Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Synthesis of dichloro-sulphoxide complexes of ruthenium (II) and their use as catalysts for homogeneous… McMillan, Roderick Stewart 1976

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1977_A1 M32_4.pdf [ 9.92MB ]
Metadata
JSON: 831-1.0060985.json
JSON-LD: 831-1.0060985-ld.json
RDF/XML (Pretty): 831-1.0060985-rdf.xml
RDF/JSON: 831-1.0060985-rdf.json
Turtle: 831-1.0060985-turtle.txt
N-Triples: 831-1.0060985-rdf-ntriples.txt
Original Record: 831-1.0060985-source.json
Full Text
831-1.0060985-fulltext.txt
Citation
831-1.0060985.ris

Full Text

SYNTHESIS OF DICHLORO-SULPHOXIDE COMPLEXES OF RUTHENIUM(II). AND THEIR USE AS CATALYSTS FOR HOMOGENEOUS ASYMMETRIC HYDROGENATION by RODERICK STEWART McMILLAN B.Sc. (Hon.). Simon Fraser University, 1971 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of CHEMISTRY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1976 (§) Roderick Stewart McMillan, 1976 In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f ree ly ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th i s thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thes i s for f i nanc ia l gain sha l l not be allowed without my writ ten pe rm i ss ion . Department of The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 ABSTRACT Syntheses of a number of chiral and non-chiral sulphoxides and corresponding Ru(II) sulphoxide compounds are described, as well as significant reactions of some of these complexes with molecular hydrogen, olefins, and carbon monoxide. The new sulphoxides presented are: (S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide, (MBMSO), (2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(methyl sulphinyl)butane"i^O, (Dios), and (2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(benzyl sulphinyl)butane-rL^O, (BDios). These sulphoxides are prepared as mixtures of diastereomers. Other sulphoxides discussed are: dimethyl (DMSO), methyl n-propyl, (MenprS0), methyl phenyl, (MPSO), and R-(+)-methyl p-tolyl sulphoxide, (MPTSO) and (2R,3R)-2,3-dihydroxy-l,4-bis(methyl sulphinyl)butane, (DDios The previously unknown complexes, [NH2Me2][RuCl^(DMSO)^], [NH 2Me 2][RuCl 3(Me nprS0) 3], [RuCl2(MBMSO) ] 3 , [RuCl 2(MPTSO) 2J 3, [RuCl 2(MPS0) 2] n, RuCl 2(DDios) 2-2H 20, RuCl 2(Dios)(DDios) and RuC12(DDios)(DMSO)(MeOH) have been prepared using newly developed synthetic routes. The previously prepared compounds, RuCl2(DMS0)^ and RuBr2(DMSO)^ are more f u l l y described and in collaboration with A. Mercer and J. Trotter of this department the structures of the chloro-complex and the [NH2Me2][RuC13(DMSO)3] compound were determined by x-ray crystal-lography. Both [NH2Me2][RuCl3(DMSO)3] and RuC12(DMSO)4 react readily with molecular hydrogen in N,N'-dimethylacetamide (DMA) in the presence of a strong base, proton sponge . The net heterolytic cleavage of FL results in hydride species which although not well characterized have anomalously high *H n.m.r. hydride chemical shifts at least for Ru(II). The anionic DMSO complex catalyses the hydrogen reduction of activated olefins in DMA at 60°C under 1 atm and kinetic and spectral studies indicate the following mechanism: Ru HCl 3(DMS0)2 + H 2 I L Ru C13(DMS0)2 + DMSO HRu I ICl 2(DMS0) 3 + HC1 k 2 j | k 2, olefin, -DMSO HRuIICl2(DMSO) (olefin)" k., -HC1 4 HRu HCl 2(DMS0) 2 + olefin —^» Ru I I.Cl 2 (DMSO)2alkyl" | k 6 H C 1 II, Ru C13(DMS0)2 + Sat. Product Activation of H 2 is thought to occur by net heterolytic cleavage of molecular hydrogen and this and an olefin insertion step are considered to be rate determining, (k^ and k 4). Reduction proceeds by two pathways, one olefin-dependent and the other olefin-independent; the f i n a l step involves protonolysis of a a-alkyl complex. Catalytic hydrogenation of acrylamide in DMA at 70°C using [RuCl2(MBMSO)2]^ is described and the postulated mechanism is summarized below: - iv -K [Ru HCl 2(MBMSO) 2] 3 TT-^ 3Ru nCl 2(MBMSO) 2 Ru nCl 2(MBMSO) 2 + H 2 H 2Ru I VCl 2 (MBMSO) + MBMSO k-3 olefin k2 olefin RuIICl2(MBMSO) (olefin) + H 2 _ M_ M S_* HRu I VCl 2(MBMSO)alkyl k5 R u n c i (MBMSO) + Sat. Product k^ MBMSO • r o RuTICl2(MBMSO) As with the anion system a two-path reduction occurs, one ole f i n -dependent and one olefin-independent, with the ^ - a c t i v a t i o n steps rate determining, (k.^  and k 4 ) ; however, H 2 activation i s this time via oxidative addition. Asymmetric hydrogenation studies using the catalysts [ R u C l 2 ( M B M S O ) 2 ] , [RuCl 2(MPTSO) 2] 3, RuCl 2(DDios) 2•2H 20, RuCl 2(Dios)(DDios), and RuCl2(DDios)(DMSO)(MeOH) are presented. The largest optical purities obtained are 25 and 15%, for the RuCl 2 (Dios)(DDios)-itaconic acid and [RuCl 2(MBMSO) 2]^-itaconic acid systems, respectively. The preparation of carbonyl derivatives of [RuCl2(MBMSO)^]^ and [RuCl 2(MPTS0) 2J 3 are described; these derivatives have anomalously high v(C0) values. - V -Table of Contents Page ABSTRACT .' '. i i TABLE OF CONTENTS v LIST OF TABLES x i LIST OF FIGURES x i i i ABBREVIATIONS x v i ACKNOWLEDGMENTS x x CHAPTER I. INTRODUCTION 1 1.1. General Introduction 1 1.2. Aim of Work 2 1.3. Homogeneous Hydrogenation of Olefinic Compounds 3 1.4. Asymmetric Hydrogenation 5 1.5. Homogeneous Hydrogenation Using Ruthenium Complexes .. 7 1.6. Thesis Contents 7 CHAPTER II. APPARATUS AND EXPERIMENTAL PROCEDURE 9 2.1. Instrumentation 9 2.2. Gas-Uptake Apparatus 10 2.3. Gas-Uptake Experimental Procedure 12 2.4. Anerobic Spectrophotometry Solution Cells 13 2.5. Procedure for Spectrophotometry Experiments with Anerobic Cells 16 2.6. Hydrogenation of Substrates 17 2.6.1. Low Pressure ••.. 17 2.6.2. Medium Pressure 17 2.6.3. High Pressure 17 2.7. Work Up of Hydrogenation Reactions 21 2.7.1. Determination of Enantiomeric Excesses of the Hydrogenated Substrates 22 - v i -Page 2.8. Materials 23 2.8.1. Gases 23 2.8.2. Solvents 23 2.8.3. Olefinic Substrates 24 2.8.4. Sulphoxide Ligands 24 '2.8.4.1. Dimethyl Sulphoxide 24 2.8.4.2. Methyl Phenyl Sulphoxide 24 2.8.4.3. Methy n-Propyl Sulphoxide 24 2.8.4.4. Enantiomerically Pure Methyl n-Propyl Sulphoxide 25 2.8.4.5. R-(+)-Methyl p-Tolyl Sulphoxide 28 2.8.4.6. (S,R;S,S)-(+)-2-Methylbutyl Methyl Sulphoxide. 31 2.8.4.7. (2R,3R)-(-)-2,3-0-Isopropylidene-2,3-dihyd-roxy-l,4-bis (methyl sulphrnyl)butane'B^O, Dios 33 2.8.4.8. (2R,3R)-(-)-2,3-0-Isopropylidene-2,3-dihyd-roxy-l,4-bis(benzyl sulphinyl)butane"^O, BDios 39 2.8.5. Ruthenium Compounds 40 2.8.5.1. Ruthenium Trichloride Trihydrate 40 2.8.5.2. Methanolic "Blue Ruthenium(II) Solutions" 40 2.8.5.3i. Dimethylammonium Trichlorotris(dimethyl sulphoxide)ruthenate(II) 41 2.8.5.3ii. Dimethylammonium Trichlorotris(d^-dimethyl sulphoxide)ruthenate (II) 41 2.8.5.4. Dimethylammonium Trichlorotris(methyl n-propyl sulphoxide)ruthenate(II) 42 2.8.5.5. Dichlorotetrakis(dimethyl sulphoxide)-ruthenium(II) 42 2.8.5.6. Dibromotetrakis(dimethyl sulphoxide)-ruthenium(II) 43 2.8.5.7. Dichlorobis(methyl phenyl sulphoxide)-ruthenium(II) 43 2.8.5.8. Ruthenium(II) Dichloro-complexes of (S,R;S,S)-(+)-2-Methylbutyl Methyl Sulphoxide 44 - v i i -Page 2.8.5.81.. Ether-Solvated Dichlorobis[(S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide Jruthenium(II). 44 2.8.5.8ii. Dichlorobis[(S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide]ruthenium(II) Trimer 44 2.8.5.9. Dichlorodicarbonylbis[(S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide Jruthenium(II) .. 45 2.8.5.10. Dichlorobis(R-(+)-methyl p-tolyl sulphoxide)-ruthenium(II) Trimer 45 2.8.5.11. Dichlorobis[(2R,3R)-2,3-dihydroxy-l,4-bis(methyl sulphinyl)butane]ruthenium(II) Dihydrate, Dichlorobis(DDios)ruthenium(II) Dihydrate 46 2.8.5.12. Dichloro[(2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(methyl sulphinyl)butane] [(2R,3R)-2,3-dihydroxy-1,4-bis(methyl sulphinyl)butane]ruthenium(II), Dichloro(Dios) (DDios)ruthenium(II) 47 2.8.5.13. Dichloro[(2R,3R)-2,3-dihydroxy-l,4-bis(methyl sulphinyl)butane][dimethyl sulphoxide] [methanoljruthenium(II), Dichloro(DDios)(DMSO) (MeOH)ruthenium(II) 48 CHAPTER III. PROPERTIES AND PREPARATION OF SULPHOXIDE LIGANDS .. 57 3.1. Structure and Bonding 57 3.2. Co-ordination of Sulphoxides 58 3.3. Effect of Co-ordination of Sulphoxide Ligand on v(S0). 59 3.4. Effect of Co-ordination on 1H N.M.R. Chemical Shifts.. 59 3.5. Determination of Stereochemistry at the Sulphur Centre in Sulphoxide Ligands 60 3.6. Preparation of Sulphoxide Ligands 62 3.6.1. Methyl n-Propyl Sulphoxide 63 3.6.2. Enantiomerically Pure Methyl n-Propyl Sulphoxide.. 64 3.6.3. R-(+)-Methyl p-Tolyl Sulphoxide 65 3.6.4. (S,R;S,S)-(+)-2-Methylbutyl Methyl Sulphoxide 66 3.6.5. (2R, 3R) -"(-) -2,3-0- Isopropylidene-2,3-dihydroxy-1,4-bis(methyl sulphinyl)butane, Dios; (2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(benzyl sulphinyl)butane, BDios 67 - v i i i -Page CHAPTER IV. PREPARATIVE ROUTES TO CHLOROSULPHOXIDE COMPLEXES OF RUTHENIUM (II) 71 CHAPTER V. DICHLOROTETRAKIS(DIMETHYL SULPHOXIDE)RUTHENIUM(II), DIMETHYLAMMONIUM TRICHLOROTRIS(DIMETHYL SULPHOXIDE)-RUTHENATE(II) AND RELATED COMPOUNDS 74 5.1. Introduction 74 5.2. [NH2Me2][RuCl3(DMSO)3], 1 and [NH 2Me 2][RuCl 3(d 6-DMSO)3], 2_ 75 5.3. [NH2Me2] [RuCl 3(Me nprSO) 3], 3_ 83 5.4. Dichlorotetrakis (dimethyl sulphoxide)ruthenium(II) , 4_. 88 5.5. Comparison of Different RuCl2(DMSO)4 Products 91 5.6. RuBr2(DMS0)4, 5_ 93 5.7. Reaction of [NH Me2][RuCl3(DMSO)3] and RuCl2(DMS0)4 with Molecular Hydrogen 99 5.8. Catalytic Hydrogenation of Some Olefins with Some Anionic and Neutral Sulphoxide Complexes 107 CHAPTER VI. HOMOGENEOUS HYDROGENATION OF ACRYLAMIDE USING DIMETHYLAMMONIUM TRICHLOROTRIS(DIMETHYL SULPHOXIDE)-RUTHENATE(II) AS CATALYST 110 6.1. Introduction 110 6.2. Determination of the Equilibrium Constant for the DMSO Dissociation from the Complex 110 6.3. Spectral Observations on the RuCl3(DMSO)~ Anion 112 6.4. Catalytic Hydrogenation of Acrylamide 119 6.4.1. Dependence on Dimethyl Sulphoxide Concentration .. 119 6.4.2. Dependence on Acrylamide Concentration 121 6.4.3. Dependence on Hydrogen Pressure 124 6.4.4. Dependence on Catalyst Concentration 124 6.4.5. Dependence on Added Acid 129 6.4.6. Dependence on Added LiCl 129 6.5. Discussion of Kinetic Results 133 6.5.1. Dependence on DMSO Concentration 141 6.5.2. Dependence on Substrate Concentration 142 - i x -Page 6.5.3. Dependence on Hydrogen Concentration 143 6.5.4. Dependence on Catalyst Concentration 144 6.5.5. Dependence on Added Acid 146 6.5.6. Dependence on Added Chloride 147 6.6. The Nature of the Non-Linear Region Reaction Rates ... 147 6.7. Discussion 148 CHAPTER VII. (S,R;S,S)-(+)-2-METHYLBUTYL METHYL SULPHOXIDE COMPLEXES OF RUTHENIUM(II) 150 7.1. Introduction 153 7.2. Ether-Solvated Dichlorobis (MBMSO)ruthenium(II), 7_ 153 7.3. Dichlorobis (MBMSO) ruthenium (I I) Trimer 8_ 156 7.4. The Reaction of [RuCl2(MBMSO)2]3 with Carbon Monoxide 160 CHAPTER VIII. HOMOGENEOUS CATALYTIC HYDROGENATION OF ACRYLAMIDE USING TRIMERIC DICHL0R0[(S,R;S,S)-(+)-2-METHYLBUTYL METHYL SULPHOXIDE]RUTHENIUM(II) 165 8.1. Introduction 165 8.2. The Reaction of [RuCl2(MBMSO)2]3 with Hydrogen 165 8.3. U.V./Visible Spectral Observations on [RuCl2(MBMSO)2J3 166 8.4. Catalytic Hydrogenation of Acrylamide 169 8.4.1. Dependence on Acrylamide 170 8.4.2. Dependence on Hydrogen 179 8.4.3. Dependence on Catalyst Concentration 179 8.4.4. Dependence on Added MBMSO Ligand 180 8.4.5. Dependence on Added Chloride 183 8.4.6. Dependence on Added Acid 183 8.5. Discussion of Kinetic Results 186 8.6. Discussion 194 8.6.1. Comparison of the [RuCl 2(MBMSO^ System with that of [NH2Me2] [RuCl3(DMSO)3] 196 - X -Page CHAPTER IX. ASYMMETRIC HYDROGENATION OF OLEFINIC SUBSTRATES USING DICHLORO[(S,R;S,S)-(+)-2-METHYLBUTYL METHYL SULPHOXIDE]RUTHENIUM(II) COMPLEXES 198 9.1. Introduction , 198 9.2. Asymmetric Hydrogenation Results 198 9.3. Discussion 199 9.3.1. Mechanistic Considerations Based on the Acrylamide Hydrogenation Catalysed by [RuCl2(MBMSO)2]3 202 CHAPTER X. POLYMERIC CHLOROSULPHOXIDE COMPLEXES OF RUTHENIUM(II): TRIMERIC DICHLOROBIS[(R)-(+)-METHYL P-TOLYL SULPHOXIDE]RUTHENIUM(II) AND POLYMERIC DICHLOROBIS-[METHYL PHENYL SULPHOXIDE]RUTHENIUM(II) 207 10.1. Introduction 207 10.2. Trimeric Dichlorobis[(R)-(+)-methyl p-tolyl sulphoxide]ruthenium(II) , 10_ 207 10.3. The Reaction of Compound 10_ with Carbon Monoxide 210 10.4. Catalytic Hydrogenation with Compound 10_ 212 10.5. Polymeric Dichlorobis(methyl phenyl sulphoxide)-ruthenium(II) 213 CHAPTER XI. DICHLORO-DIOS AND DDIOS COMPLEXES OF RUTHENIUM(II).. 215 11.1. Introduction 215 11.2. Dichlorobis(DDios)ruthenium(II) dihydrate, 1_1 216 11.3. Dichlorobis (Dios) (DDios)ruthenium(II), 12_ 219 11.4. Dichloro (DDios) (DMSO) (MeOH)ruthenium(II) , L3_ 222 CHAPTER XII. ASYMMETRIC CATALYTIC HYDROGENATION USING DIOS AND DDIOS DICHLORO-COMPLEXES OF RUTHENIUM(II) 225 12.1. Introduction 225 12.2. Asymmetric Hydrogenation Results 225 12.3. Discussion 228 CHAPTER XIII. GENERAL CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK 231 REFERENCES 235 - xi -List of Tables Number Page 5.1. I.r. spectrum (cm - 1) of [NH2Me2][RuCl3(DMSO)3], 77 1_ and of i t s deuteriated analogue, 2_ 77 5. II. Visible spectra of 1 80 5. III. n.m.r. spectra of 1_ 82 5.IV. Selected i . r . spectral data for 86 [NH 2Me 2][RuCl 3(Me nprS0) 3], 3 86 5.V. *H n.m.r. spectrum of 3_ and MenprS0 87 5.VI. Selected spectral data for RuCl2(DMS0)4 94 5.VII. 1H n.m.r. spectra of RuBr2(DMSO) 96 5. VIII. Spectral.data for hydride derivatives of (I) RuCl 2 (DMSO)' and (II) [NH2Me2][RuCl3(DMSO)3] 105 5.IX. Hydrogenation rates for [NH2Me2][RuCl3(DMS0)3], [NH 2Me 2][RuCl 3(Me nprS0) 3], and RuCl2(DMS0)4 in DMA with acrylamide'substrate 109 6.1. Spectrophotometry data for dissociation of DMSO from the RuCl3(DMS0)3 anion 115 6.II. Equilibrium constants and extinction coefficients for the RuCl3(DMS0)3 anion system 116 6. III. Linear hydrogenation rates for the reduction of acryla--mide in DMA at 60° using [NH2Me2][RuCl3(DMS0)3] 121 7.1. Spectral data for carbonyl derivatives of [RuCl 2 (MBMSO) ] 161 8.1. Linear hydrogenation rates for the reduction of acrylamide using [RuCl2(MBMSO) ] in DMA at 70°C 177 8. II. Values of Kj^K3k4 and K^k^ for the hydrogenation of acrylamide using [RuCl2(MBMSO) ] in DMA at 70°C 191 9.1. Results of asymmetric hydrogenation in DMA 201 - x i i -Number Page 10.I. I.r. spectral data for carbonyl derivatives of [RuCl 2(MPTSO) 2] 3 211 12.1. Asymmetric hydrogenation results with Dios/DDios ruthenium(II) catalysts 227 - x i i i -List of Figures Figure Page 2.1. Constant pressure gas-uptake apparatus 11 2.2. Anerobic spectral c e l l 14 2.3. Gas-uptake spectral c e l l 15 2.4. Vortex gas reaction apparatus 18 2.5. Vortex reaction bottle 19 2.6. Parr gas reaction bomb 20 2.7. n.m.r. spectra of some sulphoxide ligands 50 2.8. "^H n.m.r. spectra of some DMSO complexes of Ru(II) .... 52 2.9. *H n.m.r. spectra of some sulphoxide complexes of Ru(II) 54 2.10. *H n.m.r. spectra of some sulphoxide complexes of Ru(II) 56 3.1. Structure of DMSO 57 3.2. Resonance structures of sulphoxides 58 1 R 3.3. H n.m.r. spectrum of MBMSO with added Kiralshift 61 3.4. Synthetic scheme for Dios and BDios 68 5.1. ORTEP drawing for [NH2Me2] [RuC 13(DMSO)3], 1_ 84 5.2. ORTEP drawing for RuC 12(DMSO)^, 4 92 5.3. n.m.r. spectra of some hydride derivatives of [NH2Me2][RuCl3(DMS0)3] and RuC12(DMSO) 102 5.4. *H n.m.r. spectra of some hydride derivatives of [NH2Me2][RuC13(DMSO)3] and RuCl2(DMS0)4 104 6.1. U.V./visible spectral changes of [NH Me ][RuCl (DMSO) ], 1_ in DMA at 60°C .... 7. I l l 6.2. Effect of added DMSO on the spectrum of 1_ in DMA at 60°C 112 - xiv -Figure Page 6.3. Effect of added acryl and H on the spectrum of 1_ in DMA at 60°C 118 6.4. H uptake plots for the reduction of acryl using 1_ in DMA at 60°C 120 6.5. Dependence of linear rate on added DMSO 123 6.6. Plot of (linear rate)" 1 vs. added [DMSO] 123 6.7. Dependence of linear rate on [acryl] 125 6.8. Plot of (linear rate) 1 vs. [acryl] 1 126 6.9. Dependence of linear rate on [U^] 127 6.10. Plot of (linear r a t e ) - 1 vs. [ r ^ ] - 1 127 6.11. Dependence of linear rate on [f^] 128 6.12. Dependence of linear rate on [ R u 1 1 ] T 130 6.13. Plot of (linear rate) 1 vs. [Ru 1 1]^ 1 131 6.14. Plot of (linear rate) 1 vs. [Ru 1 1]^, 1 131 6.15. Dependence of linear rate on added p-toluene-sulphonic acid 132 7.1. Possible structures of [RuC12(MBMSO)2]3 159 7.2. Possible structure of RuC12(CO)2(MBMSO)2 162 8.1. U.V./visible spectral changes of [RuCl„(MBMSO) ] , 8 in DMA at 70°C 7 7.7 167 8.2. Effect of added acryl on the spectrum of 8_ in DMA at 70°C 168 8.3. Effect of added acryl and H_ on the spectrum of 8_ in DMA at 70°C 7 170 8.4. H 2 uptake plots for the reduction of acryl 172 8.5. Dependence of linear rate on [acryl] 174 - XV -Figure Page 8.6. Dependence of linear rate on [acryl] with added MBMSO 175 8.7. Dependence of linear rate on [acryl] with added proton sponge ^  176 8.8. Dependence of total linear rate on [H^ ] 180 8.9. Depencence of linear rate on [H^] with added proton sponge R 180 8.10. Dependence of total linear rate on [Ru 1 1]^ 181 8.11. Dependence of total linear rate on [Ru 1 1],^ 181 8.12. Dependence of linear rate on [Ru 1 1]^ with added proton sponge ^  182 II H 8.13. Dependence of linear rate on [Ru ]^,d with added proton sponge ^  182 8.14. Dependence of total linear rate on [MBMSO] 184 8.15. Dependence of (total linear r a t e ) " 1 on [MBMSO] 184 8.16. Dependence of (total linear r a t e ) " 1 on [MBMSO] 185 9.1. Prochiral olefin substrates and their hydrogenation products 200 - xvi -ABBREVIATIONS The following l i s t of abbreviations, most of which are commonly adopted in chemical research literature, w i l l be employed in this thesis. A l l temperatures are in °C. A absorbance Acryl acrylamide, CH2=CHCONH2 atm atmosphere BDios (2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(benzyl sulphinyl)butane as a mixture of three diastereomers Me Me H - C h ^ S O C r ^ O 0 - - ^ - C H 2 S O C H 2 ( J ) H bipy 2,2'-bipyridine B.P. boiling point Bu Butyl DDios (2R,3R)-2,3-dihydroxy-l,4-bis (methyl sulphinyl)butane as a mixture of three diasteromers H H O - j — - C H 2 S O C H 3 H0-^J^CH 2 S0CH 3 H - X V I I -(2S,3S)-(+)-2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis (diphenyl-phosphino)butane M e . / H 0 J 0-H -CH2F<t)2 •C^P<|)2 (2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy -1,4-bis-(methyl sulphinyl)butane as a mixture of three diastereomers Me Me H i H CH 2S0CH 3 CH 2S0CH 3 HC0N(CH3)2 (CH3)2SO N,N' dimethylacetamide CH3C0N(CH3)2 N,N* dimethylacetamide hydrochloride CH3C0N(CH3)2-HC1 N,N' dimethylformamide dimethyl sulphoxide sodium 2,2-dimethyl-2-silapentone-5-sulphonate enantiomeric excess equation ethyl figure hour infrared - x v i i i -L M MBMSO Me MenprS0 Men m.p. MPSO MPTSO M.W. T nD nm N.M.R. ol O.R.D. P P Ph PPh3 ppm R R.T. S s or sec ligand molar or metal atom (S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide CH3CH2CH(CH3)CH2S(0)CH3 CH (CH 2) 2S(0)CH 3 CH 3S(0)C 6H 5 C 7H yS(0)CH 3 methyl methyl n-propyl sulphoxide (-)-menthol melting point methyl phenyl sulphoxide R-(+)-methyl p-tolyl sulphoxide molecular weight refractive index measured at the sodium D line nanometer (10 meter) = 1 millimicron (my) nuclear magnetic resonance olefin optical rotary dispersion phosphine pressure phenyl triphenylphosphine parts per million alkyl or aryl group or Rate room temperature sulphoxide second - xix -T t TMS Tosyl U.V. Vis vpc X [a] A T 6 D ^eff v • corr XM temperature time tetramethylsilane C 7H 7 S0 2 -ultraviolet v i s i b l e vapor phase chromatography halogen specific rotation measured at the sodium D line 2 -1 -1 molar conductance, cm ohm mol chemical shift, ppm molar extinction coefficient wavelength corrected magnetic moment in Bohr Magnetrons, B.M. frequency, cm 1 phenyl corrected molar susceptibility - XX -ACKNOWLEDGMENTS I wish to thank Dr. B.R. James for his expert guidance and continual encouragement throughout the course of this work. I would also like to express my gratitude to a l l those faculty members who have helped to guide my thoughts and provide experimental help. In addition, my thanks to a l l technical support staff in this department. I gratefully acknowledge financial support from the National Research Council of Canada., - 1 -CHAPTER I INTRODUCTION 1.1. General Introduction Historically the f i r s t report of catalytic homogeneous hydro-genation of an organic substrate, that of benzoquinone in the presence of quinoline solutions of cupric acetate, occurred in 1938*. Since this time many homogeneous catalytic systems have been studied and their mechanisms deduced. Maintained interest in homogeneous catalysts generally arises from their spe c i f i c i t y towards reduction of particular substrates, (ie., high selectivity), their a b i l i t y to function under generally mild reaction conditions, their ease of study, and their industrial applicability. Indeed some industrially-used processes include 2 3 4 the Wacker process , the Oxo process , some Ziegler-Natta systems , and methanol carbonylation^. asymmetric synthesis. Use of catalytic complexes containing chiral ligands, (especially phosphines), can lead to induced optical activity in 6-8 the saturated product, for example ; Since 1970, interest in catalytic hydrogenation has spread to * R]LR2C=CH2 + H 2 RjR2CH-CHg * R1R2C=0 • H 2 - 2 -In addition, reports by Pino et a l . on asymmetric hydroformylation have recently appeared. A comprehensive summary of this rapidly expanding f i e l d of homogeneous hydrogenation, complete upto and including 1972, has recently been published in a text by James*^. 1.2. Aim of Work 11 12 Earlier studies in this laboratory and elsewhere had shown the f e a s i b i l i t y of synthesizing DMSO complexes of Ru(II). In view of the known a b i l i t y of many Ru(II) complexes to activate molecular (including 13 14 complexes with simple halide ligands , phosphine and arsine ligands , and nitrogen ligands*''), and the vast range of metal complexes that have been reported to catalytically hydrogenate, there seemed a good po s s i b i l i t y that sulphoxide complexes could be "made" to activate K^ . Sulphoxide ligands have special interest in that bonding may occur via sulphur or oxygen, and also, since they are pyramidal, sulphoxides of the type R-^S^ w i l l exhibit c h i r a l i t y at the sulphur. This suggested the p o s s i b i l i t y of catalytic asymmetric hydrogenation using Ru(II) complexes containing chiral sulphoxide ligands. Catalytic synthesis using chiral sulphoxide ligand systems had not been reported prior to the studies described in this thesis. The aim of the work then was to develop syntheses of Ru(II) complexes containing sulphoxides and test them as catalysts for hydrogen-ation; development of the synthesis of the ligands themselves, especially i f c h i r a l , was also envisaged. In view of the importance of asymmetric - 3 -and non-asymmetric homogeneous hydrogenation to this thesis, a short discussion of these two aspects of catalysis i s included below. 1.3. Homogeneous Hydrogenation of Olefinic Compounds It i s generally believed that hydrogenation of olefins requires prior, activation by co-ordination of both the hydrogen and olefin molecules 1^. Hydrogen activation i s thought to occur in three ways1^ ^ depending on the metal complex employed. 20 An overall heterolytic cleavage, reaction (1,1) * involves R u n i C l 6 " 3 + H 2 5 = ? Ru I I IHCl 5" 3 + H + + C l " (1,1) substitution of a hydride ligand, and is aided by the loss of H + andHCl, 15 and thus by addition of a base . Co-ordination of an olefin to this hydride may result in subsequent insertion of the olefin into the Ru-hydride bond to give a Ru-alkyl complex. A Ru(II) example of this has 21 been described for hydrogenation of some unsaturated ol e f i n i c acids. The reaction i s : » V *K / HN / I C : X- N C Ru-|| — > Ru ;| > Ru-C' (1,2) C "^C— -/ A 1 Electrophilic attack by a proton at the carbon attached to the metal 22 (protonolysis) results in the saturated product and can regenerate the Ru(II) catalyst. - 4 -Homolytic splitting of hydrogen by a metal complex results in the co-ordination number and oxidation state of the metal increasing by one1*'. An example of such a process is shown by aqueous solutions of [Co(CN) 5]" 3 2 3 : 2[Co(CN) 5]" 3 + H 2 2[HCo(CN) 5]" 3 (1,3) For this case, an alkyl complex formed by olefin insertion reacts with another hydride species to yield the saturated product: [(CN) 5Co-alkyl]" 3 + [HCo(CN) 5]" 3—* 2[Co(CN) 5]" 3 + saturated (1,4) product The third method of hydrogen activation is oxidative addition of H 2 to the metal, resulting in an increase in oxidation state and co-ordination number by two. Ruthenium(I) chloride complexes in DMA 24 activate hydrogen this way, a so-called hydride path : Ru 1 + H 2 ^ R u I I I h 2 t 1 ' 5 ^ A co-ordinated olefin may be reduced by consecutive transfer of two hydride ligands to i n i t i a l l y form a a-alkyl hydride intermediate and then the saturated product: H 2 R u i n o l e f i n —> HRu I I ]"alkyl —> Ru1 + saturated product (1,6) - 5 -A better documented system reacting by the hydride route is that involving 25 RhCl(PPh 3). The same systems may also activate olefin and H 2 by oxidative addition to a previously formed olefin complex, the so-called unsaturate path: I The remaining steps to saturated product are as for the hydride path of the type shown in eqn. (1,6). 1.4. Asymmetric Hydrogenation The interest in this area of hydrogenation stems from the desire to synthesize c h i r a l l y pure products especially some naturally occurring ones, eg., amino acids, from their precursor olefins. The predominance of work in this area has been with Rh(I) phosphine systems as catalysts which Knowles et a l . ^ have u t i l i z e d with remarkable success to produce ct-amino acids in a high state of optical purity. Very recently a compre-hensive review on asymmetric homogeneous hydrogenation in general, and one dealing specifically with chiral rhodium-phosphine catalysts, have . ... , ,26,27 been published Only a l i t t l e work in this area has been done with ruthenium complexes. Apparently the f i r s t asymmetric hydrogenation with a chiral 7 ruthenium catalyst was that reported by Hirai and Furuta using an in situ generated ruthenium(III) complex of poly-L-methylethylenimine. They Rh C1P 2(olefin) + P (1,7) Rh C1P2 (olefin) + H 2 ^ H^h C1P2 (olefin) (1,8) - 6 -reduced methylacetoacetate to methyl-3-hydroxybutyrates with an enantiomeric enhancement of about 5%. A Ru(II)-(+)-diop complex, 28 [Ru 2Cl 4(diop)^] has been reported to catalyse the hydrogenation of a-acetamidoacrylic acid to N-acetylalamine with a product of optical purity = 60%. L i t t l e i s known about the actual stereoselective hydrogenation 29 process. Pino et a l . have postulated f a i r l y detailed mechanisms for some asymmetric hydroformylation reactions, but they admit that the mechanism of asymmetric induction is only speculation. Some of the factors which are thought to influence asymmetric induction are; interaction between substrate and chiral transition metal atoms, the face of the olefin attacked by hydrogen, and the choice of carbon atom i n i t i a l l y attacked (Markownikoff or anti-Markownikoff addition). The size of co-ordinated ligands, the presence of groups on these ligands capable of H-bonding (for example, -OCH^), the nature of the functional groups on the substrate, temperature and pressure a l l play a role in influencing asymmetric induction. Thermodynamic equilibria governing the reaction intermediates formed and activation energies in the reaction steps \ influence the eventual product distribution. Greater effort is required to c l a r i f y the relative influence of the thermodynamic and kinetic effects as well as the effect of steric structure of the catalytic complex before the origin of asymmetric induction can be completely determined. - 7 -1.5. Homogeneous Hydrogenation Using Ruthenium Complexes Reports on homogeneous hydrogenation of ole f i n i c substrates using ruthenium complexes began appearing in 1961 with studies of 30 31 ruthenium(II) chloride complexes in aqueous acid solutions ' . These solutions were found to catalytically hydrogenate some substituted ethylenes such as maleic, fumaric, and acrylic acids, (see Section 1.3.). More recently, systems involving triphenylphosphine complexes of Ru(II), have been investigated thoroughly, in particular using RuCl 2(PPh) 3 and 32 RuClH(PPh 3) 2 . Extension of this work toward asymmetric hydrogenation 28 by using chiral phosphines has also been accomplished in this laboratory , (see Section 1.4.). Other ruthenium systems capable of activating H 2 for hydrogenation have been reviewed in some d e t a i l 1 ^ . The premier Ru(II) complex containing co-ordinated DMSO ligand to be used as a homogeneous hydrogenation catalyst was reported by Ogata et a l . in 1970*53. The complex, formulated as C 6H 6RuCl 2 (DMSO), catalysed the hydrogenation of maleic acid at 25°C and 20 atm H 2 > In 1971 the DMSO complexes, RuX2(DMS0)4, (X = Cl , Br), were reported 1 1; however, these compounds were found to be inactive towards the reduction of ol e f i n i c substrates in DMSO and other solvents under the conditions employed. 1.6. Thesis Contents A new preparative route was developed for the RuX2(DMS0)4> (X = Cl, Br), compounds and this led to isolation of a new complex, [NH2Me2][RuCl3(DMS0)3]. Both chloro-compounds were found to catal y t i c a l l y - 8 -hydrogenate activated olefins under mild conditions in DMA. Chapters IV, V and VI describe the preparative routes, the compounds and their characterization, and the kinetics of hydrogenation, respectively. In order to develop further Ru(II) hydrogenation catalysts and to extend this work to asymmetric hydrogenation, new sulphoxides were synthesized; this aspect i s described in Chapter III. New Ru(II) compounds made with these new sulphoxides are described in Chapters VII, X, and XI, while hydrogenation kinetics for one such catalyst system appears in Chapter VIII. Asymmetric hydrogenation studies using some of the catalysts with chiral sulphoxides are presented in Chapters IX and XII. General conclusions and thoughts on possible extension of the work presented in this thesis occupy Chapter XIII. - 9 -CHAPTER II APPARATUS AND EXPERIMENTAL PROCEDURE 2.1. Instrumentation Infrared spectra were recorded on a Perkin Elmer 225 or 457 spectrophotometer, as nujol or hexachlorobutadiene mulls between Csl plates. Solution spectra were obtained in CCl^ solvent in NaCl or polyethylene c e l l s . N.M.R. spectra were recorded on a Varian T60 or XL100 spectrometer in CC14, CDC13, or D20 solvent at 35°C with Tetramethylsilane or sodium 2,2-dimethyl-2-silapentone-5-sulphonate as reference. Ultra violet and visible spectra were obtained on either a Perkin Elmer 202 or Cary14 spectrophotometer, with 1 mm or 1 cm path length quartz or glass c e l l s . Both spectrophotometers could be f i t t e d with thermostated c e l l holders. Magnetic moments were determined by the Gouy or Faraday method, at 22°C. Molecular weights were determined by freezing point depression. High pressure liquid chromatographic separations were effected on a Waters Associates ALC 202 equipped with a differential U.V. detector and Corasil II, Carbowax and Cellulose columns. My thanks to Dr. J. Kutney for the use of this machine. Optical rotation data were collected on a Perkin Elmer 421 polari-meter at room temperature using a one decimeter microcell with a volume of 0.5 ml. - 10 -Conductivity data were obtained at room temperature with a dip type conductivity c e l l connected to a Thomas Serfass conductivity bridge. For air sensitive solutions Ar gas was used to blanket the c e l l . Melting points were recorded using a Fisher-Johns or Gallenkempt apparatus, and are uncorrected. Gas chromatographic analysis was conducted on a Perkin Elmer 900 with a flame ionization detector and a Chromosorb 103 column or a Bechman GC-2A unit with a thermal conductivity detector and a Poropak V/, Carbowax 1000, or Chromosorb 103 column. 2.2. Gas-Uptake Apparatus The constant pressure apparatus, (fig. 2.1), was used for kinetic and for stoichiometric experiments. A flexible glass spiral tube connected a capillary monometer D at tap C to a pyrex two necked reaction flask equipped with a dropping side arm bucket. The reaction flask was thermostated in an o i l bath and shaken by means of a piston-rod and driven by an offset wheel connected to a Welch variable speed electric motor. The manometer D contained n-butylpthalate and was connected to a gas measuring burette consisting of a mercury reservoir E and a 10 ml pipette of known diameter. The gas burette was connected via an Edwards high vacuum metering valve, M, to the gas-handling part of the apparatus. This part consisted of a mercury manometer F, gas inlet Y, and vacuum pump G. The capillary manometer and gas burette were thermostated @25°C in a perspex water bath. Thermostating of the o i l bath and water bath was controlled by Figure 2.1. Constant pressure gas-uptake apparatus - 12 -Jumo thermo-regulators.and Merc to Merc relay control c i r c u i t s , with heating accomplished by a 40 watt elongated light bulb. The baths were well stirred, and the o i l bath insulated. The temperature was held to ±0.05°C. A vertical mounted cathetometer followed the gas uptake in the burette, and time was recorded with a Labchron 1400 timer. 2.3. Gas-Uptake Experimental Procedure In a typical gas-uptake experiment 5 ml of solvent was placed in the 25 ml reaction flask. Weighed substrates were added to the solvent directly and weighed catalyst via the bucket after the solvent was degassed and the flask f i l l e d with reactant gas. Degassing for DMA solvent was effected by pumping on the solvent while shaking. For higher vapour pressure solvents the freeze thaw under static vacuum technique was employed. For both methods a degas-refill cycle was repeated three times. I n i t i a l l y the reaction flask was f i l l e d with reactant gas at a pressure somewhat less than that required for the experiment, at 0, (fig. 2.1.). The taps C and D were then closed and the reaction flask complete with spiral disconnected from 0 and attached to H and the shaker rod. The whole system up to tap C was then pumped down with taps H, K, L, J and M open. Reactant gas was admitted to this part of the system at a pressure greater than that in the reaction flask but less than that desired for the reaction. After thermal equilibration of the reaction flask was attained (=15 min.) tap C was opened and the pressure of the whole system adjusted to the desired reaction pressure by introduction of gas through Y . - 13 -Shaking of the reaction vessel was then done to saturate the solvent with gas at the reaction pressure (=5 min.)- An experimental run was then started by dropping the catalyst bucket, starting the shaker, closing taps K and L and starting the timer. Gas-uptake was indicated by a difference in o i l levels in manometer D. The manometer was balanced by admitting gas into the burette through the metering valve M. Corresponding changes in mercury levels in the pipette N were translated to volume changes of gas reacted, per unit time. Diffusion control of the reactions was eliminated by using fast shaking rates and a large indented reaction flask. 