was shown to catalyse asymmetric hydrogenation of prochiral alkenes under mild conditions, revealed that the active species contained only one DIOP per Ru(II) centre ["RuHCl(DIOP)"].18- 1 9 Recent studies by Ikariya and coworkers 2 0 on the asymmetric hydrogenation of prochiral alkenes using rra«5-RuHCl(BINAP)2 also point to "RuHCl(BINAP)", presumably produced in situ by phosphine dissociation, as the likely catalytically active species. Interestingly, RuHCl- (P-P)2 complexes containing several other diphosphines (P-P), notably CHIRAPHOS and Ph2P(CH2)nPPh2 (n = 1-3), show little alkene hydrogenation activity,15- 2 1 perhaps because the diphosphines are bound too strongly to undergo dissociation to the supposed catalytically active "Run(P-P)" species. Direct pathways to "RuX2(P-P)" moieties (X = halide, hydride) are desirable in view of these observations; such catalysts would be analogous to the well-established Rh^P-P) systems.22- 2 3 A major portion of this thesis deals with ways of accessing such "Run(P-P)" species for the purpose of conducting an in-depth kinetic and mechanistic study into their catalytic behaviour. This chapter describes preparation of the dichloro species "RuCl2(P-P)". Their role in activation of dihydrogen and the subsequent formation of hydridochloro complexes of the stoichiometry "[RuHCl(P-P)]" are discussed in Chapter 5. 76 3.2 Synthesis and Characterisation of [RuCl2(P-P)k Complexes - A Brief Review The monodentate phosphine analogues of "RuCl2(P-P)" complexes can be conveniently prepared as the dimeric [RuCl2(PR3)2l2 species by reduction of ruthenium(III) precursors such as RuCl3(PR3)2 2 4 , 2 5 Attempts by Dr. Thorburn, previously of this laboratory, to prepare RuCl3(P-P) complexes by phosphine displacement from RuCl3(PR3>2 precursors led to the discovery of the formally mixed- valence dinuclear R u 2 n > 1 1 1 compounds of the type [(P-P)ClRu(u-Cl)3RuCl(P-P)] (Equation 3.2). Several such compounds were isolated (Equation 3.2) and characterised by various spectroscopic and analytical techniques.26-27 Thorburn's work which forms the basis of the present study is summarised in this section. 2 Ru 2Cl 5(P-P) 2 + 0=PR3 hexane, reflux 4 RuCl3(PR3)2 + 4 P-P ^ + (3.2) trace H 2 0 _ „ T T^, 2 7 PR3 + 2 HCl R = phenyl, p-tolyl P-P = DPPP, DPPB, DIOP, CHIRAPHOS, NORPHOS The X-ray diffraction analysis of the mixed-valence (S,S)-CHIRAPHOS complex showed the complex to be a highly symmetric trichloro-bridged species with irregular octahedral geometry about each ruthenium centre (Figure 3.2).26>27 P—P = (5,5)-CHIRAPHOS Figure 3.2: Geometry of Ru2Cl5(CHIRAPHOS)2. 77 Reduction of the Ru2Cl5(P-P)2 complexes with H2 in the presence of an appropriate base then afforded the target "Run(P-P)" compounds as dichloro-bridged dimers (Figure 3.3).27> 2 8 The preparative chemistry leading to the synthesis of the R U 2 I I , II diphosphine complexes, [RuCl(P-P)(p.-Cl)]2, starting from RUCI33H2O is summarised in Scheme 3-1; complexes containing DPPP, DPPB, CHIRAPHOS and DIOP were isolated and characterised. However, Thorburn noted that while the CHIRAPHOS complexes were successfully prepared by this route, similar complexes containing the nearest nonchiral analogue of CHIRAPHOS (viz. Ru2Cls(DPPE)2 and consequently Ru2Cl4(DPPE)2, DPPE = PPh2CH2CH2PPh2) could not be synthesised.26.28 This was somewhat surprising because like CHIRAPHOS, DPPE forms a five-membered chelate ring on binding to a metal centre; DPPE differs from CHIRAPHOS only in having hydrogens in place of the methyl groups on the CHIRAPHOS backbone. DMA RuCl 3.3H 20 + 2PR 3 »• RuCl3(PR3)2(DMA).DMA solvate 24 h, 25 °C 50-60% DMA = MA'-dimethylacetamide R = phenyl or p-tolyl P-P (1 eq./Rura) hexanes, reflux 24 h 1 atm H 2 , 16 h, 25 °C [RuCl(P-P)(u-Cl)]2 - [(P-P)ClRu(u-Cl)3RuCl(P-P)] 40-80% Base.H+Cr Base 45-80% Base = DMA for P-P = DPPP and DPPB Base = polyvinylpyridine for P-P = CHIRAPHOS and DIOP Scheme 3-1: Synthetic route to dinuclear ruthenium complexes containing only one chelating phosphine per Ru centre. 78 Molecular weight measurements in solution (Signer method 2 9) on the CHIRAPHOS derivative indicated a dimeric structure for the "RuCl2(P-P)" species; the phosphorus NMR spectroscopic observations (see below) supported the dimeric formulation [RuCl2(P-P)]2. which consists of two five-coordinate ruthenium(U) centres in square pyramidal geometry with two edge-bridging chlorides (Figure 3.3). 2 7 , 2 8 A similar dichloro-bridged structure has been previously proposed for dimeric ruthenium(II) complexes containing monodentate phosphines such as PPh 3 and P(p-tolyl) 3 . 4 ' 2 4 ' 2 5 > 3 0 Phosphines provide an excellent NMR spectroscopic handle on the dimeric [RuCl(P-P)(u-Cl)]2 complexes. The 3 1 P{ 1 H} NMR spectra (32.4 MHz, CD 2C1 2) of the nonchiral DPPP and DPPB derivatives and the chiral DIOP complex consisted of a single AB pattern while the CHIRAPHOS dimer showed two independent AB quartets of equal integrated intensity. The single AB pattern observed for the DPPP and DPPB species is consistent with the dimeric formulation (Figure 3.3) in which PA(RU j) is chemically and magnetically equivalent to PA(RU 2 ), similarly for PB, but PA is not equivalent to PB- Chirality in the CHIRAPHOS backbone renders PA(RU !) and PA(RU 2) inequivalent thus giving rise to two independent AB systems. The chiral [RuCl(DIOP)(|i-Cl)]2 species, however, exhibited only one AB pattern, instead of the two expected by analogy with the CHIRAPHOS complex; this was suggested to be the result of coincidental degeneracy. A P-P = DPPP, DPPB, DIOP, CHIRAPHOS Figure 3.3: Suggested geometry for [RuCl2(P-P)]2 complexes. 79 The 3 1P{ !H} NMR spectroscopic data (121.42 MHz) for [RuCl(P-P)(u-Cl)]2 complexes including the ones prepared during the present study are listed in Table 3.3 (Section 3.3.2). These Ru(II) complexes containing a single chelating phosphine per ruthenium did indeed prove to be efficient catalysts for the hydrogenation of a number of alkenes at 1 atm hydrogen pressure and 20-70 °C.27> 2 8 Of particular interest, several functionalised prochiral alkenes were hydrogenated enantioselectively using as catalyst precursors [RuCl2(P-P)]2 complexes containing chiral phosphines. For example, the 5,5- CHIRAPHOS complex catalysed the reduction of (Z)-a-acetamidocinnamic acid to the (5)- product with 97% e.e. (30 °C, 1 atm H2) in TVA-dimethylacetamide (DMA) solvent.27-28 Surprisingly, no ruthenium hydrides were observed by J H NMR spectroscopy at the end of the catalytic runs. Finally, Thorburn noted that in the presence of coordinating solvents such as acetone or DMA, the dichloro-bridged [RuCl(P-P)(u.-Cl)]2 complexes showed a great propensity to form solvent-coordinated dinuclear species [Ru2Cl4(P-P)2(solvent)] (Equation 3.3).27 On the basis of a detailed NMR study, the acetone and the DMA adducts were assigned a trichloro-bridged dinuclear geometry as shown in Scheme 3-II. As will be discussed in later sections, formation of such complexes of the type [Ru2Cl4(P-P)2(L)], where L is an incoming ligand, constitutes a prime mode of reactivity for the dichloro- bridged dimers. solvent [RuCl(P-P)(u-Cl)]2 , [Ru2Cl4(P-P)2(solvent)3 (3.3) solvent = acetone or DMA 80 Gl- .v^Cl'/- Ru ^ c i ^ 2 ^ c i / P ini''"^;Ru ^"">i i ; iP/ a- :RU^"" . i i ; |P> ^ c i ,P A L = a coordinating ligand Scheme 3-JJ: Formation of trichloro-bridged species from [RuCl(P-P)((X-Cl)]2 in the presence of a coordinating ligand. 3.3 Present Work The synthetic strategy used for the preparation of [RuCl(P-P)(p>Cl)]2 complexes, as elucidated in Section 3.2, has been extended to include more diphosphines; the ligands used are shown in Figure 3.4. Ph2P(CH2)nPPh2 n = 3,DPPP; 4, DPPB; 5, DPPN; 6, DPPH Ar = phenyl, DPPCP; cyclohexyl, DPCYCP PhCH 2 H» Et—N I PhoP o PPh, PHENOP Me H4^p p^ H '\*_ P P h 2 Me BDPP DIOP Me, PPh2 h¥ H'yl^ Me' P P h 2 CHIRAPHOS BINAP Figure 3.4: Diphosphines used in the preparation of Ru-(P-P) complexes. 81 3.3.1 Ru2Cl5(P-Ph Complexes Refiuxing a hexane suspension of RuCl3(PR3)2 (R = phenyl or p-tolyl) with equimolar amounts of the appropriate diphosphines affords the corresponding formally mixed valence dinuclear complexes, Ru2Cls(P-P)2, as air-stable red-brown or yellow- brown powders. In addition to the complexes 1-4 reported by Thorburn,26- 2 7 respectively containing DPPP, DPPB, RJi-DlOP and 5,5-CHIRAPHOS, new analogous Ru2Cl5(P-P)2 complexes incorporating the diphosphines DPPN (5), DPPH (6), rac- DPPCP (7), rac-DPCYCP (8), 5,5-BDPP (9), R- and 5-BINAP (10, 11), and the aminophosphinephosphinite ligand 5-PHENOP (12), have been prepared. Details of their synthesis and characterisation (elemental analysis) are given in Section 2.5.4. The very low solubility, in dichloromethane and most other common organic solvents, of the Ru2Cls(P-P)2 complexes 6 and 9 containing the diphosphines DPPH and BDPP, respectively, posed difficulties during recrystallisation/reprecipitation procedures. Relatively large volumes of CH2CI2 had to be used and the products obtained were often analytically impure. The low solubility perhaps results from the increased alkyl chain length of the phosphine backbone. The magnetic susceptibilities of the mixed-valence complexes were determined at 20 °C by the Evans' method31 in CDCI3 solutions containing ~2% (v/v) r-butanol. The solution magnetic moments, û ff, for the complexes 2, 5, 7,10,11 and 12, containing DPPB, DPPN, rac-DPPCP, R- and 5-BINAP and 5-PHENOP, respectively, are listed below (Table 3.1). The observed u.eff values, which range from 1.8-2.2 B.M., are consistent with the presence of one unpaired electron per molecule (uspin only = 1-73 B.M.).32- 3 3 The limited solubility of complexes 6, 8 and 9 prevented reliable solution magnetic susceptibility measurements. The U^ff values for the complexes 3 (1.78 B.M.) and 4 (1.95 B.M.) have been determined previously.27 82 Table 3.1: Magnetic Moment Data for Ru2Cl5(P-P)2 Complexes (CDCI3, 20 °C). Ru2Cl5(P-P)2 Complex Solution peff, B.M. Ru2Cl5(DPPB)2) 2 2.05 Ru2Cl5(DPPN)2,5 2.20 Ru2Cl5(rac-DPPCP)2) 7 2.03 Ru2Cl5(/?-BINAP)2,10 1.82 Ru2Cl5(S-BINAP)2,11 1.90 Ru2Cl5(S-PrIENOP)2,12 2.16 The UV-visible spectra of the mixed valence Ru2Cls(P-P)2 compounds in CH2CI2 solution are shown in Figure 3.5 and the values of m̂ax> v m a x and e are given in Table 3.2. The DPPN, /?-BINAP, 5-BINAP, and 5-PHENOP derivatives exhibit spectral features similar to those reported for the analogous complexes containing DPPP, DPPB, CHIRAPHOS, and DIOP ligands (1-4; X m a x -370, 450, and 520 nm with e values of ca. 4000, 2500, 1500 M _ 1 cm - 1 , respectively).26- 2 7 Thorburn has discussed the electronic spectra (UV-visible and near-IR) of Ru2Cl5(P-P)2 complexes 1-4 in detail.2 6-2 7 Because of the analogous nature of the new complexes 5-12, these aspects will not be dealt with in this thesis beyond noting their similarity. Some variations in intensities and absorption maxima are observed with changing phosphines. The DMA solutions of Ru2Cl5(P-P)2 complexes absorb half a mole equivalent of H2 per Ru, at 1 atm of H2 and 30 °C, in keeping with the behaviour noted previously for the analogous complexes 1-4. 2 6 - 2 8 The H2-uptake plots for the complexes 5, 7, 8,10, 11, and 12 are shown in Figure 3.6. 83 300 500 700 900 nm Figure 3.5: Visible spectra of the Ru2Cl5(P-P)2 complexes in CH2C!2 at 25 °C. P-P = (a) DPPN, 5; (b) rac-DPPCP, 7; (c) rac-DPCYCP, 8; (d) fi-BINAP, 10; and (e) 5-PHENOP, 12. [Ru2l = 2.0 ± 0.1 x IO - 3 M for the complexes 5, 7, 10, and 12; 0.80 x 10~3 M for 8. The spectrum for the 5-BINAP derivative 11 is essentially identical (not shown) to that observed for the /?-BINAP analogue. Table 3.2: Visible Spectroscopic Data for the Ru2Cl5(P-P)2 Complexes. Ru2Cl5(P-P)2 Complex3 P-P = Solvent X m a x . nm e, M _ 1 cm - 1 DPPN, 5 CH 2C1 2 370 4415 420 3810 540 1170 rac-DPPCP, 7 CH 2C1 2 380 2550 515 2210 659 425 rac-DPCYCP, 8 CH2CI2 350 5225 430 2840 525 3590 rt-BINAP, 10 CH 2C1 2 405 5215 660 1135 5-BINAP, 11 CH2CI2 405 4978 660 815 S-PHENOP, 12 CH 2C1 2 340 4950 440 1485 3 [Ru2] = 2.0 ± 0.1 x IO-3 M for complexes 5, 7, 10,11, and 12; [Ru2] = 8.0 x 10 - 4 M for complex 8. The corresponding UV-visible spectra are shown in Figure 3.5. 85 1 0 0 0 0 T i m e , s Figure 3.6: H2-uptake plots for Ru2Cls(P-P)2 complexes in DMA at 30 °C under 1 atm H2 pressure; [RU2] = 4.0 ± 0.1 x 10~3 M. P-P = (a) DPPN, 5; (b) rac-DPPCP, 7; (c) rac-DPCYCP, 8; (d) fl-BINAP, 10; and (e) 5-PHENOP, 12. The uptake plot for the 5-BINAP derivative 11 is essentially identical to that shown for 10. The final stoichiometry of the H2-reaction is consistent with reduction of the mixed- valence complexes to Ru2n , n species in accordance with Equation S A 2 6 - 2 8 Ru2Cl5(P-P)2 + 0.5 H 2 - Ru2Cl4(P-P)2 + H + + Cl" (3.4) 3.3.2 [RuCl2(P-P)]2 Complexes The reaction of Ru2Cls(P-P)2 complexes with hydrogen in DMA generates the ionic species [Ru2Cl5(P-P)2] _ DMAH + 2 6 - 2 8 from which the corresponding neutral dimeric Ru(II) complexes [RuCl(P-P)(u.-Cl)J2 are isolated (P-P = DPPP, 13;27> 2 8 DPPB, 14;27. 2 8 R.R-DIOP, 15;27> 2 8 5,5-CHIRAPHOS, 16;27« 2 8 DPPN, 17; R- BINAP, 18; 5-BINAP, 19; see Section 2.5.4). Alternatively, the dimeric complexes can be obtained by the H2-reduction of Ru2Cls(P-P)2 in benzene or toluene suspension using polyvinylpyridine (PVP) as the base. The insoluble PVP and its HCl salt are easily removed by filtration, and the desired [RuCl(P-P)((i-Cl)]2 species isolated from the filtrate (Section 2.5.5). The complexes are air-sensitive in solution, and hygroscopic in the solid state. The 3 1P{ iH} NMR data for the [RuCl(P-P)(u-Cl)]2 complexes 13-19 are listed in Table 3.3. The data for the new complexes (P-P = DPPN, 17; fl-BINAP, 18; 5-BINAP, 19) are consistent with a dichloro-bridged dimeric structure suggested previously for the DPPP, DPPB, DIOP, and CHIRAPHOS analogues (13-16, respectively; see Section 3.2, Figure 3.3)27> 2 8 The 3 1P{ lH} NMR spectrum of [RuCl2(5-BINAP)]2,19, in Q5D6 solution shows two AB quartets of equal integral intensity (5A = 75.6, 8B = 5.6, 2 /AB = 40.7 Hz; 8c = 58.7, 8D = 58.1, 27CD = 42.5 Hz; see Figure 3.7 and Table 3.3). The corresponding spectrum of the /?-BINAP analogue 18 is essentially identical. The same resonances are also observed in the 3 1 P spectrum of the related mixed-phosphine derivative 87 i I j i i i i I i i i i j~7TT i | i i i i | i i i i I'Trrryi i i i i i i I T T T T T T T T I i i j i i i T j T T T T y t T T T T T T T T j T m | i i i i jn"T~T~pn~r~r~| 90 80 70 60 50 40 30 20 10 PPM 0 Figure 3.7: 31P{ 'H} NMR spectrum (121.42 MHz, 20 X ) of [RuCl 2 (S-BINAP)l2,19, in C6D 6 . Table 3.3: 31p{ lR) NMR Data (121.42 MHz, 20 'Q for [RuCl(P-P)(u-Cl)]2 Complexes. [RuCl(P-P)(u-Cl)]2 Complex Solvent Chemical Shifts, 8 (ppm) VpP, (Hz) P-P = DPPP, 13 Q>D6 8A = 59.0, 8B = 51.0 57.0 C D ^ 8 8A = 58.0, 8B = 50.5 57.4 DPPB,14 C6D6 8A = 64.0, 8B = 54.9 47.3 CD2CI2 8A = 62.0, 8B = 53.8 46.6 R.R-DIOP, 15 C6D 6 8A = 50.7, 8B = 47.5 46.1 CTJ^Cl^ 8A = 50.0, 8B = 47.1 46.4 5,5-CHIRAPHOS, 16 C6D 6 8A = 88.0, 8B = 78.3 38.2 8C = 87.0, 8D = 75.7 39.2 C D 2 a 2 a 8A = 87.8, 8B = 77.9 39.1 8C = 87.1, 8D = 77.9 39.1 DPPN,17 C5D6 8A = 55.8, 8B = 42.3 35.0 fl-BINAP, 18 C6D 6 8A = 75.8, 8B = = 5.8 40.6 8C = 58.6, 8D = 58.2 43.2 5-BINAP, 19 8A = 75.6, 8B =  5.6 40.7 8C = 58.7, 8D = 58.1 42.5 5,5-BDPP, 20 C5D6 8A = 64.5, 8B = 52.9 __b a Spectrum recorded at 32.4 MHz; data taken from Ref. 26. b Broad signals at ambient temperature with unresolved coupling. 89 R u C l 2 ( B I N A P ) ( P P h 3 ) , 21, which, like the analogous D P P B and D I O P complexes, dissociates the PPh.3 ligand in solution to form the dimeric [RuCl2(BINAP)]2 species (see Equation 3.5 in Section 3.4.1, and Chapter 4, Section 4.6). The resonances at 75.6 and 5.6 ppm are assigned to an apical/basal (PA/PB) pair of phosphorus nuclei by comparison with the reported chemical shifts and chemical shift differences observed for other square pyramidal ruthenium complexes containing similar apical/basal pairs of phosphines.13-30 The remaining two resonances are assigned to the B I N A P ligand which occupies two cis positions in the basal plane. Thus, based on the 3 1 P N M R data, the B I N A P complexes 18 and 19 are assigned a slightly different geometry (Figure 3.8) compared to that proposed for other dichloro-bridged complexes (cf. Figure 3.3) . a P-P =R- orS-BINAP Figure 3.8: Suggested geometry of [RuCl(BINAP)(u-Cl)]2. The additional peaks in the spectrum started growing in as the FED acquisition proceeded, and are due to unidentified impurities. In fact, a 3 1 P NMR spectrum of the same solution recorded after 48 h showed a large number of new peaks, with a corresponding decrease in the intensity of signals assigned to 19 (or 18). The high reactivity of these complexes is perhaps consistent with the presence of two coordinatively unsaturated Ru centres as shown in the suggested dichloro-bridged dimeric structure (Figure 3 .8) . Ikariya et al. have reported the synthesis of the related 90 [Ru2CU(BINAP)2(NEt3)] species by a different route ([RuCl2(COD)]n + 1 equiv BINAP, NEt3).33 The 5,5-BDPP analogue (20) was obtained in very low yields (<10%, see Section 2.5.5.8 for details) and only after leaving a suspension of the mixed-valence precursor under H 2 in the presence of PVP base for over two months. On the other hand, the complex Ru2Cls(DPPH)2 failed to undergo reduction by H 2 to the corresponding R u 2 n » n species (Equation 3.4). Relative insolubility of the respective precursor complexes in toluene (in fact, in most organic solvents) appears to have hampered the reductions. The difficulties encountered in the synthesis of [RuCl(BDPP)(|i-Cl)]2 via reduction of Ru2Cl5(BDPP)2, and also the failure to obtain the DPPH analogue by the same route, led us to investigate other ways of getting to "Ru(n)-(P-P)" species. 3.4 Other Synthetic Routes to "Run(P-P)" Complexes One of the objectives of the current work was to develop alternative syntheses of "Run(P-P)" species (for the reasons stated above) while continuing to utilise the strategy outlined in Scheme 3-1. This part of the chapter describes the synthesis of dinuclear Ru 2 n« 1 1 complexes using routes other than that outlined in Scheme 3-1. The choice of ruthenium starting material seems to play a crucial role in determining the results of the phosphine displacement reactions. For example, while the reaction in hexanes of one equivalent of a diphosphine P-P with the ruthenium(III) precursor RuCl3(PPh3)2(DMA) gave the mixed valence Ru2Cls(P-P)2 complexes26'27 (see Section 3.3.1), that with the ruthenium(II) species [RuCl2(PPh3)2]2 generally yielded a mixture of the unreacted precursor, free PPh3 and the tra«s-RuCl2(P-P)2 complexes (P-P = DPPM, DPPE, DPPP, CHIRAPHOS and BDPP). The frans-RuCl2(P-P)2 complexes were easily identified by comparison of their respective characteristic 31p resonances, which appear as 91 singlets, with those of the authentic samples.§ Reaction of the Ru(U) precursor with DPPB or D IOP resulted in an essentially complete conversion to the known mixed-phosphine species RuCl2(P-P)(PPh3) 1 3> 1 5 which were characterised by N M R spectroscopy and elemental analysis. Of particular note, reaction of the Ru(III) complex RuCl3(PPh3)2(DMA)DMA solvate (0.1 g, 0.1 mmol) with one equivalent of DPPB in DMA solution instead of in hexanes afforded RuCl3(DPPB)(DMA), 22, as the initial product (reaction time 16-24 h), as characterised by elemental analysis and IR spectroscopy.^ Interestingly, the Ru(II) mixed-phosphine complex RuCl2(DPPB)(PPh3), 23, (see Section 2.5.2.1) was obtained when the reaction mixture was left stirring for longer periods (4 days). It should be remembered that the mixed-valence Ru2(II, III) dimer, Ru2Cl5(DPPB)2, is the product obtained in the hexanes reaction (Section 3.3.1). The relatively high solubility in D M A of the initially formed Ru(III) product, RuC l3 (DPPB ) (DMA) , perhaps facilitates further reduction to the corresponding Ru2(0, II) complex; triphenylphosphine in the presence of trace water is likely the reducing agent. The DPPB-derivative [RuClQDPPB)(u-Cl)]2,14, thus formed could then react with free PPh3 in the reaction mixture to generate RuCl2(DPPB)(PPh3). Addition of PPh3 to a solution of 14 indeed results in the immediate formation of RuCl2(DPPB) (PPh3). Conversely, the essentially zero solubility of the Ru2Cl5(P-P)2 complexes in hexanes perhaps slows down or even prevents a Ru2(H, III) to Ru2(II, II) reduction and therefore any further reaction. § 3 1P{ JH) NMR data for rraw-RuCl2(P-P)2 complexes; P-P, 8 ppm in CDCI3 at 20 °C: DPPM, -8.2; 1 3 DPPE, 44.5;13 DPPP, -5.0; 1 3 5,5-CHIRAPHOS, 46.9;21 5,5-BDPP, 8.7 (present work, see Section 2.5.8.4). 1  Anal. Calcd for RuCl3(DPPB)(DMA), C32H37NOCI3P2RU: C, 53.31; H, 5.17; N, 1.94. Found: C, 53.2; H, 5.3; N, 2.2. IR (Nujol, cm-1): v ( C 0) at 1602 (m, coordinated DMA). 92 Two approaches were taken in search of new synthetic routes to "Run(P-P)" complexes: (a) modification within precursor complexes, such as RuCl2(DPPB)(PPh3), which already contain a single diphosphine ligand, and (b) reactions of non-phosphine containing starting materials, such as cw-RuCl2(DMSO)4, with one equivalent of diphosphine ligand per Ru. 3.4.1 Reactions of RuCl2(DPPB)(PPh3), ZI The choice of the Ru(II) mixed-phosphine complex, RuCl2(DPPB)(PPh3), as a starting material for preparation of the dinuclear RuH-DPPB complex appeared particularly attractive, because the bright green precursor compound is known to dissociate in solution into free PPh3 and the target dinuclear complex, [RuCl(DPPB)(u-Cl)]2,14, in accordance with Equation 3.5.13 A more detailed description of the mixed-phosphine complex is provided in the next chapter (Section 4.2), while its reactions leading to the formation of dinuclear species containing the "RuCl2(DPPB)" unit are presented in this chapter. (3.5) P = PPh3; P—P = DPPB (or DIOP) It should be noted that, like the nonchiral DPPB ligand, the chiral phosphines DIOP and BINAP also form a seven-membered ring upon coordination to the metal. In this respect, it is significant that both DPPB and DIOP form a mixed phosphine complex and a diphosphine-bridged species (RuCl2(P-P)(PPh3) and Ru2Cl4(P-P)3, respectively, see 93 Figure 3.1). The DPPB and the DIOP analogues show identical solution behaviour (cf. Equation 3.5)13-15>16 and the same reactivity with H 2 and CO (Equations 3.6-3.8).15'16 Ru2Cl4(P-P)3 + H 2 RuHCl(P-P)2 + RuCl2(P-P) + HCl (3.6) Ru2Cl4(P-P)3 + 2H 2 P-P 2RuHCl(P-P)2 + 2 HCl (3.7) Ru2Cl4(P-P)3 + 2 CO (solid state) Ru2Cl4(P-P)3(CO)2 (3.8) P-P = DPPB or DIOP The chelate size of diphosphines within a metal complex has been suggested to play an important role in determining the reactivity properties of the complex,13'34 with ligands forming chelates of the same size often showing similar reactivity and selectivity in catalytic hydrogenation reactions. It is reasonable therefore to assume that the chemistry involving the DPPB (or DIOP) ligand may be extended to complexes containing the BINAP ligand. Indeed, the mixed-phosphine complex RuCl2(BINAP)(PPh3) has been synthesised during the present work (Chapter 4, Section 4.6). 3.4.2 Reactions of Non-phosphine Precursors with One Equivalent of P-P Several other ruthenium compounds were investigated as possible precursors to "RuCl2(P-P)" species. The reactions summarised in Equations 3.9-3.12 show the expected products. Reactions of RUCI3 and [RuCl2(nbd)]n with diphosphines (Equations 3.9 and 3.12) were unsuccessful and gave complex mixtures of products; however, reactions of RuCl2(DMSO)4 and [RuCl2(p-cymene)]2 (Equations 3.10 and 3.11) did produce isolable ruthenium-diphosphine complexes of the desired 1:1 stoichiometry, the results being influenced by the choice of the diphosphine ligand (Sections 3.7 and 3.8). 94 RuCl 3.xH 20 + P-P RuCl3(P-P) (3.9) RuCl2(DMSO)4 + P-P RuCl2(DMSO)y(P-P), y = 1 ) 2 (3.10) [RuCl2(arene)]2 + P-P [RuCl(arene)(P-P)]Cl (3.11) [RuCl2(diene)]n + P-P RuCl2(diene)(P-P) (3.12) arene = p-cymene diene = 2,5-norbomadiene 3.5 Attempted Removal of PPh3 from RuCl2(DPPB)(PPh 3), 21: Reaction of RuCI2(DPPB)(PPh 3) with Methyl Iodide The use of a "phosphine sponge" to remove a triphenylphosphine dissociated from RuCl2(DPPB)(PPh3) in solution could (Equation 3.5), in principle, yield [RuCl(DPPB)(u- Cl)]2- Such a "phosphine sponge" would have to form a stable, easily separable adduct with the dissociated phosphine. Alkyl halides, such as methyl iodide, are known to react with tertiary phosphines, R 3 P , to give quaternary phosphonium salts of the type R3PMe +I -. 3 5 These salts are generally insoluble in aromatic solvents and therefore easily removed by filtration. In preliminary experiments, reactions of RuCl2(PPh3)3 and RuHCl(PPh3)3 (0.10 g, 0.1 mmol) with ca. 10-fold excess of CH3I in benzene solution (5 mL) gave encouraging results, wherein quantitative formation (isolated yield) of only one equivalent of Ph3P(CH3)+I_ was observed (Equation 3.13). The white precipitate was identified as Ph3P(CH3)+I- by comparing its 3 1 P chemical shift (21.2 ppm, s, CH2CI2 solution-C6D6 lock, 20 °C) with that of an authentic sample. benzene, 20 °C (3.13) P h 3 P ( C H 3 ) + r 95 But surprisingly, the dark brown ruthenium products that were isolated from the reactions of the dichloro and the hydridochloro derivatives with Mel exhibited very similar 3 1 P NMR spectra. Two independent sets of 3 1 P NMR AB quartet patterns were observed, each likely indicative of a different, possibly dimeric species (8A = 56.9, 8B = 46.9 ppm, 2 JAB = 31.5 Hz; 8C = 47.8, 8D = 42.2 ppm, 2 J C D = 23.5 Hz). Presumably, the Ru(II) precursors, or the "RuCl2(PPh3)2" and "RuHCl(PPh3)2" fragments resulting from the PPh3-abstraction (Equation 3.13) react further with the excess CH3I to give the similar set of products which remain uncharacterised. The reaction of RuCl2(DPPB)(PPh3), 23 (0.10 g, 0.12 mmol), with - 1 0 times excess methyl iodide was carried out in benzene solution under argon atmosphere. The initially green suspension turned dark brown over - 2 4 h. The white precipitate of P h 3 P ( C H 3 ) + I - , tinted slightly pink presumably because of I2 formed from CH3I decomposition, was separated by filtration (65% isolated yield). The 3 1 P NMR spectrum (C6D6, 20 °C) of the brown solid obtained by work-up of the filtrate did exhibit an AB quartet pattern (5 A = 71.1, 8B = 56.6 ppm, 2JAB = 40.0 Hz) indicating the presence of a possibly dimeric complex. However, these 3 1 P NMR parameters are quite different from the shifts for the known [RuCl(DPPB)(|i-Cl)]2 complex (8A = 64.0, 8B = 54.9 ppm, 2 - / A B - 47.3 Hz). Again, the precursor complex 2 3 , or the chloro-bridged dimer [RuCl(DPPB)(u-Cl)]2 formed in situ by PPh3-dissociation/abstraction from 23 (see Equations 3.5 and 3.13) likely reacts with the excess CH3I to give the observed, as yet unidentified product. Of particular note, the reaction of pure [RuCl(DPPB)(u-Cl)]2.14, with -100-fold excess of methyl iodide in CDCI3 solution led to the in situ partial formation of a different product, as monitored by phosphorus NMR spectroscopy (8A = 52.6, 8B = 51.7 ppm, 27AB = 43.4 Hz; 8c = 48.6, 8D = 41.8 ppm, 2 / C D = 36.7 Hz); the new complex is identified as a trichloro-bridged dinuclear ruthenium complex with a coordinated methyl iodide (see below, and Section 3.6.5 for details). 96 3.6 Synthesis of Trichloro-bridged Diruthenium(II,II) Complexes, [(L)(DPPB)Ru(u-Cl)3RuCl(DPPB)] As mentioned in Section 3.2, the dimeric [RuCl(P-P)(|i-Q)]2 complexes readily form solvent-coordinated adducts in coordinating solvents (Equation 3.3). In fact, the acetone adducts (P-P = DPPB, 14a; CHIRAPHOS, 16a) have been previously isolated and characterised by elemental analysis and IR spectroscopy (V(c=0)» cm - 1, for coordinated acetone: 1645,14a; 1624,16a). 2 7» 2 8 Also, solutions of the acetone adducts were found to be relatively more stable to air-oxidation on account of the saturated coordination sphere about the ruthenium centres; however, the catalytic hydrogenation activity of 14a and 16a remained essentially same as that of the corresponding [RuCl(DPPB)(u-Cl)]2 complexes. Reactions of RuCl2(DPPB)(PPh3), 23, with a variety of ligands were investigated with the objective of trapping as a ligand adduct the [RuCl(DPPB)(u-Cl)]2 species formed by PPh3-dissociation (Equation 3.5). This would provide a convenient shorter route into the dimer chemistry. The synthesis and characterisation of some trichloro-bridged [(L)(DPPB)Ru((i-Cl)3RuCl(DPPB)] complexes are described in Sections 3.6.1 through 3.6.5, while the 3 1 P NMR spectra of these compounds are discussed in Section 3.7. 3.6.1 Synthesis of [(Amine)(DPPB)Ru(u-Cl)3RuCI(DPPB)], (Amine = NEt 3,14b; NHBu2,14cJ In recent years Noyori, Takaya and coworkers have reported on the enantioselective hydrogenation catalysed by Ru(II)-BINAP complexes.36- 3 7 They have noted that the dinuclear complex Ru2CU(BINAP)2(NEt3) is a highly effective catalyst precursor for the asymmetric reduction of functionalised substrates including ketones.38-39 The DPPB analogue, Ru2CU(DPPB)2(NEt3), 14b, can be easily obtained by addition of triethylamine to a solution of [RuCl(DPPB)(u.-Cl)]2,14. Moreover, the amine 97 appears to act as a base during an overall heterolytic activation of H2, and help generate a Ru(II)-hydridochloride species (see Chapter 5). Stirring a benzene or toluene solution of the mixed-phosphine complex RuCl2(DPPB)(PPh3), 23, with ~20-fold excess of triethylamine precipitates an orange solid. Filtration, followed by a washing of the solid with ethanol and hexanes to remove PPI13 and excess NEt3, yields the analytically pure Ru2Cl4(DPPB)2(NEt3>, 14b (cf. Scheme 3-U). The methylene and the methyl *H NMR signals of the free NEt3 ligand at 2.39 (q, 6H) and 0.95 (t, 9H) ppm, respectively, are shifted on coordination to 3.20 (broad m, 6H) and 1.08 (broad m, 9H) ppm. Reaction of RuCl2(DPPB)(PPh3), 23, with tri-n-butylamine, in benzene:hexane (1:4) under reflux conditions, similarly yielded an orange-brown amine adduct, 14c. Examination of the li\ NMR spectrum of this product Q?igure 3.9) revealed that the integral intensities for the amine protons, relative to those of the DPPB ligand protons, did not correspond to those expected for a bound N[(CH.2)3CH3]3. For example, the triplet at 0.95 ppm assigned to the methyl protons of the butyl group integrates to ~6H instead of the expected 9H; the product actually contains a coordinated di-n-butylamine ligand, and indeed the IR spectrum of the complex shows a band at 1571 cm - 1 (m) which is assigned to the N-H bending mode characteristic of secondary amines.40 This band is absent in the IR spectrum of the NEt3-analogue. Reactions of 14 or 23 with di-n-butylamine also yield Ru2Cl4(DPPB)2(NHBu2), 14c, as confirmed by NMR and IR spectroscopy and by elemental analysis. The 3 1 P NMR spectra of 14b and 14c in CDCI3 showed a single resonance at 48.3 and 48.2 ppm, respectively, from 30 to -60 °C (see Section 3.7 for details). Formation of NHBu2 from NBU3 in the presence of RuCl2(DPPB)(PPh3) was unexpected; the reaction amounts to an overall de-alkenylation of tributylamine. Such conversion of tertiary amines to the secondary and even primary amines, in the presence of transition metal complexes, has been reported previously.41-42 98 O. OZ 'ZHW 00£) £ D C O u ! 'TO 4(adda)lDn^£(OTl)ny(adda)(znaHN) JO uirujoads HWN Hi 3 j n 3 H Wdd t 2 E ^ S 9 ^ 8 3.6.2 Synthesis of [(CO)(DPPB)Ru(^-Cl)3RuCI(DPPB)], J l d Direct reaction of the complexes 14 or 23 with CD yields an isomeric mixture of RuCl2(DPPB)(CO)2 complexes, and some monocarbonyl species 'RuCl2(DPPB)(CO)', and the observed stoichiometry of ~ 1.8 mole equivalents of CO per Ru (as determined by gas uptake measurements) for the carbonylation of 14 and 23 is consistent with this. The 3 1 P NMR spectrum of the off-white products shows a number of peaks in the 0-50 ppm region, while the infra-red spectrum of the same off-white solid reveals several bands in the 1900-2100 cm - 1 region assignable to terminal CO ligands. However, the dinuclear carbonyl complex of interest, [(CO)(DPPB)Ru(p--Cl)3RuCl(DPPB)], 14d, (see below), was successfully prepared by stoichiometric decarbonylation of aldehydes. The reaction of 14 with gaseous formaldehyde, acetaldehyde or benzaldehyde in dichloromethane solution, followed by work-up of the reaction mixture as described in Section 2.5.6.3, affords an orange-coloured complex which is identified as [(CO)(DPPB)Ru(|i-Cl)3RuCl(DPPB)], 14d, by IR and NMR spectroscopy, and elemental analysis (Section 2.5.6.3). The terminal CO stretch in the ER spectrum is observed at 1977 c m - 1 (s). The phosphorus NMR spectrum in C6D6 consists of two independent AB patterns (designated as AB and CD) centred at 53.55 (2/AB = 45.2 Hz) and 40.0 ppm (27CD = 29.6 Hz), respectively (see Table 3.6 and Section 3.7 for further details). Decarbonylation of organic carbonyl compounds, such as aldehydes and acid chlorides, by transition metal complexes is a well-known reaction;43-46 several ruthenium and rhodium phosphine complexes are known to effect stoichiometric decarbonylation of aldehydes under mild conditions. Of interest, the reaction of RuCl2(DPPB)(PPti3), 23, with Mo(CO)6 also yields the carbonyl adduct 14d by decarbonylation of the hexacarbonyl species. Varshavsky et al. have reported on decarbonylation of metal carbonyls by rhodium complexes,47-49 For example, the reaction of RhCl(PPh3)3 with the carbonyl complexes Mo(CO)6, W(CO)6, 100 Fe(C0)5, or Ni(CO)4 resulted in a rapid, partial decarbonylation to give phosphine- substituted metal carbonyls and [Rh(CO)2Cl]2 as outlined in Equation 3.14; a complete decarbonylation by [Rh(diene)Cl]2 complexes was noted in the absence of ligands (such as PPh3) capable of stabilizing partially decarbonylated species.47 Ruthenium phosphine complexes, however, were found to be much less efficient in decarbonylating other metal carbonyl species.49 M(CO)n + RhCl(PPh3)3 M(CO)n_!(PPh3) + M(CO)n_2(PPh3)2 (3.14) + 1/2 [Rh(CO)2Cl]2 The reaction of RuCl2(DPPB)(PPh3), 23, with Mo(CO)6 presumably parallels the reaction elucidated in Equation 3.14, the dinuclear CO adduct 14d being the ruthenium product. 3.6.3 Synthesis of [(DMS_0)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)], l£e. Addition of one equivalent of DPPB to a dichloromethane:acetone (1:1) solution of c/j--RuCl2(DMSO)4 causes a rapid change in the colour of the solution, the initially bright yellow solution turning bright orange. A small amount of a green precipitate (< 2%), that formed during the reaction, was identified as the known phosphine-bridged species [RuCl 2(DPPB)i.5] 2 (see Figure 3.1 and Section 2.5.1 l .l). 1 6 Dark red crystals of the DMSO adduct [(DMS0)(DPPB)Ru(u.-Cl)3Ru(Cl)(DPPB)], 14e, were isolated from a concentrated orange filtrate as a Et20/CFi2Cl2 solvate (0.67:0.33 per molecule, lU NMR spectral and X-ray crystallographic evidence, see below) by slow recrystallisation with diethyl ether at 0 °C. The intense IR absorption band at 1090 cm - 1 assigned to the S=0 stretch of the bound DMSO is within the range reported for an S-bonded sulphoxide ligand (1060-1130 cm - 1 ) in other ruthenium complexes;50 the S=0 stretch for an O-bonded 101 sulphoxide is observed generally in the range 920-980 cm - 1 . 