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The synthesis, characterization, and reactivity of nickel 2-pyridylphosphine complexes Le Page, Matthew Derek 2000

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T H E SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF NICKEL 2-PYRJDYLPHOSPHINE COMPLEXES by M A T T H E W DEREK L E PAGE B.Sc, Trinity Western University, 1994 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE F A C U L T Y OF GRADUATE STUDIES (Department of Chemistry) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September 2000 © Matthew Derek Le Page, 2000 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver, Canada Date Q r i . (O. q C X ) 0 DE-6 (2/88) ABSTRACT Numerous nickel(O) and nickel(II) 2-pyridylphosphine complexes were synthesized as they are potentially water-soluble, and may be of use in catalysis (e.g., in olefin hydration). Four different coordination modes of 2-pyridylphosphines were observed: coordination through the phosphorus only (P), through the phosphorus and one pyridyl group in a chelating fashion (P,N), through the phosphorus and one pyridyl group in a bridging fashion (ji-P,N), and through all three pyridyl groups in a chelating fashion (N,N',N"). Isolated complexes were characterized in general by NMR, IR and UV-Vis spectroscopies, mass spectrometry, elemental analysis, conductivity, magnetic susceptibility, and melting point, while seven complexes and one compound (used as a ligand) were also characterized by X-ray crystallography. Complexes synthesized in situ were characterized by " P f H J N M R . The water-soluble, diamagnetic, P-coordinated NiX2(P-P) complexes la-5a, lb-5b (X = Cl (1), Br (2), I (3), NCS (4), N 0 3 (5); P-P = dpype (l,2-bis[bis(2-pyridyl)phosphino]ethane) (a) and dpypcp (l,2-bis[bis(2-pyridyl)phosphino]cyclopentane) (b)) and Ni(CO)2(P-P) (20a-b) were obtained by ligand substitution of NiX 2(PPh 3) 2 or Ni(CO)2(PPh3)2 with P-P; X-ray crystal structures were obtained for five of the Ni(II) and one of the Ni(0) species. In aqueous media, the Ni(II) species form [Ni(H20)2(P-P)]2+, and the Ni(0) species form N-atom protonated [Ni(CO)2(2H-P-P)]2+, as shown by comparison of in situ NMR data to those of the isolated species [Ni(H20)2(P-P)](PF6)2 (6a-b) and [Ni(CO)2(2H-P-P)](PF6)2. The novel [Ni(H 20) 2-(dppe)](PF6)2 (13) (dppe = Ph2P(CH2)2PPh2) was also prepared. The known, water-soluble, paramagnetic, NiX 2 (PN x ) 2 species 9a-9c, lOa-lOc (X = Cl (9)', Br (10); PN X = PPh3.xpyx, where x = 1 (a), 2 (b), 3 (c), and py = 2-pyridyl) were briefly examined and proposed to form either [Ni(H 20) 2(PN x) 2] 2 + or NiX 2(wH-PN x) 2 n + in water. Factors affecting the in situ yields of the known Ni(CO) 2(PN x) 2 species (19a-c), prepared via ligand substitution of Ni(CO)2(PPh3)2 by PN X , were examined. The known, tetrahedral, P./Y-coordinated complex NiCl 2(PN 3) (7), uniquely prepared from Ni(CO)2(PPh3)2 in CH 2C1 2 via a photolytically-induced chlorine-abstraction process, converted ii over 15 d to the octahedral, water-soluble, N,N',^"-coordinated complex [Ni(PN3)2]Cl2 (8) whose X-ray crystal structure was obtained. A species tentatively characterized as the P.JV-coordinated dimer [Ni2(CO)4Cu-PN2)2]Cl4 (19d) was prepared from Ni(CO)2(PPh3)2 and P N 2 in CH 2C1 2. The air-sensitive, P-coordinated, tertiary Ni(0) phosphine complexes Ni(PR3)2(dppe) (21a-d), Ni(PR3)2(dpype) (22a-d), Ni(PR3)2(dpypcp) (23a-d) (PR3 = PPh3 (a), PNi (b), P N 2 (c), P N 3 (d)), Ni(P-P)2 (P-P = dpypcp (24a), dppe (24b), dpype (24c)), Ni(P-P)(P'-P') (P-P/P'-P -dppe/dpype (25a), dppe/dpypcp (25b), dpype/dpypcp (25c)), and the known Ni(PR 3) 4 species (PR3 = PPh 3 (26a), PN, (26b), P N 2 (26c), P N 3 (26d)) were prepared from Ni(l,5-COD) 2. Reactions of Ni(PN 3) 4 and Ni(dpypcp)2 with C2H4, H 2 0 , 0 2 , or C l 2 were not delineated, but reaction of several of the Ni(0) complexes with CH 3 I yielded the zraws-iodo(methyl) species. The monomethyl phosphonium salts [(CH3)(PN3)]I, [(CH3)(dppe)]I, [(CH3)(dpype)]I, [(CH3)(dpypcp)]I, and [(CH3)(PPh3)]I, and the bismethyl phosphonium salts [(CH3)2(dppe)]I2, [(CH3)2(dpype)]I2, and [(CH3)2(dpypcp)]I2 were also prepared as some of these species were observed in situ in the formation of the Ni(II) £ra«s-iodo(methyl) complexes. NiCl2(dppe), Ni(CO)2(PPh3)2, and complexes la, 2b, 7, 8, 10b, and 20a-b were not effective as catalysts for hydration of maleic acid in aqueous media, but some catalytic isomerization to fumaric acid (up to 11%) occurred after 48 h at 100°C. NiCl 2(PN 2) 2 was an effective catalyst for the water-gas-shift reaction (WGSR) in aqueous, alkaline EtOH, with a turnover frequency for H 2 / C 0 2 production of 27 h"1 obtained at 100°C with 40 atm CO, in the range reported for typical homogeneous WGSR catalysts. NiCl 2(PPh 3) 2, NLBr2(PPh3)2, Nil2(dppe), N i C l 2 . 6H 20, anhyd. NiBr 2, N i l 2 • 6H 2 0, 3a-b, 10a, and 10c were effective precursor catalysts for the transfer hydrogenation of cyclohexanone in refluxing, alkaline z-PrOH, with the activity of NiBr 2 and Ni l 2 • 6H 2 0 being ~ 3 and ~ 5 times that of the 2-pyridylphosphine and phenylphosphine complexes, respectively. Optimization of reaction conditions (~ 1.5 M cyclohexanone, ~ 5 mM NiBr 2, ~ 0.5 M NaOH) resulted in 100% conversion to cyclohexanol after 30 min refluxing. Kinetic dependences on NiBr 2, NaOH, cyclohexanone, and z'-PrOH were determined, as well as the effect of various additives (acetone, cyclohexanol, water, H 2 , halides, and PPh3); discussion of a plausible mechanism is presented. The catalyst was shown to be homogeneous, with activity decreasing over four cycles. Transfer hydrogenation of 1-octene, 2-butanone, and 2-pentanone by NiBr 2 proceeded at useful rates (i.e., ~ 99% iii conversion after Vi to 48 h), while hydrogenation of cyclohex-2-ene-l-one, nitrobenzene, and 4-nitrobenzaldehyde was also observed. The hydrogenation of acetophenone and 1-heptanal proceeded at rates similar to the Ni-free, "base-only" system. Experiments with 2,4-pentanedione and 2,5-hexanedione yielded sodium acetylacetonate and an aldol condensation product, respectively. No hydrogenation was observed for *raws-2-octene, cyclooctene, 1,5-cyclooctadiene, benzene, acetonitrile, benzonitrile, propionic acid or 3-buten-2-one; selective hydrogenation of 1-octene over frara^-octene in a 1:1 mixture of the two was noted. iv TABLE OF CONTENTS ABSTRACT ii T A B L E OF CONTENTS v LIST OF TABLES xiii LIST OF FIGURES xvii ABBREVIATIONS AND SYMBOLS xx LIST OF COMPLEXES xxiii ACKNOWLEDGEMENTS xxv C H A P T E R O N E : Introduction 1 1.1 Homogeneous Catalysis in Aqueous Media Using Phosphine Complexes 1 1.2 Historical Use of 2rPyridylphosphines Within this Laboratory 3 1.3 Objective of this Thesis 4 1.4 General Developments in 2-Pyridylphosphine Chemistry 4 1.4.1 Synthesis of 2-Pyridylphosphines..: 5 1.4.2 Complexes and Coordination Modes of 2-Pyridylphosphine Ligands 7 1.4.3 Catalysis with 2-Pyridylphosphine Complexes 10 1.5 Homogeneous Catalysis Using Ni Complexes 10 1.6 Scope of this Thesis 11 1.7 References • 12 C H A P T E R T W O : General Experimental 20 2.1 General Materials 20 2.1.1 Solvents 20 2.1.2 Gases 20 2.1.3 General Reagents 20 2.2 General Instrumentation 21 2.2.1 Nuclear Magnetic Resonance Spectroscopy 21 2.2.2 UV-Visible Spectroscopy 22 v 2.2.3 Infrared Spectroscopy 22 2.2.4 Mass Spectroscopy 22 2.2.5 Gas Chromatography 22 2.2.6 Conductivity 23 2.2.7 Elemental Analysis/Melting Points 23 2.2.8 Magnetic Suscpetibility 23 2.2.9 X-ray Crystallography 24 2.3 Phosphines 24 2.3.1 Diphenyl(2-pyridyl)phosphine, PNi 24 2.3.2 Bis(2-pyridyl)phenylphosphine, PN 2 24 2.3.3 Tris(2-pyridyl)phosphine, PN 3 24 2.3.4 l,2-Bis[bis(2-pyridyl)phosphino]ethane, dpype 26 2.3.5 Racemic l,2-Bis[bis(2-pyridyl)phosphino]cyclopentane, dpypcp 26 2.3.6 l,2-Bis(diphenylphosphino)ethane, dppe 26 2.4 Nickel Precursor Compounds 27 2.4.1 NiCl 2(PPh 3) 2 27 2.4.2 NiBr 2(PPh 3) 2... 28 2.4.3 NiI2(PPh3)2 28 2.4.4 /ram-Ni(NCS)2(PPh3)2 29 2.4.5 Ni(N0 3) 2(PPh 3) 2 29 2.4.6 Ni(CO)2(PPh3)2 (19«) 30 2.5 Growth of Crystals for X-Ray Analysis 30 2.5.1 Ni(CO)2(P-P) complexes 31 2.5.2 NiX2(P-P) complexes 31 2.5.3 [Ni(PN3)2]Cl2 31 2.5.4 dpypcp 32 2.6 Deoxygenation of Solvents by N2(g) Sparging 32 2.7 References 32 CHAPTER THREE: The Synthesis, Characterization, Reactivity, and Aqueous Solution Chemistry of Ni(H) 2-Pyridylphosphine Complexes 34 3.1 Introduction 34 3.2 Experimental 35 3.2.1 Preparation of Diamagnetic Ni(II) 2-Pyridylphosphine Compounds 35 vi 3.2.1.1 NiCl2(dpype) (la) 35 3.2.1.2 NiCl2(dpypcp) (lb) 35 3.2.1.3 NiBr2(dpype) (2a) 36 3.2.1.4 NiBr2(dpypcp) (2b) 36 3.2.1.5 Nil2(dpype) (3a) 36 3.2.1.6NiI2(dpypcp) (3b) 36 3.2.1.7 Ni(NCS)2(dpype) (4a) 37 3.2.1.8 Ni(NCS)2(dpypcp) (4b) 37 3.2.1.9 Ni(N03)2(dpype) (5a) 37 3.2.1.10 Ni(N03)2(dpypcp) (5b) 38 3.2.1.11 [Ni(H20)2(dpype)](PF6)2 (6a) 38 3.2.1.12 [Ni(H20)2(dpypcp)](PF6)2 (6b) 39 3.2.2 Preparation of Paramagnetic Ni(II) 2-Pyridylphosphine Compounds 39 3.2.2.1 NiCl 2(PN 3) . H 2 0 (^Coordinated) (7) 39 3.2.2.2 [Ni(PN3)2]Cl2 (W,A^"-coordinated) (8) 39 3.2.2.3 NiCl 2(PNi) 2 . H 2 0 (9a) 40 3.2.2.4 NiCl 2(PN 2) 2 (9b) 40 3.2.2.5 NiCl 2 (PN 3 ) 2 . 