2.4. Anerobic Spectrophotometry Solution Cells Two types of anerobic c e l l were employed for recording U.V. and visible spectra of air sensitive solutions or of solutions undergoing anerobic gas reactions. Fig. 2.2 shows one type of c e l l . A solid compound was put in the L tube and a solvent in the c e l l and the two mixed under the appropriate anerobic conditions. The quartz c e l l had a 1 cm path length. Fig. 2.3 shows an anerobic c e l l designed to f a c i l i t a t e the recording of the simultaneous gas uptake and U.V., visible spectra of a solution. A solid was added to the stirred solvent by means of the side arm bucket. The s t i r r e r was driven by a magnetic s t i r r e r held directly above the c e l l . The circulation time of the solution through the c e l l window was less than ten seconds. The c e l l window was pyrex of approximately 2 mm path length. The solution as well as the gas above the solution was thermostatable. The gas-- 14 -7 mm O-ring joint \ f— B 7 socket Teflon high vacuum stopcock Quartz cell Figure 2.2. Anerobic spectral c e l l - 1 5 -Glass encapsulated magnet B 3 4 cone 8 socket B 10 socket . B 19 cone S socket Bucket Water jacket Teflon disc Stirrer blade Glass cell 2 X 1.5 X 0.2cm Figure 2.3. Gas-uptake spectral c e l l - 16 -uptake was recorded with a gas burette similar to that described previously. 2.5. Procedure for Spectrophotometry Experiments with Anerobic Cells 2.5.1. Simple Anerobic Solution Cell With the c e l l shown in f i g . 2.2 , kinetic and equilibrium experiments were conducted. In a typical experiment a sample of solid was weighed into the L tube. The solvent (DMA, 4 ml) and any substrate were placed in the c e l l , which was assembled with a DMA resistant Viton O-ring and O-ring clamp. The c e l l was evacuated and f i l l e d with argon or hydrogen three times. The c e l l and i t s contents were allowed to temperature equilibrate and a base line spectrum recorded. The solid and solution were then quickly mixed and spectra run. 2.5.2. Gas-Uptake Spectrophotometric Cell With the gas-uptake spectrophotometer c e l l , the procedure was similar to above for the c e l l . A sample of solid was weighed into the glass bucket and the c e l l assembled with the solvent and any substrate in the c e l l . The s t i r r e r was operated while degassing and f i l l i n g with gas was done. The pressure of gas at the last f i l l was set to approximately 5 cm x below the desired reaction pressure. The solution was then temperature equilibrated, with s t i r r i n g , the pressure in the c e l l and gas burette set to reaction pressure and^a base line spectrum run. The bucket was then dropped, the gas burette taps K and L closed and the timer started. Sepctra with corresponding gas-uptakes were then recorded with time; gas-uptakes as described previously with a gas-uptake experiment. - 17 -2.6. Hydrogenation of Substrates 2.6.1. Low Pressure For pressure up to 1 atm., reactions were carried out using the same apparatus and in the same way as described for kinetic gas-uptake experiments. 2.6.2. Medium Pressure Reactions using between 1 to 4 atms. were carried out using a Vortex Hydrogenation apparatus, (fig. 2.4.). A 5 ml solution of catalyst (0.025 M) and substrate (1 M), in degassed DMA, was placed in a glass thimble (15 mm x 80 mm), with a teflon coated spin bar, under an Ar blanket. The apparatus was then assembled as per diagram 2.5. The reaction bottle and thimble were evacuated, flushed with hydrogen three times and f i n a l l y f i l l e d to the approximate desired pressure with hydrogen. The reaction vessel was then heated, and stirred, and the reaction pressure and temperature recorded when temperature equilibrium was attained (=0.5 hr). Reactions were allowed to continue for four to ten days. \ 2.6.3. High Pressure Reactions at between 80 and 145 atms. were carried out in a stainless steel Parr high pressure (3000 psi) reaction bomb, f i g . 2.6".). 5 ml solutions analogous to those used for the medium pressure reactions were placed in a 35 mm x 110 mm glass sleeve under an Ar blanket. The glass sleeve with spin bar was placed into the bomb and the bomb assembled. The reaction bomb was f i l l e d directly from a high pressure hydrogen cylinder and the gas - 18 -Medium pressure copper Medium pressure wire weave Evacuation Line Figure 2.4. Vortex gas reaction apparatus - 19 -Wire weave encased rubber aircraft tubing Snap connector equipped pressure valve Rubber bung Stainless steel tube Inlet 500ml glass reaction bottle Rubber bung Glass reaction thimble Solution with stir bar Figure ,2.5. Vortex gas reaction bottle - 20 -0 - 3 0 0 0 psi gauge Gas inlet line Valve Sealing bolts Teflon seal Collar Stainless steel bomb • Glass sleeve 6. Parr gas reaction bomb - 21 -bled off. This was repeated once and the bomb f i l l e d . Gas was then bled off to the desired pressure and the reaction solution stirred by a st i r r e r hot plate. Pressure and temperature were recorded when thermal equilibration was attained. Reactions were continued for five to ten days. 2.7. Work Up of Hydrogenation Reactions Low, medium, and high pressure reactions were a l l worked up in the same way, with variation in technique depending on the substrate involved. A l l reaction solutions were pumped to dryness at 0.2 mm pressure and 40°C to leave a gummy residue. If metal was present this was f i l t e r e d off f i r s t through c e l i t e . The gummy residue was then worked up as follows: a) Acrylamide substrate; white crystals of propanamide sublimed out of the residue at 0.2 mm and 100°C. b) Itaconic acid, atropic acid, and a-and 3-methylcinnamic acid; the residue was dissolved in 25 ml of 10% NaOH solution and f i l t e r e d through c e l i t e . The f i l t r a t e was extracted with chloroform (5 x 25 ml) to remove sulphoxide, and catalyst and then made just acidic with 10% HCT. The products, a-methysuccinic acid, 2-phenylpropanoic acid, 2-methyl-3-phenyl propanoic acid, and 3-phenyl butanoic acid, respectively, and unreacted substrate were then extracted from the aqueous phase with diethyl ether (5 x 25 ml) and dried over MgSO^ . Reduction in volume of ether yielded the product and substrate. c) 2-acetamidoacrylic acid; the residue was dissolved in 25 ml of water, f i l t e r e d , and extracted with chloroform as with previous substrates. Removal of the water l e f t a brown o i l which on addition of 15 ml of diethyl - 22 -ether and cooling gave white microcrystals of N-acetylalanine and unreacted substrate. The above product and substrate mixtures were used without further purification for *H n.m.r. determination of % product purity and optical rotation in the appropriate solvents. Optical rotations of N-acetylalanine, and a-methylsuccinic acid, were measured in H^O and 95% EtOH respectively. For *H n.m.r. spectra CDCl^ was used in every case, except for the acetoamido-acrylic/acetylalanine system when D^ O was used. 2.7.1. Determination of the Enantiomeric Excesses of the Hydrogenated Substrates The enantiomeric excesses of the hydrogenated substrates were deter-mined by two methods. Comparison of the specific rotation of the hydrogenated substrate samples with that for the pure chiral substrate gives the enantiomer excess, where; T lOOctJ Specific rotation = [a]^ = — T and [alp is the optical rotation of the sample at the NaD line at temperature T, I is the path length in decimeters and c is the concentration in grams/100 ml solvent. T Enantiomer Excess = e.e. = [a]^ of substrate sample x 100% _ [a]^ of the pure chiral substrate Use of the chiral shift reagent Kiralshift ^-E7, in CCl^, with the hydrogenated substrate samples gave *H n.m.r. spectra with resolved peaks for the enantiomers. For acid substrate samples that were insoluble in CO., the - 23 -methyl esters were made and their spectra with shift reagent recorded. Integration of peak areas for each enantiomer gave the amount of each enantiomer present. From this information the enantiomeric purity was calculated. Enantiomeric Purity = ~ =—f x 100% (F+ + r-J where F+ and F- are the mole fractions of each enantiomer with F+ in excess. In conjunction with the specific rotation of the hydrogenated substrate sample, the stereoisomeric configuration of the excess enantiomer could be assigned. 2.8. Materials 2.8.1. Gases Prepurified hydrogen and CP grade carbon monoxide were obtained from the Matheson Gas Co., while purified nitrogen and argon were from the Canadian Liquid Air Ltd. For kinetic experiments the hydrogen was passed through a Deoxo Hydrogen Purifier. 2.8.2. Solvents Spectral grade or analytical grade solvents were supplied by MCB, Mallinckrodt, Eastman or Fisher Chemical Co.'s and used without further p u r i f i -cation. DMA was supplied by Fisher Chemical Co., and was refluxed over calcium hydride, vacuum d i s t i l l e d and stored under nitrogen before use in kinetic experiments. - 24 -2.8.3. Olefinic Substrates Olefinic substrates were obtained as CP grade reagents. Acrylamide and 1-hexene were supplied by K § K Laboratories Inc., itaconic acid by Eastman Chemical Co., ct-methylcinnamic acid, and methylvinyl ketone by Aldrich Chemical Co., and 2-acetamidoacrylic acid by Fluka Chemical Co. These substrates were used without further purification. 2.8.4. Sulphoxide Ligands 2.8.4.1. Dimethyl Sulphoxide This liquid was supplied by Continental Bio-Systems Ltd., as analytical grade, and was used as such for a l l experiments. 2.8.4.2. Methyl Phenyl Sulphoxide This liquid was used as supplied by K ^  K Laboratories. 2.8.4.3. Methyl n-Propyl Sulphoxide, I 2.8.4.3i. Methyl n-Propyl Sulphide 5 4, II 1.025 mole of NaOH was dissolved in 250 ml of water in a 1 1. three-necked flask equipped with a dropping funnel, reflux condenser, teflon gland and motor-driven s t i r r e r . 1 mole (76.2 g, 90.7 ml) of n-propyl mercaptan was added slowly to the vigorously stirred basic solution. When a l l the mercaptan had reacted 1 mole of methyl iodide (62.25 ml) was added as fast as the resulting exothermic reaction would allow. As the methyl iodide was being added the product sulphide formed a layer on top of the basic solution. On completion of the addition, the stirred reaction mixture was refluxed, by - 25 -external heating for three hours^. The product was then steam d i s t i l l e d from the reaction mixture, washed with 3 x 100 ml portions of water, 3 x 100 ml of 10% NaOH (aq) and 100 ml of H,,0 and dried over calcium chloride. D i s t i l l a t i o n from a helix f i l l e d fractionating column yielded 85 g (95%) of pure sulphide. 6TMS l 3 0 - 9 8 ( t r iP l e t> 3 H> ~ C H3)> 1 > 2 5 " 1 , 8 0 (multiplet, 2H, -CH2~), 2.0 (singlet, 3H, CRj-S), 2.39 (tr i p l e t , 2H, S-CH2-). 2.8.4.3ii. Methyl n-Propyl Sulphoxide 0.92 mole (83.1 g) of the sulphide, II_, 150 ml of acetone and 104 g of 30% H 20 2 were allowed to react in a 500 ml R.B. flask, at 5°C for one hour, and let stand overnight at R.T. The solvent was removed at reduced pressure and the remaining liquid dried over BaO and vacuum d i s t i l l e d (b.p. = 47°C @0.2 mm) to give a colorless liquid, 91 g,(93%). 5 T M g 3 1.10 (t r i p l e t , 3H, CH3-), 1.45 - 2.00 (multiplet, 2H, -CH2-), 2.60 (tr i p l e t , 2H, -CH -S), 2.50 (singlet, 3H, S-CHJ. v n e a t 1050 cm"1 (S=0). ^ 6 3 max v 2.8.4.4. Enantiomerically Pure Methyl n-Propyl Sulphoxide 35 2.8.4.4i. Methanesulphinyl Chloride , III 0.5 mole of methyl lithium (Alfa) in ether was transferred under nitrogen to a 1 1. three-necked flask equipped with a teflon gland, mechanical sti r r e r , calcium chloride drying tube and a gas-inlet tube, and contained in a dry ice bath. 25 ml (=35 g, 0.55 mole) of S0 2 was condensed in a trap with a dry ice-acetone bath. After cooling the methyl lithium solution to approximately -70°C the liquid S0 2 was allowed to warm up slowly and introduced ^ A vapour tight s t i r r e r gland is required here to prevent loss of sulphide vapour. - 26 -as S0 2 gas above the methyl lithium solution in a nitrogen stream. A white solid, lithium methanesulphinate, formed immediately. After a l l the SC^ was added through the inlet tube, s t i r r i n g was continued for 0.5 hour. With nitrogen flushing, 300 g (2.5 moles) of thionyl chloride was added to the reaction mixture maintained at -15° to -20°C. The mixture changed from white to yellow during this addition, as the sulphinate reacted to give methane-sulphinyl chloride and LiCl precipitated. After the addition was completed the mixture was allowed to warm up to room temperature, and s t i r r i n g continued for four hours. The LiCl was fi l t e r e d off under nitrogen and washed with benzene. The solvent, ether and benzene and thionyl chloride, in the f i l t r a t e were removed at reduced pressure (flash evaporator, =50 mm) at 30°C u n t i l infrared absorption of the residue at 1225 cm * (SOC^) was very weak compared to absorption at 1150 cm 1 (CH^SO^l). The d i s t i l l a t e was light yellow in colour due to methanesulphinyl chloride which does c o - d i s t i l l with the solvent to a small extent^. The yield of sulphinyl chloride was 33.5 g (67%) and was used as such in the next step. 35 2.8.4.4ii. (-)Menthyl Methanesulphinate , IV 51.6 g (0.33 mole) of (-)menthol (Aldrich) 95% optically pure in 60 ml of anhydrous pyridine was added dropwise to a nitrogen flushed solution of 33 g (0.33 mole) of methanesulphinyl chloride, III, in 150 ml of ether cooled to -75°C. (Dry Ice - acetone bath). The addition was slow enough to Lower pressure and higher temperature leads to greater c o - d i s t i l l a t i o n . - 27 -maintain the temperature of the solution below -70°C. During addition pyridinium hydrochloride precipitated. Stirring was continued for 3 hours after addition was finished as the reaction mixture was allowed to warm up slowly. The pyridinium hydrochloride was dissolved by adding 250 ml of water and the ether layer was washed with water (1 x 150 ml), 1% aqueous hydrochloric acid until the washings were acidic, aqueous sodium bicarbonate (saturated solution) un t i l the washings were neutral, and f i n a l l y with water (1 x 150 ml). The ethereal solution was dried over anhydrous sodium sulphate and the ether removed at reduced pressure at room temperature. The yield of crude menthyl methanesulphinate was 53.5 g (69%). The ester was a viscous yellow orange liquid. •zc 2.8.4.4iii. Stereochemical Calibration The crude ester was stereochemically calibrated by the formation of methyl p-tolyl sulphoxide. A solution of 2.5 g (0.012 moles) of methyl methan-sulphinate in 20 ml of anhydrous ether was added to the Grignard reagent, p-tolyl magnesium bromide, so that vigorous refluxing occurred. The Grignard reagent was prepared from 5.15 g (0.30 mole) of p-bromotoluene (Eastman), 2.16 g (0.090 mole) of magnesium shavings and 11.3 g (0.60 mole) of 1,2 dibromoethane. It was found necessary to use an entraining agent to activate the magnesium . Addition of the Grignard reagent to the menthyl methanesul-phinate caused the reaction mixture to become cloudy. After s t i r r i n g for 5 minutes, the reaction mixture was hydrolyzed with saturated aqueous ammonium chloride. The crude reaction mixture was extracted with water (5 x 50 ml). The combined aqueous extracts were extracted with petroleum ether, 30 - 60°C, (5 x 50 ml) to remove traces of menthol, saturated with sodium chloride and extracted with chloroform (5 x 50 ml). The combined chloroform extracts were - 28 -dried over anhydrous magnesium sulphate and the solvent removed at reduced pressure. Hot box horizontal sublimation at 0.05 mm yielded 1.2 g (65%) of 22 methylp-tolyl sulphoxide. [a]^ = +31.2°, (C = 5.1 acetone), 21% enantiomeric 25 excess. [aj^ = +145.5% (C = 1, acetone) for (R)-(+)-methyl p-tolyl sulphoxide 2.8.4.4iv. Resolution of (-)Menthyl Methanesulphinate Separation of the diastereotopic mixture was attempted using liquid chromatography. Cyclohexane, chloroform, carbon tetrachloride, benzene, methanol and ethyl acetate were used as eluting solvents on neutral alumina and s i l i c a gel columns. High pressure liquid chromatography on Corasil II, Carbowax, and Cellulose columns with chloroform, methanol, cyclohexane, and mixtures of these solvents as elutants was tried. Paper chromatography with ethyl acetate, benzene, carbon tetrachloride and chloroform was also u t i l i z e d . Lastly, gas phase chromatography with Carbowax, Apiezon J, SF 90, SE 30, and HMPF columns was tried. None of the above techniques achieved separation of the diastereomers on the preparative scale. On a smaller scale the high pressure liquid chromatography using chloroform eluting from a Corasil II column showed some separation, two overlapping peaks. V.P.C. with SF 90 showed the same effect. 2.8.4.5. (R)-(+)-Methyl p-Tolyl Sulphoxide, V 2.8.4.5i. p-Toluenesulphinyl Chloride, VI 96 g (0.45 mole) of sodium paratoluene sulphinate (Eastman) was slowly added to 220 ml of thionyl chloride in a flushed 500 ml three-necked flask equipped with a mechanical s t i r r e r , and gas-inlet tube. The exothermic reaction gave an orange-yellow mixture containing a precipitate of NaCl. After - 29 -stirring overnight excess thionyl chloride was d i s t i l l e d off at reduced pressure (flash evaporator) and p-toluenesulphinyl chloride d i s t i l l e d from the reaction mixture. B.p. 86 - 88°C, 0.01 mm. Yield 77.7 g, (99%) of orange viscous air and water sensitive liquid. 2.8.4.5ii. (-)Menthyl p-Toluenesulphinate, VII The preparation of the methyl diastereomers was done in anhydrous -conditions under nitrogen. A solution of 64 g (0.41 mole) of (-)menthol in 100 ml of anhydrous ether and 36 ml of pyridine, dried over BaO, in a 500 ml three-necked flask equipped with a gas-inlet tube, mechanical s t i r r e r and equilizing addition funnel was cooled to dry ice-acetone temperature. A solution of 71.1 g (0.41 mole) of p-toluenesulphinyl chloride in 100 ml of anhydrous ether was slowly added and the reaction mixture stirred and allowed to warm up to room temperature over 1 hr. 100 ml of IN aqueous HC1 solution was added, the ether layer extracted with water, (2 x 100 ml), and the aqueous layer with ether (1 x 100 ml). The combined ether extracts were dried over anhydrous magnesium sulphate and the ether pumped off (flash evaporator). The o i l y residue was dissolved in 30 ml of hot petroleum ether (60 - 80°C) and the resulting solution stored at 0°C for one day. 30.3 g of solid was collected and washed with petroleum ether (30 - 60°C). The combined f i l t r a t e was taken to dryness, 20 ml of petroleum ether (60 - 80°C) added along with a crystal from the f i r s t crop, and anhydrous HC1 gas slowly bubbled through the solution u n t i l crystallization began. After cooling 51 g of product separated. A further 7.3 g was obtained by repeating the above process with the second crop f i l t r a t e . The total product 88.6 g (0.25 mole) (60%) was recrystallized from hot acetone, 2 ml per gram of product, as colourless rods and stored at 4°C - 30 -25 37 25 to prevent decomposition. [ a ] D = -197 (C = 1, acetone) l i t . [ a ] Q = -199°, acetone. 2.8.4.5iii. (R)-(+)-Methyl p-Tolyl Sulphoxide Preparation of this compound was accomplished by reaction of the optically pure menthyl p-toluenesulphinate prepared above with methyl magnesium iodide. The Grignard reagent was prepared under nitrogen in a 250 ml three-necked flask equipped with an equilizing addition funnel and reflux condenser with drying tubes, and a gas-inlet tube. To 5.3 g (0.22 mole) of magnesium shavings in 100 ml of anhydrous ether was added 35 g (0.25 mole) of methyl iodide^. The Grignard solution was added dropwise under nitrogen to a well stirred solution of 30 g (0.17 mole) of menthyl p-toluenesulphinate in 250 ml of anhydrous ether at 0°C, in a 1 1. two-necked flask equipped with a gas-inlet tube, and a gas-equilization addition funnel with drying tube. After addition was complete the solution was stirred at room temperature for 0.5 hr then hydrolyzed with 150 ml of a saturated ammonium chloride solution. The aqueous phase was then immediately made just basic with aqueous ammonium hydroxide 1 7. The ether layer was separated, dried over anhydrous magnesium sulphate, taken to dryness, diluted with 50 ml of ACS Hexanes, and cooled to 0°C overnight to yield 6.4 g of crude sulphoxide. The aqueous phase was extracted thoroughly with ether (6 x 200 ml), and the combined ether extracts treated as with the i n i t i a l ether layer to yield 5 g of sulphoxide. The ^1,2 dibromoethane may be needed to ini t i a t e reactions, i f any moisture i s present or the magnesium is coated with impurity. ^ This prevents decomposition of the sulphoxide to a yellow material. - 31 -combined crude sulphoxide fractions (0.074 mole, 42%) were recrystallized 1 25 from hot cyclohexane', (7 ml/g) to give lustrous white flakes. [ a ] Q = +143° (C = 1, acetone), l i t . 3 6 [ a ] 2 5 = +145.5° (acetone). Found; C (62.52), H (6.64), 0 (10.53), S (20.82); Calc. for CgH SO; C (62.34), H (6.49), 0 (10.39), S (20.78). S ^ g 1 3 2.45 (singlet, 3H, CHj-), 2.74 (singlet, 3H, CHj-S), 7.46 (quartet, 4H, ArH). v ™ ^ 0 1 = 1055 cm - 1 (S=0). 2.8.4.6. (S,R;S,S)-(+)-2-Methylbutyl Methyl Sulphoxide, VIII 2.8.4.6i. (S)-l-Bromo-2-methylbutane, IX 100 g of (S)-(-)-2-methylbutan-l-ol (K & K) was dried over anhydrous magnesium sulphate, refluxed, and d i s t i l l e d from magnesium metal activated with iodide to give 82 g of pure alcohol. The distillate was 95% optically 25 38 20 pure; [a]^ = -5.6° l i t . [aj^ = -5.9°. Bromination of the alcohol was done in two batches of 50 and 32 g. In a 1 1. three-necked flask equipped with a nitrogen gas-inlet tube, a thermometer, a gas-equilization funnel and a magnetic s t i r r e r was mixed in a nitrogen atmosphere 50 g (0.57 mole) of the dry alcohol, 159 g (0.61 moles) of triphenylphosphine and 500 ml of DMF dried over and d i s t i l l e d from BaO. Bromine, dried over phosphorous pentoxide, was added over a 45 min period while the reaction mixture temperature was main-tained below 55°C. Addition of bromine was stopped when 2 drops persisted in giving the solution an orange t i n t . The bromide, unreacted alcohol, and DMF were removed from the triphenylphosphine oxide by vacuum d i s t i l l a t i o n into a Dry Ice cooled receiver. One l i t r e of cold water was added to the d i s t i l l a t e and 73 g (85%) of (S)-l-bromo-2-methylbutane separated. The liquid product ^ Charcoal is required to remove yellow impurity. - 32 -was removed and dried over anhydrous magnesium sulphate, n^" = 1.4428, b.p. = 120 - 122 ( l i t . 3 8 n 2 0 = 1.4451, b.p. 121.6). 2.8.4.6ii. (S)-l-Mercapto-2-methylbutane, X In the preparation 120 g (0.795 mole) of bromide, IX_, 60.5 g (0.795 mole) of thiourea, and 400 ml of 95% ethanol were refluxed for 12 hours in a 1 1. three-necked flask equipped with a mechanical s t i r r e r , addition funnel and reflux condenser. A solution of 47.7 g (1.19 mole) of sodium hydroxide in 300 ml of water was added and the mixture refluxed for 4 hours. During refluxing the mercaptan separated out as an o i l . The layers were separated and the aqueous layer made acidic with 14 ml of cone, sulphuric acid in 200 ml of water. On acidification some mercaptan separated and this was combined with the previous mercaptan layer. The aqueous layer was then extracted with benzene (1 x 100 ml). The extract was added to the crude mercaptan layer and the whole washed with water (2 x 200 ml) and dried over anhydrous sodium sulphate. The solvent was removed and the residual o i l d i s t i l l e d through a vigreaux column to give 63 g (0.60 mole) (70%) of a clear liquid. B.p. 116 - 118°C ( l i t . 3 9 b.p. = 118.2°C). 2.8.4.6iii. (S)-2-Methylbutyl Methyl Sulphide, XI This compound was prepared by the analogous method described for methyl n-propyl sulphide, II_ by using 62.7 g (0.60 mole) of mercaptan, 24.8 g (0.62 mole) of sodium hydroxide in 150 ml of water, and 85.8 g (0.60 mole) of iodomethane. The iodomethane was added over one hour and the resulting mixture refluxed for 3 hours. Steam d i s t i l l a t i o n gave 48 g (68%) of CH'T clear liquid. 6 ^ 3 0.90 - 1.70 (multiplet, 9H, CH 3-CH 2-CH ), 2.1 (singlet, 3H, S-CH3), 2.78 - 2.60 (multiplet, 2H, -CH 2-S). - 53 -2..8..4,6iv, (S,R:;5.,5)-fr)-2-MethylbutyI Methyl Sulphoxide As described fox the preparation of methyl n-propyl sulphoxide, 1^, 48 g (0.40 mole) of the sulphide, XI_ and 43 ml of 30% hydrogen peroxide i-Ti 160 ml of acetone were allowed to react overnight. The vacuum d i s t i l l a t e fraction (65 - 70°C,0,2 mm) was dried over barium oxide and vacuum-distilled to give 44 g (82%) of clear o i l y sulphoxide, B,p. 63°C,0.1 mm. Micro-25 d i s t i l l a t i o n of this clear o i l gave; [a]^ = +20,3; neat, p = 0.993 g/ml. Found; C (53,90), H (10,64); Calc, for C^H^SO; C (53.68), H (10.51), 6TMS l 3 °- 9° S~ 1 * 2 0 (multiplet, 8H, CH3-CH2-C-CH3), 1.25 - 1.60 (multiplet, IH, -CH-), 2.40 - 2.80 (t r i p l e t , 2H, -CH2-S), 2.55 (singlet, 3H, S-CHj), nujol , - 1 , iso-octan-e ,, o r i r _ r (.^ v J 1025 cm , (5=0> A (loge) 205 ran (3,55). 2.8.4.7. (2R,5R)-(-)-2,3-0-Isopropylidene-2,3-dihydroxy-l,4-bis (methyl sulphinyl)butane - H^ O (Dios), XII 40 2.8.4.71, Diethyl-Lg-tartrate , XIII 500 g (3.23 mole) of Lg-(+)-tartaric acid, 100% optically pure 25 41 20 (I>] D = +12,8, C = 17, water; l i t . [a] = +12,7, C = 17.4, water), was converted to the diethyl ester by azeotropic d i s t i l l a t i o n . The acid, 535 g (11.6 mole) of 99.9% ethanol, 20 g of proton charged cation exchanger and 700 ml of petroleum ether 30 - 60° were mixed into a 3 1. two-necked flask equipped with a teflon gland, mechanical s t i r r e r , and a Dean-Stark tube with condenser. The reaction mixture was stirred and refluxed for seven days, while =300 ml of a water-ethanol azeotrope was removed. The cation exchanger was f i l t e r e d off, solvent removed at reduced pressure and the resulting yellow - 34 -o i l vacuum d i s t i l l e d to give 450 g (66%) of the colourless diester^. 40 rnn B.p. 130°, 0.02 mm l i t . b.p. 138°, 4 mm. 6 ^ 3 1.33 ( t r i p l e t , 3H, -CH3), 3.55 (singlet, 2H, -OH), 4.34 (quartet, 2H, -CH - ) , 4.57 (singlet, 2H, -CH). n 2 5 = 1.4449, [ a ] 2 6 = +8.6, neat ( l i t . 4 0 n 2 5 = 1.4454, l i t . 4 2 [ a ] 1 6 = +7.9 neat) 2.8.4.7ii. Diethyl-2,3-0-Isopropylidene-Lg-(+)-tartrate 4 5, XIV A solution of 450 g (2.18 mole) of diethyl-Lg-(+)-tartrate, 229 g (2.61 mole) of 2,2,-dimethoxypropane (Eastman), one l i t r e of sodium dried benzene and 1 g of p-toluenesulphonic acid monhydrate was placed in a 3 1. R.B. flask equipped with a helix f i l l e d d i s t i l l a t i o n column. The yellow solution was refluxed while the benzene-methanol azeotrope , b.p. 88°C, was removed at the top of the column. After 9 hrs the temperature of the refluxing vapour was 78°C. The acid catalyst was neutralized by adding 2.5 g of anhydrous potassium carbonate to the orange reaction mixture and s t i r r i n g overnight. The solvent and unreacted 2,3-dimethoxypropane were removed under reduced pressure and the product mixture vacuum d i s t i l l e d to give 478 g (91%) of light yellow liquid, b.p. 88 - 96 (0.04 mm); 67% diethyl ester, 30% ethyl CDC 1 methyl ester, and 3% dimethylester. 6 ^ 3 1.35 ( t r i p l e t , 3H, C-0C-CH3), 1.51 (singlet, 6H, C(CH 3) 2), 3.83 (singlet, 6H, C-0CH3), 4.30 (quartet, 4H, C-0CH2-), 4.76 (singlet, 2H, CH). 44 2.8.4.7iii. 2,3-0-Isopropylidene-Lg-threitol , XV A suspension of 32.4 g of LiAlH^ in 350 ml of anhydrous diethyl ether ^ An analogous preparation with 227 g tartaric acid, 17 g ion exchanger and 350 ml of benzene as the azeotroping agent gave after six days 300 g (96%) of diethyl tartarate. - 35 -was refluxed for 30 rain with vigorous s t i r r i n g in a 2 1. three-necked R.B. flask. The flask was equipped with a reflux condenser, an addition funnel, and stirred with a glass s t i r r e r with a 5" x 3" teflon paddle passed through a water cooled mercury sealed s t i r r e r gland and turned with an enclosed explosion proof electrical motor. The condenser and funnel employed drying tubes f i l l e d with anhydrous CaCl,,. 79.4 g (0.33 mole) of the above tartrates, XIV in 350 ml of anhydrous diethyl ether was added dropwise over a 3 hour period, so that gentle refluxing resulted. After the addition was finished, the reaction mixture was refluxed for 2 hr, cooled to room temperature, 50 ml of ethyl acetate added carefully, and the mixture cooled to 0 - 5°C. 32 ml of water, 32 ml of 15% NaOH, and f i n a l l y 96 ml of water were added cautiously and successively and the resulting white inorganic precipitate removed by f i l t r a t i o n , washed with warm diethyl ether and Soxhlet extracted for 24 hr. The ethereal extracts were dried over MgSO^ and evaporated under reduced pressure. Vacuum d i s t i l l a t i o n of the residual yellow o i l yielded a 44 clear liquid, 40 g (74%), b.p. 99 - 102°C (1 mm) [ l i t . b.p. 96 - 96.5° 25 45 71 77 (0.5 mm)], n D 3 1.4606 ( l i t . n " 1.4347), [a]^ = +1.9° (C = 5, CHCl^ [ l i t . 4 5 [ a ] 2 6 = -3.1 (C = 5, CHC13) for D enantiomer]. 6^ JJ|° 1.34 (singlet, 6H, C(CH 3) 2), 3.33 - 3.60 (multiplet, 4H, -CH2~), 3.60 - 3.82 (multiplet, 2H, CH), 4.77 (triplet, 2H, OH). N.B. This L1AIH4 reduction is potentially a dangerous reaction. During addition of the tartrates the reaction mixture takes on the consistency of very thick Scottish porridge. The use of a st i r r e r with a 2"xl" paddle leads to inadequate s t i r r i n g . The use of a non-enclosed explosion proof e l e c t r i c a l motor further compounds the situation. During one such reduction with the latter s t i r r e r and motor an explosion and f i r e resulted. The cause of this catastrophe was determined to be "bumping" ether touched off by a spark from the motor or heat from the hot s t i r r e r gland. - 36 -2.8.4.7iv. l,4-Ditosyl-2,3-0-isopropylidene-Lg-threitol , XVI 50 g (0.31 mole) of the alcohol XV and 330 ml of dry freshly d i s t i l l e d pyridine were placed in a 2 1. R.B. flask and cooled to -10°C. 125 g (0.65 mole) of finely powdered, p-toluenesulphonyl chloride, re-crystalized from hexane, was added in total. The mixture was shaken u n t i l homogeneous^ and held at 0°C for 12 hours. Crystallization of the product was induced by the slow addition of water. Once crystals began to form, water was added more rapidly u n t i l a total of at least 540 ml had been added. Crystallization was allowed to proceed overnight. After f i l t e r i n g and drying in vacuo the crude white solid weighed 143 g (98%). Recrystallization from 375 ml of absolute ethanol gave 140 g (96%) of compact white needles; m.p. 77 - 78. [ a ] 2 4 -24.0 (C = 4, CHC13) [ l i t . 4 5 m.p. 80.8 - 82.0; [ a ] 2 4 -12.4° (C - 5, CHC1 3)]. CDC1 6 T M S 3 1.30 (singlet, 6H, C(CH 3) 2), 2.43 (singlet, 6H, CH 3), 3.83 - 4.18 (multiplet, 6H, -CH2> CH), 7.21 (doublet, 4H, ArCH-C-C), 7.65 (doublet, 4H, ArCH-C-S). 2.8.4.7v. S,S-Diacetyl-2,3-0-isopropylidene-l,4-dithio-Lg-threitol 4 5, XVII A mixture of 140 g (0.30 mole) of the ditosylate XVI, 77 g (0.675 mole) of potassium thiolacetate, and 750 ml of absolute ethanol was refluxed and stirred under dry nitrogen in a three-necked 2 1. R.B. flask. During the refluxing, white potassium tosylate precipitated out. After ten hours refluxing, the mixture was cooled, f i l t e r e d , and the solid tosylate washed with diethyl At this point pyridinium hydrochloride precipitates out of solution. - 37 -ether. The ether wash was combined with the ethanol f i l t r a t e and the resulting solution concentrated, diluted with diethyl ether and f i l t e r e d . The solution was again concentrated, diluted with ether and f i l t e r e d . The solution was stripped of solvent and the remaining yellow liquid d i s t i l l e d under reduced pressure, b.p. 100 - 115°C (0.02 mm), to give 75 g (90%) of a yellow liquid. V x * 5 - 9 2 y ( C = 0 ) ' 6TMS4 1 - 3 4 ( S I N S L E T > 6 H ' C ( C H 3 ^ 2 } ' 2 - 3 5 <> i ng l e t> 6 H> -CH ), 2.97 - 3.16 (multiplet, 4H, -CH2~), 3.58 - 3.84 (multiplet, 2H, -CH). [ a ] 2 3 = *39.6 (C = 3.5, CHC1_) [ l i t . 4 3 v " e a t 5.91 u (C = 0); fiS?.^ as found L JD 3J L max v 1 TMS above; [ a ] 2 2 = -39.3° (C = 3.1, CHClj)]. 2.8.4.7vi. 2,3-0-Isopropylidene-l,4-dithio-Lg-threitol 4 3, XVIII 75 g (0.27 mole) of S,S-diacetyl-2,3-0-isopropylidene-l,4-dithio-Lg-threitol was added to a 250 ml R.B. flask containing 50 mg of sodium in 100 ml of dry methanol. Over a period of 8 hours, the methanol, methylacetate azeotrope (b.p. 54 - 56°) was removed through a 15 cm Vigreaux column. 50 mg of sodium dissolved in 40 ml of methanol was then added and the d i s t i l l a t i o n continued for 4 hr. The remaining solvent was then removed and the yellow liquid residue vacuum-distilled to yield 42 g (80%) of colourless liquid; b.p. 60°C (0.10 mm). [ a ] 2 4 = 1.4° (C = 3.3, CHC1 ). 6 ^ a t 1.38 (singlet, 6H, C(CH 3) 2), 1.24 (triplet, J = 8 cps, 2H, -SH), 2.58 - 2.95 (multiplet, 4H, -CH2~), 3.76 - 4.05 (multiplet, 2H, CH). [ l i t . 4 3 , [ a ] 2 3 = 13.0° (C = 3.2, CHClj); 5 ^ f a t as found above]. TMS J 2.8.4.7vii. (2R,3R)-(-)-2,3-0-Isopropylidene-2,3-dihydroxy-l,4-bis(methylthio)-butane , XIX To a 250 ml three-necked R.B. flask equipped with a gas-inlet tube, a reflux condenser, an addition funnel and internal s t i r r i n g was added 12.7 g - 38 -(0.32 mole) of NaOH in 75 ml of water. 30 g (0.15 mole) of 2,3-0-isopropylidene-1,4-dithio-Lg-threitol was slowly added to the vigorously stirred, nitrogen flushed solution^. When this reaction was complete, 43.8 g (0.31 mole) of iodomethane was added as rapidly as the resultant exothermic reaction would allow. On completion of this addition the stirred reaction mixture was refluxed for 4 hr. The sulphide layer was separated from the reaction mixture, washed with water, 10% sodium hydroxide solution and f i n a l l y water before drying with calcium chloride. The aqueous layer of the reaction mixture was extracted with pet. ether (30 - 60°) (4 x 100 ml), washed with water, 10% sodium hydroxide solution, water, and the solvent then stripped off. The liquid residue was washed with 10% sodium hydroxide solution, water and dried over calcium chloride. The two dried sulphide fractions were then combined and vacuum-d i s t i l l e d to give 20.6 g (60%) of clear colourless liquid, b.p. 66°C,(0.02 mm). [a]D° = -6.8 (C = 4.9, CHC13). 6 ^ 4 1.37 (singlet, 6H, C(CH 3) 2), 2.17 (singlet, 6H, -CH3), 2.58 - 2.80 (multiplet, 4H, -CH2-), 3.77 - 4.05 (multiplet, 2H, -CH). v n u j 0 1 9.6 u(S=0). max ^ 1 2.8.4.7viii. (2R,3R)-(-)-2,3-0-Isopropylidene-2,3-dihydroxy-l,4-bis(methyl  sulphinyl)butane-H,,0, (Dios) 20.2 g (0.091 mole) of XIX and 50 ml of acetone were placed in a 250 ml R.B. flask. 9.6 ml (0.18 mole) of 30% hydrogen peroxide was added slowly to the cooled (5°C) stirred solution. After s t i r r i n g overnight the solvent was flash evaporated with the final traces of water removed at the ^ At this point some white solid pptd. out. On addition of iodomethane this ppt. dissolved. - 39 -vacuum pump. The resulting clear o i l s o l i d i f i e d over a period of one week, to give a hygroscopic white solid, (18.9 g (82%), m.p. 63 - 85° in vacuo). Found; C (39.24), H (7.05); Calc. for c9ti2o°sS2' C ( 3 9 > 6 8 ) > H ( 7- 40)- t " ] ^ 3 = r n n -85.8° (C = 5.2, CHC13). sljfjjg 3 1-43 (singlet, 6H, C(CH ) 2 ) , 2.66 (singlet, 6H, -CH3), 2.90 - 3.35 (multiplet, 4H, -CH2~), 4.05 - 4.02 (multiplet, 2H, -CH) . 6 T M S A C e t ° n e 3-° ( s i n 8 l e t » 2 H > H 2 ° ) -2.8.4.8. (2R,3R)-(-)-2,3-0-Isopropylidene-2,3-dihydroxy -1,4-bis(benzyl sulphinyl)butane-H 2Q (BDios), XX 2.8.4.8i. (2R,3R)-(-)-2,3-0-1sopropylidene-2,3-dihydroxy-l,4-bis(benzylthio)-butane , XXI 11.3 g (0.058 mole) of 2,3-0-isopropylidene-l,4-dithio-Lg-threitol was added to an aqueous sodium hydroxide solution (4.76 g, 0.12 mole NaOH in 30 ml water) in a nitrogen purged 100 ml R.B. three-necked flask equipped with an addition funnel, reflux condenser, gas-inlet tube and internal s t i r r i n g . After dissolution was complete, 19.9 g (0.12 mole) of a-bromotoluene was added with vigorous s t i r r i n g . On completion of this addition the reaction mixture was heated to reflux for 3 hr. During this time the sulphide layer formed. Diethyl ether (400 ml) was added to the cooled reaction mixture to dissolve the sulphide. The two layers were then separated and the aqueous layer extracted with diethyl ether (3 x 75 ml). The ether fractions were combined, washed with water, 10% sodium hydroxide solution and water, and dried over anhydrous calcium chloride. Removal of the ether solvent gave a white solid. Recrystallization from carbon tetrachloride gave a white solid, (18.3 g (84%), m.p. 86 - 88°C). [ a ] * = -56.7° (C = 2.7; CHC1 ). ajjjg 3 1.38 (singlet, 6H, C(CH ) 2 ) , 2.50 - 2.70 (multiplet, 4H, -CH2~), 3.65 - 3.95 (multiplet, 2H, -CH), 3.72 (singlet, 4H, ArCH 2~), 7.22 (singlet, 10H, Ar-H). - 40 -2.8.4.8ii. (2R,3R)-(-)-2,3-0-1sopropylidene-2,3-dihydroxy-l,4-bis(benzyl  sulphinyljbutane-H^O (BDios) 15.93 g (0.043 mole) of XXIand 50 ml of acetone were placed in a 100 ml R.B. flask. 