5 0 For example, the S=0 stretches for the S-bonded DMSO of cw-RuCl2(DMSO)4 appear at 1125 and 1095 cm"1, while that for the O-bonded sulphoxide is observed at 925 cm - 1 . 5 1 - 5 2 Phosphorus NMR spectrum of 14e in C6D6 consists of two independent, equal intensity AB patterns (designated as AB and CD; see Section 3.7 and Table 3.6) centred at 52.1 (27AB = 43.8 Hz) and 35.3 ppm (VCD = 32.1 Hz), respectively. 3.6.4. Molecular Structure of [(DMS.O)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)] The single crystal X-ray diffraction study of the DMSO adduct 14e, carried out by Dr. S. J. Rettig of this department, reveals the complex to be the dinuclear trichloro- bridged species with the S-bonded dimethyl sulphoxide ligand as shown in Figure 3.10. The various structural parameters are given in the Appendix (A-2.2), and some selected bond lengths and bond angles are listed in Tables 3.4 and 3.5, respectively. The geometry about each ruthenium in 14e is irregular octahedral. The bond distances Ru(l)-S (2.244 A), S-O (1.474 A), and Ru(l)-Cl(3) (2.429 A) for the bridging chloride trans to DMSO, are comparable to those found in c/s-RuCl2(DMSO)4 (average 2.276, 1.485 and 2.435 A, respectively)53 and/ac-[RuCl30DMSO)3]-complexes (average 2.262, 1.477 and 2.426 A, respectively),54 which also contain S-bonded sulphoxides trans to a chloride ligand. The slight shortening of the Ru-S bond of 14e is likely because of the reduced trans influence of the bridging chloride as compared to that of a terminal Cl. While the respective Ru(l)-P(l, 2) and Ru(2)-P(3, 4) bond lengths of 2.305 and 2.26 A (average -2.28 A) are within normal range found for Ru(II) tertiary phosphine complexes,55-57 the difference between the two sets is indicative of the different environments about the Ru(II) centres. The Ru-Cl bond length for the bridging chlorides which are trans to phosphorus (average 2.493 A) is longer than the Ru(2)-Cl(l) distance 102 Figure 3.10: An ORTEP stereoview of [(DM£0)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)] showing the atom numbering scheme used. The thermal ellipsoids for non- hydrogen atoms are drawn at 50% probability. See Appendix A2.2 (p. 296) for a larger view. Table 3.4: Selected Bond Lengths (A) for [(DMSO)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)] with Estimated Standard Deviations in Parentheses. Bond Length (A) Bond Length (A) Ru(l>—Cl(l) 2.469(1) Ru(2>—Cl(l) 2.418(1) Ru(l)—Cl(2) 2.495(1) Ru(2)—Cl(2) 2.517(1) Ru(l)—Cl(3) 2.429(1) Ru(2)—Cl(3) 2.492(1) Ru(l)—S(l) 2.244(1) Ru(2)—Cl(4) 2.399(1) Ru(l)—P(l) 2.305(1) Ru(2)-P(3) 2.261(1) Ru(l)—P(2) 2.305(1) Ru(2)—P(4) 2.257(1) P(l)—O(l) 3.433(3) S(l)-C(9) 1.788(5) S(l)-0(1) 1.474(3) S(l)—C(10) 1.792(5) Ru(l)—Ru(2) 3.3542(4) 103 Table 3.5: Selected Bond Angles (deg) for [(DMSO)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)] with Estimated Standard Deviations in Parentheses. Bonds Angle (deg) Bonds Angle (deg) Cl(l)—Ru(l>—Cl(2) 78.25(3) Cl(l)—Ru(2)—Cl(2) 78.78(3) Cl(l)--Ru(l>—Cl(3) 78.46(3) Cl(l)—Ru(2)—Cl(3) 78.23(3) Cl(l>--Ru(l)—S(l) 91.86(4) Cl(l)—Ru(2)—Cl(4) 163.48(4) Cl(l)--Ru(l)-P(l) 172.23(4) Cl(l)—Ru(2>—P(3) 102.24(4) Cl(l)--Ru(l)-P(2) 93.62(4) Cl(l>-Ru(2)—P(4) 94.23(4) Cl(2)--Ru(l>—Cl(3) 80.80(3) Cl(2>—Ru(2)—Cl(4) 79.18(3) Cl(2)--Ru(l)—P(l) 94.73(4) Cl(2)—Ru(2>—Cl(4) 88.45(4) Cl(2)--Ru(l)-P(2) 169.35(4) Cl(2)—Ru(2>—P(3) 172.71(4) Cl(2)--Ru(l)—S(l) 91.94(4) Cl(2>—Ru(2>—P(4) 95.12(4) Cl(3)--Ru(l)—P(l) 97.29(4) Cl(3)—Ru(2>—P(3) 93.92(4) Cl(3)--Ru(l)—P(2) 90.90(4) Cl(3)—Ru(2)—P(4) 171.26(4) Cl(3)--Ru(l)—S(l) 168.87(4) Cl(3)—Ru(2)—Cl(4) 89.18(4) P(D- -Ru(l)—S(l) 91.68(4) Cl(4>—Ru(2)—P(3) 93.92(4) P(2)- -Ru(l>-S(l) 95.23(4) Cl(4)—Ru(2)—P(4) 89.13(4) P(D- -Ru(l)—P(2) 92.93(4) P(3)—Ru(2>—P(4) 92.00(4) Ru(l)--S(l)—0(1) 120.8(1) 0(1>-S(1)-C(9) 105.6(2) Ru(l> -S(l)—C(9) 112.6(2) O(l>-S(l>-C(10) 104.9(2) Ru(l)--S(l)—C(10) 112.7(2) C(9)—S(l>—C(10) 97.5(3) Ru(l)--Cl(l)—Ru(2) 86.69(3) Ru(l)—Cl(2)—Ru(2) 85.01(3) Ru(l)--Cl(3)—Ru(2) 85.93(3) 104 (2.418 A) where Cl(l) is trans to the terminal chloride Cl(4). The stronger trans influence of phosphine, compared to chloride, clearly results in a weaker and consequently longer bond. Two regular octahedra sharing one face have a bridging angle 0 of 70.5° (given by cos 0/2 = 2/3).57 In this complex the average bridging angle (Z Ru-Cl-Ru) is 85.54°, implying that the two Ru atoms are further apart than they would be in a regular cofacial bioctahedron. Indeed, the distance between the ruthenium centres (3.35 A) is well outside the range (2.28-2.95 A) usually observed for a Ru-Ru bond.25- 5 8 > 5 9 This is perhaps only the second crystal structure of a dinuclear Ru complex containing a chelating diphosphine, the first being the structure of the formally mixed valence Ru2(II,IH)-CHIRAPHOS derivative mentioned earlier (Section 3.2).26- 2 7 The two structures are drawn schematically in Figure 3.11 for comparison. P—P = DPPB P—P = 5,5-CHIRAPHOS a b Figure 3.11: Geometry of a) [Ru2CU(DPPB)2(DM£0)], 14e and, b) [Ru2Cl5(CHIRAPHOS)2], 4.2 6>2 7 The various bond lengths and bond angles in the two complexes are very similar in spite of the different formal oxidation states (i.e. II, U vs. II, III) at the ruthenium centres. However, there is one striking difference in the geometries: unlike in the highly symmetrical CHIRAPHOS complex, the positioning of the diphosphines in the DPPB complex is unsymmetrical in that one of the octahedra has been rotated by ±120° about the 105 Ru-Ru vector. The analogous Ru2U* n thiocarbonyl complex containing triphenyl- phosphines, [(CS)(PPh3)2Ru(U--Cl)3RuCl(PPh3)2l, reported by Fraser and Gould56b also shows a similar unsymmetrical arrangement of the PPh3 ligands (Figure 3.12). P = PPh3 Figure 3.12: Geometry of [(CS)(PPh3)2Ru(u-Cl)3RuCl(PPh3)2].56b 3.6.5 Other [(L)(DPPB)Ru(u-CI)3Ru(CI)(DPPB)] Complexes Several other trichloro-bridged dinuclear complexes of the general formula [(L)(DPPB)Ru(|i-Cl)3Ru(Cl)(DPPB)] were prepared in situ by reaction of various coordinating ligands with the dimeric precursor [RuCl(DPPB)(u-Cl)]2,14, or with the mixed-phosphine complex RuCl2(DPPB)(PPh3), 23, and characterised spectroscopically, chiefly using N M R and IR techniques. Of particular interest is the in situ formation of trichloro-bridged dinuclear complexes incorporating molecular hydrogen and dinitrogen ligands (L = T | 2-H2 and ri1-N2, respectively) from [RuCl(DPPB)(u.-CI)]2, 14, under 1 atm of the respective gases.60 Detailed discussion of their characterisation has been deferred to Chapter 5 of this thesis. The 'non-nucleophilic' bases Proton Sponge® (PS) and DBU (Figure 3.13) readily coordinate to the DPPB dimer 14. The 3 1 P NMR AB quartet of 14 in CDCI3 disappeared when either reagent was added, and singlets assigned to [(PS)(DPPB)Ru- (fi-Cl)3RuCl(DPPB)] and to the corresponding DBU analogue became apparent at 5 48.4 and at 44.8 ppm, respectively (see Section 3.7). B 106 Me2N NMe2 a b Figure 3.13: The'non-nucleophilic'bases (a) Proton Sponge® and (b) DBU. Notably, addition of ~100-fold excess of methyl iodide to a CDCI3 solution of 14 resulted in the appearance in the 3 1 P NMR spectrum of two additional sets of AB patterns, centred at 52.2 and 45.2 ppm, which are assigned to [(MeI)(DPPB)Ru(|i- Cl)3RuCl(DPPB)] (see Section 3.7). Oxidative addition reactions of Mel at a transition metal centre have been studied extensively,61 but examples of Mel acting as a neutral ligand are rare. Recently, Crabtree and coworkers have reported the synthesis of a series of complexes of the type [Cp*M(L)2(R1I)]+ where M = Ru or Fe; R1 = Me, Et, p-tolyl, Cy; L = CO,PPh3orDPPE.62 Further, the reaction of 14 or 23 (0.1 mmol) with benzonitrile (2 mL) in CH2CI2 (10 mL) followed by addition of Et20 (20 mL) to the reaction mixture concentrated to 5 mL precipitated a yellow microcrystalline solid, which is identified as a bisQ?hCN)-ccordinated dinuclear species, [RuCl(DPPB)(PhCN)(u-Cl)]2. A single infra-red C=N stretch for the two end-on coordinated benzonitrile ligands is observed at 2238 cm - 1 (m). The principal resonance in the 3 1 P NMR spectrum (CDCI3,20 °C) of the bis(nitrile) derivative consists of a single AB pattern (8A = 48.8, 8B = 45.2 ppm, 2 /AB = 35.7 Hz; Figure 3.14). Examination of the proton NMR spectrum confirms the presence of only one PhCN ligand per Ru-DPPB unit based on proton integral intensities (Figure 3.15). The observed IR and NMR spectral data are consistent with the dinuclear bis(PhCN) formulation of structure 3-1; a singlet phosphorus resonance would be expected for a complex of geometry 3-JJ. 107 Analogous bis(nimUe)diruthenium complexes, containing monodentate phosphines in place of the bidentate DPPB, have been reported previously by Cole-Hamilton and Wilkinson.63 Similar symmetric structures have been proposed to explain the presence of a single IR stretch for CsN, and a single AB quartet observed in the 3 * P NMR spectra of the [RuCl2(PPh3)2(RCN)J2 analogues, where RCN = CH3CN, PhCN 6 3 Some mononuclear complexes containing nitrile and chelating phosphine ligands (e.g. RuCl2(DPPE)(RCN)2; R = Me, Et) are also known.64 An additional pair of AB quartets of -15% total integral intensity, seen in the phosphorus N M R spectrum of the bis(benzonitrile) complex (Figure 3.14), is assigned to the mono(benzonitrile) species [(PhCN)(DPPB)Ru(u-Cl)3RuCl(DPPB)], 14f, formed by PhCN-dissociation in solution (Equation 3.15). 3-1 L = PhCN 3-II [RuCl(DPPB)(PhCN)(u-Cl)]2 [(PhCN)(DPPB)Ru(u-Cl)3RuCl(DPPB)] (3.15) 14f + PhCN 108 II 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 j 1 1 1 1 11 1 1 1 1 1 1 ] 1 1 1 1 1 ) ] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 5 4 5 2 5 0 4 B 4 6 4 4 PPM 4 2 Figure 3.14: 3lP{ Ĥ} NMR spectrum of [Rua2(DPPB)(PhCN)]2 in CDC13 (121.42 MHz), The peaks marked with asterisks belong to Ru2Cl4(DPPB)2(PhCN), 14f; see text. 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I j l 1 1 1 1 1 1 1 I j l 1 1 1 1 1 1 1 I j l 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 Ij 1 1 1 1 1 1 1 1 l j Figure 3.15: *H NMR spectrum of [Rua2(DPPB)(PhCN)] 2 in C D C I 3 (300 MHz, 20 "Q. 109 3.7 NMR Studies on [(L)(DPPB)Ru(u-Cl)3Ru(CI)(DPPB)] Complexes 3.7.1 3l P{lH} Solution NMR Studies The ambient temperature 31P{ ^U) NMR spectra of C6E>6 or CDCI3 solutions of the complexes Ru2Cl4(DPPB)2(L), where L = Me2CO, CO, Me2SO, PhCN, Mel, or DMA, all consist of two independent AB quartet patterns of equal integral intensity. The data are summarised in Table 3.6. The presence of two independent AB patterns (assigned as AB and CD) is consistent with the unsymmetric, trichloro-bridged dinuclear structure of these species in solution (Figure 3.16). In the absence of a ligand (L) dissociation/re-association process, or in a system where such a process is slow on the NMR time-scale, the two ruthenium centres are different, making all four phosphorus nuclei chemically and magnetically inequivalent; this would give rise to two 3 1 P NMR AB patterns of equal intensity. T h e single crystal X-ray study on the Me2SO-adduct 14e shows that the same unsymmetrical arrangement of the DPPB ligands relative to each other is maintained in the solid state (Section 3.6.4). It should be noted that for a complex, containing a nonchiral diphosphine such as D P P B , a symmetric dinuclear structure possessing a plane of symmetry through the terminal and one of the bridging chlorides and the coordinated ligand L would render PA equivalent to PB and Pc to PD (Figure 3.17); this would likely result in just two singlets of equal integral intensity in the 3 1 P NMR spectrum. Figure 3.16: Proposed structure of Ru2CU(DPPB)2(L) complexes. 110 Table 3.6: 31P{ I R ) N M R Data (121 .42 MHz, 2 0 °C) for the Trichloro-Bridged Dinuclear Complexes, [(L)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)]. L (Complex) Solvent Chemical Shifts, 8 (ppm) 2Jpp, (Hz) Me2CO (14a) C5D6 6A = 52.8, 8B = 51.5 43.7 8C = 50.1, 6D = 48.7 38.4 CO (14d) C6D 6 6A = 53.8, 8B = 53.3 45.2 8c = 46.9, 8D = 33.1 29.6 Me2SO (14e) C5D6 8A = 53.6, 8B = 50.6 43.8 8C = 41.6, 8D = 28.9 32.1 CDCI3 8A = 53.5, 8B = 50.7 42.6 8C = 41.6, 8D = 29.3 32.5 DMSO-̂ s 8A = 53.9, 5B = 51.6 43.8 8C = 42.8, 8D = 32.3 32.0 PhCN (14f) C5D6 8A = 52.6, 8B = 51.8 42.1 8C = 50.3, 8D = 44.7 36.5 Mel (14g)a CDCI3 5A = 52.6, 8B = 51.7 43.4 8C = 48.6, 5D = 41.8 36.7 DMA (14h)a C 6 D 6 8A = 53.5, 8B = 52.2 43.6 8c = 52.7, SD = 50.7 39.6 CDCI3 8A = 52.2, 8B =50.3 43.3 5C = 51.4, 8D = 49.2 39.9 NEt3 (14b) CDCI3 48.3, s — NHBu2(14c) CDCI3 48.2, s — Proton Sponge3 C D C I 3 48.4, s — DBU3 C D C I 3 44.8, s — These complexes were prepared in situ by reaction of 14 with the appropriate ligand. I l l C.p ,|HII»";RU ^ "'U^' ,"»IIP\ \r< ^ c i - ^ >p/ D B Figure 3.17: A symmetric dinuclear structure for Ru2Cl4(DPPB)2(L) complexes. The 3 1P{1H} spectra for some Ru2Cl4(DPPB)2(L) complexes (L = Me2CO, 14a; CO, 14d; Me2SO, 14e; Mel, 14g; DMA, 14h) are shown in Figures 3.18a through 3.18e. The relatively lower field AB pattern is quite insensitive to the nature of the coordinated ligand (L) as it remains essentially invariant in position (8AB ~52±1) as well as in the magnitude of the coupling constant (2/AB ~44±1 HZ). It is therefore assigned to the resonances of the -C^Ru^QXP-P) portion of the molecule, which is in a locked conformation. The other set of signals is, however, much more sensitive to the nature of L as evidenced from the much larger spread of chemical shifts (8CD ~35-52) and coupling constants ( 2 / C D -29-40 Hz; see Table 3.6) and is therefore attributed to the (L)(P-P)Ru2(|i-Cl)3- fragment of die molecule. Also apparent in the spectra of the Mel, and DMA adducts (Figure 3.18d, 3.18e) are the resonances due to the dichloro-bridged complex [RuCl(DPPB)(u-Cl)]2, 14 (8 = 59.5 ppm, 27pp = 47 Hz). This implies that the binding of these ligands to ruthenium is relatively weak, and only a partial equilibrium conversion to the trichloro- bridged species occurs even in the presence of ca. 100-fold excess of the respective ligands. Some 14 is also present in solutions of the acetone analogue 14a (Figure 3.18a). The ligand exchange must be slow on the NMR time scale because resonances of the individual species are observed. In contrast, the Me2SO and the CO complexes show no evidence of ligand dissociation to the dichloro-bridged precursor (Figure 3.18b, 3.18c), consistent with the much stronger binding of CO and Me2SO to ruthenium. 112 a u Me2CO (14a) C6D6 C O (14d) C 6 D 6 [ i i i i | i i i i I i i I I | I i I I i l I I I j I I I i | I l i I I I I i i 65 60 55 50 45 40 35 30 PPM Figure 3.18a-e: 3lp{iH} NMR spectra (121.42 MHz, 20 *C) of [(L)(DPPB)Ru- (u-Cl)3Ru(Cl)0DPPB)] complexes. The ligand L and the solvent are indicated with each individual spectrum. L = (a) Me2CO; (b) CO; (c) Me2SO; (d) Mel; and (e) DMA. The resonances due to [RUC1(DPPB)(JI-C1)]2 are marked by asterisks. 113 Figure 3.18, continued: i I i j i i i I | i ) 40 35 30 PPM 114 Figure 3.18, continued: 115 The formation of trichloro-bridged complexes of the type (L)P2Ru(u-Cl)3RuClP2, where P is a monodentate phosphine (L = CO, 6 5 CS, 6 6 PF3, 6 7 N2, 6 8 D M A , 6 9 acetone69), has been reported previously; two sets of 3 1 P NMR A B patterns have been observed in each case, but there is no clear evidence for the existence of a dynamic equilibrium as found in the current study. The phosphorus NMR spectra of the corresponding amine adducts (L = NEt3, NHBu2, PS, DBU; see Table 3.6) consist of only a sharp singlet at - 4 8 . 3 ± 0.2 ppm (at 44.8 ppm when L = D B U ) even down to - 6 0 °C. This is explained by a rapid equilibrium on the NMR time scale between the trichloro-bridged Ru2CU(DPPB)2(arnine) species and the dichloro-bridged complex 14 formed by dissociation of the amine ligand bound to Ru 2 in solution {cf. Scheme 3-II); the dissociated amine can then recoordinate to either ruthenium centre, resulting in scrambling of all four phosphorus centres. The ligand dissociation/re-association process must involve both ruthenium centres in the dinuclear complex (Ru2 and Ru1). The exchange at only one ruthenium centre O^u2) will result in scrambling of the Pc and PD resonances, assuming that the amine can recoordinate at any one of the three non-bridging sites, but this will not affect the PA and PB resonances. 3.8 Reactions of C/s-RuCl 2(DMSO) 4 with Other Bidentate Phosphines The successful synthesis of the dinuclear Ru(II) complex [(DMSO)(DPPB)Ru- (u-Cl)3RuCl(DPPB)], 14e, by reaction of ris-RuCl2(DMSO)4 with one equivalent of DPPB as outlined in Sections 3.6.3 and 3.6.4, prompted further investigation into the reactivity of m-RuCl2(DMSO)4 with other chelating phosphine ligands. The studies have been extended to include the phosphines: DPPM, DPPE, and 5 ,S -BDPP. The reactions with one equivalent of D P P M and DPPE yield bright yellow solids (Chapter 2, Section 2.5.7). The products are readily identified by NMR spectroscopy as the previously reported bis(bidentate phosphine) complexes:9'13' 7 0 RuCl2(DPPM)2 116 (100% cis isomer) and RuCl2(DPPE)2 (a 50:50 rnixture of cis and trans isomers, based on NMR spectral intensities). The 3 1 P NMR data are listed in Table 3.7. In each case, resonances of the unreacted precursor complex cw-RuCl2(DMSO)4 (~50%) were apparent in the 'H NMR spectrum (2-3 ppm region).71 Addition of excess phosphine to the solution results in a complete conversion to the RuCl2(P-P)2 species as evidenced by lH NMR spectroscopy. Reaction of c/s-RuCl2(DMSO)4 with S.S-BDPP produced a mixture of products. The 3 1P{ ]H) NMR spectrum (Figure 3.19) of the mixture in C6D6 reveals two sets of AX patterns of equal intensity, centred at 59.8 and 40.3 ppm (2/pp = 51.0 and 40.1 Hz, respectively), which are assigned to a trichloro-bridged DMSO adduct [(DMSO)(BDPP)Ru(u-Cl)3RuCl(BDPP)] by analogy to the corresponding DPPB complex (see Sections 3.6.3 and 3.6.4). The relatively low intensity (-6%) AX patterns centred at 61.8 and 59.6 ppm (27pp = 52.1 and 49.0 Hz, respectively) remain unassigned, but probably arise from related dinuclear species. The singlet at 9.2 ppm constituting -40% of the total intensity is attributed to the trans-RuCl2(5,S-BDPP)2 complex (observed at 8.7 ppm in CDCI3), which has been isolated by another route and characterised crystallographically (see Section 3.8 and Appendix A-2.3). The S=0 stretch for the bound DMSO ligand of [(DMSO)(BDPP)Ru(u-Cl)3RuCl(BDPP)] is observed at 1089 cm"1 in the IR spectrum and is characteristic of coordination through the S atom.50 117 J f i»l i i<rtWW»i f T M i I l l I i I M i I ] I I ! I j I I I-11111111111111111111)111111111111111111111 70 60 50 40 30 20" 10 PPM Figure 3.19: 31P{ 1H} NMR spectrum of the niixture of products isolated from the reaction of m-RuCl2(DMSO)4 with one equivalent of S.S-BDPP: (a) rra«5-RuCl2(BDPP)2; (b) [(DMSO)(BDPP)Ru(u-Cl)3RuCl(BDPP)] The comparison of reactivity of c/i,-RuCl2(DMSO)4 with one equivalent of various bidentate phosphines, viz. DPPM, DPPE, S,S-BDPP, and DPPB, clearly reveals the influence of relative chelate size of the respective ligands (i.e. bite angle and steric factors) on the nature and distribution of the resulting products. The diphosphines DPPM and DPPE, which form four- and five-membered rings, respectively, upon coordination to the metal, give only the bis(P-P) complexes. The use of 5,S-BDPP (chelate size six) results in the formation of a mixture of dinuclear "RuCl2(P-P)" species and a mononuclear RuCl2(P-P)2 complex in ca. 60:40 ratio (see above). In contrast, the reaction of DPPB with RuCl 2(DMSO)4 results in the formation of the dinuclear complex [(DMSO)(DPPB)Ru(u-Cl)3RuCl(DPPB)], 14e, in -80% isolated yield (see Section 2.5.6.4). 118 Table 3.7: 31P{ lH} NMR Data (121.42 MHz, C6D6, 20 *C) for the Complexes Obtained by the Reaction of Cw-RuCl20DMSO)4 with One Equivalent of Bidentate Phosphine. Complex Chemical Shifts, 6 Oppm) 2/pp, (Hz) cw-RuCl2(DPPM)2 6A - -1.4, 6B = -27.6, A2B2 pattern 36.2 cw-RuCl2(DPPE)2 6A =  51.9, 6B = 37.2, A2B2 pattern 19.7 rra« -̂RuCl2(DPPE)2 44.5, s — trans-RuC\2(S,S-BDPP)2 9.2, s — [Ru2Cl4(5,S-BDPP)2(DMSO)] 6A = 65.3, 6B - 54.2, AX pattern 51.0 8c = 49.6, 5D = 30.9, AX pattern 40.1 3.9 Reactions of [RuCl(p-cymene)(u-Cl)]2 with Bidentate Phosphines Previous work from this laboratory has reported on the synthesis of the mononuclear cationic Ru(II) complexes, [RuCl(MeCN)3(DPPB)]+PF6_ and [RuCl(ri6-C6H5CH3)(DPPB)]+PF6- (Equation 3.16), which contain a single diphosphine per R u . 2 7 ' 7 2 The acetonitrile derivative was found to be an active catalyst for the H2-hydrogenation of imine and nitrile substrates under relatively mild conditions (50 °C, 1 atm of H 2 ) . Reactions of Ru(arene) precursors with one equivalent of a bidentate phosphine were investigated in an attempt to find a synthetic route that would bypass the dinuclear RU211-11 complexes (cf. Equation 3.16). 119 [RuCl(DPPB)(u-Cl)]2 + 2 AgPF6 [RuCl(DPPB)(S)3]+PF6- (3.16) (S) = CH 3 CN or (S)3 = r|6-toluene The complex [RuCl(p-cymene)(u-Cl)]2 was chosen as the precursor over other arene analogues (e.g. benzene, toluene, xylene)73 because of its generally greater solubility in organic solvents. A recent report by Mashima et al. describes a series of complexes of the general formula [RuX(arene)(S-BINAP)]+X_ (X = Cl, Br, I; arene = benzene, toluene, or p-cymene) which have been prepared by reaction of the appropriate arene precursor with one equivalent of 5-BINAP. 7 4 The corresponding fl-BINAP derivative, [RuCl(p-cymene)(#-BINAP)]+Cl- has been prepared in high yields (90%) and characterised during the present study (see Section 2.5.8 for details). The 3 1 P NMR spectrum of this complex consists of an AX pattern (5A = 40.0, 5x = 23.5 ppm, VAX = 62.5 Hz). The observed parameters are in agreement with those reported by Mashima et al. for the S-BINAP analogue.74 The *H NMR spectrum (Figure 3.20) of the complex is consistent with the formulation suggested by Mashima et al. (Figure 3.21).74 Resonances of the BINAP protons are seen spread over the 8.3-6.8 ppm region, while resonances of die aromatic protons of the ri6-boundp-cymene ligand are observed as doublets centred at 6.35, 5.95, 5.90 and 4.30 ppm, respectively (IH each). The singlet at 2.0 ppm is assigned to the lone methyl group of the p-cymene, while resonances due to the methyl of the isopropyl substituent are observed as doublets at 1.35 and 0.95 ppm, respectively. The septet pattern at 3.0 ppm is attributed to the methine proton of the isopropyl group. 120 121 + P—P = BINAP p ̂ " X X Figure 3.21: Geometry of [RuX(arene)(BINAP)]+X- complexes. The additional broad resonance observed at 4.30 ppm (~1H) in the *H NMR spectrum is tentatively assigned to a molecule of water; the chemical shift is close to that expected for hydrogen-bonded water. The presence of water in the sample is confirmed by IR spectroscopy and the elemental analysis is also consistent with the presence of 0.5 mole equivalents of water per Ru complex. One possible mode of binding is shown below: Reaction of equimolar amounts of 5,5-BDPP with [RuCl(p-cymene)(u-Cl)]2 under similar preparative conditions (Section 2.5.8), however, yielded a mixture of products as evidenced by the 3 1 P NMR spectroscopy. An AX pattern observed at 35.1 ppm (8A = 39.2, 6B = 29.1 ppm, 2 / A X = 60.7 Hz) and constituting ca. 25% of the total integral intensity has been assigned to the desired [RuCl(p-cymene)(5,5-BDPP)]+Cl~ complex by comparison of the data for the BINAP analogues. One of the products was isolated and identified from its 3 1 P NMR chemical shift (8.7 ppm, s) as the bis(diphosphine) complex rra/w-RuCl2(5,5-BDPP)2. The trans arrangement of the chloro [Ru]+Cr Cr[Ru]+ H [Ru] represents [RuX(arene) (BINAP)] 122 ligands was confirmed by a single crystal X-ray diffraction analysis (see Appendix A-2.3 for the structural details). While the Ru-(arene)BINAP complexes could be obtained in almost quantitative yields, the corresponding BDPP derivative is formed in only about 25% yield. This observation supports the earlier suggestion (see Section 3.8) that the steric bulk and chelate size of the diphosphine ligands perhaps influence the nature of the products generated. 123 3.10 References - Chapter 3 1. Schroder, M.; Stephenson, T. A. in Comprehensive Coordination Chemistry; Wilkinson, G.; Gillard, R. D.; McCleverty, J. A., Eds.; Pergamon Press: Oxford, 1987; Vol. 4, Chapter 45. 2. Bruce, M. I. in Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol.4, p. 651. 3. Seddon, E. A.; Seddon, K. R. The Chemistry of Ruthenium; Elsevier: Amsterdam, 1984. 4. Jardine, F. H. Prog. Inorg. Chem. 1984,37, 265. 5. Some journals periodically publish special reports on the chemistry of individual or a group of transition metals. See for example, Annual Survey of Ruthenium Chemistry for the Years 1983/84: (a) Keister, J. B. / . Organomet. Chem. 1987, 318, 297. (b) Shapley, P. A. J. Organomet. Chem. 1987,318, 409. 6. James, B. R. in Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol.8, p. 285. 7. James, B. R. Homogeneous Hydrogenation; Wiley: New York, 1973. 8. Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987; p. 545. 9. (a) Chatt, J.; Hayter, R. G. / . Chem. Soc. 1961,772; 896; 5507. (b) ibid., 1963, 6017. 10. James, B. R.; Wang, D. K. W.; Voigt, R. F. J. Chem. Soc, Chem. Commun. 1975, 574. 124 11. Mason R.; Meek, D. W.; Scollary, G. R. Inorg. Chim. Acta 1976,16, Ll 1. 12. McAuliffe, C. A.; Levason, W. Phosphine, Arsine and Stibine Complexes of the Transition Elements; Elsevier: Amesterdam, 1979. 13. Jung, C. W.; Garrou, P. E.; Hoffman, P. R.; Caulton, K. G. Inorg. Chem. 1984,23,726. 14. Joshi, A. M.; Batista, A. A.; James, B. R. unpublished results. 15. (a) Wang, D. K. W., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1978. (b) James, B. R.; Wang, D. K. W. Inorg. Chim. Acta 1976,19, L17. 16. Bressan, M.; Rigo, P. Inorg. Chem. 1975,14, 2286. 17. Henrici-Olive, G.; Olive, S. Angew. Chem., Int. Ed. Engl. 1971,10, 105. 18. James, B. R.; McMillan, R. S.; Morris, R. H.; Wang, D. K. W. Adv. Chem. Ser. 1978, 167, 122. 19. James, B. R.; Wang, D. K. W. Can. J. Chem. 1980,55, 245. 20. Kawano, H.; Ikariya, T.; Ishii, Y.; Saburi, M.; Yoshikawa, S.; Uchida, Y.; Kumobayashi, H. J. Chem. Soc, Perkin Trans. 1989, 1571. 21. Thorburn, I. S.; James, B. R. unpublished results. 22. (a) Kagan, H. B. in Asymmetric Synthesis; Morrison, J. D., Ed.; Academic Press: New York, 1985; Vol. 5, p. 1. (b) Koenig, K. E., ibid:, p. 71. 23. Bosnich, B., Ed., Asymmetric Catalysis; Martinus Nijhoff: Dordrecht, 1986. 125 24. James, B. R.; Thompson, L. K.; Wang, D. K. W. Inorg. Chim. Acta 1978,29, L237. 25. Dekleva, T. W.; Thorburn, I. S.; James, B. R. Inorg. Chim. Acta 1985,100, 49. 26. Thorburn, I. S.; Rettig, S. J.; James, B. R. Inorg. Chem. 1986,25, 234. 27. Thorburn, I. S., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1985. 28. James, B. R.; Pacheco, A.; Rettig, S. J.; Thorburn, I. S.; Ball, R. G.; Ibers, J. A. J. Mol. Catal. 1987,47, 147. 29. (a) Clark, E . P. Indust. Eng. Chem. Anal. Ed. 1941,13, 820. (b) Zoellner, R. W. J. Chem. Ed. 1990, 67, 714. 30. Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97, 4221. 31. Evans, D. F. J. Chem. Soc. 1959, 2003. 32. Figgis, B. N. Introduction to Ligand Fields; Wiley: New York, 1966; Chapter 10. 33. Day, M. C ; Selbin, J. Theoretical Inorganic Chemistry; Van Nostrand Reinhold: New York, 1969, 2nd Edn.; p. 483. 34. Brown, M . J.; Chaloner, P. A.; Murrer, B. A.; Parker, D. ACS Symp. Ser. 1980, 779, 170. 35. Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; Wiley-Interscience: New York, 1980, 4th Edn.; p. 467. 36. Noyori, R.; Takaya, H. Acc. Chem. Res. 1990,23, 345. 126 37. Noyori, R. Science 1990,245, 1194; Chem. Soc. Rev. 1989, 75, 187. 38. Ikariya, T.; Ishii, Y.; Kawano, H.; Arai, T.; Saburi, M.; Yoshikawa, S.; Akutagawa, S. J. Chem. Soc, Chem. Commun. 1985, 922. 39. Noyori, R.; Ohkuma, T.; Kitamura, M.; Takaya, H.; Sayo, N.; Kumobayashi, H.; Akutagawa, S. J. Am. Chem. Soc 1987, 709, 5856. 40. Gordon, A. J.; Ford, R. A. The Chemist's Companion, A Handbook of Practical Data, Techniques and References; Wiley: New York, 1972; p. 186. 41. Chaudhuri, N. K.; Servando, O.; Markus, B.; Galynker, I. J. Indian Chem. Soc. 1985, 62(77), 899. 42. McCrindle, R.; Ferguson, G.; Arsenault, G. J.; McAlees, A.. J. J. Chem. Soc, Chem. Commun. 1983, 571. 43. Reference 8, Chapters 6, 12 and 15. 44. Tsuji, J. in Organic Synthesis via Metal Carbonyls; Wender, I. and Pino, P., Eds.; Wiley-Interscience: New York, 1977; Vol. 2,p.595. 45. Domazetis, G.; Tarpey, B.; Dolphin, D.; James, B. R. J. Chem. Soc, Chem. Commun. 1980, 939. 46. Domazetis, G.; James, B. R.; Tarpey, B.; Dolphin, D. ACS Symp. Ser. 1981,752, 243. 47. Varshavsky, Yu. S.; Shestakova, E. P.; Kiseleva, N. G.; Cherkasova, T. G.; Buzina, N. A.; Bresler, L. S.; Kormer, V. A. J. Organomet. Chem. 1979, 770,81; and references therein. 48. Kuhlman, E. J.; Alexander, J. J. J. Organomet. Chem. 1979, 774, 81; Inorg. Chim. Acta 1979, 34, 197. 127 49. Albers, M. O.; Coville, N. J.; Nicolaides, C. P.; Webber, R. A.; Ashworth, T. V.; Singleton, E. J. Organomet. Chem. 1981,217, 247. 50. Bora, T.; Singh, M. M. Transition Met. Chem. 1978,3,27; and references therein. 51. James, B. R.; Ochiai, E.; Rempel, G. I. Inorg. Nucl. Chem. Lett. 1971, 7, 781. 52. Evans, I. P.; Spencer, A.; Wilkinson, G. / . Chem. Soc, Dalton Trans. 1973, 204. 53. Mercer, A.; Trotter, J. / . Chem. Soc, Dalton Trans. 1975, 2480. 54. McMillan, R. S.; Mercer, A.; James, B. R.; Trotter, J. J. Chem. Soc, Dalton Trans. 1975, 1006. 55. (a) LaPlaca, S. J.; Ibers, J. A. Inorg. Chem. 1965,4, 778. (b) Skapski, A. C; Troughton, P. G. H. J. Chem. Soc, Chem. Commun. 1968, 1230. 56. (a) Alcock, N. W.; Raspin, K. A. / . Chem. Soc. (A) 1968, 2108. (b) Fraser, A. J. F.; Gould, R. O. J. Chem. Soc, Dalton Trans. 1974, 1139. (c) Cotton, F. A.; Matusz, M.; Torralba, R. C. Inorg. Chem. 1989, 28, 1516. 57. Chioccola, G.; Daly, J. J. J. Chem. Soc. A 1968, 1981. 58. For example: (a) Mattson, B. M.; Heiman, J. R.; Pignolet, L. H. Inorg. Chem. 1976,15, 564; and references therein. (b) Schumann, H.; Opitz, J.; Pickardt, J. / . Organomet. Chem. 1977,128, 253. (c) Hursthouse, M. B.; Jones, R. A.; Abdul Malik, K. M.; Wilkinson, G. J.Am. Chem. Soc. 1979,101, 4128. (d) Jones, R. A.; Wilkinson, G.; Coloquohoun, I. J.; McFarlane, W.; Galas, A. M. R.; Hursthouse, M. B. J. Chem. Soc, Dalton Trans. 1980, 2480. 128 59. Hampton, C; Cullen, W. R.; James, B. R.; Charland, J. -R / . Am. Chem. Soc. 1988,110, 6918. 60. Joshi, A. M.; James, B. R. J. Chem. Soc, Chem. Commun. 1989, 1785. 61. Reference 8, p. 280. 62. (a) Kulawiec, R. J.; Faller, J. W.; Crabtree, R. H. Organometallics 1990,9, 745; and references therein. (b) Burk, M. J.; Segmuller, B.; Crabtree, R. H. Organometallics 1987,6, 2241. 63. Cole-Hamilton, D. J.; Wilkinson, G. J. Chem. Soc, Dalton Trans. 1979, 1283. 64. Newton, W. E.; Searles, J. E. Inorg. Chim. Acta 1973, 7, 349. 65. Armit, P. W.; Sime, W. J.; Stephenson, T. A. J. Chem. Soc, Dalton Trans. 1976, 2121. 66. Stephenson, T. A.; Switkes, E. S.; Armit, P. W. J. Chem. Soc, Dalton Trans. 1974, 1134. 67. Head, R. A.; Nixon, J. F. J. Chem. Soc, Dalton Trans. 1978, 901. 68. Gosser, L. W.; Knoth, W. H ; Parshall, G. W. J. Am. Chem. Soc. 1973, 95, 3436. 69. Dekleva, T. W. Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1983. 70. Chaudret, B.; Commenges, G.; Poilblanc, R. J. Chem. Soc, Dalton Trans. 1984, 1635. 71. Morris, R. H. Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1978. 129 72. Thorburn, I. S.; Rettig, S. J.; James, B. R. J. Organomet. Chem. 1985,296, 103. 73. (a) Bennett, M. A.; Smith, A. K. J. Chem. Soc, Dalton Trans. 1974, 233. (b) Zelonka, R. A.; Baird, M. C. Can. J. Chem. 1972,50, 3063. 74. Mashima, K.; Kusano, K.; Ohta, T.; Noyori, R.; Takaya, H. J. Chem. Soc, Chem. Commun. 1989, 1208. 130 CHAPTER 4 Reactions of RuCl2(DPPB)(PPh3) with Chelating Ligands 4.1 Introduction The mixed-phosphine complex RuCl2(DPPB)(PPh3)1 and its DIOP analogue,2 prepared by a simple phosphine exchange reaction (Equation 4.1), have been known for several years. RuCl2(PPh3)3 + P-P RuCl2(P-P)(PPh3) + 2 PPh3 (4.1) P-P = DPPB, DIOP Caulton and coworkers re-examined the preparative chemistry of complexes of the general formula RuCl2(P-P)(PPh3), where P-P represents the bidentate phosphines Ph2P(CH2)nPPh2, n = 1-4.1 Detailed variable temperature 3 1 P NMR studies of reactions of the precursor RuCl2(PPh3)3 complex with one equivalent of the appropriate phosphine in CD2CI2 solution showed that no mixed-phosphine complexes containing DPPM or DPPE were formed; rrans-RuCl2(DPPM)2 and rra«5-RuCl2(DPPE)2 were the major products. A small amount of RuCl2(DPPP)(PPh3) was observed in solution, while only the DPPB complex RuCl2(DPPB)(PPh3), 23, was isolable.1 The authors ascribed these differences in reactivity of Ph2P(CH2)nPPh2 ligands to the differences in chelate bite angles (Z P-Ru-P) in the resulting RuCl2(P-P)(PPh3) species. They concluded that as this angle became smaller, the reduced steric crowding made the RuCl2(P-P)(PPh3) complex 131 accessible lo further reaction to form a coordinatively saturated product of the type RuCl2(P-P)2- The normal apical-to-basal angle for a square-pyramidal geometry is expected to be 104°. Crysiallographic studies by Churchill and Bezman3 on pentacoordinate iridium complexes of the general formula Ir(COD)(CH3)(L2), where L = PMe 2 Ph 3 a or L 2 = DPPP, 3 b D P P E , 3 c have yielded values of 101.5,93.4 and 84.9°, respectively, for Z P-Ir- P. As mentioned in Section 3.4.1, the mixed-phosphine complexes readily lose the triphenylphosphine ligand in solution to form the chloro-bridged dimeric complexes, [RuCl(P-P)(u-Cl)]2, where P-P = DPPB or DIOP (Equation 4.2). Trapping such dimeric moieties, formed in situ, with an appropriate ligand seemed feasible. As described in Chapter 3, reactions of RuCl2(DPPB)(PPh3), 23 , with monodentate ligands, such as NEt 3, clearly provide a synthetic route into dinuclear ruthenium complexes containing a single diphosphine (DPPB) per ruthenium (Equation 4.3). RuCl2(P-P)(PPh3) 1/2 [RuCl(P-P)(u-Cl)]2 + PPh3 (4.2) P-P = DPPB or DIOP NEt3 RuCl2(DPPB)(PPh3) —*~ 1/2 [(NEt3)(DPPB)Ru(u-Cl)3RuCl(DPPB)] (4.3) -PPh 3 Much o f the chemistry of the mixed phosphine complex RuCl2QDPPB)(PPh3), 23, described here has developed out of interest in the dimer chemistry. Reactions of 23 with chelating ligands produced some unusual six-coordinate compounds; their characterisation and reactivity with H 2 (including that of 23) are described in this chapter. The structure of RuCl2(DPPB)(PPh3) was of particular interest. Based on a low- temperature 3 1 P NMR study of RuCl2(DPPB)(PPh3) in CD2CI2 solution, Caulton and 132 coworkers have proposed, for the mixed-phosphine complex 23, a structure similar to that of the RuCl2(PPh3)3 precursor, at least in solution. The tris(triphenylphosphine) derivative has been previously characterised crystallographically,4 and shows a square-pyramidal arrangement of ligands about the Ru centre with rra/w-disposed chlorides and mutually trans PPI13 ligands in the basal plane and the remaining PPh3 group occupying the apical position.4 As attempts to grow diffraction quality crystals of 23 were unsuccessful, it was decided to conduct a comparative solid-state 3 1 P NMR study of RuCl2(DPPB)(PPh3) and RuCl2(PPh3)3 complexes in the hope of extracting information about the solid-state structure of the former. The results are described in the next section. 