2H 2 0 (9c) 40 3.2.2.6NiBr 2(PNi) 2.2H 20 (10a) 41 3.2.2.7 NiBr 2 (PN 2 ) 2 . 2H 2 0 (10b) 41 3.2.2.8 NiBr 2 (PN 3 ) 2 .2H 2 0 (10c) 41 3.2.2.9 Attempted Preparation of NiI 2(PN 3) 2 (11) 41 3.2.3 Preparation of Diamagnetic Ni(II) Phenylphosphine Compounds 42 3.2.3.1 NiCl2(dppe) (12a) 42 3.2.3.2 NiBr2(dppe) (12b) 42 3.2.3.3 Nil2(dppe) (12c) 42 3.2.3.4 Ni(NCS)2(dppe) (12d) 42 3.2.3.5 Ni(N03)2(dppe) (12e) 42 3.2.3.6 [Ni(H20)2(dppe)](PF6)2 (13) 43 3.2.3.7 Attempted Preparation of [Ni(H20)2(dppe)](S03CF3)2 (14 ) 43 3.2.3.8 Attempted Preparation of [Ni(H20)2(dppe)](BPh4)2 (15a) 43 3.2.3.9 Attempted Preparation of [Ni(OH)2(dppe)]2+ (15b) 44 3.2.4 Reactivity of [Ni(PN3)2]Cl2 44 3.2.4.1 WithNiCl 2 .6H 2 0 orNiCl 2(PPh 3) 2 (16) 44 3.2.4.2 With Ni(l,5-COD) 2 (17) 44 3.2.4.3 With Ag(CF 3S0 3) (18) 44 vii 3.3 Results and Discussion 45 3.3.1 Dpype, dpypcp, and the NiX2(P-P) Complexes (X = Cl, Br, I, N 0 3 , NCS) 45 3.3.2 Aqueous Solution Chemistry of Ni(II) 2-Pyridylphosphine Complexes 63 3.3.3 Synthesis and Characterization of NiCl 2(PN 3). H 2 0 (7) and [Ni(PN3)2]Cl2 (8) 68 3.4 Conclusion 75 3.5 References 76 CHAPTER FOUR: The Synthesis, Characterization, Reactivity, and Aqueous Solution Chemistry of Ni(0) 2-Pyridylphosphine Complexes 82 4.1 Introduction 82 4.2 Experimental 83 4.2.1 Preparation of Nickel Carbonyl 2-Pyridylphosphine Complexes 83 4.2.1.1 In Situ Preparation of Ni(CO)2(PNi)2 (19a) 83 4.2.1.2 In Situ Preparation of Ni(CO) 2(PN 2) 2 (19b) 84 4.2.1.3 In Situ Preparation of Ni(CO) 2(PN 3) 2 (19c) 84 4.2.1.4 [Ni2(CO)4(/i-PN2)2]Cl4 (19d) 84 4.2.1.5 Ni(CO)2(dpype) (20a) 85 4.2.1.6 Ni(CO)2(dpypcp) (20b) 85 4.2.1.7 Attempted Preparation of Ni(CO)2(P-P) from NiCl2(P-P) 86 4.2.1.8 Preparation of Triflate Salts of Protonated Ni(CO)2(dpypcp) 86 4.2.1.9 Preparation of Triflate Salts of Protonated dpypcp 87 4.2.2 Preparation of Ni(0) Phosphine Complexes 87 4.2.2.1 Ni(PR3)2(dppe) [PR3 = PPh3, (21a); PNi, (21b); PN 2 , (21c); PN 3 , (21d)] 87 4.2.2.2 Ni(PR3)2(dpype) [PR3 = PPh3, (22a); P N 1 ; (22b); PN 2 , (22c); PN 3 , (22d)] 87 4.2.2.3 Ni(PR3)2(dpypcp) [PR3 = PPh3, (23a); PNi, (23b); PN 2 , (23c); PN 3 , (23d)]....87 4.2.2.4 Ni(dpypcp)2 (24a) 88 4.2.2.5 Ni(dppe)2 (24b) 88 4.2.2.6 Ni(dpype)2 (24c) 89 4.2.2.7 Ni(P-P)(P'-F) [P-P = dppe, P'-P' = dpype (25a); P'-P' = dpypcp (25b); P-P = dpype, P'-P' - dpypcp (25c)] 89 4.2.2.8 Ni(PR 3) 4 [PR3 = PPh3 (26a); PNj (26b); PN 2 (26c); PN 3 (26d)] 89 4.2.3 Reactivity of Methyl Iodide with Ni(0) Pyridylphosphine Complexes 90 4.2.3.1 *raHS-Ni(CH3)(I)(PN3)2 (27) 90 4.2.3.2 /raws-Ni(CH3)(l)(dpype)2 (28) 90 4.2.3.3 *ra/7s-Ni(CH3)(I)(dpypcp)2 (29)..... 90 viii 4.2.3.4 Attempted Synthesis of /ra/?£-Ni(CH 3)(I)(dppe) 2 (30) 91 4.2.3.5 Attempted Synthesis of /ra«s-Ni(CH 3)(I)(PPh 3) 2 (31) 91 4.2.4 Preparation of Monomethylated Phosphonium Salts [(CH3)(phosphine)]1 91 4.2.4.1 [(CH3)(PN3)]I (32a) 92 4.2.4.2 [(CH3)(dppe)]I (32b) 92 4.2.4.3 [(CH3)(dpype)]I (32c), 92 4.2.4.4 [(CH3)(dpypcp)]I (32d) 93 4.2.4.5 [(CH3)(PPh3)]I (32e) 93 4.2.5 Preparation of Bismethylated Phosphonium Salts [(CH3)2(phosphine)]I2 93 4.2.5.1 [(CH,)2(dppe)]I2 (33b) 93 4.2.5.2 [(CH3)2(dpype)]I2 (33c) 94 4.2.5.3 [(CH3)2(dpypcp)]I2 (33d) 94 4.2.6 Attempted Carbonylation of r)vms-Ni(CH3)(I)(phosphine)2 Species 95 4.2.6.1 Attempted Synthesis of Ni(COCH3)(I)(PN3)2 95 4.2.7 Attempted Methylation of Ni(CO)2(phosphine)2 Species 95 4.2.7.1 Attempted Syntheses of Ni(COCH3)(I)(PPh3)2 & Ni(COCH3)(CO)(I)(dpypcp)95 4.2.8 Reactivity of Ni(0) Tertiary 2-Pyridylphosphine Complexes with Small Molecules.95 4.2.8.1 Reactivity with Ethylene 95 4.2.8.2 Reactivity with Chlorine 96 4.2.8.3 Reactivity with Oxygen 96 4.2.8.4 Reactivity with Water 96 4.3 Results and Discussion 97 4.3.1 Synthesis and Characterization ofNickel(O) Dicarbonyl Phosphine Complexes 97 4.3.1.1 The Ni(CO) 2(PN x) 2 Complexes 98 4.3.1.2 Speculative Formation of [Ni2(CO)4(//-PN2)2]Cl4 (19d) 101 4.3.1.3 Characterization ofNi(CO)2(P-P) Complexes 103 4.3.1.4 X-ray Crystal Structure of Ni(CO)2(dpypcp) (20b) 104 4.3.2 Aqueous Solution Chemistry of Ni(CO)2(dpypcp) and dpypcp 107 4.3.3 Synthesis, Characterization, and Reactivity of Ni(0) Phosphine Complexes 112 4.3.3.1 Synthesis.. 112 4.3.3.2 Characterization 114 4.3.3.3 Reactivity of Ni(0) Tertiary 2-Pyridylphosphine Complexes with Small Molecules 118 4.3.4 Synthesis and Characterization of 7raHs-Ni(CH3)(I)(phosphine)2 Species 119 4.3.5 The Phosphonium Salts, [(CH3)(phosphine)]I and [(CH3)2(phosphine)]I2 121 4.3.6 Attempted Preparation of Acyl Ni(II) Phosphine Species 126 ix 4.4 Conclusions 126 4.5 References 127 CHAPTER FIVE: Catalysis of the Water-Gas-Shift Reaction and Attempted Olefin Hydration using Nickel 2-Pyridylphosphine Complexes 132 5.1 Water-Gas Shift Catalysis 132 5.1.1 Introduction 132 5.1.2 Experimental 138 5.1.2.1 Set-Up for Ambient CO Pressure Work 138 5.1.2.2 Set-Up for High CO Pressure Work 138 5.1.2.3 GC Analysis 139 5.1.3 Results and Discussion 139 5.1.4 Conclusion 143 5.2 Olefin (Maleic Acid) Hydration 144 5.2.1 Introduction 144 5.2.2 Experimental 147 5.2.2.1 Set-Up 147 5.2.2.2 ' H NMR Analysis 147 5.2.3 Results and Discussion 148 5.2.4 Conclusion 149 5.3 References 149 CHAPTER SIX: Transfer Hydrogenation of Cyclohexanone Catalyzed by Ni(H) Compounds 157 6.1 Introduction... „ 157 6.2 General Experimental 158 6.2.1 Typical Set-Up for Catalytic Transfer Hydrogenation Experiments 159 6.2.2 Analysis of the Hydrogenation Products 160 6.3 Results and Discussion 161 6.3.1 Transfer Hydrogenation of Cyclohexanone by Various Ni(II) Species 161 6.3.2 ! H NMR Spectroscopy and C 6 H i 0 O Transfer Hydrogenation 164 6.3.3 Blanks 164 6.3.4 Test for Homogeneity of the NiNa'P System 165 6.3.5 Kinetic Dependence of CeHioO Transfer Hydrogenation on Base 165 6.3.6 Kinetic Dependence of C 6 H 1 0 O Transfer Hydrogenation on [NiBr2] 168 x 6.3.7 Kinetic Dependence of C 6 H i 0 O Transfer Hydrogenation on Hydrogen-Atom Acceptor and Donor 172 6.3.8 Effect of Acetone and Cyclohexanol on the Transfer Hydrogenation of CeHioO... 177 6.3.9 Effect of Water, H 2 , Halide, and PPh3 on the Transfer Hydrogenation of C 6 H i 0 O 179 6.3.10 Catalyst Deactivation 181 6.3.11 Effect of Steric Hindrance upon the Hydrogenation of Substituted C 6 H i 0 O 182 6.3.12 Possible Mechanism for the Transfer Hydrogenation of C 6 H i 0 O by the NiNa'P System 183 6.4 Conclusion 186 6.5 References 187 CHAPTER SEVEN: Transfer Hydrogenation of Various Functional Groups by Ni(II) Systems 191 7.1 Introduction 191 7.2 Experimental 191 7.2.1 Set-up for Catalytic Trials 191 7.2.2 lH NMR Analysis of Reaction Mixture..... 193 7.2.3 GC Analysis of Reaction Mixture 194 7.3 Results and Discussion 195 7.3.1 Transfer Hydrogenation of Ketones and Aldehydes 195 7.3.2 Transfer Hydrogenation of Unsaturated Hydrocarbons 198 7.3.3 Transfer Hydrogenation of Nitriles 201 7.3.4 Transfer Hydrogenation of a, B -Unsaturated Ketones 201 7.3.5 Transfer Hydrogenation ofDiketones 206 7.3.6 Transfer Hydrogenation of Miscellaneous Functional Groups 207 7.4 Conclusion 211 7.5 References 211 CHAPTER EIGHT: Conclusions and Recommendations for Future Work 215 8.1 Coordination and Aqueous Solution Chemistry 215 8.2 Catalytic Chemistry 217 xi APPENDICES 219 APPENDIX A 220 A. 1 X-Ray Crystal Structure of dpypcp 220 A.2 X-Ray Crystal Structure of NiCl2(dpype) • CH 2C1 2 223 A. 3 X-Ray Crystal Structure of NiBr2(dpype ) 225 A.4 X-Ray Crystal Structure of NiCl2(dpypcp) 228 A.5 X-Ray Crystal Structure ofNiBr2(dpypcp) 232 A 6 X-Ray Crystal Structure of Nil2(dpypcp). CH 2C1 2 235 A 7 X-Ray Crystal Structure of [Ni(PN 3) 2]Cl 2. 8H 2 0 238 A. 8 X-Ray Crystal Structure ofNi(CO)2(dpypcp) 240 A. 9 Calculation of the Intramolecular P-P Spatial Distance for dppe 243 A. 10 Quantification of the Amount of CO Detected in the Headspace of 7 in Solution 243 APPENDLX B 244 B. 1 LSEVIS Mass Spectrum of 19d 244 B.2 Catalytic Reaction Promoted by Ni(CO)2(dppe) 244 B.3 ^Pj'H} NMR Spectra for 21-23 and 25 245 B. 4 'H, 'H COSY Spectra 247 APPENDIX C 249 C. 1 Transfer Hydrogenation of C 6 H 1 0 O by Ni(II) Species 249 C.2 Calculation of the Overall Reaction Order Using the Half-Lives Method 249 C.3 Constant Ionic Strength 253 C.4 Transfer Hydrogenation of C 6 H 1 0 O with Various Base Cocatalysts 253 C.5 UV-Vis Spectra of NiBr 2 at Various Concentrations 253 C.6 Transfer Hydrogenation of C 6 H i 0 O at Various [C 6Hi 0O] 254 C.7 Transfer Hydrogenation ofC 6HioO at Various [z'-PrOH] 255 C.8 Tertiary Butanol as a Diluent....... 256 C.9 Mixing Order Experiments 256 C. 10 Addition of Water to the Reaction Solution 256 C. 11 Addition of Halides to the Reaction Solution 257 C. 12 Catalytic Activity of the Residue Left at the End of the Reaction 257 APPENDLX D 258 D. 1 Percent Conversion Data for Figure 7.5 258 D.2 Aldol Condensation of 2,5-Hexanedione 258 D.3 Literature Compounds 260 xii LIST OF TABLES Table 1.1 Chelating Modes for a 2-Pyridyl Diphosphine to a Single Metal Centre 10 Table 2.1 Literature Values for the UV-Vis Spectra of the PN X ligands 25 Table 3.1 3 1P{ !H} and *H NMR Data for the 2-Pyridylphosphine Ligands and their Oxides 47 Table 3.2 Changes in Resonance Multiplicities in the lH NMR Spectrum of dpype and dpypcp Upon 31P-Decoupling 48 Table 3.3 UV-Vis Data for NiX2(P-P) Complexes 49 Table 3.4 3 1P{ !H} NMR Data for NiX2(P-P) Complexes 50 Table 3.5 ^P^H} NMR Data for Pd or Pt analogues of lb-3b and NiX 2(PNi) 2 51 Table 3.6 Diagnostic IR bands for S- vs. TV-terminally bonded SCN ligands to Ni(II) 53 Table 3.7 IR Bands for Ni(N03)2(P-P) Complexes 5a (P-P = dpype) and 5b (P-P = dpypcp) .... 