9.0 ml (0.086 mole) of 30% was added slowly to the cooled (5°C), stirred solution. Overnight a white solid precipitated; the mixture fi l t e r e d and the mother liquor flash-evaporated to give a clear colourless o i l which upon addition of 50 ml of diethyl ether gave more white precipitate. The ether precipitates were combined, washed with petroleum ether (30 - 60°C) and vacuum dried, (10.5 g, 50%, m.p. 158 - 168 with decomposition, in vacuo). Found; C (59.51), H (6.71); Calc. for C 2 1 H 2 8 0 5 S 2 ; C ( 5 9 > 4 1 ) > H ( 6 - 6 5 ) -[ a ] 2 5 = -15.0 (C = 1.5, CHC1J. v n U ^ 0 1 1021 cm - 1 (SO), 1605 cm"1, 1591 cm"1  1 JD v y max ^ J> (C = C). 4 M S A C e t ° n e 1 , 3 0 " 1 - 5 0 ( m u l t iP l e t> 6 H> C(CH 3) 2) , 2.90 - 3.10 (multiplet, 6H, -CH2~, H 20), 4.0 - 4.5 (multiplet, 2H, -CH), 4.0 - 4.1 (multiplet, 4H, ArCH,,-), 7.32 (singlet, 10H, Ar-H). 2.8.5. Ruthenium Compounds^ 2.8.5.1. Ruthenium Trichloride Trihydrate This was supplied on loan from Johnson Matthey Co.: The % Ru varied from 37 - 42% depending upon the batch. 2.8.5.2. Methanolic "Blue Ruthenium(II) Solutions" These solutions were produced by taking ruthenium trichloride Dried, degassed reagent grade solvents were used in a l l reactions which were also carried out under anerobic conditions, except where noted. Work up of products was done under a nitrogen or argon atmosphere. *H n.m.r. spectra of compounds and respective ligands are contained in figs. 2.7.-2.10. - 41 -trihydrate, ( 0.75 - 3.0 g) in 50 ml of methanol, in a three-necked flask equipped with gas-inlet tube, reflux condenser and magnetic s t i r r e r . Upon refluxing under (1 atm) for eight hrs a deep blue coloured solution resulted. These solutions were used directly for some preparations of Ru complexes. 2.8.5.3i. Dimethylammonium Trichlorotris(dimethyl sulphoxide)ruthenate(II), I 1 g of ruthenium trichloride trihydrate (39% Ru) and 1 ml of dimethyl sulphoxide were heated at 80°C in 20 ml of DMA under (1 atm) for 4 hrs, in a 100 ml two-necked flask equipped with a reflux condenser, a gas-inlet tube and a magnetic s t i r r e r . The resulting red solution was set aside overnight (or concentrated to 10 ml and cooled) to give a bright yellow product which was washed with acetone and ether, and vacuum dried. Recrystallization from DMA, as cubes, yielded 1.23 g (66%). M.p. 195°C (decomp. in vacuo). Found; C (19.6), H (5.3), Cl (21.6), N (2.6); Calc. for C gH 2 6Cl 3No 3RuS 3; C (19.7), H (5.4), Cl (21.6), N (2.9). 6 ^ 3 2.68 (triplet, 6H, (CH_)„N), 3.51 (singlet, 18H, CH_-S). v n U ^ ° l 1100 cm"1 (S=0) pup i 347,293 (Ru-Cl). A 3 (loge), 368 nm (2.76), 325 nm (2.58) shoulder. ITlcLX A 2 2 =43.8 (C = 10"3, DMA) cm2ohm"1mol"1. 2.8.5.3ii. Dimethylammonium Trichlorotris(d 6-dimethyl sulphoxide)- ruthenate(II) , 2 This compound was prepared in an analogous way as the preceding complex, but using d,-DMS0. - 42 -2.8.5.4. Dimethylammonium Trichlorotris(methyl n-propyl sulphoxide)- ruthenate (II), 3_ This compound was prepared in the same way as 1_ with 3 g of ruthenium trichloride (39%) and 5 ml of methyl n-propyl sulphoxide. The resulting brown reaction mixture was concentrated under vacuum to an o i l , and stored in vacuo at 5°C for 48 hr, during which time a yellow powder crystallized out. The product was washed with acetone and diethyl ether to remove the remaining o i l and vacuum dried. Recrystallization from DMA gave 1.07 g (16%) of bright yellow powder. Found; C (29.19), H (6.70), Cl (18.02), N (2.70); Calc. for C,-.H-oCl.No-RuS,; C (29.39), H (6.70), 14 o o o . o J r n n Cl (18.59), N (2.45). 6 ^ 3 1.08 (triplet, 3H, -Cty, 1.50 - 2.40 (multiplet, 2H, - C H 2 - ) , . 2 . 6 8 ( t r i p l e t , 6H, N(CH 3) 2), 3.42 (singlet, 3H, CH C-S), 3.25 - 4.40 (multiplet, 2H-, S-CH»-) . v n u J ° l 1105 cm - 1 (S=0), •J /. I U c l X -1 THP1 * 355, 290 cm (Ru-Cl). X 3 (loge), 377 nm (2.77), 328 nm (2.50) • in 3.x shoulder. A 2 2 =46.0 (C = 10"4, DMA) cm 2ohm _ 1mol _ 1. 2.8.5.5. Dichlorotetrakis(dimethyl sulphoxide)ruthenium(II), 4 2.8.5.5'i. As for the synthesis of compound 1_ ruthenium trichloride t r i -hydrate (3 g, 41% Ru), 5 ml of DMSO and 20 ml of DMA were heated together under hydrogen at 65°C overnight. Reduction in volume of the orange reaction mixture gave 3.4 g (58%) of yellow powder. Found; C (19.76), H (4.72); Calc. for C g H ^ C l ^ R u S ^ C (19.83), H (4.99), Cl (14.63). P H P " ! 6TMS 3 2 * 6 0 ( s i nS l e t> CH3-S, uncoordinated), 2.73 (singlet, =1 DMSO, CH--S), 3.33, 3.42, 3.49, 3.52 (singlets, 3 DMSO, CH,-S). v n U 1 0 1 1110, 3 V & J 3 j m a x 1090, 930, (S=0). A C H 5 l 3 (loge) 358 nm (2.69), 309 nm (2.55). I U c l X - 43 -2.8.5.5ii. To the blue methanolic solution produced from 1 g of ruthenium trichloride trihydrate (39% Ru) was added 4 ml of dimethyl sulphoxide. Refluxing under rL, (1 atm) was continued for 12 hours yielding a red solution. Upon cooling 1.1 g (59%) of yellow cubes formed. M.p. 208°C (decomp. in vacuo). Found; C (19.76), H (5.10), Cl (14.43). A 2 2 = 0.70 -3 2 - 1 - 1 1 (C = 10 , DMA) cm ohm mol . I.r. and H n.m.r. data were the same as those recorded for samples prepared by the previous method. 2.8.5.6. Dibromotetrakis(dimethyl sulphoxide)ruthenium(II), 5 0.5 g of ruthenium tribromide, 2 ml of DMSO in 20 ml of DMA were reacted as in the preparation of dimethyl ammonium trichlortris(dimethyl sulphoxide)ruthenate (II) , 1_. Reduction in volume of the resulting orange solution yielded 0.2 g (24%) of orange powder. Found; C (17.23), H (4.19); Calc. for CgH^Br^RuS^ C (16.75), H (4.22). 6 ^ 3 2.62 (singlet, 1 DMSO, CH_-S), 3.52 (singlet, 3 DMSO, CH_-S). v n u ^ o ] " 1080, 944 (S=0). 2.8.5.7. Dichlorobis(methyl phenyl sulphoxide)ruthenium(II), 6 1.30 g of methyl phenyl sulphoxide was added to the methanolic : blue solution (formed from 0.75 g (41.33% Ru) of ruthenium trichloride trihydrate), and refluxing under (1 atm) was continued overnight. During this period a gold coloured solid separated from a red solution. The product was fi l t e r e d , washed with 100% ethanol, and acetone and vacuum dried to give 0.87 g (63%) of a gold solid. Found; C (36.94), H (3.70), Cl (15.90); Calc. for C ^ H ^ C l ^ R u S ^ C (37.17), H (3.56), Cl (15.67). ^nujol -1 r S = 0 ) 33 0 (Ru_ci) . max v 1 - 44 -2.8.5.8. Ruthenium(II)dichloro-complexes of (S,R;S,SJ-(+)-2-Methyl- butyl Methyl Sulphoxide 2.8.5.8i. Ether-solvated Dichlorobis[(S,R;S,S)-(+)-2-methylbutyl  methyl sulphoxide]ruthenium(II), 7_ In a preparation analogous to that of 6,4 ml of (S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide was added to a methanolic blue solution produced from 2.0 g (41.33% Ru) of ruthenium trichloride trihydrate and refluxing continued for 48 hr under H 2 (1 atm). The resulting yellow brown solution was pumped down to a brown o i l and diethyl ether added. The resulting yellow brown solution was cooled to 5°C for 3 hr, 0.5 g of small yellow crystals were f i l t e r e d off and washed with ether.. The mother liquor was cooled to 5°C for 96 hr yielding 0.6 g of green-tinted yellow crystals. Found; C (38.70), H (7.73), Cl (14.1); Calc. for C 1 2 H 2 8 C 1 2 ° 2 R u S 2 C 4 H 1 0 ° ; C ( 3 7' 3 5)> H (7.44), Cl (13.78). 0.90 -1.80, 1.82 - 2.60 (multiplets, 24H, CH3-CH2-CH(CH3), CH 3~(ether)), 2.72 (singlet, 3H, CH3-S), 2.80 - 3.80 (multiplets, 14H, -CH2-S-CH3, -CH2-(ether))'. vnu^°l 1105 cm-1, (S=0), 347 (Ru-Cl). x C H C 1 3 (loge) 364 nm TTlcLX IT13.X (2.63), 450 nm (1.84) (shoulder). A 2 2 = 4.5 (C = 10 - 3, DMA) cm2ohm"1mol"1, 2.8.5.8ii. Dichlorobis[(S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide ]- ruthenium(II) Trimer, 8_ As for the preparation of 6, 1.1 ml of (S,R;S,S)-(+)-2-methyl-butyl methyl sulphoxide was added to the methanolic blue solution formed from 1 g (41.38% Ru) of ruthenium trichloride trihydrate and refluxing under H 2 (1 atm) continued for 48 hr. The resulting yellow brown solution was f i l t e r e d from metal and the methanol solvent pumped off, leaving a - 45 -brown o i l . 40 ml of benzene was added and the resulting solution freeze-dried to give 1.75 g (97%) of a gold-coloured powder. Found C (33.13), H (6.56), Cl (16.2), S (14.76). Calc. for [ C ^ H ^ C l ^ R u S ^ ; C (32.72), H (6.41), Cl (16.1), S (14.56). M.w. 1273 g/mole (benzene). 6TMS4 0 , 7 " 1 - 7 5 ( m u l t i P l e t > 1 6 H> CH -CH2-C(CH3), 1.85 - 2.5 (multiplet, 2H, -CH-), 2.8 - 4.2 (multiplet, 10H, CH_-S-CH0-). v n u 3 ° l 1105 cm, (S=0), 330 (Ru-Cl). A0"6"6 (loge as trimer), 351 nm (3.41), 446 nm (2.98) ins. x shoulder; x ^ A 3 3 5 1 n m (3.44), 445 nm (3.01) shoulder. A = 7.2 max (C = IO - 4, DMA) cm2ohm"1mol"1. 2.8.5.9. Dichlorodicarbonylbis[(S,R;S,S)-(+)-2-methylbutyl methyl  sulphoxide jruthenium(II), 9_ 0.35 g of 8 was refluxed in benzene (40 ml) under CO (1 atm) for twelve hours. During this time the solution went from dark brown to light yellow in colour. On freeze-drying the reaction mixture a dark o i l resulted. Carbon tetrachloride (20 ml) was added to effect solution of the o i l and n-hexane until the solution became cloudy. On cooling to CC1 -20°C white crystals (cubes) separated. 6 T M S 4 °- 8 - 1.9 (multiplet, 18H, CH3-CH2-CH(CH3), 2.80 - 3.00 (multiplet, 10H, -CH2-S-CH3). \>nujol 2135, 2059 cm"1 (C = 0), 930 cm"1 (S=0), 320, 295 cm"1 (Ru-Cl). max 2.8.5.10. Dichlorobis[(R)-(+)-methyl p-tolyl sulphoxide]ruthenium(II)  Trimer, 10 1.33 g of (R) -(+) -methyl p-tolyl sulphoxide was added to a methanol blue solution formed from 1.0 g (41.49% Ru) of ruthenium trichlroide trihydrate. Refluxing under H 2 (1 atm) was continued for 96 hr. At this point the brown solution was pumped to dryness and 15 ml of chloroform - 46 -added to dissolve the residue . The solution was fi l t e r e d and diethyl ether added to precipitate a yellow solid. The solid was fi l t e r e d and dissolved in 15 ml of chloroform. Slow precipitation with diethyl ether, f i l t e r i n g , and washing with diethyl ether resulted in 1.2 g (61%) of a yellow powder. Found; C (40.44), H (4.41), Cl (14.54); Calc. for C 1 6H 2 QCl 20 2RuS 2; C (40.00), H (4.20), Cl (14.76). M.W. 1358 g/mole (benzene). <5™g l 3 2.04 - 2.58 (multiplet, 6H, CRj-Ar), 3.34 - 3.96 (multiplet, 6H, S-CH,), 6.44 - 7.90 (multiplet, 8H, Ar-H). v n u J o 1 1110 cm"1 (S=0). A 2 2 = 4.6 (C = 10"4, DMA) cm2ohm"1mol"1. 2.8.5.11. Dichlorobis[(2R,3R)-2,3-dihydroxy-l,4-bis(methyl sulphinyl)- butane]ruthenium(II) Dihydrate, Dichlorobis(DDios)ruthenium  (II) Dihydrate ,11 2.8.5.Hi. To a methanolic blue soln. formed from 0.75 g ruthenium trichlroide trihydrate (41.83% Ru) was added 1.56 g of Dios. Refluxing under H 2 (1 atm) was continued for another 12 hr. During this time a faint green solid precipitated (0.90 g, 46%) and this was f i l t e r e d and washed with methanol. The reaction f i l t r a t e was concentrated (10 ml) and a yellow precipitate f i l t e r e d off (0.52 g, 27%). Combination of the solids and precipitation from a water solution with acetone yielded 1.33 g (68%) of pale yellow solid. Found; C (22.70), H (4.62), Cl (11.30); Calc. for C 1 2H 3 2Cl 20 1 ( )RuS 4; C (22.6), H (5.07), Cl (11.14). 6p|g 3.25 -4.30 (multiplet, 26H, DDios). v n U J o 1 3370 cm"1 (-0H, HO), 1095 cm"1 (S=0). A 2 2 = 7.6 (C = 10"4M, DMA) cm2ohm"1mol"1. ^ In one preparation, benzene was used in place of CHCl^, the solution f i l t e r e d and freeze-dried to give the yellow product. - 47 -2 . 8 . 5 . l l i i . The compound was also prepared from RuCl2(DMS0)4 (0.50 g) and Dios (0.63 g) by allowing them to react in refluxing methanol (40 ml) overnight. During the reaction a yellow precipitate formed. Reduction in volume to 15 ml, and cooling to 3°C yielded, after washing with acetone and drying in vacuo, 0.45 g (69%) of a yellow powder. 2.8.5.12. Dichloro[(2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-l,4- bis (methyl sulphinyl)butane] \ (2R, 3R)-2,3-dihydroxy-l ,4- bis (methyl sulphinyl)butane]ruthen ium(II), Dichloro (Dios)-(DDios)ruthenium(II), 12 RuCl2(DMS0)4 (0.94 g) and Dios (0.80 g) in CHC13 (50 ml) were refluxed for 120 hr. During this period the solution changed from an i n i t i a l yellow colour to golden. The chloroform was removed from the reaction solution and the residue dissolved in acetone (15 ml), f i l t e r e d and ether (50 ml) added slowly to the f i l t r a t e . The resulting yellow precipitate was f i l t e r e d off, dissolved in acetone (10 ml) and ether (60 ml) added slowly to the resulting solution to precipitate a light yellow solid. The solid was f i l t e r e d off, washed with ether (25 ml x 2) and vacuum dried to give 0.57 g (46%) of a pale yellow solid. Found; C (28.30), H (5.13), Cl (11.04); Calc. for C 1 5H 3 2Cl 20 gRuS 4; C (28.12), H (5.03), Cl (11.07). S y J J g 1 3 1.42 (singlet, 6H, (CH^C), 2.58 (singlet, 3H, S-CH3, uncoordinated), 2.61 - 2.90 (multiplet, 5H, -CH2SCH3), 3.07 - 3.80 (multiplet, 17H, -CH2SCH3, -OH), 3.90 - 4.70 (multiplet, 4H, -CH). v n u i o 1 3500 cm"1 (-0H), 1065 cm"1 (C-OH), 1100, 932 cm"1 (S=0), 335 cm"1 (Ru-Cl). X C H C 1 3 (loge); 309 nm (2.67), nictx 356 nm (2.74). A 2 2 = 2.6 (C = 10"4, H20) cm2ohm"1mol"1. - 48 -2.8.5.13. Dichloro[(2R;3R)-2,3-dihydroxy-l,4-bis(methyl sulphinyl)- butane][dimethyl sulphoxide][methanol]ruthenium(II),  Dichloro (DDios) (DMSO) (MeOH)ruthenium(II) , 1_3 RuCl2(DMS0)4 (1.0 g) and Dios (0.57 g) were allowed to react together with refluxing in 50 ml of methanol. After 18 hr.a yellow solid began precipitating out of the reaction solution. At the end of 42 hr the reaction mixture was allowed to cool and a lemon yellow powder f i l t e r e d off, washed with methanol, and ether and vacuum dried to yield 0.90 g (88%). Recrystallization from DMA gave yellow microcrystals. Found; C (21.69), H (4.68), Cl (14.57); Calc. for C gH 2 4Cl 20 6RuS 3; C (21.77), H (4.87), Cl (14.24). 6°|° 3 . 5 2 , 3.60, 3.63, 3.75 (singlets, 19H, CH3S-CH2, CH3S, CH^O), 3.9 - 4.1, 4.2 - 4.4 (multiplets, 5H, OH, CH). v n u ; ) o 1 3400 cm"1 (0-H), 1123, 1100 cm"1 (S=0) , 325, 305 cm"1 (Ru-Cl) . in 3.x A 2 2 = 4.4 (C = 10"4, DMA) cm2ohm"1mol"1. Figure 2.7. H n.m.r. spectra of some sulphoxide ligands; 1) MenprSO, 2) MBMSO, 3) Dios, 4) MPTSO, 5) BDios - 50 -Figure 2.8. "LH n.m.r. spectra of some DMSO complexes of Ru(II); 1) [NH2Me2][RuCl3(DMSO) ] in CDC1 2) '* in D20, 3) RuCl2(DMSO)4 in CDC13, 4) " in D20, 5) RuBr2(DMSO)4 in CDClj, 6) " in D20 - 53 -Figure 2.9. 'lH n.m.r. spectra of some sulphoxide complexes of Ru(II); 1) Ether-solvated RuCl2[MBMSO)2 in CDC13, 2) [NH 2Me 2][RuCl 3(Me nprS0) 3] in CDCl,, 3) RuCl„(DDios)• 2H_0 in D„0, 4) RuCl2(DDios)(DMSO)(MeOH) in D20 - 55 -Figure 2.10. AH n.m.r. spectra of some sulphoxide complexes of Ru(II); 1) [RuCl2(MBMSO)2] in CDC13, 2) RuCl2(C0)2(MBMS0)2 in CC14, 3) [RuCl 2(MPTS0) 2] 3 in CDCl^, 4) RuCl 9(Dios)(DDios) in CDC17 - 57 -CHAPTER III PROPERTIES AND PREPARATION OF SULPHOXIDE LIGANDS 3.1. Structure and Bonding 3 46 The sulphur of sulphoxides is sp hybridized with a non-bonding pair of electrons of the sulphur occupying one position of the tetrahedron. The result is a pyramidal-shaped molecule. Fig. 3.1. 47 o -shows the structure of dimethyl sulphoxide . The angle OSC is 107 while the angle CSC is 98°. The S-C bond length is 1.80 - 1.82 A. Replacement of one methyl group with another alkyl or aryl group w i l l affect the bond angles and C-S bond lengths due to steric and inductive effects, as w i l l replacement of both methyls. Figure 3.1. Structure of DMSO - 58 -The sulphur-oxygen bond consists of a sigma bond formed from 3 overlap of a sp orbital on sulphur and a p^ orbital on oxygen, along 46 with two pi bonds of the type d -p and d -p . Such d-p pi overlap xz z X is not very effective. The overall result is that the oxygen remains electronegative compared to the sulphur and the bond strength is on the order of common double bonds. The three resonance structures for the 48 S-0 bond are shown below; structure II is dominant: • • •t • • • • • • • I Ii III Figure 3.2. Resonance structures of sulphoxides 3.2. Co-ordination of Sulphoxides Both the sulphur and oxygen have unpaired electrons enabling 46 the sulphoxide to act as a Lewis base . Co-ordination to Lewis acids can occur through the hard oxygen to class a metal ions or through the 49 soft sulphur to class b metal ions - 59 -On co-ordination through the sulphur atom to Ru(II), the resulting geometry about the sulphur atom is the expected distorted tetrahedral. With DMSO the O-S-C and C-S-C angles, SO and SC bond lengths are similar to those found in the free l i g a n d 5 0 . Co-ordination through the oxygen does not alter the geometry about the sulphur atom to any extent, the geometry remaining pyramidal, however the SO bond o °51 length is longer than i f sulphur bonded, 1.56 A as compared to 1.48 A 3.3. Effect of Co-ordination of Sulphoxide Ligand on v(SO) I.r. and *H n.m.r. are two spectroscopic tools which are avail-able to help elucidate the nature of the bonding of the sulphoxide ligand. Co-ordination through the oxygen atom decreases the SO bond order by enhancing the contribution of resonance structure (I), (fig. 3.2.), due to the withdrawal of electrons from oxygen. This w i l l result in a _1 48,52 lowering of the SO stretching frequency, by approximately 100 cm Co-ordination through the sulphur atom increases the SO bond order by enhancing the contribution of resonance structure (III), thus raising the l l y this ha: -1 12,48,50 48 v(S0) . Experimentally this has proven correct and is on the order of approximately 70 cm 3.4. Effect of Co-ordination on 1ti N.M.R. Chemical Shifts Co-ordination of sulphoxides to metal centres causes the adjacent proton nuclei to resonate at lower f i e l d positions. Methyl protons of - 60 -DMSO and other methyl alkyl and methyl aryl sulphoxides are deshielded =1 p.p.m. on co-ordination to Ru(II) through sulphur and =0.1 p.p.m. on co-ordination through oxygen. 3.5. Determination of Stereochemistry at the Sulphur Centre in Sulphoxide  Ligands The stereochemical configuration at the sulphur atom of free sulphoxide ligands can be determined by the combination of two methods. The correlation of the Cotton effect with the sulphur stereochemistry has 53 been achieved by Mislow . For methyl alkyl sulphoxides a negative Cotton effect centred at the strong n-d electronic transition, at approximately 205 nm (isooctane), indicates an R configuration at sulphur. This method gives the configuration but not the amount of each enantiomer or diastereomer present. The second method involves the use of a chiral lanthanide n.m.r. shift reagent. One particular shift reagent is Kiral-shift , E7, tris[3-(heptafluorobutyryl)-d-camphorato]europium(III). This reagent used in an equal molar ratio with DMSO co-ordinates to the ; sulphoxide and causes the methyl proton singlet to s p l i t into two equal 54 area singlets seaparated by 0.40 p.p.m. . For methyl alkyl or aryl sulphoxides the methyl resonance of each enantiomer or diastereomer w i l l occur at different chemical shifts, (fig. 3.3.). The area under the respective peak then gives the amount of each isomer present. This method in conjunction with the O.R.D. method, above, w i l l give the amount of A B i ON 10 8 i 1 R Figure 3.3. H n.m.r. spectrum of MBMSO with added Kiralshift - 62 -each isomer present and i t s stereochemical configuration. Because of the limitation of the O.R.D. method to methyl alkyl sulphoxides only, absolute stereochemical information is available for these sulphoxides only. 3.6. Preparation of Sulphoxide Ligands Sulphoxides are generally made by the oxidation of the corres-ponding sulphide, which in turn has usually been made from a mercaptan and alkyl iodide. This general procedure has been followed in the preparation of most sulphoxides reported in this work. In one case, the synthesis of methyl n-propyl sulphoxide was attempted using a diasteromeric mixture of (-) menthyl methanesulphinates. The preparation for chiral (R)-(+)-methyl p-tolyl sulphoxide was achieved from a diasteromerically pure (-) menthyl-p-toluene sulphinate. For the general procedure most of the synthetic work involved preparation of the appropriate mercaptan for subsequent reaction with methyl iodide to give the alkyl-, or aryl-methyl sulphoxide. The general preparative scheme for this mercaptan to sulphide to sulphoxide procedure is shown below: : RSH I] N a0H/»20 > RSCH H 20 2/acetone ? R S ( 0 ) C H RSH = n-propyl and (S) - 2-methy l b u t y 1 mercaptan and 2,3-O-isopropylidene-1,4-dithio-Lg-threitol. The mercaptan was converted to the sulphide in a two-step process, according to the procedure .of Fidler et a l . 3 4 . Aqueous sodium - 63 -hydroxide caused the mercaptan to dissolve and dissociate with formation of RS and H + ions. Addition of methyl iodide (to this solution) results in displacement of the iodide by the RS anion, presumably by an S^ 2 substitution. Steam d i s t i l l a t i o n of the reaction mixture gives a product contaminated with mercaptan; however, washing with aqueous sodium hydroxide solution followed by fractional d i s t i l l a t i o n removes most of the contaminant. This procedure was modified somewhat for the Dios and BDios syntheses, since the sulphide was d i f f i c u l t to steam d i s t i l . In these cases the crude sulphide layer of the reaction mixtures was separated and the aqueous layer extracted with petroleum ether (for Dios) or diethyl ether (for BDios). After solvent removal, the combined layers were treated as for the other sulphides above, except BDios which was not d i s t i l l e d . Oxidation of the sulphide to the sulphoxide was accomplished by the action of a stoichiometric amount of hydrogen peroxide 5 5. This reagent smoothly gave the product in high yield after vacuum d i s t i l l a t i o n (or crystallization). The liquid product sulphoxides were stored over molecular sieves 5 A. The oxidation process gave sulphoxides which were racemic at the sulphur atom as shown by the use of n.m.r. and examining' the S(0)CHg moiety with a co-ordinated chiral europium n.m.r. shift reagent, and where applicable by the absence of a Cotton curve. 3.6.1. Methyl n-Propyl Sulphoxide This ligand was prepared in 87% overall yield from commercial n-propyl mercaptan as a racemic liquid by the route outlined previously. - 64 -The ligand was a clear liquid at room temperature, soluble in water, alcohols, acetone, diethyl ether, and halogenated solvents but insoluble in hexanes. 3.6.2. Enantiomerically Pure Methyl n-Propyl Sulphoxide A procedure for preparing this ligand enantiomerically pure was 35 worked out based on a modification of work done by Mislow and Jacobus The preparative route is shown below: S0 2(g) -ggi > CH3S(0)OLi S ° C l 2 > CH3S(0)C1 (-) menthol CH3S(0)n-pr < n-prMgBr CH3S(0)Omen The nucleophilic attack of methyl lithium on sulphur dioxide resulted in production of lithium methanesulphinate which was then reacted in situ with thionyl chloride to give methanesulphinyl chloride. Esterification of this product with naturally occurring (->) menthol gave a diastereomeric mixture of two menthyl methanesulphinates in the ratio of 61/39, R/S at the sulphur atom. The abundance of each isomer '• was determined by reacting the diastereomer mixture with p-tolyl magnesium bromide to give an enantiomerically enriched mixture of methyl p-tolyl sulphoxide. This Grignard reaction proceeds by direct inversion at the 35 sulphur centre to give the sulphoxide . The diastereomeric ratio of the esters is then equal to the enantiomeric ratio of the sulphoxides. Comparison of the specific rotation of the mixture to the absolute - 65 -rotation of (R)-(+)-methyl p-tolyl sulphoxide, gives the enantiomeric excess and enantiomer ratio. Production of enantiomerically pure methyl n-propyl sulphoxide required that the liquid diastereomeric mixture of menthyl methanesulphinate be separated into i t s two diastereomers. Many attempts to effect this resolution of isomers failed. The following techniques were used; liquid column chromatography, paper chromatography, gas phase chromatography, fractional d i s t i l l a t i o n , and high pressure liquid chromatography. With both V.P.C. and the latter technique there was some separation of isomers but not enough to be useful even on the micro-preparative scale. Clearly i f the diastereomeric mixture was composed of solids and not liquids, resolution by fractional crystallization could have been employed. This was the technique used for the following sulphoxides. 3.6.3. (R)-(+)-Methyl p-Tolyl Sulphoxide The procedure below used for preparation of this enantiomeri-ca l l y pure sulphoxide and the experimental detail described previously was worked out by Dr. Heather Boucher and is a modification of work by If* 17 Holloway et a l . and Mis low and Jacobus . The synthetic route employed was as follows: p-CH3<j>S(0)0Na-2H20 S 0 C l 2 — > p-CH <|)S(0)C1 (-) menthol R-(+)-p-CH3<j>S(0)CH3 < C H 3 M g I p-CH3<f>S(0)Omen - 6 6 -Chlorination of sodium p-toluenesulphinate gave p-toluenesulphinyl chloride which on reaction with (-) menthol gave a diastereomer mixture. Fractional crystallization gave one diastereomer which on reaction with methyl magnesium iodide gave the solid chiral sulphoxide in an overall yield of 25% and optical purity of 96% R(+). By variation of the Grignard reagent, chiral t-butyl p-tolyl sulphoxide and o-tolyl p-tolyl sulphoxide were also made. These ligands are white solids at room temperature and have similar s o l u b i l i t y properties as DMSO and methyl n-propyl sulphoxide; however, the t o l y l sulphoxides are soluble in hexanes. 3.6.4. Preparation of (S,R;S,S)-(+)-2-Methylbutyl Methyl Sulphoxide This ligand was prepared as a mixture of two diastereomers. The 2-methylbutyl moiety contained an S centre at the "2" carbon in 95% optical purity as determined by the specific rotation of the i n i t i a l starting reagent (S)-(-)-2-methyl-l-butanol. As no chemistry was done at this carbon atom the ch i r a l i t y at this carbon centre was not altered during the reactions to produce the sulphoxide. As the oxidation process from the sulphide to the sulphoxide is not stereospecific the two diastereomers are the (S,R) and (S,S) isomers. As shown by the use of a chiral *H n.m.r. shift reagent the abundance of each isomer i s equal, (fig. 3.3.). No Cotton effect was observed for this sulphoxide in the region 200 to 350 nm. As the sulphoxide is a liquid, preparative resolution of the diastereoisomers was not attempted. (S)-2-methyl-butyl mercaptan was prepared by the following route: - 67 -ROH ******* , RBr I] CNH^CS/EtOH , RSH DMF 2) NaOH(aq) R = CH3CH2CH(CH3)CH2-Bromination of the starting chiral alcohol was accomplished smoothly using 58 the method of Chung et a l . . The alcohol was essentially titrated with bromine in dry DMF. Conversion of the chiral bromide to the mercaptan 59 was achieved using a two step process . Thiourea in ethanol converted the bromide to an isothiourea hydrobromide salt which was then decomposed to the mercaptan with aqueous sodium hydroxide. The mercaptan was then converted to the sulphoxide in 36% overall yield, by the general route outlined previously. This ligand mixture is a clear, colourless, odour-less, viscous o i l at room temperature. The sol u b i l i t y characteristics are as for DMSO and methyl n-propyl sulphoxide (except for a very limited s o l u b i l i t y in water). 3.6.5. (2R,3R)-(-)-2,3-0-Isopropylidene-2,3-dihydroxy-l,4-bis(methyl  sulphinyl)butane, (Dios) and (2R,3R)-(-)-2,3-0-Isopropylidene- 2,3-dihydroxy-l,4-bis(benzyl sulphinyl)butane, (BDios) These ligands were prepared by the scheme shown below in an overall yield of 15%, and 13% respectively. Naturally occuring Lg(+)-tartaric acid, which was 100% optically pure as determined by i t s specific rotation, was used in the synthesis. The acid was converted easily to the diethyl ester by azeotropic d i s t i l -40 Iation . The following five steps of the synthetic route, from the diethyl 43 ester to the mercaptan, were worked out by Cormack and Kelley . The - 68 -H-HO-COOH -OH -H E t 0 H H-H*(catalyst) HO-COOEt -OH -H XIII COOH Lg (+Martaric ocid COOEt 2,2- dimethoxypropane H +(catalyst) XV Me-M e ' H L - CH^OH L j A | H 4 < ^ -CH 2OH Me Me H -C02R XIV G C 0 2 R ' H p-CH^SOgCI R= R'= Et R = Me ; R*= Et R - R'= Me XVI Me Me -CH 2O2S0CH 3 0 -^|~~CH 20 2 S(J)CH 3 CH 3 COSK Me Me H 0--4— - CH 2 SOCCH 3 XVII • C H 2 S O C C H 3 NaOCH, H ,0-/ w " — i — C H p S O C H , / u ' M e X » M e x H XII -CH^SCH k H -son-, 2 3 CH 3I M e ^ / - C H 2 S C H 3 ^ M 6 ^ \ 0 -XIX -CH 2 SH •CH,SH H XVIII (JiCKjBr/NaOH M e v V Me^X XX H H ^ H 20 2 ^ J * * M e ^ X CH 2SOCH 2({l N0"^|^' C H2 S C H2 (1 ) H H XXI Figure 3.4. Synthetic Scheme for Dios and BDios, - 69 -diketal linkage was obtained by azeotropic d i s t i l l a t i o n with dimethoxy-propane, to form the diacetal, the three possible products were obtained, in the following abundance, as determined by n.m.r.; diethyl ester; 67%, ethylmethyl; 30%, and dimethyl ester; 3%. Reduction of the diester mixture to the diol was accomplished with lithium aluminium hydride. The ditosyl derivative of the threitol was easily obtained (by electro-p h i l i c attack of the sulphonyl chloride on the alcohol) as the lower 44 melting polymorphic form . Nucleophilic displacement of the tosyl groups by potassium thiolacetate resulted in the dithioacetate. The sulphur-carbonyl linkage of the moiety was then cleaved with sodium methoxide to give the mercaptan, 2,3-0-isopropylidene-l,4-dithio-Lg-threitol. Up to and including this product, a l l spectroscopic and optical rotation data confirmed the proper product formation and their accompanying optical purity. None of the reactions had altered the stereochemical configuration of the chiral carbons. Conversion to the sulphoxides was completed using the general format described previously, with two exceptions. The sulphide reactions were done under a nitrogen atmosphere to prevent the formation of a d i t h i o k e t a l 4 3 , and the sulphide product was extracted and not steam d i s t i l l e d from the reaction mixture as : noted previously. Use of a chiral lanthanide shift reagent on Dios failed to show the ratio of diasteromers produced. The proton shifts for each isomer were small and overlapping and as a result the abundance of each diastereomer could not be determined. Since the oxidation process from the sulphide to the sulphoxide is not stereospecific for any other sulphoxide produced by this method i t can be assumed that this - 70 -process i s not stereospecific during the production of Dios. Dios should then be a mixture of four diastereomers; (2R,S;3R,S), (2R,R;3R,R), (2R,R;3R,S) and (2R,S;3R,R), in equal abundance. Because the molecule possesses a 0.^ a x i s the last two diastereomers are equivalent. Dios i s a white hydroscopic solid which is soluble in water, alcohols, acetone, halo-genated hydrocarbons, benzene and diethyl ether, and is slightly soluble in hexanes. For the same reason as presented for the Dios ligand, the exact ratio of diastereomers comprising BDios could not be determined experimentally. Due to the non stereospecific oxidation process the diastereomers should be as for Dios. BDios is a white non-hygroscopic solid with similar solubility properties as Dios except for insolubility in hexanes, and a slight solubility in benzene and diethyl ether. Both Dios and BDios are produced with one associated molecule of water, as shown by *H n.m.r. and elemental analysis data. The water molecule could possibly be hydrogen-bonded to one of the sulphoxide oxygen atoms. - 71 -. CHAPTER IV PREPARATIVE ROUTES TO CHLOROSULPHOXIDE COMPLEXES OF RUTHENIUM(II) Chldrosulphoxide complexes of ruthenium(II) were made by three general synthetic routes. One route u t i l i z e d the methanolic "blue ruthenium(II) solutions". Commercially available RuCl^'SH^O, a mixture of Ru(III) and Ru(IV), containing oxy- and hydroxy-chloro s p e c i e s ^ 0 , ^ was reduced in methanol to the blue solutions under reflux with (1 atm). These blue solutions are thought to contain chlororuthenate(II) 62 species , but the exact nature of the species present is a matter of some controversy^ 2 The solutions were f i r s t prepared and used 65 synthetically by Wilkinson et a l . to prepare a number of compounds. This group prepared the blue solutions in the presence of platinum black 62 or Adam's catalyst under 2 atm of hydrogen . We have found that production of these solutions requires no external catalyst, and can be accomplished under 1 atm of hydrogen in refluxing methanol. Reduction of the Ru(III) and Ru(IV) is almost certainly done catalytically involving ruthenium(III) hydride species, which are known to be present during the hydrogenation 64 of Ru(III) and Ru(IV) in aqueous HC1 solutions and DMA solutions The synthetic route is then: - 72 -RuClT-3H„0 „,H2 — > "blue solution" 3 2 MeOH , . , X I \ T O R u C l 2 ( L 1 ) 4 [RuCl 2(L , i) 2] 3 RuCl 2(L 4) 2-2H 20 L 1 = DMSO; L 2 = Dios; L 3 EE MBMSO, MPSO, and MPTSO; L 4 = DDios SYNTHETIC ROUTE 1 Addition of the ligands to the "blue solution" with continued refluxing under hydrogen (1 atm) afforded the dichlororuthenium(II) compounds. 50 The second preparative route, using RuCl3*3H20 or RuBr^, is shown below: RuC V3H 20 + L 1 \ n f C > [NH2Me2] ^ 1 3 ( ^ ) 3 ] .2 H2, 60°C n r. ,.2. + — % S " R U C 1 2 ( L 5 4 R u B r 3 + L ' H 7 D M ! 0 ° C ^ * « B r 2 C L 2 ) 4 L 1 EE DMSO, d6DMS0 and Me nprS0; L 2 EE DMSO SYNTHETIC ROUTE 2 Use of stoichiometric amounts of ligand at 80°C or 60°C under 1 atm hydrogen easily yields the ionic or neutral complexes respectively. The hydrogen reduction of the ruthenium(III,IV) to ruthenium(II) in DMA 64 with production of protons i s well known . In this acidic reaction solution at 80°C formation of the dimethyl ammonium cation apparently stabilizes the RuCljCL 1)^ - anions. The presence of acetic acid and - 73 -dimethyl amine, hydrolysis products of DMA, in the reaction mixture was confirmed by gas chromatography. Hydrolysis of DMA is known to occur at high temperatures50, ca. 350°C, but this process could be catalysed at 80°C by the ruthenium. An extra equivalent of ligand results in the tetrakis ligand route. The third preparative route uses as a ruthenium(II) source dichlorotetrakis(dimethyl sulphoxide)ruthenium(II) prepared either from 12 synthetic route 1 or 2 or by the method of Wilkinson et a l . . This 12 group have already reported the successful use of this compound as a source of ruthenium(II) complexes. The third route is then: RuCl2(DMSC04 + L 1 2^ > RuCl 2(L 2) 2; RuC 1 2 (L 2) (DMSO) (MeOH) + ^ CHCI3 3 R u C l ^ C L 2 ) 1 2 1/ = Dios; L = DDios SYNTHETIC ROUTE 3 These exchange reactions proceed easily in methanol or chloroform, with however, different results. This aspect w i l l be discussed later. - 74 -CHAPTER V DICHLOROTETRAKIS(DIMETHYL SULPHOXIDE)RUTHENIUM(II), DIMETHYLAMMONIUM TRICHLOROTRIS(DIMETHYL SULPHOXIDE)RUTHENATE(II) AND RELATED COMPOUNDS 5.1. Introduction While a number of ruthenium(II) complexes containing DMSO are 66 "*"2 known, for example the cationic species [RufNH^)^(DMSO)] , and a 33 possible dimeric species (C6H6)RuCl2(DMSO), the most investigated complex is RuCl2(DMSO)^, reported f i r s t by Rempel et a l . * * and 12 67 subsequently by Wilkinson et a l . and Stephenson et a l . . Although a l l three research groups employed different preparative methods, the products appear to be similar, with three S-bonded DMSO ligands and one O-bonded ligand. Whether the cis or trans isomers are prepared i s 12 less clear. Wilkinson et a l . reported their product to be a mixture of cis and trans isomers while Rempel et al.