4.2 Solid-State 3 1 P N M R Studies on R u C l 2 ( D P P B ) ( P P h 3 ) and R u C l 2 ( P P h 3 ) 3 The samples were packed as powders (-0.2-0.3 g) in Teflon® holders of -8 mm ED. High-resolution, solid-state NMR spectra were obtained on a Bruker CXP200 FT- NMR machine operating at 80.99 MHz for 3 1 P , by combining high-power proton decoupling5 with J H - 3 1 P cross polarisation (CP)6 (5.5 |is 90°y *H pulse, 1 ms contact time, 1 s recycle time) and magic-angle spinning (MAS)7 at -2.5—4.0 kHz (for general reviews on CP/MAS NMR spectroscopy, see Refs. 8-10). The CP/MAS 3 1 P NMR spectra of the complexes RuCl2(DPPB)(PPh3) and RuCl2(PPh3)3 are shown in Figure 4.1. The chemical shift anisotropy interaction in the solid-state results in a spectrum which consists of isotropic peaks and peaks at integral values of the spinning frequency (spinning sidebands).8-12 The isotropic peaks were differentiated from the spinning sidebands by obtaining spectra at different rotor speeds. Positions of the spinning sidebands change with the spinning frequency of the sample 133 I i a T —1 1 1 1 1 [ — I 1 1 1 1 1 1 1 1 [ I _ ~* 1 1 i ' FFM Figure 4.1: The 80.99 MHz CP/MAS 3 1P NMR spectra of the complexes (a) RuCl2(PPh3)3, and (b) RuCl2(DPPB)0?Ph3), at a MA spinning frequency of 3.5 kHz. 134 while the isotropic peaks remain invariant in position.8-12 Alternatively, the isotropic chemical shifts were obtained by using a routine TOSS (TOtal Suppression of Sidebands) pulse sequence to suppress the sidebands.11 Caulton and coworkers have reported the low-temperature 3 1 P NMR data for RuCl2(PPh3)313 and RuQ2(DPPB)(PPh3)1 in dichloromethane solution (Table 4.1). The spectra of the two complexes exhibit an AX 2 and an ABX pattern, respectively. The TOSS spectra for the two complexes, along with the respective low-temperature solution NMR spectra which were simulated using the parameters reported in the literature,1'13 are shown in Figures 4.2 and 4.3. The solid-state NMR data are listed in Table 4.2. 4.2.1 Comparison of Solid-State and Solution 3 1 P NMR Data The two mutually trans basal PPh3 ligands of RuCl2(PPh3)3 which are equivalent in solution become inequivalent in the solid-state, presumably because of solid-state packing effects, and give rise to the AB part of the ABX pattern (SAB ~19.9 ppm, Figure 4.2). The non-equivalence of the two basal PPh3 ligands in the solid state is also evident in the molecular structure of RuCl2(PPh3)3 in which the two basal Ru-P bond lengths differ by -0.04 A (2.412 and 2.374 A). 4' 1 4 The coupling constant 2 /AB of 333 Hz is within the range expected for rrans-disposed phosphines bound to ruthenium.15'16 The single low- field resonance at 72.5 ppm is proposed to constitute the AX/BX part of the system, the cis couplings, 2 / A X and 2/BX> being too small (typical range -60 to +60 Hz15>16) to be resolved in the relatively broad CP/MAS spectrum. The observed solid-state chemical shifts of 19.9 ppm (8AB) for the basal and of 72.5 ppm for the apical PPh3 ligands are close to the corresponding solution values of 24.1 and 75.7 ppm, respectively. 135 E0 40 22 FFM Figure 4.2: (a) A simulated solution NMR spectrum of RuCl2(PPh3)3 obtained using the literature data13 given in Table 4.1. (b) A CP/MAS 3 1 P NMR (TOSS) spectrum of RuCl2(PPh3)3. 136 -, 1 1 1 1 r 1 r 80 £0 42 20 PPM Figure 4 . 3 : (a) A simulated solution NMR spectrum of Rua2(DPPB)(PPh3) obtained using the literature data1 given in Table 4 . 1 . (b) A CP/MAS 3 1 P NMR (TOSS) spectrum of RuCl2(DPPB)(PPh3). 137 Table 4.1: Literature 31P{ lH] NMR Spectral Data for (a) RuCl2(PPh3)313 at -97 °C, and (b) RuCl2(DPPB)(PPh3)l at -63 *C in CD2C12 Solution. Chemical Shift, 8 ppm (Assignment) Complex (Vpp, Hz) RuCl2(PPh3)3 24.1 (Px) 75.7 (PA) AX 2 Pattern (2/AX = 30.5) RuCl2(DPPB)(PPh3) 26.3 (PA) 35.2 (Pb) 83.2 (Px) ABX Pattern (VAX = -22.6) (2/AB = 302.4) (2/BX =-37.5) Table 4.2: Solid-State 3 ! P CP/MAS NMR Spectral Data for (a) RuCl2(PPh3)3, and (b) RuCl2(DPPB)(PPh3). Chemical Shift, 8 ppm (Assignment) Complex (2^PP, Hz) RuCl2(PPh3)3 16.9 (PA) 22.8 (PB) 72.5 (PX) ABX Pattern (VAB - 333) RuCl2(DPPB)(PPh3) 30.4 (PA) 39.2 (PB) 86.3 (PX) ABX Pattern (VAB = 320) 138 The move of the solid-state chemical shifts to higher field relative to the solution values implies increased shielding in the solid state, particularly for the resonance at 16.9 ppm designated as 8A- Such chemical shift differences between the solid-state CP/MAS and solution NMR data have been observed for other compounds, including tertiary phosphines and their transition metal complexes.17-21 Differences of a few ppm 5-6 ppm) are common, and the compounds are still considered to possess similar structures in solution and in the solid state, at least qualitatively.17-21 Larger chemical shift differences are often considered a manifestation of major structural differences.18 The highest-field signal at 16.9 ppm may be attributed to the basal PPh3 with a longer Ru-P bond (2.412 A). An empirical linear correlation between the crystallographically determined Ru-P distances in a series of Ru(U)-uiarylphosphine complexes and the corresponding 3 -̂chemical shifts observed in solution has been suggested,22 with the chemical shifts becoming more high- field with increasing Ru-P bond lengths. The difference of 52.7 ppm between the basal and the apical phosphorus chemical shifts in the CP/MAS spectrum is close to the 51.6 ppm difference observed in the solution spectrum. Overall, the 3 1 P CP/MAS NMR data for RuCl2(PPh3)3 are consistent with the previously established solid-state geometry of the complex4-14 (Figure 4.4), and comparison with the solution data indicates that there are no major differences in the solid-state and the low-temperature solution structures. PA-Ru-PB 156.4° PA-Ru-P x 101.1° Cl(l)-Ru-Cl(2) 157.2° PA-Ru-Cl(l) 92.4° PA-Ru-Cl(2) 83.7° Figure 4.4: Geometry of RuCl2(PPh3)3 as determined by an X-ray diffraction study.4'14 The bond length and bond angle data are taken from Reference 4. '"«. Ru tm" Cl(l) Cl(2 Ru-PA 2.412 A Ru-PB 2.374 A Ru-Px 2.230 A Ru-Cl(l) 2.387 A Ru-Cl(2) 2.388 A 139 The ambient temperature 3 1P spectrum of 23 in CDCI3 is shown in Figure 4.5. The AB quartet seen in the spectrum (6A = 63.1, 8B = 53.9 ppm; 2 /AB = 46.8 Hz) is assigned to the dichloro-bridged [RuaQOPPB)(u,-Cl)]2 species formed by dimerisation of "RuCl2(DPPB)M after dissociation of PPI13 from 23 (Equation 4.2). The signal due to free PPI13 is evident at ca. -6 ppm. Caulton and coworkers have assigned the triplet-like set of resonances at -24 ppm as a part of an AB2 pattern due to 23 resulting from a fast exchange at room temperature of PB and Px belonging to the DPPB ligand (see Figure 4.7, Section 4.2.2).1 The observed line spacing of 139.5 Hz is essentially identical to the average of the static values of 2 /AB and 2 /AX (302.4 and -22.6 Hz, respectively, see Table 4.1) obtained from the expected ABX pattern which is resolved at -60 *C.1 Figure 4.5: 3lp{lH) NMR spectrum (121.42 MHz, 20 *C) of RuCl2(DPPB)(PPh3) in CDCI3. |i 1 1 : I 1 1 1 1 I 1 1 1 1 ) 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 ) 1 I 1 1 1 1 j 1 1 1 i ) 1 60 50 40 30 1 U I I I ) 111 I I I j I I I 1 1 I I I I I 11 I I 1 I I I I j 20 10 0 PPM -10 140 The solid-state 3 1 P CP/MAS NMR spectrum of the mixed-phosphine complex RuCl2(DPPB)(PPh3), 23, exhibits an A B X pattern similar to that observed1 in the low- temperature solution NMR spectrum (Figure 4.3). The solid-state chemical shifts of 30.4, 39.2, and 86.3 ppm correspond well with the reported solution parameters1 of 26.3, 35.2, and 83.2 ppm, respectively. The shift of ~3-4 ppm in the CP/MAS phosphorus resonances towards low field relative to the solution values indicates reduced shielding of the phosphorus nuclei in the solid state. Interestingly, this low-field shift in going from solution to the solid state is in the direction opposite to that observed for RuCl2(PPh3)3, which shows increased shielding in the solid state (see above). The high-field AB quartet centred at 34.8 ppm with a scalar coupling 2 /AB of 320 Hz indicates rra/w-disposed non : equivalent phosphines. The 320 Hz value for the trans coupling is somewhat greater than the corresponding coupling of 302.4 Hz obtained from the solution spectrum, suggesting the presence of additional constraints and interactions in the solid-state which may not exist, or are averaged out, in solution. The low-field signal at 86.3 ppm is assigned to an apical phosphine ligand; because of the forced cis configuration of the chelating DPPB ligand, the apical phosphine must be a part of the diphosphine. Again, the cis P-Ru-P couplings, 2 /AX and 2/BX> cannot be seen in the CP/MAS NMR spectrum because their magnitudes are much smaller than the typical line-widths encountered in the solid-state NMR spectrum (wi/2 -50-100 Hz). The resonances at 30.4 (SA) and 39.2 ppm (SB) are assigned to the PPI13 ligand and the basal -PPh2 part of the DPPB chelate, respectively, based on the results of a non- quaternary suppression (NQS) experiment,23 in which only the peaks due to phosphorus atoms attached to a non-quaternary carbon are suppressed (presumably because of relatively fast relaxation of the phosphorus nucleus by the protons on the non-quaternary carbon). The NQS spectrum depicted in Figure 4.6 shows the almost complete loss of 141 i 5 0 1 r-*-i 1 1 p —i 1 1 1 [— 120 50 0 FFM -50 Figure 4.6: The CP/MAS 3 1 P NMR spectra of RuCl2(DPPB)(PPh3) showing (a) /Von-Quatemary Suppression (NQS) with a dipolar dephasing delay of 303 p.s. The corresponding TOSS spectrum (b) is shown for comparison. 142 intensity for the resonances at 86.3 and 39.2 ppm, the signals which are due to phosphorus nuclei attached to a non-quaternary carbon (i.e. alkyl chain of DPPB). The resonance at 30.4 ppm remains unaffected and is therefore assigned to the PPI13 ligand, in which all three P-phenyl linkages are through a quaternary carbon atom. The similarities between the solution and the solid-state NMR data for RuCl2(DPPB)(PPh3) clearly suggest very similar solution (at least at low temperature) and solid-state structures for the mixed- phosphine complex. 4.2.2 Comparison of the 3 1 P CP/MAS NMR Data for RuCl2(PPh3)3 and RuCI2(DPPB)(PPh3) Complexes Based on the comparison of the respective 3 1 P CP/MAS NMR data, the mixed- phosphine complex RuCl2(DPPB)(PPh3) is proposed to have a solid-state geometry very similar to that of RuCb(PPh3)3 (Figure 4.7). The 3 1 P CP/MAS NMR spectra of RuCl2(PPh3)3 and RuCl2(DPPB)0?Ph3), including the sideband structure, are very similar except that each of the signals (5A, 5B and the 5x) for the latter are less shielded than the corresponding signals for the tris(triphenylphosphine) complex by about 14-16 ppm (Figures 4.1—4.3, Table 4.2). The solid-state effects, structural or otherwise, which may be responsible for such a considerable and fairly uniform deshielding effect are not obvious. In any case, the deshielding (relative to RuCl20?Ph3)3) cannot be entirely due to solid-state factors; for example, even in the solution spectra, the apical chemical shifts for RuCl2(PPh3)3 and RuCl2(DPPB)(PPh3) differ by 7.5 ppm. Seven-membered chelates, such as the one formed by DPPB on coordination to Ru, have been noted to exhibit considerable deshielding relative to the free ligand (coordination shift),15 and probably also contribute to the observed relative 3^-deshielding in the solid-state spectra. Assuming that the empirical correlation between the 3 1 P chemical shift and the Ru-P bond lengths observed for Ru-monophosphine complexes2 2 can be extended to Ru-diphosphine 143 complexes, the relative 3 ^-deshielding in 23 may reflect a shortening of Ru-P bonds. A crystal structure determination of RuCl2(DPPB)(PPh3), 23, and a careful examination of solid-state 3 1 P NMR spectra for a series of analogous complexes, incorporating diphosphines of varying chelate size (e.g. 4-9, for DPPM through DPPH), may shed more light on these aspects. However, as noted earlier (Section 4.1), the mixed-phosphine complexes containing DPPM, DPPE or DPPP are not isolable.1 Attempts during the present study to synthesise the DPPN or DPPH analogues of 23 resulted in the formation of diphosphine-bridged species of the type [RuCl2(P-P)i.5]2> which have been characterised by elemental analysis and 3 1 P NMR spectroscopy (see Chapter 2, Section 2.5.11 for details). Both RuCl2(PPh3)3 and RuCl2(DPPB)(PPh3) have a trans arrangement of two non-equivalent phosphines in the basal plane as evidenced by the characteristic, relatively large coupling (2/AB) of ~325 ± 10 Hz. The chemical shift differences between the basal and the apical phosphines within the two complexes are essentially identical (5X-OAB = 52 ± 1 ppm, see Table 4.2). Figure 4.7: Proposed solid-state geometry of RuCl2(DPPB)(PPh3) based on the present 3 1P-CP/MAS NMR studies. In recent years, the high-resolution 3 1 P-CP/MAS NMR technique has been employed in the study of biological membranes,24 inorganic phosphides,25 phosphates and polyphosphates,26 as well as phosphorus-containing polymers27 such as poly- phosphazenes. The relatively small number of 3 ^-CP/MAS NMR studies reported to date p (CH 2) 4 / x ci(2; ,.C1(1) 144 on phosphines, transition metal complexes containing phosphines, and their polymer- supported analogues, has clearly established the utility of such studies in structure elucidation in the solid-state;17-21 comparison of solid-state and solution NMR data provides a direct way of examining correlation between the solid and solution structures of such compounds. 1 2 1 1 7 - 2 1 The 2/pp constants have been used extensively to determine the stereochemistry of metal phosphine complexes.12' 1 5 < 2 8 In solution, various fluxional processes can often result in the chemical and magnetic equivalence of two phosphine ligands with accompanying loss of such 31p_31p coupling information.1-12 However, phosphorus nuclei that may be equivalent in solution often become inequivalent in the solid state, as demonstrated for RuCl2(PPh3)3 in the present study (see above); the 2/pp values, particularly for trans-disposed phosphorus nuclei, can be obtained by examination of CP/MAS NMR spectra of such complexes. Despite the potential usefulness of 3 1P-CP/MAS NMR studies of transition metal phosphine complexes, the application of this technique has remained surprisingly limited to complexes of only a few metals. Phosphine complexes of R h , 1 7 ' 1 8 Pt , 1 9 ' 2 0 and C u 1 7 - 2 9 are perhaps the most studied, with those of N i , 1 9 b P d , 1 9 b - 2 8 A u , 1 7 and H g 3 0 completing the list. The results described above are to our knowledge the first examples of a 3 1 P - CP/MAS NMR spectroscopic investigation of ruthenium(II) monodentate and bidentate phosphine complexes. The present study clearly illustrates the potential of phosphorus solid-state NMR spectroscopy as a tool for establishing or refuting the similarity in the solid-state stereochemistry of a series of related compounds, through a simple comparative examination of their 3 ^-CP/MAS NMR spectra, particularly when the X-ray structure of one of the compounds is known. 145 4.3 Reaction of RuCl2(DPPB)(PPh3), 22, with H 2 Reaction of the mixed-phosphine complex 23 with H 2 was investigated with the objective of synthesising a ruthenium hydride complex, RuHCl(DPPB)(PPh3). Such a complex would be analogous to the triphenylphosphine complex RuHCl(PPh3)3,31' 3 2 which is one of the most active catalysts for the hydrogenation of terminal alkenes.32-35 Stirring an initially brown DMA solution (5 mL) of 0.1 g of RuCl2(DPPB)(PPh3) under one atmosphere of H 2 pressure for one hour produced a dark red-brown solution. Work-up of the solution, by concentration to a viscous oil followed by addition of dry, deoxygenated methanol, yielded a green solid which was identified as the starting mixed- phosphine complex by 3 1 P NMR spectroscopy (Figure 4.5). The reaction of 23 with H 2 in DMA as monitored by gas-uptake studies at 50 "C, however, consistently showed ~0.20 mole equivalent H 2 uptake per Ru. Under the same conditions, the analogous RuCl2(PPh3)3 takes up 1 mole equivalent of H 2 per Ru with the resultant formation of RuHCl(PPh3)3 and DMAH+C1- in accordance with Equation 4.4.36 DMA RuCl2(PPh3)3 + H 2 »- RuHCl(PPh3)3 + DMAH Cl - (4.4) Examination of the H2-uptake solution by 3 1 P NMR spectroscopy (C6D6 lock) clearly shows the presence of more than one species in solution 07igure 4.8); the *H NMR spectrum of the ruthenium phosphine-containing species could not be obtained because of the large amount of non-deuterated DMA solvent present. Several of the 3 1 P NMR peaks in the 45-55 ppm region could be correlated as AB quartets, simply based on the coupling constants (2/pp) and the observed intensities (Figure 4.8, inset). The relatively small chemical shift separations (<4 ppm) between the various related 8A and 8B resonances imply that the corresponding phosphorus nuclei occupy similar chemical and magnetic environments. The presence of the triplet-like resonance at ~24 ppm indicates that some 23 146 Figure 4.8: 31p{lH) NMR spectrum (121.42 MHz, lock, 20 'Q of the H2-uptake solution of RuCl2(DPPB)(PPh3), 23, DMA. is present in the solution (compare with the ambient temperature 3 1 P NMR spectrum of 23 shown in Figure 4.5). Because of the apparently reversible nature of the reaction of 23 with H2 in DMA, and because of the large number of species produced in the reaction, further investigations into the nature of the various species in solution were not pursued. In the presence of Proton Sponge® (PS), the mixed-phosphine complex 23 absorbed ~0.90 mole equivalent of H2 per Ru over about 25 min (50 *C, 1 atm of H2, DMA); the resultant solution was distinctly darker red in colour compared to the H2-uptake solution obtained in the absence of added PS (see above). Stirring a C6D6 solution of RuCl2(DPPB)(PPh3) and PS (-1.1 eq.) under 1 atm H2-pressure, for 18 h at room temperature, also produced a dark red solution with some suspended solid (presumably PSH+Cl-). These red solutions generated by reaction of 23 with H2 were extremely air- sensitive, turning green within seconds of exposure to air. The 31P{1H} and J H NMR spectra of the reaction mixture in C^De sealed under hydrogen atmosphere are shown in Figures 4.9 and 4.10, respectively. The major peak in the phosphorus NMR spectrum is a singlet at 48.4 ppm which is assigned to the trichloro-bridged dinuclear complex containing coordinated PS, viz. [(PS)(DPPB)Ru(u-Cl)3RuCl(DPPB)] mentioned in Chapter 3 (Section 3.6.5); addition of PS to a solution of 23 in the absence of hydrogen does indeed result in the appearance of the 48.4 ppm resonance. The triplet-like resonance at ca. 39.5 ppm with a line spacing of 129 Hz is assigned, by analogy to the phosphorus spectrum of the starting dichloro complex 23 (Figure 4.5),1 as part of an AB2 pattern due to the desired RuHCl(DPPB)(PPh3) species. 148 I J ~1 I i—i I | — i — i — i — r - | — r — i — i — i — | — i — i — i — i — | — i — r — i — r i O S O 4 0 - i — | — i — i i i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—r 7 0 I 0 | i i i i I i i i i | 0 PPM - IC Figure 4.9: 3,P{ 'H} NMR spectrum (121.42 MHz, 20 °C) of the reaction mixture obtained after stirring 23 in C6D6 solution under 1 atm H 2 for 18 h in the presence of Proton Sponge® (~1 equiv./Ru). o —i—i—i—i—i— i—i—i— i—i— i—i—i—i— i— i—i—i—i—i— i— i— i—i—i— i— i—i—i—i— i—i—i—i—i— i—i—i i i—i -i i i i i i i i—r—i 10 8 6 4 2 PPM 0 Figure 4.10: 'H NMR spectrum (300 MHz, 20 *C) of the reaction mixture obtained after stirring 23 in solution under 1 atm H 2 for 18 h in the presence of Proton Sponge® (~1 equiv./Ru). The dark red colour of the reaction mixtures obtained after reaction with H2 in the presence of DMA or PS is consistent with the formation of five-coordinate hydride(s); six- coordinate Ru-hydride complexes are typically pale yellow in colour whereas the five- coordinate complexes are generally intensely coloured.37 The extremely air-sensitive nature of die red solutions also supports the presence of pentaccordinate Ru(II) species. The proton NMR spectrum (Figure 4.10) principally consists of resonances due to [(PS)(DPPB)Ru(u-Cl)3RuCl(DPPB)]. The phenyl and naphthyl proton resonances span the 8 8.3-6.8 ppm region and the methylene protons of DPPB appear as broad multiplets at 8 3.5, 2.3, 1.9 and 1.5 ppm (4H each). The singlets at 2.85 and 2.6 ppm are assigned to the N-methyl protons of the bound and the free PS, respectively. Support for the presence of small amounts of Ru-hydride moieties in the solution comes from the signals in high- field region of the proton NMR spectrum, which consists of a pseudo-quartet (an overlapping doublet of triplet, dt, pattern) at 8 -17.4 ppm, a doublet of triplets centred at -18.65, and a very broad peak at -19.25 ppm (w\/2 -90 Hz). The peaks at -17.4 and -18.65 ppm are tentatively assigned to two different species of the composition 'RuHCl(DPPB)(PPh3)' (Figure 4.11); of note, the hydride resonance of the analogous RuHCl(PPh3)3 is observed at -17.75 ppm (q, 2 / P H = 26.0 Hz, CDCI3).31 The observed 2 / p H of -25-30 Hz for the pseudo-quartet and the doublet of triplets indicate that the hydride is cis to the three phosphine ligands in both die 'RuHCl(DPPB)(PPh3)' species (Figure 4.11). The broad resonance at -19.25 ppm, which is of approximately double the integral intensity of the pseudo-quartet at -17.4, may be due to a coordinated dihydrogen ligand (r| 2-H2) 3 8~ 4 0 likely trans to the Ru-hydride (Structure 4-IV in Figure 4.11). Reliable spin-lattice relaxation time (7j) measurements on this signal could not be obtained because of the very low intensity of the hydride peaks. Alternatively, the 2:1 integral intensity ratio for the broad resonance at -19.25 and the dt pattern at -17.4 ppm may be purely coincidental, then the -19.25 ppm resonance could belong to a different species such as 4-II, with all three hydrogens (a hydride and a molecular H2 moiety) in mutually 151 cis positions. Fast exchange among the three hydrogens at ambient temperature would give a broad proton NMR signal. Such fast exchange, at least on the NMR time-scale, and the consequent broadening of hydride signals in proton NMR spectra, have been observed for other polyhydride complexes containing three mutually cis hydrogens. The complexes Co(H)(r]2-H2)(PTi2P(CH2)3PPri2),41 [(ri5-C5H5)Ir(L)H3]+ (L = PCy 3, PMe2Ph, P I ¥ 3 , AsPh 3), 4 2 and [{ri5-(l,3-SiMe3)2-C5H3}NbH3]43 are some examples of complexes which exhibit exchanging hydride ligands. The resonance at -18.65 ppm (dt, 2 /pH = 29 and 25 Hz) could result from either of the two species, 4-1 or 4-in, depicted in Figure 4.11. (CH 2) 4 (CH 2) 4 / / , , P" D ..H P"« ' * Ru ^Ru xxH (CH 2) 4 / P"«i Ru ( C H 2 ) 4 / „nH P "" H Ru' .**H H C l ^ X p C l ^ I H - L - H a ci 4-i 4-n 4-m 4-rv Figure 4.11: Possible structures for Ru-hydrides formed from RuCl2(DPPB)(PPh3). On the whole, H2-reactivity of RuCl2(DPPB)(PPh3) in the presence of either DMA or PS as an external base parallels that noted by C. Hampton of this department for some related mixed-phosphine complexes of general formula RuCl2(P-N)(PPh3),44 where P-N represents a ferrocenylarninophosphine ligand such as PPFA or isoPFA,45 which is similar to the BPPFA ligand shown in Chapter 1, Figure 1.1. Hampton's studies showed that the PPFA and isoPFA derivatives reacted with 1 atm H2 in the presence of DMA or PS in an apparently reversible fashion; the H2-uptake in DMA for these complexes corresponded to -0.39 and 0.19 mole/Ru at 30 and 50 °C, respectively. An H2-uptake of -0.57 mole/Ru was observed in the presence of Proton Sponge® at 30 * C . 4 4 The 3 1 P NMR spectra of solutions of RuCl2(P-N)(PPh3) complexes sealed under hydrogen consisted of a large 152 number of peaks suggesting the presence of several species in the reaction mixture, most of which could not be isolated and identified with certainty. The presence of some Ru- hydride species was evident from signals in the high-field region of the proton NMR spectra. The hydrides RuHCl(isoPFA)(PPh3) and RuHCl(PPh3)3, and a dinuclear dihydrogen complex, [(r|2-H2)(isoPFA)Ru(u-Cl)2(u-H)RuH(PPh3)2],46 were the only products that could be isolated and characterised from the reaction of RuCl2(isoPFA)(PPh3) with H2 in benzene/methanol solutions.44 During the present study, attempts to isolate 'RuHCl(DPPB)(PPh3)' and related hydrides formed in the reaction of 23 with H2 were not successful; however, as described in the following sections, reactions with chelating reagents L - L (see Sections 4.4,4.5 and 6.2) of these hydrides prepared in situ generally resulted in the displacement of the triphenylphosphine ligand to afford six-coordinate RuHCl(DPPB)(L-L) complexes. 4.4 Synthesis of RuCl 2(DPPB)(PPh 2Py) Reaction of RuCl2(DPPB)(PPh3) with one equivalent of diphenyl(2-pyridyl)- phosphine, PPh2Py, in dichloromethane gave an orange-yellow product which was identified as rran5-RuCl2(DPPB)(PPh2Py), 24, as shown in Figure 4.12. The complex was characterised by NMR spectroscopy and elemental analysis. a a Figure 4.12: 7ra«5-RuCl2(DPPB)(PPh2Py), 24. 153 The 3 1 P NMR spectrum of this compound in C6D6 solution displayed an AMX pattern which consisted of three doublet of doublets of equal integral intensity (Figure 4.13). The doublet of doublets centred at - 2 1 . 0 ppm is assigned to the PPh2Py ligand (PA) and the remaining two sets at 24.9 (PM) and 45.0 (Px) ppm, respectively, are attributed to the DPPB ligand. The 2 / A M of 328.5 Hz is indicative of two mutually trans phosphines, each of which shows a further coupling of 28.1 and 36.9 Hz, respectively, due to the third phosphine (Px) in the cis position. The coordination shift of - 1 6 ppm for the Ru(II)-bound PPh2Py, relative to the free ligand singlet at-5.0 ppm, is in the same direction and range as that observed for an orr/io-metallated PPI13 ligand bound to a Ru(U) centre.47 A ring contribution15 (AR) can be calculated for the chelating PPh2Py by subtracting from its chemical shift that for the non-chelating PPI13 ligand in the formally analogous RuCl2(DPPB)(PPh3) complex, 23; the AR value of -47.3 ppm (AR = - 2 1 . 0 - 26.3 = -47.3 ppm) is characteristic of formation of a four-membered ring.15 The 45.0 ppm resonance for 24 is ~38 ppm high-field of the resonance due to the apical phosphorus of 23, strongly suggesting that the trans site in the PPh2Py derivative is occupied by the pyridyl group giving a six-coordinate complex. The additional sets of resonances in the 31p NMR spectrum of fra/«-RuCl2(DPPB)(PPh2Py) at 47.2, 35.9 and -21 .4 ppm are attributed to the cj*s-RuCl2(DPPB)0?Ph2Py) complex (see below). The lH NMR spectrum of 24 (Figure 4 .14) shows the pyridyl proton resonances shifted upfield of the corresponding free ligand proton values of ~7.2-7.1 ppm (m, 4H) to - 6 . 6 (m, 3H) and 6.2 (m, IH) ppm. The reaction of 23 with PPh2Py was carried out with a view of incorporating a nitrogenous base, in this case the pyridyl group, in a ruthenium-bound ligand. Because of what appeared to be a reversible reaction of 23 with H2 in the presence of an external base such as DMA (Section 4.3), it seemed appropriate to introduce a basic site in a coordinated 154 U l U l I I I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I 50 40 30 20 10 0 -10 -20 PPM Figure 4.13: The ̂ P[lH] NMR spectrum (121.42 MHz, 20 *C) of rra/w-RuCl2(DPPB)(PPh2Py). The peaks marked with asterisks are due to the cis isomer (-12% of total integral intensity). 156 ligand which could, under hydrogenation conditions, perhaps promote hydride formation by "picking up" the HCl (heterolytic cleavage of H2; 3 3 , 3 4 cf. Chapter 1, Section 1.3), and simultaneously providing a coordination site for subsequent substrate binding (Equation 4.5). As mentioned at the end of the previous section, ongoing H2-activation work from this department has involved Ru(II) complexes of ferrocenylaminophosphine ligands, such as PPFA and isoPFA, which contain both phosphorus and nitrogen centres (cf. Chapter 1, Figure 1.1 ). 4 4 " 4 6 - 4 8 The amino group of the PPFA ligand in RuCl2(PPFA)(PPh3) has been shown to participate in dihydrogen activation.44 Heating a toluene solution of rra^s-RuCl2(DPPB)(PPh2Py) at 80 °C under 1 atm of H 2 for 8 h resulted in the precipitation of a yellow-orange solid, 25. The 31P{ ^H} and the *H NMR spectra of the product in CDCI3 solution at 20 °C are shown in Figures 4.15 and 4.16, respectively. The absence of proton resonances in the high-field region (0 to -30 ppm) means no hydride(s) were formed during the reaction. The 3 1 P NMR spectrum shows overlapping doublet of doublet patterns centred at -21.4, 35.9 and 47.2 ppm with 27pp of 23-35 Hz, which are characteristic of a mutually cis arrangement of the three phosphine groups. The same resonances are also present in the 3 1 P spectrum of the trans isomer in about 12% of the integral intensity (see Figure 4.13). Furthermore, heating a solution of the trans isomer in the absence of H2 leads to the formation of the same product(s) as evidenced by *H and the 3 1 P NMR spectroscopy. All of these observations are consistent with the cis formulation for 25 as illustrated in Figure 4.17. ci H Cl a 157 (^Hdd)(addO) z Dn^PI° O . OZ ' £ DCD 4*HW ZfrTZl) uiaqoads yiMN (HiJdie M̂X SIP am^d •(^ zqdd)(Hdd(l)ZDnH-*Pi° O. OZ 4 £DCD 'ZHW 00£) ujtujosds yj^K Hi 341 -9VP a»n3ij O W d d P 2 E f S 9 f 8 6 I i . I I I i i II 1 i i • i 1 I I i i 1 II II I i i i i I i i II I I I i i I i i i : I i i i i I I I I I I l I I J J I I I I 1 I I I I 1 I l l l I l l l l I I l l l I I 1 L J J T Cl Figure 4.17: C«-RuCl2(DPPB)(PPh2Py), 25. The additional set of three 1:1:1 doublet of doublet 3 1 P NMR patterns of ca. 4% integral intensity, and centred at -18.0, 17.8 and 36.0 ppm in the spectrum of 25 (Figure 4.15), remains unassigned. The observed P-Ru-P coupling constants (Vpp ~25-30 Hz) for this as yet unidentified product are characteristic of a mutually cis arrangement of the three phosphine groups. The relative insolubility of the cis isomer 25 (vs. trans) in nonpolar solvents such as benzene or toluene is consistent with a higher dipole moment, and therefore an increased polarity, expected for the cis complex. Such differences in solubility in polar and nonpolar solvents have been noted for other cisltrans six-coordinate Ru(II) complexes (e.g. cis,cis,trans- and all rra/j,s-RuHCl(CO)2(PPh3)249), the cis isomers generally being relatively less soluble in nonpolar solvents and the trans complexes in polar solvents. The observed isomerisation of the trans derivative, 24, to the corresponding cis complex, 25, under hydrogenation conditions specified earlier was unexpected, but in retrospect not surprising. Complex 24 obtained by reaction of 23 with PPh2Py must be the kinetic product, which on heating isomerises to the thermodynamically more stable cis species 25. The relative insolubility of 25 in aromatic solvents likely aids the isomerisation process by continually driving the equilibrium toward the formation of more cis isomer which continues to precipitate from the benzene or toluene solutions. For Ru(Tt) complexes such as RuCl2(Ph2P(CH2)i-3PPh2)2, which contain two chelating phosphine ligands, the cw-dichloro arrangement is often thermodynamically favoured over the trans 160 configuration.50 Interestingly however, the kinetically favoured trans- RuCl2(diphosphine)2 complexes are almost always more prevalent.51 Presumably, the diphosphines bind to Ru too strongly to permit dissociation of one end of the chelate to produce a five-coordinate fluxional intermediate that could undergo rearrangement to give the cis isomer. A possible mechanism for the formation of 24 from 23 and the subsequent isomerisation of 24 to 25 is outlined in Scheme 4-1. The incoming pyridylphosphine ligand occupies the vacant coordination site trans to the apical phosphine end of the DPPB ligand of 23 to give a six-coordinate intermediate (A); dissociation of PPI13 and coordination of the pyridyl nitrogen would give the observed trans- kinetic product (24). In view of the relative inertness of the rrans-RuCl2(diphosphine)2 complexes to isomerisation to the respective cis analogues, it is reasonable to assume that the pyridyl group, rather than a phosphine, undergoes dissociation to give a five-coordinate intermediate (B). The coordinated DPPB ligand, however, is known to dissociate at one end and become "dangling" in some Ru(II) systems.52 To test for possible involvement of DPPB, the new complex rranj-RuCl2(DPPB)(DPPM), 27, analogous to 24 in geometry and also in that it contains a four-membered chelate similar to PPh2Py, but without a nitrogen centre, was synthesised. No isomerisation to the cis isomer was detected for 27, even after heating in toluene solution at 80 "C for 48 h (see Section 4.5 for details). This observation provides some indirect support for the non-involvement of the DPPB ligand in the isomerisation of 24, and by the same token suggests that the presence of the pyridyl group in 24 plays a key role in the isomerisation of 24 to the cis derivative 25. Related isomerisation reactions in some pyridylphosphine Pt and Pd complexes also occur via dissociation of the pyridyl functionality.53 Five-coordinate Ru(U) complexes are known to be stereochemically non-rigid,1- 3 » 1 3 > 5 4 and can readily rearrange via a Berry pseudo- 161 (23) (A) (24) (25) Scheme 4-1: A possible mechanism for the formation of 24 and 25 from 23; DPPB and PPh2Py are denoted by P—P and P—N, respectively. 162 rotation mechanism.55 Rec<x>rdination of the pyridyl group to the ruthenium centre in the rearranged five-ccordinate intermediate C then produces the cis isomer 25. The cis complex 25 can exist in two enantiomeric forms designated A and A 5 4 b > 5 6 as illustrated in Figure 4.18; however, the two isomers cannot be differentiated from each other by NMR spectroscopy. However, substitution of the nonchiral DPPB ligand by a chiral DIOP or BINAP ligand would result in the formation of diastereomers, and would be of interest. Cl a A A Figure 4.18: Enantiomeric forms of c/s-(/ac)-RuCl2(DPPB)(PPh2Py), 25. Although the attempts to make the hydride complex RuHCl(DPPB)(PPh2Py) or RuHCl(DPPB)(PPh2PyH+Cl-) by reaction of rra^-RuCl2(DPPB)(PPh2Py) with H2 were unsuccessful, and instead resulted in the isomerisation of the starting complex to the corresponding cis isomer, 25, the former hydride complex was eventually synthesised using a different approach. As described earlier (Section 4.3), the reaction of RuCl2(DPPB)(PPh3) with H2 in the presence of Proton Sponge® produces hydride species such as RuHCl(DPPB)(PPh3) in solution. Addition of PPh2Py (1 equiv./Ru) to a dark red solution of ruthenium hydrides, generated in situ by treating 23 (0.2 g, 0.23 mmol) in ~20 mL toluene with 1 atm H2 in the presence of PS at 65 °C, resulted in a rapid colour-change to orange. The yellow-orange solid that precipitated over two hours of stirring the reaction mixture under 163 H 2 was separated by filtration, washed with ethanol to remove any PSH+C1-, and vacuum- dried (yield: 0.08 g). The 3 1 P and J H NMR spectra of the yellow-orange solid were identical to those observed for the cw-RuCl2(DPPB)Q?Ph2Py) complex (see Figures 4.15— 4.17). An orange-brown solid was then isolated from the toluene filtrate by concentration to ~5 mL followed by addition of hexanes (yield: 0.08 g). The 3 1 P and lH NMR spectra of the orange-brown product in C6D6 solution are shown in Figures 4.19 and 4.20, respectively. The high-field overlapping doublet of triplet pattern at -13.7 ppm in the proton NMR spectrum is indicative of a hydride species, 26 (see Figure 4.21). The magnitude of the H-Ru-P coupling constants suggests that the hydride is cis to the three phosphine groups ( 2 / P H = 23.1 Hz, d; 21.6 Hz, t). Proton NMR signals due to Ru-H moieties trans to a chloride ligand of trans- RuHCl(Ph2P(CH2)nPPh2)2 species for n = 1-4 have been reported, and are observed in the range 8 -13 to -20 ppm (q, 2 / P H -19-22 Hz).2 Examination of the phosphorus NMR spectrum points to the presence of at least three species. One of the products is readily identified as the rran.s-RuCl2Q3PPB)(PPh2Py) complex, 24 (-43% based on integral intensity), by comparison of the phosphorus NMR data (Figure 4.13); a small amount of the cis isomer 25 is also evident (-7% based on integral intensity). The new sets of resonances centred at -12.9, 40.9 and 59.9 ppm (AMX pattern), amounting to -50% of the total integral intensity, are assigned to the hydride species; one trans and two cis P-Ru-P couplings (27p.p) are evident. The resonances centred at -12.9 ppm (8A) are attributed to the bound PPh2Py and the remaining two sets of signals centred at 40.9 (8M)» 59.9 (8x) ppm to the DPPB ligand for reasons elucidated earlier. All phosphorus resonances of 26 show a small residual coupling of -8-11 Hz because of inadequate broadband proton decoupling, particularly of the high-field ruthenium hydride; the extra splittings disappeared when the broadband decoupler power was increased to the maximum available. 