53 Table 3.8 Selected Bond Lengths and Angles for dpype and the NiX2(dpype) Complexes 58 Table 3.9 Selected Bond Lengths and Angles for dpypcp and the NiX2(dpypcp) Complexes 59 Table 3.10 Selected Parameters for lb-3b, dpypcp, and dpcp 60 Table 3.11 Selected Parameters for la-2a, dpype, and dppe 60 Table 3.12 Conductivity and ^P^H} NMR Data for 1-3 64 Table 3.13 Molar Conductivity Data for NiX 2(PN x) 2 Complexes in H 2 0 67 Table 3.14 Selected Bond Lengths and Angles for [Ni(PN3)2]Cl2 74 Table 4.1 Amounts of Reagents Used in Preparation of 21-23 88 Table 4.2 Amounts of Reagents Used in Preparation of 25a-c 89 Table 4.3 Amounts of Reagents Used in Preparation of 26a-d 89 Table 4.4 3 1 P NMR Data for Ni(CO)2(PPh3)(PNx) Complexes 98 Table 4.5 Effect of Reaction Medium on the Ratio of 190 to 19b* to 19b 99 Table 4.6 Effect of Time on the Ratio of 190 to 19b" to 19b 99 Table 4.7 Effect of Excess PN 2 on the Ratio of 190 to 19b* to 19b 99 Table 4.8 3 1 P NMR and IR Data for Ni(CO) 2(PR 3) 2 Complexes 100 Table 4.9 Selected 3 1 P NMR and IR Data for Ni(CO)2(P-P) Complexes 104 Table 4.10 Selected Bond Lengths and Angles for Ni(CO)2(dpypcp) (20b) 106 Table 4.11 107 Possible Ni(0)L4 Complexes obtained by Combining PR 3 and P-P Ligands 112 Table 4.12 3 1P{1H} NMR Data for Homoleptic Complexes 24 and 26 114 Table 4.13 Selected 3 1P{ TL} NMR Data for Complexes 21-23 and 25 in C 6 D 6 116 Table 4.14 3 1P{1H} NMR Data for the Monomethylphosphonium Salts 32a-e in C 6 D 6 122 Table 4.15 NMR Data for the Monomethylphosphonium Salts 32a-e in CDC13 122 Table 4.16 NMR Data for the Bismethylphosphonium Salts 33b-d 123 xiii Table 4.17 Total Downfield Shift of *H NMR Signals of P-P Ligands Upon Bismethylation.... 124 Table 5.1 Various Industrial CO Sources 133 Table 5.2 Equilibrium Constant (KP) of the WGSR vs. Temperature 133 Table 5.3 Thermodynamic Parameters for the WGSR Using Either H20(7) or H 20(g) 134 Table 5.4 Examples of Homogeneous WGSR Catalyst Systems 137 Table 5.5 H 2 and C 0 2 Production Using Ni Complexes in the Water-Gas Shift Reaction 140 Table 5.6 H 2 Turnovers Obtained With NiCl 2(PN 2) 2 Under Varying Conditions 141 Table 5.7 Catalytic WGSR Systems Where H 2 / C 0 2 ~ 1 Without Acidification Treatment 142 Table 5.8 Reaction Mixture Distribution in the Attempted Hydration of Maleic Acid 148 Table 6.1 Transfer Hydrogenation of Cyclohexanone to Cyclohexanol With Various Ni(II) Catalyst Precursors Species 161 Table 6.2 Effect of Systematic Exclusion of Reaction Components ("Blank" Trials) 165 Table 6.3 Dependence of Initial Rate (r0) of Formation of Cyclohexanol on [NaOH] 166 Table 6.4 Transfer Hydrogenation of C 6 H i 0 O with Various Base Cocatalysts 168 Table 6.5 Effect of Varying [NiBr2] on Transfer Hydrogenation of C 6 H i 0 0 169 Table 6.6 Transfer Hydrogenation of C 6 H i 0 O vs. Amount of Acetone Added 178 Table 6.7 Transfer Hydrogenation of C 6 H i 0 O at Various Added [C 6 H u OH] 179 Table 6.8 Effect of PPh3 on the Transfer Hydrogenation of C 6 H i 0 O 181 Table 6.9 Transfer Hydrogenation of C 6 H 1 0 O , 2-Me-C 6H 90, and 4-Me-C 6 H 9 0 183 Table 7.1 Amounts of Catalyst and Substrate Used and Sampling Times 192 Table 7.2 *H NMR Resonances of Substrate/Hydrogenated Substrate Pairs 193 Table 7.3 GC Settings Used 194 Table 7.4 Settings and Retention Times (tR) for the Reaction Mixtures Analyzed by GC 195 Table 7.5 Percent Conversions for the Transfer Hydrogenation of Ketones and Aldehydes to the Corresponding Alcohols 196 Table 7.6 Percent Conversions for the Transfer Hydrogenation of Unsaturated Hydrocarbons to the Corresponding Saturated Hydrocarbons 199 Table 7.7 Transfer Hydrogenation of Cyclohex-2-ene-l-one 202 Table 7.8 Percent Conversions for the Transfer Hydrogenation of Nitrobenzene to Aniline 208 Table 7.9 Transfer Hydrogenation of 4-Nitrobenzaldehyde to Various Products 209 Table A. 1 Crystal Data and Details of the Structure Determination for dpypcp 220 Table A.2 Atomic Coordinates and B e q for dpypcp 221 Table A. 3 Bond Lengths for dpypcp 221 Table A.4 Bond Angles for dpypcp 222 Table A. 5 Crystal Data and Details of the Structure Determination for NiCl2(dpype) • CH2C12.223 Table A.6 Atomic Coordinates and U e q for NiCl2(dpype) • CH 2C1 2 224 xiv Table A.7 Bond Lengths for NiCl2(dpype) • CH 2C1 2 224 Table A.8 Bond Angles for NiCl2(dpype) • CH 2C1 2 225 Table A. 9 Crystal Data and Details of the Structure Determination for NiBr2(dpype) 225 Table A. 10 Atomic Coordinates and B e q for NiBr2(dpype) 226 Table A. 11 Bond Lengths for NiBr2(dpype) 227 Table A. 12 Bond Angles for NiBr2(dpype) 227 Table A. 13 Crystal Data and Details of the Structure Determination for NiCl2(dpypcp) 228 Table A. 14 Atomic Coordinates and B e q for NiCl2(dpypcp) 229 Table A. 15 Bond Lengths for NiCl2(dpypcp) 230 Table A. 16 Bond Angles for NiCl2(dpypcp) 230 Table A. 17 Crystal Data and Details of the Structure Determination for NiBr2(dpypcp) 232 Table A. 18 Atomic Coordinates and B e q for NiBr2(dpypcp) 233 Table A. 19 Bond Lengths for NiBr2(dpypcp) 23 3 Table A.20 Bond Angles for NiBr2(dpypcp) 234 Table A. 21 Crystal Data and Details of the Structure Determination for NiI2(dpypcp).CH2Cl2235 Table A. 22 Atomic Coordinates and B e q for Nil2(dpypcp). CH 2C1 2 236 Table A.23 Bond Lengths for Nil2(dpypcp). CH 2C1 2 236 Table A.24 Bond Angles for Nil2(dpypcp). CH 2C1 2 237 Table A.25 Crystal Data and Details of the Structure Determination for [Ni(PN 3) 2]Cl 2.8H 20.238 Table A.26 Atomic Coordinates and B e q for [Ni(PN3)2]Cl2 • 8H 2 0 239 Table A.27 Bond Lengths for [Ni(PN3)2]Cl2- 8H 2 0 239 Table A.28 Bond Angles for [Ni(PN 3) 2]Cl 2. 8H 20... 239 Table A. 29 Crystal Data and Details of the Structure Determination for Ni(CO)2(dpypcp) 240 Table A. 30 Atomic Coordinates and B e q for Ni(CO)2(dpypcp) 241 Table A31 Bond Lengths for Ni(CO)2(dpypcp) 241 Table A.32 Bond Angles for Ni(CO)2(dpypcp) 242 Table C. 1 Percent Conversion vs. Time for Six Ni(II) Catalyst Precursors 249 Table C.2 Half-Lives Method of Determining the Overall Reaction Order Using NiBr 2 250 Table C.3 Half-Lives Method of Determining the Overall Reaction Order Using Six Different Ni(II) species 251 Table C.4 Rate Constants and Half-Lives for the Transfer Hydrogenation of C 6HioO by Various Catalysts 252 Table C.5 Transfer Hydrogenation of C 6 H i 0 O with Various Hydroxide Base Cocatalysts 253 Table C.6 Absorbance vs. [NiBr2] Data for Figure 6.9 253 Table C.7 Transfer Hydrogenation of C 6 H i 0 O at Various [C 6 Hi 0 O] o 254 Table C.8 Dependence of r0 on [z-PrOH] for the Reduction of 0.1 M C 6 H 1 0 O 255 xv Table C.9 Dependence of Turnover Frequency on Mixing Order of Reactants for the Transfer Hydrogenation of Cyclohexanone 256 Table C. 10 Effect of H 2 0 on Transfer Hydrogenation of C 6 H 1 0 O 256 Table C. 11 Effect of Addition of Halide Ion on the Transfer Hydrogenation of CeHioO 257 Table C. 12 Recharging of the Reactor Vessel for Transfer Hydrogenation of CeHioO 257 Table D. 1 Reaction Mixture Distribution for the Transfer Hydrogenation of Cyclohex-2-ene-l-one 258 Table D.2 Observed and Calculated Resonances for 5-Methyl-5-undecen-2,7,10-trione 259 xvi LIST OF FIGURES Figure 1.1 Biphasic system for separation of products from catalyst 1 Figure 1.2 Sulfonated phosphines 2 Figure 1.3 Ruhrchemie/Rhone-Poulenc Oxo process for conversion of propylene to butyraldehyde via hydroformylation in a biphasic system 2 Figure 1.4 The 2-pyridylphosphine ligands 5 Figure 1.5 Synthesis of the PN X ligands 6 Figure 1.6 Synthesis of the diphosphine ligands dpype and dpypcp 6 Figure 1.7 Coordination binding modes of 2-pyridyl monophosphines with transition-metals 8 Figure 1.8 2-Pyridyl diphosphine ligands, showing the six donor-atoms 10 Figure 2.1 Numbering scheme for 2-pyridylphosphines 25 Figure 2.2 Crystallization chamber employed in growing crystals 31 Figure 2.3 Apparatus for de-oxygenating solvents by sparging 32 Figure 3.1 Numbering scheme for 2-pyridylphosphines. 47 Figure 3.2 'H NMR (CDC13) spectra of dpype and dpypcp 48 Figure 3.3 Metal d-orbital splitting in a square-planar complex with bonds in the xy plane 49 Figure 3.4 lH NMR spectra of the pyridyl region of lb, 2b, and 3b 52 Figure 3.5 ORTEP of the molecular structures of dpypcp and dpype 55 Figure 3.6 ORTEP of the molecular structure ofNiCl2(dpype) (la) 55 Figure 3.7 ORTEP of the molecular structures of NiBr2(dpype) (2a) and NiCl2(dpypcp) (lb). ..56 Figure 3.8 ORTEP of the molecular structures of NiBr2(dpypcp) (2b) and Nil2(dpypcp) (3b). ..57 Figure 3.9 Spatial configurations of the pyridyl moieties in various compounds 61 Figure 3.10 ' H NMR spectrum of NiCl2(dpype) in D 2 0 at t = 120 min 65 Figure 3.11 Complexes 7 and 8 68 Figure 3.12 Synthesis of 7 via novel method J and conventional method 2.'.. 