*"* reported the trans isomer ; only. Mixed S- and O-bonding i s known for other DMSO complexes, notably 68 + 2 the cationic species , Pd(DMSO)4 , and such. This type of co-ordination for Ru(II) i s not surprising considering this metal centre is on the 39 borderline of class a/class b (hard/soft) character Reports of halosulphoxide complexes as catalysts for hydrogenation of unsaturated organics are non-existent, and indeed i t is well - 75 -known that sulphur donors poison heterogenous systems. Nevertheless, this chapter reports on three such hydrogenation catalysts: RuCl2(DMSO)4 and two anionic ruthenium(II) halosulphoxide complexes, [NH^Me^][RuCl^DMSO)^], and [NH2Me2][RuCl^(MenprSO) ^ ] , a l l of which reduce acrylamide, and methylvinyl ketone at 60°C, under 1 atm W^; anionic complexes containing sulphoxide ligands have not been reported previously. 5.2. [NH2Me2] [RuCl., (DMSCQ ] , 1_ and [NH^ Me,,] [RuCl3(d^DMSO^], 2^ Compound _1 is prepared as an analytically pure bright yellow powder in a 66% yield. Use of d^ -DMSO gives the analogous deuteriated complex, 2_. Crystallization of 1 as powder from DMA gives bright yellow cubes. Determination of the magnetic moment of complex 1 by the Gouy method gives a zero V e££ consistent with a diamagnetic Ru(II) complex. 69 Conductivity in DMA under N 2 indicates two ions in solution, with a 22 2 -1 -1 value of A = 43.8 cm ohm moi , which remains unchanged for 48 hr. In 22 2 -1 -1 aqueous solution, the i n i t i a l conductivity (A = 134 cm ohm moi ) . This corresponds to two ions, but slowly increases over 48 hr to that 22 2 -1 -1 corresponding to the presence of three to four ions, (A = 327 cm ohm moi ). This change in conductivity can be explained i f the complex rapidly dissociates one chloride, giving a neutral ruthenium species plus two ions in solution (cation and chloride). The vis i b l e spectral data (see later) are consistent with this interpretation. Slower dissociation of the remaining chloride ligands results in the higher conductivity. If the i 50 T The compounds are reported elsewhere - 76 -complex is dissolved in aqueous silver nitrate, rapid precipitation of silver chloride occurs followed by slower precipitation until after 90 hr, 96% of the total chloride present in the complex has been precipitated (as determined gravimetrically). The ruthenium species present in solution could then be [Ru(Me 2S0) 3(H 20).j] + 2 which is analogous to 12 cationic species formed from the RuCl2(DMS0)4 complex Compound 1_ is very soluble in water, DMA, and methanol, soluble in chloroform, slightly soluble in benzene and acetone, and insoluble in ether and alkanes. It is relatively air-stable in the solid state but undergoes air-oxidation in DMA, slowly in the presence or more slowly in the absence of light, to give a green solution. The action of light on an anerobic DMA solution of 1_ does not give the green solution. 5.2.1. I.r. Spectra From accepted data for DMSO and i t s transition metal com-11,12,48,56,70 . . . , _ . , _ , . , , T , . plexes the i . r . bands of 1_ and 2_ can be assigned (Table 5.1.) . The spectra of both complexes have a strong band at 1100 cm 1 930 cm - 1 indicates no 0-bonded DMSO12. The Ru-Cl stretches in the far which is indicative of sulphur-bonded DMSO. The absence of a band at f 71,72 i . r . can be assigned from the strength and position of the bands v(Ru-Cl) are at 347 and 293 cm - 1 in the spectrum of i and 335 and 292 cm 1 71 in that of 2_, the presence of two v (Ru-Cl) bands indicating a fac-isomer The corresponding mer-isomer would be expected to have three v(Ru-Cl) bands in the region 360 - 250 cm The observed spectra in this region are similar to that of fac-[RuCl^(py)^] which has twov(Ru-CD bands at -1 73 -1 346 and 301 cm . The band at 266 cm in the spectrum of 1 is - 77 -Table 5.1. I.r. spectra (cm-1) of [NH2Me2] [RuCl3(DMSO)3] , 1_ and of i t s deuterated analogue,^ _ _ a b Frequency Assignment ' Frequency Assignment 3125br,S vfNH) 3125br,S v(NH) 3015s v(CH)cation 3015s v(CH)cation 2975m v(CH)cation 2975s v(CH) 2255m v(CD) 1 .32 2925s v(CH) 2125m v(CD) 1 .38 1605w 6d(NH) 1605w 6d(NH) 1570w 6d(NH) 1570w 6d(NH) 1465w 6'd(CH) cation 1430w « d(CH) cation 1465s <Sd(CH) 1082m 6d(CD) 1 .35 1430s 6d(CH) 1020m 6d(CD) 1 .40 1400s 6d(CH) lOlOsh 6d(CD) 1 .39 1310s 6d(CH) not obs. 1287s 6d(CH) not obs. 1250w v(CN) 1250w v(CN) 1100br,s v(S0)S-bond 1100s v(SO)S-bond 1025s pr(CH) 819s pr(CD) 1 .25 975m pr(CH) 785m pr(CD) 1 .24 cont'd - 78 -Table 5.1 (cont'd...) Frequency Assignment a,b Frequency Assignment v(CH) v(CD) 930m 843w 820m 714m 675m 422s 386m 347m 293m 266m pr(CH) Cation Cation v a(CS) v s(CS) 6 s ( C S O ) 6a(CS0) . v(Ru-Cl) v(Ru-Cl) 765m 895w 840w 625m 390s 360m 335m 292m pr(CD) Cation Cation v a(CS) Not obs, 6s(CS0) 6a(CS0) v(Ru-Cl) v(Ru-Cl) Not obs. 1.22 1.14 1.08 1.07 Subscripts: v a = asym. str., v s = sym. str., 6^  = degenerate def., 6 = sym. def., 6 = asym. def., pr = rocking. S 3. k s = strong, m = medium, w = weak, sh = shoulder, br = broad. - 79 -70,72 unassigned but could be due to a methyl torsion mode . The absence of a band at ca. 480 cm * in the spectra of 1_ and 2_, combined with the 11,12 presence of such a band in the spectra of RuCl2(DMSO)4 ' makes possible a tentative assignment of this band as v(Ru-O). This band in the spectrum of RuCl 2(DMS0) 4 > where mixed S-and O-bonding occurs, has been 12 previously assigned as either v(Ru-O) or v(Ru-S). Bands are assigned 74 to the cation by comparison with those for known compounds , although assignment of the exact vibrational mode is not possible in a l l cases. 5.2.2. Visible Spectra Inspection of the solid state and solution spectra and use of the i . r . assignment, shows that the fac-isomer persists in both chloroform and DMA solutions (Table 5. II.). In water the i n i t i a l solution spectrum of 1_ is different and also slowly changes with time. On addition of chloride ion, the spectrum rapidly becomes the same as for the complex in chloroform or DMA. These data, together with the conductivity and the *"H n.m.r. data (Table 5. III.) indicate that on dissolution of the complex in water, rapid loss of chloride ligand occurs to give RuC12(DMSO)3(H20), followed by slow loss of further chloride to give cationic ruthenium(II) species. Addition of chloride at any state regenerates the anion of 1_. - 80 -Table 5.II. Visible Spectra (nm) of 1_ Solvent Absorbance max (logs) Solid State 370, 330 sh DMA 369(2.76), 325(2.47) sh CHC13 368(2.76), 325(2.58) sh H20(6M-HC1)C 369(2.76), 325(2.50) sh 346(2.60), 215(2.51) sh a At R.T. k Nujol mull. ^ Cl added to suppress dissociation. I n i t i a l spectrum, taken after dissolution. - 81 -5.2.3. H n.m.r. Spectra", (Table 5. I l l ) In CDClj the spectrum, of the complex, 1_ shows a singlet at 63.51 attributed to the eighteen equivalent methyl protons of the S-12 66 bonded DMSO ligands ' . The presence of the singlet and the integration ratio of this peak to that due to the six methyl protons of the cation (a t r i p l e t at 62.68) indicate that in CDC13 solutions the fac-isomer is present exclusively, and this i s consistent with the visible spectral data. In X)^) the immediate spectrum of the complex after dissolution i s different from that of the complex in CDCl^; the S-bonded DMSO ligands have peaks at 63.48, and 3.39 in a ratio of 2:1, and the cation has a peak at 62.71. Addition of chloride ion, as KCl or DC1, generates the same spectrum in the S-bonded DMSO region, as found for the complex dissolved in CDCl^. These spectral changes are consistent with those observed for the v i s i b l e spectra. The two singlets observed in are due to a RuC^^MSO)^^ 0) species, where two DMSO ligands are equivalent. Addition of chloride regenerates the fac-anion. The DMSO ligands can be exchanged with d^ -DMSO ligands. Addition of ca. 10% by volume of d^ -DMSO to a CDCl^ solution of the complex results in the slow disappearance of the singlet due to the three S-bonded DMSO ligands. After 8 hr.the exchange is complete with the spectrum now consisting of a t r i p l e t at 62.68 due to the cation and a singlet at 62.60 due to free DMSO. The same exchange, only slower, occurs in M^) with added chloride ion, the total exchange taking 16 hr. See also Chapter II, for spectral diagrams, (fig. 2.8.). - 82 -Table 5 . I l l , *H n.m.r. Spectra of 1 Solvent 6(Me) Integration Peak Ratio Type CDC13 3.51 3 s 2.68 1 t D20(6M-DC1, in D 20) a 3.51 3 s 2.76 1 s D 20 b 3.48 2 s 3.39 1 s 2.71 1 s 3-Cl added to suppress dissociation. b I n i t i a l spectrum taken after dissolution, s = singlet, t = t r i p l e t . - 83 -5.2.4. Crystal Structure^ The solid state structure of the complex 1_ is shown in f i g . 5.1. Two crystallography non-equivalent anions are linked by two non-equivalent cations. The anions a l l have approximate octahedral co-ordination with three S-bonded DMSO ligands in a fac configuration, as predicted by the *H n.m.r., and i . r . spectra. There is slight distortion of the octahedral environment, possibly due to steric interference between the DMSO groups; the Cl-Ru-Cl angles are s l i g h t l y smaller than 90° (mean 87.6°), while those for S-Ru-S are slightly larger (mean 92.6°). 75 76 The strong trans-influence of S-bonded DMSO ligands i s o illustrated in the Ru-Cl distance (mean 2.426 A) which is significantly o longer than those for the mutually trans-chlorine atoms (mean 2.390 A) 77 in the octahedral complex [RuCl 3 (N^B^Me) (PPh 3) 2]-Me 20 . 5.3. [NH2Me2] [RuCl 3(Me n prS0) 3] 3 This compound was prepared in an analogous way to 1_, giving a bright yellow solid; recrystallization from DMA gave yellow cubes. The : 22 2 -1 -1 complex is a 1:1 electrolyte in DMA, under N 2 (A = 46.0 cm ohm moi ) and like the analogous DMSO compound, 1_, the conductivity remains unchanged for 48 hr. The solubility characteristics of this complex are the same as for complex 1. * i wish to thank Anthony Mercer for this structure. - 85 -5.3.1. I.r. Spectra, (Table 5. IV.) The i . r . spectrum of the recrystallized complex is similar to that of complex 1_. The presence of a strong band at 1105 cm 1 indicates S-bonded methyl n-propyl sulphoxide ligand, (for the free sulphoxide v(SO)=1050 cm"1). It is d i f f i c u l t to detect 0-bonded sulphoxide since the region 930 - 970 cm 1 of the spectrum is complicated by the presence of bands due to methyl rocking modes11. Deuteriated methyl n-propyl sulphoxide was not available to help simplify this region of the spectrum. Bands at 355 and 290 cm 1 indicate the complex i s again the fac-isomer. A strong band at 3110 cm assigned to v(NH) by comparison with complex 1_, shows the presence of the [NK^M^]* cation. 5.3.2. 1H n.m.r. Spectrum^, (Table 5.V.) The 1H n.m.r. spectrum of the complex in CDCl^ confirms the structural data implied from the i . r . data. A singlet at 63.42 due to the methyl protons adjacent to the sulphur atom indicates S-bonded sulphoxide ligands while the integration ratio of this peak to that for the cation at 62.68 indicates that only S-bonded ligands are present. The singlet also indicates that the fac-isomer is present exclusively. The methylene protons of the carbon a to the sulphur occur in the S-bonded region of the spectrum as a multiplet at 63.25 - 4.40. The methylene protons of the ^ See also Chapter II, (fig. 2.9.). - 86 -Table 5. IV. Selected i . r . spectral data (cm for [NH 2Me 2][RuCl 3(Me nprSO) 3] Frequency Assignment3 3110br,s v(NH) 1105s v(S0)bS-bond 355m v(Ru-Cl) 290m v(Ru-Cl) a s = strong, m = medium. b Free ligand: v(S0) = 1050. - 87 -Table 5.V. N.m.r.a spectrum of 3_ and MenprSO 6(Assignment) free ligand Integration Ratio for 3 Peak Type 3 free ligand 3.42 (aCH3) 3.25-4.40 (a-CH2-) 1.50-2.40 (B-CH2-) 1.08 (yCH3) 2.68 (CH3 cation) 2.50 2.60 1.45-2.00 1.10 3 2 s m m t t s t m t a In CDC13. s = singlet, t = t r i p l e t , m = multiplet - 88 -carbon are shifted downfield ca. 0.15 p.p.m. with respect to the free sulphoxide ligand and appear in the spectrum as a multiplet at 61.50 -2.40. The y carbon methyl group shows a small shift. As stated earlier, the downfield shift of the protons, on sulphur co-ordination becomes less with increasing distance from the sulphur atom; a-carbon > 3-carbon > y-carbon (^zero s h i f t ) . 5.4. Dichlorotetrakis(dimethyl sulphoxide)ruthenium(II), 4 As outlined previously, this compound i s prepared by two methods; from the methanolic "blue solutions", and by ^-reduction of RuCl3'3H20 in DMA in the presence of DMSO. Since both preparative routes give similar products only that from the methanolic "blue solutions" w i l l be described in detail. 5.4.1. RuCl2(DMS0)4 from a Methanolic "Blue Solution" The crystalline solid, obtained from the reaction solution, can be recrystallized from methanol to give yellow cubes. Conductivity in 69 22 2 i -i DMA ; (A = 0.70 cm ohm moi j indicates a non-electrolyte, however the conductivity measured in air does increase with time to a value of 2 -1 -1 ca. 28 cm ohm moi , (48 hr). The solution is now dark green and the increased conductivity must be due to formation of some cationic Ru(II) and Ru(III) species. Air oxidation to give a green, presumedly Ru(111) solution occurs with [NH2Me2][RuCl3(DMSO)3], RuBr 2(DMS0) 4 6 7, and RuCl 9 (DMSO)^ as prepared by James et a l / 1 . - 89 -The compound 4_ is quite air stable in the solid state, and i t s solubility characteristics are similar to those of 1_. The former is much more soluble in chloroform and benzene. 5.4.2. I.r. Spectral Data As the i . r . spectrum of compound 4_ i s v i r t u a l l y identical to 12 that recorded for a supposedly cis-trans isomer mixture of RuCl^CDMSO)^ , the i . r . band assignment of this can be used to assign some bands in our compound; these at 1120 and 1090 cm 1 indicate the presence of S-bonded DMSO ligands while a band at 920 cm 1 indicates O-co-ordinated DMSO. Comparison of the spectrum of 4_, in the region 370 - 295 cm with that of RuBr,,(DMS0)4 (this work and that of James et a l . 1 1 ) allows the assignment of vibrations due to metal-chloride bonds, and one band at 344 cm * can be unambiguously assigned as v(Ru-Cl). For a dichloro-complex two bands are expected for a cis-isomer and one for a trans-isomer. The presence of only one Ru-Cl band in complex 4_ would indicate that the recrystallized product is exclusively the trans-isomer. However, this w i l l be shown later to be incorrect, and the complex is in fact a cis-isomer. : 5.4.3. H^ n.m.r. Spectra^ The proton n.m.r. spectrum of compound 4_ in CDCl^ is identical 12 to that found by Wilkinson et a l . . Four singlets due to the methyl protons of the sulphur-bonded DMSO ligands occur at 63.33, 3.42, 3.49, and ^ See also Chapter II, (fig. 2.8.) - 90 -3.52. The equivalent methyl protons of O-co-ordinated and free DMSO are observed at 62.73 and 2.60 respectively. The integration ratio of the downfield singlets to the upfield pair indicate that compound 4_ contains three S-bonded and one O-bonded DMSO ligand. The presence of four singlets for the S-bonded DMSO ligands may be readily rationalized. S-bonded ligands trans to Cl- or O-bonded DMSO could give two different methyl resonances. Extra methyl resonances could also result from a mixture of isomers of five-co-ordinate trigonal bipyramidal and square 12 pyramidal structures. Wilkinson et a l . suggests that some degree of methyl inequivalence could also be present, but this i s not necessary to explain the four singlets. The closely spaced four singlets can not be unambiguously integrated to provide further information on the matter. In D2O, compound 4_ has a more simple spectrum. In the S-bonded region there are two singlets at 63.48 and 3.40 with a peak height ratio of about 2:1. There i s a singlet at 62.70 attributed to the equivalent methyl protons of free DMSO, and this assignment i s confirmed by the addition of DMSO to the solution, with subsequent increase in the height of this peak. The integration ratio of the downfield pair of singlets to the free DMSO peak is 3:1, confirming that in D20 the O-bonded DMSO dissociates. A l l possible octahedral RuCl2(DMSO)^(D20) isomers would give rise to the observed spectrum with the observed 2:1 integration ratio of S-bonded DMSO ligands. The spectrum of compound £ in 38% DC1/D20 or on addition of 38% DC1 to the compound in D20 consists of two singlets at 63.47 and 3.13, with an integration ratio of 3:1 respectively. Addition of DMSO causes the - 91 -peak at 63.13 to increase in height. The peak at 63.47 can be attributed to the equivalent methyl protons of the fac-RuCl^(DMSO)^ anion. The peak at 63.13 is thought to be due to a DMS0-DC1 adduct. The formation of the fac-trichloro isomer suggests that cis-RuCl 2 (DMSO) ^  (D^O) i s present in D^ O implying that compound 4_ is cis-RuCl 2 (DMSO)^; this assumes that no rearrangement occurs in D^O during the substitution of O-bonded DMSO by C l " . 51 5.4.4. Crystal Structure The crystal structure of recrystallized compound 4_ shows i t to be the cis-isomer, with three S-bonded and one O-bonded DMSO ligands, (fig. 5.2.). The O-bonded sulphoxide is trans to a S-bonded DMSO. The strong trans-influence of the S-bonded DMSO is apparent in 51 o this compound , as in compound 1_. The Ru-Cl bond lengths (2.435 A) are again significantly greater than would be expected i f DMSO was purely a a donor. The effect of S- and O-bonding on the S-0 bond lengths and hence the multiple bond character of the S-0 bond is clearly shown in this o structure. The S-0 bond length for S-bonded DMSO is 1.435 A compared o to 1.557 A for the O-bonded case, while the estimated S-0 single bond o 51 length i s (1.70 A) . 5.5. Comparison of Different RuCl2(DMS0)4 Products As outlined, RuCl2(DMS0)4 has been prepared to date by five different preparative routes by four different research groups. The compound seems an important precursor for the synthesis of a wide range - 93 -of ruthenium(II) complexes, and i t is worthwhile to evaluate any differences in the products from the different preparations. Available spectral data for a l l the products are presented in Table 5.VI. The i . r . , *H n.m.r. and vis i b l e spectral data presented show that the products from preparations I, IV, and V are the same, i.e., the cis-isomer with three-S-bonded and one O-bonded DMSO ligands. Although 70 one expects two v(Ru-CTj bands for the cis-isomer only one band, at 344 cm has been assigned unambiguously to date. Spectra of I, II, IV and V contain weak bands at 330 cm * and 295 cm either of which could be the second Ru-Cl band. The spectrum of RuBr2(DMSO)4 (see later), also contains a weak band at 330 cm \ and the assignment of this band 12 as the second v(Ru-Q) as done by Wilkinson et a l . is incorrect, v(Ru-Cl) bands at ca. 344 and 295 cm - 1 is similar to that found for [NH2Me2]-[RuCljfDMSO)^]. Preparations I, II, IV and V give the same isomer product, however, preparation III appears to be a mixture of isomers; the additional methyl resonances in the *H n.m.r. at 63.38 and 2.69 may be due to either a eis-chloride isomer with the O-bonded DMSO ligand trans to a chloride, or to a trans-chloride isomer. 5.6. RuBr2 (DMSO) 5_ This compound was prepared by the reduction of ruthenium(III) bromide in DMA solution containing excess DMSO. The preparation follows that for RuCl2(DMSO)^, except that a larger mole ratio of DMSO ligand to the ruthenium is used for the bromide. The [NH2Me2][RuBr^(DMSO)^] complex, - 94 -Table 5.VI. Selected spectral data for RuCl.(DMSO) 11 12 67 (I) Rempel, et a l . , (II) Wilkinson, et a l . , (III) Stephenson, et a l . (IV) This work from Methanolic "Blue Solutions" , (V) This work, from Reduction of RuCl3-3H20 in DMA. I.R.*3 *H n.m.r.0 Visible^ v(SO) v(SO) v(Ru-Cl) (CH3) S-bond O-bond S-bond O-bond X (loge) max 6 1 (I) 1100-1120 930 345,295e 361(2.72), 316(2.56) (II) 1120,1090 928 345 330, 3.32,3.43, 2.72 295f 3.48,3.50 (III) - 930 - 3.34,3.38, 2.73 3.43,3.49, 2.69 3.52 (IV) 1110,1090 930 344,295 3.33,3.42, 2.73 358(2.69) 3.49,3.52 309(2.55) (v) 1110,1090 930 344,295 3.33,3.42, 2.73 358(2.69) 3.49,3.52 309(2.55) Shown by crystal structure to be cis isomer. b In cm *; nujol mull. C In CDC13 relative to TMS. ^ In nm; CHC13 solvent. A new band found on re-examination of the preparation. f This band is not reported by the authors as v(Ru-Cl). - 95 -would probably be formed using a 3:1 stoichiometric amount of DMSO. The product, 5_, i s an orange powder which has similar s o l u b i l i t y and physical properties to RuCl2(DMSO)^. 5.6.1. I.r. Spectrum The i . r . spectrum of complex 5_ has strong bands at 1080 and 944 cm"1 which on comparison with RuCl2(DMS0)4 can be assigned as v(S0) (S-bonded), and v(S0) (O-bonded), respectively. The far i . r . contains a band 70,72 weak at 330 cm"1, which could be due to a ligand methyl torsion mode 5.6.2. 1H n.m.r. Spectra^ The "^H n.m.r. spectrum of compound 5_ in CDCl^ contains two singlets at 63.52 and 2.62 with an integration ratio of 2:1 respectively, Table 5.VII. Assignment of the peaks can be done on comparison with 67 RuCl2(DMS0)4 and previous work ; the 62.62 peak is then assigned to the six equivalent methyl protons of free DMSO, and the singlet at 63.52 i s due to the eighteen equivalent methyl protons of the three S-bonded DMSO ligands. Addition of d6~DMS0 (ca. 10% by volume) to the CDC13 solution of complex 5_ results in the very rapid (<2 min) decrease in the peak at 63.52, a resultant growth in the peak at 62.62 and the growth of a new peak at 62.72. This new peak at 62.72 must be due to O-bonded DMSO. On dissolution of complex 5_ in CDClg the O-bonded DMSO rapidly (<2 min) dissociates to give a RuBr2(DMSO)^ species. The five co-ordinate ^ See also Chapter II, (fig. 2.8.) - 96 -Table 5.VII, 1. H n.m.r. spectra of RuBr2(DMSO)4 Solvent 6(Me) CDCl, a 2.72 L3 2.62 Integration Peak Ratio Type CDClj 3.52 3 s 2.62 1 s D 20 b 3.43 3 3.33 1 s 2.70 4 s a d6-DMS0 (10% by volume) added. I n i t i a l spectrum taken after dissociation, s = singlet - 97 -species has .a single S-bonded resonance and the structure of the species could be trigonal bipyramidal with the sulphoxides in the equatorial plane. Such a structure satisfies the steric requirements of the sulphoxide ligands, with the least steric interaction resulting for the 78 sulphoxides in the equatorial plane . The site preference for axial and equatorial positions in a trigonal bypyramide structure 78 has been established . Axial bromides (d-donor) and equatorial S-bonded sulphoxides (a-donor, iT-acceptor) satisfy this generality. Alternate explanations of the single S-bonded resonance for the five co-ordinate species are possible. Rapid equilibrium between two square pyramidal isomers through a trigonal bipyramidal intermediate could result in the observed spectra, as could rapid equilibrium between monomer and dimeric species. One would expect these spectra to consist of a broad singlet, (the square pyramidal and dimer species would result in two closely spaced singlets) rather than the observed sharp singlet. The addition of the d,.-DMSO results in the formation of o RuBr2(d^-DMSO)2(DMSO), which appear to be in rapid equilibrium with RuBr2(d6-DMS0)4 through the five co-ordinate species RuBr2(d^-DMSO)^. If rapid exchange did not occur the only six co-ordinate species would be : RuBr2(d^-DMSO)^ and no singlet at 62.72 would be observed. Resonances in the S-bonded region are not present with added d^ -DMSO which implies that exchange with the S-bonded ligands is much less rapid. That the S-bonded are more substitution inert than O-bonded DMSO can be seen from the i n i t i a l spectrum where the O-bonded DMSO is completely dissociated. 12 With RuCl (DMSO) addition of d,-DMSO causes rapid loss of O-bonded DMSO - 98 -and a slower loss of S-bonded DMSO showing that O-bonded DMSO is more labile than the S-bonded DMSO. Comparison of the d^ -DMSO exchange 12 rates of RuCl2(DMS0)4 and RuBr2(DMSO)4 shows that the S-bonded DMSO are more substitution inert in the chloro-complex. Since O-bonded d^-DMSO rapidly exchanges with O-bonded DMSO in RuBr2(d^-DMSO)4 and not in RuCl0(d,-DMSO)., the O-bonded ligand is less labile in the dichloro-2 6 4 complex. Thus a l l the sulphoxide ligands in RuBr2(DMSO)4 are more labile than in RuCl2(DMS0)4. The increased l a b i l i t y would appear to be an indication of the greater kinetic trans-effect of Br compared to Cl . 79 80 In rhodium(III) octahedral complexes ' this has been rationalized in terms of a greater degree of charge transfer to the rhodium from the softer Br~, resulting in a greater pola r i s a b i l i t y of the metal, or a softer or more class b character. The more covalent bond p a r t i a l l y 81 deprives the bond trans to i t of a-bonding orbitals , and thus weakens that bond. It seems lik e l y that the ruthenium sulphoxide system can be rationalized in terms of this same explanation. For RuCl2(DMS0)4 an SN1 mechanistic exchange goes via a trigonal pyramid or the more stable 82 square pyramid intermediate ; the latter requiring rearrangement to ensure complete exchange. The pentagonal bipyramid intermediate of an S^ 2 mechanism is another poss i b i l i t y for complete exchange. It i s interesting to note that the spectrum of RuBr2(DMSO)4 in 6 7 CDClj as reported by Stephenson et a l . i s composed of four singlets in the S-bonded region at 63.51, 3.48, 3.44, and 3.39, and one for free DMSO at 62.61, with relative intensity of the S-bonded to free DMSO being 3:1. The resonance at 63.51 corresponds to that we obtained; the extra - 99 -resonances could be due to some polymeric RuBr2(DMS0)2 and RuB^CDMSO)^ (all S-bonded) species which would preserve the 3:1 integration ratio. This would be consistent with their findings, that the S-bonded peak intensities change with added DMSO; the i . r . spectrum was equivocal concerning the presence of O-bonded DMSO. The *H n.m.r. spectrum of complex 5_ in D^ O is more complicated than that for CDCl^. There are three singlets present at 6 3.43, 3.33 and 2.70. The f i r s t two are due to S-bonded DMSO while the singlet at 6 2.70 (in comparison with the spectrum of RuCl^fDMSO)^ in D^ O) is due to free DMSO. The intensity ratio of the peaks is 3:1:4. This could best be explained by the presence of two species in solution; trans-RuB^-(DMSO)2(D20)2 and cis-RuBr2(DMSO) (DO) 2 ( a l l ligands c i s ) . 5.7. Reaction of [N^MeJ [RuCl 3 (DMSO) ] and RuCl,, (DMSO)^ with Molecular  Hydrogen In terms of potential use for catalytic hydrogenation both com-pound 1_ and compound 4_ were found to react with H 2 (1 atm) at 60°C in DMA, although the extent of the reaction was never more than 10%, (assuming a Ru:H2 stoichiometry of 1:1). For complex 1_ the total extent of hydrogen up-take was completed by 1500 sees, ([Run]=0.0195M, and [H ]=0.97xlO~3M). For II -3 a similar solution, ([Ru )=0.0108M, and [H ]=0.95x10 ), equilibrated at 60°C under Ar, the extent of H 2 uptake was 14.8%. Similar solutions, ([RuII]=0.03M, [H2]=0.95xl0"3M), with added L i C l , (0.30M), or p-toluenesul-phonic acid, (0.015M) had no measurable reaction with H 2 > With the addition R 83 of a 3-fold excess of "Proton Sponge" (1,8-bis(dimethylamino)napthalene) a remarkably strong base in water (pK 12.34), the extent of the reaction _2 varied from 85-100% and is very rapid (<2000 s e c , [Ru] = 10 M). These data strongly imply the possible formation of a ruthenium(II) hydride via the - 100 -heterocyclic cleavage of H^' [ R u C l n ( L ) 6 _ n ] 2 " n + H 2 ^ [RuCl n_ 1H(L) 6_ n] 2- n + HC1 (5,1) L = DMA or DMSO The addition of a strong base would cause the equilibrium to shift to the right. During the reactions the solutions change from a lemon yellow to a bright orange colour. At the end of the reaction the DMA could be pumped off to give a red o i l which dissolved in d^ -DMSO to give a red solution; the *H n.m.r. of the solution was recorded. The d,-DMSO was o then pumped off, 5 ml of DMA added to give an orange solution, and ether added to precipitate a bright orange solid. After dissolving in acetone and f i l t e r i n g , the orange precipitate could be reprecipitated with more ether; this process removed some of the soluble proton sponge. The i . r . and n.m.r. of the orange solid were then recorded. The spectral data are presented in Table 5.VIII., and spectra in fi g s . 5.3. and 5.4. The n.m.r. of a reaction residue (after removal of DMA and dissolution in d^ -DMSO) and the corresponding isolated orange solid in d^ -DMSO, were the same. The product from RuC^tDMSO)^ is similar to that from the anionic ruthenium(II) species; both have a group of resonances centred at ca. 6 - 22.6, a single resonance at ca. 6 - 27.6, and resonances due to free DMSO (52.61) and S-bonded DMSO (ca. 63.4). The i . r . spectrum of the orange product isolated from the RuCl^tDMSO)^ system showed the presence of both S-bonded and O-bonded DMSO. The peaks at 1980 cm * and 2258 cm * are in the region for ruthenium(II) 84 85 -1 terminal hydrides ' although 2258 cm seems an exceptionally high frequency. No evidence of a bridging hydride (ca. 1400 ± 200 cm could -101-Figure 5.3. AH n.m.r. spectra of some hydride derivatives of [NH2Me2][RuCl3(DMS0) ], 1 and RuCl2(DMS0)4, 4_; 1) hydrides formed from 1 in d^ -DMSO (rH.i^/nRn =1:1), 2) the same solution after six days. -22.85 -22.65 -22.45 - 103 -Figure 5.4. '"'H n.m.r. spectra of some hydride derivatives of [NH Me 2][RuCl 3(DMS0) 3], 1 and RuCl2CDMS0)4> 4_; 1) low f i e l d spectrum of hydrides formed from 4 in d,-DMS0 (nH„/nRu =1:1), 2) low f i e l d spectrum of hydrides formed from 1_ in d^ -DMSO (nH2/nRu =1:1), 3) high f i e l d spectrum of hydrides formed from 4_ in dfi-DMS0 (nH9/nRu =1:1) - 104 --22.68 - 105 -Table 5.VIII. Spectral data for hydride derivatives of (I) RuCl2(DMS0}4 and (II) [NH2Me2][RuCl2(DMS0)3] I.r. a 1980(w), 2258(w) l u b H n.m.r. (I) (II)  1100(s), 935(s) high f i e l d i ) d -24.56 (4)C,-22.68(1) -27.70(4),-22.85(1), -22.48(1), -22.34(2) -22.65(1) i i ) 6 -27.56(2), -22.68(1) -22.48(1), -22.34(2) i i i ) f - -27.70(1),-22.85(1), -22.65(1),-22.45(4) d low f i e l d 3.35,3.55,3.69, 3.38,3.45,2.61 2.61 In cm ; nujol mull. 1 0 In d6-DMS0; p.p.m. relative to TMS; for either isolated orange solid or i n i t i a l reaction mixture residue. A l l peaks are singlets. Solutions under Ar. e Relative Peak Intensity in parentheses. ^ Reaction complete nH2/nRu = 1:1 Reaction 50% complete nH2/nRu = 0.5:1 f Solution spectrum of II measured again after six days, s = strong, w = weak - 106 -be found, although this region of the spectrum is obscured with other bands, The low f i e l d n.m.r. is indicative of S-bonded DMSO ligands. The 62.61 peak is due to either S-bonded or O-bonded DMSO ligands that have exchanged with d^ -DMSO. Whether O-bonded ligands are present cannot be discerned from these n.m.r. data. The high-field n.m.r. spectra contain exceptionally high-field hydride resonances. The usual 84 range for ruthenium hydrides i s 7 - 20 p.p.m. above T.M.S. , although complexes of other metals with high hydride shifts exist, e.g., the t 86 complex HRhCl2(PBu2Me)2 with 6-30 has been reported by Masters et a l . They attribute the high chemical shift to a very short metal-hydrogen distance for a hydride in the apical position of a square pyramidal 87 structure. Johnson et a l . have suggested that, for derivatives of the same metal, the resonance of bridging hydrogen appears at higher f i e l d than that of terminally bonded hydrogen. Comparison of HMn(CO)j-, 6 - 7.5, and H^Mn^CCO)^* 6 - 24.0 would appear to bear this out. Bridging hydrides are known to be present in a-H^Ru^(CO)^> where the hydride shift 84 i s 6 - 17.6. Kaesz and Saillant suggest that a hydride trans to a ligand of low trans-influence has a higher chemical shift than one trans to a ligand of high trans-influence. Compare for example, HRuCl(PPh^)^, 6 - 17.44, where the hydride i s trans to C l " and cis-H 2RuCO(PPh 3) 3, 6 -6.69, where the hydride i s trans to phosphine or carbonyl. Thus a hydride trans to chloride or O-bonded sulphoxide would have a higher chemical shift than a hydride trans to S-bonded sulphoxide. U t i l i z i n g the above data, one can speculate on the nature of the chlorohydridoruthenium(II) species, although the system i s clearly complex. The high f i e l d resonance, - 107 -ca. 6 - 27, could be due to bridging hydride possibly trans to a chloride or O-bonded DMSO, while the lower f i e l d resonance, ca. 6 - 22, could be due to a terminal hydride again with the hydride possibly trans to chloride or O-bonded DMSO. Since the extent of reaction determines the relative intensity of the lower to higher f i e l d resonances, one would have to postulate the existence of both bridging- and terminal-hydride species. The disappearance of the 6-27 resonance with time with concomitant growth of a peak at ca. 6-22 could be consistent with a process involving dissociation of a bridging hydride species into a species containing a terminal hydride. The presence of more than one resonance at ca. 6-22 could be due to different isomers of the terminal hydride species, although i t is surprising that the integration ratio is invarient with time. This discussion of the hydride systems is clearly highly speculative and d i f f i c u l t to jus t i f y and a detailed interpretation of the data would require considerable more work. The only real conclusion i s that hydrides are formed. 5.8. Catalytic Hydrogenation of Some Olefins with Some Anionic and  Neutral Sulphoxide Complexes The [NH2Me2][RuCl^(DMSO)^] complex, the corresponding methyl n-propyl sulphoxide complex and RuC^fDMSO)^ a l l catalytically hydrogenate acrylamide to proponamide under mild conditions (1 atm H^, 60°C) in DMA. The proponamide was isolated from the reaction mixture and identified by n.m.r. Under comparable conditions, i.e., similar concentrations of olefins, catalyst and hydrogen, a l l three catalysts have similar hydro-- 108 -genation rates. The catalyst systems display similar hydrogen uptake curves, (fig. 6.4; Chapter VI); an i n i t i a l faster reaction, gradually slows down to give linear uptake, the rates of which are given in Table 5.IX. The kinetics and mechanism for the hydrogenation of acrylamide with the [Nh^ Me;,] [RuCl^DMSO)^ catalyst is presented in detail in Chapter VI. - 109 -Table 5.IX. Hydrogenation rates a for [NH^Me^][RuCl^(DMSO)^], [NH2Me2] [RuCl 3(Me nprSO) 3], and RuCl2(DMSO)4 in DMA with acrylamide substrate pH 2 mm [acrylamide] [Ru ] 10 linear rate, Ms I) 728 0.50 0.0050 1.24 II) 730 0.54 0.0050 1.18 III) 704 0.50 0.0053 1.32 I) [NH2Me2][RuC13(DMSO)3]. II) [NH2Me2] [RuCl 3(Me nprSO) 3] . III) RuCl2(DMS0)4. a Linear uptake region; at 60 C in DMA (5 ml). - 110 -CHAPTER VI HOMOGENEOUS HYDROGENATION OF ACRYLAMIDE USING DIMETHYLAMMONIUM TRICHLOROTRIS(DIMETHYL SULPHOXIDE)RUTHENATE(II) AS CATALYST 6.1. Introduction The t i t l e catalyst is effective for the hydrogenation of some unsaturated organic substances. In DMA at 60°C at hydrogen pressures less than 1 atm, acrylamide and methylvinyl ketone are hydrogenated to proponamide and ethylmethyl ketone, respectively. Under the same conditions, hex-l-ene and cyclohexene are not hydrogenated. In aqueous solution under the same mild conditions the activated substrates are not hydrogenated, although the ruthenium complex is readily soluble. The physical properties of the catalyst are described in the previous chapter. 6.2. Determination of the Equilibrium Constant for the DMSO Dissociation  from the Complex In DMA at 60°C under 1 atm argon the t i t l e catalyst was found to dissociate dimethyl sulphoxide. Fig. 6.1. shows the U.V./Visible spectral changes of the catalyst with time, while f i g . 