164 fTTTI | I M I | I I I ! | I I I I | I I II | I I I I | ITTT | I I I I | I I I ! | I I ! I f! I I I | I I I \~\ 1 I! I | I I I I | II I I | I I I I | I 1 I I | I I I I | 60 50 40 30 20 10 0 -10 -20 PPM Figure 4.19: The 3 *P NMR spectrum (121.42 MHz, QJDk 20 *C) of the orange-brown solid obtained from the reaction of PPh2Py with hydrides formed in situ from the reaction of 23 with H 2 in the presence of Proton Sponge®. p I I I | I I I I [ I I I I | I I I I | I I I I | I I I I | I I I i | I I I I | I I I I j I I I I | I I I I | I I I I | I 1 I I | I I I I | I I I I | I I I I | I I I I | I I 1 I | 9 8 7 6 5 4 3 2 1 PPM 0 Figure 4.20: The *H NMR spectrum (300 MHz, C6D6.20 *C) of the orange-brown solid obtained from the reaction of PPh2Py with hydrides formed in situ from the reaction of 23 with H 2 in the presence of Proton Sponge®. The peaks assigned to the hydride complex 26 (see text) are marked by asterisks. The hydride resonance is also shown (INSET). Overall, the dichloro- complexes (24 and 25 together) and the hydridochloro- derivative (26) were produced in ca. 2:1 ratio based on relative NMR integral intensities; further purification and isolation of the hydride derivative were not attempted. Consistent with the available NMR spectral data, the hydride complex, 26, is assigned the trans geometry shown in Figure 4.21. The 3 1 P NMR spectral data for the Ru(II)- pyridylphosphine complexes 24-26 are listed in Table 4.3. The phosphorus chemical shifts of the hydridochloro complex 26 are observed to low field of the corresponding resonances of the dichloro analogue 24. A similar relative low-field shift in 3 1 P chemical shifts on replacing a chloride by a hydride ligand is observed for other Ru(II)-phosphine complexes; for example, the 3 1 P chemical shifts for rra/u-RuHCl(P-P)2 complexes2 are: P-P, 5 ppm (s) = DPPM, -3.8; DPPE, 60.8; DPPP, 15.6, as compared to the chemical shifts for the corresponding rrarcs-RuCl2(P-P)2 complexes:1 P-P, 8 ppm = DPPM,-7.7; DPPE, 44.3; DPPP,-5.0. H Cl Figure 4.21: 7>a/w-RuHCl(DPPB)(PPh2Py), 26. 167 Table 4.3: 31P{ lpi} NMR Spectral Dataa for RuXCl(DPPB)(PPh2Py) Complexes 24-26 (X = Cl, H). Complex Chemical Shift, 8 ppm (Assignment) (2/pP,Hz) rrans-(mer)-RuCl2(DPPB)(PPh2Py) (24) AMX Pattern -21.0 (PA) (2/AX = 28.1) 24.9 (PM) (27AM = 328.5) 45.0 (PX) (2/MX = 36.9) Oy-(/bc)-RuCl2(DPPB)(PPh2Py) (25) AMX Pattern -21.4 (PA) (2/AX = 23.7) 35.9 (PM) (2/AM = 27.3) 47.2 (PX) (27MX = 34.7) Tra/z5-(mer)-RuHCl(DPPB)(PPh2Py)b -12.9 (PA) (26) AMX Pattern ^ A X = 31.2) 40.9 (PM) (2/AM = 288.3) 59.9 (PX) (27MX = 36.7) a 121.42 MHz, at 20 *C; in C^De for complexes 24 and 26, in CDCI3 for 25. PPh2Py is designated as PA while PM and Px refer to the phosphorus nuclei of the DPPB ligand. b lH NMR (300 MHz, Q D 6 , 20 °C) signal for Ru-H is observed at -13.7 ppm (dt; 2 / p H = 23.1 Hz, d; 21.6 Hz, t). 4.5 Synthesis of 7Yflns-RuCl 2 (DPPB)(DPPM) Addition of one equivalent of the diphosphine DPPM to a dichloromethane or benzene solution of RuCl2(DPPB)(PPh3) resulted in a rapid colour change from the initial green to yellow. A pale brownish-yellow solid that was isolated from the yellow solution is identified as rraw-RuCl2(DPPB)(DPPM), 27 (Figure 4.22), by lH and 3lp NMR spectroscopy and elemental analysis; full preparative details are given in Section 2.5.9.2. 168 a H •H a Figure 4.22: 7Va>w-RuCl2(DPPB)(DPPM), 27. The *H NMR spectrum of 27 in C6D6 (Figure 4.23) shows a triplet at 8 4.65 (2H) for the methylene protons of DPPM, and broad multiplets at 8 2.95 (4H) and 2.60 (4H) for the methylene protons of DPPB. The resonances for the orf/w-phenyl protons are observed at 8 7.65 (8H, DPPB) and 7.45 (8H, DPPM) while those for the meta- and para- phenyl protons of DPPB and DPPM are observed as overlapping multiplets in the 7.0-6.8 ppm region (total 24H). The 3 1 P NMR spectrum of 27 is second order in nature (A8/7 < 6;9 Figure 4.24). That the complex patterns seen in the spectrum of 27 arise from a single compound was confirmed by a 31p_3lp homonuclear correlation (COSY) experiment. It is evident from the contour plot shown in Figure 4.25 that all the resonances are connected with each other via off-diagonal peaks, thus indicating that all four phosphorus nuclei within 27 are coupled with each other. Complexes of the type fra/w-RuCl2(P-P)2 generally exhibit just a singlet in the 31p NMR spectrum, all four phosphorus nuclei being chemically and magnetically equivalent. For example, the chiral Ru(II) analogues containing the diphosphines 5,5-CHIRAPHOS56 or 5,5-BDPP (present work, see Chapter 2, Section 2.5.8.4), for which the two ends of the chiral diphosphine are magnetically equivalent, show just a singlet in the 3 1 P spectra (cf. Chapter 3, Section 3.4). A combination of relative flexibility of diphosphine backbone and molecular motion in solution can sometimes result in the apparent equivalence of the phosphorus nuclei as seen for RuHCl(CHIRAPHOS)2.12,56 The relatively large scalar 169 Ll '(WddaXaddOJ^Dnii-^^ i° O. OZ '9CPD ' Z H W 00£) uiiujMds ^ W N " ° l ° J a -IZv O W d d T 2 E V S 9 Z • B B I I I I I I I I M I I M I I I I I I 1 I I I I 1 I I I I I I I I I I I I I t I I I I I 1 I I I I 1 I I I I 1 I I I 1 1 I I I ! I I I I I I I I I I I I I I I I I I I I I I 1 I 1 1 1 r r J 18.777 18.519 -V 18.253 \- 18.240 r 16.006 J- 15.957 15.744 15.454 -8.087 r -22.523 r -22.812 J- -23.025 -25.343 •25.587 _ -23.06 ^- -23.076 r -25.31 I- -25.32 -25.845 I \J F2 (PPM) 20 15 10 5 0 -5 -15 F l (PPM) Figure 4.25: 31p_31p homonuclear COSY contour plot (121.42 MHz, 20 'Q of rraw-RuCl2(DPPB)(DPPM), 27, in CsDe solution. 172 due to rra/is-disposed phosphines, 2/pp (~200-350 Hz 1 5), is in fact seldom seen in solution spectra of trans-RuCl2(P-P)i complexes. In complex 27, however, the two diphosphine ligands, viz. DPPB and DPPM, are sufficientiy different from each other that separate resonances are observed, giving rise to the second order AA'BB' 3 1 P NMR pattern in solution (Figures 4.24, 4.26). The high-field pattern centred at -24.2 ppm is assigned to DPPM, and the pattern at 17.1 ppm to the DPPB ligand, in keeping with the reported shielding of phosphorus nuclei in four-membered rings and the observed deshielding of phosphorus nuclei in seven-membered chelates.1-15>57 Figure 4.26 shows a simulated 3 1 P NMR spectrum for an AA'BB' spin-system which corresponds well with that observed for 27 (Figure 4.24). The P-P coupling constants obtained from the simulated spectrum are listed in Table 4.4. Table 4.4: 3 1 P NMR Spectral Parameters3 (121.42 MHz) Used to Obtain the Simulated Spectrum for Tra^-RuCl2(DPPB)(DPPM), 27, Shown in Figure 4.26. Spectral Parameter15 Value Spectral Parameter15 Value 6A, 8a- (DPPB) 6 8 5 4 . 0 (17.1 ppm) 8B, 8B' (DPPM) 1 8 4 7 . 0 ( - 2 4 . 2 ppm) 27AB 3 0 3 . 0 27AB' 3 0 3 . 0 2/AA' 2 9 . 6 2/BB- 3 1 . 3 2/AB' (or 2/A-B) - 3 0 . 6 2/A-B (or27AB') - 3 4 . 3 a Obtained using a Varian spectral simulation package, assuming an AA'BB' spin- system. All values are in Hz, unless indicated otherwise, with a reference frequency of 4779.9 Hz for 85% H3PO4 at 0.0 ppm. b The coupling constants 2/AB and ^A'B' are due to trans-disposed phosphines (2 t̂rans); the rest arise from mutually cis phosphines (2/cis)- Signs of 27 ci s are reported relative to one another while the 2/trans is positive. 173 Figure 4.26: A simulated 3 1 P NMR spectrum (121.42 MHz, AA'BB' spin-system) for fra/w-RuCl2(DPPB)(DPPM), 27, obtained using the parameters listed in Table 4.4. As mentioned in the previous section, synthesis of 27 was undertaken in order to check, albeit indirectly, if DPPB dissociation was involved in the isomerisation of rran^-RuCl2(DPPB)(PPh2Py), 24, to the corresponding cis derivative, 25. The phosphine DPPM was chosen to replace the chelating PPh2Py ligand of 24 because it forms a similar four-membered ring upon coordination to a metal centre. Moreover, it was thought that a study of the isomerisation behaviour of rrarw-RuCl2(DPPB)(DPPM) might indicate whether the presence of pyridyl moiety in 24 was important for the isomerisation of 24 to 25. The 3 1 P NMR spectrum of a toluene solution of 27 remained unchanged even after heating the solution at 80 °C for 48 h under argon, showing that no isomerisation of the trans derivative to the corresponding cis species occurred under these conditions. The stability of 27 to isomerisation must result from its inability to dissociate a phosphine-end, of either DPPB or DPPM, to give a fluxional five-coordinate intermediate that is likely essential for the isomerisation to proceed. As mentioned in the previous section, this result provides some indirect evidence of the coordinative stability of DPPB, and support for the involvement (dissociation) of the pyridyl group of the PPh2Py ligand in the trans to cis isomerisation of RuCl2(DPPB)(PPh2Py). Reaction of 'RuHCl(DPPB)(PPh3)' (prepared in situ from 23 and H2/PS in 10 mL benzene as described in Section 4.3) with one mole equivalent DPPM ligand produced a yellow solution. Addition of hexanes (20 mL) to the reaction mixture after concentration of the benzene solution to ~5 mL resulted in precipitation of a yellow solid which was isolated by filtration, washed with diethyl ether (5 mL) and vacuum-dried (yield: 0.075 g). The lH NMR high-field quintet at -15.55 ppm (2/PH = 18.9 Hz) observed for the yellow solid in C6D6 solution is indicative of the Ru-hydride complex, rrans-RuHCl(DPPB)(DPPM), 28, with the hydride being cis to all four phosphorus nuclei. The proton NMR spectrum also shows that RuCl2(DPPB)(DPPM), 27, is present in substantial amounts - in ca. 2:1 ratio relative to the hydride as calculated from the integral intensities (Figure 4.27). 175 | I I 1 I | I I 1 I 1 I I I I | I I I I | I I I 1 ] I I I I ) I I I I | I I I I | I I I I | I I I I 1 I I I I | I I I I i I I I I | I 11 I | I I 1 I ] I I I I ] 8 7 6 5 4 3 2 1 PPM Figure 4.27: The »H NMR spectrum (300 MHz, C ^ , 20 *C) of the yellow solid obtained from the reaction of DPPM (1 eqTRu) with hydrides formed in situ from the reaction of 23 with H 2 in the presence of Proton Sponge®. The peaks due to the dichloro complex 27 (see text) and impurities are marked while the rest are assigned to franj-RuHC103PPB)(DPPM). - J rT-r-r 40 l | I I I l | i l l 30 I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I j I 20 10 0 -10 l l l | l l I I | I I l -20 PPM Figure 4.28: The 31p{lH) NMR spectrum (121.42 MHz, Q d ^ 20 *C) of the yellow solid obtained from the reaction of DPPM with hydrides formed in situ from the reaction of 23 with H 2 in the presence of Proton Sponge®. The peaks due to the dichloro complex 27 (see text) and impurities are marked while the rest are assigned to rrans-RuHCl(DPPB)(DPPM). The 3 1 P NMR spectrum of the yellow solid confirms the presence of 27 in the product mixture (Figure 4.28, see above). Resonances centred at 37.8 and -8.0 ppm are attributed to the DPPB and DPPM ligands, respectively, of fra/w-RuHCl(DPPB)(DPPM), 28. These NMR patterns are similar in appearance to those observed for 27, but are shifted to high field of the corresponding signals due to 27, as expected for a hydridochloro complex (see the previous section). Spectral simulation to obtain various 31p_3lp coupling constants by comparison with the observed spectrum was not carried out for the hydridochloro complex 28. Of note, attempts to synthesise 28 by reaction of 27 with NaBR* in refiuxing ethanol were unsuccessful, the starting complex 27 being recovered unchanged after 24 h (31P NMR evidence). Significantly, comparison of reactions of 'RuHCl(DPPB)(PPh3)' with the phosphines PPh2Py and DPPM shows that the corresponding hydridochloro complexes 26 and 28 are formed in approximately the same ratio (ca. 1:2, i.e. -34% formation of the hydridochloro products) relative to the respective dichloro derivatives (24+25 and 27, ~66% formation), which are the other products in these reactions. It should be noted that in each case 'RuHCl(DPPB)(PPh3)' was prepared in situ from RuCl2(DPPB)(PPh3). Provided that the PPh2Py and DPPM ligands react with the 'RuHCl(DPPB)(PPh3)7 RuCl2(DPPB)(PPh3) equilibrium mixture irreversibly and much more rapidly than the equilibrium could be re-established to form 'RuHCl(DPPB)(PPh3)' from 23 and H2/PS, the observed distribution of the hydridochloro (34±3%) and the dichloro products (-66%) may be a reflection of the initial proportions of 'RuHCl(DPPB)(PPh3)' and RuCl2(DPPB)(PPh3) in solution at the time of phosphine addition (Scheme 4-II). 178 H2/Proton Sponge® RuCl2(DPPB)(PPh3) 'RuHCl(DPPB)(PPh3)' + HCl 66% QH6 34% -PPh3 +L-L L-L = PPh2Py or DPPM fast fast -PPh3 +L-L RuCl2(DPPB)(L-L) RuHCl(DPPB)(L-L) 66% 34% Scheme 4-H 4.6 Characterisation of RuCl2(R-BINAP)(PPh3), ZI The reaction of RuCl2(PPh3)3 with one equivalent of BINAP affords the BINAP analogue of the mixed-phosphine complex in high yield; the preparative details are given in Section 2.5.2.2. The 3 1 P NMR spectrum of RuCl2(#-BINAP)(PPh3), 21 (Figure 4.29) is similar to that observed for the DPPB derivative (Figure 4.5), and consists of resonances due to the dimeric [RuCl2(#-BINAP)]2 species (8A = 75.8, 8B = 5.8 ppm, 27AB = 40.6 Hz; 8c = 58.6, 8D = 58.2 ppm, 27AB = 43.2 Hz), which is formed by partial dissociation of the PPh3 ligand in solution (8 -6.0 ppm. s). The additional reasonances at 65.8 and 56.1 ppm and the triplet-like pattern centred at 21.0 ppm are assigned to the mixed- phosphine species RuCl2(/?-BINAP)(PPh3), 21, by comparison with the corresponding spectrum of RuCl2(DPPB)(PPh3), 23. Based on the similarity of the 3 1 P NMR spectra of 21 and 23, the BINAP complex is assigned a structure similar to that of the DPPB complex (cf. Figure 4.7). 179 •9(r93 ui \z ' ( f M d d ) ( d V N i a i / ) z D n H i ° O . OZ ' Z H W ZfrlZl) uiauMds ̂ Wi { H i Jdi£ =63 > 3jn3y 4.7 References - Chapter 4 1. Jung, C. W.; Garrou, P. E.; Hoffman, P. R.; Caulton, K. G. Inorg. Chem. 1984, 23, 726. 2. (a) Wang, D. K. W„ Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1978. (b) James, B. R.; Wang, D. K. W. Inorg. Chim. Acta 1976,19, L17. 3. (a) Churchill, M. R.; Bezman, S. A. Inorg. Chem. 1972,11, 2243. (b) Ibid. 1973,12, 531. (c) Ibid. 1973,12, 260. 4. LaPlaca, S. J.; Ibers, J. A. Inorg. Chem. 1965,4, 778. 5. Schaefer, J.; Stejskal, E. O. J. Am. Chem. Soc. 1976, 98, 1031. 6. Pines, A.; Gibby, M. G.; Waugh, J. S. J. Chem. Phys. 1972,56, 1776; 1973,59, 569. 7. Andrew, E. R. Prog. Nucl. Magn. Reson. Spectrosc. 1971, 5, 1. 8. (a) Fyfe, C. A. Solid State NMR for Chemists; C.F.C. Press: Guelph, Ont, Canada, 1983; and references therein. (b) Wasylishen, R. E.; Fyfe, C. A. Ann. Rep. NMR Spectrosc. 1982,12, 1; and references therein. 9. Sanders, J. K. M.; Hunter, B. K. Modern NMR Spectroscopy: A Guide for Chemists; Oxford Press: Oxford, U.K., 1987; Chapter 9. 10. (a) Mehring, M. in NMR Basic Principles and Progress; Diehl, P., Fluck, E. and Kosfeld, R., Eds.; Springer Verlag: New York, 1976; Vol.11. (b) Fukushima, E.; Roeder, S. B. W. Experimental Pulse NMR; Addison- Wesley: Reading, MA, USA, 1981; Chapter 4. 181 11. Dixon, W.T.; Schaefer, J.; Sefcik, M. D.; Stejskal, E. O.; McKay, R. A. J. Magn. Reson. 1982, 49, 341. 12. Mann, B. E. Adv. Organomet. Chem. 1988,28, 397. 13. Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97, 4221. 14. For a review of chemistry and properties of RuCl2(PPh3)3, see: Jardine, F. H. Prog. Inorg. Chem. 1984,31, 265. 15. Garrou, P. E. Chem. Rev. 1981, 81, 229. 16. (a) Pregosin, P. S.; Kunz, R. W. in NMR Basic Principles and Progress; Springer-Verlag: Heidelberg, 1979; Vol. 16, p. 55. (b) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistery; University Science Books: Mill Valley, CA, 1987; p. 72. 17. Diesveld, J. W.; Menger, E. M.; Edzes, H. T.; Veeman, W. S. J. Am. Chem. Soc. 1980,102, 7935. 18. Maciel, G. E.; O'Donnel, D. J.; Greaves, R. Adv. Chem. Ser. 1982,196, 389. 19. a) Bemi, L.; Clark, H. C ; Davies, J. A.; Drexler, D.; Fyfe, C. A.; Wasylishen, R. E. J. Organomet. Chem. 1982, 224, C5. b) Bemi, L.; Clark, H. C ; Davies, J. A.; Fyfe, C. A.; Wasylishen, R. E. J. Am. Chem. Soc. 1982,104, 438. c) Clark, H. C ; Davies, J. A.; Fyfe, C. A.; Hayes, P. J.; Wasylishen, R. E. Organometallics 1983,2,177. d) Fyfe, C. A.; Clark, H. C ; Davies, J. A.; Hayes, P. J.; Wasylishen, R. E. J. Am. Chem. Soc. 1983,105, 6577. 20. Kroto, H. W.; Klein, S. I.; Meidine, M. F.; Nixon, J. F.; Harris, R. K.; Packer, K. J.; Reams, P. / . Organomet. Chem. 1985,280, 281. 182 21. Komoroski, R. A.; Magistro, A. J.; Nicholas, P. P. Inorg. Chem. 1986,25, 3917. 22. Dekleva, T. W., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1983; Chapter 2. 23. Opella, S. J.; Frey, D. M. H. J. Am. Chem. Soc. 1979,101, 5855. 24. a) Haberkorn, R. A.; Herzfeld, J.; Griffin, R. G. J. Am. Chem. Soc. 1978, 100, 1296. b) Waltham, M. C; Cornell, B. A.; Smith, R. Biochim. Biophys. Acta 1986, 862, 451. 25. Nissan, R. A.; Vanderah, T. A. J. Phys. Chem. Solids 1989,50, 347. 26. a) Rothwell, W. R.; Waugh, J. S.; Yesinowski, J. P. J. Am. Chem. Soc. 1980,102, 2637. b) Rao, K. M.; Gobetto, R.; Iannibello, A.; Zecchina, A. J. Catal. 1989,119, 512. 27. a) Haw, J. E.; Crosby, R. C; Maynard, S. J.; Reese, R. L. Polym. Prepr. 1988,29, 78. b) Pratt, R. G.; Ackerman, J. L. Polym. Mater. Sci. Eng. 1983, 49, 293. 28. Nixon, J. F. and Pidcock, A. in Ann. Rev. NMR Spectrosc; Mooney, E. F., Ed.; Academic Press: New York, 1969; Vol. 2, p. 345. 29. Bowmaker, G. A.; Cotton, J. D.; Healy, P. C; Kildea, J. D.; Silong, S. B.; Skelton, B. W.; White, A. H. Inorg. Chem. 1989,28, 1462; and references therein. 30. Allman, T. J. Magn. Reson. 1989, 83, 637. 31. Schunn, R. A.; Wonchoba, E. R.; Wilkinson, G. Inorg. Syntheses 1972,75, 131. 183 32. Hallman, P. S.; McGarvey, B. R.; Wilkinson, G. J. Chem. Soc, A 1968, 3143. 33. James, B. R. in Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol.8, p. 285. 34. James, B. R. Homogeneous Hydrogenation; Wiley: New York, 1973. 35. Reference 16b; p. 545. 36. Markham, L. D., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1973. 37. Chaudret, B. N.; Cole-Hamilton, D. J.; Nohr, R. S.; Wilkinson, G. J. Chem. Soc, Dalton Trans. 1977, 1546. 38. (a) Kubas, G. J.; Ryan, R. R.; Swanson, B. I.; Vergamini, P. J.; Wasserman, H. J. J. Am. Chem. Soc. 1984,106, 451. (b) Crabtree, R. H.; Lavin, M. J. Chem. Soc, Chem. Commun. 1985, 794; ibid., 1661. (c) Morris, R. H.; Sawyer, J. F.; Shiralian, M.; Zubkowski, J. D. J. Am. Chem. Soc. 1985,107, 5581. 39. Kubas, G. J. Acc. Chem. Res. 1988, 21, 120; and references therein. 40. (a) Crabtree, R. H.; Hamilton, D. F. Adv. Oraganomet. Chem. 1988,28, 299; and references therein. (b) Crabtree, R. H. Acc. Chem. Res. 1990,23, 95; and references therein. 41. Ng, J. B., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1990; Chapter 5. 42. Heinekey, D. M.; Millar, J. M.; Koetzle, T. F.; Payne, N. G.; Zilm, K. W. J. Am. Chem. Soc. 1990,112, 909. 184 43. Antinolo, A.; Chaudret, B.; Commenges, G.; Fajardo, M.; Jalon, F.; Morris, R. H.; Otero, A.; Schweitzer, C. T. J. Chem. Soc, Chem. Commun. 1988, 1210. 44. Hampton, C , Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1989; Chapter 4. 45. (a) Cullen, W. R.; Einstein, F. W. B.; Huang, C.-H.; Willis, A. C ; Yeh, E.-S. J. Am. Chem. Soc. 1980,102, 988. (b) Butler, I. R.; Cullen, W. R.; Kim,T.-J. Synth. React. Inorg. Met.-Org. Chem. 1985, 75, 109. 46. Hampton, C ; Cullen, W. R.; James, B. R.; Charland, J.-P. J. Am. Chem. Soc. 1988,110, 6918. 47. (a) Cole-Hamilton, D. J.; Wilkinson, G. / . Chem. Soc, Dalton Trans. 1977, 797. (b) Pez, G. P.; Grey, R. A.; Corsi, J. J. Am. Chem. Soc. 1981,103, 7528. 48. Rodgers, G. E.; Cullen, W. R.; James, B. R. Can. J. Chem. 1985, 61, 1314. 49. Markham, L. D.; James, B. R. unpublished results. 50. Schroder, M.; Stephenson, T. A. in Comprehensive Coordination Chemistry; Wilkinson, G.; Gillard, R. D.; McCleverty, J. A., Eds.; Pergamon Press: Oxford, 1987; Vol. 4, Chapter 45, pp. 379-390. 51. (a) Chatt, J; Hayter, R. G. / . Chem. Soc. 1961, 772; 896; 5507; ibid. 1963, 6017. (b) James, B. R.; Wang, D. K. W.; Voigt, R. F. J. Chem. Soc, Chem. Commun., 1975, 574. (c) Mason, R.; Meek, D. W.; Scollary, G. R. Inorg. Chim. Acta 1976,16, L l l . 185 52. (a) James, B. R . ; Mahajan.D. J. Orgamomet. Chem. 1985,279,31.; Can.J. Chem. 1980,58, 996. (b) James, B. R. ; McMillan, R . S.; Morris, R . H . ; Wang, D. K . W. Adv. Chem. Ser. 1978,167, 122. 53. Xie, Y., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1990. 54. (a) Cotton, F. A. and Wilkinson, G. Advanced Inorganic Chemistry; Wiley- Interscience: New York, 1980,4th Edn.; Chapter 28, pp. 1217-1233. (b) Douglas, B. E.; McDaniel, D. Ft.; Alexander, J. J. Concepts and Models of Inorganic Chemistry; Wiley: New York, 1983,2nd Edn.; Chapter 8. 55. Berry, R . S. J. Chem. Phys. 1960, 32, 933. 56. "IUPAC Proposals for Nomenclature of Absolute Configurations Concerned with Six-Coordinated Complexes Based on the Octahedron" Inorg. Chem. 1970, 9 , 1. 57. (a) Thorburn, I. S., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1985; Chapters 3 and 4. 186 CHAPTER 5 Activation of Dihydrogen by Chloro-Bridged Diruthenium(II,II) Complexes Containing Chelating Ditertiary Phosphines 5.1 Introduction Although direct addition of dihydrogen to an unsaturated substrate is thermodynamically favourable in the ground state, the process is symmetry forbidden and mediation by a catalyst is generally essential in order to overcome the net symmetry restrictions.1 Transition metal complex-catalysed H2-hydrogenation of unsaturated substrates proceeds presumably through a series of symmetry allowed reaction steps involving metal hydride intermediate(s), wherein in general activation of both dihydrogen and substrate at the metal centre must be followed by a successful stepwise hydrogen transfer to the substrate and release of the reduced product. 2 - 4 Recently, however, Eisenberg and coworkers have demonstrated evidence for a "pairwise" hydride transfer to alkene substrates, with the transfers occurring faster than relaxation of the hydrogen nuclear spins in para hydrogen.5 Transition metal hydride complexes have been synthesised by a number of routes. 2 - 4 These include, for example, the use of molecular hydrogen, oxidative addition of H X , protonation, reactions with hydride reagents such as NaBH* and L i A l H 4 , and hydrogen transfer from organic donors (e.g. alcohols). The choice of a synthetic route obviously depends on the nature of the starting material and the desired hydride product. 187 Reaction of ruthenium halide precursors with H2 provides a convenient route to ruthenium hydride complexes; a base is usually necessary to remove the HX formed in such a reaction . Thus ruthenium hydrido(phosphine) complexes of the type RUHCIP3, where P represents a monodentate phosphine, are prepared by reaction of RUCI2P3 precursors with H2 in the presence of an appropriate base (Equation 5.1).6 The choice of base is also important as exemplified by reactions 5.2 and 5.3, in which the nature of the product is clearly influenced by the choice of the base employed (DMA 7 vs. Proton Sponge8-9). The highly nucleophilic character of the strongly basic m'alkylamines,̂  such as NEt3, can sometimes lead to complications through coordination and/or dehydrogenation and dealkylation of the amines.10 RuCl2(PR3)3 + H 2 2 RuCl3(PR3)2 + H 2 2 RuCl3(PR3)2 + 4 H 2 The reasons for interest in the synthesis and catalytic applications of Ru(II) complexes containing a single chelating phosphine per ruthenium have been elucidated in an earlier chapter (Chapter 3, Sections 3.1, 3.2), and some synthetic routes to dichloro complexes of the stoichiometry "RuCl2(P-P)" have been described. Generation of the corresponding hydride species is the next logical step. Thorburn's attempts to synthesise a hydride complex from chloro-bridged dinuclear Ru2Cl5(DPPB)2 or Ru2CU(DPPB)2 precursors by reaction in benzene solution with H2 in the presence of added Proton Sponge® yielded trichloro-bridged dinuclear anionic species [Ru2Cl5(DPPB)2]-PSH+ as the major isolable product (-60-65% yield; 3 1P{ !H} NMR, NEt3 RuHCl(PR3)3 + Et 3 NH + Cr (5.1) DMA PS [RuCl2(PR3)2]2 + 2 DMAH+C1_ (5.2) H2/PS [RuH2Cl(PR3)2]2 + 4 P S H + C r (5.3) 188 CD2CI2, 20 *C: 54.6 ppm, s).n>12 Examination of the minor component ( 5 - 1 0 % ) by lH NMR spectroscopy in CD2CI2 solution did indicate the presence of a small amount of hydride species, which was evident from broad triplet resonances at 6 -17 .65 and - 2 1 . 9 0 ppm in ca. 1:1 ratio ( 2 / P H ~32 Hz).11 The rather high solubility of [Ru2Cls(DPPB)2]-- PSH+, even in the relatively nonpolar solvent benzene, complicated the separation of products, and attempts to isolate the hydride derivative(s) in a pure form were unsuccessful. The high 'chloride-affinity' of Ru2Cl4(P-P)2 complexes is thought to be responsible for formation of the anionic complexes through reaction with the initially formed PSH+Ch (Equation 5 . 4 ) . 1 1 . 1 2 Ru2Cl4(P-P)2 + PSH+Cr (5.4) PSH+Cr [ R U 2 C 1 5 ( P - P ) 2 ] - P S H + The choice of base proved to be an important factor in the reaction of [RuCl(P-P)(u-Cl)]2 with H 2 , where P-P = DPPB (14) or 5,5-CHIRAPHOS (16). In preliminary studies carried out by Thorburn, the use of NEt3 (1 equiv./Ru or 2 equiv./Ru2) in place of Proton Sponge® in reaction 5.4 resulted in the formation and subsequent isolation, albeit in very low yields ( 5 - 1 0 % ) , of novel hydridochloro derivatives of the stoichiometry 'RuHCl(P-P)' (see below). The triethylamine adducts [(Et3N)(P-P)Ru- (u-Cl)3RuCl(P-P)] (14b and 16b), presumably formed by coordination of the added amine to the corresponding R U 2 1 1 , 1 1 precursors (see Chapter 3, Section 3.6.1), were the major products of the respective reactions (~70% yield). The hydride complexes were characterised by proton NMR spectroscopy, and identified as the trinuclear Ru(II)-hydride species [RuHCl(P-P)]3 (P-P = DPPB, 2 9 ; CHIRAPHOS, 30), on the basis of a single PS Ru2Cl5(P-P)2 + H 2 189 crystal X-ray diffraction study on the CHIRAPHOS complex 30. These preliminary results have been published as part of a review.12 More recently, dimeric Ru-BINAP analogues of 14 and 16, including the corresponding triethylamine derivative, [Ru2CU(BINAP)2](NEt3), have proved to be highly effective as catalyst precursors for asymmetric H2-hydrogenation of a wide range of substrates, with enantiomeric excesses close to 100% being achieved in a number of cases. 1 3 - 1 6 As outlined in the introduction to Chapter 3, the possible involvement of 'RuHCl(DIOP)' species in RuHCl(DIOP)2-catalysed H2-hydrogenation of alkene substrates, as indicated by a detailed kinetic study,1 7'1 8 provided the impetus for devising ways of accessing such 1:1 'Ru(P-P)' complexes in pure form. Involvement of 'RuHCl(BINAP)' as the catalytically active species in related systems, including those incorporating dimeric Ru-BINAP analogues of the complexes 14 and 16, has also been suggested.12,19>20 Described in this chapter are the results of a detailed investigation into the H 2 - reactivity of dichloro-bridged dimeric [RuCl(P-P)(u.-Cl)]2 complexes leading to the corresponding trinuclear [RuHCl(P-P)]3 derivatives. The original synthetic procedure has been optimised during the course of this work to obtain the hydridochloro trimers 29 and 30 in >50% isolated yield. A detailed spectroscopic characterisation of complexes 29 and 30 is presented. A mechanism for their formation is proposed; much of the work was done on complexes 14 and 29 containing the nonchiral DPPB ligand. The present study reveals the intermediacy of molecular hydrogen C n 2 - H 2 ) 2 1 species in the synthesis of the hydridochloro trimers and, therefore, a brief look at the general properties of transition metal molecular hydrogen complexes, including the various criteria used for their characterisation, seems appropriate. 190 5.2 Molecular Hydrogen Complexes: A Brief Review The initial interaction of molecular hydrogen with a transition metal during H 2 - activation processes has been considered for many years, but remained a topic of speculation until recently.21 In 1976, Ashworth and Singleton, based on their observations that all the reactions of the complexes RuH4(PPh3)3 and RuH3(DPPE)2+ occurred by initial loss of H 2 and by analogy with the similar behaviour found for complexes containing reversibly bonded dioxygen ligand, proposed the possibility of stable H 2 binding at the Ru centre whereby these complexes could be considered as H 2 adducts of Ru(U)22 Further, Kubas in a 1980 report inferred, from an IR spectroscopic study and the observed lability of hydrogen, that the bonding of H 2 in MH2(CO)3(PR3)2 (M = Mo, W; R = Pr', Cy) complexes "may be novel".23 The first direct evidence for the unusual H 2 binding in these and other reported systems came with the discovery in 1983, also by Kubas et al.24 of the first molecular hydrogen complex, viz. W(CO)3(PPr'3)2(r|2-H2) (cf. Chapter 1, Figure 1.13), which was shown to contain a side-on (n2-) bonded H 2 ligand by X-ray (H—H = 0.75 (16) A) and neutron diffraction (H—H = 0.84 A) analysis.25 The lH NMR spectrum of the HD isotopomer showed a 1:1:1 triplet with a 1JHD of 33.5 Hz; 2 1* 2 5 the coupling in hydride-deuteride complexes is typically <2 Hz. 2 1 The large HD coupling value, which is close to that found for free gaseous HD (1JUD = 43.2 Hz2 6), clearly indicated a somewhat reduced H-D bond order and provided conclusive evidence for the presence of a 'nonclassical' dihydrogen (rj2-H2) ligand.21 The report by Kubas et al. was followed by the reported synthesis of [IrH(Tj2- H2)(bq)(PPh3)2]+ (Figure 5.1; bq = 7,8-benzoquinolinate) by Crabtree and Lavin.27 The report by Morris et al, that the complexes [MH0H2)(DPPE)2]+ (M = Fe, Ru; Figure 5.1) formed by protonation of MH2(DPPE)2 contained bound dihydrogen,28 followed in quick succession. The X-ray crystal structure of the Fe complex showed a short H-H bond length ( A) for the T | 2 - H 2 moiety, and the observation of large *H NMR HD coupling 191 constants for the respective HD isotopomers confirmed the 'nonclassical' nature of H 2 ligand,28 consistent with Ashworth and Singleton's original speculation about the Ru complex.22 PR, OC CO OC >R " N C,t. I ..^PPh3 Ph,P :ir'. H H + H H - r - H ' ? » » . . I | ^ P > H + M = Mo, W R = Pr', Cy N—C = 7,8-benzoquinolinate M = Fe, Ru P—P = DPPE Figure 5.1: Some early examples of molecular hydrogen complexes. Since their initial discovery,24- 2 5 molecular hydrogen complexes of transition metals have continued to be of great interest as evidenced by the large number of literature reports in recent years 2 7 - 3 4 including review articles21- 3 5 - 3 7 and studies on theoretical aspects of metal-dihydrogen bonding.38 A number of previously known polyhydrides are now reformulated as containing an ri2-H2 ligand. For example, the complex RuH4(PPh3)3 has been reformulated as RuH2(r|2-H2)(PPh3)3,39 while a dinuclear complex of the empirical formula [RuH2Cl(PPh3)2]2 is now recognized as being [(r|2-H2)(PPh3)2Ru(u- H)(u-Cl)2RuH(PPh3)2].40-41 Transition metals for which molecular hydrogen complexes have been reported to date are shown in Table 5.1. While the known dihydrogen complexes span a range of formal d-electron configurations ( d ° - d l u ) , coordination numbers (4-9) and formal oxidation states (0-VI), all are either neutral or cationic, formally 18 electron species, with a large majority being of octahedral geometry.21-36-41 Interestingly, more than half the known dihydrogen complexes contain ruthenium;21 almost all contain one or more 7t-acceptor ligands, the "ligand-free" cluster complexes Cu2H2(H2)x and Cu3(H2)42 and the matrix-isolated Pd(H2)43 being the only exceptions. 192 Some interesting examples, such as an T|2-H2 ligand bound to a lanthanide metal (Eu)4 4 and in an osmium-porphyrin system,45 have also appeared in the literature. Table 5.1: Transition Elements Found in Molecular Hydrogen Cn2-H2) Complexes. V Cr Mn Fe Co Ni Cu Nb Mo Ru Rh Pd W Re Os Ir Pt The existence of a dihydrogen-dihydride tautomerism in solution has been demonstrated for some complexes (Equation 5.5), which lends credence to the notion that dihydride formation via oxidative addition of H2 may be preceded by the formation of an ri2-H2 complex. 2 1- 3 6- 3 7 H / H M 1 ^ M (5.5) H \ H The Ti2-H2 ligand can be considered as a neutral, o-bonded two-electron donor. The bonding scheme can be represented by a Dewar-Chatt-Duncanson type model 2 1- 3 6- 3 7 (Figure 5.2) commonly used to elucidate metal-alkene bonding. 