69 Figure 3.13 Novel and conventional syntheses of 8 and 8 • H 2 0 69 Figure 3.14 Possible pathway for conversion of 7 to 8 70 Figure 3.15 ORTEP of the molecular structure for the cation in [Ni(PN3)2]Cl2 (8) 73 Figure 3.16 Various chain polymers of -[M-8-M]- 75 Figure 4.1 Numbering scheme for monomethylated diphosphines 92 Figure 4.2 Equilibrium among dicarbonyl species in the in situ formation of Ni(CO) 2(PN x) 2 from Ni(CO)2(PPh3)2 in CDC13 97 Figure 4.3 Plot of the number of N-atoms in the PN X ligand vs. the separation between the two doublets in the Ni(CO)2(PPh3)(PNx) complexes (19*) 101 xvii Figure 4.4 Proposed structure for the purple complex 19d 102 Figure 4.5 ! H NMR spectrum of the pyridyl region of 19d 103 Figure 4.6 ORTEP of the molecular structure of Ni(CO)2(dpypcp) 105 Figure 4.7 Diprotonated form of 20b 108 Figure 4.8 Proposed fate of Ni(CO)2(P-P) complexes in water 110 Figure 4.9 The 22 Ni(0) phosphine complexes synthesized in this thesis work 113 Figure 4.10 Synthesis of Ni(0) phosphine complexes from Ni(l,5-COD) 2 113 Figure 4.11 3 1P{ !H} NMR spectrum of Ni(PN3)2(dpype) (22d) 115 Figure 4.12 N-atom count for PN X vs. 5P of the triplet assigned to PN X or P-P 117 Figure 4.13 Synthesis of fra/«-Ni(CH 3)(I)(phosphine) 2 species 119 Figure 4.14 Labelling scheme for the mono and bismethyl phosphonium ligand salts 121 Figure 4.15 Hydrolysis of monoalkyl salts of ditertiary bisphosphines to yield the monoxide quantitatively 122 Figure 4.16 ! H NMR spectra of the 5CH 3 region of various phosphonium salts. 124 Figure 4.17 *H NMR spectra of the pyridyl region of various phosphonium salts 125 Figure 4.18 Possible routes to formation of acyl Ni(II) phosphine complexes 126 Figure 5.1 Fischer-Tropsch synthesis of organics using supported catalysts 132 Figure 5.2 Other possible product mixtures from the WGSR 134 Figure 5.3 Various catalytic cycles for the WGSR 136 Figure 5.4 Hydration and isomerization of maleic acid 144 Figure 5.5 Possible mechanistic pathways for maleic acid hydration with an M L 2 catalyst 145 Figure 5.6 Fischer projection of malic acid showing the *H NMR assignments 147 Figure 6.1 Experimental set-up for transfer hydrogenation catalytic trials 159 Figure 6.2 Transfer hydrogenation of C 6 H i 0 O by various Ni(II) phosphine complexes 162 Figure 6.3 Transfer hydrogenation of C 6 H i 0 O with NiBr 2 163 Figure 6.4 lH NMR spectra of a typical catalytic run 164 Figure 6.5 Dependence of initial rate on [NaOH] at p. = 0.05 M ; log r0 vs. log [NaOH] 167 Figure 6.6 Dependence of initial rate on [NaOH] at p = 0.60 M ; log r0 vs. log [NaOH] 167 Figure 6.7 Dependence of initial rate on [NaOH]2 and [NaOH] (combining all data) 167 Figure 6.8 Initial rate of C 6 H i 0 O transfer hydrogenation vs. [NiBr2] 169 Figure 6.9 UV-Vis spectra of 1 xlO"4 M NiBr 2 and 0.47 M NaOH in /-PrOH; Absorbance at 432 nm vs. [NiBr2] 170 Figure 6.10 UV-Vis spectra of 1 xlO"5 M NiBr 2 and 0.47 M NaOH in /-PrOH 171 Figure 6.11 Initial rate vs. [C 6Hi 0O] for the transfer hydrogenation of C 6 H i 0 0 172 Figure 6.12 Initial rate vs. [/-PrOH] for the transfer hydrogenation of C 6 H i 0 0 172 Figure 6.13 Process I and II mixing orders 174 xviii Figure 6.14 Turnovers per minute vs. time for two different mixing orders 175 Figure 6.15 IR spectrum of NiBr2(PPh3)2 in CeFLj with either /'-PrOH, C 6 H i 0 O , or both 176 Figure 6.16 Transfer Hydrogenation of CeHioO with various amounts of water added 179 Figure 6.17 Recharging of NiBr 2/NaOH residue with C 6 H i 0 O and /-PrOH 182 Figure 6.18 Proposed mechanism for transfer hydrogenation of CeHioO by the NiNa'P system. 184 Figure 7.1 Transfer hydrogenation of ketones 195 Figure 7.2 Transfer hydrogenation of aldehydes 196 Figure 7.3 Transfer hydrogenation of alkenes to alkanes 199 Figure 7.4 Possible products from the transfer hydrogenation of cyclohex-2-ene-l-one 201 Figure 7.5 Transfer hydrogenation of cyclohex-2-ene-l-one 202 Figure 7.6 Possible products from the transfer hydrogenation of 3-buten-2-one 203 Figure 7.7 Plausible reaction of NiBr 2 with 3-buten-2-one to form a nickellacycle 203 Figure 7.8 T L C of the stoichiometric NiBr 2 /MVK reaction mixture solution 205 Figure 7.9 *H NMR spectrum of the stoichiometric NiBr 2 /MVK reaction mixture solution 205 Figure 7.10 Transfer hydrogenation of diketones 206 Figure 7.11 Formation of sodium acetylacetonate in basic media 206 Figure 7.12 Formation of 5-methyl-5-undecen-2,7,10-trione from 2,5-hexanedione 207 Figure 7.13 Transfer hydrogenation of nitrobenzene to aniline 208 Figure 7.14 Transfer hydrogenation of 4-nitrobenzaldehyde to observed products 209 Figure B. 1 Simulated and observed isotopic splitting patterns in the mass spectrum of 19d 244 Figure B.2 Dimerization of diquinoethylene to tetraquinocyclobutane 244 Figure B.3 "Pf/H} NMR spectra of the Ni(PR3)2(dppe) complexes 21a-d 245 Figure B.4 "Pf/H} NMR spectra of the Ni(PR3)2(dpype) complexes 22a-d 245 Figure B.5 "P^H} NMR spectra of the Ni(PR3)2(dpypcp) complexes 23a-d 245 Figure B.6 31P{lK} NMR spectra of the Ni(P-P)(P'-P') complexes 25a-c 246 Figure B.7 1 H , ! H COSY NMR Spectrum of a mixture of dpypcp and [(CH3)(dpypcp)]1 247 Figure B.8 TL lH COSY NMR Spectrum of a mixture of dpype and [(CH3)(dpype)]1 248 Figure C. 1 Reaction profile for the transfer hydrogenation of CeHioO 250 Figure C.2 Plots of log ty2 vs. log [C6HioO]o, t % and log [C 6Hi 0O] vs. time using NiBr 2 251 Figure C.3 Plots of log [C 6Hi 0O] vs. time with six different Ni(II) catalysts 252 Figure C.4 Plots of log ra vs. log [C 6Hi 0O] 254 Figure C.5 Log /•„ vs. log [/-PrOH] 255 Figure D . l Aldol condensation of 2,5-hexanedione to yield 5-methyl-5-undecen-2,7,10-trione. 259 Figure D.2 Aldol cyclization of 2,5-hexanedione to yield 3-methyl-2-cyclopenten-l-one 259 Figure D.3 Ligands and catalysts mentioned in Chapter 7 260 xix ABBREVIATIONS AND SYMBOLS The following list of abbreviations and symbols are used in this thesis. 5 chemical shift (NMR spectra) Vasym asymmetric stretching frequency (IR spectra) Vsym symmetric stretching frequency (IR spectra) A M molar conductivity t^nax wavelength at maximum absorbance [ M l parent peak (mass spectrometry) acac acetylacetonate anion anhyd. anhydrous aq. aqueous B. M . Bohr magnetons bipy 2,2'-bipyridine BzOH benzyl alcohol COD 1,5-cyclooctadiene conv. conversion Cp cyclopentadienyl (C5H5) Cp* 1,2,3,4,5-pentamethylcyclopentadienyl (CsMe5) Cy cyclohexyl d day(s) or doublet (NMR spectra) A(d-d) separation (in Hz) between the centres of two doublet resonances A(t-t) separation (in Hz) between the centres of two triplet resonances dd doublet of doublets (NMR spectra) ddd doublet of doublets of doublets (NMR spectra) dddd doublet of doublets of doublets of doublets (NMR spectra) dddt doublet of doublets of doublets of triplets (NMR spectra) ddt doublet of doublets of triplets (NMR spectra) dec. decompose dm doublet of multiplets dmad dimethylacetylenedicarboxylate dmpm l,2-bis(dimethylphosphino)methane dmso dimethyl sulfoxide XX dpcp 1,2-bis(diphenylphosphino)cyclopentane dppe 1,2-bis(diphenylphosphino)ethane dppp 1,2-bis(diphenylphosphino)propane dpypcp 1,2-bis(dipyridylphosphino)cyclopentane dpype 1,2-bis(dipyridylphosphino)ethane dq doublet of quartets (NMR spectra) dt doublet of triplets (NMR spectra) dtt doublet of triplets of triplets (NMR spectra) e molar absorptivity coefficient e.d. electron density E°./2 reduction potential EI electron impact EIMS electron impact mass spectrometry en ethylenediamine FID flame ionization detector (GC) FTIR Fourier transform infrared g gaseous state GC gas chromatography HO Ac acetic acid / liquid state lit. literature data LSIMS liquid secondary-ion mass spectrometry m multiplet (NMR spectra) m.pt. melting-point m/z parent peak (mass spectrometry) u.eff effective magnetic moment M V K methyl vinyl ketone (3-buten-2-one) NaX sodium halide NBD 2,5-norbornadiene NiNa'P NiBr 2 / NaOH / z-PrOH N1P4 a Ni species containing four P-donor atoms ORTEP Oakridge Thermal Elipsoid Plot (X-ray crystallography) OTf triflate anion, CF3SO3" p pseudo (NMR spectra) p-tol p-tolyl, -CeFLtCHj PNi diphenyl(2-pyridyl)phosphine xxi P N 2 phenylbis(2-pyridyl)phosphine PN 3 tris(2-pyridyl)phosphine py 2-pyridyl qn quintet (NMR spectra) qt quartet (NMR spectra) r.t. room temperature (~ 20°C) rearrang. rearrangement rQ initial rate rxn reaction s singlet (>JMR spectra), or strong (IR spectra), or second (time) sept septet (NMR spectra) sx sextet (NMR spectra) t triplet (NMR spectra) T temperature TCD thermal conductivity detector T L C thin-layer chromatography TPPTS tri(p-sulfophenyl)phosphine tR retention time (GC) triflate trifluoromethanesulfonate ion, CF3SO3" v/v% percent by volume w weak (IR spectra) w.r.t. with respect to wt% percent by weight xxii LIST OF COMPLEXES la NiCl2(dpype) 2a NiBr2(dpype) 3a Nil2(dpype) 4a Ni(NCS)2(dpype) 5a Ni(N03)2(dpype) 6a [Ni(H20)2(dpype)](PF6)2 7 NiCl 2 (PN 3 ) . H 2 0 9a NiCl 2 (PN!) 2 . H 2 0 9b NiCl 2(PN 2) 2 9c NiCl 2 (PN 3 ) 2 . 2H 2 0 11 NiI 2(PN 3) 2 12a NiCl2(dppe) 12b NiBr2(dppe) 12c Nil2(dppe) 12d Ni(NCS)2(dppe) 12e Ni(N03)2(dppe) 16 [Ni(PN3)2]Cl2 + N i C l 2 . 