6.2. shows the equilibrium spectrum with various amounts of added DMSO; addition of Cl did not alter this equilibrium spectrum. The dissociation of DMSO is very - I l l -T 0.8 Figure 6.1. U. v./visible spectral changes of [NH2Me2][RuCl3(DMSO)3], _1 in DMA at 60°C; [Ru] T =0.00118M, pAr =655mm; time after solution attained; 1) 80 sec, 2) 1050 sec, 3) 3200 sec, 4) 11,200 sec. b = DMA baseline. - 112 -T 0.8 5 0 0 4 0 0 X , nm Figure 6.2. Effect of added DMSO on the spectrum of 1_ in DMA at 60°C; 1) [Ru] T =0.00102M at 25°C, [DMSO] =0.0, 2) [Ru] T =0.00118M, [DMSO] =0.0, 3) [Ru] ? =0.00120M, [DMSO] =0.006M, 4) [Ru] T =0.00112M, [DMSO] =0.0012M. pAr = 650mm. b = DMA baseline. - 113 -slow, (ca. 12,000 sec) with relatively small spectral changes; analysing the spectrophotometric data of f i g . 6.2., according to eqn. (6.1) gives a Kn value of (1.9 ± 0.2) x 10_3M, (see below). KD RuCl3(DMS0)3 , ' RuCl3(DMS0)2 + DMSO (6,1) (I) (ID An iterative method of determining KQ was employed since only the extinction coefficients of species I were known; these values were obtained at room temperature with the knowledge that dissociation i s extremely slow at this temperature. The extinction coefficients were taken to be approximately constant between 20°C and 60°C. The method fo calculating the dissociation constant is presented below. Before dissociation [I]. = Ru^ ,; [ I I ] = 0; [DMSO] = DQ; at equilibrium [ I ] = Ri^ - [ I I ] ; [DMSO] = D Q + [ I I ] . The total equilibrium absorbance A is given by; A = E [ I ] + e N [ I I ] ; A = AQ + Ae[II] and AA = A e [ H ] where Ae = E J J - E j , AA = A - AQ, and and are the molar extinction coefficients of species I and I I , respectively. - 114 -Experimental data were collected for equilibria at an approximately constant total ruthenate concentration with varying amounts of added dimethyl sulphoxide ligand. Mathematically a value of Ae is guessed and a linear plot of Ru^/AA versus (D^ + AA/Ae) is constructed. The slope of the plot (eqn. 6,2) gives Kn and the intercept Ae. With this new Ae a new plot of Ru^/AA vs (D^ + AA/Ae) is done resulting in a new value of Ae and KR. This process was repeated until successive Kn's were within 2% of each other. Table 6.1. l i s t s experimental data, and 6.II. the deter-mined values of Kn and extinction coefficients. The % dissociation of species I at the concentration used (=10 M) varied from 69% with no Q Q added DMSO to 53% with 0.0012 M added DMSO. This satisfies the criterion that reliable values of equilibrium constants are obtained only i f the extent of dissociation in the experiments is between 20% and 80%. The determination of the equilibrium constant is subject to some errors. The long times required to establish equilibria produce a base line d r i f t due to evaporation of DMA; however, a f a i r l y good isosbestic point is obtained at ca. 420 nm and 365 nm for each dissociation experiment, f i g . 6.1.^ With no added DMSO the f i r s t order dissociation rate constant, -4-1 measured from i n i t i a l rate data, was 2.6 x 10 s ; using the value for K the reverse DMSO complexation rate constant was .14 M *s *. With larger amounts of added DMSO good isosbestic points were not obtained, perhaps due to formation of some tetrakis(DMSO) species. - 115 -TABLE 6.1. Spectrophotometric data for the dissociation of DMSO from the RuCl (DMSO)" anion 450 nm 460 nm 350 nm 1 DQ(M) 103RuT(M) A A o A A o A A o 0 1.18 .19 .04 .19 .03 .63 .43 0.60 1.20 .17 .04 .18 .03 .61 .45 1.20 1.12 .15 .04 .14 .03 .55 .41 - 116 -TABLE 6.II. Equilibrium constant and extinction coefficients for the RuCT,(DMSO), anion system X (nm) (cm M ) e2(cm M ) 10° KD(M) 460 450 350 23.5 33.5 371 219 214 613 2.0 2.2 1.6 - 117 -6.3. Spectral Observations on the RuCl^(DMSO)^ Anion In the presence of a large excess of acrylamide (0.4 M), RuCl^fDMSO)^ (0.001 M) showed the same spectral changes as observed under the same conditions without acrylamide, (fig. 6.1.). The catalyst (0.001 M) under 1 atm \{ also showed the same spectral changes. These data suggest that l i t t l e reaction occurs between the catalyst species, either (I) or (II) with either or acrylamide separately. A rapid reaction of the catalyst with to a small extent, (as monitored by gas-uptake), was observed with a more concentrated catalyst solution, (see Section 5.7., Chapter V). In the presence of both acrylamide (0.4 M) and (1 atm), however, the catalyst solution (0.001 M) exhibits significantly larger spectral changes, (fig. 6.3.). Most of the change occurs before 3300 sees and is especially noticeable in the region 350 to 390 nm/ In the region 400 to 500 nm the spectral changes are similar to those observed for the loss of the DMSO ligand. Consideration of these data together with the kinetic data, (see Section 6.4.), suggests a possible interpretation in terms of formation of a Ru-hydrido-olefin and/or Ru-alkyl complex (following DMSO dissociation), which reaches a near constant concentration after about 3300 sees. Comparison of these times with those for the gas-uptake experiments must be done with caution since the spectral measurements and these reactions could be in part diffusion controlled as the solutions were not continually agitated. T 1.0 500 x 400 A , nm Figure 6.3. Effect of added acryl and on the spectrum of 1_ in DMA at 60°C; [Ru] T =0.00103M, [acryl] =0.39M, pH 2 =670mm; time after reactants combined; 1) 80 sec, 2) 530 sec, 3) 1410 sec, 4) 3300 sec, 5) 4950 sec. b = DMA baseline. - 119 -6.4. Catalytic Hydrogenation of Acrylamide The kinetics of acrylamide hydrogenation using DMA solutions of [NH2Me2][RuCl3(DMSO)3], (0.005 - 0.05 M), were studied under varying conditions of substrate concentrations, hydrogen pressure, catalyst concentrations and added DMSO and acid concentrations, by measuring the gas-uptake rate of the reaction solution. The gas-uptake experiments were conducted as outlined previously in Chapter II. The total uptake of hydrogen indicated complete reduction of acrylamide, while n.m.r. identified the product as proponamide. Fig. 6.4., shows gas-uptake plots under varying conditions; the curves have an i n i t i a l non-linear region followed by a linear region. The linear region extends to about 60% of the total, uptake and then the rate begins to f a l l off slowly. The i n i t i a l non-linear region lasts=1500 sees, and in a l l cases except with added chloride and DMAHC1 involves a decreasing rate of uptake with time. With added chloride and DMAHC1 the non-linear region involves increasing rate with time, (autocatalytic type). The linear uptake rates were measured usually between 2000 and 8000 sees and are tabulated in Table 6.III. 6.4.1. Dependence on Dimethyl Sulphoxide Concentration A plot of the linear rate of acrylamide hydrogenation against the added concentration of DMSO with other parameters fixed is shown in fi g . 6.5. The rates vary inversely with added DMSO concentration and at high [DMSO] approach a limiting value. A plot of the reciprocal rate versus the added DMSO concentration is linear, (fig. 6.6.). o TD a> o o 2.4 4-2.0 .6 4-.2 t 0.8 0.4 + 0.0 O [ R U ] T =0.037M, [ a c r y l ] =0.54M, pH2 =728mm • [ R U ] ? =0.005M, [ a c r y l ] =0.026M, pH =728rara A [Ru] T =0.005M, [ a c r y l ] =0.40M, pH 2 =728mm O [Ru] T =0.005M, [ a c r y l ] =0.-49M, pH- =728mm, to o 2000 4000 6000 8000 Figure 6.4.. t , s e c . H uptake p l o t s f o r the r e d u c t i o n o f a c r y l u s i n g 1 i n DMA at 60°C - 121 -TABLE 6. I I I. Linear hydrogenation rates for the reduction of acrylamide in DMA at 60°C using [ (NH2Me2)][(RuCl3 (DMSO)3)] [Ru ] pH„ [hi?] [acrylamide] Linear Rate xlO 3 nm xlO 3 xlO 7 Ms - 1 5.01 728 2.06 0.011 3.84 5.00 728 2.06 0.011 4.11 5.00 728 2.06 0.026 5.27 5.00 728 2.06 0.053 6.92 4.98 728 2.06 0.179 11.89 4.95 728 2.06 0.404 12.30 5.03 728 2.06 1.024 12.29 4.98 728 2.06 1.88 12.34 4.98 195 0.55 0.450 6.00 5.00 297 0.84 0.478 7.73 5.01 398 1.13 0.471 9.80 5.02 540 1.53 0.482 11.40 5.03 401 1.14 0.011 2.46 5.00 544 1.54 0.011 2.86 5.47 723 2.05 0.554 13.7 8.23 728 2.06 0.540 20.6 2.8 728 2.06 0.481 28.9 :i.9 728 2.06 0.486 42.0 - 122 -Table 6.III. (cont'd) xl03 PH2 nm [H21 xlO 3 [acrylamide] Linear Rate xlO 7 Ms-1 22.8 728 2.06 1.10 43.3 30.5 728 2.06 1.13 50.0 36.8 728 2.06 0.544 49.3 48.5 728 2.06 1.09 61.0 49.6 728 2.06 1.17 65.0 4.98 728 2.06 0.464 8.92a 5.05 " 728 2.06 0.500 7.36b 4.99 728 2.06 0.494 3.95C 5.02 728 2.06 0.477 13.9d 5.01 727 2.06 0.483 14.2e 4.99 728 2.06 0.488 f 17.0 5.00 728 2.06 0.480 15.6g 5.00 727 2.06 0.477 11. 7 h 5.01 728 2.06 0.502 9.751 5.04 728 2.06 0.486 6.53} 5.00 732 2.07 0.463 6.44k 5.00 736 2.08 1.038 7.73k 5.00 728 2.06 0.478 3.601 Added DMSO; a 0.036 M; 0.065 M; C 0.190 M. Added LiCl; d 0.033 M; e 0.067 M; f 0.104 M; § 0.132 M; h 0.631 M. Added p-toluene sulphonic acid; 1 0.023 M; J 0.096M; k 0.191 M. Added DMAHC1; 1 0.043 M. - 123 " I-2H 0.8H 0 . 4 H 0 . 5 1 — 1 . 0 -i— 1 . 5 [ D M so] Figure 6.5. Dependence of linear rate on added DMSO; [Ru] T =0.005M, [acryl] =0.49M, pH_ =728mm 2.5H 2.0H I.5H i.oH 0 . 0 5 0 . 2 0 0 . 1 0 0 . 1 5 [ D M S O ] Figure 6.6. Plot of (linear r a t e ) " 1 vs added [DMSO]; [ R U ] T =0.005M, [acryl] =0.49M, pH 2 =728mm - 124 -6.4.2. Dependence on Acrylamide Concentration The uptake rates at constant hydrogen and total catalyst concentration with the absence of added DMSO and acid vary non-linearly with increasing acrylamide concentration to a constant value (fi g . 6.7.), indicating that the olefin dependence varies between f i r s t and zero order. With added acid, the rate dependence on [acrylamide] from 0.46 to 1.04 M, becomes greater than zero order. An unusual feature of the substrate dependence is that the rate extrapolated to zero olefin concen--7 -1 tration appears to give a positive intercept of =3 x 10 Ms , and (fig. 6.8.), a "reciprocal plot" of rate 1 versus [acrylamide] tends to support this, since such plots are commonly linear when used to analyse for an olefin dependence which starts at the origin and goes from f i r s t to zero order. 6.4.3. Dependence on Hydrogen Pressure At 0.005 M Ru(II), and 0.47 M acrylamide the variation of rate with hydrogen pressure is non-linear, (fig. 6.9.). The dependence is going from f i r s t to zero order with increasing hydrogen pressure up to 1 atm. >. Fig. 6.10, a plot of (rate)" 1 vs [ H ^ - 1 is linear. At 0.005 M Ru(II) and 0.011 M substrate the rate is now f i r s t order in hydrogen up to 1 atm. (fig. 6.11.). 6.4.4. Dependence on Catalyst Concentration Plots of rate vs catalyst concentration at constant high concen-tration of hydrogen and two high concentrations of acrylamide are non-a CD e 0.1 0.2 03 0.4 [acryl] Figure 6.7. Dependence of linear rate on [acryl]; [Ru] =0.005M, pH =728mm - 126 -- 127 -to -o o or o CD C 0.5 0.0 0.5 1.0 1.5 2.0 [H 2 ] X I03 Figure 6.9. Dependence of linear rate on [H^]; [ R U ] T =0.005M, [acryl] =0.47M 0.5 1.0 1.5 2.0 [H 2 ] H X I0"3 -1 -1 Figure 6.10. Plot of (linear rate) vs [H 2] ; [Ru] T =0.005M, [acryl] =0.47M - 128 -Figure 6.11. Dependence of linear rate on [H^]; [ R U ] T =0.005M, [acryl] =0.011M - 129 -linear, (fig. 6.12.). The i n i t i a l f i r s t order dependence up to 0.015 M total catalyst concentration drops towards zero order at higher concentra-tions of catalyst, and this decrease in order occurs at lower concentration of catalyst when the substrate concentration i s lower. The inverse plot, (R - 1 vs [ R u 1 1 ] ^ 1 ) , at 0.52 M substrate concentration, shows a slight curvature, (fig. 6.13.), while that at 1.10 M acrylamide i s linear, (fig. 6.14.). 6.4.5. Dependence on Added Acid Fig. 6.15 shows that there is a very small inverse dependence of rate on added p-toluenesulphonic acid at constant total catalyst = (0.005 M), acrylamide = (0.48 M), and hydrogen = (.00206 M), concentrations. Plots of Rate - 1 vs [ H + ] - 1 were not linear and this implies a non-regular inverse dependence of rate on added p-toluenesulphonic acid. Under the same catalyst and hydrogen concentrations but with [acrylamide] = 0.085 M and added [ H + ] = 0.030 M, (p-toluenesulphonic acid), a total inhibition of hydrogenation occurred. With the same catalyst and hydrogen concentrations as used above but with [acrylamide] = 0.478 M and [DMAHC1] = 0.043 M the hydrogenation -7 -1 rate was 3.60 x 10 Ms ,lowered from the value for a comparable experiment without added DMAHC1, implying an inverse acid dependence. 6.4.6. Dependence on Added LiCl Addition of 0.03 M LiCl to the catalyst solutions in the presence of 0.5 M acrylamide,. (see Table 6.III.), resulted in a small rate - 130 -Figure 6.12. Dependence of linear rate on [Ru ]^,; pH2 =728mm, • [acryl] =0.52M, O [acryl] =1.10M - 131 -- 132 -Figure 6.15. Dependence of linear rate on added p-toluenesulphonic acid; [Ru]^ =0.005M, [acryl] =0.48M, pH =728mm - 133 -increase (ca. 1.1 times). Further addition up to 0.10 M LiCl resulted in a maximum rate increase (1.4 times), and further increase up to 0.63 M LiCl resulted in rate decrease. The overall effect of added chloride is small. 6.5. Discussion of Kinetic Results As shown in Chapter V, (Section 5.7.), the RuCl3(DMS0)3~ anion does react rapidly to a small extent with hydrogen and the promotion of the reaction in the presence of added base and the complete inhibition of the reaction in the presence of chloride or acid indicates a net heterolytic s p l i t t i n g of the H^. This, together with the inverse acid dependence, and the shape of the i n i t i a l uptake curve in the presence and absence of acrylamide suggests a "hydride path" reduction i e . , the transfer of hydrogen to the olefin occurs via a process involving addition of olefin to a ruthenium(II) hydride, (eqn. (6,3)). Ru 1 1 + H 2 ^ 1 " RuH" + HC1 K 2 H + RuH + olefin v v Ru-alkyl Products (6,3) Using the gas-uptake data of Section 5.7., an approximate maximum value for K^ , the equilibrium constant for the tt^ reaction with the [RuCl3(DMS0)3] anion, (eqn. (6,3)), is calculated to be 0.1; i t is assumed that a negligible amount of [RuCl3(DMSO)^] species are involved in this reaction due to the long times required for sulphoxide dissociation and the short period over which gas-uptake is measured. - 134 " The vi s i b l e spectral evidence also shows a f a i r l y rapidly formed intermediate, possibly a hydrido-olefin or alkyl complex, implying that both the equlibria for hydride formation and subsequent olefin complexation are rapidly established. Hydrogen could also be activated via an "unsaturate path", in which an olefin complex reacts correspondingly with hydrogen, eqn. (6,4). H + II K' 2 H Ru + olefin Ru olefin > Ru alkyl — * products (6,4) Such a heterolytic cleavage of hydrogen could also give rise to the observed inverse acid dependence. Processes such as; Ru 1 1(olefin) + H 2 ;==± H 2Ru I V(olefin) fol e f i n Ru 1 1 + products < — HRu(alkyl) (6,5) or the corresponding hydride route; II IV o l e f i n i v Ru 1 1 + H 2 ^ H 2 R u H2Ru (olefin) (6,6) as written show no acid dependence. There i s as yet no precedent in the literature for such processes involving Ru(II) complexes, (see Chapter VIII). There is no visible spectral evidence for the olefin equilibrium (K1) in a process shown in eqn. (6,4). Both reactions (6,3) and (6,4) are written as involving loss of HC1 rather than a solvated proton; this seems highly l i k e l y whether the processes involve a direct hydride substitution, or an i n i t i a l oxidative addition followed by reductive elimination, - 135 -since the HC1 can be stabilized as the DMA-HC1 adduct 1 5. The dependence on added DMSO as well as the visible spectral evidence, suggests that at least one active catalyst species in solution has lost a DMSO ligand. The positive intercept of the rate vs [acrylamide] plot, (fig. 6.7.), implies that a catalyst species functions by a path independent of the amount of substrate present in solution. Scheme 6-A, involving the hydride pathways of eqn. (6,3) is the most satisfactory for accounting for the observed kinetic and spectra data. (I) (II) RuCl 3S 3 + H 2 f a i t HRuCl 2S 3 + HC1 ft (V) RuCl 3S 2 + S fast ^K2 olefin,-S (III) HRuCl 2S 2 olefin slow |k 4H 2,-HCl (VI) k 3 > slow (IV) HRuCl„S"+olefin RuCl„S„ alkyl 2 2 fast 2 2 J • [k HCl fast (V) RuCl 3S 2~ + Sat. Product SCHEME 6-A (solvent molecules excluded; S=DMSO) is the equilibrium constant for hydride formation, Kn is the equilibrium constant for sulphoxide dissociation, (see Section 6.2.), K~ - 136 -is the equilibrium constant for olefin binding to give a hydrido-olefin complex (III), kg is the rate constant for a process involving isomeriza-tion of (III) and hydride transfer steps, k^ is the rate constant for a rate determining addition to the bis-sulphoxide species (V), k^ is the rate constant for the process of olefin complexation to (VI) and subsequent insertion into the metal-hydride bond, and k^ is the rate constant for the fin a l protonolysis step yielding saturated product and regenerated catalyst species (V). The mechanistic pathways, when steady concentrations of species (I-III) and (V) have built up, (linear uptake region), leads to the following rate expression; -d[H ] Rate = R = = k ^ I I I ] + k 4[V][H 2] (6,7) K 1K 2k 3[I][H 2] [olefin] K ^ f T ] ^ ] R = [HC1][S] + [S] ( 6 , 8 ) The total ruthenium(II) concentration, [Ru**],^ ,- is given by; [ R u H ] T = [I + II + III + V] (6,9) the concentrations of species IV and VI are negligible due to the fast reaction steps governed by k<. and k^. Eqn. (6,9) can be rewritten to give; r„ II, m n W [olefin] Kn [Ru ]T= [i](i + - 1 H C T r + — [ H C I H S ] + Ts]> C6'10) - 137 -Hence: K 1K 2k 3[Ru I I] T[H 2][olefin] [HC1][S] + K X[H 2][S] + K XK 2[H 2] [olefin] +. ^[HCl] + W^\[H2]  K [H][S] K K [ H ][olefin] ™ + [HcJl] + [Hd] + KD ( 6 ' U ) Eqn. (6,11) i s exact for conditions of olefin concentration where the concentration of species (III) is negligible compared to the concentration of free olefin, [olefin]. At low concentrations of total added olefin, [olefin]^, the following expression holds; K K [H ][I] [olefin] = [olefin] (1 + t j . . , - . ) (6,12).. Rewriting eqn. (6,11) in terms of (6,12) gives; K 1 K 2 K 3 [ R u I I ] T [ H 2 ] [ o l e f i n ] T R = K K [H ][olefin] [HC1][S] +K 1[H 2][S] + K^K 2[H 2][I] + ^ [ H C 1 ] [ H 2 ] ( [ I ] + [II] ^  [III] + [V]) 1 + [HC1] [S] K D k 4 [ R u H ] T [ H 2 ] + K X[H 2][S] K I K 2 [ H 2 ] [ o l e f i n ] T ( 6 ' 1 3 ) [ S ] + [HC1] + K 1K 2[H 2][I] + KD 1 + [HC1][S] where ([I] + [II] + [III] + [V]) is of course equal to [ R u 1 1 ] ^ (eqn. (6,9). Equation (6,13) is the exact rate expression for a l l concentrations - 138 -of olefin. Over the range of acrylamide concentrations employed at [Ru* 1]^ = 0.005 M the concentration of hydrido-olefin complex (III) should be small compared to the concentration of added acrylamide. The maximum value of [III] is 0.005 M which should only occur at very high [acrylamide]. At [acrylamide] = 0.011 M the amount of species (III) present should be small compared to 0.011 M. For a l l practical purposes then, eqn. (6,11) can be used accurately with [olefin] = [olefin]^. At higher concentrations of total catalyst the amount of species (III) could be significant compared to the added olefin concentration and as a result eqn. (6,11) would be inaccurate. Rate expression (6,11) has two terms corresponding to the two pathways, (I -»-II-»- III -* IV V) and (I -> V-> VI IV->-V), respectively. The f i r s t term i s an olefin-dependent path, while the second term represents an olefin-independent path, (the names are assigned on the basis of their olefin-dependence neglecting the denominator terms in [olefin]. The olefin-dependent term of (6,11) increases in value up to a constant value as the concentration of olefin is increased, i e . , this describes a f i r s t - .to zero-order dependence on [olefin]^ since the denominator term K . ^ [ H ^ l [ o l e f i n ] T at constant [H^] becomes large compared to the other denominator terms. The dominance of this term at high constant [olefin]^ results in a f i r s t to zero order dependence of the f i r s t term rate with increasing [H^] at high constant [olefin]^. The olefin-independent term decreases in relative value compared to the olefin-dependent term as the concentration of olefin is increased; at high olefin and H_ concentrations the relative contribution of this term - 139 -to the total rate should be negligible; the maximum value of this term, - 7 - 1 according to the plot of f i g . 6.7. , is ca. 3 x 10 Ms at zero [olefin]^ and ca. 1 atm H^ . The rate expression (6,11) is clearly complex although limiting forms can be derived. One mathematical limit of eqn. (6,11) becomes evident at some very high olefin and hydrogen concentration when the total rate becomes; R = k 3 [ R u H ] T (6,14) ie . , the rate i s independent of hydrogen and olefin concentrations (as observed experimentally), due to the olefin complex (III) being f u l l y formed. Fig. 6.12. shows that the rate i s f i r s t order in [Ru 1 1]^, at low [Ru^]^, and higher acrylamide concentrations. Using eqn. (6,14) and -4 -1 data from f i g . 6.7., a value of k 3 can be calculated to be =2.5 x 10 s . At lower olefin concentrations the relative contributions of both the olefin-dependent and independent paths to the total rate are significant. As well, the [H2] [ o l e f i n ] T term in the denominators of eqn. (6,1) are now not dominant and this can reduce to; K K k [Ru11] [H ] [olefin] L k [Ru 1 1] [H ] R = 1 1 * L-—t + JLA \—£_ (6,15) ([HC1][S] + KptHCl]) ([S] + KD) corresponding to the predominance of species (I) and (V). Here again the f i r s t term of eqn. (6,15) i s for the olefin-dependent path and the second for the olefin-independent path. The experimentally observed dependence - 140 -on [ole£in]T, ( f i g . 6.7.), at lower [ o l e f i n ] T is consistent with this expression as is the f i r s t order dependence on [H 2], (fig. 6.11.) i f the concentrations of HC1 and S are relatively constant with varying [B^]. If the olefin-independent path i s predominant at 0.011 M acrylamide the second term of eqn. (6,15) gives the rate. In this path the concentration of DMSO produced w i l l be constant at a constant concentration of olefin; (increasing the concentration of olefin w i l l decrease the concentration of species (V) by increasing that of (I), (II) and (III) and result in a varying [DMSO]). An approximate value of k^ can be calculated from this term, using a slope value from f i g . 6.11. (a plot of rate vs [H^] at 0.011 M acrylamide), a previously calculated value of (see Section 6.2.), a value of [S] calculated from Kn, and a value of [Ru 1 1]^, = 0.005 M. The -4 -1 -1 -1 slope of 1.92 x 10 s gives a value of k^ - 0.08 M s Extrapolating to zero [olefin]^ on f i g . 6.7., gives the intercept rate for the olefin-independent term of eqn. (6,15 ). This equation can be used to obtain an approximate value of k^ at zero olefin concentration. Using the same values as used in the k^ calculation above and a rate of -7 -1 -1 -1 3 x 10 Ms for zero [olefin]^, gives a value for k^ of =0.06 M s , in good agreement with the previously obtained value for k^. In general, any concentration changes which can reverse the equilibria governed by and K^, w i l l result in a decrease in rate of the olefin-dependent path and thus increase the relative contribution of the olefin-independent path to the total observed rates; added DMSO w i l l , - 141 -however, decrease the rates of both paths. 6.5.1. Dependence on DMSO Concentration Added DMSO should affect the hydrogenation pathways by reversing somewhat the equilibria governed by the constants K^ , K2 and Kn; this lowers the concentrations of (II), (III), and (V) and increases that of (I). The net result w i l l be an overall rate decrease. Eqn. (6,11) can be rewritten to give; ([HC1] + K [H ]) R = [S] • 1 Z ( K 1 K 2 k 3 [ o l e f i n ] T + K Qk 4 [HC1] ) [ R u 1 1 ] ^ ] K 1 K 2 [ H 2 ] [ o l e f i n ] T + KD[HC1] ( K ^ k ^ o l e f i n ^ + K nk 4[HCl])[Ru H] T[H 2] (6,16) A plot of R 1 vs added [DMSO] at high [acrylamide]^ is found to be linear 5 - 1 6 - 2 with a positive intercept of 7.8 x 10 M s and slope of 9.3 x 10 M s, . (fig. 6.6.). The slope and intercept of eqn. (6,16) both contain [HC1] terms, although in the numerator of the intercept the K n[HCl] term should be negligible compared to K^K 2[H 2][olefin]^. The concentration of HC1 at any time should be equal to the concentrations of (II) plus (III), (Scheme 6-A); the maximum value of the [HC1] is [Ru 1 1]^, in these experiments 0.005 M. The observed rate decrease with added DMSO (a factor of one-third with [DMSO] = 0.19 M) is largely due to a decrease in the [III] by one-third, (eqn. (6,7)), implying a maximum decrease in the [HC1]' of one-third i e . , the [HC1] decreases from 0.005 M with no added - 142 -DMSO to a minimum of 0.0017 M, the actual decrease depending upon and' K 2 > The linear plot of f i g . 6.6. implies that the fluctuation in the [HC1] is small enough to result in an essentially constant slope value. By neglecting the small numerator term, K^fHClJ, and the denominator term Kpk^fHCl] from the intercept expression, (eqn. (6,16), a value of k^ can -4 -1 be calculated to be 2.6 x 10 s , in good agreement with the value obtained previously from the maximum rate data, (eqn. (6,14)); this sugggests that the contribution from the olefin-independent path to the total rate under these conditions is small, (ie., K^k^fHCl] << K 1 K 2 k 3 [ o l e f i n ] T ) . 6.5.2. Dependence on Substrate Concentration Inspection of eqn. (6,11) shows that the reciprocal of the rate is a complex function of [olefin]^, due to the contribution of both olef in-dependent and :- independent terms except at high olefin concentrations. A limiting form of the reciprocal rate expression at higher [olefin]^ can be derived (assuming the olefin-independent path is insignificant at these high olefin concentrations): .! ! ([HC1][S].,+ K ^ H S ] + KD(HC1]) R - 143 -Fig. 6.8. is a plot of R 1 vs [olefin] ~* which at high [ o l e f i n ] T 4 approaches a limiting slope of 4.2 x 10 s and has a positive intercept of 7 x 105 M *s. With increasing [olefin]^ the slope approaches zero due to the growing contribution of the olefin-independent path to the total rate. Here again the [S] and [HC1] vary with the [ o l e f i n ] ^ 1 causing a minor variation in the numerator of the slope term of eqn. (6,1 A value of k^ can be obtained from the intercept of the curve of f i g . 6.8. and eqn. (6,17) and is found to be 2.9 x 10 4 s in good agreement with the previously found values, (see Section 6.5. and 6.5.1.). 6.5.3. Dependence on Hydrogen Concentration Eqn. (6,11) can be rewritten to give; _! j . ([HC1][S] + KD[HC1]) R [ H 2 ] (K 1K 2k' 2[olefin] T + K ^ [HC1]) [ R u H ] T K [S] + KK [olefin] + _ _ i 1 z ; j-g ( K 1 K 2 k 3 [ o l e f i n ] T + K ^ [HC1] ) [ R u H ] T The plot of R _ 1 V S [ H ^ - 1 at high [olefin] , (fig. 6.10.), is linear 2 5 - 1 with a slope of 6.7 x 10 s and a positive intercept of 4.6 x 10 M s. A decrease in [H2] could increase the relative significance of the olefin-independent path, i f the effect of decreasing [H2] on the olefin-dependent path equilibria (K^, K2) is smaller than the effect on the olefin-independent path rate determining step (k^). If the relative contribution of the olefin-independent path to the total rate at this - 144 " high acrylamide concentration (0.47 M), is insignificant at high [H,,], then the intercept term of eqn. (6,18) approximates to 1/k^[Ru*1]^; by neglecting the K^[S] term, a value of 4.4 x 10 4 s 1 is obtained, which is in reasonable agreement with the previously obtained values. It would be expected that the slope term of eqn. (6,18) would not be constant due to the [HC1] and [S] dependence on [rl,] . However, the linear plot obtained in f i g . 6.10., implies that the numerator of the slope term .is relatively constant. This could occur i f the [S] increases somewhat as the [HC1] and the f ^ ] decreases. Decreasing the concentra-tion of decreases the [S] for the olefin-dependent path but could increase the [S] from the olefin-independent path. 6.5.4. Dependence on Catalyst Concentration This dependence is again complex owing to the non-zero contribu-tion of the olefin-independent path to the total rate at the higher total catalyst concentration. The dependence appears to be i n i t i a l l y f i r s t order in total catalyst concentration and then decreasing in order with increasing [Ru 1 1]^. At these higher catalyst concentrations, the olefin substrate to total catalyst ratio is decreasing, and the amount of substrate present is not large enough to f u l l y form complex (III). This results in a decreasing [III]:[Ru* 1]^ ratio, and a decreasing order dependence of rate on [Ru 1 1]^. Concomitant with the decreasing extent of formation of (III) i s the growing significance of the olefin-independent path to the total rate. - 145 -Eqn. (6,11) can be rearranged to give; ([HC1][S]+K [H][S]+KK[H ] [olefin] +K [HC1]) R = i j — • — — (6,19) [Ru X ] T _(K 1K 2k 3[olefin] T + K ^ f H C l ] ) [H2] Figs. (6.13.) and (6.14.) show plots of (rate - 1) vs [Ru 1 1]^ 1 for two different acrylamide concentrations. The plot at [acryl]^, = 0.52 M, (fig. 6.13.), is slightly curved presumedly due to the variation of [S] and [HC1] with [Ru* 1]^, as well as the presence of the olefin-independent path. The linear plot at 1.10 M acrylamide, (fig. 6.14.) implies that complex (III) i s more f u l l y formed, the contribution from the olefin-independent path i s less and the KjK,,[H2] [ o l e f i n ] T and X^K^k^[H2] [ o l e f i n ] T terms are predominant. At these conditions the slope of eqn. (6,19) 3 reduces to l A y The slope value, (7.65 x 10 s) of this plot gives a -4 value of ^  = 2.7 x 10 s, in good agreement with previously obtained values. Both plots of R" 1 V S [ R U T I ] t , (figs. 6.13. and 6.14.) have positive intercepts implying that eqn. (6,19) should have an intercept term. As was stated earlier, eqn. (6,11) i s inaccurate at higher total . catalysts concentrations; the exact rate expression of eqn. (6,13) can be rewritten in the form of eqn. (6,19) to give an intercept term of l / k ^ [ o l e f i n ] T . The intercept corresponds to an i n f i n i t e concentration of total catalyst where the maximum rate would be equal to k ^ f l l l ] = k^folefin]^. From the intercept value (7.9 x 10 4 M ''"s) of the plot of R 1 vs [ R u I J ] T 1 (fig. 6.14.) a value of k^ = 1.2 x 10 5 s 1 is obtained. This value is in poor - 146 -agreement with previously obtained values; however, the intercept and hence the value i s subject to error created by extrapolation. 6.5.5. Dependence on Added Acid. Experimentally, the reaction rates decrease sli g h t l y at high substrate concentrations and much more at lower substrate concentrations with added p-toluenesulphonic acid. Addition of DMAHC1 under comparable conditions at high substrate concentration decreases the reaction rate far greater than does added p-toluenesulphonic acid. Addition of HC1 causes the reversal of the equilibrium governed by K^ , causing a lowering of the concentrations of species (II) and (III). Added HC1 should have l i t t l e effect on the olefin-independent path, resulting in an enhancement of this path's contribution to the overall rate. The limit in rate lowering with added HC1 should be the olefin-independent _7 rate which, from the rate vs olefin plot, (fig. 6.7.) is about 3 x 10 -1 -7 -1 Ms . The rate measured at 0.043 M DMAHC1, (3.6 x 10 Ms ) is very close to this value suggesting that K^ K^  is quite small (of the order of 0.01) ie., very l i t t l e of species (II) and (III) are present under these conditions. The marked smaller effect on rate due to p-toluenesulphonic acid as compared to DMAHC1 implies that the equilibrium i s reversed by added HC1, not just by the H + as supplied by the sulphonic acid. The observed non-regular inverse rate dependence on sulphonic acid also suggests this equilibrium is not effectively reversed by addition of this acid without.addition of Cl as well. This non-regular acid dependence - 147 -makes i t impossible to quantitatively analyse the p-toluenesulphonic acid dependence data. With added DMAHC1, (0.043 M) l i t t l e dissociation to H + and C l " 32 occurs so that v i r t u a l l y a l l the added DMAHC1 is available as HC1 to reverse the equilibrium. The complete inhibition of hydrogenation at relatively low acrylamide concentration, (0.085 M) with added p-toluenesulphonic acid is not readily explained; co-ordination of the acid to the catalysts could occur. 6.5.6. Dependence on Added Chloride As was seen earlier, (see Section 5.7. and 6.5.) addition of chloride inhibited the reaction of catalyst with by reversing equilibria such as that governed by (Scheme 6-A). Addition of chloride to the acrylamide system caused small rate increases, (see Section 6.4.6.). This could be due to the large excess of chloride forming some tetra-chloro species and these could be somewhat more active; however, spectral evidence, (see Section 6.2.) does not suggest formation of these species. This p o s s i b i l i t y was not studied further. 6.6. The Nature of the Non-Linear Region Reaction Rates As stated previously the gas-uptake plots, (fig. 6.4.), showed an i n i t i a l non-linear region. This region can be accounted for by the catalytic system approaching an equilibrium state where the concentrations - 148 -of species (I - V) have become constant. The i n i t i a l region is then attributed to the reaction of species (I) with hydrogen to produce (II) which subsequently reacts with olefin to produce species (III), (IV) and (V). I n i t i a l l y when no complex (III) is present the reaction rate of (I) with to produce (III) is large (as evident by gas-uptake data in the absence of olefin), but as the concentration of complex (III) builds up the observed rate slows down somewhat until i t becomes constant with a steady state concentration of complex (III) and (V). With added chloride or DMAHC1 the reaction of species (I) with hydrogen is inhibited, (see Section 5.7. and 6.5.). Slow dissociation of sulphoxide from species (I) to form (V) must occur (as evident by spectral data) as well as the reaction of (I) with H 2 to form some (II) and (III). The eventual build-up of species (III) and in particular (V) could result in an increasing rate as more of these species are produced. Eventually again a steady state equilibrium concentration of (III) and (V) is achieved and the rate becomes constant. An inhibition of the overall hydrogenation rate by added chloride would be expected due to the suppression of equilibrium K^ ; however the linear rate i s in fact increased somewhat. Thus a contribution from a more active tetrachloro-species seems l i k e l y . 6.7. Discussion The mechanistic scheme, 6-A, f i t s the observed kinetic data at least qualitatively and semi-quantitatively. The values of k^ obtained are reasonably consistent, adding credence to the proposed mechanism. The presence of two non-equivalent kinetic pathways makes analysis for other rate and equilibrium constants generally unattainable with the available data; however values for k^ were obtained. Both' pathways of Scheme 6-A involve activation of hydrogen and olefin via i n i t i a l formation of a metal-hydride complex and decomposition - 149 -of a common metal-alkyl species via protonolysis. This hydrogen and olefin activation process i s well known, in particular for the systems on _ i 1 c qri involving H R u C l ( P P h ) 3 , [RuCl 3(bipy)]~ z , HRh(CO)(PPh3)3 , [Ptei^SnCl^] " 2 9 1 and HIrCl 2(DMSO) 3 9 2. However, only in the case of the Ir and Pt systems has protonolysis of the metal-alkyl intermediate to form the saturated product been postulated. The reaction of hydrogen with RuCl 3S 3 or RuCl.