193 Figure 5.2: A bonding scheme for M-(rj2-H2) moiety; the shaded areas represent occupied orbitals (based on Ref. 37). According to this model, the occupied o(H2) to empty d<x(M) electron donation constitutes the principal component of the M-(rj2-H2) bonding, with a small back-bonding contribution from the filled metal djt to the empty o*(H2) orbitals. A complete back- transfer of electrons from the metal to the c* orbitals of the dihydrogen ligand, however, would result in a H-H bond scisson (oxidative addition) to give a dihydride species (cf. Equation 5.5).21- 36 , 3 7 Thus weakly rc-basic metals, high oxidation states (e.g. +U vs. 0), and the presence of 7t-acidic ligands are expected to stabilise the dihydrogen form over the dihydride. More detailed discussions on the various factors affecting the stability of Tj2-H2 complexes are available in the literature.21- 35-37,40 Several criteria have been suggested for the recognition of a nonclassical dihydrogen ligand. Detection by X-ray crystal structure determination and neutron diffraction analysis provide the most direct proof in the solid state. Unfortunately, crystals suitable for such studies can be obtained in very few cases, and even then, locating the r)2- H2 moiety may be extremely difficult because of problems of chemical instability and/or physical disorder.21, 35-37 Vibrational spectroscopy (IR, Raman) is of limited use, particularly for noncarbonyl complexes.21,35-37 Proton NMR spectroscopy has emerged as by far the most useful method for characterisation of dihydrogen complexes. A relatively large H-D coupling (VHD), similar to that observed for free HD (43.2 Hz, 2 6 see above), is a particularly useful diagnostic tool 194 for complexes that contain a relatively nonfluxional dihydrogen ligand (rj2-HD); H-D coupling values in the range 18-33 Hz have been reported.21* 3 6 However, the H-D coupling is often unresolved for many polyhydride complexes, e.g. [IrH2(T|2- H2)2(PCy3)2]+,4 6 wherein fast scrambling of protons results in the loss of coupling information. The lH NMR short Tj -relaxation time criterion (or more accurately, a short Tj(min), of <100 ms37), introduced by Crabtree et al.46-47 and refined by Morris and coworkers,323 for identifying a dihapto bonded dihydrogen species in solution is now well- established,21' 3 5 - 3 7 although some reports have advised caution.37'48 This method relies on the fact that for protons less than -2 A apart, dipole-dipole or spin-lattice relaxation constitutes the principal mode of NMR relaxation in solution. The rate of spin-lattice relaxation, R(DD), is related to the internuclear distance by the equation shown below: R(DD)={r7(DD))-l = 0.3YH4(h/27i)2(rHH)-6{1 \ , + , f ° 9 9 ) (5-< 1 + C0 2 T C 2 1 + 4C0 2T C 2 where, Tc rotational correlation time (s rad-1) = 0.62/co at 6(min); 8 = temperature (K) y gyromagnetic ratio co Larmorfrequency (rads-1) h Planck's constant (6.626 x 10 - 3 4 J s) iHH H-H internuclear distance (cm). Binding of H2 in a dihapto fashion to a metal causes some lengthening of the H-H bond (from 0.74 A in free H 2 2 1 to an estimated range of -0.8-1.2 A); H-H(TI 2 -H2) distances of 0.75-1.0 A have been determined by X-ray or neutron diffraction techniques in a few cases.21' 3 6 > 4 0 On the other hand, the H - H distance in a dihydride complex is typically of the order of 1.5 A or more. Because of the high order of spin-lattice relaxation 195 time dependence on the internuclear distance (Ty(DD) a r 6 , see Equation 5.6), the 77(ri2-H2) is expected to be an order of magnitude shorter (r = 0.8-1.2 A, Tj ~4-100 ms) than the Tj observed for a classical dihydride moiety (r = 1.5 A, Tj ~1 s).36>37 Further, Equation 5.6 predicts that the Tj value should pass through a rninimum, Tj(min) at 0(min). when the correlation time %c = 0.62/co, from which the internuclear distance I H H can be estimated.36'37 In the absence of structural characterisation, spectroscopic evidence by more than one techniques is desirable for a definite, positive identification of a nonclassical dihydrogen ligand. 5.3 Interaction of [RuCl(DPPB)(u-CI)]2,11, with H 2 and N 2 in the Absence of an Added Base 5.3.1 Interaction with H 2 : Formation of a Molecular Hydrogen Complex In the absence of an added base, interaction of [RuCl(DPPB)(ji-Cl)]2,14, with H 2 (1 atm) in benzene or toluene solution leads to the rapid, reversible in situ formation of the molecular hydrogen complex 31a (Equation 5.7), as identified by *H and 3 1 P NMR spectroscopy (Figures 5.3 and 5.4).49 [RuCl(DPPB)(u-Cl)]2 + H 2 [(ri 2-H2)(DPPB)Ru(u.-Cl)3RuCl(DPPB)] 14 31a (5.7) P—P = DPPB 196 The *H NMR spectrum of a C7D8 solution of 14 under H 2 atmosphere shows a new broad resonance at 8 -11.02 ppm, with a typically short Tj relaxation time of 14 ms (300 MHz, 292 K, wj/2 = 30 Hz, see Table 5.2), which is assigned to the ri 2-H2 moiety of 31a (cf. Equation 5.7); the resonance disappears if the H 2 atmosphere is removed under vacuum, or replaced by argon. Species 31a is akin to other dinuclear Ru-(T| 2-H 2) complexes that contain monodentate PR3 ligands, and terminal and bridging H - ligands in place of some or all of the chlorides of 31a.40-41 Temperature dependence of the T\ relaxation times was studied in the temperature range 235-324 K. The *H NMR T | 2 - H 2 resonance of 31a broadens with decrease in temperature (Table 5.2). The plot of In Tj against 1/0 is sharp V-shaped (Figure 5.5) as predicted by Equation 5.6. Only four dinuclear r j 2 - H 2 complexes, all containing ruthenium, have been reported so far.40- 41, 50, 51 j n c a s e D f t n e other dinuclear Ru(II)- (ri2-H2) complexes,40' 41> 50> 5 1 rapid exchange among the T i 2 - H 2 and the terminal or bridging hydride hydrogens results in averaging of the Tj times of the respective ligands, and consequently, such V-shaped In Tj vs. 1/0 plots with a clearcut minimum are not obtained. The 3 1 P{ 1 H) NMR spectrum (Figure 5.4) of the same solution of 14 under H 2 shows, in addition to the single AB pattern of 14, two other independent AB patterns of equal integrated intensity which are assigned to the dihydrogen complex 31a; the data are summarised in Table 5.3. The existence of two sets of 3 1 P{ 1 H) NMR AB patterns is consistent with the suggested geometry of 31a (cf. Equation 5.7). Also, the chemical shifts and 2Jpp coupling constants are very similar to those observed for other related triply chloro-bridged complexes [(L)(DPPB)Ru(u-Cl)3Ru(Cl)(DPPB)], also prepared from 14 (L = Me 2CO, 14a; CO, 14d; Me2SO, 14e; PhCN, 14f; Mel, 14g; see Chapter 3: Sections 3.6, 3.7, and Table 3.6). The ] H and 3 1 P NMR spectra indicate ca. 60% 197 I I I M I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I I I I I I I I I I[I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 8 6 4 2 0 -2 -4 -6 -B -10 PPM -12 Figure 5.3: *H NMR spectrum (300 MHz, toluene-^, 292 K) of the complex [RuCl(DPPB)(u-Cl)]2,14, sealed under ~1 atm H 2 pressure. The resonance due to the T | 2 -H2 moiety is observed at 5 -11.02 ppm • J1 ~i—i—r—i—|—i—i—i—i—|—r—i—i—i—|—i—r—i—i—|—r—1—i—i—|—i—i—i—i 65 60 55 50 45 40 PPM Figure 5.4: 3 1 P { lH} N M R spectrum (121.42 M H z , toluene-a>, 292 K) of a sample of rRua(DPPB)(u-Cl)]2,14, sealed under ~1 atm H 2 pressure. Table 5.2: Temperature Dependence of the J H NMR Tj Relaxation Time Data3 (300 MHz, toluene-dg) for the (r)2-H2) resonance of 31a at 5 -11.0 ppm. Temperature, 0, K Tj, ms Linewidth, wj/2, Hz 7Y, msb 324 19 ± 2 19 16.8 313 17 ± 1 24 13.5 292 14 ± 1 30 10.6 276 12 ± 1 36 8.9 255 15 ± 2 61 5.2 235 19 ± 2 68 4.7 3 Tj data were obtained by the inversion-recovery method52 using the conventional 180°-r-90° pulse sequence. b 72* values were calculated from the observed linewidths, according to the relation: linewidth = \lnT2* -3.8 -4.4" -4.6 H • 1 • 1 • 1 1 1 1 2.8 3.2 3.6 4.0 4.4 i/e x 103, K _ 1 Figure 5.5: Temperature dependence of Tj for the molecular hydrogen (rj2-H2) moiety in [(rt2-H2)(DPPB)Ru(u-Cl)3RuCl(DPPB)],31a. 200 equilibrium conversion of 14 to 31a (see Figures 5.3 and 5.4) at 1 atm of H2 and 20 "C; removal of H2 atmosphere results in a complete disappearance of the two AB patterns due to 31a. Table 5.3: 31P{ lR) NMR Data (121.42 MHz, Q D 6 or toluene-dg, 20 °C) for the Complexes [(L)(DPPB)Ru(u-Cl)3RuCl(DPPB)] (L = rj2-H2,31a; o-N2,31b).* Complex: L = 8A, ppm 6B, ppm 2 7 A B , Hz 14 64.0 54.9 47.3 T)2-H2,31a 53.7 53.2 44.4 53.8 38.3 33.8 0-N2, 31b 54.4 53.5 45.1 46.6 36.8 32.1 a The complexes were prepared in situ by sealing solutions of 14 under 1 atm of the respective gas. Further characterisation of the dinitrogen complex 31b is described in Section 5.3.3. The presence of two relatively sharp, independent sets of 3 1 P NMR AB patterns for 31a suggests that exchange between bound and free H2 is slow on the NMR time scale and thus, in the absence of inter- or intra-molecular hydrogen exchange, the broadness of the rj2-H2 resonance of 31a may be due to rapid internal rotation of the r)2-H2 ligand as suggested by some workers.21, 3 0 a « 3 2 a > 3 6 Further broadening of the TJ 2 -H2 signal on cooling (cf. Table 5.2) implies slowing of the internal motion, consistent with the behaviour of many other dihydrogen complexes.21,30a' 3 2 a > 3 3 a - 3 6 201 From the r;(min) value of 12 ms at 277 K (6(min)) obtained from the plot of In Tj vs. 1/0 (Figure 5.5), an internuclear H-H distance of 1.08C A , where C is a correction factor, is calculated for the r|2-H2 moiety of 31a following the method described by Crabtree and Hamilton.36- 3 7 - 4 7 Using a value of C = 0.794 suggested by Morris and coworkers,323 when the Tj2-H2 rotation is relatively rapid, and assuming a ±20% error in the Tj (min) value, an H - H distance of 0.86 ± 0.02 A is obtained. The estimated bond distance is comparable with that determined by X-ray crystallography, 0.80(6) A , within one of the related dinuclear Ru species,40-51 as well as with distances reported for other mononuclear transition metal-dihydrogen complexes. 2 1- 3 2 a- 3 6- 3 7 Of particular interest, the complex 14 catalyses, presumably via 31a, isotope exchange between H2 and D2 to give HD and the ri 2-HD isotopomer of 31a. A C6D6 solution (2 mL) of 14 (0.020 g) was stirred under 1.2 atm of H2 and 1.8 atm of D2 for 24 h at 20 °C; a portion of the solution was carefully transferred under hydrogen atmosphere to an NMR tube for examination by proton NMR spectroscopy. The ! H NMR signal of the ri 2-HD ligand (C6D6, 292 K) is a relatively narrow 1:1:1 triplet (wj/2 = 4.5 Hz, ^ H D = 29.4 Hz) of 1:2:1 triplets (cis, 2JHP = 7.5 Hz) centred at 8 -11.07 ppm Q?igure 5.6). The resonance due to free HD dissolved in C6D6 is seen as a 1:1:1 triplet (1JUD = 42.7 Hz; cf. reported value of 43.2 Hz 2 6) at 4.43 ppm. While the ^ H D for the r]2-HD isotopomer is within the range 18-34 Hz reported for other ri 2-HD complexes,21- 3 6 resolution of further coupling to phosphorus ( 2 7HP ) or other nuclei is unusual.21- 3 6 Resolved 2 7 J J P coupling with values of 2.0-3.6 Hz has been observed previously in some r| 2-HD complexes.30d- 3 1 c - 5 3 Morris and coworkers have calculated using NMR simulations 2 / H p values of 5.0 and 5.8 Hz for [M(r| 2-H2)(H)(DEPE) 2]+ where M = Fe and Os, respectively, and DEPE = l,2-bis(diethylphosphino)ethane.54 The value of 7.5 Hz observed for the r| 2-HD isotopomer of 31a is the second largest seen so 202 daSNa) papuBdxa si uoiSaj p p y uSiq auj, Z Q JO UIJB g-1 pus Z H i° "JJB Z' I J 3 P U N >I )̂(addO)Ony 1 2UIAB3I iCq MI pauuoj ,[(adda)DnH£(DTJ)ny(adda)(aHzLi)] jo 0 .02 â̂ D '2H1M 00£) ujaqoads ̂ WN Hi -9'S Wdd I 2 E f S 9 Z 8 6 I i i ) i I i i i i I i i i i I i i i i I i i 1 i 1 i i i 1 I i i i i I i i i i I i i i i I i i i i I i i i i 1 i i i i I i i i i 1 i i i i I i i i i 1 i i i i I i i i i 1 far for such complexes; Cotton and Luck have reported a 2 / H P of 19 Hz for ReCl(T|2-H2)(PMePh2)4.55 The observation of V^p in the *H NMR spectrum of the T| 2-HD isotopomer of 31a is further evidence that the on/off exchange between the bound and free dihydrogen must be slow on the NMR time scale. Facile H2/D2 HD exchange in the presence of other ri2-H2 complexes has been noted previously.303 For example, the complexes RuCp(PPh3)(BufNC)0H2)+,30d and W(CO)3(PPr'3)2(ri2-H2)30a are known to catalyse the isotope exchange reaction; interestingly, the latter species catalyses the exchange even in the solid state by an as yet unexplained mechanism.303 A similar gas-solid reaction using H2/D2 and 31a (i.e. 14) was not attempted during the current work. In another interesting case, Upmacis et al. observed that while H2/D2 ==• HD exchange ocurred in the presence of Cr(CO)4(H2)2 in liquid xenon at -70 °C, the analogous Cr(CO)s(H2) complex was completely inactive,56 implying that simultaneous coordination of two H2 ligands at the same metal centre may be important in the formation of HD from H2/D2 mixtures. Based on molecular orbital calculations, Pacchioni has suggested the formation of a polyhydrogen chain at the Cr centre in CrQ}l2)(D2) leading to a seven-coordinate dihydrogen-dihydride intermediate on the way to Cr(HD)2 species (Scheme 5-I):38a y H D M--TX% H X \ / X D H ' \ / *SD Cr w Cr yD FL H-r-D Scheme 5-1 204 Formation of FID from H2/D2 mixtures in the presence of 14 may be proceeding by a similar mechanism, possibly through a bis(dihydrogen) intermediate formed from 31a, in which the dinuclearity of the complex is maintained (Figure 5.7a). Involvement of a mononuclear species of the type RuCl2(DPPB)(H2)2 (Figure 5.7b), which would be analogous to the known RuH2(PR3)2(H2)2 complexes,50 cannot be ruled out completely. However, it is considered less likely because the dinuclear structure of the precursor seems to be maintained even in the presence of large excess (~50 eq.) of ligands such as amines and nitriles (see Chapter 3, Sections 3.6 and 3.7), which are known to coordinate much more strongly compared to H2. Indeed, the addition of PhCN to 14, for example, yields a bis(PhCN) derivative, [RuCl(DPPB)(PhCN)(u-Cl)]2, with the dinuclear structure still intact (Chapter 3, Section 3.6.5). a a b Figure 5.7: Possible intermediates in 14-catalysed H2/D2 HD isotope exchange. 5.3.2 Gas-Uptake Studies Rapid H2 uptakes of -0.4 equiv. per dimer are observed for D M A solutions of 14 at 1 atm of H2 pressure and 30 °C; these fractional uptakes can be attributed to the partial formation of the dihydrogen complex 31a. Interestingly, 14 itself is prepared by reduction of the mixed valence precursor Ru2Cls(DPPB)2,2, also in D M A solution under identical hydrogenation conditions (see Sections 2.5.5 and 3.3.1). However, it should be pointed 205 out that [Ru2Cl5(DPPB)2J-DMAH+ is the initial product in the reduction of 2, and the neutral dimeric product [RuCl(DPPB)(u,-Cl)]2,14, is obtained only after the addition of methanol which breaks up the ionic species into DMAH+Cl- and 14. ^ 1 2 5.3.3 Interaction of Other [RuCl(P-P)(u.-CI)]2 Complexes with H 2 DMA solutions of [RuCl(5,5-CHIRAPHOS)(u-Cl)]2,16, were found to absorb ca. 0.40 mole equivalents of H2 per dimer at 1 atm of H2 and 30 "C. However, the proton NMR spectrum of a solution of 16 in C6D6 sealed under 1 atm of H2 failed to reveal a broad high-field signal (down to -30 ppm) assignable to a bound dihydrogen ligand. Although the CHIRAPHOS complex 16 could be considered to form a dihydrogen complex, simply by analogy to the H2-uptake behaviour of its DPPB counterpart, further work, including low temperature NMR studies possibly on samples sealed under relatively high H2 pressures (1-10 atm) will be necessary in order to substantiate the presence or absence of the corresponding dihydrogen complex. 5.3.4 Interaction of 14. with N 2 : Formation of a Dinitrogen Complex Complex 14 also reacts reversibly with 1 atm of N2 to give a dinitrogen complex, 31b, with an equilibrium conversion of ca. 70% at 20 °C. The spectroscopic data are consistent with a structure akin to 31a with the T|2-H2 replaced by 0-N2 (see below). N = N a E, P Figure 5.8: Suggested geometry for the dinitrogen complex, 31b. 206 The *H and the 3 1P{ lH) NMR spectra of the dinitrogen complex 31b (i.e. of 14 under a N2 atmosphere; CgDg, 20 °C) shown in Figures 5.9 and 5.10, respectively, closely resemble those of other trichloro-bridged dinuclear species (cf. corresponding spectra of compounds 14a, 14d-14g and 31a; also see Tables 5.3 and 3.6). The phosphorus NMR signals for 31b are relatively sharp, again implying that the inter- and intra- molecular N2 exchange is likely slow on the NMR time-scale. The presence of C - N 2 ligand in 31b is confirmed by the V N = N IR stretch at 2175 cm - 1 (m, CH2CI2 solution in 0.1 mm anaerobic NaCl cell, Figure 5.11), which is absent in the IR spectrum of 14 under argon atmosphere. The 2175 cm - 1 value compares well with those found for the related ruthenium dinuclear complexes (complex, VN=N cm - 1): Ru2H4(PCy3)4(N2), 2145;50 Ru2H4(PPh3)4(N2),- 2140;5? and Ru2Cl4(PPh3)4(N2), 2165.58 It also lends further support to Morris' suggestion that "when the dinitrogen stretching frequency in MLn(N2) is >2060 cm - 1 , then the corresponding T|2-H2 adduct will be stable near room temperature" (and vice versa);50 indeed, stable dihydrogen adducts have been characterised for all the dinuclear ruthenium complexes mentioned above.4 0-5 0 207 I I II I I I II I I I F I I | I I I I | II I I | I I I I j I I I I | I I I I | I I I I | I I I I | I I I I | I I II | I I I I | I I I I | I I I I | I I I I | I I I I | 9 8 7 6 5 4 3 2 1 PPM Figure 5.9: *H NMR spectrum (300 MHz, 20 *C) of the dinitrogen complex 31b formed in situ from [RuCl(DPPB)(u.-Cl)h, 14, under ~1 atm N 2 pressure. — | — i — i — i— i—|— i — i — i — i — | — i — i — i — i — | — i — i — i — i — | — i — r — i — i — | — i 60 55 50 45 40 PPM 35 Figure 5.10: 3,P{ lH} NMR spectrum (121.42 MHz, QDfr 20 'Q of the dinitrogen complex 31b formed in situ from [RuCl(DPPB)(u-Cl)]2,14, under ~1 atm N 2 pressure. I 1 \ 1 < 2 6 0 0 . O 2 3 0 0 . • 2 0 D D . O 1 8 5 0 . O 1 7 0 0 . O W A V E N U M B E R S <CM-15 Figure 5.11: Infra-red spectrum of a CH2CI2 solution of 14 sealed under N2 atmosphere. The solvent spectrum has been subtracted. 5.4 Reaction of [RuCl(P-P)(u-Cl)]2 Dimers with H 2 in the Presence of Triethylamine: Synthesis of [RuHCl(P-P)b Complexes As described in the introduction (Section 5.1), reaction of [RuCl(P-P)(u-Cl)]2 dimers with H2 in the presence of two mole equivalents of NEt3 led to the formation and subsequent isolation of Ru2CU(P-P)2(NEt3) (ca. 70%) and small amounts of trimeric hydride complexes of formula [RuHCl(P-P)]3 (ca. 5-10%).12 The essential chemistry leading to the formation of the trinuclear hydrides and the NEt 3 adducts is summarised in Scheme 5-II. 210 a) argon, C 6 H 6 [(Et3N)(P-P)Ru(u-Cl)3RuCl(P-P)] / a) 90% b) 70% [RuCl(P-P)(u-Cl)]2 b) 1 atm H 2 + C 6 H 6 , 24 h, 25 *C 2 equiv. NEt3 [RuHCl(P-P)]3 + Et 3N +Cr P-P = DPPB or 5,5-CHIRAPHOS 5-10% 10-20% Scheme 5-JJ 5.4.1 Improved Synthesis of [RuHCl(P-P)]3 The original procedure for the synthesis of the novel trimeric hydridochloro complexes, [RuHCl(P-P)]3, involved addition of two equivalents of triethylamine to a benzene suspension/solution of the appropriate dimer precursor [RuCl(P-P)(u-Cl)]2 (P-P = DPPB, 14; 5,5-CHIRAPHOS, 16); the mixture was then stirred under an atmosphere of H 2 for 24 h at room temperature. Formation of large amounts (>70%) of the triethylamine adducts (14b or 16b; Scheme 5-TJ), which are essentially unreactive toward H2, appears to be the principal reason for poor yields of the hydridochloro trimers. Reaction of the dimer precursors with NEt3 in die absence of H2 does result in quantitative formation of the corresponding amine adducts, which have been characterised by elemental analysis and NMR spectroscopy (see Section 2.5.6.1 for 14b, and Section 2.5.9.2 for The procedure for the synthesis of the hydridochloro trimers has been revised during the course of this work, particularly in view of the finding that the DPPB dimer 14 formed a molecular hydrogen complex under H2 atmosphere (Section 5.3.1).49 In the modified synthesis, a benzene solution of the appropriate dimeric [RuCl(P-P)(u.-Cl)]2 precursor was stirred under H2 atmosphere for about one hour, prior to the addition of two 16b). 211 equivalents of NEt3 base, which was then added under a blancket of hydrogen. This simple change in the order of addition of the two reagents (i.e. from NEt3 + H 2 to H 2 + NEt3) resulted in a dramatic increase in the yields of the hydridochloro trimers (29,30), from the <10% obtained in the original synthesis to >50%, with concomittant decrease in the yields of the NEt3-adducts (14b, 16b). Indeed, the in situ yield of the hydride trimers is at least as high as 65-70%, based on the isolated yield of NEt3H+Cl~. 5.5 Characterisation of [RuHCl(P-P)]3 Complexes 5.5.1 Molecular Structure of [RuHCl(S,S-CHIRAPHOS)]3, 3J1 A single crystal X-ray diffraction study of the CHIRAPHOS complex, 30, carrried out by Thorburn and Ball, reveals a highly unsymmetrical trinuclear structure for 30 as shown in Figure 5.12.12 The structural parameters are listed in the Appendix (A-2), and some selected bond distances and bond angles are given in Tables 5.4 and 5.5, respectively. The three hydride ligands could not be detected in the X-ray structure, but NMR spectral studies (next section) suggest the presence of two terminal and one bridging hydride in 30 and its DPPB analogue 29. The highly unsymmetrical structure shows just one metal-metal bond (Rul-Ru2 = 2.8079(6) A), with three bridging chlorides between Rul and Ru3, while Ru2 is bonded to a single chloride Cll that bridges all three Ru atoms. The chloride bridges are unsymmetric with the Ru-Cl distances ranging from 2.452 A for Rul-C12 to 2.569 A for Ru3-C12. Interestingly, the observation of the shortest and the longest Ru-Cl distances for Ru-Cl bonds which are very likely trans to a bridging and a terminal hydride ligand, respectively (see the following section), is consistent with the lower trans influence of a bridging vs. a terminal hydride ligand. The Ru-P distances are within the normal range expected for Ru(II)-phosphine complexes. 212 CMftl CI2 CIIRI Figure 5.12: Molecular structure of [RuHCl(S,5-CHIRAPHOS)]3,30, showing the atom numbering scheme used. For the sake of clarity, the hydrogen atoms and all atoms of the phenyl rings except the a-carbon have been omitted. another view: 213 Table 5.4: Selected Bond Lengths (A) for [RuHCl(5,5-CHIRAPHOS)]3, 30, with Estimated Standard Deviations in Parentheses. Bond Length (A) Bond Length (A) Ru(l)—Cl(l) 2.519() Ru(l)—Ru(2) 2.808() Ru(l)—Cl(2) 2.452() Ru(l)—Ru(3) 3.3570 Ru(l)—Cl(3) 2.521() Ru(l)-P(l) 0 Ru(2>—Cl(l) 2.488() Ru(l)-P(2) 0 Ru(2)—Cl(3) 2.827() Ru(2)-P(3) 0 Ru(3)—Cl(l) 2.539() Ru(2>—P(4) 0 Ru(3)—Cl(3) 2.551() Ru(3)—P(5) 0 Ru(3)—Cl(2) 2.569() Ru(3>-P(6) 0 Table 5.5: Selected Bond Angles (deg) for [RuHCl(S,S-CHIRAPHOS)]3, 30, with Estimated Standard Deviations in Parentheses. Bonds Angle (deg) Bonds Angle (deg) Ru(2)—Ru(l>—Cl(l) 55.38() Ru(l)—Cl(l)—Ru(3) Ru(2)—Ru(l)—Cl(2) 130.82() Ru(l)—Cl(2)—Ru(3) Ru(2)—Ru(l>—Cl(3) 63.81() Ru(l)—Cl(3)—Ru(3) Ru(2)—Ru(l)—P(l) 102.74() Ru(2>—Ru(l)—P(2) 123.790 214 5.5.2 lH and 3ip NMR Studies The trimeric [RuHCl(P-P)]3 complexes 29 and 30 in C6D6 solution at ambient temperature exhibit three 1:1:1 high-field resonances, one each for the three hydride ligands, in the respective ! H NMR spectra. The observed 2 / P H coupling constants, which range from 13 to 33 Hz, are indicative of a cis arrangement of hydride and phosphine ligands. The 3 1P{ *H} NMR spectra of both complexes consist of six discrete resonances. The similarity of the respective *H (hydride region) and 3 1 P NMR spectra for die DPPB- and the CHIRAPHOS-derivatives suggests similar structure for the two complexes (see below). The proton NMR spectrum (300 MHz, C6D6,20 °C) of the DPPB trimer is shown in Figure 5.13. The hydride resonances for [RuHCl(DPPB)]3, 29, are observed as a triplet at -17.65 ( 2 7 P H = 31.7 Hz), a complex multiplet at -21.1 ( 2 / P H -13-18 Hz), and another triplet centred at -21.9 ppm ( 2 / P H = 33.2 Hz), the triplets being assigned to two terminal hydrides and the complex multiplet to a bridging hydride ligand of 29. The ratio of combined integration of the hydride resonances to that for the DPPB ligand resonances is close to the expected value of 1:28. The 31p{lH} NMR spectrum of 29 (121.42 MHz, C 6 D 6 , 20 'C; Figure 5.15) consists of six discrete resonances of equal intensity ratio centred at 71.8, 69.5, 61.9, 59.7, 57.6 and 48.9 ppm, each being part of an AB quartet pattern. The P-P couplings are unresolved as they are comparable to the unusually large line-widths (wj/2 -40 Hz) of the resonances. The spectrum remained essentially unchanged over +40 to -80 °C temperature range, except for even more broadening at lower temperatures. In the absence of well-resolved P-P couplings, the phosphorus chemical shifts could not be assigned with certainty; attempts to obtain 3 l P-31p 2D-COSY maps were unsuccessful because of high level of spectral noise and limited instrument time. However, the apparent line-shapes of the phosphorus resonances 0?igure 5.14) do give some hint of 215 issui am in uoi3ai apupXq am SUIMOUS O. QZ ' Z H W 00£) uopnios 9^ in '6Z 'q(addO)DHnHJ jo uirujDads ^WN Hi -£V£ anulM 0 Wdd I 2 E f G ? f a i 111111II11111111II1111II1111111IIIIIIIII111IIIIIII1111111111111111111111111111111111111111  possible correlations. Thus the resonances at 71.8, 69.5 and 59.7 ppm can be tentatively correlated to the ones at 48.9, 61.9 and 57.6 ppm, respectively. This assignment was confirmed by selective phosphorus decoupled-proton ^Hf 3 1?}) NMR studies, which proved to be a powerful tool in assigning not only the mutually coupled phosphorus resonances, but also in establishing correlations between hydride and phosphorus NMR signals. The ^ p l p ) NMR spectra for [RuHCl(DPPB)]3,29, are shown in Figure 5.15. The !H NMR triplet at -17.65 ppm due to a terminal hydride shows loss of coupling when the phosphorus resonances at 69.5 and 61.9 ppm are decoupled selectively (Figure 5.15b and 5.15c), confirming mutual coupling between the two phosphorus resonances and their correlation to the hydride ligand that resonates at -17.65 ppm. Irradiation of 6 71.8 and 48.9 ppm 3 1 P signals causes loss of coupling for the signals at -21.1 and-21.9 ppm in the proton NMR spectrum (Figure 5.15a and 5.15f), while selective 3^-decoupling at 59.7 and 57.6 ppm affects only the -21.1 ppm proton NMR multiplet assigned to the bridging hydride (Figure 5.15d and 5.15e). Finally, broad-band phosphorus decoupling results in collapse of the hydride signals to three singlets (Figure 5.15g). These results along with the assignments of the phosphorus and the hydride signals are summarised in Table 5.6. 218 Figure 5.15: lH{31P} high-field NMR spectra of [RuHCl(DPPB)]3,29, in C6D6 solution (500.13 MHz for ! H, 202.46 MHz for 31p, 23 *C) with selective phosphorus decoupling at: (a) 71.8; (b) 69.5; (c) 61.9; (d) 59.7; (e) 57.6; (f) 48.9 ppm; andOj) with broad-band decoupling. 219 Figure 5.15, continued. -1,5 -u.o - U . I -li.O -H.S - » 0 - » s -ii o - » i » -B.O 220 Table 5.6: Results of a Selective {3lP)-Decoupled *H NMR Spectral Study of [RuHCl(DPPB)]3) 29, in C6D 6 Solution.3 8(Ru-H) ppm Coupled to 8(Ru-P) ppm Placement of Ru-H Ru Atomb Placement of Ru-P Ru Atomb -17.65 (t) 69.5, 61.9 Terminal, at Ru(3) Ru(3) -21.1 (m) 71.8, 48.9 Bridging between Ru(2) 59.7, 57.6 Ru(l)and Ru(2) Ru(l) -21.9 (t) 71.8, 48.9 Terminal, at Ru(2) 3 C6D6 solvent, 23 °C; 500.13 MHz for ^H, 202.46 MHz for 3 l R b Atom numbering based on the molecular structure of the CHIRAPHOS trimer 30; also see Figure 5.16 below P—P = chelating phosphine Figure 5.16: Schematic structural representation of [RuHCl(P-P)]3 complexes (based on the X-ray structure of the CHIRAPHOS derivative; Figure 5.12). 221 The three hydride ligand resonances for [RuHCl(CHIRAPHOS)]3,30, in the proton NMR spectrum (CeD^ 20 *C; Figure 5.18) are observed as doublet of doublet (dd) patterns centred at -17.0 (?Jpn = 36.6, 26.4 Hz) and -24.8 ppm (2/PH = 36.3, 31.8 Hz) and a complex multiplet centred at -19.4 ppm with 2 / P H in the 8-21 Hz range. Again, by analogy to the *H NMR spectrum for the DPPB analogue (see above), the two dd patterns are respectively assigned to two terminal hydride ligands - one each on Ru(3) and Ru(2), while the complex multiplet is assigned to the bridging hydride between Ru(l) and Ru(2) (see Figures 5.12 and 5.16). J 1 | ]! !! | I! ! I 11II I | 11 I I'j I I 11 j FT -17 -18 -19 i j i j i i n ; -20 i i ; i i H i i i i i i i i i ] i : i i i i i i ) j i i i ! n i l ! -21 -22 -23 -24 -25 PPM Figure 5.17: *H NMR spectrum (hydride region, 300 MHz, C6D6, 20 *C) of [RuHCl(S,5-CHJRAPHOS)]3, 30. The 31P{1H} NMR spectrum of a crude reaction mixture containing 30 and the NEt3 adduct 16b, recorded at ambient temperature in C^De solution, is shown in Figure 5.18. The spectrum consists of six doublet resonances centred at 8 102.7, 100.5, 97.0, 94.0, and 86.5 ppm in a 1:1:1:1:2 integral ratio, the two highest-field signals (86.5 ppm) 222 Figure 5.18: 31P{ ]H) NMR spectrum (121.42 MHz, CftDfi, 20 *Q of a crude reaction mixture showing resonances of the hydridochloro trimer [RuHCl(CHIRAPHOS)l3,30, and the dinuclear coproduct [(Et3r^(CHIRAPHOS)Ru- (U-Cl)3RuCI(CHIRAPHOS)], 16b. being coincidentally degenerate. Unlike the 31p{lH} NMR spectrum for the DPPB analogue (see above), the spectrum for the CHIRAPHOS complex exhibits relatively sharp peaks with well-resolved 31p_31p couplings. The six resonances constitute three AX patterns, as expected for a trinuclear complex containing only one chelating phosphine per Ru centre, and are readily assigned based on the observed coupling constants; 8A, 8X ppm ( 2 / A X H Z ) : 102.7, 94.0 (46.6); 100.5, 86.5 (40.6); and 97.0, 86.5 (41.4). The additional AB quartet (8A = 87.3, 8B = 80.2 ppm, 2 7 A B = 37.3 Hz) is assigned to the triethylamine adduct 16b, which has been isolated and characterised (see Section 2.5.10.2). The BINAP analogue [RuCl2(BINAP)]2(NEt3) reported by Ikariya et al. also exhibits an AB quartet pattern (62 and 57 ppm, 2/pp = 35 Hz). 1 5 b The 3 1 P NMR spectrum is solvent dependent, with slight variation in the chemical shifts being observed with a change in the solvent; for example, the two overlapping resonances of 30 (85.5 ppm, C6D6) are sufficiently resolved to permit measurement of the respective coupling constants when toluene-dg is used as the solvent. Also, extra splittings are sometimes apparent because of insufficient/incomplete *H decoupling of the hydride region. 5.6. Interaction of [RuHCl(DPPB)]3 with H 2 and Nitriles Interaction of the hydridochloro trimers [RuHCl(P-P)]3 with hydrogen was of interest because these complexes are effective catalysts for hydrogenation of a variety of substrates (Chapter 7). Also, the corresponding Ru(JJ) tertiary phosphine analogues, previously characterised in our laboratory,8 were later shown to be the dinuclear hydridochloro species containing a molecular hydrogen ligand: Cn2-H2)[RuHCl(PR3)2]2, R = phenyl or p-tolyl.9 Addition of 1 atm of H2 to a solution of [RuHCl(DPPB)]3,29, in toluene-ds did not produce any visible colour change, but the *H NMR spectrum of the solution showed a 224 broad resonance (w;/2 = 50 Hz at 20 °C) at -13.05 ppm with a short Tj relaxation time of 24 ms. The three original hydride resonances of 29 (see Table 5.6) could be discerned only at the noise level. The 3 1 P NMR spectrum showed two new broad resonances of equal intensity at 63.5 and 40.2 ppm (wj/2 ~60 Hz); the resonances of 29 (Table 5.6) had disappeared. Removal of H 2 under vacuum resulted in the reappearance of the NMR signals due to [RuHCl(DPPB)]3, 29, indicating a reversible binding of H 2 . The limited data are consistent with the formation of a dinuclear hydridochloro derivative, 32, containing a molecular hydrogen ligand (r]2-H2), which is assigned a geometry similar to that found for the corresponding tertiary phosphine analogues (Figure 5.19).8-9 P—P = DPPB Figure 5.19: Suggested geometry for [RuHCl(DPPB)]2(ri2-H2) complex, 32. The variable temperature ! H NMR spectra (hydride region, toluene-as) of 32 are shown in Figure 5.20. The signal at -13 ppm broadens with decrease in temperature and decoalesces ~224 K. Below 220 K, three broad signals centred at ca. -7, -13 and -18 ppm become apparent, with the two outer signals sharpening on further cooling. By analogy to the corresponding spectra reported for (rj2-H2)[RuHCl(PR3)2]2,9- 4 0 the resonances at -7 and -18 ppm are respectively assigned to the bridging and the terminal hydride ligands of 32, while the relatively broad signal at -13 ppm (estimated W7/2 ~500 Hz at 199K) is attributed to the bound dihydrogen moiety. Both intramolecular and intermolecular H-exchange processes are evident from the NMR spectra of 32. The -13 ppm resonance in the *H NMR spectrum obtained at ambient H 225 temperature is an average signal due to the exchanging r| 2-H2 ligand and the bridging and the terminal hydrides of 32, and the corresponding Tj relaxation time of 24 ms is also an averaged value. The Tj relaxation time for the T | 2 - H 2 moiety (as opposed to an averaged value) could not be measured accurately because of the very large linewidth of the signal at low temperature (Figure 5.20). The signal for dissolved H2 (4.46 ppm) was also relatively broad (wi/2 ~ 1 0 Hz), implying exchange between the bound and the free dihydrogen. Further evidence of intra- and intermolecular exchange processes comes from the 3 1 P NMR spectrum. For a species of the geometry suggested in Figure 5.19, two sets of AB patterns will be expected if the exchange is too slow (or non-existent) on the NMR time-scale. A fast intermolecular on/off equilibrium between the bound and the free H2 at the Ru1 centre will result in scrambling of the P A and P B signals provided that the H2 can bind any of the three non-bridging sites on Ru1, but will not affect Pc and Pp pair on Ru2 if the -(|j.-H)(u-Cl)2Ru2H(DPPB) fragment remains in a locked conformation. The observed scrambling of the Pc and P D resonances, at ambient temperature, indicates that the intramolecular exchange between the bridging and the terminal hydride on Ru2 must also be fast on the NMR time-scale. Exchange between rj2-H2 and the bridging hydride constitutes the third mode of exchange. It has been observed previously for the dinuclear hydridochloro Ru(II) tertiary phosphine analogoues of 32.9> 4 0 Interestingly, the resonances of ( PA , P B ) R u 1 a n d (Pc> P D ) R U 2 remained distinct, at least at 20 °C, implying (ri2-H2)Ru1 <-» Ru2(rj2-H2) process (if occuring) is slow on the NMR time-scale. The lower field 3 1 P resonance at 63.5 ppm is tentatively assigned to the (Pc, P D ) R U 2 pair consistent with the general trend observed for Ru-phosphine complexes containing a terminal hydride ligand (see Section 4.4, p. 167), while the 40.3 ppm signal is attributed to the (PA, P B ) R U ! pair. 226 III M j I I I 1 1 I I I I |I I I I] I I I I [ I I I ) ] I I M [ I I II | I I I I | I I ITTI I i l j I I 1 1 ] I I I I j I I I I ; - 6 -B -10 -12 -14 - I B - 1 8 PPM Figure 5.20: Variable temperature *H NMR spectra of the dinuclear T j 2 - ^ complex [(Ti2-H2)(DPPB)Ru(u-H)(p.-Cl)2RuH(DPPB)], 32, generated in situ from the reaction of [RuHCl(DPPB)]3 with H 2 . 227 Addition of one equivalent of MeCN or PhCN per Ru to a solution of 29 also resulted in complete in situ conversion of the trimeric hydride to give dinuclear complexes similar to the rj 2 -H2 complex 32 described above; the products have been characterised in situ by NMR spectroscopy. The *H and 3 1 P NMR data are listed in Table 5.7. The 3 1 P NMR spectra of the nitrile derivatives (MeCN, 33a; PhCN, 33b) consisted of two AB quartet patterns of equal intensity, indicating that unlike the T | 2 - H 2 complex 32, the ligand exchange was slow on the NMR time-scale. The lH NMR spectra (hydride region) consisted of a complex multiplet assigned to the bridging hydride ligand, and a triplet resonance attributed to the terminal hydride. The breakdown of the hydridochloro trimer [RuHCl(DPPB)J3, 29, under an atmosphere of H 2 to give the dinuclear Cn 2 - H 2 ) derivative, 32, is a significant finding. The complex 29 and its CHIRAPHOS analogue 30 are catalyst precursors for hydrogenation of a variety of substrates (see Chapter 7); the dinuclear dihydrogen complex 32 must be the species present under hydrogenation conditions. The studies should be extended to the CHIRAPHOS system. Generation of nitrile derivatives 33a and 33b (which appear to be analogous to 32), in the presence of equimolar quantities of the nitriles MeCN or PhCN, also suggests that dinuclear species are likely to be present during hydrogenation of nitrile substrates for which 29 is an effective catalyst. 