6H 2 0 17 [Ni(PN3)2]Cl2 + Ni(l,5-COD) 2 18 [Ni(PN3)2]Cl2 + Ag(CF 3S0 3) 190 Ni(CO)2(PPh3)2 19" Ni(CO)2(PPh3)(PNx) 20a Ni(CO)2(dpype) 21a Ni(PPh3)2(dppe) 21b Ni(PN!)2(dppe) 21c Ni(PN2)2(dppe) 21d Ni(PN3)2(dppe) lb NiCl2(dpypcp) 2b NiBr2(dpypcp) 3b Nil2(dpypcp) 4b Ni(NCS)2(dpypcp) 5b Ni(N03)2(dpypcp) 6b [Ni(H20)2(dpypcp)](PF6)2 8 [Ni(PN3)2]Cl2 10a NiBr 2 (PNi) 2 . 2H 2 0 10b NiBr 2 (PN 2 ) 2 . 2H 2 0 10c NiBr 2 (PN 3 ) 2 . 2H 2 0 13 [Ni(H20)2(dppe)](PF6)2 14 [Ni(H20)2(dppe)](S03CF3)2 15a [Ni(H20)2(dppe)](BPh4)2 15b Ni(OH)2(dppe)2+ 19a Ni(CO) 2(PNi) 2 19b Ni(CO) 2(PN 2) 2 19c Ni(CO) 2(PN 3) 2 19d [Ni2(CO)40-PN2)2]Cl4 20b Ni(CO)2(dpypcp) 22a Ni(PPh3)2(dpype) 22b Ni(PNi)2(dpype) 22c Ni(PN2)2(dpype) 22d Ni(PN3)2(dpype) xxiii 23a Ni(PPh3)2(dpypcp) 23c 23b Ni(PN02(dpypcp) 23d 24a Ni(dpypcp)2 25a 24b Ni(dppe)2 25b 24c Ni(dpype)2 25c 26a Ni(PPh3)4 2 7 26b Ni(PN04 28 26c Ni(PN 2) 4 29 26d Ni(PN 3) 4 30 31 32a [(CH3)(PN3)]I 33b 32b [(CH3)(dppe)]I 33c 32c [(CH3)(dpype)]I 33d 32d [(CH3)(dpypcp)]I 32e [(CH3)(PPh3)]I Ni(PN2)2(dpypcp) Ni(PN3)2(dpypcp) Ni(dppe)(dpype) Ni(dppe)(dpypcp) Ni(dpype)(dpypcp) fra«s-Ni(CH 3 )(I)(PN 3 ) 2 /raws-Ni(CH3)(I)(dpype)2 /ra«5-Ni(CH3)(I)(dpypcp)2 /ra«5-Ni(CH3)(I)(dppe)2 /ra«s-Ni(CH 3 )(I)(PPh 3 ) 2 [(CH3)2(dppe)]I2 [(CH3)2(dpype)]I2 [(CH3)2(dpypcp)]I2 xxiv ACKNOWLEDGEMENTS I wish to thank Professor Brian R. James for his guidance throughout the preparation of this thesis. I would also like to thank past and present members of the "James Group" for their help with experiments, useful discussions, and stress relief. I would also like to express my appreciation to the late Dr. Steven J. Rettig,1 Mr. Peter Borda, the N M R room staff, mass spectroscopy staff, and mechanical services staff. Thanks also go to the undergraduate-lab-technician Angelo Ariganello for the use of equipment and the provision of gallons of coffee over ~ 400 TAing sessions. I would especially like to thank the "freshly-minted" doctors Ian Baird and Jim Sawada for their friendship during our many years of Ph.D. candidacy, and also my parents for their continual encouragement and support. Thanks also go to my in-laws for their support and the occasional retreats to their lake-side cabin in Montana. Finally, a special acknowledgement goes to Karin, my lovely wife of five years, for encouraging, supporting, and loving me, and —during the final months of thesis preparation— for tolerating my exclusive devotion to the computer and maintaining my physical and mental well-being. 1. Deceased on Oct. 27, 1998 xxv Chapter 1 CHAPTER ONE Introduction 1.1 Homogeneous Catalysis in Aqueous Media Using Phosphine Complexes The separation of product from catalyst is a drawback of homogeneous catalysis in a one-phase organic or aqueous media. This can be overcome by conducting the reaction in a biphasic system where the catalyst is water-soluble and the products, which are extracted into the organic phase, can be decanted off the reaction mixture (Figure 1.1). reactants organic phase water-soluble catalyst \aqueous phase products Figure 1.1 Biphasic system for separation of products from catalyst. Water-soluble phosphine complexes are typically attained upon incorporation of a polar functional group (e.g., amino, ammonium, carboxylate, hydroxyl, phosphate, phosphonium, or sulfonate) into the phosphine.1 The ground-breaking work of Kuntz with trisulfonated triphenylphosphine (TPPTS, Figure 1.2) resulted, in 1984, in the Ruhrchemie/Rhone-Poulenc Oxo process whereby propylene is converted to butyraldehyde via hydroformylation in a biphasic system (Figure 1.3).2 The success of this process resulted in many water-insoluble ligands, such as l,2-bis(diphenylphosphino)ethane (dppe) and 2,2'-bis(diphenylphosphino)-l,l'-binaphthyl (binap), being made water-soluble via sulfonation3'4 and employed extensively as water-solubilizing agents (Figure 1.2). Of note, the biphasic Oxo process has been changed twice since 1 Chapter 1 references on page 12 Chapter 1 1984 by switching from TPPTS to bisbis (in 1990) and then to norbos (in 1992, see Figure 1.2), resulting in a 100-fold increase in activity over the original catalyst.1'5 bisbis norbos Figure 1.2 Sulfonated phosphines; Ar = /?-C6H4S03Na. Figure 1.3 Ruhrchemie/Rhone-Poulenc Oxo process for conversion of propylene to butyraldehyde via hydroformylation in a biphasic system (L = TPPTS). 2 Chapter 1 references on page 12 Chapter 1 Though attractive, sulfonated phosphines suffer from drawbacks in their synthesis as it is difficult to avoid formation of phosphine oxides, laborious to sulfonate all of the aryl groups, and hard to attain high yields.1 As another means to water-solubilize a phosphine is via incorporation of a pyridyl group, with the idea being that protonation of non-coordinated pyridine atoms on the ligand will make the phosphine water-soluble, Xie from our laboratory began work with the 2-pyridylphosphine ligands PPh3.xpyx (where py = 2-pyridyl and x = 1, 2, 3) in the mid-1980s.6 These phosphines have been given the abbreviations PNi, PN 2 , and PN 3 throughout this thesis, the subscript designating the number of 2-pyridyl groups (see Section 1.4). 1.2 Historical Use of 2-Pyridylphosphines Within this Laboratory The complexes Pt(PN3)4 and Pt(PN])3 with solely P-bonding ligands were prepared and reacted with olefins to yield Pt(PNx)2( ^ -olefin) complexes (olefin = acrylo-, methacrylo-, and crotonitrile, maleic anhydride, diethyl maleate, and diethyl fumarate), with HCl(g) to yield trans-PtH(Cl)(PNx)2 (x = 1 and 3), and with CH 3I to yield fra«s-Pt(CH 3)(I)(PN x); 6' 7 some of these complexes were tested for the catalytic hydration of acrylonitrile in aqueous media.7 The complexes PtCl 2(P-PN 3) 2 and Pt2X2(/i-P,./V-PN3)2 (X = halide) were prepared, along with an A-frame Pt 2I 2(^-PN 3) 2(//-DMAD) complex (DMAD = dimethylacetylenedicarboxylate);8 similar water-soluble palladium complexes [PdX 2(P-PN 2) 2 and Pd 2X 2(/i-P,/V-PN x) 2 (X = halide, x = 1 -3)] were also prepared9 (see Section 1.4.2 and Figure 1.7 for the various coordination modes of PN X ligands). Schutte conducted extensive coordination chemistry studies with PN X complexes of ruthenium.10 The [RuCl(772-P,/V-PNx)2(P-PNx)]Cl (x = 2 and 3) species were prepared and found to yield [Ru(7^-P,JV-PNx)3]2+ in water, while water-soluble [RuCl(PPh3)(//2-P,#-PN3)2]Cl was also prepared.10 Both cis- and zra«5,-RuCl2(dppb)(772-P,/Y-PNx) species, and P,7Y,7Y'-coordinated [RuCl(PPh3)(773-P,W'-PN3]PF6 were also prepared, the last of which formed [RuCl(CO)(PPh3)-(7J-P,AA,iv"-PN3]PF6 upon reaction with C O . " Similar reaction of the N,N',^"-coordinated species RuCl2(PPh3)(773-7V;#',7vr"-PN3) with L afforded either RuCl2(L)(^-Ar/V',/V''-PN3) or 3 Chapter 1 references on page 12 Chapter 1 [RuCl(L)(PPh3)(773-A^',JV"-PN3)]PF6 (L = CO, MeCN, PhCN). 1 2 Attempts to hydrate maleic acid catalytically with some of the Ru/PNX species were unsuccessful.10 Smith first synthesized the 2-pyridyl diphosphine ligands dpype13 and dpypcp14 (see Figure 1.4), and prepared P-bonded MX 2(P-P), M(CH3)2(P-P), M(CH3)(I)(P-P), [M(P-P)2]C12, M(P-P) 2 (M = Pd, Pt; X = halide; P-P = dpype, dpypcp), and [MCl(l,5-COD)(PNx)] (M = Rh, Ir) species.15 Baird then used dpype and the PN X ligands to prepare P-bonded c/5-NiX 2(PN x) 2 (X = CI, Br), c/5-Ni(CO)2(PNi)2, Ni(PN x) 4 (x = 1 and 2), Ni(dpype)2, NiBr2(dpype), and Ni(CO)2(dpype) species, of which the last two were water-soluble.13 Jones and MacFarlane have also used dpypcp to prepare cz's-PtX2(dpypcp) and RuX2(773-P,P,A7-dpypcp)(PPh3) • H 2 0 species (X = halide).14 1.3 Objective of this Thesis The initial objective of this thesis was the synthesis of new Ni 2-pyridylphosphine complexes (Chapters 3 and 4), and the investigation of the aqueous chemistry of both these and water-soluble NiBr2(dpype) and Ni(CO)2(dpype).13 The previous studies within our group on olefin hydration led to similar studies being conducted with the Ni 2-pyridylphosphines (Chapter 5), while their water-solubility led to studies on their use as water-gas-shift catalysts (Chapter 5). A report published in 1995 on transfer hydrogenation with NiCl 2(PPh 3) 2 1 6 led to corresponding studies with NiBr 2 and various Ni 2-pyridylphosphines on a variety of organic substrates (Chapters 6 and 7). Before the scope of this thesis is discussed, a short review of chemistry with 2-pyridylphosphines is presented. 