^(DMA)~ can proceed by either "direct substitution" of hydride anion for chloride, or oxidative addition of H 2 to form an eight-co-ordinate species followed by reductive elimination of HC1. For the olefin-dependent pathway the reaction of RuCl 3S 3 with H 2 is written as a fast equilibrium step while the corresponding reaction of RuCl3S2(DMA) i s a slower rate determining step; this could be rationalized in terms of the extra sulphoxide ligand acting as a iT-acid (relative to DMA), and thereby stabilizing hydride formation. Scheme 6-A can be expanded to show both kinetic pathways in more detail. The olefin-dependent pathway is shown below; - K l RuCl 3S 3 + H 2 |=| HRuCl 2S 3 + HC1 (6,20) - V HRuCl 2S 3 HRuCl2S2(DMA) + S (6,21) K2 , T HRuCl2S2(DMA) + olefin f==| trans-HRuCl^ (olefin) (6,22) - k3 ~ -trans-HRuCl 2S 2 (olefin) c i s - H R u C l ^ (olefin) (6,23) - V cis-HRuCl 2S 2 (olefin) R u C l ^ a l k y l (6,24) - 150 -Since hydride has a high trans-labilizing effect, reaction (6,21) w i l l result in the loss of a sulphoxide trans to the hydride. Equilibrium (6,22) should result in an olefin co-ordinated trans to the hydride ligand. For insertion of the olefin into the metal hydride bond to occur, (eqn. 6,24), the olefin has to be co-ordinated cis to the hydride ligand. The isomerization step, (eqn. 6,23), is thought to be the slow step of the pathway, since isomerization of a six-co-ordinate species should be relatively d i f f i c u l t . A few hydrido-olefin complexes are known but 22 their stereochemistry is uncertain 93-95 Reports of kinetic studies on the insertion process involving trans-hydrido-olefin complexes of platinum(II) have shown that for such square-planar complexes, isomerization to the cis-isomer can occur via co-ordination of an olefin, solvent molecule or counter-anion to form a five-co-ordinate intermediate which rearranges and dissociates a ligand to form the cis-square planar complex. This complex then undergoes insertion of the olefin to form the metal-alkyl. The rate determining step for these systemswas thought to be the insertion step and not the trans-cis isomerization. With the present six-co-ordinate DMSO species, trans to cis isomerization could proceed via either a five-co-ordinate,, or less likely, a seven-co-ordinate intermediate. The olefin-independent path of Scheme 6-A is shown in more detail below; KD RuCl_S_ RuCl_S_(DMA) + S (6,25) - 151 -RuCl3S2(DMA) + H. HRuCl S2(DMA) + HC1 (6,26) HRuCl2S2(DMA) + olefin f a i t cis-HRuCl S (olefin) (6,27) HRuCl 2S 2(olefin) 'ast (6,28) Kinetic data require that the monohydride complexes formed in the olefin-dependent and -independent paths, (eqns. (6,21) and (6,26)), respectively be different isomers. Further, co-ordination of olefin to these complexes (eqns. (6,22) and (6,27)), respectively, must produce a trans- and c i s -hydrido-olefin isomer respectively, i e . , the data exclude any crossing of the olefin-independent path into the olefin-dependent path via monohydride or hydrido-olefin complexes. It is impossible that the slow step, (eqn. (6,26)) could involve isomerization to produce a solvated hydride complex perhaps with a hydride ligand trans to a sulphoxide; when the olefin replaces DMA in the co-ordination sphere a l l isomers with hydride trans to sulphoxide would yield cis-hydrido-olefin complexes. The insertion step, (eqns. (6,24) and (6,28)), involves promotion of the electrons of the metal-hydride bond into the olefin anti-bonding : orbitals, and transfer of the hydrogen to form the alkyl derivative. Promotion of the electrons into the olefin anti-bonding orbital becomes more d i f f i c u l t with increasing electron density in this anti-bonding orbital. An octahedral Ru(II)-olefin complex is lik e l y to have consider-able electron density within the olefin anti-bonding orbital due to effective TT-backbonding from the metal. As this transfer step i s 22 usually fast some electronic redistribution is li k e l y occurring to - 152 -f a c i l i t a t e insertion. With "activated" olefins such as acrylamide, hydrogen transfer (as hydride) to the more positive Y carbon atom is probably more favoured than transfer to the other olefin carbon atom. This polarization of the olefin could well promote the insertion reaction; CHo=CH-C0NH_ + H-Ru > CH--CH-CONH. (6,29) Ru Such a rationale also explains the non-hydrogenation of simple terminal olefins such as hex-l-ene. The question of the direction of addition of a metal-hydride across an olefin link (Markownikoff or anti-96 Markownikoff), i s in general a complex problem As stated, the. last step of Scheme 6-A is the rapid protonolysis step by HC1. Electrophilic attack of HC1 on the metal-bonded carbon atom yields the saturated product as well as the catalyst species, either as the mer or fac chloride isomers. - 153 -CHAPTER VII (S,R;S,S)-(+)-2-METHYLBUTYL METHYL SULPHOXIDE COMPLEXES OF RUTHENIUM(II) 7.1. Introduction Homogeneous catalytic asymmetric hydrogenation using compounds 6,28,97,98 containing chiral phosphine ligands has been known for some time > and high enantiomeric excesses have been achieved particularly with 98 a-acetamido amino acid substrates . The following studies present the f i r s t asymmetric hydrogenation catalysts containing a chiral sulphoxide. This chapter describes the physical characteristics of the compounds, while later chapters describe the kinetics of hydrogenation, and asymmetric hydrogenation using one of the catalysts, dichloro((S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide)ruthenium(II), 8_. A rather poorly characterized ether-solvated dichlorobis-sulphoxide complex 7_, and the products of the reaction of compound 8_ with carbon monoxide wi l l also be : discussed. Complex 8_ is the f i r s t of a series of three bis-sulphoxide polymer species. The remaining two w i l l be discussed later. 7.2. Ether-Solvated Dichlorobis(MBMSO)ruthenium(II), 7 This compound was prepared by adding (R,S;S,S)-(+)-2-methylbutyl methyl sulphoxide to a methanolic "blue solution" (nMBSO/nRu = 3.6/1). - 154 In the presence of ether the reaction residue yielded green-tinted yellow crystals. The amount of ether present in the product, which could not be removed in vacuo varied with the preparation. The elemental analysis of one preparation shows diethyl ether impurity, ca. 19%. 2 -1 -1 Compound 7 i s a neutral complex in DMA, (A = 4.5 cm ohm mol ) , the solution in air turns green slowly, li k e l y giving a ruthenium(III) species. The green tint of the solid could be due to traces of the oxidized product. The complex is soluble in water and polar organic and halogenated solvents, but insoluble in ether and alkanes. 7.2.1. I.r'. Spectrum The i . r . spectrum contains a strong band at 1100 cm 1 assigned to the SO stretch of S-bonded sulphoxide, (free MBMSO, v(SO)=1025 cm - 1). A band due to possible O-bonded sulphoxide could not be detected due to ligand absorbances. Strong bands due to diethyl ether are present at 842, 1120, and 1300 cm"1. The far i . r . has a broad band at 347 cm"1, which i s assigned to v(Ru-Cl). 7.2.2. 1H n.m.r. Spectrum^ Compound ]_ in CDCl^ has a complicated 1H n.m.r. spectrum. In the region 60.9 - 1.4 there are large peaks due to the protons of the 8, y a n a 6 carbons of the sulphoxide as well as the methyl groups of diethyl ether. In the region 62.9 - 3.8 there are both broad and sharp See also Chapter II, (fig. 2.9.). - 155 -peaks due to the protons of the a carbons of S-bonded sulphoxide and the methylene protons of diethyl ether respectively. At 62.7 - 2.9 there is a singlet and a broad peak due to the protons of the a carbon of O-bonded sulphoxide. An exact integration ratio between the peaks due to S and 0-bonded sulphoxides is not possible due to the presence of the diethyl ether peaks, however a rough integration indicates predominantly sulphur co-ordination. 7.2.3. Discussion Collective data for the complex suggest a dichloro bis-sulphoxide complex, with predominantly S-bonded sulphoxide, but also containing O-bonded sulphoxide. The sulphoxide to ruthenium ratio of the compound (2:1) compared to that of the reaction solution (ca. 3.6:1), is indicative of the steric interference that would be present in a dichlorotris- or tetrakis- sulphoxide complex, (species that are readily formed with for example DMSO). The low co-ordination number of ruthenium, excluding ether,(which shows no sign of co-ordination according to the i . r and n.m.r. spectra) suggests that the compound is not monomeric and could be dimeric or polymeric with possibly bridging chlorides, although the i . r . shows terminal chlorides are definitely present as well. In analogy to a dichlorobis (MBMSO) ruthenium (I I) trimer 8_ (see later) compound 1_ could similarly be a trimer with diethyl ether solvated in the crystals. Molecular weight studies for compound 7_ were not carried out however. - 156 -7.3. Dichlorobis(MBMSO)ruthenium(II) trimer 8^  Compound 8^  i s again prepared from a methanolic "blue solution" with a reaction mole ratio of 2:1- for sulphoxide to ruthenium. The reaction residue was freeze-dried from benzene to yield the product. Attempts at recrystallizing this compound from various solvent systems, in particular, CK^C^-n-hexane, gave o i l s . During the freeze-drying, , residual methanol and water are presumably pumped off,.together with excess chloride as HC1. The compound varies in colour, depending on the preparation, from tan to gold. Anerobic elution of the compound on an alumina column (grade III) with chloroform, methanol or a mixture of the two results in a light yellow solid which has the same elemental analysis (C,H,C1) as the parent compound. A non-moving green band remains on the column; since the parent compound in CCl^, benzene, or CHCl^ turns green readily in a i r , this band li k e l y contains ruthenium(III) species. After a few days in a i r the green solution deposits green crystals, possibly a ruthenium(III) sulphoxide complex, although this was not studied further. In benzene the compound shows a degree of association of 2.9 (M.W. = 1273 g/mole) indicating a probable trimer in the solid state. A 22° measured y g££ of 0.57 ± .17 B.M. per trimer (Gouy method) which, in view of the air sensitivity of the compound, is consistent with a diamagnetic ruthenium(II) complex with some paramagnetic ruthenium(III) impurity, (see discussion). 22 2 -1 -1 The conductivity in DMA, (A = 7.2 cm ohm moi ), indicates an essentially non-ionic complex; Compound 8_ is soluble in organic solvents except alkanes and diethyl ether where i t is insoluble, and slightly soluble in water. - 157 -7.3.1. I.r. Spectrum The i . r . spectrum of compound 8_ contains a strong band at 1105 cm 1 attributed to v(S0)of S-bonded sulphoxide. Again the detection of an O-bonded sulphoxide band is not possible due to other ligand absorbances. The far i . r . has a broad strong band centred at 330 cm 1 attributed to terminal Ru-Cl stretches. 7.3.2. *H n.m.r. Spectra^ The proton n.m.r. spectrum of compound 8_ in CCl^ or CHCl^ is : complicated, consisting of broad peaks. Peaks due to the sulphoxide protons of the y and 6 carbons are found in the region 60.7 - 1.75 while peaks of the 3 carbon protons are at 61.85 - 2.50. In the region 62.8 -4.2 are peaks due to the protons of the a carbons of the sulphoxides. The peak areas show that mainly S-bonded sulphoxides are present however the p o s s i b i l i t y of some O-bonded sulphoxide cannot be entirely ruled out, due to the close proximity of the peaks. Integration of the region 60.7 - 2.7 and 62.8 - 4.2 yields the proton ratio 1.75:1, similar to the ratio of the 8, y, and 6 carbon's protons to the a carbon protons for the free ligands (1.80:1). The broadness of the peaks can be explained by the many different chemical environments of the ligand protons. Since the compound is associated in solution, even in polar DMA (kinetic data, see later), the number of different environments is compounded. The long See also Chapter II, (fig. 2.10.). •t - 158 -alkyl t a i l of the sulphoxide ligand could rotate about somewhat, giving a variable chemical environment and broad peaks. Dissolution of compound 8_ in d^ -DMSO gives a simple spectrum. The spectrum, 5 min after solution, is essentially that of free MBMSO and the solution eventually deposits yellow crystals, presumably of RuCl2(d6-DMSO)4. Addition of varying amounts of d6-DMSO to a CC14 solution of compound 8_ gives equally simple spectra. Addition of 1% (by weight) of d^ -DMSO results in 50% exchange. As well as peaks due to the protons of the 8, y and 6 carbons of free and co-ordinated MBMSO there a singlet at 62.52 due to a methyl protons of the free MBMSO ligand. In the S-bonded region there are a methyl singlets at 63.12, 3.4-0, and 3.52. Addition of a further 1% of d^ -DMSO results in 75% exchange with singlets in the S-bonded region at 63.12 and 3.40. Addition of a further 2% of d^ -DMSO results in complete exchange. The singlets in the S-bonded region are due to the a methyl protons of the different sulphoxide ligands of the trimer or of perhaps monomers with the composition RuCl2(d^-DMSO)^-(MBMS0)m (n + m <_ 4) . The rate of exchange of d^DMSO with MBMSO is of the order of that found for DMSO in RuBr2(DMS0)4. 7.3.3. Discussion Association of co-ordinatively unsaturated monomers is a convenient way of alleviating deficiency in co-ordination. One can envisage two possible structures for the trimer, u t i l i z i n g chloride bridges and S-bonded sulphoxide ligands, (fig. 7.1.). The two possible structure types are linear (I) and triangular (II), along with isomers of - 159 -each, although sufficient data are not available to definitely assign the Cl S S S Cl Cl—Ru I S Ru—Cl S s s s s I II S = MBMSO, S-bonded Figure 7.1. Possible structures of [RuC1 (MBMSO)2J3 structure. The sulphoxide ligands are distributed evenly to give the least steric interference. Of the two structures the linear form gives more chemically different sulphoxide ligands (cf. n.m.r. data). The trimer 8^  i s related in some ways to the ruthenium cluster compounds 62 99 reported by Rose and Wilkinson , and Spencer and Wilkinson . The compound is made from a methanol blue solution which the former report _2 as containing the cluster anion Ru^-Cl^ • They suggest that these blue solutions on the addition of Cs + yield salts of the trinuclear anion Ru^Clg which i s thought to consist of a triangle of ruthenium atoms while the pentanuclear species i s thought to have a trigonal bipyramidal structure of ruthenium(II) atoms. Both these species are formulated as having metal-metal «bonds with terminal chlorides. - 160 -Trinuclear ruthenium(II) and (III) carboxylates, both with and without a central oxygen atom and containing bridging carboxylates, are 99 known . The ruthenium(III) oxo species has a U e££ = 1.77 B.M., while [Ru 30(C0 2Me) 6(H 20) 3] i s diamagnetic and [Ru 1 1(C0 2Me) 6(H 20) 3] and i t s derivatives are weakly paramagnetic, (the trisaquo complex has a U e f f = 0.4 B.M., per Ru 3). Trimer 8_ appears to be similar to the ruthenium(II) acetate complexes with a similar magnetic moment and could perhaps on oxidation produce an oxo species, although there is no evidence for this species. In summary i t would appear that cluster complexes of co-ordinatively unsaturated ruthenium(II) or (III) may not be particularly rare, (see also Chapter X). 7.4. The Reaction of [RuCl2(MBMSO)2]3 with Carbon Monoxide In order to help elucidate the structure of the trimer 8_ and to develop new hydrogenation or hydroformylation catalysts, the reaction of carbon monoxide with the trimer 8_ in methanol, benzene and toluene, was studied. In toluene at 42°C under 660 mm CO the reaction is stoichio-metric with a 2:1 mole ratio of CO to Ru. The reaction solution changes . from an i n i t i a l dark brown colour to orange and f i n a l l y pale yellow during the course of the reaction. Spectral data for these reactions are collected in Table 7.1. 7.4.1. Discussion An even distribution of CO in the reaction products would suggest the formation of a monomer; RuCl„(C0)„(MBMSO)„. Isomers with c i s -- 161 -TABLE 7.1. Spectral data for carbonyl derivatives of [RuCl9(MBMSO)A 2 J3 I.R.a ltt N.M.R.b Reaction v(CO) 6(MC0) v(SO) v(Ru-Cl) 6(CH3) IV 1) 2070,2058, - 1130, - 3.3,2.9, 2008,1985 938 2.52 2) 2070,2058, 615,575, 1130, 310, 2008,1985 485 928 . 280 II 1) 2130sh,2058 - - - 2.95 2) 2133,2059 620,580, 932 320, 470 297 III 2130sh,2052 - - -2010 I) Oily residue after MeOH removed for the reaction of 8_ with CO in MeOH. II) Crystals from the reaction of CO with 8_ in benzene. III) Oily residue following toluene removal after the stoichiometric reaction of CO with 8_ in toluene. a -1 In cm ; CCl^ solution in NaCl ce l l s except 12, which is neat between Csl plates, and 112 a nujol mull between Csl plates. In CDC13, relative to T.M.S., (fig. 2.10.) sh = sharp. - 162 -carbonyls should have two v(CO)bands, (a^ + b^), and three 6(MC0) bands, 70 (a^ + b^ + b^), active in the i . r . , while isomers with trans-carbonyls w i l l have one v(C0)band, (b^ ) and two 6(MC0) bands, ( b 2 u + °^u) • The i . r . spectrum of the crystalline product II, from the reaction of CO with trimeric 8_, has two v(C0)bands, three 6 (MCO)bands and two v(Ru-CI) bands indicating two cis-carbonyl and cis-chloride ligands; (the assignment of the 5(MCO) bands are made to the strongest bands in this region of the spectrum, but must be considered somewhat tentative due to the presence of other sulphoxide ligand bands). The band at 932 cm 1 and a sharp singlet resonance at 62.95 indicate only O-bonded sulphoxide. Collectively these data suggest the following structure for cis-RuCl 2 (CO) 2 (MBMSO) 2, (fig. 7.2.). OS OC^ I / C l Ru 0C-" | ^Cl OS OS = MBMSO, O-bonded (I) Figure 7.2. Possible structure of RuCl (CO) (MBMSO) A confirmation of the empirical formula is not available as analytic data were unfortunately not obtained for this crystalline product due to lack of sample. Repeats of the preparation have so far only yielded o i l s , which do, however, have the same spectra as the crystalline product. Compounds of the type RuCl„(CO)-P- have been - 163 -previously prepared, where P = PEt^? PEt^Ph^^ and PPh^ 1' 1^ 2. The isomer which is thought to have cis-carbonyls., chlorides and trans--1100-102 PPh3 has v(CQ)bands at 2064, and 2001 cm . A compound with the the same empirical formula, but with perhaps an a l l cis structure, has _l!02 v(C0)bands at 2042 and 1967 cm . Decreasing the electron density on the phosphorus atom by aromatic substitution in the phosphine ligand results in increased ir-acidity of the triphenylphosphine and an increase 103,104 in CO stretching frequencies . The same arguments have been presented for corresponding FeCl2(CO)2P2 systems1^. Replacing the ir-acid phosphines with O-bonded MBMSO, essentially a a-donor (and perhaps tr-donor, cf. H^ O, and OH ), should result in an increase in ir-donation from the metal to the TT* orbitals of the carbonyls and a lowering of the CO stretching frequencies. The compound of structure (I), f i g . 7.2, would thus be expected to have two v(C0)bands in the region ca. 2050 - 1900 cm The experimentally observed bands at ca. 2130 and 2059 cm"1 are thus contradictory to structure (I), although the other spectral data are consistent with this structure. A compound of structure (I) with S-bonded sulphoxide could possibly give the observed v(C0)bands i f such a ligand were a stronger ir-acid than triphenyl phosphine. The presence of S- : bonded sulphoxide is however contradictory to the i . r . and n.m.r. data. A crystal, structure determination is required to elucidate the problem. The appearance of an additional v(C0)band at 2010 cm 1 for reaction III indicates that another isomer is present in the reaction mixture. Presumedly the isomer could also be formed in the benzene reaction but is not present in the crystalline product. - 164 -Reaction I has two groups of v(CO) bands centred at ca. 2064 and 1996 cm 1 with each group s p l i t into two bands. This s p l i t t i n g i s not a solid state site symmetry effect as i t is also present in the solution spectra. The probable cause is a mixture of two similar isomers of the same compound, perhaps with cis-CO's trans to chloride or sulphoxide. The observed stretching frequencies are similar to those observed for the chlorocarbonyl phosphine complexes mentioned earlier, and to those 12 reported by Wilkinson et a l . , for the poorly characterized RuCl2(C0) (DMS0)2, (v(C0), 2082 and 2036 cm"1). The po s s i b i l i t y of dichlorotriscarbonyl(MBMSO)ruthenium(II) species being produced in reaction I, II, and III can not be entirely ruled out, since a fac-carbonyl isomer of the above composition would also be expected to have two v(C0) bands and three 8(MCO) bands**0. The products of carbonylation of the trimer 8_ may be a mixture and the CO stretches appear to be anomalous when compared to some analogous phosphine complexes. The systems are worthy of more detailed study although the synthetic problems are not t r i v i a l . - 165 -CHAPTER VIII HOMOGENEOUS CATALYTIC HYDROGENATION OF ACRYLAMIDE USING TRIMERIC DICHLORO [(S,R; S,S)- (+)-2-METHYLBUTYL METHYL SULPHOXIDE]RUTHENIUM(II) 8.1. Introduction Kinetic, studies of the t i t l e catalyst were undertaken with a relatively simple substrate in order to help elucidate the hydrogenation mechanism as an aid to understanding systems involving asymmetric hydro-genation. Trimeric 8_ readily hydrogenates acrylamide to proponamide at 70°C and hydrogen pressures <1 atm; however, the pro-chiral substrates employed were found to require higher pressures to effect reduction, and these systems were,less suitable for mechanistic study. 8.2. The Reaction of [RuCl2(MBMSO)2] with Hydrogen : Trimer 8_ was found to react with molecular hydrogen at 1 atm pressure in DMA at 70°C, hydrogen uptake being complete after 2100 sec. The extent of the reaction as monitored by gas-uptake was 5%, (total uptake = (.4 ± .1) x 10 5 moles of H 2 for a 5 ml solution) based on a 1:1 reaction uptake with the catalyst trimer, (ie., H 9 = Ru = 1:1, [Ru 1 1] = - 166 -0.018 M, [H2] = 1.24 x 10_3M) The resulting yellow solutions had essentially the same spectrum as solutions which had not been subjected to H^, and indeed the spectral changes observed at 70°C during the treatment were the same as those observed in the absence of H,,, under Ar, (see Section 8.3., and f i g . 8.1.). The presence of DMA-HC1 did not alter the extent of ^ r e a c t i o n discussed above, ([Ru 1 1] = 0.017 M, [H2] = 1.24 x 10_3M, [DMA-HC1] = 0.0085 M, H 2 uptake = 0.35 x IO - 5 moles H 2). With the addition of a R 2:1 mole excess of "proton sponge" the trimer reacted with further hydrogen at 70°C to a total extent of =20% to produce an orange solution. 8.3. U.V./Visible Spectral Observations on [RuCl2(MBMSO)2]3 The trimeric compound in DMA at 70°C under Ar gave a u.v./visible spectrum which showed a very slight spectral change with time, the majority of the change occurring within the f i r s t 1000 sec after dissolution, (fi g . 8.1.). Addition of MBMSO (3:1 mole excess) resulted in no change to the f i n a l yellow solution. Addition of a 200-fold excess of acrylamide to the catalyst solution at 70°C resulted in small spectral changes in the 320 - 350 nm region, (fig. 8.2.). A freshly prepared solution of the complex, (ca. 0.003 M), 0.6 M acrylamide in DMA at 70°C and under 1 atm H_, gave similar spectral changes to those solutions without hydrogen, The concentrations of Ru(II) are expressed in terms of monomer concen-trations . 1 1 1 1 1 4 0 0 • 3 0 0 A , nm Figure 8.1. U.v./visible spectral changes of [RuCl2CMBMSO)2]3, 8 in DMA at 70°C; [Ru] T =0.0032M as monomer, pAr = 620mm; time after solution attained; 1) 150 sec, 2) 1,100 sec. - 168 -T 0.8 4 5 0 3 5 0 X, nm Figure 8.2. Effect of added acryl on the spectrum of 8_ in DMA at 70°C; [RuJ T =0.0036M as monomer, [acryl] =0.63M, pAr =620mm; 1) spectrum of 8_, 2) spectrum with acryl added, 3) 1,000 after acryl added. - 169 -and after about the f i r s t 1500 sec of the catalytic hydrogenation the spectrum remained unchanged, (fig. 8.3.). The combined spectral data taken together with some kinetic data (see later) are consistent with the trimer dissociating to a slight extent, perhaps to monomers, (eqn. (8,1)), and the monomers reacting with acrylamide to form an olefin complex, (eqn. (8,2)). V [RuC 1 ^  (MBMSO)2]3 7 ^ - ^ 3RuCl 2 (MBMSO) (DMA) (8,1) K l RuCl 2 (MBMSO)2 (DMA) + acrylamide ^ ± RuCl 2 (MBMSO) (acryl ) (DMA) (8,2) 8.4. Catalytic Hydrogenation of Acrylamide Catalytic solutions were prepared by the sidearm bucket addition method described in Chapter II. The hydrogen uptake plots were generally recorded from the i n i t i a l point of solution to ca. 6,000 sec. The uptake plots had an i n i t i a l "autocatalytic type" non-linear region, the rate increasing to a constant value for a long period, (fi g . 8.4.). For the same solutions but with added proton sponge , (0.056 M), the i n i t i a l ; non,-linear region lasted approximately twice as long. The constant rate of uptake lasted u n t i l approximately 60% reduction of the substrate had occurred, when the rate began to drop; the total uptake corresponded to total reduction of the substrate with no metal v i s i b l e at this stage. The linear rates of uptake were measured graphically from ca. 1000 to 6000 sec. The rate dependencies on catalyst, hydrogen, substrate, added acid, added - 170 -+ 0.6 Figure 8.3. Effect of added acryl and H 2 on the spectrum of 8_ in DMA at 70°C; [Ru] T =0.0038M as monomer, [acryl] =0.05M, pH2 =610mm; time after reactants combined; 1) 125 sec, 2) 1500 sec. - 171 -Figure 8.4. uptake plots for the reduction of acryl using DMA solutions of 8 at 70°C; ° [ R U ] ? =0.0020M as monomer, [acryl] =0.43M, pH^ =685mm, • [Rujj, =0.0068M as monomer, [acryl] =0.43M, pH 2 =685mm, O [Ru] T =0.00113M as monomer, [acryl] =0.44M,.pH2 585mm, [proton sponge] =0.056M - 172 -t, sec - 173 -chlorides and added MBMSO ligand were studied by the variation of the concentration of one species while holding a l l other constant. In addition, the variation of rate with the concentration of catalyst, hydrogen, and substrate were studied at a constant added concentration of R proton sponge . The summarized data are presented in Table 8.1. 8.4.1. Dependence on Acrylamide Fig. 8.5., shows the linear plots of total experimental rate versus the concentration of acrylamide. The plot shows a first-order dependence on substrate but there is a non-zero intercept. A plot of Rate 1 vs [acryl] 1 is a curve, showing that the dependence is not of the form k(olefin)/(a+b(olefin)), and that the intercept on the ordinate axis is real. If the non-zero intercept is subtracted from the total rate, the so-called unsaturate path rate curve is obtained, (the rationale behind this w i l l be explained later in Section 8.5.). The slope of the lines i s 4.82 x 10" s~ while the intercept i s 1.79 x 10 M s . A similar piot, linear rate vs [acryl], (f i g . 8.6.), is constructed for experiments with added MBMSO (see Table 8.1.). The linear plot has a slope of 1.72 x 10 ^ s 1 and an intercept of 0.66 x 10"^ Ms"1. The ' linearity implies again a f i r s t order dependence of rate on acrylamide. The intercept value is decreased from that for comparable experiments with-out added MBMSO. Fig. 8.7., shows the variation of rate with acrylamide for experiments with added proton sponge ; i t is not readily apparent whether the three data points represent a linear or curved plot. A curved plot implies a dependence on acrylamide between f i r s t and zero - 174 -- 175 -0.5 1.0 1.5 2.0 [acryl] igure 8.6. Dependence of linear rate on [acryl] with added MBMSO; [Ru] ? =0.00234M as monomer, pH 2 =586mm, [MBMSO] =0.0062M, o total rate, Q unsaturate rate - 176 -m o o CO 2.5 T 2.0 + 1.5 + £ 1.0 + a or 0.5 + 0.0 0.0 0.5 [acryl] 1.0 Figure 8.7. Dependence of linear rate on [acryl] with added proton sponge ; [Ru]^ = 0.00114M as monomer, pH 2 =585mm, [Proton sponge] =0.56M - 177 -TABLE 8.1. Linear hydrogenation rates for the reduction of acrylamide using [RuCl (MBMSO) ] in DMA at 70°C [Ru ] a pH 2 [H2] [acrylamide] Linear Rate xlO ,Ms ^ xlO 3 mm xlO 3 Total Unsat. Path 6.74 685 2.06 0.106 2.01 0.22 6.72 685 II 0.207 2.79 1.00 6.77 685 II 0.433 4.30 2.51 6.75 687 2.07 0.884 6.22 4.43 6.74 683 2.06 1.868 11.07 9.28 6.74 684 2.06 2.651 14.29 12.50 6.76 343 1.03 0.430 2.01 6.74 521 1.57 0.432 3.13 1.07 685 2.06 0.430 2.47 1.97 686 2.07 0.430 3.58 18.1 685 2.06 0.428 5.81 23.0 685 2.06 0.431 6.62 2.35 585 1.76 II 2.60C 2.33 585 ti it 1.97d 2.36 584 II II 1.686 2.34 585 it 0.432 1.43f 2.33 586 1.76 0.926 f 2.21 2.33 585 1.76 1.340 f 2.93 2.35 585 1.76 1.801 f 3.78 continued - 178 -TABLE 8.1. (cont'd) xlO 3 PH 2 mm [H2l xlO 3 [acrylamide] Linear Rate xlO^,Ms 1 Total Unsat. Path 4.56 584 ti 0.431 3.32g 4.56 685 2.06 1.201 6.24h 4.55 685 2.06 1.200 11.271 6.72 585 1.76 0.434 10.27^ 6.72 584 1.76 0.435 15.02k 1.15 585 1.76 0.218 9.17k 1.13 585 1.76 0.436 14.84k 1.14 584 1.76 0.748 22.69k 1.18 251 0.76 0.436 6.12k 1.16 344 1.04 0.436 v 6.22 0.41 684 2.06 0.437 8.97k 1.13 685 II 0.436 14.84k 2.25 685 tt 0.435 18.18k a Total amount of ruthenium expressed as the concentration of RuC12(MBMSO)2 monomer. Unsaturate path contribution = total linear rate - olefin-independent linear rate, (see text). C Added MBMSO; 0.0008M; 0.0012M; 6 0.0027M; 0.006M g Added LiCl, 0.010M h Added DMAHC1, 0.066M; 1 0.320M j Added "proton sponge R", 0.026M; k 0.056M - 179 -order, while a linear plot implies again a f i r s t order dependence. A linear plot would have a slope of 2.55 x 10 ^ s 1 and an intercept of 3.66 x 10"6 Ms"1. 8.4.2. Dependence on Hydrogen Plots of total linear rate against the concentration of hydrogen are shown in fig s . 8.8., and 8.9., the latter for experiments with added proton sponge . Both plots are linear and pass through the origin, indicating a f i r s t order rate dependence on hydrogen. Without added R -3 -1 proton sponge , the slope is 2.07 x 10 s , and for the unsaturate - 3 - 1 path, 1.20 x 10 s . The latter slope is obtained by subtracting the intercept value of f i g . 8.6., and correcting for the hydrogen concentration, assuming the intercept i s linearly proportional to [ ^ j , (see Section R -3 -1 8.5..). With added proton sponge , the total rate slope is 8.03 x 10 s 8.4.3. Dependence on Catalyst Concentration Figs. 8.10., and 8.12., show plots of total linear rate vs the total monomer catalyst concentration. Both curves are f i t t e d to a rate = afRu 1 1]!^ curve, where n = 0.28 without proton sponge ^, and 0.42 with; : the' latter case has less data points. These data suggest a one-third order dependence of rate on [Ru11],^. This is confirmed by plotting the total linear rate vs the total monomer catalyst concentration to the one-third order. The results are shown in figs. 8.11., and 8.13. The linear plots have slopes of 2.17 x 10~5 M^ 3 s" 1 and 1.22 x 10~5 M^ 3 s' 1 for the total and unsaturate paths, respectively, without added proton sponge , - 180 -Figure 8.9. Dependence of linear rate on [H_] R with added proton sponge ; [Ru]^, = 0.00116M as monomer, [acryl] = 0.44M, [proton sponge] =0.056M - 181 -6 r 3 + 12 [RiflT X ICT 18 24 Figure 8.10. 11 Dependence of total linear rate on [Ru pH_ =685mm, [acryl] =0.43M 8 T 6 + 4 f 2 + 0 ©— 0.0 0.1 0.2 0.3 0.4 Figure 8.11. Dependence of total linear rate on [Ru 1 1]^ 3; pH_ =685mm, [acryl] =0.43M - 182 -m O o CC o co 2.0 + Figure 8.12. Dependence of linear rate on [Ru* 1]- with added proton sponge ; pH^ =585mm, [acryl] =0.43M, [proton sponge] =0.056M m O x o cn o CO 2.0 + 1.0 + 1 1 1 — 0.05 0.10 0.15 [Ruf/ 3 Figure 8.13. Dependence of linear rate on [ R u 1 1 ] ^ with added proton sponge ; pH^ =585mm, [acryl] =0.43M, [proton sponge] =0.056M - 183 --4 rA, -1 -4 4-i _ i and 1.40 x 10 M d s and 1.05 x 10 M d s , respectively, with added proton sponge . (The unsaturate path slopes are obtained by the same method as described previously (Section 8.4.2.), assuming the intercept II V i s proportional to [Ru ]^, 3, (see Section 8.5.)). 8.4.4. Dependence on Added MBMSO Ligand Figs. 8.14. and 8.15., are plots of total linear rate and reciprocal total linear rate,respectively, against the concentration of added MBMSO. Fig. 8.16., shows the reciprocal linear rate vs the cube-root of the concentration of added MBMSO. The experiments were studied in the absence of proton sponge . Fig. 8.14., shows a definite inverse dependence of rate on the concentration of added MBMSO; the reciprocal plots^however, do not yield good linear relationships. 8.4.5. Dependence on Added Chloride Addition of upto 0.01 M lithium chloride to a catalyst solution (see Table 8.I.), had no significant effect on the uptake plot. 8.4.6. Dependence on Added Acid Acid was added to the catalytic solutions as the HC1 adduct of DMA. With 0.066 M DMA-HC1 no observable effect on the uptake curve was detected. Further addition to 0.32 M acid at the conditions l i s t e d , (see Table 8.1.), resulted in an increase in total rate from 6.24 x 10 to 1.13 x 10"5 Ms"1. 