5.7 Suggested Mechanism for Formation of [RuHCl(P-P)]3 Complexes Based on the results described in the previous sections, the following mechanism (Scheme 5-III) is proposed for the formation of the trimeric hydride derivatives [RuHCl(P-P)]3, 29 and 30, from the corresponding dimeric [RuCl(P-P)(u-Cl)]2 complexes (14 and 16). The mechanism involves formation of a molecular hydrogen complex followed by deprotonation of the bound H 2 by triethylamine to give the 228 Table 5.7: *H and 31P{ lU) Data3 for [(RCN)(DPPB)Ru(u-H)(u-Cl)2RuH(DPPB)] Complexes, R = Me, 33a; Ph, 33b. RCN = Chemical Shift 8 ppm Coupling Constant Hz Assignment̂ *H NMR data, Hydride Region MeCN, 33a -17.5 (br, complex m) 2 / P H -16-20 Bridging Hydride -17.7 (br, t) 2/ P H = 30 Terminal Hydride PhCN, 33b -16.65 (br, pseudo q) 2/PH -16-25 Bridging Hydride -17.55 (br, t) 27PH = 35 Terminal Hydride 31P{1H) NMR data MeCN, 33a 8A = 60.0, 8B = 57.6 2 / A B = 35 8c =71.7, 8D = 58.8 2 7 C D = 52 PhCN, 33b 6A = 59.6, 8B = 56.8 2/AB = 37.7 5c = 71.7, 8D = 58.8 2/ C D = 41.3 3 C6D6 solvent, 20 °C; 300 MHz for ] H, 121.42 MHz for 3 1P. b Cf. Figure 5.19 for assignments intermediate I. A repeat of this sequence via the intermediate H would yield the dinuclear [RuHCl(P-P)]2 species (intermediate HI) which, under H 2 atmosphere, could generate the dinuclear hydridochloro species containing an rj2-H2 moiety, 32. During work-up of the reaction mixture, when the H 2 atmosphere is removed under vacuum, the complex 32 converts to the trimeric hydride species 29 which is the isolated product. The reaction of 29 with H 2 is reversible, and affords the molecular hydrogen complex 32. Similarly, reactions of 29 with nitriles generate the dimeric species with a coordinated nitrile (33a, 33b), as evidenced by NMR spectroscopy. 229 p — X C 1v ..•••••°"-..J..̂ p '-Rn' 'Ru* T S -Et,NH+Cr .NEt, T ' -Et3NH+Cl" j >̂ ,p.»'>'Ru|—" c , --;Ru-. , , , ,py > - ^ V VP< ^ c i " ^ 31a -NEt - E t 3 N H + C r { 3 • ci II ^ C l ^ ^ H + H 2 [RuHCl(P.P)]3 32 29 p»... «vRu ' C - - 1 * ^ * Ru i».. i ,pJ L = MeCN, 33a; PhCN, 33b Scheme 5-HI 230 5.8 References - Chapter 5 1. Pearson, R. G. Acc Chem. Res. 1971,4, 152. 2. James, B. R. in Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 8, Chapter 51. 3. James B. R. Adv. Organomet. Chem. 1979,17, 319. 4. James, B.R. Homogeneous Hydrogenation; Wiley: New York, 1973. 5. (a) Eisenschmid, T. C; Kirss, R. U.; Deutsch, P. P.; Hommeltoft, S. I.; Eisenberg, R.; Bargon, J.; Lawler, R. G.; Balch, A. L. J. Am. Chem. Soc. 1987,109, 8089. (b) Kirss, R. U.; Eisenschmid, T. C; Eisenberg, R. J. Am. Chem. Soc. 1988, 110, 8564. (c) Kirss, R. U.; Eisenberg, R. J. Organomet. Chem. 1989,359, Cll. (d) Eisenschmid, T. C; McDonald, J.; Eisenberg, R.; Lawler, R. G. J. Am. Chem. Soc. 1989, 111, 7267. 6. Hallman, P. S.; McGarvey, B. R.; Wilkinson, G. J. Chem. Soc, A 1968, 3143. 7. James, B. R.; Wang, D. K. W. Inorg. Chim. Acta 1978, 29, L237. 8. Dekleva, T. W.; Thorburn, I. S.; James, B. R. Inorg. Chim. Acta 1985,100, 49. 9. Hampton, C; Dekleva, T. W.; James, B. R.; Cullen, W. R. Inorg. Chim. Acta 1988,145, 165. 10. McCrindle, R.; Fergusson, G.; Arsenalut, J.; McAlees, A. J. J. Chem. Soc, Chem. Commun. 1983, 571. 231 11. Thorburn, I. S., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1985. 12. James, B. R.; Pacheco, A.; Rettig, S. J.; Thorburn, I. S.; Ball, R. C ; Ibers, J.A. J. Mol Catal 1987,41, 147. 13. Noyori, R. Science 1990,248, 1194; Chem. Soc. Rev. 1989,18, 187. 14. (a) Miyashita, A.; Yasuda, A.; Takaya, H.; Toriumi, K.; Ito, T.; Souchi, T.; Noyori, R. J. Am. Chem. Soc. 1980,102, 7932. (b) Miyashita, A.; Takaya, H.; Souchi, T.; Noyori, R. Tetrahedron 1984,40, 1245. (c) Takaya, H.; Mashima, K.; Koyano, K.; Yagi, M.; Kumobayashi, H.; Taketomi, T.; Akutagawa, S.; Noyori, R. J. Org. Chem. 1986,57,629. 15. (a) Kawano, H.; Ishii, Y.; Ikariya, T.; Saburi, M.; Yoshikawa, S.; Uchida, Y.; Kumobayashi, H. Tetrahedron Lett. 1987,28, 1905. (b) Ikariya, T.; Ishii, Y.; Kawano, H.; Arai, T.; Saburi, M.; Yoshikawa, S.; Akutagawa, S. J. Chem. Soc, Chem. Commun. 1985, 922. 16. (a) Mashima, K.; Kusano, K.; Ohta, T.; Noyori, R.; Takaya, H. J.Chem. Soc, Chem. Commun. 1989, 1208. (b) Kitamura, M.; Ohkuma, T.; Inoue, S.; Sayo, N.; Kumobayashi, H.; Akutagawa, S.; Ohta, T.; Takaya, H.; Noyori, R. J. Am. Chem. Soc. 1988, 110, 629. (c) Noyori, R.; Ohkuma, T.; Kitamura, M.; Takaya, H.; Sayo, N.; Kumobayashi, H.; Akutagawa, S. J. Am. Chem. Soc. 1988,109, 5856. 17. James, B. R.; McMillan, R. S.; Morris, R. H.; Wang, D. K. W. Adv. Chem. Ser. 1978,167, 122. 18. James, B. R.; Wang, D. K. W. Can. J. Chem. 1980,58, 245. 19. Kawano, H.; Ikariya, T.; Ishii, Y.; Saburi, M.; Yoshikawa, S.; Uchida, Y.; Kumobayashi, H. J. Chem. Soc, Perkin Trans. 1989, 1571. 232 20. James, B. R.; Joshi, A. M.; Kvintovics, P.; Morris, R. H.; Thorburn, I. S. in Catalysis of Organic Reactions; Blackburn, D. W., Ed.; Marcel Dekker: New York, 1990; Chapter 2. 21. (a) Kubas, G. J. Acc. Chem. Res. 1988,21, 120; and references therein. (b) Kubas, G. J. Comments Inorg. Chem. 1988, 7, 17; and references therein. 22. Ashworth, T. V.; Singleton, E. J. Chem. Soc, Chem. Commun. 1976, 705. 23. Kubas, G. J. J. Chem. Soc, Chem. Commun. 1980, 61. 24. (a) Kubas, G. J.; Ryan, R. R.; Vergamini, P. J.; Wasserman, H. J. 185th Am. Chem. Soc. National Meeting, Seattle, WA, 1983; Abstr. # INOR 229. (b) C&EN 1983, 61(13), 4. 25. Kubas, G. J.; Ryan, R. R.; Swanson, B. I.; Vergamini, P. J.; Wasserman, H. J. J. Am. Chem. Soc. 1984,106, 451. 26. Nageswara Rao, B. D.; Anders, L. R. Phys. Rev. 1965,140, A112. 27. Crabtree, R. H.; Lavin, M. J. Chem. Soc, Chem. Commun. 1985, 794; 1661. 28. Morris, R. H.; Sawyer, J. F.; Shiralian, M.; Zubkowski, J. D. J. Am. Chem. Soc. 1985,107, 5581. 29. A recent Chemical Abstracts computer search (July 1990) on molecular hydrogen complexes yielded a listing consisting of about seventy references. Some representative examples are cited in references 30 through 34. 30. (a) Kubas, G. J.; Unkefer, C. J.; Swanson, B. I.; Fukushima, E. J. Am. Chem. Soc. 1986,108, 7000. (b) Wasserman, H. J.; Kubas, G. J.; Ryan, R. R. J. Am. Chem. Soc. 1986, 108, 2294. (c) Kubas, G. J.; Ryan, R. R.; Wrobleski, D. A. J. Am. Chem. Soc. 1986, 108, 1339. 233 (d) Conroy-Lewis, F. M . ; Simpson, S. J. / . Chem. Soc, Chem. Commun. 1986, 506. 31. (a) Morris, R. H . ; Earl, K . A. ; Luck, R. L . ; Lazarowych, N . J.; Sella, A . Inorg. Chem. 1987,26, 261A. (b) Kubas, G. J.; Ryan, R. R.; Unkefer, C. J. / . Am. Chem. Soc 1987, 109, 8113. (c) Chinn, M . S.; Heinekey, D. M . J. Am. Chem. Soc. 1987,109, 5865. (d) Bianchini, C ; Mealli, C ; Peruzzini, M . ; Zanobini, F. J. Am. Chem. Soc. 1987,109, 5548. 32. (a) Bautista, M . T.; Earl, K . A. ; Maltby, P. A. ; Morris, R. H. ; Schweitzer, C. T.; Sella, A . J. Am. Chem. Soc. 1988,110, 7031. (b) Bautista, M . T.; Earl, K. A. ; Maltby, P. A. ; Morris, R. H . J. Am. Chem. Soc. 1988,110, 4056. (c) Bianchini, C ; Peruzzini, M . ; Zanobini, F. J. Organomet. Chem. 1988,354, C19. (d) Fontaine, X . L . R.; Fowles, E. H . ; Shaw, B . L . J. Chem. Soc, Chem. Commun. 1988, 482. 33. (a) Jia, G.; Meek, D. W. J. Am. Chem. Soc. 1989, 111, 757. (b) Arliguie, T.; Chaudret, B . J. Chem. Soc, Chem. Commun. 1989, 155. (c) Chinn, M . S.; Heinekey, D. M . ; Payne, N . G.; Sofield, C. D. Organometallics 1989,5, 1824. (d) Cappellani, E . P.; Maltby, P. A. ; Morris, R. H. ; Schweitzer, C. T.; Steele, M . R. Inorg. Chem. 1989,28, 4437. (e) Howdle, S. M . ; Poliakoff, M . / . Chem. Soc, Chem. Commun. 1989, 1099. 34. (a) Chinn, M . S.; Heinekey, D. M . J. Am. Chem. Soc. 1990,112, 5166. (b) Van der Sluys, L. S.; Eckert, J.; Eisenstein, O.; Hall, J. H.; Huffman, J. C ; Jackson, S. A. ; Koetzle, T. F.; Kubas, G. J.; Vergamini, P. J.; Caulton, K. G. J. Am. Chem. Soc. 1990,112, 4831. (c) Howdle, S. M . ; Healy, M . A. ; Poliakoff, M . J. Am. Chem. Soc. 1990, 112, 4804. (d) Harman, W. D.; Taube, H . J. Am. Chem. Soc. 1990,112, 2261. 234 (e) Jia, G.; Morris, R. H. Inorg. Chem. 1990,29, 581. (f) Amendola, P.; Antoniutti, S.; Albertin, G.; Bordignon, E. Inorg. Chem. 1990,29,318. (g) Mediati, M.; Tachibana, G. N.; Jensen, C. M. Inorg. Chem. 1990,29, 3. 35. Henderson, R. A. Transition Met. Chem. 1988,13(6), 474. 36. Crabtree, R. H ; Hamilton, D. G. Adv. Organomet. Chem. 1988,28, 299; and references therein. 37. Crabtree, R. H. Acc. Chem. Res. 1990,23, 95. 38. (a) Pacchioni, G. J. Am. Chem. Soc. 1990,112, 80; J. Organomet. Chem. 1989,577, C13. (b) Burdett, J. K.; Pourian, M. R. Inorg. Chem. 1988,27, .4445. (c) Burdett, J. K.; Phillips, J. R.; Pourian, M.; Turner, J. J.; Upmacis, R. Inorg. Chem. 1987,26, 3054. (d) Hay, P. J. J. Am. Chem. Soc. 1987,109, 705. (e) Jean, Y.; Einstein, O.; Volatron, F.; Mouche, B.; Sefta, F. J. Am. Chem. Soc. 1986,108, 6587. 39. Crabtree, R. H ; Hamilton, D. G. J. Am. Chem. Soc. 1986,108, 3124. 40. Hampton, C , Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1989; Chapter 3. 41. (a) Hampton, C ; Dekleva, T. W.; James, B. R.; Cullen, W. R. Inorg. Chim. Acta 1988,145, 165. (b) Dekleva, T. W.; Thorburn, I. S.; James, B. R. Inorg. Chim. Acta 1985, 100, 49. 42. Hauge, R. H ; Kafafi, Z. H ; Margrave, J. L. Proceedings, The Physics and Chemistry of Small Clusters, Richmond, VA, Oct 1986; through Reference 21. 43. Ozin, G. A.; Garcia-Prieto, J. J. Am. Chem. Soc. 1986,108, 3099. 235 44. Nolan, S. P.; Marks, T. J. J. Am. Chem. Soc. 1989, 111, 8538. 45. Collman J. P.; Wagenknecht, P. S.; Hembre, R. T.; Lewis, N. S. J. Am. Chem. Soc. 1990,112, 1294. 46. Crabtree, R. H.; Lavin, M.; Bonneviot, L. J. Am. Chem. Soc. 1986,108, 4032. 47. Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988,110, 4126. 48. (a) Antoniutti, S.; Albertin, G.; Amendola, P.; Bordignon, E. J. Chem. Soc, Chem. Commun. 1989, 229. (b) Cotton, F. A.; Luck, R. L. Inorg. Chem. 1989, 28, 6. 49. Joshi, A. M.; James, B. R. J. Chem. Soc, Chem. Commun. 1989, 1785. 50. Arliguie, T.; Chaudret, B.; Morris, R. H ; Sella, A. Inorg. Chem. 1988, 27, 598. 51. Hampton, C ; Cullen, W. R.; James, B. R.; Charland, J. -P. J.Am. Chem. Soc. 1988,110, 6918. 52. Sanders, J. K. M.; Hunter, B. K. Modern NMR Spectroscopy: A Guide for Chemists; Oxford University Press: Oxford, 1987; pp. 61-65. 53. Conroy-Lewis, F. M.; Simpson, S. J. J. Chem. Soc, Chem. Commun. 1987, 1675. 54. Bautista, M.; Earl, K. A.; Morris, R. H ; Sella, A. J. Am. Chem. Soc. 1987, 109, 3780. 55. Cotton, F. A.; Luck, R. L. J. Chem. Soc, Chem. Commun. 1988, 1277. 56. Upmacis, R. K.; Poliakoff, M.; Turner, J. J. J. Am. Chem. Soc. 1986,108, 3645. 236 57. (a) Chaudret, B.; Devillers, J.; Poilblanc, R. Organometallics 1985,4,1727; J. Chem. Soc, Chem. Commun. 1983 , 641. 58. Gosser, L. W.; Knoth, W. H.; Parshall, G. W. / . Am. Chem. Soc. 1973, 95, 3436. 237 CHAPTER <5 Ruthenium(II) Hydrido-Diene Complexes Containing Bidentate Phosphines 6.1 Introduction The ruthenium(II) hydrido(diene) complex RuHCl(nbd)(PPh3)2, first reported by Wilkinson et al. in 1968,1 exists in solution as a single (trans) isomer in which the metal, the hydride, and the alkene 7t-bond form a coplanar cis arrangement2'3 which is favourable for olefin insertion into the Ru-H bond. Earlier work from this laboratory2'3 has reported formation of the stable six-coordinate norbornenoyl complex RuCl(COC7H9)(CO)2(PPh3)2 via an irreversible reaction of CO with rra/w-RuHCl(nbd)(PPh3)2, 34 (Equation 6.1). Coordination of CO, presumably to a five-coordinate intermediate, promotes the hydride migratory-insertion to give a carbonyl(alkenyl) species which subsequently undergoes CO migratory-insertion to give the acyl; coordinative saturation is attained via further coordination of CO. Detailed NMR studies, including selective homonuclear decoupling experiments by Dekleva from this laboratory, established the geometry for the norbornenoyl complex, as depicted in Equation 6.1 2>3 238 (6.1) The unusual stability of this acyl species (acyls are typically kinetically unstable with respect to carbonyl-deinsertion4 or reductive elimination5- 6) permitted further investigation into its reactivity with H2.7 The H2-hydrogenolysis of a transition metal-acyl complex to afford the product aldehyde and the metal hydride -often the catalyst precursor- is commonly the final step in both stoichiometric and catalytic hydroformylation of alkenes, but has been little studied.7"9 Hydrogenolysis of RuCl(COC7H9)(CO)2(PPh3)2 in DMA or toluene solutions (1 atm H2, 40-70 °C) results in the formation of 2-norbornene-5- carboxaldehyde and c/5,ci5,rra« -̂RuHCl(CO)2(PPh3)2 (Scheme 6-1). A detailed kinetic study of this reaction was undertaken and a mechanism, involving PPh3 dissociation as the rate-determining first step followed by hydrogenolysis of the resulting intermediate, was proposed to account for the observed kinetic data (Scheme 6-I).7>8 Further, the hydrido(diene) complex, 34, reacts with H2 with loss of norbornane to yield a dinuclear rj2-H2 complex,10 (Equation 6.2): 5 H 2 RuHCl(nbd)(PPh3)2 ?—- (Ti2-H2)(PPh3)2Ru(p.-Cl)2(u-H)Ru(H)(PPh3)2 (6.2) + Norbornane 239 Scheme 6-1: Proposed mechanism for the H2-hydrogenolysis of the Ru(II) acyl complex RuCl(COC7H9)(CO)2(PPh3)2. The work described in this chapter was undertaken to explore further reactions as outlined in Equations 6.1 and 6.2 by using a chelating ditertiary phosphine (P-P) in place of two PPh3 ligands in the 'precursor' complex 34. The phosphine Ph2P(CH2)nPPh2 (n = 4, DPPB) was chosen as the chelating phosphine particularly because of: (a) the known tendency of DPPB (compared to the n = 1-3 analogues) to become monodentate at a metal centre, i.e. to become dangling,11 (b) its formation of seven-membered chelate rings, similar to the well-known, chiral DIOP 1 1- 1 2 and BINAP ligands,13-14 (c) isolation of the dinuclear molecular hydrogen complexes containing DPPB, (T|2-H2)(DPPB)Ru(u-Cl)2- (u-X)Ru(X)(DPPB) (X = C l , 1 5 H; cf. Equation 6.2; also see Chapter 5), and finally, because of (d) the related dichloro(norbornadiene)Ru(II) complex16 was previously synthesised in this laboratory (see below). Thorburn16 investigated the reaction of the dichloro-bridged dinuclear complex [RuCl(DPPB)(p.-Cl)]2,14, with excess norbornadiene in benzene. The orange product, 240 characterised by elemental analysis and ! H and 3 1P{ 1H} NMR spectroscopy^ was identified as rrans-RuCl2(nbd)(DPPB)-0.5 C6H6 solvate, 35 (64% yield). An X-ray crystal structure determination confirmed the mutually trans chloride ligands.16- 1 7 Thorburn also noted that the norbornadiene ligand of 35 slowly dissociated in solution to give the dinuclear precursor 14 (Equation 6.3), which was evident from the gradual disappearance of the 17.0 ppm singlet due to 35 and the concomitant appearance of die AB quartet pattern due to 14 (8A = 62.8, 8B = 53.5 ppm, 2 7 AB = 46.8 Hz) in the 3 1 P NMR spectrum of an aged solution of 35.1 6-1 7 In the corresponding *H NMR spectrum, free nbd (8 6.8 ppm, t, olefinic protons) soon became detectable, and after 24 h peaks due to 35 constituted only ~40% of the total integral intensity. RuCl2(nbd)(DPPB) „ 1/2 [RuCl(DPPB)(u-Cl)]2 + nbd (6.3) 35 14 Interestingly, a preparative scale reaction of the dichlorodiene complex 35 with H 2 in the presence of Proton Sponge® led to the isolation of the previously known [Ru2Cl5(DPPB)2]-PSH+ complex16"19 as the major product (-63% yield, 31P{ ]H} NMR, CD2CI2, 20 °C: 53.6 ppm, s) instead of a hydridochloro species such as "RuHCl(DPPB)" or an ri2-H2 analogue containing DPPB (cf. Equation 6.2). A small amount of brown solid (-5% yield) subsequently isolated from the reaction mixture (filtrate), though analytically impure, showed evidence of hydride formation. The proton NMR spectrum of the brown solid principally consisted of a high-field resonance at -9.69 ppm (t, 27PH = 21 Hz; C6D6> § Anal. Calcd for C35H36Cl2P2Ru0-5 C 6 H 6 : C, 62.55; H, 5.35; Cl, 9.74. Found: C, 62.5; H, 5.4; Cl, 9.5. *H NMR (CD 2C1 2, 20 X): 8 7.7-7.2 (20 H, br m, phenyl region, DPPB), 8 4.50 (4 H, m, olefinic, nbd), 8 3.59 (2 H, m, methine, nbd), 8 2.90 and 1.67 (4 H each, br m, methylene, DPPB), 8 1.39 (2 H, s, bridgehead methylene, nbd); 3 1P{ 1H} NMR: 17.0 ppm (s). 241 20 °C) characteristic of a Ru-hydride species, along with resonances in the 4.0-0.8 ppm region characteristic of bound norbornadiene protons; the resonances were tentatively assigned to rra/w-RuHCl(nbd)(DPPB), 36. 1 6' 1 7 6.2 Synthesis and Characterisation of 7>a7Js-RuHCI(nbd)(DPPB), 3j£ The minor, impure product obtained by Thorburn from the reaction of 35 with H2 (see above), and tentatively identified as trans-RuRC\(nbd)(DPPB), was synthesised in pure form by two routes (Section 2.5.3). One, giving a 40% yield, involves the simple displacement of the PPh3 ligands of rraw-RuHCl(nbd)(PPh3)2, 34, by DPPB in benzene solution (Equation 6.4). RuHCl(nbd)(PPh3)2 + DPPB RuHCl(nbd)(DPPB) + 2PPh3 (6.4) C 6 H 6 34 36 The second method for the preparation of 36 also involves PPh3 displacement, this time by nobornadiene, from the mixed phosphine Ru(II) precursor RuCl2(dppb)(PPh3), 23, under hydrogenation conditions (1 atm H2, Proton Sponge, 60 °C) in benzene (Equation 6.5). The off-white 36 is isolated in 62% yield, although the accompanying PSH+C1- salt, which was identified by J H NMR spectroscopy, is formed in quantitative yield. H2/PS RuCl2(DPPB)(PPh3) + nbd — RuHCl(nbd)(DPPB) + PPh3 (6.5) 23 36 + PSH+C1" The 31P{ NMR spectrum of 36 in C^>e solution consists of a singlet at 43.2 ppm, while the lH NMR Ru-hydride resonance is observed as a triplet at 5 -9.69 ppm, 242 with 2/pn = 20.7 Hz (Figure 6.1). This means the two phosphorus atoms of the DPPB ligand are chemically and magnetically equivalent, and are cis to the hydride. 11 ] I I I I | I I I I | I -B.5 -9.0 -9.5 i | i i i i | : i i i j •10.0 -10.5 PPM-11.0 Figure 6.1: The *H NMR (300 MHz, C6D6,20 *C) hydride region for trans- RuHCl(nbd)(DPPB), 36. The J H NMR spectrum of 36 was fully assigned using a combination of 2D-COSY and NOED1FF experiments (Figures 6.2 and 6.3, respectively). The replacement of an 'axial' chloride of RuCl2(nbd)(DPPB), 35, by a hydride ligand to give 36 leads to the expected doubling in number of peaks for the olefinic protons (8 3.89,2.84 ppm, 2H each, br m) and methine protons (8 3.67, 3.36 ppm, IH each, br m) of nbd, and the methylene backbone protons (8 3.75, 2.07, 1.22, 0.98 ppm, 2H each, br m) of the DPPB ligand (compare with the proton NMR data for 35 given in the previous section). This doubling of the number of proton NMR peaks is due to the presence in 36 of two different ligands (H -, Cl") above and below the Ru-DPPB plane. The two multiplets for the ortho-phenyl protons of the DPPB ligand are separated by over 0.9 ppm (8 8.25,7.33), again reflecting the axial asymmetry across the Ru-DPPB plane. Irradiation of the 8 8.25 resonance induces a large positive NOE enhancement of the Ru-H resonance at -9.69 ppm and vice versa (Figure 6.3); thus the 8.25 ppm resonance is assigned to the four orr/io-phenyl protons (one from each of the phenyl groups on the two P atoms) closest to the hydride, 243 while the higher field 7.33 ppm signal is attributed to the remaining four ortho-phenyl protons. • - C H 2 - , dppb F l (ppm) Figure 6.2: The ! H NMR 2D-COSY spectrum (300 MHz, C6D6, 20 *C, aliphatic proton region) of rra/w-RuHCl(nbd)(DPPB), 36. 244 HJJ, Hp Ho i / JJ 9.0 B Ha He UU Hb 5.0 (ppm) Ru-H 1.0 -9.0 -10.0 Figure 6.3: The *H NMR NOEDIFF spectra (400 MHz, C ^ , 20 *C) of trans- RuHCl(nbd)(DPPB), 36. (A) ! H NMR spectrum of 36; see Figure 6.4 for assignments. (B) Spectrum with irradiation of the Ru-H resonance (8 -9.69 ppm). (C) Spectrum with irradiation of the 8 8.25 ppm resonance (see text). 245 Irradiation of the hydride signal also results in a large positive enhancement of the 8 3.89 ppm resonance, which is therefore assigned to the pair of olefinic protons (Ha) closest to the hydride; He and Hd are then assigned because of their observed coupling to H a and Hb, respectively. The V ( R U _ H ) JR absorption band for 36 is observed at 2045 cm - 1 (w). The spectroscopic data of 36 resemble closely those for the corresponding RuHCl(nbd)Q?Ph3)2 complex, 34, and are consistent with the rra/w-RuHCl(nbd)ODPPB) formulation shown in Figure 6.4. Figure 6.4: Proposed geometry for RuHCl(nbd)(DPPB), 36, including the proton assignment, based on analysis of the solution NMR spectral data. Reactions of the mixed-phosphine complex RuCl2(DPPB)(PPh3), 23, with nbd in the absence of H2 and PS were also investigated. The complex 23 reacts with excess norbornadiene in benzene at 60 "C to produce a greenish yellow suspension. Complete removal of the solvent from the reaction mixture at this stage yields mostly the green starting complex 23, while addition of hexanes precipitates a mixture of green and yellow solids. Examination by 3 1 P NMR spectroscopy of a reaction mixture in C^D^ indicates equilibrium formation of the dichloronorbornadiene derivative RuCl2(nbd)(DPPB), 35 (Equation 6.6), as evidenced by the resonance at 17.0 ppm (s); additional signals assignable to 23 and free PPh3 are also apparent (for a 31P{ lH} NMR spectrum of 23, see Chapter 4, Figure 4.5). 246 RuCl2(DPPB)(PPh3) + nbd 23 6 n 6 RuCl2(nbd)(DPPB) + PPh3 (6.6) 35 6.3 Discussion The overall chemistry of formation of 35 and 36 from various starting materials, coupled with the solution behaviour (PPI13 disociation) and H2-reactivity of 23 (to give 'RuHCl(DPPB)(PPh3)' species; see Chapter 4, Section 4.3), are summarised in Scheme 6-II. RuCl2(nbd)(P-P) 35 -nbd nbd ^ 1/2 [RuCl(P-P)(u-Cl)]2 14 RuCl2(P-P)(PPh3) 23 H2/PS 'RuHCl(P-P)' + PSH+Cr H2/PS 'RuHCl(P-P)(PPh3)' PSH+cr nbd -PPh, P-P = DPPB nbd 14 RuHCl(nbd)(P-P) [Ru2Cl5(P-P)2]-PSH+ 36 P-P RuHCl(nbd)(PPh3)2 34 Scheme 6-TJ 247 Thorburn has noted the dissociation of coordinated nbd from RuCl2(nbd)(DPPB), 35, in solution (see above).16 Interestingly, the corresponding RuCl2(nbd)(PR3)2 complexes (where R = Ph, 2 0 p-tolyl3) or RuHCl(nbd)(PPh3)2, 34, do not undergo dissociation of the diene,2 ,3 and indeed solution reactivity of 34 probably stems from the loss of PPh3 (see Section 6.1, and see below). Structural data are not available for the monodentate phosphine systems, but steric factors (e.g. two m-PPh3 ligands vs. DPPB) probably promote PPh3 dissociation. Complex 35 had seemed initially to be an appropriate precursor either to (a) the target hydrido(diene) complex RuHCl(nbd)(DPPB), 36, by treatment with H2, if necessary by addition of a base to consume liberated H C l , 2 1 or (b) coordinatively unsaturated hydrides, following hydrogenation of and displacement of the diene as norbornene and/or norbornane. In retrospect , however, the chemistry becomes more complicated because of the loss of diene from 35. Treatment with H2 in the presence of Proton Sponge® (PS), in fact, yields mainly the trichloro-bridged species [Ru2Cl5(DPPB)2]~PSH+ (A) and only small amounts of impure 36. Complex A was synthesised previously by reaction of 14 with H2 in the presence of PS,16> 1 8 > 1 9 and this likely provides the pathway for synthesis of A from 35 (Scheme 6-II). Some 36 could presumably be formed by direct reaction of H2 with 35, or via 14 and the intermediate 'RuHCl(DPPB)' shown in Scheme 6-II; the non-reactivity of monodentate phosphine analogues of 35, RuCl2(nbd)(PR3)2» toward H2 tends to favour the latter suggestion. Indeed, addition of norbomadiene (~1 equiv./Ru) to a C6D6 solution of [RuHCl(DPPB)]3 (cf. Chapter 5, Section 5.4) resulted in the formation of 36, as confirmed by NMR spectroscopy. The reaction of 35 with H2 (1 atm H2, 50 "C, DMA solvent) in the presence of PS was monitored using a conventional gas uptake apparatus; the final uptake corresponded to 1.7 mole equivalents H2 per mole of the complex in about 1.5 h . 1 6 Formation of 36 by hydrogenation of 35 would require 0.5 H2/RU, whereas complete hydrogenation of 248 coordinated nbd on 35 would utilise 2.0 H2 /RU. The less than 2.0 (or 2.5) equivalent H2- uptake probably corresponds to partial formation of 36 and partial hydrogenation of the diene, the ratio being governed by loss of nbd from 35. The low yield of 36 via this '35 + H2 route' must result in part from loss of available diene as hydrogenated product. Support for this comes from the attempted catalytic hydrogenation of norbornadiene, using as catalyst 14 (1.0 mM), which readily hydrogenates 1-hexene, styrene and acrylamide (max. rate = 4.9, 3.0 and 1.3 x 10-4 Ms' 1, respectively; [alkene] = 0.40 M, 1 atm H2, 50 °C, DMA). 1 6 Under identical conditions, hydrogenation of norbornadiene is much slower (max. rate = 1.4 x 10"5 M s"1) and stops after ca. 3 h with an uptake corresponding to the reduction of only 2.5% of the available substrate (total turnovers, norbornane/Ru, -10).16 The inability to effectively reduce norbornadiene suggests that a catalytically inactive complex is being formed during the reaction with H2. The simple displacement of PPh3 from RuHCl(nbd)(PPb.3)2,34, by the chelating DPPB ligand to yield 36 (Equation 6.4) appears to be general; under similar reaction conditions (see Section 2.5.3), use of Ph2P(CH2)6PPh2 (DPPH) yields the corresponding rra«5-RuHCl(nbd)(DPPH) complex.̂  The norbornadiene ligand in 34 must be bound to ruthenium more strongly than PPh3. Alkenes are generally considered to have both a higher trans influence (thermodynamic), and trans effect (kinetic), compared to PR3 ligands.22 Displacement by DPPB of the monodentate PPh3 of 34, rather than the dialkene, is therefore not surprising. In addition, the chelate effects of the bidentate nbd and the incoming DPPB ligands presumably play an important role in the phosphine exchange reaction. § Spectroscopic data for /ra/js-RuHCl(nbd)(DPPH): IR (cm"1), V R U - H 2016(w); lH NMR (CDCI3, 20 °C), 8 -10.56 (IH, t, Ru-H, 2 / P H = 23 Hz); 3ip{lH} NMR (CDCI3, 20 °C), 35.7 ppm (s). 249 Formation of 36 under hydrogenation conditions from RuCl2(DPPB)(PPh3), 23, and excess nbd (Equation 6.5) almost certainly occurs via the intermediate RuHCl(DPPB)(PPh3) as shown in Scheme 6-II. In solution, the bright green species 23 exists in rapid equilibrium with the orange-brown 14 and free phosphine (see Chapters 3 and 4); addition of nbd to 23 in solution leads to formation of 35 in a reversible equilibrium. However, as described in Section 4.3, DMA solutions of 23 in the presence of added PS take up ~0.9 equivalents of H 2 per Ru to generate in situ a hydride species which is considered to be 'RuHCl(DPPB)(PPh3)'. This is then trapped by nbd by displacement of PPh.3 to give 36. Conversion of 23 to 36 cannot proceed via 14 because A is not formed as a co-product (Scheme 6-II). It should be noted also that RuHCl(nbd)(PPh3)2, 34, is formed similarly from RuHCl(PPh3)3 by displacement of PP113.1 Of note is the relatively high isolated yield (62%), and perhaps close to quantitative conversion (based on yield of PSH+C1~, see above), of the hydridochloro(diene)- complex, 36, obtained by the '23 + H2/PS + nbd' route (Equation 6.5). Although the dichloro analogue 35 is also formed during the course of the reaction (Equation 6.6), only trace amounts (< 5%) of 35 could be sometimes detected at the end of the reaction. Under similar conditions, however, reactions involving PPh2Py or DPPM in place of nbd produced mixtures of the corresponding hydridochloro and dichloro products in ca. 1:2 ratio (complexes 26:24+25 for PPh2Py and 28:27 for DPPM, respectively; see Chapter 4, Scheme 4-II); the observed distribution of hydridochloro vs. dichloro products was suggested to reflect initial (or more likely, equilibrium) ratios of 'RuHCl(DPPB)(PPh3)' and RuCl2(DPPB)(PPh3) species, reactions of the phosphines with both species being rapid and irreversible (see Chapter 4, Section 4.5). As noted earlier, reaction of nbd with RuCl2(DPPB)(PPh3) to produce 35 and free PPh3, however, is reversible (3lp NMR evidence, see above; Equation 6.6) while that with 'RuHCl(DPPB)(PPh3)' to give 36 is 250 not. A possible explanation for the almost exclusive formation of 36, in accordance with Equation 6.5, is presented in Scheme 6-IJJ. H2/Proton Sponge® RuCl2(DPPB)(PPh3) ^ -tr •RuHCl(DPPB)(PPh3), + HCl 23 +PPh3 -nbd QH6 B -PPh +nbd 3 A RuCl2(nbd)(DPPB) 35 -PPh3 -t-nbd RuHCl(nbd)(DPPB) 36 Scheme 6-III Reaction of nbd with an equilibrium mixture of RuCl2(DPPB)(PPh3) and 'RuHCl(DPPB)(PPh3)' may lead initially to formation of 35 and 36 in the expected proportion (steps A and C, respectively, in Scheme 6-III). However, the reversibility of step A and the irreversible nature of step C together ensure further formation of 'RuHCl(DPPB)(PPh3)' through a continual shift in equilibrium steps A and B in favour of the five-coordinate hydridochloro complex, which is then trapped irreversibly by the dialkene to give more of the hydrido(diene) complex 36. 6.4 Reactivity of 7ra/is-RuHCl(nbd)(DPPB), 2£, toward H 2 and CO Benzene or DMA solutions of 36, in the absence or presence of added PS (or DBU, l,8-diazabicyclo-[5.4.0]-undec-7-ene), do not react with 1 atm H 2 at 30-50 °C. This is consistent with the formation of 36 as the catalytically inactive species during the ineffective hydrogenation of nbd catalysed by 14 (see above). Although 36 is best synthesised by a procedure carried out under H 2 , the failure of 36 to react with H 2 was 251 somewhat surprising in view of the known behaviour of the PPh3 analogue, 34, which gives cleanly a binuclear r|2-H2 complex10 and reduction of the bound diene to norbornane (Equation 6.2). Mechanistic details of reaction 6.2 are not known, but lH and 3 1 P NMR studies carried out by Dekleva3 showed initial formation of some RuHCl(PPh3)3 (C6D6, 8RU-H -17.5 ppm, q, 2 /pn = 26 Hz) 2 3 and slower subsequent generation of the r)2-H2 complex and norbornane. Which of 34, the trisphosphine species, or a necessarily present phosphine-deficient species, effects hydrogenation of the diene is unclear. Perhaps phosphine dissociation is a critical step for reactivity toward H2, and this is not realized with the bidentate DPPB ligand, although (as noted in the Introduction) dissociation to monodentate DPPB 1 1 is well substantiated. The hydrido(diene) complex 36 also shows no reaction with 1 atm CO in refiuxing benzene or in DMA at 70 °C. Although 36 has the coplanar arrangement of metal, hydride and alkene 7t-bond required for stereospecific migratory-insertion of the dialkene to form an alkenyl species,24- 2 5 the insertion is not promoted by coordination of CO. Such an insertion was however found earlier for the bis(PPh3) analogue 34 under 1 atm CO at 20 °C (Equation 6.1).2 ,3 Again, the inability of DPPB to dissociate in order to provide the required site for CO-binding perhaps leads to the observed unreactivity of this complex; also important, however, will be the enforced cis disposition of the two P donors of DPPB in any resulting product Of note, the PPh3 ligands in the acyl product of Equation 6.1 are mutually trans; the disposition of the phosphines in the alkenyl intermediate(s), prior to CO insertion, is not known, but any step requiring the initially dissociated PPh3 to re-associate trans to die remaining PPh3 (for steric or electronic reasons) cannot be accommodated with the DPPB ligand Of interest, the nature of the diene can also determine whether migratory-insertion occurs. The bis(PPh3) complex rra^-RuHCl(l,3-cyclohexadiene)(PPh3)2,7 in contrast to the nbd analogue 34, reacts with two equivalents of CO to yield, with displacement of the diene, the well-known cis,cis,trans-RnHC\(CO)2(PPh-i)2 species.7- 8 The factors 252 affecting the choice between coordination of CO to (a) promote olefin insertion or (b) replace coordinated diene are probably balanced quite closely. This conclusion is supported by other findings where 'subtle' changes in the incoming nucleophile also determine the reaction pathway. Thus the hydrido(ethylene) complex [CpRhH(C2H4)PMe3] + gives on reaction with CO the hydrido(carbonyl) species [CpRhH(CO)PMe3]+ via displacement of ethylene, while the insertion reaction to give an ethyl product, [Rh(C2H5)Cp(C2H4)PMe3]+, is promoted by addition of C2H4 itself.26 Similarly, within a related hydrido(ethylene) complex of Mo, again CO gives a hydrido(carbonyl) complex while PPh3 promotes the insertion reaction.27 Thus the 'minor' change of replacing two ris-PPh3 ligands by a flexible chelating diphosphine ligand (DPPB) within a precursor complex (rrartS-RuHCl(nbd)(PPh3)2,34) induces for the DPPB-derivative relative non-reactivity toward H2 and CO. 253 6.5 References - Chapter 6 1. Hallman, P.S.; McGarvey, B. R.; Wilkinson, G. J. Chem. Soc A, 1968, 3143. 2. Dekleva, T. W.; James, B. R. J. Chem. Soc, Chem. Commun. 1983, 1350. 3. Dekleva, T. W., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1983; Chapters 2 and 7. 4. Tsuji, J. in Organic Synthesis via Metal Carbonyls; Wender, I. and Pino, P., Eds.; Wiley-Interscience: New York, 1977; p. 595. 5. Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987; Chapter 5. 6. (a) Cardaci, G.; Reichenbach, G.; Bellachioma, G.; Wassink, B.; Baird, M. C. Organometallics, 1988, 7, 2475. (b) Webb, S. L.; Giandomenico, C. M.; Halpern, J. J. Am. Chem. Soc. 1986, 108, 345. (c) Nappa, M. J.; Santi, R.; Halpem, J. Organometallics, 1985,4, 34. (d) Nappa, M. J.; Santi, R.; Diefennbach, S. P.; Halpern, J. J. Am. Chem. Soc. 1982,104, 619. 7. Joshi, A. M., M.Sc. Dissertation, The University of British Columbia, Vancouver, Canada, 1986; Chapters 2 and 3. 8. Joshi, A. M.; James, B. R. Organometallics 1990,9, 199. 9. Hoff, C. D.; Ungvary, F.; King, R. B.; Marko, L. J. Am. Chem. Soc. 1985, 107, 666. 254 10. (a) Dekleva, T. W.; Thorburn, I. S.; James, B. R. Inorg. Chim. Acta 1985, 100, 49. (b) Hampton, C ; Dekleva, T. W.; James, B. R.; Cullen, W. R. Inorg. Chim. Acta 1988,145, 165. 11. (a) James, B. R.; Mahajan, D. J. Organomet. Chem. 1985,279, 31; Can. J. Chem. 1980,58, 996. (b) James, B. R.; McMillan, R. S.; Morris, R. H.; Wang, D. K. W. Adv. Chem. Ser. 1978,167, 122. 12. Dumont, W.; Poulin, J.-C; Dang, T.-P.; Kagan, H. B. J. Am. Chem. Soc. 1973, 95, 8295. 13. Noyori, R. Science 1990, 248, 1194; Chem. Soc. Rev. 1989,18, 187. 14. Mashima, K.; Kusano, K.; Ohta, T.; Noyori, R.; Takaya, H. J. Chem. Soc, Chem. Commun. 1989, 1208. 15. Joshi, A. M.; James, B. R. J. Chem. Soc, Chem. Commun. 1989, 1785. 16. Thorburn, I. S. Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1985; Chapter 5. 17. Dekleva, T. W.; Joshi, A. M.; Thorburn, I. S.; James, B. R.; Evans, S. V.; Trotter, J. lsr. J. Chem. 1990; in press. 18. James, B. R.; Pacheco, A.; Rettig, S. J.; Thorburn, I. S.; Ball, R. C ; Ibers, J. A. J. Mol. Catal. 1981,41, 147. 19. Gamage, S. N.; Morris, R. H ; Rettig, S. J.; Thackray, D. C ; Thorburn, I. S.; James, B. R. J. Chem. Soc, Chem. Commun. 1987, 894. 20. Robinson, S. D.; Wilkinson, G. J. Chem. Soc. A 1966, 300. 255 21. James, B. R. in Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A. and Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 8, p. 295. 22. Appleton, T. G.; Clark, H. G; Manzer, L. E. Coord. Chem. Rev. 1973,10, 335. 23. Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97, 4221. 24. Crabtree, R. H. Acc. Chem. Res. 1979,12, 331. 25. Reference 5, p. 383. 26. Werner, H.; Feser, R. Angew. Chem. Int. Ed. Engl. 1979,18, 157. 