1.4 General Developments in 2-Pyridylphosphine Chemistry The general class of 2-pyridylphosphine ligands includes any phosphine ligand with a pyridine moiety coordinated to a phosphorus atom ortho to the aromatic nitrogen atom. For this thesis, 2-pyridylphosphines are restricted to those which are either the mono, bis, or tris 2-pyridyl analogues of PPh3 (PPh2py, PPhpy2, Ppy3, respectively), the tetrakis 2-pyridyl analogue of dppe (py 2P-CH 2CH 2-Ppy 2), or the tetrakis 2-pyridyl analogue of dpcp (py 2P-C 5H 8-Ppy 2) (Figure 1.4). The following abbreviations are employed: PNi = PPh2py, P N 2 = PPhpy2, PN 3 = Ppy3, PN X = PNi-4 Chapter 1 references on page 12 Chapter 1 PN 3 , dpype = pyridyl analogue of bis(diphenylphosphino)ethane, and dpypcp = pyridyl analogue of bis(diphenylphosphino)cyclopentane. Figure 1.4 The 2-pyridylphosphine ligands: (a) PPh3.xpyx, n = 1 to 3; PNi = PPh2py, P N 2 = PPhpy2, PN 3 = Ppy3, (b) dpype (ethane backbone) or dpypcp (cyclopentane backbone). The 2-pyridylphosphine PN 3 was first prepared in 1944 by Davies and Mann, 1 7 while PNi and P N 2 were synthesized four years later by Mann and Watson.18 The use of dpype in studies on the biological properties of Au(I) complexes was reported in 1987 1 9 but details of its synthesis and characterization, conducted within this UBC group in 1993, did not appear until 1995.13 The synthesis of dpypcp, also conducted within this UBC group, was reported in 1999.14 The first complexes containing a 2-pyridylphosphine ligand were prepared by Uhlig and Maaser in 1966 with (2-py(CH2)2)PPh2 and Ni(II), Co(II), Zn(II), and Cu(I),20 while the first X-ray structure for a 2-pyridylphosphine complex was reported by Parks et al. in 1970.21 A much greater understanding of the coordination within 2-pyridylphosphine complexes came with the advent of 3 1P{1H} NMR spectroscopy and X-ray analysis.22 An extensive review on 2-pyridylphosphine chemistry was written by Newkome in 1993.22 1.4.1 Synthesis of 2-Pyridylphosphines The preparation of the PN X ligands has been modified over the years22 and in general now involves the method of Kurtev et al.23 for the low temperature (-78°C) synthesis of 2-lithiopyridine (2-Lipy) from 2-bromopyridine (2-Brpy) and w-BuLi, followed by reaction with the appropriate commercially available chlorophosphine [PClPh2, (PNi); PCl 2Ph, (PN2); PC13, (PN3)] to yield the ligand in a one-pot synthesis (Figure 1.5). The first step must be conducted at low temperature to prevent 2-Lipy from coupling with 2-Brpy to produce 2,2-dipyridine and LiBr, PPh 3.xpy x (a) (b) 5 Chapter 1 references on page 12 Chapter 1 and also because the reaction affords 2-Bupy and LiBr when conducted at r.t. Complete conversion of 2-Brpy to 2-Lipy must be attained prior to addition of chlorophosphine to prevent formation of PBupy2, PBu2py, or PBu 3. Upon completion of the reaction with chlorophosphine, PN X is converted to P(pyH)x x + by addition of aq. acid and then extracted from the ethereal solution, leaving behind the «-BuBr side-product. Dilution of the acid with saturated aq. NaOH yields a precipitate of PN X which is separated from the soluble LiCl co-product via filtration. PN X is then washed with water (to remove NaS04 that may have formed upon neutralization of the acid solution) and purified by re-precipitation from acetone/hexanes. >?-BuBr Sp^ j ff^ PPh3-nCln P N 1 ( ) + w-BuLi — — \( )\ • P N 2 + LiCl BrAf^ Et2°'-78°C uAf^  - 1 . 2 , 3 m 2 3 Figure 1.5 Synthesis of the PN X ligands. The synthesis for the 2-pyridyl diphosphines is essentially the same as that for PN X , with the exception that C1 2PCH 2CH 2PC1 2 and C12P(C5H8)PC12 precursors are employed (Figure 1.6). Although C1 2PCH 2CH 2PC1 2 is now commercially available from Strem, for this thesis work it was synthesized by others in our laboratory13'14'24 from C2FLt, white phosphorus and PC13, following the literature method;25 Cl 2 P(C 5 H g )PCl 2 was prepared in a similar fashion14 from C 5 H 8 (Eq. 1.1) by following the method of Green et al. X-ray crystal structures of PNi, PN 3 , and dpype are known, while the structure of dpypcp was obtained in this thesis work. a 7 p ' ' p a , OJ»X ^PQ, py2P Ppy2 dpype .A py 2 P' ^Ppy2 dpypcp Figure 1.6 Synthesis of the diphosphine ligands dpype and dpypcp (* indicates a chiral centre, see Section 2.3.5, p.26). 6 Chapter 1 references on page 12 Chapter 1 o + PC13 + p 4 220°C 69 h *. product mixture- distil *• 4th fraction = PC12 (Eq. 1.1) C12P Of note, 3- and 4-pyridylphosphines are not so commonly used in coordination chemistry as their syntheses are more difficult,23'29 while use of 4-pyridylphosphines generally results in formation of polymeric complexes. The large bite angle of 3-pyridylphosphines also precludes bidentate or bridging coordination modes. 1.4.2 Complexes and Coordination Modes of 2-Pyridylphosphine Ligands A literature search shows that PN X complexes of two-thirds of the 30 d-block metals and of uranium30 are known (see below for examples; Sc, Y, Ti, Zr, Hf, V, Nb, Ta, and Tc complexes are not yet reported), while dpype complexes of Pt, 1 4 Pd, 1 5 Rh, 1 5 Ir,1 5 N i , 1 3 and Ag , 3 1 and dpypcp complexes of Pt, 1 4 Pd, 1 5 Ru, 1 4 Rh, 1 5 and Ir1 5 are also known. Of note, dppe (the phenylphosphine analogue of dpype), which was first prepared in 1939,32 has been coordinated to all but four (Sc, Y, Zn, and Cd) of the d-block transition-metals33 and to eight of the p-block elements (see references for examples).34 Similarly, PPh3 complexes have been prepared for all but six (Sc, Y, Hf, Nb, Ta, and Zn) of the d-block metals35 and for five of the p-block elements.36 Coordination Modes of 2-Pyridylphosphines 2-Pyridyl monophosphines, with their heteropolydentate advantage of containing both a basic "hard" N-atom and a basic "soft" P-atom, yield diverse coordination chemistry with transition-metals by binding in a mono-, bi-, tri-, or tetradentate fashion (Figure 1.7). The type I //-^-coordination mode is known, for example, for the following complexes: NiX 2 (PN x ) 2 , 1 3 Ni(CO) 2(PN x) 2, 1 3 Ni(PN x) 4, 1 3 PdX 2(PN x) 2 , 9 Pd(PN03,37 Pt(PN 3) 4, 7 Pt(PN03,7 Pt(PNx)2( ^ -olefin) (olefin = acrylo-, methacrylo-, and crotonitrile, maleic anhydride, diethyl maleate, and diethyl fumarate),7 PtH(Cl)(PNx)2 (x = 1 and 3),7 Pt(CH3)(I)(PNx)2,7 PtX 2(PN x) 2 (X = halide, x = 1-3),6'38'39 [MCl(l,5-COD)(PNx)] (M = Rh, Ir),15 RhCKCOXPNO,, 4 0 Rh(^-7 Chapter 1 references on page 12 Chapter 1 acac)(CO)(PN2),41 Ir 4(CO)i 0(PN 1) 2, 4 2 HgCl 2(PN 3), 4 3 Mo(CO) 5(PN 2), 4 4 Fe(NO) 2Cl(PN 1), 4 5 AuCl(PNx) (x = 1,3),46'47 Os3(CO)io(PN3)2,4 8 Re 2(OAc)Cl 4(PNi) 2, 4 9 and Cu 2Cl 2(//-Cl) 2(PNi) 2. 5 0 M — P . / Y* i.p M — N n,p,N ^P N I I M M HI, fJrP.N .N-M N -IV, N,N' N I M V V, N,N',N" M" VI, P,N,N' N ^ P - M I M 1 , . ,N N VH, P,N,N',N" Figure 1.7 Coordination binding modes of 2-pyridyl monophosphines with transition-metals (Figure adapted from ref. 10). The mononuclear rf-P.TV-chelating mode, type II, is reported, for example, for: [RUC1(T7 2 -PN X ) 2 (T / -PN X ) ]C1 (x = 2 and 3),10 [Ru(PN x) 3] 2 +, 1 0 [RuCl(PPh3)(PN3)2]Cl,10 cis- and fram-RuCl2(dppb)(PNx),n Ru(PNi)(CO) 2Cl 2, 5 1 PdCl2(PNx) (x = 1-3),52 [PtI(PNi)2]PF6,38 [Pt(/^-PN 1 ) ( / 7 / -P -PN,)Cl] + , 3 9 [Pt(/7 2-PN1)(7 7 /-P-PN 1)Me]+, 5 3 Ni(CO) 2(PN!), 5 4 U(BH 4 ) 3 (PN 1 ) 2 , 3 0 UCl 3(Cp)(PN0, 3 0 [Rh(l,5-COD)(PNi)]X (X = C104, PF 6 ) , 5 5 RhCl(/7 2-PN 3) 2. 2 3 The complex MnI 2(PNi) 2 can perhaps be classified as type n , although the Mn—P interactions (3.143(5) and 3.080(5) A) are unusually long.56 The complexes RhCl(CO)(PNx)2 (x = 2 and 3) have also been shown to exist as an equilibrium between types I and II in solution.57 The //-P./V-bridging coordination mode, type i n , can be subdivided into homo- and heterobimetallic complexes. Examples of the former include [Ag 2(PNi) 2](BF 4) 2, 5 8 [Ir4(//-C O ) 3 ( C O ) 5 C U - P N 3 ) ( T 7 / - P - P N 3 ) 2 ] , 5 9 Pt 2X 2(PN 3) 2 (X = halide),8 Pt 2I 2(PN 3) 2(//-DMAD), 8 8 Chapter 1 references on page 12 Chapter 1 Pd 2 X 2 (PN x ) 2 (X = halide, x = 1, 2, 3),9 Os 3(CO) 1 0(PN 3), 4 8 [Re2Cl4(PN,)3](PF6)2,60 Re 2(0 2CR) 2Cl 2(PNi) 2 , 6 1 [Co(NO)2(PN1)2Co(NO)](BF4),6 2 and R h . C k O C O X P N j ) , , 6 3 while examples of the latter include (CO) 3Fe(PNi) 2ML 2 (M = Zn, Cd, Co, Ni, Mn, Cr, Mo; L = SCN or CI), 6 4 PtPdX 2(PN 3) 2 (X = CI, Br, I),6 [Ir 4Cu(CO) 1 0(PN 1) 2]PF 6, 4 2 RhPtCl 3(PN0 2 , 3 9 AgAu(PNi) 2(C10 4) 2, 5 8 PdMoCl 2Cu-CO)(CO) 2(PN0 2, 6 5 RhPdCMCOXPNifc, 4 0 PdW(PNi) 2(^ CO)(CO) 2 Cl 2 , 6 6 HgCl(PN0 2FeCl(CO) 2, 6 7 and Rh(l,5-COD)(PN1)2Cu-Cl)PdCl2.5 5 The only known examples of the mononuclear rf -N,/^'-chelating mode, type IV, are MoI 2(CO) 3(PN 2), 4 4 Mo(CO) 4(PN 2), 4 4 CoCl 2(PN 2), 6 8 and Cl(PN3)(CO)2W=CPh.6 9 The mononuclear ^-A^TV'TY'-chelating mode, type V, is common among the first row transition-metals. Cationic "sandwich" complexes of the general formula [M(PN 3) 2]X 2 (M = Co, Cu, Fe, Mn, Ni, Ru, Zn; X = C104, C 7 H 7 S 0 3 , N0 3 ) are known.70"75 Recent work within our group has led to the synthesis of the rare "half-sandwich" complexes RuCl2(PPh3)(PN3), RuCl2(L)(PN3) and [RuCl(L)(PPh3)(PN3)]PF6 (L = CO, MeCN, PhCN). 1 2 The complexes Zn(PN 3)(N0 3) 2 7 6 and Mo(CO) 3(PN 3) 7 7 are also known. The first examples for the mononuclear //-P.Af TV'-chelating mode, type VI, come from recent work within our group11 for the synthesis of [RuCl(PPh3)2(PNx)]PF6 (x = 2 and 3) and [RuCl(CO)(PPh3)(PN3)]PF6. Attempts to prepare the ju-Tf-P,N,N',N"-bndgmg mode, type VH, were briefly conducted in this thesis work by reacting a type V species with another metal centre (Section 3.2.4, p.44). The number of potential modes in which 2-pyridyl diphosphines can coordinate to transition-metals is more diverse than that described above, as six donor-atoms are present within the ligand (Figure 1.8). The 12 potential modes for the case where a 2-pyridyl diphosphine chelates to a single metal centre are listed in Table 1.1; the potential bridging modes are myriad. The P,P,iV-chelating mode has been reported for RuX2(P,P,N-dpypcp)(PPh3) (X = CI, Br, I),1 4 while only the P,P-chelating mode is observed in this thesis work. 9 Chapter 1 references on page 12 Chapter 1 1 Figure 1.8 2-Pyridyl diphosphine ligands, showing the six donor-atoms. Table 1.1 Chelating Modes for a 2-Pyridyl Diphosphine to a Single Metal Centre a NhN,' N,,N3 Nl,NI',N2 Ni, Ni', N2, N2 Pi,N, Pi, N,, N', Pu Pi Pi, Pi, Ni Pi, P2, Nj, Ni' Pn P2, Nh N2 Ph P2, Ni, N,', N2 Ph P2, Nh N/, N2, N2' (a) Subscript numbers refer to an N-atom of either Pi or P 2 in Figure 1.8. 