4.0 T 184 10 O 3.0 + o or o c 2.0 + o I-1.0 0.0 2.0 4.0 6.0 8.0 [MBMSO] X I 0 3 Figure 8.14. Dependence of total linear rate on [MBMSO]; [ R U ] t =0.00235M as monomer, pH 2 =585mm, [acryl] = 0-.43M i n o o CC o co o 8.0t 6.0 4.0 + 2.0 0.0 2.0 4.0 6.0 [MBMSO] X I 0 3 Figure 8.15. Dependence of (total linear rate) on [MBMSO]; [Ru] T =0.00235M as monomer, pH 2 =585mm, [acryl] = 0.43M -1 - 185 -8.Or 6.0 + o 4.0 + 2.0 + o 0.05 0.10 0.15 0.20 [MBMSO]73 Figure 8.16. Dependence of (total linear r a t e ) - 1 on [MBMSO] 1 / 3 [ R u ] T =0.00235M as monomer, pH 2 =585mm, [acryl] =0.43M - 186 -8.5. Discussion of Kinetic Results As stated previously (Chapter VI, Section 6.5), the activation of molecular hydrogen and olefin can occur via either an unsaturate path or a hydride path, or possibly via both paths. The spectral data show some interaction of acrylamide with the trimer, suggesting a possible unsaturate pathway; while an observed reaction of (gas-uptake) with the starting catalyst likewise suggests a possible hydride pathway. The hydride pathway could occur with the formation of either a d i - or monohydride, for example as in eqns. (8,3) and (8,4), written for an octahedral Ru(II) monomeric species. RuCl2(MBMSO) (DMA) + H 2 H2RuCl2(MBMSO) + nDMA (8,3) RuCl2(MBMSO)2(DMA)n + H 2 ^ HRuCl(MBMSO) (DMA) + HC1 (8,4) The non-variance of the H2~uptake in the absence and presence of excess HC1 favours the former, (see Section 8.2.). The formation of a ruthenium(IV) dihydride by oxidative addition to ruthenium(II) is well known106, and as written would be expected to show no significant dependence on added acid or chloride. The formation of a monohydride by the heterolytic cleavage 15,89-93 of hydrogen and loss of HC1 is also well known ; and this process should be inversely dependent on acid, although not necessarily chloride R 15 dependent. Proton sponge should aid a reaction such as (8,4) . If either reactions (8,3) or (8,4) are rate determining steps and are followed in a catalytic pathway by faster reaction steps,then neither reaction - 187 -necessarily leads to an observable inverse acid dependence. The non-linear induction period suggests the build up of active catalyst by trimer dissociation. The extension of this period in R the presence of proton sponge , together with enhanced activity, could imply more trimer dissociation due to equilibrium (8,4). The inverse dependence on added MBMSO suggests a) the possible loss of sulphoxide ligand prior to or during the rate determining step or b) co-ordination of sulphoxide to form a less active catalyst. These data combined suggest two plausible mechanisms for the hydrogenation of acrylamide with-in out proton sponge ; after a steady concentration of catalyst species has been set up, Schemes 8-A, and 8-B could be operative. (I) [ R u I I C l 2 S 2 ] 3 (II) 3 R u H C l 2 S 2 (II) R u H C l 2 S 2 + H. (Il l ) » H 2Ru I VCl 2S + S fast (IV) RuCl 2S 2olefin + H, low > HRu Cl 2Salkyl (V) fast (VI) RuCl_S + sat. product -S fast (II) Scheme 8-A (solvent molecules omitted; S = MBMSO) - 188 -(I) (II) [RuCl 2S 2] 3 V 3RuCl 2S 2 (II) k (HI) R u C 1 2 S 2 + H 2 slow > HRuClS 2 + HCl £ast||K olefin f a s t j k 2 olefin (IV) ' k (V) k -HCl cm RuCl 2S 2olefin + H 2 ^ > RuClS^lkyl f a g t > R u C l ^ + sat. product slow Scheme 8-B (solvent molecules omitted; S = MBMSO) In Scheme 8-A the trimer (I) dissociates to monomers, (II), which react with either hydrogen or olefin to form the dihydride (III) or olefin complex (IV), respectively. The oxidative addition step to form (III) i s considered rate determining. Reaction of olefin with (III) in a fast step produces, : presumedly via a dihydrido-olefin complex, a hydrido-alkyl complex (II). Oxidative addition of hydrogen to the olefin complex (IV) is also considered a rate determining step, and forms via a dihydride-olefin complex the hydrido-alkyl (V). Saturated product i s formed by reductive elimination from (V) in a fast step and the catalyst (II) is reformed by co-ordination of sulphoxide. - 189 -Scheme 8-B is similar to 8-A except that the slow steps are reaction of H 2 with (II) and (IV) by heterolytic cleavage to form the monohydride (III) and alkyl complex (V), respectively, plus HC1. This reaction can proceed by either direct substitution (hydride for chloride), or by oxidative addition of H 2 followed by reductive elimination of HC1. Insertion of olefin into the hydride bond of (III) in a fast -step produces the alkyl complex (V). Rapid protonolysis of (V) with HC1 yields the saturated product and regenerates the catalyst species (II). In Scheme 8-B as written, MBMSO is not dissociated although i t is in Scheme 8-A. When a steady concentration of species (I-IV) i s reached (in the linear uptake region), the rate expression for both mechanisms i s given by: -d[H ] Rate = R = ^ = k 4[IV][H 2] + k ^ I I ] ^ ] (8,5) = Kj / 3K 3k 4[I] k3 [R2] [olefin] + [1]^ f ^ ] (8,6) If the concentration of species (II - IV) i s much smaller than that of (I) then; [I] = [Ru**]^ and [olefin] = [olefin]^ (where the subscript T refers to total concentration), and eqn. (8,6) becomes: R. = K ^ 3 K 3 k 4 [ R u n ] ^ [ H 2 ] [ o l e f i n ] T + K ^ t R u 1 1 ] . ^ ^ ] . (8,7) Eqn. (8,7) has the experimentally observed f i r s t order dependence on hydrogen and total olefin and the cube-root dependence on total trimer concentration. Rate expression (8,7) has an olefin-independent path, (I -> II III -»- V), whose contribution to the total rate can be evaluated by - 190 -extrapolating the experimental rate vs [acryl] curve to zero [acryl], (fig. 8.5.). This olefin-independent hydrogen reduction of acrylamide arises from the rate determining step occurring prior to olefin co-ordination. Subtracting the olefin-independent (or hydride) path rate, eqn. (8,7), from the total rate gives the unsaturate path rate. The rate dependence plots yield values for K^K^k^ and Kj^k^. The value of K^K^k^ is found from the slope of the rate vs [acryl] plot, and the value of K^k^ from this plot's positive intercept. With this value for K n 3k^, values for K^K^k^ are calculated from the rate vs II V and [Ru ] T 3 plots. These values are tabulated in Table 8.II. The values are consistent which adds credence to the proposed mechanistic schemes. The decision as to which mechanistic scheme, 8-A, or 8-B is more correct is not t r i v i a l . Both schemes as written should be independent of added acid or MBMSO, since reaction steps, where either i s formed, are rate determining and have no reverse contributions. With Scheme 8-A, addition of MBMSO could decrease the reaction rate of the unsaturate path by interferring with oxidative addition of hydrogen to (IV); oxidative addition to form a seven-co-ordinate species could be less easy than addition to form a six-co-ordinate species. Inhibition of the olefin-independent, hydride pathway with the addition of MBMSO could arise i f oxidative addition of involves a prior dissociation of sulphoxide; the addition of MBMSO could reverse this dissociation equilibrium. Experi-mental data in the presence of added sulphoxide show a decreased total rate and a decreased olefin-independent rate, while s t i l l retaining a first-order rate dependence on olefin substrate, ( f i g . 8.6.). The - 191 -TABLE 8 .II. Values of K D / 3K 3k 4 and K^ 3^ for the hydrogenation of acrylamide using [RuCl2(MBMSO)2]3 i n D M A a t 7 0 ° c p l o t a K^K 3k 4 K^3 k l I 0.012 0.0046 II 0.015 0.0046 III 0.014 0.0046 Plot of Rate versus: I) [acrylamide]; II) [H 2]; III) [ R u 1 1 ] ^ . - 192 -decrease in both rates is by a factor of about one-third implying that added sulphoxide affects both pathways approximately equally. These data suggest that perhaps an additional MBMSO ligand co-ordinates to the active catalyst species (II) to form a less active species such as RuC^S^ (DMA)n; however, no evidence for such a species was found from spectral data, (Section 8.3.), nor from the synthetic reaction, (Chapter VII). Scheme 8-B, as written, has no MBMSO dependence; however, as stated earlier, addition of MBMSO could by further co-ordination decrease the amount of active bis-sulphoxide catalysts (II), and hence decrease both the unsaturate and hydride path rates. A rate lowering with added MBMSO could occur i f formation of the monohydride intermediate in the reaction of IV with H 2 proceeds via oxidative addition to form a seven-co-ordinate species which then dissociates sulphoxide to become six-co-ordinate; this then reductively eliminates HCl and undergoes insertion of olefin into the metal-hydride bond to form (V). This rate lowering w i l l only occur for the unsaturate path since a seven-co-ordinate species is not present in the hydride path. With Scheme 8-B, addition of proton sponge , should result in an overall rate lowering by impeding the f i n a l protonolysis step, while experimentally the opposite is observed, a large rate enhancement. The MBMSO and proton sponge dependencies, as well as the acid independent reaction of trimer with H^ , strongly favour Scheme 8-A involving activation of H^  by oxidative addition to give a dihydride. The experi-mentally observed doubling of rate with added 0.32 M DMA-HCl is probably not significant. Variations in H„ solubility could well explain such - 193 " small changes. The po s s i b i l i t y of the production of more active anionic species such as [RuCl^S^fDMA)^ was not investigated in any detail although added chloride to 0.01 M had no effect on the observed hydrogenation rates. The catalytic scheme that is operating in the presence of proton sponge i s not clear. The overall rate dependencies are similar R to those found in the absence of proton sponge , although the olefin dependence is somewhat ambiguous. Scheme 8-A has no obvious base dependence, while in (8-B) formation of monohydride species would be promoted but the fin a l protonolysis impeded. The earlier presented uptake data for the reaction of 8_ with could be accounted for by base-promoted formation of hydrido species containing no chlorides, for example eqn. (8,4) followed by: (I) (II) (III) HRu HClS 2 + H 2 :== [H 3Ru I VClS 2] ^ H 2Ru HS 2 + HC1 (8,8) (HI) (IV) H 2Ru HS 2 + H 2 ^ H 4Ru I VS 2 (8,9) These processes involve both a net heterolytic cleavage of H 2 to form a dihydride species, and then oxidative addition of to form a tetra-hydrido complex. Reduction of an olefin co-ordinated to such hydrides could give the saturated product through hydride-transfer and reductive elimination. Proton sponge could enhance formation of dihydride (III), (eqn. (8,8)). A H^RufPPh^)^ complex has been synthesized by reaction of 107 RuCl 2(PPh 3) 3 with H 2 in the presence of added triethylamine base , presumedly via reactions (8,4), (8,8), and (8,9), and such processes 108 have been postulated by Strathdee and Given to account for a rapid D2 exchange reaction in the presence of benzene solutions of RuHCl(PPh^)^. - 194 -8.6. Discussion The mechanism proposed in Scheme 8-A, is basically similar to that proposed for the RhCl(PPh 3) 3 system by Wilkinson 1 0 6 and for Ru(I) 24 systems by James and Hui . The olefin-independent hydride path can be expanded from that previously postulated to that shown below: i it k k R u I I c i 2 S 2 f t k R u I I c i 2 S + S s ioTH 2 H 2 R u I V c i 2 S <8'10) H 2Ru I VCl 2S + olefin H 2Ru I VCl 2S (olef in) (8,11) ti v IV 2 TV H2Ru C12S (olefin) g^* HRu C12S (alkyl) (8,12) (solvent molecules omitted) 8 7 For the d Rh(I) and d Ru(I) systems mentioned above, the rate determining step was written as involving the reaction of olefin with the dihydride rather than formation of the dihydride. With the present Ru(II) system the change in rate determining step could result from the more d i f f i c u l t oxidative addition of IL, to a d^ system. Eqn. (8,10) involves loss of sulphoxide and the reaction of a monosulphoxide complex with H 2 to form a hydride having an accessible co-ordination site for the olefin; this dissociation can account in part for the observed inverse rate dependence on sulphoxide. Eqn. (8,11) involves formation of the dihydride-olefin complex, and eqn. (8,12), insertion of the olefin into the metal-hydride tt bond; both are fast steps, in comparison to k^. - 195 -The unsaturate path i s shown in more detail below: R u I I C l 2 S 2 + olefin g = | R u H C l 2 S 2 (olef in) (8,13) • Ru I ICl.S_ (olefin) ^ ± Ru I ICl.S(olefin)+ S (8,14) 1 1 fast 2 I! k Ru I ] CCl 0S (olefin) + H. -r 4-* H_RuIVCl.S (olefin) (8,15) 2 2 slow 2 2 in k H 2Ru I VCl 2S (olefin) f-^| HRu I VCl 2S(alkyl) (8,16) The slow step is reaction (8,15), again oxidative addition of H 2 to a d^ metal species to form a six-co-ordinate dihydride complex. The prior dissociation of sulphoxide, (eqn. (8,14)), could be partly responsible for the observed inverse added MBMSO dependence. Seven-co-ordinate hydride 107 species do exist, for example H^RuCPPh^)^ , but here four of the ligands 109 are small. James and Ng propose such an oxidative addition of H 2 to an olefin complex, as the rate determining step for a number of Rh(I) systems, including some with sulphide ligands, and certain of the RhClP^ systems 106 may operate via this same unsaturate route The last steps of mechanism 8-A involve reductive elimination : of saturated product and reformation of the catalyst by co-ordination of sulphoxide. k HRu I VCl 2S alkyl Ru I ICl 2S + Sat. product (8,17) R u H C l 2 S + S R u H C l 2 S 2 (8,18) - 196 -Experiments have shown for the Ru(I) system and the Rh(I) system that the two hydride ligands of the H^ M (olefin) complexes are transferred • , no consecutively 8.6.1. Comparison of the [RuCl2(MBMSO)2] System with that of [NH2Me2][RuCl3(DMS0)3] At f i r s t glance close similarity might have been expected between the hydrogenation catalysis by the [RuCl3(DMSO)3] anion and the RuCl2(MBMSO)2 monomer by virtue of their related ligands and their same i n i t i a l ruthenium oxidation state. The marked differences, (type of activation, lack of an unsaturate path for the anion system, and. type of f i n a l step which is protonolysis for the anion system and hydride ligand transfer for the trimer system) possibly stem from the number and type of co-ordinated sulphoxide ligands. The i n i t i a l catalyst species in the former system is six-co-ordinate,while in the latter i t is four co-ordinate, neglecting solvent molecules . I n i t i a l oxidative addition of H 2 and olefin complexation to the four co-ordinate species seems intuitively more li k e l y than to the co-ordinatively saturated six-co-ordinate species. For example,for oxidative addition the latter would require the loss of two co-ordinated ligands or else formation of an eight co-ordinate species. The larger number of chloride ligands of RuCl3(DMSO)3 could favour heterolytic cleavage of and loss of HCl. Both systems feature an olefin-independent path, which results from a rate determining reaction with H 2 followed by a fast olefin complexation and hydride ion transfer. - 197 -The mechanistic scheme proposed for [RuC1^ (MBMSO)^]^, (8-A), is a precedent in that the system features as an i n i t i a l reaction oxidative addition of to form a dihydride species; the HRuClP^ catalysed systems are believed to involve oxidative addition of to an intermediate metal-alkyl complex as the rate determining step. The [RuCl^(DMSO)^]~ anion system is similar to the aqueous chlororuthenate(II) systems of Halpern 13 et a l . , which feature olefin co-ordination, followed by hydrogen a c t i -vation by heterolytic cleavage of H 2 and protonolysis of the resulting metal-alkyl complex. - 198 -CHAPTER IX ASYMMETRIC HYDROGENATION OF OLEFINIC SUBSTRATES USING DICHLOROBIS [(5,R;S,SK+)-2-METHYLBUTYL METHYL SULPHOXIDE]-RUTHENIUM(II) COMPLEXES 9.1. Introduction As mentioned earlier, homogeneous catalytic asymmetric hydro-genation with complexes containing chiral phosphine ligands is well 6,97,98111 known . The t i t l e catalyst i s the f i r s t example of such hydrogenation using complexes containing chiral sulphoxide ligands. The enantiomeric excesses are modest in comparison to the phosphine systems but are none-theless significant, i The similarity of the two catalysts, ether-solvated complex 7_ and the trimeric complex 8^was pointed out in Chapter VII. The kinetics and mechanism of hydrogenation of acrylamide using 8_ were presented in Chapter VIII. It seems highly l i k e l y that both catalysts 7_ and 8_ w i l l hydrogenate the pro-chiral substrate olefins by the same mechanism,which presumedly w i l l be similar to that by which 8_ reduces acrylamide. 9.2. Asymmetric Hydrogenation Results Many hydrogenation experiments were conducted in DMA with ether-solvated 7_ or trimeric 8_, as catalysts. The substrate concentrations and hydrogen pressures were varied as were the reaction times. - 199 -Several olefin substrates could not be reduced over a resonable time period (several days) at high pressure ( 1300 psi.H^). These included a- and 8-methylcinnamic acid,(I) and (II), citraconic (III) and mesaconic acid(IV), (fig. 9.1.). No metal was produced in these experiments. Itaconic acid(V) and 2-acetamidoacrylic acid(VI) were hydrogenated to ct-methylsuccinic acids (VII) and N-acetylalanines (VIII), respectively, (fig. 9.1.), under homogeneous conditions with no production of metal. Atropic acid (IX) was hydrogenated to 2-phenyl-propanoic acids(X) at 1 atm H 2 and 60°C in DMA, but metal formed rapidly during the reaction, (fig. 9.1.); in any case,the acid products had no optical rotation. There are only a limited number and type of olefinic substrates that are available to be hydrogenated to products whose specific rotation of their R and S isomers is known. The useful olefins are mainly substi-tuted mono- or dicarboxylic acids. In Table 9.1., are listed the results of asymmetric hydrogenation experiments, completed with I) ether-solvated RuCl 2 (MBMSO) 2, complex 7_, and II) trimeric 8_, [RuC 1 2 (MBMSO) 2] 3• It can be seen that the largest enantiomeric excesses occur for itaconic acid at lower hydrogen pressure. Both catalysts appear to be similarly effective for stereoselective hydrogenation. 9.3. Discussion A common feature of the four o l e f i n i c substrates that could not be reduced to any extent is their bulkiness. a- and B-methylcinnamic, citraconic,and mesaconic acids are tri-substituted olefins with bulky substituents at the double bond. The large size l i k e l y results in poor co-ordination to the ruthenium(II) catalysts and hence ineffective - 200 -COOH (J)(CH 3)C=^ ^ O O H H O O C x ^ O O H / C = C N H3C / C O O H C=C HOOC / X H IV COOH \ C H 2 C O O H COOH 1 H ^ C - * C H , : CH 2 C00H COOH H , C ^ g ^ H CH 2 COOH VII R(+-) VII S(-) COOH H2C=C / \ Ho NHC(0)CH 3 2 COOH 1 H*-C-« NHC(0)CH 3 C H , COOH C H 3 C ( 0 ) H N ^ ^ H C H , VI VIII R( + ) VIII S(-) 7 C00H COOH COOH H ? C=C > ( ] ) ^ £ ^ H H ^ C - « j ) <P * C H , C H , IX x X R(+) S(-) Figure 9.1. Prochiral olefin substrates and their hydrogenation products. TABLE 9.1. Results of asymmetric hydrogenations in DMAa Compound [ R u 1 1 ^ Substrate [Substrate] T°C pH 2 % t(hr.) e.e. d % (psi) Reaction I b 0.018 2-acetamido 0.45 60 1500 100 240 1.5e'.(R) acrylic acid 0.014 " 0.31 42 45 87 170 0.456(S) f 0.021 itaconic 0.44 60 1300 74 68 4.3e (R) acid 0.014 " 1.00 42 49 37 240 12.I 6 (R) I I C 0.018 " 1.35 40 44 53 240 14.8J (R) a 5 ml. solution Concentration as monomer M.W. = 542 g/mole including diethyl ether. c Concentration as monomer. d Predominant enantiomer in parentheses, e e 16. f (R) Enantiomeric excesses determined from the specific rotation of the sample; based on the maximum ac f of the pure chiral acid; (S)-N-acetylalamine, [[a]26=-66.5°; C2, H20] , (R)-a-methylsuccinic cia, [[ct]20=+17.09°; C10, abs. EtOH] 1 1 2. Enantiomeric excess determined with chiral shift reagent on the dimethyl ester of the product. - 202 -hydrogenation. Itaconic acid and 2-acetamidoacrylic acid, on the other hand, are both terminal olefins. The result is perhaps less steric interference to co-ordination and the av a i l a b i l i t y of reduction pathways. Atropic acid appears to be a special case since i t was the only substrate system that produced metal under the hydrogenation conditions. Formation of metal could result from destabilization of a hydrido-olefin complex with tendency to give metal formation, (eg., H^Ru^^ (olefin) * Ru° + 2H+ + olefin). This destabilization could be enhanced by either large a-electron donation to the metal from the olefin, or small TT back-donation from the metal to the olefin. Atropic acid has an aromatic substituent which is capable of donating or withdrawing electron density to or from the metal-centre. The non-production of metal in the a- and B-methylcinnamic acid system is perhaps indicative of the lack of formation of hydrido-olefin complexes in these cases. 9.3.1. Mechanistic Considerations Based on the Acrylamide Hydrogenation  Catalysed by [RuCl2(MBMSO) ] The catalyst and substrate concentrations employed for the ; previous kinetic study on acrylamide hydrogenation (Chapter VIII), overlap with those used for the present asymmetric reductions. The pressures employed in the latter are however ca. 3 or 100 times those used for the former. The use of acid substrates should have l i t t l e effect on the basic mechanism of Scheme (8-A), (see Section 8.5., Chapter VIII). Both the olefin-independent hydride and olefin-dependent unsaturate paths involve complexation of the olefin and hydrogen to form a dihydrido-olefin complex, followed by hydrogen transfer to form the products. Complexation by - 203 -itaconic acid and 2-acetomidoacrylic acid i s not limited to co-ordination through the double bond. It is possible that co-ordination by way of the carboxylic acid anion oxygen to the metal could occur. Hydrogen bonding i s also possible between the non-ionized acid protons of the substrate or the proton of the amido NH group and the sulphoxide oxygen. Olefin movement could be restricted by electronic repulsion between a negatively charged carboxylic acid group, and the electron-rich sulphoxide oxygen. In short then, there are many ways that the olefins could co-ordinate and lock themselves into position on the catalyst so that the addition of hydrogen to the double bond is stereospecific. Restricted rotation of the olefin about the metal-olefin bond can also arise from steric interaction of the bulky olefin substituents with the catalyst sulphoxide ligands. This cannot be the sole reason for stereoselective hydrogenation as both hydrogenation pathways l i k e l y involve species with only one co-ordinated sulphoxide. Restricted rotation of the olefin alone w i l l not result in high stereoselectivity, since i t i s also important which face of the olefin i s presented to the catalyst for the hydrogen transfer steps. Indeed, the asymmetric process is probably a combination of a l l the above factors, electronic and steric. The fact that high pressures are required for effective reduction of the acid substrates compared to the <1 atm hydrogenation of acrylamide offers indirect support that addition of i s involved in the rate determining step. Furthermore, the major pathway at higher olefin concentrations appear to be oxidative addition of to a Ru 1 1(olefin) moiety, (cf. Scheme 8-A, Section 8.5. Chapter VIII). The - 204 -olefinic acid substrates when co-ordinated to the Ru1* may well act as stronger n-acids than acrylamide; this would increase the promotion 113 energy for the oxidative addition, and lead to the requirement of more severe conditions, such as higher pressures. Each of the mechanistic steps, olefin co-ordination, hydrogen co-ordination,and hydrogen transfer, are li k e l y concerned in the overall process leading to an enantiomer excess in the product. In both pathways the olefin and hydrogen activation steps govern which hydride-olefin complex is in excess, depending on the free energies of formation (AG°) and activation (AG^) of these complexes; the AG's are of course related II it 1 to the equilibrium constants K^ , and K^ , and the AG' activation energies i t i to the rate constants, k^, k^, and k^, eqns. (8,10) - (8,16). The amount of each hydrido-alkyl complex formed in the f i r s t hydride transfer step is dependent upon the activation energies for the it it in processes, and hence upon the rate constants, k^ and k^, and k^ , eqns. (8,12), (8,15), and (8,16). Reductive elimination of saturated product is the last governing factor on enantiomeric product distribution. The activation energies and hence k^'s for production of each enantiomer controls this product distribution. For the fast steps governed by the different k2's and k^'s,the extent of enantiomer ratio enhancement should be relatively small since these are fast steps. The slow steps, represented by the k^'s and k^'s could have a larger bearing on the overall stereo-selectivity of the hydrogenation. The order of fast and slow steps in the reduction mechanism could have a major influence on the overall enantiomeric excess. The hydride path involves a fast step for olefin co-ordination and hydride transfer; the unsaturate route involves an equilibrium' - 205 -governing olefin co-ordination and a slow step for oxidative addition. The result could be less stereoselectivity for the hydride path relative to the unsaturate path. The effect of severe conditions, (for example high pressure), could be the removal of differentiation between stereo-selective pathways. Higher pressure could cause the AG° 1s or AG^'s of a reaction step to become similar and make that step less stereoselective. Higher pressures could as well invert the relative orders of AG°'s or AG^'s of a reaction step,thus favouring a different product isomer. The effect of pressure on the catalytic system is large,with stereoselectivity reduced at higher pressures with itaconic acid^and the predominant enantiomer produced reversed at high pressures with 2-acetamidoacrylic acid (Table 9.I.). Reasons for the low stereoselectivity for the reduction of 2-acetamidoacrylic acid are not obvious. In comparison to itaconic acid, the carboxyl Or carboxylate group i s not as far removed from the double bond as is one such group of itaconic acid. Co-ordination of the carboxy-late anion oxygen to ruthenium or H-bonding of the carboxyl proton to a sulphoxide oxygen, or even a chloride ligand may not occur as with itaconic acid. Such reasoning, however, is in contradiction to the 6 published work of Knowles et a l . , who feel that for their Rh(I) phosphine systems with 2-acetamidoacrylic acid, co-ordination of the carboxylate anion oxygen to metal occurs as well as H-bonding of the N-H proton to an appropriate ligand atom: however, some very recent data by this group 114 indicates the H-bonding hypothesis may not be correct The general low stereoselectivity for catalyst 8_ could result - 206 -from one or both of two reasons; a) the presence of the olefin-independent path where olefin co-ordination and hydride transfer is fast and perhaps low in stereoselectivity, and b) the nature of the chiral MBMSO ligand which is a mixture of two diasteromers. A catalyst prepared from only one diastereomer may have a higher stereoselectivity for hydrogenation. - 207 -CHAPTER X POLYMERIC CHLOROSULPHOXIDE COMPLEXES OF RUTHENIUM(II): TRIMERIC DICHLOROBIS[(R)-(+)-METHYL P-TOLYL SULPHOXIDE] RUTHENIUM(II) AND POLYMERIC DICHLOROBIS[METHYL PHENYL SULPHOXIDE]RUTHENIUM(II) 10.1. Introduction This chapter presents studies on two more polymeric ruthenium(II) compounds. The f i r s t member of this series, [RuCl 2 (MBMSO)2] ^ , was presented earlier, (Chapter VII). Trimeric [RuCl 2(MPTSO)J ,. 10, contains sulphoxide ligands with completely chiral sulphur centres; to our knowledge this i s the f i r s t ruthenium(II) complex of this type. Complex 10 catalytically hydrogenates ol e f i n i c substrates, for example acrylamide, atropic and itaconic acids, in DMA at 60°C under 1 atm of hydrogen; however, olefinic reduction occurs concomitant with the formation of ruthenium metal. The complex also reacts with carbon monoxide (1 atm) at 60°C in toluene. Compound _6_, [RuCl 2 (MPSO) ^ j ^ ^ a s limited solubility in a l l solvents and hence has no observed hydrogenation properties. 10.2. Trimeric Dichlorobis[(R)- (+) -methyl p-tolyl sulphoxide] ruthenium (I I), 10 This compound was prepared by the addition of (R)-(+)-methyl p-tolyl - 208 -sulphoxide to a methanolic "blue solution" using a mole ratio of sulphoxide to Ru(II) of 2:1. The reaction residue, after f i l t e r i n g and removal of methanol by pumping, was dissolved in either chloroform or benzene and f i l t e r e d . The product was precipitated from chloroform with diethyl ether or freeze-dried from benzene. The solid product could not be successfully recrystallized from various solvent systems, for example, CHClg-diethyl ether; only o i l s resulted. Solutions of compound 10_ turned green in air over a few days, and on analogy to [RuCl2(MBMSO)2] ^  probably contains ruthenium(III) species. A degree of association of 2.8, (M.W. = 1358 g/mole) was obtained in benzene via freezing point depression, implying a trimer in 22 the solid state. A measured y of 0.67 ± 0.15 B.M. per trimer, eff r (Guoy Method), is consistent with a diamagnetic ruthenium(II) complex probably containing some paramagnetic ruthenium(III) impurities, (see 22 2 -1 -1 Section 7.3., Chapter VII). The conductivity in DMA (A = 4.6 cm ohm moi ) indicates essentially a neutral complex. Complex 10_ has similar solubility characteristics to [RuC12 (MBMSO)2 ] 3 • 10.2.1. I.r. Spectrum '• A strong broad band centred at 1110 cm 1 is indicative of S-bonded sulphoxide and is assigned to v(S0); v(S0) for the free ligand is at' 1055 cm 1. The presence of bands due to O-bonded sulphoxide in the region 900 to 980 cm~^is equivocal, since this region is complicated by strong bands present in the complex and free ligand at 950 and 975 cm In the far i . r . a medium, broad band centred at 325 cm 1 is tentatively assigned to terminal Ru-Cl stretches. - 209 -10.2.2. H n.m.r. Spectrum' The n.m.r. spectrum of 10^  in CDCl^ consists of three rather broad resonances. At 62.04 - 2.58 are resonances due to protons of the p-tolyl methyl group. From 63.34 - 3.96 are resonances due to the sulphoxide methyl protons of S-bonded sulphoxide. From 66.44 - 7.90 are resonances due to the aromatic protons. The free ligand has resonances at 62.45, 2.74,and 7.46,due to the para-methyl, sulphoxide methyl, and aromatic protons, respectively. No definite resonances due to sulphoxide methyl protons of O-bonded sulphoxide are observed; however, there is low intensity broad absorbance between 62.58 and 3.34 which complicates this detection. A ratio of intensities of the S-bonded region to this broad low intensity region indicates that l i t t l e i f any O-bonded sulphoxide is present. The broadness of the peaks could be due to the many different chemical environments in the trimer, coupled with restricted ligand motion; the presence of paramagnetic impurity could be a problem, although the solution for n.m.r. study was prepared under Ar. 10.2.3. ' Discussion Compound 1_0 appears to be similar to complex 8_; both are neutral mainly S-co-ordinated, presumedly chloride.bridged trimeric solids. The possible structures for this trimer are similar to those See also Chapter II, (fig. 2.10.). - 210 -suggested for compound 8_, (see Section 7.3.3., Chapter VII). The difference in size between the two sulphoxides of compounds 8_ and 10_ (a sec-butyl group as compared to a para-tolyl group), apparently causes no changes in co-ordination or in the degree of monomer association. 10.3. The Reaction of Compound 10 with Carbon Monoxide Complex 1_0_ reacts with CO (1 atm) in toluene at 50°C. The total uptake ratio of CO to Ru is 2:1. I.r. spectra of the reaction solution,and the reaction residue after the toluene was pumped off and either dissolved in CC14 or neat, were recorded,. (Table 10.I). A poorly resolved far i . r . resulted in no useful data from this region. A solid product could not be isolated from the reaction residual o i l either by precipitation with ether or crystallization from pet. ether (30-60°)-diethyl ether solvent. 10.3.1. Discussion The similarity between compound 10_ and 8_ is again apparent with the formation of an apparent dichlorodicarbonylbis(sulphoxide)ruthenium(II) complex. The empirical formula is assigned from the CO uptake data and comparison with the CO derivatives of complex 8_. No microanalytical data were collected on the product o i l to confirm the formula. Here again the product formed from the CO-reaction is an apparent cis-carbonyl isomer, although a small third MCO) band is present as a shoulder of the band at 2060 cm This could be due to the presence of a small amount of another c i s - or even trans-carbonyl isomer. The - 211 -TABLE 10.I. I.r. spectral data for carbonyl derivatives of [RuCl 2(MPTS0) 2] 3 v(C0) a v(S0) a 2137s, 2080sh, 2060 -I I ) C 2137s, 2080sh, 2060 -I I I ) d 2138s, 2068br HOObr a T - i In cm b Reaction mixture; toluene solvent in NaCl c e l l s . Reaction residue in CCI4 after the toluene was removed; in NaCl c e l l s . d Reaction residue after the toluene was removed; between Csl plates. s = sharp, sh = shoulder, br = broad - 212 -product again features the very high v(CO) band; the present band is higher than that found for the carbonyl derivatives of trimer 8_, (v(CO) = 2130 cm * ) . Inspection of the v(S0) band illustrates the difference between this product and that from 8_. Whereas the present product with a higher v(S0) has S-co-ordination, the product from 8_ has O-co-ordination. In view of the arguments raised for the CO derivatives of 8_, (see Section 7.4.1., Chapter VII), i t would appear that i f methyl p-tolyl sulphoxide was a stronger i r-acid than triphenyl phosphine then the high v(CO) could be rationalized. A f u l l e r characterization of the carbonyl product must await further work. 10.4. Catalytic Hydrogenation with Compound 10 It. was hoped that stereoselective hydrogenation of olefins would be attained using a complex such as 1_0_ containing a pure chiral sulphur centre. However, with a l l olefinic substrates tested, acrylamide, itaconic and atropic acids, the hydrogenations were accompanied by the production of ruthenium metal. Experiments were done at high and low hydrogen pressures, (ca. 1800 and 14 psi), at 60°C in DMA with similar results. Complete hydrogenation of the olefinic substrates occurred; presumedly heterogeneously catalysed by metal, but with no observable stereoselectivity. Catalyst 10_ in the presence of 1 atm H 2 at 60°C in DMA, for the same reaction time as used in the substrate experiments, did not - 213 -produce any metal. This suggests that any ruthenium hydride species produced were stable towards reduction to metal. The reduction of the ruthenium(II) sulphoxide catalyst must then occur by way of a reaction with hydrogen and olefin to produce an unstable hydrido-olefin complex which subsequently decomposes to metal; similar conclusions were drawn for the [RuCl^(MBMSO)3-atropic acid systems. The combination of poor i r-electron acceptor a b i l i t y of the co-ordinated olefin substrate with insufficient ir-acceptor strength of the sulphoxide, or strong a donation of the olefin and of the sulphoxide, could lead to a high electron density on the Ru(II) with the subsequent reduction of the hydrido-olefin complex to metal. Available evidence, namely the lack of formation of metal with the [RuC^(MBMSO)^\^-acrylamide system under similar reaction conditions, suggests that methyl p-tolyl sulphoxide is a weaker i r-acid, or stronger a-donor than 2-methylbutyl methyl sulphoxide. Data on 102-104 phosphmes however, suggest that triphenylphosphine is perhaps a poorer a-donor than t r i a l k y l phosphines. These data tend to suggest that the difference in the two sulphoxides is perhaps a n-effect. 10.5. Polymeric Dichlorobis(methyl phenyl sulphoxide)ruthenium(II), 6_ Compound 6_ was prepared from a methanolic "blue solution" by the addition of racemic methyl phenyl sulphoxide in a mole ratio of sulphoxide:ruthenium = 3:1. During the course of the reaction,a red solution precipitated a gold coloured solid in 63% yield. Recrystallization attempts failed due to limited solubility; the compound is very slightly soluble in acetone, CH„C1 9, EtOH, and DMA. Elemental analysis confirmed - 214 -the product to be the t i t l e compound. Determination of the magnetic moment of 6_ by the Faraday method showed i t to be diamagnetic or feebly corr -6 paramagnetic. The measured X^ ' was (76 ± 91) x 10 c.g.s. per monomer 22 resulting in a u e f £ which is negative or 0.42 B.M. 10.5.1. I.r. Spectrum The i . r . spectrum contains a strong, f a i r l y broad band centred at 1130 cm 1 assigned to v(S0) (S-bonded); the free sulphoxide v(S0) is at 1045 cm 1. A band due to v(S0) (O-bonded) is not observed, although again this region of the spectrum, 900 - 980 cm 1 is complicated by a strong ligand band at 960 cm In the far i . r . a medium intensity band at 330 cm 1 is assigned to the terminal metal-chloride stretching mode. 10.5.2. Discussion Compound 6_ is similar to complexes 8_ and 10. The striking difference between 6_ and the other two compounds i s i t s solubility. The low solubility could be due to a large aggregation size, although i t is not readily apparent why a trimer is not formed. The lack of an alkyl substituent on the phenyl ring might perhaps lower i t s solubility relative to compound 10, as perhaps would alignment of the phenyl rings by restricting solvation. The steric problems in forming t r i s - or tetrakis-sulphoxide complexes is again present with methyl phenyl sulphoxide since the bis substituted complex is formed in the reaction mixture in the presence of an excess of sulphoxide ligand. Hydrogenation properties of this compound were not explored due to i t s low solubility. - 215 -CHAPTER XI DICHLORO-DIOS AND -DDIOS COMPLEXES OF RUTHENIUM(II) 11.1. Introduction Several research groups, including those of Knowles et a l . 6 , Kagan and Dang^8 and Cullen et a l . 