27. Benfield, F. W. S.; Green, M. L. H. J. Chem. Soc, Dalton Trans. 1974, 1324. 256 C H A P T E R 7 Catalytic Hydrogenation Studies 7.1 Introduction The di- and trinuclear ruthenium complexes containing a single bidentate phosphine per Ru ([RuCl(P-P)(u-Cl)]2 and [RuHCl(P-P)]3, respectively), described in the previous chapters, were found to catalyse hydrogenation of a range of unsaturated organic substrates, including alkenes, ketones, imines, and nitriles under relatively mild conditions (1-12 atm H2, 30-100 *C). The hydrogenation reactions proceeded at measurable rates under ~1 atm of H2 pressure, thus making the kinetics and mechanisms of these hydrogenation systems amenable to detailed studies. Such studies were undertaken toward the end of this work, and some results are presented in this chapter. 7.2 Hydrogenation of Styrene Catalysed by [RuCI(DPPB)(u.-Cl)]2,14 The kinetics of H2-hydrogenation reactions catalysed by [RuClQ3PPB)(|i-Cl)]2, 14, and its analogues containing other diphosphine ligands (e.g. CHIRAPHOS, 16) are of interest because of the dimeric nature of the catalyst precursor and the possible involvement of the T|2-H2 species, 31a (see Chapter 5, Section 5.3), in the catalytic cycle. The results of a kinetic investigation into the hydrogenation of styrene to ethylbenzene catalysed by 14 are presented here. DMA solutions of styrene rapidly absorbed hydrogen (30 *C, 1 atm of H2) in the presence of catalytic amounts of [RuCl(DPPB)(|i-Cl)]2,14. The presence of ethylbenzene as the hydrogenation product was confirmed by examination of the final H2-uptake solution 257 by *H NMR spectroscopy (8 1.03, t, P I 1 C H 2 C / / 3 ; 2.04, q, PhC//2CH3). Resonances due to styrene protons (7.3-5.0 ppm region) had disappeared indicating that the reduction was essentially complete. The catalyst precursor 14, which remains dimeric in DMA solution (see Chapter 3, Section 3.7.1), was recovered intact at the end of the catalytic run as evidenced by the 3 1P{ 1H) NMR spectrum of the red-brown residue (obtained by pumping off the DMA and ethylbenzene under vacuum at 50 *C) in C 5 D 6 (AB q: 8A = 64, 8B = 54.9 ppm ,2/AB = 47 Hz; see Chapter 3, Table 3.3). The 3 1P NMR spectrum of 14 in C 6 D 6 in the presence of ~50-fold excess of styrene was essentially unchanged, except for a slight broadening of the resonances from initial linewidths of ~7 Hz observed in the absence of styrene to ~11 Hz. 7.2.1 Solubility of Hydrogen in DMA The solubility of hydrogen in DMA has been determined previously in our laboratory, at a range of temperatures (15-80 *C) and at various H2-pressures (100-800 Torr) , 1 - 6 employing a constant pressure gas-uptake apparatus and by a procedure described elsewhere.6 The H2-solubility in DMA obeys Henry's law at least up to one atmosphere pressure of hydrogen over the temperature range studied, the plots of molar solubility against partial pressure of H2 being linear. The solubility data at various temperatures, expressed as Henry's law constants K H derived from the slope of such straight-line plots ( K H = [H2]/P0H2) M Ton-1), are listed in Table 7.1. The constant K H essentially represents an equilibrium constant for the dissolution of H2: H2(gas) ==• H2(solution). The van't Hoff plot for the temperature dependence of H2-solubility in DMA is linear (Figure 7.1). The values of -655 K and -10.8 for the slope and the Y-intercept, respectively, obtained from this In K H V S. 1/temperature plot, can be used to calculate the H2-solubility in DMA at any temperature at least within the 15-80 "C range. 258 Table 7.1: Solubility8 of H2 in A -̂Dmiemylacetaniide. Temperature, K CC) KHxltf.MTorr-l Reference 288.2 (15.0) 2.11 (±0.02) 1 298.2 (25.0) 2.24 2 303.2 (30.0) 2.32 3 308.2 (35.0) 2.37 1 308.2 (35.0) 2.38 4 323.2 (50.0) 2.70 5 333.2 (60.0) 2.82 5 333.2 (60.0) 2.83 1 338.2 (65.0) 2.86 6 353.2 (80.0) 3.20 4 a Expressed as Henry's law constant KH, where KH = [H2]/P(H2). -12.6 -12.7" -12.8" * -12.9- c -13.0- -13.1" « -13.2" 2.80 3.00 3.20 3.40 3.60 1/Temperature x 1 0 3 , K"1 Figure 7.1: The van't Hoff plot for the temperature dependence of H2-solubility in DMA. 259 7.2.2 Rate Measurements The hydrogenation of styrene was monitored using a constant pressure gas-uptake apparatus.6 A typical plot of H2-uptake against time in DMA for the hydrogenation of styrene is shown in Figure 7.2. The uptake-plots were 5-shaped, and showed an induction period of -100-200 s. Maximum linear rates were attained in the initial 10-20% Hi-uptake region. The H2-uptakes were measured at total ruthenium (monomer) concentrations, [Ru]x, ranging from 1.0 x 10"3 to 3.1 x 10 - 3 M, at different H2-pressures (410-785 Torr), and at various substrate concentrations ([styrene] = 0.010-42 M), changing only one parameter at a time. /v",A -̂Dimethylacetamide (DMA) was chosen as the solvent because of its convenient low vapour pressure (<5 Torr at 30 *C).7 200 -> r 500 1000 i 1 1 1 • 1500 2000 2500 3000 Time, s Figure 7.2: A typical H2-uptake plot for the hydrogenation of styrene catalysed by [RuCl(DPPB)(u-Cl)]2,14, in DMA at 30 *C and 785 Torr pressure of H2. [Styrene] = 0.18 M, [Ru]T = 1.58 x 10 - 3 M, [H2] = 1.82 x 10 - 3 M. 260 The dependence of the maximum rates on the total ruthenium monomer concentration [ R U ] T , initial substrate concentration [styrene], and hydrogen concentration [H2] were investigated at 30 * C . The rate data for hydrogenation of styrene in DMA at 30 'C are summarised in Table 12. The ruthenium dependence of hydrogenation rates was studied at the initial substrate concentration [styrene] =0.415 M, under 785 Torr of H2 pressure ([H2] c 1.82 x 10~3 M), for total ruthenium monomer concentrations [ R U ] T ranging between 1.0-3.1 x 10-3 M. The individual rate plots are shown in Figure 7.3. The plot of the maximum rate against [ R U ]T is shown in Figure 7.4 and is linear, implying a first-order dependence on [ R U ] J for the hydrogenation rate. The dependence of the maximum hydrogenation rate on the initial substrate concentration was studied at 30 *C, for [styrene] = 0.009-0.415 M, at [ R U ]T = 1-58 x 10"3 M, under 785 Torr of H2 pressure. The plot of maximum rate vs. [styrene] is shown in Figure 7.5. The rate of hydrogenation was found to increase on increasing the substrate concentration, but levelled off at higher substrate concentrations (2:0.2 M). The increase in rates was close to linear at lower styrene concentrations (< 0.05 M), indicating a first-order dependence, while a transition from first- to zero-order dependence was apparent at the higher styrene concentrations. The effect of varying the H2 pressure was studied at [Ru]j = 1.58 x IO - 3 M and at [styrene] = 0.043 M OFigure 7.6). A less than first-order dependence on H2 pressure (i.e. [H2] concentration) was observed from 785 to 410 Torr ([H2] = 1.82-0.95 x 10"3 M). 261 Table 7.2: Kinetic Data for Hydrogenation of Styrene Catalysed by [RuCl(DPPB)(u-Cl)]2 in DMA at 30 "C [RUJTXIO 3 [styrene] x 102 P(H2) [H2] x 103 Max. Rate3 x 105 M M Torr M Msr 1 3.04 41.5 785 1.82 20.5 2.05 41.5 785 1.82 12.7 1.58 41.5 785 1.82 11.1 1.01 41.5 785 1.82 6.57 1.58 18.0 785 1.82 10.6 1.58 4.30 785 1.82 4.84 1.58 3.70 785 1.82 4.00 1.58 2.40 785 1.82 3.10 1.58 1.80 785 1.82 2.53 1.58 1.80 785 1.82 2.49 1.58 0.90 785 1.82 1.39 1.58 4.30 685 1.59 4.11 1.58 4.30 590 1.37 3.93 1.58 4.30 500 1.16 3.57 1.58 4.30 410 0.95 3.13 a Error in rate values is estimated at ca. ±5%. 262 •fe K 300 200- 100" [Ru]Txl(r\M * 3.04 • 2.05 n 1.58 • 1.01 • • 8° 0 500 1000 Time, s 1500 2000 Figure 7.3: Rate plots for styrene hydrogenation catalysed by 14 in DMA, at 30 "C, at various [RU]T. [styrene] = 0.415 M, [Hd = 1.82 x 10 - 3 M. 30.0 (A © CQ n 2 20.0- 10.0- 0.00 1.00 2.00 3.00 4.00 [Ru]T x 103, M Figure 7.4: Dependence of the maximum hydrogenation rate on [RU]T at 30 "G. 263 0.0 f 1 1 > 1 • 1 • i • 1 0.00 0.10 0.20 0.30 0.40 0.50 [Styrene], M Figure 7.5: Dependence of the maximum hydrogenation rate on [styrene] at 30 *C. [Ru]T = 1.58 x 10~3 M , PCHj) = 785 Torr ([HJ = 1.82 x 10 - 3 M). The INSET shows the initial portion of the rate plot expanded. 6.0 [H2] x 10 3, M Figure 7.6: Dependence of the maximum hydrogenation rate on [H2] at 30 *C. [RU]T = 1.58 x IO" 3 M , [styrene] = 0.043 M . 264 7.2.3 Analysis of the Kinetic Data and Discussion The 100-200 s induction period observed during hydrogenation of styrene catalysed by [RuCl(DPPB)(u,-Cl)]2,14, as monitored by H2-uptake measurements, is attributed to the time taken for the catalyst (precursor) to dissolve in D M A . The complex 14 remained unchanged at the end of the catalytic runs. Attempts at detecting the possible catalytic intermediate(s) by examination of the hydrogenating solution using 3 1 P NMR spectroscopy were unsuccessful because of the relatively high hydrogenation activity of 14 (typical turnover frequencies ~8-10 min - 1 M - 1 of 14) as the dissolved H2 was quickly depleted. However, as noted in Section 5.3,14 forms the trichloro-bridged dihydrogen complex [(L)(DPPB)Ru(n-Cl)3RuCl(DPPB)], 31a (L = n.2-H2), under H2 atmosphere in benzene,8 while the D M A analogue (L = DMA), 14h, is obtained in D M A solution in the absence of H2 (Chapter 3, Section 3.6.5). Furthermore, D M A solutions of 14 absorb a small amount of H2 even in the absence of an alkene substrate, with the final uptake corresponding to ~0.4 mole equivalents per dimer at 30 *C under 785 Torr of H2 pressure (Section 5.3.2). These observations suggest that the binding of H2 to Ru is considerably stronger than that of D M A , which is present in large excess. Therefore, the formation of some of the dihydrogen complex 31a under the catalytic hydrogenation conditions seems plausible. The slight broadening (~3-4 Hz) of the 3 1 P resonances of 14 in the presence of a ~50-fold excess of added styrene suggests a relatively weak interaction between the catalyst precursor and the substrate. To explain the first-order dependence on [RU]T, the first- to zero-order dependence on [styrene], and the less than first-order dependence on H2 pressure, the following mechanism is suggested: 265 (K2) [RuCl(DPPB)Oi-Cl)]2 + H 2 a. [(n2-H2)(DPPB)Ru(u.a)3RuCl(DPPB)] (7.1) 14 k " 1 3 1 a l k 2 [(Ti2-H2)(DPPB)Ru(u.-Cl)3RuCl(DPPB)] [RuCl(DPPB)(u-Cl)]2 (7.2) + + CgH5CH=CH2 C5H5CH2CH3 where ki, k_i, and k2 are the rate constants of the individual steps, and Ki represents the equilibrium constant for reaction 7.1. Applying the steady-state treatment to the intermediate, [(r|2-H2)(DPPB)Ru- (u-Cl)3RuCl(DPPB)], 31a, the following rate law is obtained: P a t * - ° ™ _ kik2[Ru2Mstyrene]-[H2] n - K a t e - - d t - ^ + k l [ H 2 ]+k 2 [s tyrene] where [Ru2lT = [14] + [31a] = 1/2 [Ru]T (7.4) 7.2.3.1 Dependence of the Rate on Catalyst Concentration At constant [H2] and constant [styrene], the rate equation 7.3 reduces to: Rate = kobs[Ru]T where v . _ 1/2 kik2[styrene]-[H2] n « * ° b s " k_i + ki[H2] + k2[styrene] The first-order dependence of the maximum rate on [RU]T, as predicted by Equation 7.5, is evident from the straight-line plot shown in Figure 7.4. A value of 6.7 x IO - 2 s - 1 is obtained from the slope of the plot of maximum rate vs. [RU]T. The plot of maximum rate VS.[RU2]T (not shown; [RU2]T = concentration in terms of the dimer) is linear as expected 266 with the corresponding doubling of the kobs value to 0.13 s_1. Thus, these kinetic data do not distinguish between a monomelic and a dimeric catalyst species. 7.2.3.2 Dependence of the Rate on Styrene Concentration At sufficiently lower styrene concentrations, the k2[styrene] term in the denominator of Equation 7.3 could become negligible compared to Qc-i + ki[H2]) term, the rate equation then approximates to Equation 7.6, and a first-order dependence on [styrene] is expected. Such is indeed the case at [styrene] < 0.025 M, and the plot of maximum rate against [styrene] is linear (see Figure 7.5, INSET). p.., _ 1/2 kik2[styrene]-[Ru]T n ~ K a t e " k_i+ki[H2] On the contrary, at higher styrene concentrations the k2[styrene] term in the denominator of Equation 7.4 may become predominant, and the rate equation (Equation 7.4) is expected to approximate to: Rate = 1/2 ki[Ru]r[H2] (7.7) which is independent of styrene concentration. Whether the k2[styrene] » Qc-l + ki[H2]) condition is fulfilled at the maximum styrene concentration of 0.415 used in this study is not clear. Further, the rate equation 7.4 can be rearranged to give: 1 = k-i +ki[H2] 1 1 n os Rate 1/2 kik 2[Ru] r[H2] [styrene] 1/2 ki[Ru]T[H2] v * ' 267 At constant [RU]T and [H2], therefore, the plot of lA-ate vs. l/[styrene] should be a straight line, and the rate constant ki can then be calculated from the intercept Such a plot (Figure 7.7) gives a straight line with slope = 583 s and intercept = 7521 s M - 1 , and the ki value of 93 M _ 1 s - 1 is obtained from the intercept for conditions when [RU]T = 1.58 X IO - 3 M and [H2] = 1.82 x IO"3 M, at 30 *C 0 T ' I ' I ' I ' I 1 I ' 0 20 40 60 80 100 120 l/[Styrene], M " 1 Figure 7.7: Plot of l/(Maximum Rate) against l/[Styrene]. [Ru]j= 1.58 x 10 - 3 M , [H 2 ] = 1.82 x 10-3 M , at 30 *C. 7.2.3.3 Dependence of the Maximum Rate on Hydrogen Concentration At high alkene concentrations where the rate equation 7.3 reduces to Equation 7.7 because k2[styrene] » (k_i +ki[H2]), i.e. under conditions when the [styrene] dependence of the maximum rate is of zero-order, the H 2 dependence is expected to be first-order over the entire range of hydrogen concentrations. At lower alkene concentrations, however, a transition from first- to zero-order dependence is expected in accordance with Equation 7.6. 268 In this study, the [H2] dependence of the maximum rate was investigated at [styrene] = 0.043 M , which is not high enough to show a stricdy first-order dependence, and a less than first-order dependence is observed Q?igure 7.6); also, it can be shown that a plot of log(Maximum Rate) vs. log([H2]) yields n = 0.67, where n is the order of the reaction in [H2]. However, Equation 7.3 can be reorganised to give: _L_ = k-i + k2[styrene] _ J _ . I ,7 m Rate 1/2 kik2[Ru]T[styrene] [H2] 1/2 k2[Ru]T[styrene] v ' The plot of 1/Rate vs. 1/[H2] should be linear, and value of the rate constant k2 can be calculated from the intercept. In fact, such a graph 0?igure 7.8) yields a good straight-line, with slope = 20.9 s and an intercept of 10130 s M - 1 , from which a k 2 value of 2.9 M _ 1 s-1 is obtained for [RU]T = 1.58 x 10-3 M and [styrene] = 0.043 M , at 30 *C. 34000 T 1 18000 H ' 1 1 1 1 1 1 1 • 1 • — 500 600 700 800 900 1000 1100 1 / [H 2 ] , M " 1 Figure 7.8: Plot of l/(Maximum Rate) against 1/[H2]. [RU]T = 1.58 x 1 0 - 3 M, [styrene] = 0.043 M at 30 "C . These values of ki (93 M _ 1 s -1) and k2 (2.9 M _ 1 s-1) can be used to derive the value of k_i (see Equations 7.1 and 7.2) from the slope of one of the lines plotted 269 according to Equations 7.8 or 7.9. Thus, values of 0.056 sr1 and 0.066 s - 1 for k_i, at 30 *C, are calculated from the slope of the lines shown in Figures 7.8 and 7.9, respectively, for the conditions specified earlier. This yields a value of 1.5 x 103 ± 150 M _ 1 for the equilibrium constant Ki = ki/k_i, at 30 *C (see Equation 7.1), and a value of 48 ± 5 M _ 1 for the relative magnitudes of k 2 and k_i k2/k_i). Further, the equilibrium constant Ki for the formation of the dihydrogen complex 31a can be obtained direcUy from H2-uptake measurements on the dimeric precursor 14 in the absence of styrene substrate. The observed H2-uptake of ca. 0.4 mole equivalent per dimer (14) in DMA solution at 785 torr of H2 pressure and 30 *C, from which a Ki value of 3.7-x-lO2 M - 1 is calculated, does not take into account any uptake by 14 in the solid state, and the Ki value is likely an underestimate. Therefore, the Ki values of 3.7 x 102 and 1.5 x 103 M _ 1 obtained respectively from the direct H2-uptake measurements and by analysis of the rate data for styrene hydrogenation, although a factor of four different, can be considered in acceptable agreement The k_i values of 0.056 and 0.066 s - 1 obtained from the [styrene]- and the [In- dependences, respectively, of the maximum rate of styrene hydrogenation catalysed by the dimeric [RuCl(DPPB)Qi-Cl)]2 complex, 14, are in reasonable agreement and show that the data are internally consistent The values of the rate constants kj, k_i, k2, and the equilibrium constant Ki (c/. Equations 7.1 and 7.2) are comparable to the corresponding values obtained in an earlier study from this laboratory on a similar hydrogenation system3-9 Hydrogenation of 1-hexene catalysed by the dinuclear Ru-(PPh3) complex [(rj2-H2)(PPh3)2Ru(n-H)- (|i.-Cl)2RuH(PPh3)2], containing a dihydrogen ligand (analogous to 31a in the current study), has been suggested to proceed via a mechanism similar to that outlined in Equations 7.1 and 7.2.9 The values of ki = 156 M - 1 sr1, k_! = 0.028 sr1, k2 = 0.57 M" 1 r 1 , and Ki = 5.6 x 103 M - 1 at 30 *C have been calculated.9 270 It should be noted that the rate data for the hydrogenation of styrene catalysed by 14 may well be analysed for a reaction sequence in which formation of a catalyst-substrate adduct ([(styrene)Ru2]) precedes the hydrogen transfer step (cf. Equations 7.1 and 7.2). The steady-state approximation is then applied to the mtermediate [(styrene)Ru2] (instead of the dihydrogen complex 31a), with the equilibrium constant Ki and the rate constants ki and k_i now refering to the formation of the [(styrene)Ru2] adduct The relatively large Ki-value of -1500 M - 1 is consistent with the experimental observation (and characterisation, see Chapter 5) of the Tj 2 -H 2 complex 31a, whereas there is no detectable formation of the corresponding styrene adduct, [(styrene)Ru2]. Intermediate(s) similar to the ones suggested for the 14-catalysed H2/D2 exchange reaction to give HD (see Section 5.3.1, Scheme 5-1), but with one of the dihydrogen molecules replaced by a rc-bonded alkene, may be involved in the alkene hydrogenation (k2-step, Equation 7.2). 7.3 Hydrogenation of Ketones and Imines Catalysed by [RuCl(P-P)(u-CI)]2 and [RuHCl(P-P)]3 Complexes Various aspects of catalytic homogeneous hydrogenation of unsaturated organic substrates have been discussed previously in Chapter 1. The dinuclear dichloro-, and the trinuclear hydridochloro ruthenium complexes were found to catalyse hydrogenation of a variety of unsaturated substrates including ketones, imines and nitriles, as well as alkenes (Section 7.2).8>10-12 A short summary of the preliminary results from these studies is presented below. 271 7.3.1 Transfer Hydrogenation of Acetophenone The dinuclear ruthenium complexes [RuCl(P-P)(u-Cl)]2, P-P = DPPB, 14 or 5,5-CHIRAPHOS, 16, are extremely effective catalyst precursors for transfer hydrogenation of ketone substrates using 2-propanol/KOH as the source of hydrogen (Equation 7.10). O OH OH o II I Ruj/KOH | || C 6 H 5 -C-CH 3 + CH3-C(H)-CH3 ^ C 6H 5-C(H)-CH 3 + CH3-C-CH3 (7.10) Ru2 = [RuCl(P-P)(u-Cl)]2; P-P = DPPB, 14 or 5,5-CHIRAPHOS, 16 All reactions were carried out in thick-walled glass bombs under an argon atmosphere. Typically, acetophenone followed by 2-propanol were added to the solid catalyst and KOH mixture under a flow of argon. The system was then closed and the mixture heated in a constant temperature oil-bath rxmintained at the specified temperature (±1 *C). The products were separated from the catalyst residue by distillation, and analysed by GC to determine the % conversion and the enantiomeric excess where appropriate (see Chapter 2, Sections 2.3 and 2.4 for details). The results are summarised in Table 7.3. The initially orange suspension turned dark red within a couple of minutes in the heating bath. Turnover frequencies of > 500 Ir1 [R^lf 1 at equilibrium conversions (ca. 80% under typical conditions, see Table 7.3) are realised for transfer hydrogenation of acetophenone to l-phenyleû anolmrefluxmg2-prĉ anol 0>oilmgrx)mt: 83 *C); however, the CHIRAPHOS system gives only 2% e.e. Of interest, 14 and 16 catalyse, albeit slowly, the hydrogen transfer from 2-propanol to acetophenone even in the absence of the KOH base (see for example, Run # 7 in Table 7.3). In the absence of the Ru catalyst, KOH alone is also capable of catalysing the transfer hydrogenation of acetophenone at a 272 much slower rate compared to the Ru catalysed reaction (Table 7.3, Run # 5,6), which is consistent with some earlier reports.13 The KOH-catalysed hydrogen transfer to acetophenone probably contributes in part to the observed low e.e. for the CHIRAPHOS system. Table 7.3: Data for Transfer Hydrogenation of Acetophenone in 2-Propanol/KOH Catalysed by [RuCl(P-P)(u-Cl)]2 Complexes.8.b Run #° Time, h % Conversion*1 Comments 1. 48 81 2. 4 82 Acetone detected in the distillate by GC. 3. 1 82 Turnover Frequency £ 520 h-1[Ru2J_1. 4. 46 82 P-P = S,S-CHIRAPHOS; e.e.= 0.4% (R). 5. 48 31 Blank run with KOH; no Ru2 catalyst added. 6. 7.5 7 Blank run with KOH; no Ru2 catalyst added. 7. 48 6 No KOH; Ru2 catalyst present 8. 4 77 At 50 *C. 9. 1.5 78 At 50 *C; P-P = S.S-CHIRAPHOS; e.e.= 2% (R). 10. 48 17e At 50 *C; reverse reaction (cf. Equation 7.10).e a General conditions: 5.0 mL 2-propanol [acetophenone] = 1.43 M [Ru2] = 2.25 x 10~3 M [KOH]/[Ru2] = 4 [acetophenone]/[Ru2] = 630. b p_p = DPPB, unless stated otherwise. c Run # 1-7 were carried out at 100 'C (bath temperature; refiuxing solution). d Conversion to 1-phenylethanol. e Using 1.43 M 1-phenylethanol in 5.0 mL acetone; the conversion refers to % acetophenone. 273 The ca. 82% conversions seen in Runs # 1-4 represent the equilibrium yields under the specified conditions. The reversibility of the transfer hydrogenation reaction (see Equation 7.10) and catalysis of the reverse reaction by the Ru catalyst are clearly demonstrated by the result of Run # 10 in which acetophenone is formed by transfer hydrogenation of acetone from 1-phenylethanol. The *H NMR spectrum (hydride region) of the dark red residue recovered at the end of a typical run, with the CHIRAPHOS complex 16 as the catalyst precursor, is shown in Figure 7.9. The three resonances of equal intensity, and centred at 8 -17.0 (dd, 2/PH = 36.6, 26.4 Hz), -19.4 (m, 2 7 P H -8-21 Hz) and -24.8 ppm (dd, 2/ P H = 36.3, 31.8 Hz) are readily assigned to the trinuclear hydridochloro species [RuHCl(CHIRAPHOS)]3, 30, described earlier (see Chapter 5, Sections 5.4 and 5.5). The remaining hydride resonance at -12.6 ppm, belonging to an as yet unidentified complex and constituting ~33% of the total intensity, also exhibits a doublet of doublet pattern with 27PH = 37.2 and 25.2 Hz. The magnitudes of the coupling constants indicate a mutually cis arrangement of the hydride and two inequivalent phosphorus nuclei in the new hydride species. [ i i i i i i i i i | i i i i [ i i i i | i i i i j II i i | 11 II | i i i i j II i i 1 i i i i | i i i i ] i i i i | i i i i | -12 -14 -16 -18 -20 -22 -24 PPM Figure 7.9: *H NMR spectrum (hydride region, 300 MHz, 20 °C, toluene-d$) of the residue obtained from transfer hydrogenation of acetophenone using the CHIRAPHOS system (Run # 4, Table 7.3). 274 The chemical shift of -12.6 ppm for the hydride is in the region found for other known tra flj-hydridochloro-Ru(II) species.1'14 A mononuclear species of the type "trans- RuHCl(CHIRAPHOS)(L)2", with ketone or alcohol molecules (L) from the transfer hydrogenation system occupying the available coordination sites, seems plausible. Alternatively, the -12.6 ppm resonance could belong to a dinuclear complex containing only a single hydride ligand: [(P-P)HRu(u.-Cl)2RuCl(P-P)] (cf. Intermediate I in Scheme 5-IH, Section 5.7), or a related trichloro-bridged complex with a coordinated ketone or alcohol (L): [(P-P)HRu(n-Cl)3Ru(L)(P-P)] (cf. Figures 3.16, 3.17 in Section 3.7.1). The 3 1 P NMR spectrum of the same residue consists of an AB quartet pattern centred at 84.0 ppm (AVAB = 0.5 ppm, 2/pp = 34.0 Hz, ~27% integral intensity) along with the signals assignable to the CHIRAPHOS trimer 30 (73% integral intensity; see Section 5.5 for chemical shifts). The new 84.0 ppm resonance is assigned to the species which exhibits the high-field J H NMR resonance at -12.6 ppm (see above). The observed integral intensity ratios for the new hydride species with respect to the resonances of [RuHCl(CHIRAPHOS)]3 support the mononuclear Va*$-RuHCl(CHIRAPHOS)(L)2" formulation. Moreover, two sets of 3 1 P NMR AB quartet patterns will be expected for a "[(P-P)HRu(u-Cl)3Ru(L)(P-P)]" species, whereas only one exists in the actual spectrum Of particular note, the NMR spectrum of the residue obtained from the corresponding DPPB system also showed a similar, unassigned hydride signal as a triplet centred at -11.5 ppm ( V P H = 34.4 Hz). Again, the chemical shift and the P-H coupling constant point to a species of the type "trans-RuHCKP-P)". In addition, several other broad signals were apparent in the -7 to -20 ppm region, none of which could be assigned to the DPPB trimer analogue, 29, described earlier (see Sections 5.4 and 5.5). Formation of the trinuclear hydride complex rRuHCl(CHIRAPHOS)]3,30, from the dimeric precursor 16 under transfer hydrogenation conditions (2-propanol/KOH) is not surprising, and probably proceeds by a mechanism similar to that proposed for its 275 formation under H2 in the presence of NEt3 base (cf. Scheme 5-JJJ in Section 5.7), but with 2-propanol and KOH respectively acting as the hydrogen source and the base. Further studies are necessary in order to establish the nature of the new hydride species formed from [RuCl(P-P)(|i-Cl)]2 precursors under the transfer hydrogenation conditions. Which of the major species, the dimeric precursor [RuCl(P-P)(p.-Cl)]2, the trinuclear hydride complex [RuHCl(P-P)b, or the tentatively formulated "rrflw-RuHCl(P-P)" species, is (are) the principal catalyst(s) remains to be seen. 7.3.2 H2-Hydrogenation of Ketones and Imines The [RuCl(P-P)(n-Cl)h and [RuHCl(P-P)]3 complexes catalysed the H2-hydrogenation of ketones and imines under relatively mild conditions (1-12 atm H2, 30-100 "C) with turnover frequencies in the 1-10 h _ 1 [Ru]-1 range. In general, the trimeric hydridochloro ruthenium(II) complexes 29 and 30 exhibited hydrogenation activity which was an order of magnitude higher than their dimeric dichloro analogues (14 and 16). As exemplified by the data for acetophenone hydrogenation (Table 7.4), the best results for ketone hydrogenation were obtained in the relatively nonpolar toluene solvent. Preliminary data using [RuHCl(S,S-CHIRAPHOS]3,30, as catalyst (1.5 mM RU3 and 1.4 M acetophenone in toluene, 80 *C, 12 atm of H2, 7 days) revealed asymmetric hydrogenation of acetophenone to the /?-alcohol in ca. 55% e.e at 30% conversion. The use of [RuCl(CHIRAPHOS)(u-Cl)]2,16, in the presence of 2 equivalents of NEt3 also gave similar results; the dimeric NEt3-adduct 16b and the trimeric hydridochloro complex 30 were identified in the catalyst residue (-1:1 ratio) at the end of the runs by 3 1 P NMR spectroscopy (Section 5.4). In the absence of added NEt3, however, the complex 16 showed poor hydrogenation activity (only -3% conversion and -17% e.e. under identical conditions). The hydridochloro derivative 30 is clearly the more effective precursor. 276 Table 7.4: Data for H2-Hydrogenation of Acetophenone Catalysed by [RuCl(DPPB)(u-Cl)]2 and Related Complexes.8 Run# Catalystb Solvent Time,h % Conversion T.CF.ch- 1 [Ru]"1 1. 14 DMA 24 1.0 0.13 2. 14 Toluene 24 2.6 0.34 3. 14b Toluene 24 1.1 0.14 4. 29 DMA 24 0.8 0.10 5. 29 THF 24 1.3 0.17 6. 29 Toluene 24 14.6 1.9 7. 29d Toluene 24 13.6 3.2 8. 29d Toluene 13 8.5 3.7 9. 29d e 18 4.4 2.8 8 General conditions: Solvent: 5.0 mL; temperature: 100±2*C; latmofH2; Acetophenone = 8.6 x IO -3 mols; Ru catalyst (monomer) = 2.7 x 10~5 mols. b Catalyst precursors: [RuCl(DPPB)(u-Cl)]2,14; [Ru2Cl4(DPPB)2(NEt3)], 14b; [RuHCl(DPPB)]3, 29. c Turnover frequency. d [Ru] = 1.5 x 10"5 mols. e Neat acetophenone, 17.2 x 10-3 mols. Results of hydrogenation of imines using the hydride trimer 30 as catalyst were less encouraging. For example, the imine shown in Figure 7.10 was hydrogenated with only 2% e.e. (R) and 4% conversion under conditions employed for acetophenone hydrogenation (see above). 277 y C H 2 - O M e Me N=C ft** Figure 7.10: An imine substrate tested for asymmetric H2-hydrogenation using [RuHCl(5,5-CHIRAPHOS)]3 as catalyst 7.3.3 Hydrogenation of Nitriles Homogeneous hydrogenation of nitriles has been little studied, from either synthetic or mechanistic viewpoints; the required use of relatively severe conditions has been a major drawback.15 Very few catalytic systems capable of hydrogenating nitriles under relatively mild conditions have been reported.10-15-18 The trimeric hydride complex [RuHCl(DPPB)]3,29, catalyses hydrogenation of nitriles at 1 atm of H 2 . N,N-Dimethylacetamide solutions containing ImM 29, and typically 2 M PhC=N, give measurable rates even at 50 'C; under such conditions, the intermediate imine PhCH2N=CHPh is seen en route to the final product dibenzylaniine, (PhCH 2) 2NH. At 150 *C complete selectivity to the amine (and NH3) is observed (Equation 7.11): P h O N + 4 H 2 (PhCH2)2NH (7.11) A catalytic reaction sequence at a Ru-phosphine centre for production of secondary from primary amines, with elimination of N H 3 and intermediacy of a coordinated imine, has been reported in the literature.19 A plausible reaction sequence is shown in Equations 7.12-7.14. 278 P h C s N + H 2 PhCH=NH + H 2 * • PhCH2NH2 (7.12) PhCH2NH2 + PhCH=NH PhCH2N=CHPh + NH 3 (7.13) PhCH2N=CHPh + H 2 (PhCH2)2NH (7.14) Turnover frequency for loss of PhCN is only about 1 Ir 1 [RU3]- 1 at 70 *C and 1 atm of H 2 , but at higher temperatures and pressures, effective conversions are realised. For example, at 100 'C, about 70% of the PhCN is converted to (PhCH2)2NH and the imine PhCH2N=CHPh (in a 4:1 ratio) in 24 h at 35 atm H 2 . At 110 atm H 2 , 85% of PhCN converts to the amine and mine (7:1). The use of toluene or THF as solvent, or precursor complexes such as [RuCl(DPPB)(p.-Cl)]2, with or without added base to promote in situ formation of 29, give much less effective catalytic systems. Kinetic studies on the hydrogenation of nitriles catalysed by [RuHCl(DPPB)]3 are of particular interest because of the possibility of catalysis at a Ru3 cluster site. Preliminary kinetic studies on the hydrogenation of MeCN catalysed by 29 (50 *C, 1 atm of H 2 , 2 M MeCN in DMA) show increasing turnover numbers per Ru3 with increasing concentration of the trimer (for [RU3] = 0.60-3.5 mM, T.O. frequency = 0.5-4.8 h"1 [ R U 3 ] - 1 ) , 1 2 implying catalysis at an aggregated site.20 Stoichiometric hydrogenation of MeCN at Fe3 cluster sites is well-documented by structural data,21 but to our knowledge, there is no previous kinetic evidence to substantiate nitrile hydrogenation at a polynuclear site. Kinetic studies on the hydrogenation of PhCN have also been conducted,12 but will not be discussed here. 279 7.4 References - Chapter 7 1. Wang, D. K. W., PhX>. Dissertation, The University of British Columbia, Vancouver, Canada, 1978. 2. Chan, C. -Y., PhD. Dissertation, The University of British Columbia, Vancouver, Canada, 1974. 3 Thorburn, I. S., M.Sc. Dissertation, The University of British Columbia, Vancouver, Canada, 1980. 4. Hui, B.C., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1969. 5. Gamage, S. N., Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1985. 6. Joshi, A. M., M.Sc. Dissertation, The University of British Columbia, Vancouver, Canada, 1986. 7. DMA General Information Bulletin, Industrial and Biochemicals Department, E. I. Du Pont de Nemours and Co., Wilrrtington, Delaware, USA, 1962. 8. Joshi, A. M.; James, B. R. J. Chem. Soc, Chem. Commun. 1989, 1785. 9. Hampton, C , Ph.D. Dissertation, The University of British Columbia, Vancouver, Canada, 1989. 10. James, B. R.; Pacheco, A.; Rettig, S. J.; Thorburn, I. S.; Ball, R. G.; Ibers, J. A. 7. Mol Catal 1987,41, 147. 11. James, B. R.; Joshi, A. M.; Kvintovics, P.; Morris, R H.; Thorburn, I. S. in Catalysis of Organic reactions; Blackburn, D. W., Ed.; Marcel Dekker New York, 1990; Chapter 2. 280 12. (a) Joshi, A. M.; Frediani, P.; James, B. R. "Vth IUPAC Symposium on Organometallic Chemistry Directed Towards Organic Synthesis (OMCOS V)", Florence, Italy, October 1989; Abstract # PS2-13. (b) Joshi, A. M.; James, B. R. "72nd Canadian Chemical Conference and Exhibition, Symposium on Bimetallic and Polymetallic Complexes", Victoria, B. C , Canada, June 1989; Abstract # 301. (c) Joshi, A. M.; Thorburn, I. S.; James, B. R. "Vlth International Symposium on Homogeneous Catalysis (ISHC-6)", Vancouver, B. G, Canada, August 1988; Abstract #P-146. 13. (a) Spogliarich, R.; Kaspar, J.; Graziani, M. 7. Catal. 1985,94, 292. (b) Sasson, Y.; Blum, J. J. Org. Chem. 1975,40, 1887. 14. Dekleva, T. W.; Joshi, A. M.; Thorburn, I. S.; James, B. R; Evans, S. V.; Trotter, J. Isr. J. Chem. 1990,30(4); in press. 15. James, B.R. Homogeneous Hydrogenation; Wiley: New York, 1973; see 'Nitriles' in Index. 16. Grey, R. A.; Pez, G. P.; Wallo, A. J. Am. Chem. Soc. 1981,103, 7536. 17. Yoshida, T.; Okano, T.; Otsuka, S. J. Chem. Soc, Chem. Commun. 1979, 870. 18. Thorburn, I. S.; Rettig, S. J.; James, B. R. J. Organomet. Chem. 1985,296, 103. 19. Jung, C. W.; Fellman, J. D.; Garrou, P. E. Organometallics 1983,2, 1042. 20. Laine, R. M. / . Mol. Catal. 1982,14, 137; and references therein. 21. Andrews, M. A.; Kaesz, H. D. / . Am. Chem. Soc. 1977, 99, 6763. 281 CHAPTER 8 General Conclusions and Suggestions for Future Work The objective of the work described in this thesis was to develop general synthetic routes to ruthenium complexes containing one chelating ligand per ruthenium centre. Incorporation of chiral diphosphines in such complexes would then allow these species to be tested as potential catalysts for asymmetric hydrogenation of unsaturated substrates. The complexes of general formula [RuCl(P-P)(u-Cl)]2 (P"P = DPPP, DPPB, DIOP, CHIRAPHOS, or NORPHOS) were previously synthesised in this laboratory via H2-reduction of the corresponding mixed-valence precursors, Ru2Cls(P-P)2. The synthesis of mixed-valence dimers was extended to include the diphosphines: P-P = DPPN, DPPH, rac-DPPCP, rac-DPCYCP, 5,5-BDPP, R- and 5-BINAP, and 5-PHENOP. The Ru2 n - n dimers were characterised only for DPPN, BDPP, and BINAP Much of the chemistry was conducted on the DPPB derivative. The dichloro- bridged complex [RuCl(DPPB)(p.