1.4.3 Catalysis with 2-Pyridylphosphine Complexes A literature search shows that pyridylphosphine complexes have been used as catalysts for hydroformylations (of 1-hexene,23 and tetradec-l-ene78), carbonylations (of MeOH to acetic acid,79 and to methylmethacrylate80), cycloadditions (of C 0 2 and diynes to yield a-pyrones81), chlorinations (of primary or secondary alcohols to yield alkyl chlorides82), epoxidations (of alkenes by PhIO, hypochlorates, and H 2 0 2 8 3 ) , dimerizations (of isoprene with C 0 2 to afford various methyl esters84), hydrogenations (of styrene85), and exchange reactions (deuteron/hydrogen (D +-H 2) exchange for deuterated-solvent synthesis86). 1.5 Homogeneous Catalysis Using Ni Complexes Reviews on the uses of nickel complexes (containing any ligand) in homogeneous catalysis have been recently written by Keim, Rajashekharam, Beattie et al., Brull et al, Sawamoto and Kamigaito,91 and Downing et al91 Of historical interest, the first phosphine complex to exhibit greater rates of catalysis than non-phosphine catalysts was Ni(CO) 2(PPh 3) 2 for olefin and acetylene polymerizations.93 10 Chapter 1 references on page 12 Chapter 1 1.6 Scope of this Thesis As noted in Section 1.3, the initial objective of this thesis was the synthesis of new Ni 2-pyridylphosphine complexes and an investigation of their aqueous solution chemistry. General experimental procedures, including the syntheses for compounds used as ligands and Ni(0) and Ni(II) precursors, are described in Chapter 2. Chapter 3 describes Ni(II) 2-pyridylphosphine chemistry, with the preparation and characterization of water-soluble P,P-coordinated NiX 2(P-P) species (X = Cl, Br, I, NCS and N0 3 ; P-P = dpype and dpypcp). The aqueous chemistry of both these halo species and the NiX 2(PN x)2 complexes of Baird et al.13 is examined, along with the preparation of [Ni(H20)2(P-P)](PF6)2 species (P-P = dppe, dpype, dpypcp). The formation of tetrahedral, P,iV-chelated NiCl 2 (PN 3 ) .H 2 0 from Ni(CO)2(PPh3)2, and its conversion to octahedral, JY/W'-chelated [Ni(PN3)2]Cl2 is discussed. X-ray structures for dpypcp, [Ni(PN3)2]Cl2, and five of the NiX2(P-P) species are also presented, along with spectroscopic characteristics of dpype and dpypcp. Chapter 4 describes Ni(0) 2-pyridylphosphine chemistry, with the preparation and characterization of three Ni(CO) 2(PN x) 2 species, two Ni(CO)2(P-P) species, four Ni(PR 3) 4 species, two Ni(P-P)2 species, and fifteen Ni(0) tertiary mixed-phosphine species. The aqueous solution chemistry of the dicarbonyl complexes, and the reactivity of the tertiary Ni(0) phosphine complexes with C2H4, CI2, 0 2 , and CH 3I is examined. The preparation and characterization of three rra«s-Ni(CH 3)(I)L 2 species (L = PN 3 , dpype, or dpypcp) and the mono- and bismethylated phosphonium salts of PN 3 , dpype, and dpypcp are discussed, along with attempts to prepare the o-acyl complexes Ni(COCH3)(I)Ln. The preparation of a possible dimetallic Ni(II) carbonyl species is also presented. Successful catalysis of the water-gas-shift by NiCl2(PN2)2 at rates comparable to the range of turnovers reported for other homogeneous catalysts is presented in Chapter 5. The effects of acid, base, organic media, and CO pressures are briefly investigated. The unsuccessful attempts to catalyze the hydration of maleic acid in water with a variety of Ni(0) and Ni(II) 2-pyridylphosphines are also discussed in Chapter 5. Chapter 6 reports investigations into the transfer hydrogenation of cyclohexanone to cyclohexanol in alkaline alcoholic media by a few Ni(II) 2-pyridylphosphine complexes and also 11 Chapter 1 references on page 12 Chapter 1 by the N i X 2 salts (X = Cl, Br, I). Certain aspects of the kinetics of the NiBr2-based catalytic system are examined. Chapter 7 continues the above line of investigation, with attempts to transfer hydrogenate further ketones (2-butanone, 2-pentanone, and acetophenone), aldehydes (1-heptanal and benzaldehyde), unsaturated hydrocarbons (1-octene, trans-2-octene, cyclooctene, 1,5-cyclooctadiene, and benzene), nitriles (acetonitrile and benzonitrile), a,/3-unsaturated ketones (cyclohex-2-ene-l-one and 3-buten-2-one), diketones (2,4-pentanedione and 2,5-hexanedione), nitrobenzene, 4-nitrobenzaldehyde, and propionic acid. 1.7 References 1. Herrmann, W. A.; Kohlpainter, C. W. Angew. Chem., Int. Ed. Engl. 1993, 32, 1524. 2. Kuntz, E. G. Chemtech. 1987, 570. 3. Bartik, T.; Bunn, B. B.; Bartik, B.; Hanson, B. E. Inorg. Chem. 1994, 33, 164. 4. Wan, K. T.; Davis, M . E. J. Chem. Soc., Chem. Commun. 1993, 1262. 5. Haggin, J. Chem. Eng. News 1994, 72, 28. 6. Xie, Y. Ph. D. Thesis, The University of British Columbia, 1990. 7. Xie, Y.; James, B. R. J. Organomet. Chem. 1991, 417, 277. 8. Xie, Y.; James, B. R. Inorg. Chim. Acta 1994, 217, 209. 9. Xie, Y.; Lee, C. L. ; Yang, Y.; Rettig, S. J.; James, B. R. Can. J. Chem. 1992, 70, 751. 10. Schutte, R. P. Ph. D. Thesis, University of British Columbia, 1995. 11. Schutte, R. P.; Rettig, S. J.; Joshi, A. M . ; James, B. R. Inorg. Chem. 1997, 36, 5809. 12. Schutte, R. P.; Rettig, S. J.; James, B. R. Can. J. Chem. 1996, 74, 2064. 13. Baird, I. R.; Smith, M B . ; James, B. R. Inorg. Chim. Acta 1995, 235, 291. 14. Jones, N. D.; MacFarlane, K. S.; Smith, M . B.; Schutte, R. P.; Rettig, S. J.; James, B. R. Inorg. Chem. 1999, 38, 3956. 12 Chapter 1 references on page 12 Chapter 1 15. Smith, M . B.; James, B. R. Unpublished work. University of British Columbia, 1994. 16. Iyer, S.; Varghese, J. P. J. Chem. Soc, Chem. Commun. 1995, 465. 17. Davies, W.C.; Mann, F.G. J. Chem. Soc. 1944, 276. 18. Mann, F. G.; Watson, J. J. Org. Chem. 1948, 13, 502. 19. Mirabelli, C. K.; Hill, D. T.; Faucette, L. F.; McCabe, F. L.; Girard, G. R.; Bryan, D. B.; Sutton, B. 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Wasserman, H. J.; Moody, D. C ; Paine, R. T.; Ryan, R. R ; Salazar, K. V. J. Chem. Soc, Chem. Commun. 1984, 533. 31. Berners-Price, S. J.; Bowen, R. J.; Harvey, P. J.; Healy, P. C ; Koutsantonis, G. A. J. Chem. Soc Dalton Trans. 1998,11, 1743. 32. Chatt, J.; Mann, F. G. J. Chem. Soc. 1939, 1622. 33. For example: (a) Jones, R. A ; Schwab, S. T.; Whittlesey, B. R. Polyhedron 1984, 3, 505 [For TiCl2(dppe)('-BuS)2]; (b) Shah, S. S.; Maverick, A. W. J. Chem. Soc, Dalton Trans. 13 Chapter 1 references on page 12 Chapter 1 1987, 12, 2881 [For [Y(dppe)3][V(CO)6]2]; (c) Piana, H.; Schubert, U. J. Organomet. Chem. 1991, 411, 303 [For M(H)Cl(CO)3(dppe) (M = Cr, Mo, WYJ; (d) Mandal, S. K.; Ho, D. M.; Orchin, M. Inorg. Chem. 1991, 30, 2244 [For Mn(CO)3(dppe)OCH3 and Re(CO)3(dppe)OC6H5]; (e) Sellmann, D.; Weber, W. J. Organomet. Chem. 1986, 304, 195 [For [CpFe(dppe)CO]PF6]; (f) Wei, G.W.; Liu, H. Q.; Huang, Z. Y.; Hong, M. C ; Huang, L. G.; Kang, B. S. 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Annalen 1948, 560, 104. 19 Chapter 1 references on page 12 Chapter 2 CHAPTER TWO General Experimental 2.1 General Materials 2.1.1 Solvents Spectral and reagent grade solvents were obtained from Aldrich or Fisher and dried and distilled under N 2 prior to use as per standard techniques.1 Benzene, toluene, hexanes, THF, and Et 2 0 were dried over sodium/benzophenone, and acetone and CHCI3 were dried over K 2 C 0 3 . MeOH, EtOH, and H - B U O H were dried over the corresponding magnesium alkoxide formed by reaction of the alcohol with Mg turnings and trace I2. CH2C12 and MeCN were distilled from CaH2, and the MeCN was then fractionally distilled and stored under Ar in the dark. /-PrOH and H-PrOH were distilled from CaO. Glacial acetic acid was used without purification. Deuterated solvents (acetone-^, benzene-^, chloroform-^, dmso-fi?6, methanol-^, and toluene-rfg) were obtained from Cambridge Isotope Laboratories, dried over molecular sieves (BDH 4A 1/16" pellets), de-gassed via freeze-pump-thaw cycles, and stored under Ar. 2.1.2 Gases Ar, CO, N 2 , NH 3 , and 0 2 were supplied by Union Carbide of Canada (Praxair). Cl 2 , C2H4, and H 2 were from Mattheson. All gases except Ar and C2FL, were used without further purification; Ar was passed through an anhydrous CaS04 column, while C2Fl4 was passed through an anhydrous P 2 0 5 column. 