1 , 1 1 have had good success with stereo-selective hydrogenation of olefins using rhodium(I) complexes containing the chiral bidentate phosphine ligand, Diop. Very recently, similar good results were reported for such hydrogenation using ruthenium(II)-Diop catalysts. . It was decided in this laboratory that a sulphoxide analogue of this ligand could be made, along with corresponding ruthenium(II) complexes. The resulting compounds were indeed found to be stereoselective homogeneous hydrogenation catalysts for a number of olefin substrate systems, although the level of stereoselectivity attained is generally considerably less than that found for the Rh(I)- or Ru(II)-Diop systems reported above; however,this i t s e l f i s of interest. Studies on the corresponding rhodium sulphoxide systems are currently being carried out in this laboratory 1 1*'. This chapter discusses the characterization of stereoselective homogeneous hydrogenation catalysts containing the Dios ligand and/or DDios ligand; RuCl 2 (DDios)2•2H20, RuCl 2(Dios)(DDios), and RuCl2(DDios)(DMSO)(MeOH). The stereoselective hydrogenation studies with these catalysts are presented in the next chapter. - 216 -11.2. Dichlorobis(DDios)ruthenium(II)dihydrate, 11 Compound 1_1_ was prepared from a methanolic "blue solution" via preparative route 1 (Chapter IV),or by sulphoxide exchange in methanol of Dios with RuCl2(DMS0)4, preparative route 3, (Chapter IV). From the "blue solution" a light green solid i n i t i a l l y precipi-tated during the reaction, and on cooling a yellow solid precipitated. " Dissolution of both solids in water and precipitation with acetone yielded a yellow solid. The exchange reaction yielded a yellow solid. I. r. and n.m.r. spectral data showed a l l the above products to be similar in composition. Elemental analysis of the product from the "blue solution" confirmed the composition of the products as 11. Conductivity 22 2 -1 -1 in DMA (A = 7.6 cm ohm mol ), showed compound 11_ to be essentially non-ionic. The compound is soluble in H^ O, slightly soluble in DMA, very s l i g h t l y soluble in alcohols,and insoluble in acetone. II. 2.1. I.r. Spectrum The i . r . spectrum of 11_ contains a strong band at 1095 cm 1 due to the SO stretching mode of S-bonded sulphoxide. No definite band can be; assigned to O-bonded sulphoxide; however, there is an absorbance at 970 cm which on comparison with previous sulphoxide complexes is possibly due to a methyl rocking mode. A strong broad absorbance centred at 3370 cm 1 together with a medium, broad absorbance centred at 1630 cm 1 indicates the presence of 1^0. A definite vPI) band for the diol . cannot be assigned, but this band would be expected to occur in the 3400 cm 1 region. Bands due to v(Ru-Cl) cannot be assigned due to a poorly resolved far i . r . region. - 217 -11.2.2. H n.m.r. Spectra 1 Compound 1_1_ in d^ -DMSO and in has similar n.m.r. spectra. Both have closely spaced narrow resonance peaks in the region of 63.25 -3.70 and broader absorbance in the region 63.70-4.30. In d^ -DMSO there is an additional small peak at 63.10 which i s not present in the U^O spectrum. Further, a narrow resonance at 63.25 is present in the former spectrum which decreases in height with the addition of molecular sieve 5A. These data suggest this peak is due to water. The narrow resonances in the 63.25 - 3.70 region are due to the methylene and methyl protons of the S-bonded DDios ligand. The broad absorbances from 63.70 - 4.30 are due to the methine and hydroxyl protons. The small peak at 63.10 is thought to be due to methylene or methyl protons of S-bonded sulphoxide of a different structural isomer not found in D2O. No resonance absorption due to O-bonded or free sulphoxide are present in the region 62.00 - 3.00. There is also an absence of peaks in the region 61.00 - 2.00 where,in comparison to the free Dios ligand, the isopropylidene methyl protons of a co-ordinated Dios would be expected to resonate. 11.2.3. Discussion Spectral and elemental analytical data together indicate compound 1_1 contains, FLO and DDios ligand ie., Dios ligand that had the See also Chapter II, (fig. 2.9.). - 218 -isopropylidene group cleaved to give the d i o l , DDios. Acetal groups are extremely susceptible to cleavage by dilute acid in the presence of water 1 1^; cleavage of Dios results in DDios plus acetone, (eqn. 11,1). Dios + H20 DDios + (CH )2C0 (11,1) The "blue solution" reaction mixture contains HC1 produced from the H 2 reduction of ruthenium trichloride trihydrate, while the source of protons in the exchange reaction is not obvious. It is possible that the methanol is i t s e l f acidic enough to cleave the acetal or contains some acid impurity. The three required water molecules, (two WjO are associated with.compound 11_ and one H^ O is required for cleavage of the acetal), are supplied from the ruthenium trichloride trihydrate or from the hygroscopic Dios ligand which has at least one molecule of water associated with i t , (see Section 2.8.4.7viii). With complex 11_ the two water molecules could be hydrogen-bonded to the alcohol groups rather than just present as molecules of solvation. Compound 11_ is unique among sulphoxide complexes in that i t has four S-co-ordinated sulphoxide moieties; this contrasts with RuCl^tDMSO)^ where one DMSO ligand is O-bonded. These data suggest that the O-bonded DMSO results from steric interactions. The DDios ligand i s f a i r l y flexible with considerable distance between the two sulphur atoms. This presumedly allows two such ligands to co-ordinate to ruthenium(II) through their sulphur atoms with much less steric interaction than four DMSO ligands with their s t e r i c a l l y interacting methyl groups. - 219 -The limited spectral data available do not allow assignment of the structure of product 1_1_. It is possible that the product as isolated is a mixture of isomers with trans- or cis-chlorides, as well as isomers containing different diastereomers of the sulphoxide ligand. 11.3. Dichloro(Dios)(DDios)ruthenium(II), 12 Compound 1_2_ was prepared by the method described in preparative route 3 (Chapter IV), by exchange of Dios with RuCl2(DMSO)4 in CHC13. The two reagents were allowed to react with refluxing for 120 hr, at which time no further colour changes had occurred. After removal of CHCl^ the o i l y residue was dissolved in acetone and the resultant solution f i l t e r e d ; this operation separated out any unreacted RuCl2(DMSO)4 which is insoluble in this solvent. Slow addition of diethyl ether precipitated the yellow product. Dissolution in acetone and precipitation were repeated to purify the product. Attempts at crystallization of the product from either CHCl^-ether or acetone-ether solvent systems resulted in only 22 2 -1 -1 precipitates. Conductivity in water, (A =2.6 cm ohm moi )showed product 1_2_ to be a neutral complex. Exposure of this solution to a i r gave; green solutions which could possibly contain ruthenium(III) species. Complex 1_2_ i s soluble in polar and halogenated solvents, and insoluble in ether and alkanes. 11.3.1. I.r. Spectrum The i . r . spectrum of 1_2_ contains a strong band at 1100 cm corresponding to v§0), S-bonded,and a medium strength band at 932 cm which - 220 _ could bevgO),O-bonded. Bands at 3500 and 1065 cm are due to v(OH) and tentatively v(C0)of the diol,respectively; assignement of the C-0 stretching mode is d i f f i c u l t , as this region of the spectra has other ligand bands. A medium strength doublet absorbance at 1104 and 1113 cm 1 is assigned to 117 the C-H bending mode of a geminal dimethyl group . The far i . r . region of the spectrum is not well resolved but an absorbance at 335 cm 1 is tentatively assigned to v(Ru-Cl). 11.3.2. H^ n.m.r. Spectra^ The proton n.m.r. spectrum of 1_2_ in CDCl^ contains a singlet at 61.42 due to the six equivalent isopropylidene methyl protons, and a singlet at 62.58 due to the three equivalent protons of a methyl group a to an unco-ordinated sulphur atom. Between 62.61 - 2.90 are multiplet resonances due to the five protons of a methyl and a methylene group a to an unco-ordinated or O-bonded sulphur atom. Between 63.07 - 3.80, and 63.90 - 4.70,are multiplet peaks due to the remaining protons of S-bonded Dios and DDios ligands. The integration ratios between the peaks due to the S-bonded, O-bonded, free sulphoxide methyl and methylene protons, and isopropylidene methyl protons,indicate that in CDCl^ three of the four sulphoxide moieties are S-bonded, and one O-bonded or unco-ordinated, and that the amount of Dios and DDios is equal. Compound 12_ in D^ O has essentially the same spectrum as in CDCl^,except there are two overlapping singlets at 62.80 and 2.70 of approximately equal intensity due to the methylene and ^ See also Chapter II, (fi g . 2.10.). - 221 -methyl protons of one sulphur moiety which is in part O-bonded and unco-ordinated. Addition of 50% by volume of 38% DC1 in D^O to the above solution rapidly (<2 min) results in a spectrum with no peak at 51.42)and a singlet at 62.05 attributed to acetone; these data show the cleavage by DC1 of the isopropylidene groups of co-ordinated Dios to form DDios and acetone. 11.3.3. Discussion It is apparent that two Dios ligands cannot be chelated to a Ru^C^ moiety. Cleavage of one Dios to give DDios l i k e l y increases the f l e x i b i l i t y , and decreases the size of the ligand, and this allows both ligands to co-ordinate. Even then, co-ordination through one sulphoxide oxygen atom appears necessary to decrease steric interactions. The Dios ligand i s more l i k e l y than DDios to alleviate steric interference by co-ordination through oxygen. A probable structure for compound 12^  involves a bidentate DDios ligand chelated through sulphur atoms, with the Dios ligand co-ordinated through one sulphur and one oxygen atom. Although the far i . r . spectrum has only one apparent v(Ru-Cl) band, which suggests a trans-chloride octahedral structure, product 1_2_ could be a cis-chloride isomer or a mixture of isomers, with the second cis v(Ru-Cl) band unresolved. Product 1_2 behaves like RuC^CDMSO)^ in regard to the dissociation of O-bonded sulphoxide in chloroform and water; however,dissociation i s not complete in water solution as shown by the n.m.r. spectra. A ready explanation - 222 -of this l i e s i n the "chelate effect" reducing the effective l a b i l i t y of the "dangling O-atom". The source of acid required to cleave the Dios ligand in the reaction solution i s again not readily apparent. The chloroform could contain traces of HC1,since i t s commercial production from methane 118 and C l ^ produces HC1 . The water required for cleavage i s supplied by the Dios ligand. 11.4. Dichloro(DDios)(DMSO)(MeOH)ruthenium(II), 13 Exchange of Dios with RuC^^MSO)^ in a 1:1 mole ratio i n refluxing methanol resulted in the mixed sulphoxide complex, L3. The solid yellow product began precipitating from solution after 18 hr. Recrystallization from DMA affords the pure compound, as shown by elemental analysis, (see Chapter II). 22 2 -1 -1 Conductivity i n DMA (A = 4.4 cm ohm mol ) showed product 1_3 to be a neutral complex. Complex 13 is soluble in DMA and t^O^and very slig h t l y soluble in alcohols. 11.4.1. I.r. Spectrum The i . r . spectrum of compound 1_3_ contains a strong broad band centred at 3400 cm 1 assigned to the alcohol OH stretching mode. This band cannot be confused with vfOHH^O) since the accompanying expected H^O band at ca. 1600 cm 1 is not present. Strong bands at 1123, and 1100 cm 1 indicate S-bonded sulphoxide and are assigned to v(S0). The - 223 -region 1000 to 1080 cm has multiple adjacent absorbances and one sharp band at 1018 cm 1 which are presumedly due to v(C0) for the three alcohol groups. Sharp absorbances are present in the region 900 - 980 cm 1 but none can be definitely assigned to v(S0) (O-bond). The far i . r . spectrum contains bands at 325 and 305 cm 1 which are tentatively assigned to v(Ru-Cl). 11.4.2. n.m.r. Spectrum^ The *H n.m.r. spectrum of complex L3 in D^ O consists in part of sharp closely spaced resonances (perhaps singlets). The peaks are at 63.52, 3.60, 3.63, and 3.75 and are due to the twelve methyl protons of S-bonded DDios and DMSO, the three methyl protons of methanol,and the four methylene protons of DDios. A pair of broad peaks between 63.9 -4.1 and 4.2 - 4.4 are resonances of the methine protons of DDios, and three alcohol protons of DDios and methanol. Integration does not discern which protons are responsible for each of the broad peaks. An integration ratio of the sharp resonances to the broad resonances is about 4:1 confirming the peak assignments. No resonances due to O-bonded or free DMSO or DDios, (62.0 - 3.0) are observed,nor are resonances due to isopropylidene methyl protons of Dios, (ca. 61.45). It seems likely that the observed n.m.r. spectrum in water is of RuCl^(DDios)(DMSO)(t^O) since methanol i s a rather weak Lewis base and is labile to replacement 77 by water ^ See also Chapter II for a Spectral Diagram, (fig. 2.9.). - 224 -11.4.3. Discussion The exchange of Dios with RuCl2(DMS0)4 in methanol gave the expected product in so far as the cleavage of Dios to DDios occurred. The reaction is similar to that which forms complex 11_, except for the 1:1 mole ratio of Dios used. Considering the nature of complexes 11_ and 12_(this 1:1 reaction could be expected to produce RuCl 2(DDios) (DMS0)2 or RuCl2(DDios)(DMSO)(MeOH). The former product could have one O-bonded sulphur atom (possibly of a DMSO ligand) to limit unfavourable steric interaction. Formation of the co-ordinated methanol product is probably a result of the smaller size and higher concentration of the methanol ligand as compared to DMSO, and the limited s o l u b i l i t y of the product in methanol. Compounds containing co-ordinated methanol are known, in 1 1 q qq particular [Cr(MeOH) 4Cl 2]Cl , and [Ru (C02Me)6(MeOH)3] . The latter features i . r . bands at 3400 and 996 cm while compound 1_3 has a band at 3400 cm and a sharp band at 1018 cm * which could be the v(C0) band of co-ordinated methanol. The far i . r . spectral data suggest a cis-chloride structure for complex 13, of which there are many isomers with, for example, methanol or DMSO or both ligands trans to chloride, or one of these trans to DDios. Product L3 as isolated could be a mixture of isomers, including some with different diastereomers of DDios. - 225 -CHAPTER XII ASYMMETRIC CATALYTIC HYDROGENATION USING DIOS AND DDIOS DICHLORO-COMPLEXES OF RUTHENIUM(II) 12.1. Introduction As stated in Chapter XI the degree of stereoselectivity using the Dios/DDios ruthenium(II) catalysts is far below that found with compounds containing the Diop ligand. Nevertheless,higher stereo-induction i s obtained than with the other Ru (II)-sulphoxide catalysts discussed in Chapter IX. This chapter presents the results of some asymmetric hydro-genation experiments using the Dios/DDios complexes. 12.2. Asymmetric Hydrogenation Results In DMA or water solution compound 1_1_, RuCl 2 (DDios) 2 • 2H20 (0.01 M), under 1 atm hydrogen at 60°C with acrylamide (0.8 M) displayed no measurable hydrogen uptake. Addition of a two-fold excess of proton R sponge to the DMA catalyst solution resulted in an extremely slow hydrogen reaction. A chloride-free solution of a lik e l y cationic catalyst formed from 11_ (the chloride being removed by f i l t e r i n g after treatment with AgPF^), with the same concentration of substrate and Ru and under the same relatively mild conditions as above,also reacted extremely slowly - 226 -with hydrogen. Addition of a two-fold excess of proton sponge to this solution resulted in a slightly faster hydrogen reaction. Catalyst 11 in DMA at 45 psi hydrogen with itaconic acid resulted in no measurable hydrogenation; however, at a much higher pressure of hydrogen using diethyl itaconate and proton sponge 100% hydrogenation occurred, (see Table 12.1.). Catalyst 12,RuCl2(Dios)(DDios) (0.013 M),with itaconic acid (0.51 M) in DMA at 50°C under 1 atm H 2 gave a H 2 uptake plot similar to that of the [NH2Me2][RuCl3(DMSOy-acrylamide system, (fig. 6.4.)., and -7 -1 had a linear uptake rate of 4.9 x 10 Ms . The same solution under a pressure of 3 atm at 55°C resulted in 49% hydrogenation after seven days and an enantiomeric excess = 25%, with the R enantiomer predominant. Catalyst 12_also asymmetrically hydrogenated atropic and 2-acetamidoacrylic acids, but with less stereoselectivity. Catalyst 1_3, RuCl 2 (DDios) (DMSO) (MeOH) , under conditions similar to those used for 12, stereoselectively hydrogenated itaconic acid to give an enantiomeric excess = 5%, with the R enantiomer predominant. The details of the above asymmetric hydrogenations are summarized in Table 12.1., which shows that the most stereoselective hydrogenation cata-lyst is RuCl 2(Dios)(DDios) and that i t s asymmetric induction decreases with increasing temperature. A l l three catalysts give predominantly the R enantiomer of a-methylsuccinic acid, as did the [RuCl2(MBMSO)2]^ catalyst, (Chapter IX). The hydrogenation of the diethyl ester of itaconic acid was complete, but with the production of some metal at an undetermined step. The catalytic solutions containing 12_ turned from yellow to orange TABLE 12.1. Asymmetric hydrogenation results using Dios and DDios ruthenium(II) catalysts in DMAa Catalyst [ R u H ] T Substrate [Substrate] pH ? psi T °C t hr. % hydrogenation ee c % I 0.0074 Diethyl itaconate 0.49 1800 60 288 100 3.8(R)d I 0.015 Itaconic acid 1.81 45 42 144 0 -I I 6 0.013 Itaconic acid 0.51 44 55 168 49 25.2(R) I I f 0.013 Itaconic acid 0.51 50 71 168 100 8.1CR) I I 6 0.016 Atropic acid 0.62 46 52 144 17 4.1(S) I I e 0.016 2-acetamide-acrylic acid 0.45 47 55 240 62 7.2(S) III 0.016 Itaconic acid 0.61 48 63 240 29 5.4(R) a 5-11 ml solutions. b I) RuCl 2(DDios) 2-2H 20; (II) RuCl 2(Dios)(DDios); (III) RuCl2(DDios)(DMSO)(MeOH). c d R Predominant enantiomer in parenthtesis. 0.0063M proton sponge added; some metal present at the end of the reaction; a-methyl succinic acid diethyl ester product hydrolyzed to the di-acid before enantiomeric excess e f determined. I n i t i a l yellow solutions became orange by the end of the reaction time. I n i t i a l yellow solu-tion became red by the end of the reaction time with no metal produced. The enantiomeric excesses are based on the specific rotation of the chiral acid; (S)-N-acetylalanine, [ [ a ] ^ = -66.5°; C2, H-O] 1 1 1, (R)-a-methylsuccinic 20 112 75 112 acid, [ [ a ] D = +17.09°; C10, abs. EtOH] , and (S)-2-phenylpropanoic acid, [[a]^ = +76.1°, C8, CHC13] - 228 -over the course of the reaction in the atropic and 2-acetamidoacrylic acid systems,and at complete hydrogenation of itaconic acid the solution was red with no metal produced. Qualitatively these solutions appear similar to those resulting from the reactions of RuCl2(DMSO)4 and R [NI-^N^] [RuCl^(DMSO)^] with hydrogen in the presence of proton sponge , (see Section 5.7.). 12.3. Discussion Catalysts 11_ - 13_ are similar in composition to RuC^fDMSO)^ , and indeed 1_2_ exhibits similar hydrogen uptake curves to those found for the DMSO catalysts, RuCl (DMSO)4 and [NHMe2][RuCl (DMSO) ]. The necessity of adding proton sponge to increase the hydrogenation rate of catalyst 1_1_ suggests that the hydrogen i s activated by a net heterolytic base-promoted reaction, and the systems summarized in Table 12.1. probably involve hydrogenation mechanisms similar to those invoked for the RuCl3(DMS0)3~ anion and perhaps RuCl2(DMSO)4, (Chapter VI). The higher pressures required to effect efficient catalysis using 1_1_ - 1_3_ suggests that activation of hydrogen is a rate determining step,as i t is for the , [NH2Me2][RuCl3(DMSO)3]-acrylamide system. Whether olefin is co-ordinated prior to or after this rate determining step cannot be ascertained without kinetic data. Catalyst 11_ under high H 0 pressure f u l l y hydrogenates diethyl itaconate with production of metal, and with low but significant stereoselectivity. These data suggest that formation of metal occurs after or during asymmetric hydrogenation with the homogeneous catalyst 11, although the poss i b i l i t y of asymmetric hetereogeneous hydrogenation cannot - 229 -be entirely ruled out. Attempts to activate catalyst 11_ in a cationic form by removal of the two chloride ligands essentially failed. This suggests that formation of a metal-hydride species by heterolytic cleavage of hydrogen is aided by the elimination of HCl; these data corroborate earlier data suggesting that the activation is rate determining. Catalyst 12 i s a far more effective catalyst,than 11, and at low pressure, (1 atm), is comparable in act i v i t y to [N^P^] [RuCl^(DMSO)^]. The similarity in colour of the hydrogenation reaction solution (orange) and hydrogen uptake curves suggests a close similarity to the DMSO catalyst-system, ie; formation of a ruthenium(II)-hydride complex prior to olefin complexation. The increased effectiveness in rate of hydrogenation of this catalyst over 1_1_ is probably due to the O-co-ordinated sulphoxide ligand which dissociates more easily than the f u l l y S-bonded sulphoxide ligands of catalyst 11. The stereoselectivity sequence 1_2_ > L3 parallels the number of bulky chiral chelalate sulphoxide ligands. With higher temperature the stereoselectivity of 1_2_ is decreased. This could be due to greater ligand dissociation, and hence less stereo-selective catalytic species present,or more freedom of movement of the co-ordinated olefin substrate. The lower stereoselectivity of 12_ for reduction of atropic and 2-acetamidoacrylic acids as compared to itaconic acid could result from differences in substrate bonding due to electronic effects of the substrate, as outlined previously for the [RuCl2(MBMSO)2]g systems, (Chapter IX). H-bonding involving one carboxyl group of itaconic acid and the OH group - 230 -of DDios could be important. It is not clear why 13, which has a labile methanol, gives much slower hydrogenation rates than 12. A point that remains to be tested for is whether cleavage of the co-ordinated Dios occurs in the presence of the olefin substrates. - 231 -CHAPTER XIII GENERAL CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK One of the most important findings of this work is the realization of asymmetric hydrogenation using Ru(II) complexes of chiral sulphoxides as catatlysts. New sulphoxides with c h i r a l i t y in the associated alkyl groups were synthesized, for example, MBMSO, Dios, and BDios; Ru(II)-dichloro compounds were prepared from the f i r s t two, and asymmetric hydrogenation of itaconic, atropic and 2-acetamido-acrylic acids accomplished with these new compounds. The extent of asymmetric induction in the products was not large, for example, the [RuCl2(MBMSO)2]^-itaconic acid system gave a typical enantiomeric excess of 15%,while for the RuC^ (Dios)(DDios)-itaconic acid system this value was 25%. Hydrogen pressures above 1 atm were required to effect asymmetric hydrogenation in a reasonable time period. ; The whole area of asymmetric hydrogenation using Ru(II) sulphoxide catalysts is primed for future work. For example, isolation of chiral sulphoxides which are diastereometrically pure and the preparation of corresponding metal catalysts could well result in higher optical yields. Another important area dealt with in this work involves the nature of DMSO bonding to Ru(II). The structure of a new complex, fac-[NH Me_][RuCl,(DMSO) ], was determined by spectral means and confirmed by - 232 -crystallographic studies to have three S-bonded DMSO ligands. The literature confusion on the structure of RuCl2(DMS0)4 was alleviated by similar studies, and the complex found to be the cis-isomer with three S-bonded and one O-bonded DMSO, the latter being trans to a S-bonded DMSO. The complex [NH2Me2] [RuCl^(MenprSO)3] was prepared and spectral data demonstrated a structure analogous to the corresponding DMSO complex. The complex RuBr2(DMS0)4 was also prepared and spectral data showed i t to have three S-bonded and one O-bonded DMSO. The major criterion for the presence of mixed or a l l S-bonded sulphoxides at Ru(II) appears to be a steric effect, although additional work involving more Ru(II) sulphoxide complexes should be carried out to catagorically establish this. The complexes [NH Me2][RuCl3(DMSO)3] and RuCl2(DMSO)4 readily R reacted with 1 atm H 2 in DMA at 60°C in the presence of proton sponge . The resulting hydride species exhibited very high n.m.r. hydride chemical shifts. The isolation of these hydrides and a study of their possible catalytic properties is most certainly a topic for future consideration. Based on kinetic and spectral studies a mechanism was formulated for the catalytic hydrogenation of acrylamide using the RuCl^S^ anion in DMA. The proposed mechanism i s ; - 233 -R u H C l 3 S 3 + H 0 HRu I ICl 2S 3 + HC1 K - k - 2 1l k2' ° l e f i n ' " S Ru T ICl 3S2 + S HRu I 1 CCl 2S 2 (olefin)" H2 1 V - H C 1 • | k 3 HRu I ICl 2S 2 + olefin —^» R i ^ C l ^ a l k y l " HC1 R u I I C l 3 S 2 + Sat. Product Activation of hydrogen is by two pathways, both involving net heterolytic fission. One such step and an olefin insertion step are considered rate determining, (k 3 and k^). The Dios group of catalysts appeared to hydrogenate by similar mechanisms. The catalyst [RuC12(MBMSO)2J3 i s interesting because of i t s degree of association, although the catalytic a c t i v i t y results from a monomeric species formed by dissociation of the trimer. The kinetics of acrylamide hydrogenation using this catalyst led to the following mechanism: K [ R u T I C l 2 S 2 ] 3 ==i 3 R u H C l 2 S 2 II 1 IV Ru C1 2S 2 + H 2 H Ru C12S + S k 3 I k3 °^- e^ n 2^ ^ ^ ^ i ™ V( I k R u H C l n S 0 o l e f i n — ^ c HRu I Cl.S alkyl Z Z 2' II 5 Ru C12S + Sat. Product 1 k S III 6 Ru C 1 2 S 2 - 234 -The catalyst was far more active than the RuCl^fDMSO)^ anion catalyst. Rate determining hydrogen activation by two pathways appears to occur via oxidative addition to the Ru(II); olefin reduction via such ruthenium dihydrides has not previously been invoked. Comparison of the catalytic properties of [RuCl2(MBMSO)2]^ and [RuCl2(MPTS0)2]g suggests that differences in the relative i r-acid strengths of the two sulphoxide ligands may be important (MBMSO> MPTSO), and further studies in this area seem worthwhile, for example, for comparison with triphenylphosphine,etc. [RuCl2(MBMSO)2] and RuCl2(MPTSO)2] were found to react readily with CO to give dicarbonyl species, some of which have anomalously high v(CO) bands. Further work in isolating and characterizing these carbonyl compounds would certainly be rewarding. A general area worthy of effort involves supporting the sulphoxide catalysts on a polymer, which results in possible dual homogeneous/ heterogeneous catalysts. Support of the asymmetric catalysts could be accomplished in a way similar to that used for phosphine-supported catalysts but using polymer-S-metal linkages rather than polymer-P-metal linkages. - 235 -REFERENCES 1) M. Calvin, Trans. Faraday Soc, 34, 1181 (1938). 2) A. Agulio, Adv. Organomet. Chem., 5_, 321 (1967) and references therein; G. Szonyi, Adv. Chem. Series, 70, 53 (1968). 3) I. Wender and P. Pino, eds., "Organic Synthesis via Metal Carbonyls", Vol. 1, Interscience-Wiley, 1968; W. Rupilus, J.J. McCoy and M. Orchin, Ind. Eng. Chem. (Prod. Res. Devel.), 1£, 142 (1971); G.F. Pregaglia, A. Andreeta, and G.F. Ferrari, J. Organomet. Chem., 30, 387 (1971). 4) A.D. Ketley, ed., "The Stereochemistry of Macromolecules", Vols. I-III, Arnold (London, Dekker (N.Y.), 1967; J. Boor, Jr., Ind. Eng. Chem. (Prod. Res. Devel.), 9_, 437 (1970); W. Cooper, Ind. Eng. Chem., 9, 457 (1970); CA. Tolman, J. Am. Chem. Soc, 92, 6777 (1970). 5) J.F. Roth, J.H. Craddock, A. Hershman, and F.E. Poulik, Chem. Tech., 600 (1971). 6) W.S. Knowles, M.J. Sabacky, and B.D. Vineyard, Adv. Chem. Series, 132, 274 (1974). 7) H. Hirai and T. Furata, J. Polym. Sci., 9(B). 459 (1971). 8) T.D. Inch, Synthesis, 466, (1970). 9) P. Pino, S. Pucci, F. Piacenti, and G. Dell'Amico, J. Chem. Soc, C, 1640 (1971). 10) B.R. James, "Homogeneous Hydrogenation", John Wiley and Sons, Toronto, 1973. 11) B.R. James, E. Ochiai, and G.I. Rempel, Inorg. Nucl. Chem. Lett., 1_, 781 (1971). 12) I.P. Evans, A. Spencer, and G. Wilkinson, J. Chem. Soc, Dalton, 204 (1973). 13) Reference 10, p. 78. 14) Ibid., pp. 83-94. 15) Ibid., pp. 82-83. 16) J. Halpern, Adv. in Chem. Series, 70_, 1 (1968). - 236 _ 17) J. Halpern, Ann. Rev. Phys. Chem., 16^ , 103 (1965). 18) J. Halpern, Proc. 3rd. Intern. Congr. Catal., North-Holland, Amsterdam, 146 (1965). 19) J. Halpern, Chem. Eng. News, 44, 68 (1966). 20) Reference 10, p. 43. 21) Ibid., p. 80. 22) Ibid., p. 402. 23) Ibid., pp. 108-109. 24) Ibid., pp. 95-96. 25) Ibid., pp. 204-219. 26) J.D. Morrison and W.F. Mosler, Adv. Catal., 25, 81 (1976). 27) J.D. Morison, W.F. Mosler, and S. Hathaway, "Catalysis in Organic Syntheses", Academic Press Inc., New York, 1976, p. 203. 28) B.R. James, D. Mahajan, and D.K.W. Wang, Seventh Internat. Confer. Organomet. Chem., Venice, 135 (1975); B.R. James, D.K.W. Wang, and R.F. Voigt, Chem. Comm., 547 (1975). 29) P. Pino, G. Consiglio, C. Botteghi, and C. Solomon, Adv. Chem. Series, 132, 295 (1974). 30) J. Halpern, J. Harrod, and B.R. James, J. Am. Chem. Soc, 8_3, 763 (1961). 31) J. Harrod, S. Ciccone, and J. Halpern, Can. J. Chem., 39, 1372 (1961). 32) L.D. Markham, Ph.D. Dissertation, University of British Columbia, : Vancouver, British Columbia, 1973. 33) I. Ogata, R. Iwata, and Y. Ikeda, Tetrahedron Letters, 3011 (1970). 34) D.T. McAllen, T.V. Cullum, R.A. Dean, and F.A. Fidler, J. Am. Chem. Soc, 73_, 3627 (1951). 35) J. Jacobus and K. Mislow, J. Am. Chem. Soc, 89_, 5228 (1967). 36) K. Mislow, M.M. Green, P. Lour, J.T. Melillo, T. Simmons, and A.L. Ternay, Jr., J. Am. Chem. Soc, 87_, 1958 (1965). - 237 -37) H.F. Herbrandson, R.T. Dickerson, Jr., and J. Weinstein, J. Am. Chem. Soc, 78_, 2576 (1956). 38) R.C. Weast, ed., "Handbook of Chemistry and Physics", 49th Ed., Chemical Rubber Co., Cleveland, 1968, p. C-217. 39) Ibid., p. C-221. 40) B.J. Hazzard, "Organicum: Practical Handbook of Organic Chemistry", Addison-Wesley, New York, 1970, p. 61. 41) R.C. Weast, Op. Cit., p. C-558. 42) Ibid., p. C-559. 43) M. Carmack and C.J. Kelley, J. Org. Chem. 33, 2171 (1969). 44) P.W. Feit, J. Med. Chem., 7, 14 (1964). 45) L.J. Rubin, H.A. Lardy, and H.O.L. Fischer, J. Am. Chem. Soc, 74, 425 (1952). 46) C.R. Johnson, Quarterly Reports on Sulphur Chemistry, 3_, 91 (1968). 47) W.L. Reynolds, Progr. Inorg. Chem., 1_2, 1 (1970). 48) F.A. Cotton, R. Francis,, and W.D. Horrocks, Jr., J. Phys. Chem., 64, 1534 (1960). 49) R.G. Pearson, J. Am. Chem. Soc, 8_5, 3533 (1963). 50) R.S; McMillan, A. Mercer, B.R. James, and J. Trotter, J. Chem. Soc. Dalton, 1006 (1975). 51) A. Mercer, and J. Trotter, J. Chem. Soc Dalton, 2480 (1976). 52) M.J. Bennett, F.A. Cotton, and D.L. Weaver, Acta. Cryst., 23_, 581 (1967). 53) M. Axelrod, P. Bickart, M.L. Goldstein, M.M. Green, A. Kjaer, and K. Mislow, Tetrahedron Letters, 2_9, 3249 (1968). 54) G.M. Whitesides, and D.W. Lewis, J. Am. Chem. Soc, 93, 5914 (1971). 55) Von Siegfried Hunig, and Otto Boes, Ann. Chem., 579, 23 (1953). 56) J. Holloway, J. Kenyon,:arid H. Ph i l l i p s , S. Chem. Soc, 3000 (1928). 57) M. Axelrod, P. Bickart, M.M. Green, and K. Mislow, J. Am. Chem. Soc, 90, 4835 (1968). - 238 -58) G.A. Wiley, R.L. Hershkowitz, B.M. Rein, and B.C. Chung, J. Am. Chem. Soc, 86_, 964 (1964). 59) N. Rabjohn, ed., Organic Syntheses, Coll. Vol. 4, 937 (1963). 60) W.P. G r i f f i t h , "The Chemistry of the Rarer Platinum Metals", Interscience, London, 1967, p. 136. 61) . J. Halpern, and B.R. James, Can. J. Chem., 4_4, 495 (1966). 62) D. Rose, and G. Wilkinson, J. Chem. Soc, A, 1791 (1970). 63) E.E. Mercer, and P.E. Dumas, Inorg. Chem., 10_, 2755 (1971). 64) B.C. Hui, and B.R. James, Can. J. Chem., 52, 348 (1974). 65) J.D. Gilbert, D. Rose, and G. Wilkinson, J. Chem. Soc, A, 2765 (1970) . 66) A.D. Allen, F. Bottomley, R.O. Harris, V.P. Reinsalu, and C.V. Senoff, J. Am. Chem. Soc, 8J9, 5595 (1967). 67) L. Ruiz-Riamirez, T.A. Stephenson, and E.S. Switkes, J. Chem. Soc Dalton, 1770 (1973). 68) B.B. Wayland, and R.F. Schramm, Inorg. Chem., 8_, 971 (1969). 69) B.R. James, R.S. McMillan, and E. Ochiai, Inorg. Nucl. Chem. Lett., 8_, 239 (1972). 70) W.D. Horrocks, Jr., and F.A. Cotton, Spectrochem. Acta, 17, 137 (1961). 71) D.M. Adams, "Metal-Ligand and Related Vibrations", Arnold, London, 1967, p. 72. 72) B.F.G. Johnson, and R.A. Walton, Spectrochim. Acta, 22_, 1853 (1966). 73) J. Lewis, F.E. Mables, and R.A. Walton, J. Chem. Soc, (A), 1366 (1967). 74) C.R. Johnson, and D.J. Pasto, "Organic Structure Determination", Prentice-Hall, New York, 1969, p. 121. 75) T.G. Appleton, H.C. Clark, and L.E. Manzer, Co-ordination Chemistry Reviews, 10, 335 (1973). 76) Y.N. Kukushkin, M.A. Kuz'mina, and A.F. U'yugina, Radiokhimija, 10, 470 (1968). - 239 -J.V. McArdle, A.J. Schultz, B.J. Corden, and R. Eisenberg, Inorg. Chem., 1_2, 1676 (1973). J.R. Shapley, and J.A. Osborn, Acc. Chem. Res., 6_, 305 (1973). H.L. Bott, E.J. Bounsall, and A.J. Poe, J. Chem. Soc., (A), 1275 (1966) . A. J. Poe, and C.P.J. Vuik, J. Chem. Soc. Dalton, 2250 (1972). F. Basolo, and R.G. Pearson, "Mechanisms of Inorganic Reactions", Wiley, New York, "2nd edn., 1967, ch. 3. Ibid., Ch. 5. R.W. Alder, P.S. Bowman, W.R.S. Steele, and D.R. Winterman, Chem. Comm., 723 (1969). H.D. Kaesz, and R.B. Saillant, Chem. Revs., 72, 231 (1972). M.L.H. Green, and B.J. Jones, Advan. Inorg. Chem. Radiochem., 7_, 115 (1965). C. Masters, W.C. McDonald, G. Raper, and B.L. Shaw, J. Chem. Soc, (D), 210 (1971). B. F.G. Johnson, R.D. Johnson, J. Lewis, and B.H. Robinson, J. Chem. Soc, (A), 2856 (1968). D. A. Deranleau, J. Am. Chem. Soc, 91_, 4044, 4050 (1969). Reference 10, p. 85. Ibid., p. 250. Ibid., p. 330. Ibid., p. 310. H.C. Clark, and C.R. Jablonski, Inorg. Chem., L3, 2213 (1974). H.C. Clark, C.R. Jablonski, and K. Von Werner, J. Organomet. Chem., 82, C51 (1974). H.C. Clark, and C.S. Wong, J. Am. Chem. Soc, 96, 7213 (1974). Reference 10, p. 172. - 240 -97) A. Levi, G. Modeno, and G. Scorrano, Chem. Comm., 6 (1975). 98) H. Kagan, and T-P Pang, J. Am. Chem. Soc, 94_, 6429 (1972). 99) A. Spencer, and G. Wilkinson, J. Chem. Soc Dalton Trans., 1570 (1972). 100) J. Chatt, B.L. Shaw, and A.E. Field, J. Chem. Soc, 3466 (1964). 101) N. Ahamad, S.D. Robinson, and M.F. Uttley, J. Chem. Soc. Dalton, 843 (1972), and references therein. 102) B.R. James, B.C. Hui, L.D. Markham, and G.L. Rempel, J. Chem. Soc Dalton, 2247 (1973). 103) P. John, Chem. Ber., 103, 2178 (1970). 104) CA. Tolman, J. Am. Chem. Soc, 92_, 2953 (1970). 105) G. Booth, and J. Chatt, J. Chem. Soc, 2099 (1962). 106) Reference 10, pp. 204-206. 107) Ibid., p. 103. 108) G. Strathdee, and R. Given, Canad. J. Chem., 53_, 106 (1975). 109) Reference 10, p. 276. 110) Ibid., p. 214 111) W.R. Cullen, A. Fenster, and B.R. James, Inorg. Nucl. Chem. Letters, 10, 167 (1974). 112) R.E. Burnett, Ph.D. Dissertation, University of New Hampshire, Durham, New Hampshire, 1971. 113) J.P. Collman, and W.R. Roper, Advan. Organomet. Chem., 7_, 53 (1968). 114) W.S. Knowles, A.C.S. Regional Homogeneous Catalysis Symposium, Univ-ersity of Reno, Reno, Nevada, June 1976. 115) B.R. James, R.S. McMillan, and K.J. Reimer, J. Molecular Catalysis, 1_, 439, 1976. 116) R.T. Morrison, and R.N. Boyd, "Organic Chemistry", Allyn and Bacon Inc., Boston, 1959, 1st Ed., p. 635. - 241 -117) J.R. Dyer "Applications of Absorption Spectroscopy of Organic Compounds", Prentice-Hall Inc., London, 1965, p. 33. 118) R.T. Morrison, Op. Cit., p. 32. 119) K.I. Hardcastle, D.O. Skovlin, and A. Eidawood, Chem. Comm., 190 . (1975). PUBLICATIONS B.R. James, R.S. McMillan and K.J. Reimer, J. Moi. Cat. 439 (1976). Catalytic Asymmetric Synthesis Using Ruthenium Complexes Containing Chiral Sulfoxide Ligands B.R. James and R.S. McMillan, Inorg. Nucl. Chem. Letters, J U , 837 (1975). A Convenient Synthesis of Potassium Hexachlororuthenate(III) and Potassium Tetra-chloromono(bipyridine)ruthenate(III) and the Analogous Mono(phenathroline) Complex R.S. McMillan, A. Mercer, B.R. James and J. Trotter, J.C.S. Dalton 1006 (1975). Preparation, Characterization and Crystal and Molecular Structure of Dimethylammoniumtrichlorotris(dimethyl sulphoxide)-ruthenate(II) B.R. James, R.S. McMillan and E. Ochiai, Inorg. Nucl. Chem. Letters, _8, 239 (1972). N,N'-Dimethylacetamide Complexes of Ruthenium from Hydrogenation Reactions 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0060985/manifest

Comment

Related Items