-Cl)]2 reacted readily with a variety of coordinating ligands to give the corresponding trichloro-bridged dinuclear species containing one coordinated ligand. The coordinative unsaturation at the two Ru(II) centres (C.N. = 5) and the availability of non-bonding electron pairs on the chloride are perhaps responsible for the observed propensity to form such trichloro-bridged complexes. Several new complexes of the type [(L)(DPPB)Ru(u-Cl)3RuCl(DPPB)] (L = CO, DMSO, NEt 3, NHBu2, Mel, rj2-H2, CJ-N2) were isolated or characterised in situ by NMR spectroscopy. A single crystal X-ray diffraction study of the DMSO analogue confirmed the trichloro- bridged structure with an unsymmetrical arrangement of the two diphosphine ligands; the DMSO ligand was found to be coordinated through the sulphur atom. 282 Of the trichloro-bridged species characterised during this work, the ones containing the rt2-H2, C-N2 and Mel are perhaps the most intersting. The presence of the r|2-H2 moiety was demonstrated by the typically short *H NMR 7j relaxation time (7;(min) = 12 ms at 277 K and 300 MHz) and the relatively large H-D coupling for the rj2-HD isotopomer (1JED = 29.4 Hz). The H-H distance was estimated to be 0.86 ± 0.02 A from the Tj data. Hydrogen (and nitrogen!) uptake measurements on the DPPB system will allow determination of equilibrium constants for the formation of the T|2-H2 (0-N2) complex, from which relevant thermodynamic parameters can be obtained. Studies should also be extended to Ru(U) dimers containing other diphosphines. Reaction of [RuCl(P-P)(u-Cl)]2 complexes (P-P = DPPB or CHIRAPHOS) with H2 in the presence of NEt3 base afforded in much improved yields the trinuclear hydridochloro complexes of the formula [RuHCl(P-P)]3, which have been characterised by NMR spectroscopy. The reaction likely proceeds via deprotonation of the rj2-H2 complex. Interestingly, more than half the molecular hydrogen complexes reported to date contain Ru, and given the reluctance of a Ru(II) centre to undergo oxidative addition reactions (to RuIV), such deprotonation of a bound H2 by an appropriate base may be a general mechanism for hydride formation in Ru systems. Reactions of other dimeric Ru(II) complexes with H2 with or without NEt3 should be investigated further. Reactions of the dimers with H2S and silanes (R3SiH or R2SiH2) may lead to some interesting chemistry and possible applications to hydrodesulphurisation and hydrosilylation processes, respectively. Possible involvement of molecular hydrogen complexes in important catalytic processes such as hydrogenation and dehydrogenation of organic substrates had been suggested earlier; however, conclusive evidence was lacking. The kinetic study on hydrogenation of styrene catalysed by [RuCl(DPPB)(p>Cl)]2 showed strong evidence for the involvement of molecular hydrogen species in the catalytic cycle. Temperature dependence of the various rate constants and the equilibrium constant of the reaction steps 283 in the proposed mechanism should be carried out to obtain the corresponding activation and thermodynamic parameters. Such data, as well as solvent dependence studies, may provide an insight into the possible mode of hydrogen transfer to the substrate. Preliminary studies showed that the hydridochloro trimers [RuHCl(P-P)]3 were indeed effective catalyst precursors for the hydrogenation of ketones and nitriles under relatively mild conditions (30-100 °C, 1-12 atm H2, typical turnover frequencies 1-10 h - 1 [Ru]'1 at 1 atm H2 and 100 °C) Detailed kinetic studies are needed in order to establish a plausible mechanism. A comparative solid-state 3 1 P NMR study of the complexes RuCl2(DPPJ3)(PPh3) and RuCl2(PPh3)3 established the close similarity between the structures of the two species. Very few such studies on organometallic compounds have been reported to date. The current work serves to highlight the potential applications of the solid-state NMR techniques to structural problems in organometallic chemistry. Reactions of the mixed- phosphine complex RuCl20DPPB)(PPh3) toward monodentate and bidentate ligands were explored in an attempt to develop an alternative route to the DPPB dimer, and indeed the reactivity was found to parallel that observed for the corresponding dichloro-bridged dimer. Reactions of the complexes cw-RuCl20^MSO)4 and [RuCl(p-cymene)(u.-Cl)]2 with one equivalent of a bidentate phosphine demonstrated the influence of the chelate ring size on the nature of products obtained. No complexes of the stoichiometry "RuCl2(P-P)" could be isolated for diphosphines with a chelate size of less than six, indicating that steric factors play a key role in determining the outcome of the reaction. The norbornadiene complex, rrarcs-RuHCl(nbd)(DPPB), containing a chelating phosphine was synthesised and characterised spectroscopically. Unlike its PPh3 analogue, however, the dppb derivative did not react with H2 or CO. Thus the 'minor' change of substituting two CW-PPI13 ligands by a flexible chelating DPPB within a similar precursor (rran5-RuHCl(nbd)(PPh3)2) induces for the DPPB species relative non-reactivity with H2 or CO. 284 APPENDIX 285 A P P E N D I X A - l Temperature and Concentration Dependence of the Optical Rotation of (R)-( + )-l-PhenyIethano! Table A - l . l : Data for the Effect of Temperature on the Optical Rotation of Pure (/?)-(+)- 1-Phenylethanol. Temperature ( ° C ) a Observed Rotation ( ° ) b (a) Density (g/mL)cAbsolute Rotation ( [ a ] D 12.4 44.215 1.0196 43.366 14.3 44.158 1.0180 43.376 17.3 44.060 1.0156 43.383 17.8 44.040 1.0152 43.380 19.9 43.972 1.0135 43.386 22.1 43.895 1.0117 43.386 24.4 43.821 1.0099 43.393 25.0 43.798 1.0094 43.391 27.6 43.715 1.0073 43.399 29.2 43.661 1.0060 43.401 29.3 43.661 1.0059 43.404 31.8 43.579 1.0039 43.410 35.9 43.444 1.0006 43.419 39.4 43.324 0.9978 43.42 39.8 43.308 0.9974 43.42 (a) error in readings is ± 0.1 °C. (b) error from instrument is ± 0.2% of the reading, while the reproducibility is ± 0.002°; measured at the sodium D line. ( c ) relative density. 286 Figure A- l . l : Plot of Observed Rotation (a) of Pure (fl)-(+)-l-Phenylethanol vs. Temperature. 44.400 44.200 H § 44.000 3 o tt > cv 43.800 H £> 43.600 O 43.400 H 43.200 i l l l y = 44.629-3.3121e-2x RA2= 1.000 i • ' • • i 10.0 15.0 20.0 25.0 30.0 35.0 40.0 Temperature (°C) 287 Table A-1.2: Data for the Effect of Concentration on the Optical Rotation of (fl)-(+)-l-Phenylethanol at 25°C. Cone. (g/rnL)a Conversion (%)b Observed Rotation (°)cAbsolute Rotation [ a ] D 2 5 ( ° ) a (A) (B) (a) (A) (B) pure pure 100 43.798 43.4 43.4 0.908 0.877 86.85 40.301 44.4 46.0 0.609 0.584 56.95 28.656 47.1 49.1 0.493 0.472 46.70 23.545 47.8 49.9 0.399 0.353 35.01 19.220 48.2 54.5 0.322 0.319 31.59 15.675 48.7 49.1 0.261 0.220 21.76 12.729 48.8 57.9 0.211 0.214 19.77 10.223 48.5 47.8 0.163 0.171 16.84 7.827 48.0 45.9 0.119 0.095 9.31 5.623 47 59.1 0.086 0.086 8.53 4.006 47 47 0.070 0.057 7.17 3.008 43 53 0 0 0 0 0 0 (a) A - calculated from the amounts of acetophenone and 1-phenylethanol added; B - calculated from the integration of the peaks in the gas chromatograms of the mixtures. (b) the conversion (or %-(R)-(+)- 1-phenylethanol) was calculated from the integration of the peaks in the gas chromatograms of the mixtures. (c) error from instrument is ± 0.2% of the reading, while the reproducibility is ± 0.002°; measured at the sodium D line. 288 Figure A-1.2: Plot of Observed Rotation of (/?)-(+)- 1-Phenylethanol vs. % of (/?)-(+)-1-Phenylethanol at a Temperature of 25°C. 50.000 40.000" e o n 5 30.000" © OS •o cv > tm o 20.000" 10.000 - i i i — i i 20 40 60 %-(R)-(+)-l-phenylethanoI 100 289 APPENDIX A-2: X-ray Crystallographic Analyses A-2.1: X-ray Crystallographic Analysis of #ner-RuCl3(PPh3)(DMA)2.DMA solvate Molecular Structure 290 Experimental Details E m p i r i c a l Formula Formula Weight C r y s t a l System L a t t i c e Parameters: Space Group Z value D c a l c 000 ^ ( M o K a) Di f f r actometer Rad i a t i on Tempe rature 26 max No. Observations (I>3c(I)) Ko. V a r i a b l e s R e s i d u a l s : R; R w Goodness of F i t I n d i c a t o r Maximum S h i f t i n F i n a l Cycle Largest Peak i n F i n a l D i f f . Map C 3 0 H 4 2 C 1 3 N 3 ° 3 P R u 731 .08 Orthorhombic a « 9 .839 (3)A b - 10 .252 (2)A c - 33 .568 (7)A V 3386 (2 )A : #19 ) P 2 1 2 1 2 1 1.43 g/cm 1508 7.72 cm - 1 Rigaku AFC6 MoKa(X = 0 .71069 A) Graphi te-monochromated 21 °C 59.9° 3861 388 0.034; 0.043 1 . 54 0.21 0.78 e" /A 3 291 T a b l e A-2.1.1: Bond Lengths (A) with estimated standard deviations in parentheses. atom atom di stance Ru 0 ( 1 ) 2 . 0 6 4 ( 3 ) Ru 0 ( 2 ) 2 . 2 0 0 ( 3 ) Ru P 2 . 2 7 3 ( 1 ) Ru C l ( 3 ) 2 . 3 1 1 ( 1 ) Ru C l ( l ) 2 . 3 4 5 ( 1 ) Ru C K 2 ) 2 . 3 5 0 ( 1 ) P C( 21 ) 1 . 8 2 8 ( 5 ) P C ( 9 ) 1 . 8 3 1 ( 5 ) P C ( 1 5 ) 1 . 8 3 9 ( 6 ) 0 ( 1 ) C( 1 ) 1 . 2 6 5 ( 5 ) atom atom distance 0 ( 2 ) C(5) 1 . 2 5 9 ( 6 ) N ( l ) C( 1 ) 1 . 3 1 4 ( 6 ) N i l ) C( 4 ) 1 . 4 6 3 ( 7 ) N i l ) C( 3 ) 1 . 4 6 3 ( 6 ) N ( 2 ) C ( 5 ) 1 . 3 3 6 ( 7 ) N ( 2 ) C( 8 ) 1 . 4 4 ( 1 ) N( 2 ) C( 7 ) 1 . 4 6 7 ( 7 ) C( 1 ) C( 2 ) 1 . 4 9 8 ( 8 ) C( 5 ) C( 6 ) 1 . 5 0 6 ( 9 ) 292 Table A-2.1.2: Bond Angles (deg) with estimated standard deviations in parentheses. atom atom atom angle 0( 1) Ru 0(2) 85 .9(1 ) 0(1) Ru P 90 .91(8) 0(1 ) Ru CM 3) 175 .15(9) 0( 1 ) Ru CMl) 68 .5(1) 0( 1 ) Ru CM2) 84 .7(1) 0(2 ) Ru P 173 .9(1) 0(2 ) Ru Cl ( 3 ) 89 .3(1 ) 0(2 ) Ru C M l ) 95 .1(1 ) 0(2) Ru Cl ( 2 ) 84 .1(1 ) P Ru Cl ( 3 ) 93 .69(4) P Ru Cl ( 1 ) 90 • 09(5 ) F Ru Cl ( 2 ) 90 .43(5) C l ( 3 ) Ru C M l ) 93 • OK 5) C l ( 3 ) Ru Cl ( 2 ) 93 .73(5) C l ( 1 ) Ru Cl ( 2 ) 173 .19(5) C( 21 ) P C( 9 ) 104 .0(2) C t 2 1 ) P C( 15) 105 .3(3) C( 21 ) P Ru 108 .8(1) atom atom atom angle C(9) P C(15) 98 .7(2) C(9) P Ru 118 .7(2) C(15) P Ru 119 .5(2) C ( l ) 0(1) Ru 133 .6(3) C(5) 0(2) Ru 136 .4(3) C ( l ) N ( l ) C(4) 120 .3(4) C ( l ) N ( l ) C(3) 123 .4(4) C( 4 ) N( l ) C( 3) 116 .2(4) C( 5 ) N(2) C(8) 120 .9(5) C( 5) N( 2 ) C( 7 ) 124 .2(6) C( 8 ) N( 2 ) C( 7 ) 114 .9(6) 0(1) C( 1 ) N( 1 ) 117 .9(5) 0(1 ) C( 1 ) C( 2 ) 123 .1(5) N( 1 ) C( 1 ) C( 2 ) 119 .0(4) 0(2 ) C( 5 ) N( 2 ) 118 .8(5) 0(2) C( 5) C(6 ) 121 .5(5) N( 2 ) C( 5 ) C( 6 ) 119 .7(5) 293 Table A-2.1.3: Final Atomic Coordinates (Fractional) and B(eq). a t o m X y z B(eq) R u 0 . 2 2 2 1 1 ( 3 ) 0 . 5 2 5 8 3 ( 4 ) 0 . 1 7 5 1 2 ( 1 ) 2 . 7 6 ( 1 ) C M l ) 0 . 2 2 4 4 ( 1 ) 0 . 7 5 4 5 ( 1 ) 0 . 1 7 3 0 5 ( 4 ) 3 . 9 5 ( 5 ) C l ( 2 ) 0 . 2 4 7 7 ( 1 ) 0 . 2 9 8 2 ( 1 ) 0 . 1 7 8 7 2 ( 4 ) 4 . 0 9 ( 6 ) C M 3 ) - 0 . 0 1 2 3 ( 1 ) 0 . 5 1 5 8 ( 1 ) 0 . 1 7 2 1 5 ( 4 ) 4 . 2 2 ( 5 ) P 0 . 2 4 7 3 ( 1 ) 0 . 5 1 8 7 ( 1 ) 0 . 1 0 7 8 5 ( 3 ) 2 • 7 8 ( 4 ) 0 ( 1 ) 0 . 4 3 0 2 ( 3 ) 0 . 5 2 9 9 ( 4 ) 0 . 1 8 2 7 4 ( 8 ) 3 . 5 ( 1 ) 0 ( 2 ) 0 . 2 1 0 5 ( 4 ) 0 . 5 1 3 3 ( 4 ) 0 . 2 4 0 4 ( 1 ) 4 . 6 ( 2 ) 0 ( 3 ) - 0 . 1 8 5 9 ( 7 ) - 0 . 0 1 2 2 ( 8 ) 0 . 5 9 0 5 ( 3 ) 1 2 . 5 ( 5 ) K ( 1 ) 0 . 6 1 7 8 ( 4 ) 0 . 4 8 7 7 ( 4 ) 0 . 2 1 6 6 ( 1 ) 3 . 6 ( 2 ) N ( 2 ) 0 . 1 1 6 6 ( 5 ) 0 . 4 8 2 2 ( 6 ) 0 . 3 0 0 3 ( 1 ) 4 . 8 ( 2 ) N( 3 ) 0 . 0 3 0 ( 2 ) - 0 . 0 1 2 ( 1 ) 0 . 5 8 2 6 ( 5 ) 5 . 7 ( 7 ) N( 4 ) 0. 0 2 6 ( 2 ) - 0 . 0 2 8 ( 1 ) 0 . 6 0 6 2 ( 4 ) 5 . 5 ( 6 ) C( 1 ) 0 . 5 0 6 6 ( 5 ) 0 . 5 5 7 2 ( 5 ) 0 . 2 1 1 9 ( 1 ) 3 . 4 ( 2 ) C( 2 ) 0 . 4 7 7 4 ( 6 ) 0 . 6 6 5 6 ( 7 ) 0 . 2 4 0 5 ( 2 ) 5 . 4 ( 3 ) C( 3 ) 0 . 7 1 8 4 ( 5 ) 0 . 5 1 3 6 ( 6 ; 0 . 2 4 7 7 ( 1 ) 4 . 4 ( 2 ) C( 4 ) 0 . 6 4 9 8 ( 6 ) 0 . 3 8 2 1 ( 6 ) 0 . 1 8 8 8 ( 2 ) 4 . 2 ( 2 ) C( 5 ) 0 . 1 3 1 0 ( 5 ) 0 . 5 5 3 3 ( 6 ) 0 . 2 6 7 2 ( 1 ) 3 . 7 ( 2 ) C( 6 ) 0 . 0 5 6 1 ( 6 ) 0 . 6 8 0 6 ( 7 ) 0 . 2 6 3 2 ( 2 ) 5 . 0 ( 3 ) C ( 7 ) 0 . 0 3 5 7 ( 8 ) 0 . 5 2 2 ( 1 ) 0 . 3 3 4 9 ( 2 ) 7 . 2 ( 4 ) C ( 8 ) 0 . 1 8 0 8 ( 9 ) 0 . 3 5 6 8 ( 8 ) 0 . 3 0 4 0 ( 2 ) 6 . 6 ( 4 ) C ( 9 ) 0 . 1 7 9 6 ( 5 ) 0 . 6 5 3 3 ( 5 ) 0 . 0 7 8 0 ( 1 ) 3 . 4 ( 2 ) C ( 1 0 ) 0 . 0 5 7 3 ( 6 ) 0 . 7 1 1 7 ( 6 ) 0 . 0 8 7 5 ( 2 ) 4 . 3 ( 3 ) C ( l l ) 0 . . 0 0 0 5 ( 7 ) 0 . 8 0 4 8 ( 7 ) 0 . 0 6 1 7 ( 2 ) 5 . 8 ( 3 ) C ( 1 2 ) 0 . , 0 6 3 8 ( 9 ) 0 . 8 3 6 8 ( 7 ) 0 . 0 2 6 7 ( 2 ) 6 . 5 ( 4 ) 294 Table (cont.) atom X y C ( 1 3 ) 0 . 1 8 1 3 ( 8 ) 0 . 7 7 8 2 C ( 1 4 ) 0 . 2 3 9 9 ( 7 ) 0 . 6 8 6 6 C ( 1 5 ) 0 . 1 7 4 2 ( 6 ) 0 . 3 8 1 9 C ( 1 6 ) 0 . 0 6 3 9 ( 6 ) 0 . 3 1 3 4 C ( 1 7 ) 0 . 0 0 1 0 ( 7 ) 0 . 2 1 9 5 C ( 1 8 ) 0 . 0 5 4 ( 1 ) 0 . 1 9 3 3 C( 19 ) 0 . 164(1) 0 . 2614 C( 20 ) o . 2250(8) 0 . 3557 C( 21 ) 0 . 4287(5) 0. 5174 C( 22 ) 0 . 4987(6) 0 . 4019 C( 23 ) 0 . 6377(7) 0 . 4026 C( 24 ) 0 . 7084(6 ) 0 . 517( C( 25 ) . 0 . 6408(6) 0 . 6335 Ci 26 ) 0 . 5014(6) 0 . 6332 C( 27 ) -0 . 065(3 ) -0 . 009 ( C( 28 ) -0 . 071(4) -0 . 03Z( C( 29 ) 0 . 001(1) 0 . 016 ( C( 30 ) -0 . 022(1 ) - 0 . 047 ( C( 31 ) 0. 1765(7 ) - 0 . 0210 z B(eq) (7) 0. 0166(2) 5.9 (6) 0. 0421(1) 4.8 (5) 0. 0797(2) 3.8 (6) 0. 0935(2) 4.4 (6) 0. 0684(2 ) 5.3 (7 ) 0. 0313(2) 6.6 (7 ) 0. 0160(2) 6.5 (6) 0 . 0412(2) 5.0 (6) 0. 0961( 1 ) 3 . 5 ( 6 ) 0. 0893(2) 4 . 3 (8) 0 . 0831(2 ) 5.5 1 ) 0 . 0850(2) 6 . 3 (8) 0 . 0928(2 ) 5.5 ( 7 ) 0 . 0983(2) 4 . 6 2 ) 0 . 577(1 ) 12(2 3 ) 0 . 612(1) 14(3 1 ) 0. 5369(3) 9.6 1 ) 0. 6507(3 ) 10.9 (8) 0. 5972(2) 6.7 295 A-2.2: X-ray Crystallographic Analysis of Ru 2 Cl 4 (DPPB) 2 (DMSO) C(3) C(2) Molecular Structure 296 Experimental Details compound formula fw color, habit crystal size, mm crystal system space group a, A b, k c, A a, deg p\ deg J, deg v, A3 z Pc g / c m 3 F(000) radiation wavelength (A) |i, cm"1 transmission factors scan type scan range, deg in co scan rate, deg/min data collected 2emax> deg cryst decay Ru2Cl4(dppb)2(dmso) • 0.67 Et 2 0 • 0.33 CH 2C1 2 C5 8 H 6 2 Cl 4 OP 4 Ru 2 S • 0.67 C 4 H 1 0 O • 0.33 CH 2C1 2 1352.60 yellow-orange prism 0.20 x 0.30 x 0.55 triclinic PI 12.796(1) 14.559(1) 18.429(1) 103.983(5) 95.036(6) 99.634(6) 3255.0(4) 2 1.380 1383.88 Mo 0.71073 8.13 0.761-0.872 (0-29 0.85 + 0.35 tan 0 2.0-20.0 -h, ±k, ±1 55 negligible 297 no. of unique reflections no. of reflcns with / £ 3o(/) no. of variables R 14845 9088 663 0.037 0.046 1.45 0.41 gof max A/a (final cycle) residual density e/A3 1.30 (near Ru) a Temperature 294 K, Enraf-Nonius CAD4-F diffractometer, Mo-Krx radiation (^K a l = 0.70930, ?iK a 2 = 0.71359 A), graphite monochromator, takeoff angle 2.7°, aperture (2.0 + tan 6) x 4.0 mm at a distance of 173 mm from the crystal, scan range extended by 25% on both sides for background measurement, o2(7) = C + 2B + [0.04(C - B)]2 (5 = scan rate, C = scan count, B = normalized background count), function rninimized Lw(IF0l- IFCI)2 where w = 4F02/o2(F02), R = ZIIF0I-IFCII/LIF0I, Rw = (2w(IF0l-IFcl)2/IwlF0l2)1/2, and gof = [Z(IF 0l-IF cl) 2/(m-«)] 1 / 2. Values given for RtRw, and gof are based on those reflections with / >3o(/). 298 Table A-2.2,1: Bond Lengths (A) with estimated standard deviations in parentheses. Bond Length(A) Bond Length(A) R u d ) - C l ( l ) 2.469( 1 ) C(21 -C(22) 1.41 (1) Ru(1)-Cl(2) 2.495< 1 ) C(23] -C(24) 1.396(6) Ru(1)-Cl(3) 2.4291 1 ) C(23] -C(28) 1.373(7) Ru(1)-P(1) 2.305( 1 ) C(24 -C(25) 1.367(7) Ru(1)-P(2) 2.305< 1 ) C(25 -C(26) 1 . 348(9) Ru(1)-S 2.244( 1 ) C(26 -C(27) 1.388(9) Ru(2)-Cl(1) 2 . 4 1 8 < 1 ) C(27 -C(2B) 1.388(7) Ru(2)-Cl(2) 2 . 51 7 < 1 ) C(29 -COO) 1.396(7) Ru(2)-Cl(3) 2.492 1 ) C(29 -C(34) 1.380(7) Ru(2)-Cl (4) 2.399< 1 ) C(30 -C(31) 1.402(8) Ru(2)-P(3) 2.261( 1 ) C(31 -C(32) 1.36(1) Ru(2)-P(4) 2.257 1 ) C(32 -C(33) 1 .36(1) P d )-C( 1 ) 1 .849 6) C(33 -C(34) 1 .376(7) P(1 )-C(11) 1 .831 ( 5) C(35 -C(36) 1 . 379(6) P( 1 )-C(17) 1 .851 5) C(35 -C(40) 1.402(6) P(2)-C(4) 1 .842 4 ) C(36 -C(37) 1 . 364 ( 7 ) P(2)-C(23) 1 .839 5) C(37 -COB) 1 . 375 ( 5 ) P(2)-C(2S) 1 .636 5) C(38 -C(39) 1 . 375 ( 6 ) P(3)-C(5) 1 .840 4 ) C(39 -C(40) 1 . 373 ( 7 ) P(3)-C(35) 1 .836 4 ) C(41 >-C(42) 1.367(7) P(3)-C(41 ) 1 .647 4) ' C (4 l )-C(46) 1.397(6) P(4)-C(8) 1 .847 5) C(42 -C(43) 1 . 387 ( 7 ) P(4)-C(47 ) 1 .832 5) C(43 -C(44) 1 .351 (8) P(4)-C(53) 1 .846 5) C(44 -C(45) 1 . 347 ( 9 ) S -0(1) 1 .474 3) C(45 )-C(46) 1.371(8) S -C(9) 1 .788 5) C(47 -C(48) 1.360(7) S -C(10) 1 .792 5) C(47 -C(52) 1.396(7) C(1)-C(2) 1 .508 6) C(48 -C(49) 1 . 403 ( 7 ) C(2)-C(3) 1 .524 8) C(49 >-C(50) 1.36(1) C(3)-C(4) 1 .527 7) C(50 )-C(5l) 1.37(1) C(5)-C(6) 1 .531 7) C(51 -C(52) 1.370(6) C(6)-C(7) 1 .491 8) C(53 >-C(54) 1.381(7) C(7)-C(8) 1 .537 7) C(53 )-C(58) 1.389(7) C d l )-C( 12) 1 .381 7) C(54 >-C(55) 1 . 383 ( 7 ) C d 1 )-C( 1 6) 1 .391 7 ) C(55 -C(56) 1.355(9) C( 12)-Cd3) 1 .386 7) C(56 >-C(57) 1.358(10) C( 13)-C(14) 1 .359 9) C(57 )-C(58) 1.362(8) C( 14)-Cd5) 1 .359 9) 0(2)--C(59) 1 .26(5) C d 5)-C( 1 6) 1 .399 8) 0(2)--C(61) 1.31(6) C( 17)-C(1B) 1 .358 8) Cl(6 -C(63) 1 .62(8) C( 17)-C(22) 1 .385 8) C l ( 5 >-C(63) 1.49(7) C (18)-C(19) 1 .381 8) C(59 >-C(60) 1 .72(4) C( 1 9)-C(20) 1 . 30 ( ) C(61 -C(62) 1.18(5) C(20)-C(21 ) 1 .36 ( ) 299 Tahle A-2.2.2; Bond Angles (deg) with estimated standard deviations in parentheses. Bonds A n g l e ( d e g ) Bonds A n g l e ( d e g ) Cl ( 1 ) -Ru( 1 )-CK2) 78.25(3) P 4)-•C(8)-C(7) 117. 2 r4 Cl ( 1: -Rut 1 )-CK3) 78.46(3) P 1 )-•C(11 ) - C( 12) 119. 4 4 Cl ( 1: -Rut 1)-P(1) 172.23(4) P 1 )-•C(1 1 )-C( 16) 124. 1 4 Cl ( i -Rut 1 )-P(2) 93.62(4) C 12) -C(11) -C(16) 1 16. 5 5 Cl ( 1 i -Rut 1 )-s 91 .86(4) c 11) -C(12) -C(13) 121 . 9 5 CK 2) -Rut 1 )-CK3) 80.80(3) c 12) -C(13) -C(14) 120. 3 6 CK 2) -Rut 1)-P(1) 94.73(4) c 13) -C(14) -C(15) 119. 8 (6 CK 2) -Rut 1 )-P(2) 169.35(4) c 14) -C(15) -C(16) 120. 2 5 Cl ( 2) -Rut 1 )-S 91.94(4) c 1 1 ) -C(16) -C(15) 121 . 2 r6 Cl ( 3) -Rut 1)-P(1) 97.29(4) p 1 )-C(17)- C( 18) 120. 9 4 Cl ( 3) -Rut 1)-P(2) 90.90(4) p 1 )-•C( 17)- C(22) 120. 7 5 Cl ( 3) -Rut 1 )-S 168.87(4) c 18) -C(17) -C(22) 118. 4 ' 5 P( 1 ) -Rut 1 )-P(2) 92.93(4) c 17) - C ( 1 8 ) -C(19) 120. 6 7 P( i ) -Rut 1 )-s 91 .68(4) c 18) - C (19) -COO) 122. 3 (8 P(2 ) -Rut 1 )-s 95.23(4) c 19) -C(20) -C(21) 118. 9 (7 Cl ( 1 ) -Rut 2)-Cl(2) 76.78(3) c 20) -C(21 ) -C(22) 121 . 4 6 Cl ( 1 ) -Rut 2)-Cl(3) 78.23(3) c 1 7 ) -C(22) -C(21 ) 118. 3 6 Ci ( l ) -Rut 2)-CK4) 163.46(4) p 2)- C(23)- C(24) 118. 3 4 CI ( 1 ) -Rut 2)-P(3) 102.24(4) p 2)- C(23)- C(28) 123. 7 4 CI ( 1 ) -Rut 2)-P(4) 94.23(4) c 24 ) -C(23) -C(28) 117. 9 4 Cl ( 2 ) -Rut 2)-CK3) 79.18(3) c 23) -C(24) -C(25) 121. 4 5 Cl ( 2 ) -Rut 2)-Cl(4) 88.45(4) C 24 ) -C(25) -C(26) 1 19. 7 5 Cl ( 2 ) -Rut 2)-P(3) 172.71(4) c 25) -C(26) -C(27) 121 . 2 5 Cl ( 2) -Rut 2)-P(4) 95. 12(4) c 26) -C(27) -C(2B) 118. 6 6 CI ( 3 ) -Rut 2)-Cl(4) 89.16(4) c 23) -C(28 ) -C(27) 121 . 1 5 Cl ( 3 ) -Rut 2)-P(3) 93.92(4) p 2)- C(29)- COO) 121 . 7 4 Cl ( 3) -Rut 2)-P(4) 171 .26(4) p 2)- C(29)- C(34) 119. 2 4 Ci ( 4 ) -Rut 2)-P(3) 89.13(4) c 30) -C(29) -C(34) 119. 1 5 Cl ( 4 ) -Rut 2)-P(4) 97.34(4) c 29) -COO) - C O D 119. 3 6 P(3 ) -Ru(2 )-P(4) 92.00(4) c 30) - C O D -C(32) 120. 0 6 Ru( 1 -CI ( 1 )-Ru(2) 86.69(3) c 31 ) -C(32) -C(33) 1 20. 7 6 Ru( 1 ) - C l ( 2)-Ru(2) 84.01(3) c 32) -C(33) -C(34) 120. 4 6 Ru( 1 ) - C l ( 3)-Ru(2) 85.93(3) c 29) -C(34 ) -C(33) 120. 5 6 Ru( 1 ) -P( 1 ) -C(1) 120.6(2) P( 3)- C(35)- C(36) 123. 1 4 Rut 1 ) -P( 1 )-ct U ) 114.2(1) P( 3)- C(35)- C(40) 116. 1 3 Ru( 1 ) -P( 1 )-C(17) 115.1(2) C( 36) -C(35) -C(40) 118. 7 4 C( 1 ) -Pt 1 ) -C(11) 99.7(3) C( 35) -C(36) -C(37) 120. 5( 5 C( 1 ) -P( 1 ) -C(17) 103.9(3) C( 36) -C(37) -COB) 120. 5( 5 C( 1 1 ) -Pt 1 )-C(17) 100.5(2) C( 37) -COB) -C(39) 119. 4 ( 5 Ru( 1 ' -P(2 )-C(4) 120.4(2) C( 38) -C(39) -C(40) 120. 8( 5 Ru( 1 ) -P(2 )-C(23) 120.3(2) C( 35) -C(40) -C(39) 120. 1 ( 5 Ru( 1 ) -P(2 )-C(29) 111.0(1) P( 3)- C(41 )- C(42) 121 . 1 ( 3 C(4 ) -P(2) -C(23) 101.2(2) p( 3)- C ( 4 D - C(46) 122. 1 ( 4 C(4 ) -P(2) -C(29) 101.6(2) C( 42) -C(4D -C(46) 116. 8 ( 4 c o n t i n u e d / . . . 300 C(23)-P(2 )-C(29) 98. 9(2) C(41 )-C(42)-C(43) 121 . 5(5) Ru(2)-P(3 )-C(5) 114. 5(1 ) C(42)-C(43)-C(44) 120. 1 (5) Ru(2)-P(3 )-C(35) 112. 5(1) C(43)-C(44)-C(45) 119. 6(5) Ru(2)-P(3 )-C(41) 122. 0(2) C(44)-C(45)-C(46) 121 . 2(5) C(5)-P(3) -C(35) 100. 9(2) C(41)-C(46)-C(45) 120. 6(5) C(5)-P(3) -C(41 ) 103. 6(2) P(4)-C(47)-C(48) 121 . 7(4) C(35)-P(3 )-C(41 ) 100. 6(2) P(4)-C(47)-C(52) 121 . 3(4) Ru(2)-P(4 )-C(8) 118. 8(2) C(48)-C(47)-C(52) 117. 0(5) Ru(2)-P(4 )-C(47) 119. 6(2) C(47)-C(48)-C(49) 121 . 4(6) Ru(2)-P(4 )-C(53) 111. 6(1 ) C(48)-C(49)-C(50) 119. 6(7) C(8)-P(4) -C(47) 102. 3(2) C(49)-C(50)-C(51) 120. 5(6) C(8)-P(4) -C(53) 100. 4(2) C(50)-C(51)-C(52) 119. 0(6) C(47)-P(4)-C(53) 101 . 0(2) C(47)-C(52)-C(51) 122. 5(6) Ru(1)-S -0( 1 ) 120. 8(1 ) P(4)-C(53)-C(54) 1 20. 4(4) Ru(1)-S -C(9) 112. 6(2) P(4)-C(53)-C(58) 121 . 4(4) Ru(1)-S -C(10) 112. 7(2) C(54)-C(53)-C(58) 117. 9(5) 0( 1 )-S -C(9) 105. 6(2) C(53)-C(54)-C(55) 120. 7(5) 0( 1 )-S -C(10) 104. 9(2) C(54)-C(55)-C(56) 1 19. 4(6) C ( S ) - S -C(10) 97. 5(3) C(55)-C(56)-C(57) 121. 2(6) P( 1 ) - C ( 1 ) - C ( 2 ) 122. 6(4) C(56)-C(57)-C(58) 119. 9(6) C( 1 ) -C(2) - C ( 3 ) 1 15. 4(5) C(53)-C(5B)-C(57) 120. 9(6) C ( 2 ) - C(3) -C(4) 113. 6(4) C(59)-0(2)~C(61) 1 62 ( 6) P(2 ) -C(4 ) -C(3) 117. 1(3) O(2)-C(59)-C(60) 171 ( 4) P(3 ) -C(5) - C ( 6 ) 117. 3(3) 0(2)-C(6l)-C(62) 76( 4) C(5 ) - C(6) -C(7) 120. 5(5) C1(6)-C(63)-C1(5) 1 04 ( 5) C ( 6 ) - C(7) - C ( 8 ) 118. 0(4 ) 301 Table A-2.2.3: Final Atomic Coordinates (Fractional x 104; Ru, Cl, P, S x 105) and Isotropic Thermal Parameters (U x 103 A 2 ) with estimated standard deviations in parentheses. Atom X y z U A eQ Rut 1 ) 23098( 2) 39241( 2) 24199( 2) 31 Rut 2) 44051( 2) 26214( 2) 21969( 2) 30 CHI ) 27687( 8) 24681( 7) 27268( 6) 37 CH2) 42465( 6) 44823( 7) 29259( 5) 36 CH3) 30744( 8) 32144( 7) 13065( 5) 38 CH4) 58 1 39 ( 9) 35609( 8) 16247( 6) 47 Pt 1 ) 2123000) 53395( 8) 21172( 7) 43 P ( 2 ) 6141 ( 9) 31461( 6) 1 6432 ( 6) 38 P(3) 44571( 9) 13776( 6) 141 10( 6) 37 P(4) 54493( 9) 25354( 8) 31382( 6) 40 S 16206( 6) 44453( 8) 35647( 6) 4 1 0(1 ) 960( 2) 5005( 2) 3667 ( 2) 56 C( 1 ) 792( 5) 5525( 4 ) 1 774 ( 4 ) 7 1 C ( 2 ) - 1 67 ( 5) 5365( 4 ) 2181 ( 4 ) 78 C (3) -91 9( 4) 4369 ( 4 ) 1 676 ( 3) 62 C(4 ) -567 ( 3) 3569 ( 3) 2 1 63 ( 3) 50 C(5) 5798( 4) 1231 ( 3) 1 175( 3) 50 C(6) 6723 ( 4) 1 556( 4 ) 1 823 ( 3) 67 C(7) 6692( 4) 1 1 36( 4 ) 2484 ( 3) 70 C(6) 5629( 4) 1 34 1 ( 4 ) 2998 ( 3 ) 58 C(9) 2924 ( 4) 51 29 ( 4 ) 4253 ( 3) 57 C ( 1 0 ) 1 461 ( 5) 3489 ( 4 ) 4006 ( 3) 64 C O O 2856( 4) 5577 ( 3) 1351 ( 3) 48 C(12) 3904 ( 4) 5455( 4 ) 1 355 ( 3 ) 58 CO 3) 4506( 5) 565 3 ( 4 ) 803( 4 ) 77 C04) 4070( 7) 5954( 4 ) 224 ( 4 ) 84 CO 5) 3034 ( 6) 6063( 4 ) 1 88 ( 3) 79 C( 16) 2429( 5) 5892( 4 ) 755( 3 ) 66 Ct17) 2661 ( 5) 6454( 3) 2871 ( 3) 57 COB) 3755( 5) 6773( 4) 3051 ( 4 ) 77 CO 9) 4 1 65 ( 7) 7604 ( 5) 36 1 7 ( 5) 108 C(20) 3555(1 0) 8 1 1 1 ( 6) 4004 ( 5) 128 C ( 2 1 ) 24790 0) 78 1 7 ( 6) 3843 ( 6) 148 C ( 2 2 ) 20 1 2 ( 6) 6989( 4) 3262 ( 5) 1 10 C(23) 269( 4) 29 1 4 ( 3) 8 1 7 { 2) 47 C(24 ) -707( 4) 23 1 6 ( 4 ) 476( 3) 60 C(25) -1023( 5) 2 1 28 ( 4) -282 ( 4) 74 C(26) -375( 6) 25 1 4 ( 5) -7 1 5 ( 3) 81 C(27) 595( 5) 3 1 28 ( 4 ) -403 ( 3) 69 C(28) 902( 4) 3324 ( 4) 369( 3) 53 C(29) 336( 3) 1 897 { 3) 1 91 9 ( 3) 48 COO) -253( 4) 1 636( 4) 2466( 3) 65 cont inued••• 302 C ( 3 1 ) -402( 5) 679 5) 25191 4) 86 C(32) 8< 5) 13 5) 2033( 5) 96 C(33) 567( 5) 264 4) 1492 < 4) 82 C(34) 742< 4) 1203 4) 1 4371 3) 64 C(35) 3729< 3) 1201 { 3) 469( 2) 42 C(36) 28031 4) 5221 4) 1 ee < 3) 55 C(37) 2239( 4) 477< 4) -500< 3) 71 C(36) 26001 5) 1 1 02 5) -9171 3) 73 C(39) 3526 5) 17741 4) -645< 3) 64 C(40) 4094 4) 1833 4) 39( 3) 54 C ( 4 1 ) 3908 4) 226( 3) 1 61 7 < 3) 44 C(42) 31 50 4) 175 3) 20921 3) 58 C(43) 2771 5) -675 4) 2280 3) ' 67 C(44 ) 3124 5) -1488 4) 1973 4) 70 C(45) 3846 5) -1467 4) 1485 4 ) 82 C(46) 4240 5) -632 4) 1298 3) 68 C(47) 6723 3) 3362 4 ) 3542 3) 50 C(4B) 6959 4) 4250 4 ) 3412 3) 62 C(49) 7940 5) 4877 5) 3717 3) 67 C(50) 8682 5) 4589 6) 4145 4 ) 94 C ( 5 l ) 8471 5) 3699 6) 4265 4) 92 C(52) 7502 4 ) 3103 5) 3992 3) 73 C(53) 4773 3) 2579 4 ) 3967 3) 47 C(54) 4662 4 ) 3441 4 ) 4528 3) 57 C(55) 429E 5) 3491 5) 5138 3) 69 C(56) 3647 5) 2686 6) 5200 4 ) 66 C( 57 ) 3542 5) 1830 6) 4677 4 ) 67 C(58) 4094 5) 1773 4 ) 4073 3) 69 C l ( 5 ) 1 8466 31 ) 7633 26) 3285 21 ) 432(17) C l ( 6 ) 1 9634 30) 8202 27) 4493 23) 591(22) 0(2) 2 7206 34 ) 7482 35) 2695 25) 477(23) C (59) 2 7161 25) 8293 28 ) 3114 19) 271 (1 4 ) C(60) 2 7305 31 ) 94 5', 31 ) 3672 23 ) 367(19) C ( £ 1 ) 2 751 1 42) 68C3 4 1 ) 2205 30) 437(31 ) C ( 6 2 ) 2 6785 24) 6370 22 ) 2408 18) 257(13) C ( 6 3 ) 1 924 1 66) 8508 56) 3744 48) 335(35) Occupancy factor 0 . 35 . "Occupancy factor 0.67. 303 A-2.3: X-ray Crystallographic Analysis of /ra/is-RuCI 2 (5,S-BDPP) 2 Molecular Structure 304 Experimental Details A . C r y s t a l Da ta E m p i r i c a l F o r m u l a F o r m u l a We igh t C r y s t a l C o l o r , H a b i t C r y s t a l D i m e n s i o n s (mm) C r y s t a l Sys tem No. R e f l e c t i o n s Used f o r U n i t C e l l D e t e r m i n a t i o n (26 range) Omega Scan Peak W i d t h a t H a l f - h e i g h t L a t t i c e P a r a m e t e r s : Space Group Z v a l u e D c a l c F o o o ^(MoKa) Di f f r a c t o m e te r R a d i a t i o n Tempera tu re T a k e - o f f A n g l e D e t e c t o r A p e r t u r e C 5 8 H 6 0 C 1 2 P 4 * U 1052 .98 r e d , p r i s m 0 .300 X 0 .400 X 0 .500 o r t h o r h o m b i c 25 ( 4 0 . 0 - 4 3 . 0 " ) 0 .36 B. a - 18.961 (3)A b - 20.826 (4)A c - 12.998 (3)A V « 5133 (2)A3 P2 12 12 1 (#19) 1.362 g / c m J 2184 5.63 c m " 1 I n t e n s i t y Measurements R i g a k u AFC6S MoKa (X - 0 .71069 A) 2 1 e C 6 . 0 ° 6 .0 mm h o r i z o n t a l 6 .0 mm v e r t i c a l C r y s t a l t o D e t e c t o r D i s t a n c e 28 5 mm 305 Scan Type Scan Rate Scan W i d t h 2 6 m a x N o . o f R e f l e c t i o n s Measured Cor r e c t i o n s C. S t r u c t u r e S o l u t i o n S t r u c t u r e S o l u t i o n Re f i nement Fu n c t i o n Minimized Least-squares Weights p - f a c t o r Anomalous D i s p e r s i o n No. O b s e r v a t i o n s ( I>3.00c ( iP No. V a r i a b l e s R e f l e c t i o n / P a r a m e t e r R a t i o R e s i d u a l s : R; R,, w Goodness o f F i t I n d i c a t o r Max S h i f t / E r r o r i n F i n a l C y c l e Maximum Peak i n F i n a l D i f f . Map Minimum Peak i n F i n a l D i f f . Map w-26 1 6 . 0 ° / m i n ( i n omega) (8 r e s c a n s ) (1 .31 + 0.35 t a n 0 ) c 7 0 . 1 ° T o t a l : 12224 U n i q u e : 12217 ( * i n t - -074) L o r e n t z - p o l a r i z a t i o n A b s o r p t i o n ( t r a n s , f a c t o r s : 0.93 - 1.00) and Re f inemen t P a t t e r s o n Method F u l l - m a t r i x l e a s t - s q u a r e s E w ( |Fo| - |Fc | ) 2 2 2 2 4Fo^ '/cr ( F o z ) 0.04 A l l non -hyd rogen atoms 7751 586 13.23 0 .035; 0.038 1.32 0.00 0.6 9 e ~ / A 3 - 0 . 5 9 e " / A 3 306 Tahle A-2.3.1: Bond Lengths (A) with estimated standard deviations parentheses. atom atom distance atom atom distance Ru( 1) C l ( l ) 2.4036(9) C d l ) C(12) 1.391(5) Ru( 1 ) Cl ( 2 ) 2.4265(9) C d l ) C(16) 1.396(6) Ru(l) P d ) 2.459(1) C(12) C(13) 1.386(6) Ru( 1) P(2) 2.441(1) C(13) C(14) 1.369(8) Ru( 1 ) P(3) 2.423(1) C(14) C(15) 1.375(8) Ru( 1 ) P( 4 ) 2.432(1 ) C(15) C(16) 1.380(6) P( 1 ) C d ) 1.866(4) C(17) C(18) 1.393(5) P( 1 ) C ( l l ) 1.847(3) C(17) C(22) 1.400(5) P l l ) C(17) 1.839(3) C(16) C(19) 1.378(5) P( 2 ) C( 3 ) 1 . 869(4) C(19) C(20) 1.384(6) P( 2 ) C(23) 1.843(3) COO) C(21) 1.369(6) P( 2 ) C(29) 1.855(4) C(21 ) CI22) 1.383(5) P( 3 ) C( 4 ) • 1.873(4) C(23) C(24 ) 1.397(5) P( 3 ) C(35) 1.854(4) C(23) COS) 1.397(5) P( 3 ) C(41 ) 1 . 842(4) C(24) C(25) . 1.390(6) P( 4 ) C( 6 ) 1.870(4) C(25) C(26) 1.369(7) P( 4 ) C( 47 ) 1.841(4) C(26) C(27) 1.384(7) P( 4 ) C(53) 1.848(5) C(27) C(28) 1.378(5) C( 1 ) C(2) 1.550(5) C(29) COO) 1.400(5) C( 1 ) C(7) 1.533(5) C(29) C(34) 1.406(5) C( 2 ) C(3) 1.522(5) COO) C O D 1.390(5) C(3) C(8) 1.536(5) C(31) C(32) 1.373(6) C(4) C( 5) 1.531(6) C(32) C(33) 1.388(6) C(4) C(9) 1.537(6) C(33) C(34) 1.372(5) C( 5) C(6) 1.521(6) C(35) C(36) 1.384(6) C( 6 ) CdO) 1.540(6) C(35) C(40) 1.398(5) 307 I n t r a m o l e c u l a r D i s t a n c e s I n v o l v i n g the Nonhydrogen Atoms ( c o n t ) atom atom d i s t a n c e C(36) C(37 ) 1. 392(6) C(37 ) C(38 ) 1. 378(7) C(38) C(39) 1. 373(7) C(39) C(40) 1. 380(6) C(41) C(42) 1. 401(5) C(41) C(46 ) 1. 396(6) C(42 ) C(43 ) 1. 381(6) C(43) C(44) 1. 381(7) C(44) C(45) 1. 358 ( 6 ) C( 45) C(46) 1. 379(7) C( 47 ) C( 48 ) 1. 385(6) C( 47 ) C(52) 1. 402(6) S. ( 4 8 ) C(49) 1. 398(6) C( 49 ) C(50) 1. 363(7) C( 50 ) C(51) 1. 384(8) C(51 ) C( 52 ) 1. 378 ( 7 ) C( 53 ) C(54) 1. 387(7) C(53) C(58) 1. 375 ( 7 ) C( 54 ) C(55) 1. 395(7) C(55) C(56) 1. 37(1) C(56) C(57) 1. 34(1) C(57) C(58) 1. 402(7) 308 le A-2.3.2: Bond Angles (deg) with estimated standard deviations in parentheses. a torn a t o m a t o m a n g l e a t o m a t o m a t o m a n g l e C M l ) R u t l ) C M 2) 177.03(3) C(23) P(2) C(29) 100.1 (2 ) C M l ) R u ( l ) P t l ) 98.57(3) R u ( l ) P(3) C(4) 105.0 (1 ) C M l ) R u ( l ) P(2) 81.46(3) R u ( l ) P(3) C(35) 120.7 (1 ) C l ( l ) R u t l ) P(3) 94.25(3) R u ( l ) P(3) C(41) 122 . 2 ( 1 ) C M l ) R u t l ) P(4) 84.00(3 ) C(4) P(3) C(35) 100.8 (2 ) C M 2) R u t l ) P t l ) 82 . 0 3(3) C(4) P(3) C (41) 1 0 5 . 8 ( 2 ) C M 2 ) Rut 1 ) P ( 2 ) 9 5 . 6 3 ( 3 ) C(35) P(3) C(41 ) 9 9 . 6 ( 2 ) C l ( 2 ) Rut 1 ) Pt 3) 8 5 . 2 4 ( 3 ) R u t l ) P( 4 ) C (6) 1 1 2 . 6 ( 1 ) C M 2 ) Rut 1 ) P(4) 9 8 . 8 9 ( 3 ) Ru( 1 ) P ( 4 ) C ( 4 7 ) 1 2 4 . 1 ( 1 ) P( 1 ) Rut 1 ) Pt 2 ) 8 9 . 0 2 ( 3 ) Rut 1 ) P( 4 ) C ( 5 3 ) 1 1 3 . 4 ( 1 ) P( 1 ) Rut 1 ) Pt 3 ) 1 6 7 . 0 8 ( 3 ) C ( 6 ) P ( 4 ) C ( 4 7 ) 9 9 . 7 ( 2 ) P( 1 ) Rut 1 ) Pt 4 ) 9 2 . 5 7 ( 3 ) C ( 6 ) P ( 4 ) C ( 5 3 ) 1 0 0 . 6 ( 2 ) P( 2 ) Rut 1 ) P ( 3 ) 9 4 . 4 6 ( 3 ) C ( 4 7 ) P( 4 ) C ( 5 3 ) 1 0 3 . 2 ( 2 ) P( 2 ) Rut 1 ) Pt 4 ) 1 6 5 . 4 7 ( 3 ) P d ) C ( l ) C ( 2 ) 1 1 1 . 3 ( 2 ) P( 3 ) Rut 1 ) Pt 4 ) 8 7 . 1 9 ( 3 ) P d ) C ( l ) C ( 7 ) 1 1 8 . 7 ( 3 ) Ru ( 1 ) Pt 1 ) C( 1 ) 1 0 8 . 3 ( 1 ) C( 2 ) C( 1 ) C ( 7 ) 1 0 6 . 6 ( 3 ) Ru { 1 ) Pt 1 ) C t l l ) 1 1 6 . 7 ( 1 ) C ( l ) C ( 2 ) C ( 3 ) 1 2 2 . 6 ( 3 ) Rut 1 ) P d ) C ( 1 7 ) 1 2 5 . 1 ( 1 ) P ( 2 ) C (3) C (2) 1 1 1 . 0 ( 2 ) C( 1 ) P t l ) C t l l ) 1 0 1 . 4 ( 2 ) P ( 2 ) C(3) C (8) 1 1 8 . 5 ( 3 ) C ( l ) P t l ) C(17) 1 0 1 . 6 ( 2 ) C(2) C(3) C (8) 1 0 6 . 9 ( 3 ) C( 11 ) P t l ) C(17) 100.5 (2 ) P(3) C(4) C (5) 1 1 3 . 6 ( 3 ) Rut 1 ) P ( 2 ) C(3) 107.3 (1 ) P ( 3 ) C (4) C (9) 1 1 7 . 9 ( 3 ) Ru( 1 ) P ( 2 ) C(23) 114.5 (1 ) C (5) C(4) C (9) 1 0 9 . 8 ( 3 ) R u ( l ) P ( 2 ) C (29) 1 2 7 . 6 ( 1 ) C(4) C(5) C (6) 1 1 9 . 5 ( 3 ) C(3) P ( 2 ) C ( 2 3 ) 1 0 3 . 6 ( 2 ) P ( 4 ) C ( 6 ) C( 5) 1 1 3 . 3 ( 3 ) C(3) P ( 2 ) C(29) 1 0 0 . 7 ( 2 ) P( 4 ) C( 6 ) C( 10 ) 1 1 5 . 6 ( 3 ) 309 Intramolecular Bond Angles Involving the Nonhydrogen Atoms (cont) atom atom atom a n g l e atom atom atom ang le C ( 5 ) C(6) C( 10) 107 . 8 ( 4 ) P ( 2 ) C(29) C(34) 120 • 8( 3 P d ) C d l ) C( 12) 121 . 5 ( 3 ) C(30) C(29) C(34 ) 117 • 2( 3 P d ) C d l ) C( 16) 121 . 4 ( 3 ) C(29) C O O ) C O D 120 .8( 3 C(12) C d l ) C( 16) 117 . 1 ( 3 ) C O O ) C O D C(32) 120 • 9( 4 C d l ) C(12) C( 13) 121 . 5 ( 4 ) C O D C(32) C(33) 119 .1 ( 4 C ( 1 2 ) C(13) C( 14) 120 . 0 ( 4 ) C(32) C(33) C(34) 120 • 6( 4 C ( 1 3 ) C(14) C( 15) 119 . 8 ( 4 ) C(29) C(34) C(33) 121 • 4( 4 C ( 1 4 ) C ( 1 5 ) C( 16) 120 . 4 ( 5 ) P O ) C(35) C(36) 119 .8( 3 c d i ) C ( 1 6 ) C( 15) 121 . 1 ( 4 ) P O ) C ( 3 5 ) C ( 4 0 ) 121 • 9( 3 P d ) C ( 1 7 ) C( 18) 120 . 7 ( 3 ) C ( 3 6 ) C ( 3 5 ) C ( 4 0 ) H B . 3( 4 P.( 1) C ( 1 7 ) C( 22) 122 . 2 ( 3 ) C ( 3 5 ) C (36 ) C ( 3 7 ) 120 • 7( 4 C( IB ) C ( 1 7 ) C( 22) 117 . 2 ( 3 ) C ( 3 6 ) C ( 3 7 ) C ( 3 8 ) 120 . 3( 4 C( 17 ) C ( 1 8 ) C( 19) 121 . 6 ( 3 ) C ( 3 7 ) C ( 3 8 ) C ( 3 9 ) 119 .2 ( 4 C( 18 ) C( 19 ) C ( 20) 119 . 8 ( 4 ) C( 38 ) C (39 ) C( 40 ) 121 . 1 ( 4 C( 19 ) C ( 2 0 ) C( 21) 120 . 1 ( 4 ) C ( 3 5 ) C ( 4 0 ) C ( 3 9 ) 120 • 3( 4 C( 20 ) C (21 ) C 22) 120 . 0 ( 4 ) P O ) C ( 4 1 ) C ( 4 2 ) 119 . 4 ( 3 C ( 1 7 ) C ( 2 2 ) C( 21 ) 121 .3(4 ) P( 3) C ( 4 1 ) C ( 4 6 ) 123 • 4( 3 P ( 2 ) C ( 2 3 ) c 24) 121 . 5 ( 3 ) C ( 4 2 ) C ( 4 1 ) C( 46 ) 117 . 1 ( 4 P( 2 ) C ( 2 3 ) C 28 ) 120 . 5 ( 3 ) C ( 4 1 ) C ( 4 2 ) C ( 4 3 ) 120 . 4 ( 4 C ( 2 4 ) C ( 2 3 ) C 28) 118 . 0 ( 3 ) C ( 4 2 ) C(43) C ( 4 4 ) 120 . 5( 5 C (23 ) C (24 ) c 25) 120 . 5 ( 4 ) C ( 4 3 ) C ( 4 4 ) C ( 4 5 ) 120 • 3( 5 C (24 ) C(25) c 26 ) 120 . 5 ( 4 ) C ( 4 4 ) C ( 4 5 ) C ( 4 6 ) 119 . 7 ( 5 C ( 2 5 ) C ( 2 6 ) c 27) 119 . 8 ( 4 ) C ( 4 1 ) C(46) C ( 4 5 ) 122 • 0( 5 C ( 2 6 ) C(27) c 28) 120 . 2 ( 4 ) P ( 4 ) C(47) C ( 4 8 ) 118 .7 ( 3 C ( 2 3 ) C ( 2 8 ) c 27) 121 . 0 ( 4 ) P ( 4 ) C ( 4 7 ) C ( 5 2 ) 123 . 1 ( 4 P ( 2 ) C( 29) c 30) 121 . 9 ( 3 ) C ( 4 8 ) C ( 4 7 ) C ( 5 2 ) 118 • 0( 4 310 Intramolecular Bond atom atom atom C(47) C(48) C(49) C(48) C(49) C(50) C(49) C(50) C(51) C(50) C(51) C(52) C(47) C(52) C(51) P(4) C(53) C(54) P(4) C(53) C(58) C( 54 ) C(53) C(58) C( 53 ) C( 54 ) C(55) C(54) C(55) C(56) C( 55) C(56) C(57) C( 56 ) C( 57 ) C(58) C( 53 ) C(58) C( 57 ) Angles Involving the Nonhydrogen Atoms (cont) angle 120.8(4) 120.2(5) 120.0(5) 120.2(5) 120.8(5) 120.5(4) 121.6(4) 117.8(4) 120.7(6) 119.7(6) 120.6(6) 120.1(6) 121.1(5) 311 Table A-2.3.3: Final Atomic Coordinates (Fractional) and B(eq). atom X y z B eq Ru(l) 0. 29874(1) 0. 25916(1) 0. 18194(2) 1 .659(8) C l ( l ) 0. 17328(4) 0. 25183(4) 0. 20561(6) 2 .34(3) Cl ( 2 ) 0. 42523(4) 0. 27196(4) 0. 16235(7) 2 .36(3) P d ) 0. 29994(5) 0. 28933(4) -0. 00099(6) 1 .92(3) P(2) 0. 27547(4 ) 0. 37116(4) 0. 22574(7) 1 .79(3) P( 3 ) 0. 32605(5) 0. 22775(4) 0. 35694 (7) 2 .07(3) P( 4 ) 0. 28971(5) 0. 14534(5 ) 0. 14227 (8) 2 .37(4) C d ) 0. 3269(2) 0. 3753(2) -0. 0107( 3) 2 .3(1 ) C(2) 0. 2670(2 ) 0. 4206(2) 0. 0257 ( 3) 2 .6(2) C( 3 ) 0. 2214(2) 0. 4061(2) 0. 1193( 3) 2 .3(1) C( 4 ) 0. 3936 ( 2 ) 0. 1626(2) 0. 344 3 ( 3) 2 .8(2) C( 5 ) 0. 3623(2 ) 0. 0971(2 ) 0. 3169( 3) 3 .3(2) C(6) 0. 2924(2 ) 0. 0937(2) 0. 2600( 3) 3 .0(2) C( 7 ) 0. 3521(2) 0. 4010(2 ) -0. 1149( 3) 3 .5(2) C( 8 ) 0. 1779(2 ) 0. 4667(2 ) 0. 1413( 3) 3 .4(2) C( 9 ) 0. 4479(2 ) 0. 1550(2) 0. 4313 ( 4 ) 4 .0(2) CdO) 0. 2744(3 ) 0. 0224(2) 0. 2430 ( 4) 4 .5(2) C d l ) 0. 3670(2 ) 0. 2501(2) -0. 0826( 2) 2 .6(1) C( 12 ) 0. 4371(2) 0. 2697(2) -0. 0815( 3) 3 .4(2 ) C( 13 ) 0. 4869(2 ) 0. 2419(3 ) -0. 1455( 4) 5 .0(2) C(14) 0. 4679(3) 0. 1930(3) -0. 2102( 4 ) 5 .8(3) C(15) 0. 3993 ( 3 ) 0. 1718(3) -0. 2116( 4 ) 5 .0(3) C(16) 0. 3493(2) 0. 1999(2) -0. 1490 ( 3) 3 .4(2) C(17) 0. 2231(2) 0. 2869(2) -0. 0872( 3) 2 .0(1) 312 atom X y z C(18) 0. 1555(2) 0. 2775(2) -0. 0481(3) 2 .7(2) C(19) 0. 0973(2) 0. 2752(2) -0. 1114(3) 3 .4(2) C(20) 0. 1055(2) 0. 2815(2) -0. 2168(3) 3 .5 (2) C(21) 0. 1713(2) 0. 2907(2) -0. 2577(3) 3 .5 (2) C(22) 0. 2296(2) 0. 2935(2) -0. 1940(3) 2 .8 (2) C(23) 0. 2198(2 ) 0. 3826(2) 0. 3405(3) 2 .1 (1) C(24) 0. 1463(2) 0. 3783(2) 0. 3352(3) 2 .8 (2) C(25) 0. 1055(2) 0. 3859(2) 0. 4231(4) 3 .6(2) C(26 ) 0. 1366(3) 0. 3961(2) 0. 5166(3) 3 .9 (2) C(27) 0. 2094(2) 0. 3992(2) 0. 5238(3) 3 .2(2) C(28) 0. 2504(2) 0. 3935(2) 0. 4367(3) 2 .5(1) C(29 ) 0. 3408(2) 0. 4363(2) 0. 2456(3) 2 .1 (1) C O O ) 0. 4106(2) 0. 4309(2) 0. 2117(3) 2 .4(1) C O l ) 0 . 4579(2) 0. 4813(2) 0. 2244 ( 3 ) 3 .2(2 ) C(32 ) 0. 4374(2) 0. 5375(2) 0. 2708(3 ) 3 .6(2) C(33) 0. 3682(2 ) 0. 5438(2) 0. 3044 ( 3 ) 3 .5(2) C( 34 ) 0. 3210(2) 0. 4945(2) 0. 2922(3 ) 2 .8(2) C( 35) 0. 3721(2) 0. 2838(2) 0. 4450(3) 2 .5 (1) C(36) 0. 4219(2) 0. .3261 ( 2 ) 0. 4063(3) 2 .9(2) C( 37 ) 0. , 4572(2 ) 0. 3684(2) 0. 4712(4 ) 3 .8(2) C( 38 ) 0. 4454(3 ) 0. 3669(3) 0. 5758(4 ) 4 .7(3) C(39 ) 0. .3976(3) 0. ,3239(3) 0. 6149(3) 4 .7(2) C(40) 0. 0 6 0 0 ( 2 ) 0. .2835(2) 0. 5511(3) 3 .6(2) C( 41 ) 0. ,2585(2) 0. ,1962(2) 0. 4454(3) 2 .5(1) C( 42 ) 0. .1916(2) 0. ,2247(2) 0. 4475(3) 3 .1(2) 313 a t o m X y z B e q C(43) 0. 1405(2 ) 0. 2027(3 ) 0. 5146(4 ) 4 . 3 ( 2 ) C (44) 0. 1 5 5 3 ( 3 ) 0. 1 5 3 3 ( 3 ) 0. 5822(4 ) 5 .0 (3 ) C (45) 0. 2 2 0 2 ( 3 ) 0. 1 2 5 8 ( 2 ) 0. 5833(4 ) 5 .0 (3 ) C (46) 0. 2713(3 ) 0. 1 4 6 9 ( 2 ) 0. 5157(4 ) 4 .0 (2 ) C (47) 0. 3527(2) 0. 1014(2 ) 0. 0607(3 ) 3 .0 (2 ) C (48) 0 . 4220(2 ) 0. 1224(2 ) 0. 0568(3 ) 3 . 3 ( 2 ) C (49) 0 . 4730(3 ) 0. 0879(2 ) 0. 0 0 2 3 ( 4 ) 4 . 3 ( 2 ) C (50) 0 . 4550(3 ) 0. 0329(3) - 0 . 0483(5 ) 5 . 3 ( 3 ) C( 51 ) 0 . 3861(4) 0. 0110(2) - 0 . 0453(5) 5 . 5 ( 3 ) C( 52 ) 0 . 3356(3 ) 0 . 0444(2 ) 0 . 0090(4 ) 4 . 0 ( 2 ) C( 53) 0 . 2032(2 ) 0 . 1222(2 ) 0 . 0884(3) 3 . 3 ( 2 ) C( 54 ) 0. 1927(3 ) 0 . 1210(2) - 0 . 0171(4) 4 . 6 ( 2 ) C( 55) 0 . 1269(4 ) 0 . 1053(3) - 0 . 0580(5) .6 . 5 ( 4 ) C( 56 ) 0. 0719(3 ) 0 . 0913(3 ) 0 . 0068(7 ) 7 . 3 ( 4 ) C( 57 ) 0 . 0806(3 ) 0 . 0929(3) 0 . 1090(6 ) 6 . 5 ( 3 ) C( 58 ) 0 . 1464(3) 0 . 1088(3) 0 . 1508(4 ) 4 . 5 ( 2 ) 314

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