2.1.3 General Reagents The following reagent-grade (or better) chemicals were used without further purification: cone. HOAc (Fisher), AgN0 3 (Mallinckrodt), AgS0 3CF 3 (Aldrich), w-BuLi (1.6 M in hexanes, Aldrich), [(Bu)4N](N03) (Fisher), CaS0 4 (Fisher), Celite 545 (Fisher), CF 3 S0 3 H (Aldrich), CH 3I (Aldrich), 1,2-dichloroethane (Aldrich), fumaric acid (Eastman), cone. HC1 (Fisher), H 2 0 2 (Fluka), cone. H 2 S0 4 (Fisher), KBr (Aldrich), KF (Aldrich), KOH (Fisher), KPF 6 (Alfa), KSCN (Fisher), maleic acid (MCB), malic acid (Aldrich), Na (Mallinckrodt), NaBPlu (Merck), NaBr 20 Chapter 2 references on page 32 Chapter 2 (Aldrich), NaCl (Aldrich), NaF (Fisher), Nal, (Aldrich), NaOH (Fisher), NiBr 2 (anhyd, Alfa), NiCl 2 - 6H 2 0 (Alfa), Ni(N0 3) 2- 6H 2 0 (Fisher), P 2 0 5 (BDH), and Zn dust (Fisher). The Ni l 2 • 6H 2 0 (Aldrich) was a mixture of the desired aquamarine-coloured crystals, covered in a red/brown surface liquid layer of presumably I2/I3" (possibly formed by reaction of the crystals with atmospheric H 2 0) and what appeared to be flakes of Ni metal. To purify the crystals, the liquid layer was first decanted and then the large blocks of contaminated N i l 2 • 6H 2 0 (~ 5 g) were broken into smaller (~ 1 mm3) blocks and placed in a round-bottom flask. Hexanes was added and the resulting mixture was sonicated for 5 min; this resulted in a bright-purple hexanes/I2 solution and significantly cleaner Ni l 2 • 6H 2 0 crystals (which do not fracture under sonication). The hexanes filtrate was discarded and the sonication procedure was repeated three times with fresh hexanes, after which time the crystals were recovered by anaerobic filtration and washed with hexanes. The physical action of this final washing dislodged the Ni metal particles, causing them to migrate to the periphery of the glass frit while leaving behind clean aquamarine crystals in the centre of the frit; the crystals were then collected by hand-picking and stored under N 2 . The crystals were not dried at the pump as a small test-batch was observed to decompose in vacuo. 2.2 General Instrumentation 2.2.1 Nuclear Magnetic Resonance Spectroscopy Nuclear magnetic resonance (NMR) spectra were acquired at room temperature (r.t. ~ 20°C) with a Varian XL300 (300 MHz for *H; 121.42 MHz for 3 1P), a Bruker AC200 (200 MHz for ! H ; 80.95 MHz for 3 1P), or a Bruker AC500 (500 MHz for ! H ; 202.5 MHz for 3 1P) spectrometer on samples prepared in 5 mm NMR tubes, using residual solvent proton (XH) or external P(OMe)3 (^P^H}: 6 141.00 vs. external 85% aq. H 3 P0 4 ) as the reference. Chemical shifts (5) are in units of parts per million (ppm); 31P{XH} data are reported with respect to 85% aq. H 3 P0 4 . 21 Chapter 2 references on page 32 Chapter 2 2.2.2 UV-Visible Spectroscopy UV-Vis spectra were recorded on a Hewlett Packard 8452A diode array spectro-photometer using Spectrosil precision quartz cells (1.0 cm path length). Values are given as Amax (nm), [e ( M 1 cm-1)]. 2.2.3 Infrared Spectroscopy Infrared spectra were recorded on an ATI Mattson Genesis FTIR spectrometer. Solid-state spectra were recorded as KBr pellets. Solution spectra were recorded by loading an IR solution cell equipped with KBr windows with the solution. Some spectra were recorded by placing a small amount of the solution between two KBr discs to form a thin film. Values are given in units of cm"1, and are assigned to the fragment listed afterwards in parentheses [e.g., "2001, 1948 (s, CO), 1437, 1100, 748 (m, dppe), 836, 557 (m, PF6)" denotes two strong bands assigned to CO, three medium bands assigned to dppe, and two medium bands assigned to PF 6]. 2.2.4 Mass Spectroscopy Liquid secondary ion mass spectrometry (LSIMS) was carried out on a Kratos Concept II HQ instrument, using samples in a thioglycerol/H20 matrix. Electron ionization mass spectrometry (EIMS) was carried out on a Kratos MS50 instrument with a 70 keV electron ionization energy and a resolution of 1000. In cases where a range of m/z values is reported for a particular peak, isotopic-splitting of the pattern has occurred, and matches that simulated by a computer programme.2 2.2.5 Gas Chromatography Gas chromatographic analyses were performed on a temperature-programmable Hewlett Packard 5 890A instrument equipped with a thermal conductivity detector (TCD), a flame ionization detector (FID), and an HP 3 3 92A integrator. The detection of CO and H 2 was achieved with a 10 ft packed molecular sieve column and a TCD with He as the carrier gas. Instrument settings for CO detection were as follows: oven temp. = 50°C; injector temp. = 115°C; detector temp. = 50°C; and column head pressure = 40 kPa. Using these settings, the following retention times (tR in min) for various gases were measured: CO = 6.64, H 2 = 1.60 22 Chapter 2 references on page 32 Chapter 2 (inverted peak),3 O2 = 2.68, N 2 = 3.57. For quantitative detection of H 2 , the detector temperature must be raised to 200°C (see Chapter 5). The detection of all organic compounds in transfer hydrogenation experiments (Chapters 6 and 7) was achieved with a HP-17 column (20 m capillary, intermediate polarity, 50% phenyl and 50% methyl polysiloxane composition) and an FID with He as the carrier gas. Instrument settings and retention times for each compound are listed in Chapters 6 and 7. 2.2.6 Conductivity Conductivity measurements were made using a model RCM151B Serfass (A.H. Thomas Co. Ltd.) conductance bridge connected to a 3403 cell from Yellow Springs Instrument Company. Measurements are referenced to an aqueous solution of KC1 (0.0100 M) (where the cell constant a = 0.001413 ohm"1 cm"1) and are given as A M (ohm"1 cm2 mol"1). A 25°C temperature was maintained by the use of a water-bath thermostat, and solutions of 1 x 10"3 M in MeOH or H 2 0 were made just prior to use. 2.2.7 Elemental Analysis/Melting Points Elemental analyses were performed by Mr. P. Borda of this department on a Carlo Erba Model 1106 Elemental Analyzer or a Fisons (Erba) Instruments E A 1108 CHN-0 Elemental Analyzer, and the results have an absolute accuracy of ± 0.3%. Melting points (m.pt.) were determined using a MelTemp apparatus and are uncorrected. 2.2.8 Magnetic Susceptibility Magnetic susceptibility studies were conducted with a Johnson-Matthey magnetic susceptibility balance and the mass susceptibility per gram of sample, %g, was calculated according to the equation below. Xg = (Cbal)(/)(R-R<,) 1 0 ^ where: Cbai = balance calibration constant (1.158) / = sample length (cm) R = reading for tube plus sample Ro = reading for empty tube m = sample mass (g) 23 Chapter 2 references on page 32 Chapter 2 2.2.9 X-ray Crystallography X-ray crystal structures were solved by the late Dr. Steven. J. Rettig of this department on a Rigaku/ADSC CCD area detector (graphite monochromator, Mo Koc radiation) or Dr. Victor G. Young, Jr. at the University of Minnesota on a Siemens SMART Platform CCD area detector (graphite monochromator, Mo Ka radiation). 2.3 Phosphines PPh3, PCI3, PPhCl2, and 2-bromopyridine were purchased from Aldrich. Only PPh 3 was used without further purification (5P = -5.1 in CDC13, -3.4 in C 6 D 6 , -5.5 in acetone-di;)- PC13 and PPhCl 2 were refluxed under N2(g) for 1 h followed by fractional distillation, while 2-bromopyridine was stirred over K O H pellets for 24 h at r.t. prior to vacuum distillation from CaH 2 . The preparations of the 2-pyridylphosphine ligands PPh3.xpyx, the 2-pyridyldiphosphine ligands dpypcp and dpype, and the bidentate phosphine ligand dppe are described below. The PPh3.xpyx phosphines are designated as PNi, PN 2 , and PN 3 for convenience, the number referring to the number of pyridyl groups incorporated in the ligand. All ligand syntheses were conducted under an inert atmosphere (N 2 or Ar) unless otherwise specified. All 3 1P{1H} and ! H N M R data were measured at 121.42 and 500 MHz, respectively, at r.t. in CDC13, except for dppe where *H NMR data was gathered at 300 MHz. 2.3.1 Diphenyl(2-pyridyl)phosphine, PNi The title compound was prepared by a procedure reported by Balch and coworkers4 and was kindly provided by Dr. R. P. Schutte of this group. See Table 3.1 (p. 47) for N M R data. 2.3.2 Bis(2-pyridyl)phenylphosphine, PN2 The procedure for P N 2 is identical to that described for PN 3 in the next section, except PPhCl 2 (7.2 mL, 53 mmol) is used in place of PC13; PN 2 was also provided by Dr. R. P. Schutte. See Table 3.1 (p. 47) for NMR data. 2.3.3 Tris(2-pyridyl)phosphine, PN3 P N 3 was prepared by a literature procedure.5 To a solution of w-BuLi (100 mL, 1.6 M in hexanes, 160 mmol) in Et 2 0 (100 mL) cooled to -78°C (acetone/C02(s) bath)6 was added dropwise 2-bromopyridine (16 mL, 160 mmol; clear and colourless, yellow indicates impurities) 24 Chapter 2 references on page 32 Chapter 2 via a syringe over 10 min. The mixture was stirred for 4 h during which time it turned a deep cherry-red colour. A solution of PC13 (4.8 mL, 53 mmol) in Et 2 0 (25 mL) was then added dropwise via a syringe. The beige slurry obtained was stirred for a further 2 h and then allowed to warm to r.t. The mixture was extracted with de-gassed H2SO4 (aq) (2 M , 2 x 100 mL) and the aqueous solution made alkaline by adding saturated NaOH (aq) (14 M) dropwise while cooling in an ice bath. The resulting yellow precipitate was collected by vacuum filtration, washed with H 2 0 , and reprecipitated from acetone/hexanes as a beige coloured powder. Yield: 8.86 g (63%). Anal. Calcd for Ci 5 H 1 2 N 3 P: C, 67.92; H, 4.56; N, 15.84%. Found: C, 67.79; H, 4.60; N, 16.03%. ! H NMR: 5 7.20 (m, 3H5), 7.39 (m, 3H3), 7.60 (m, 3H4), 8.71 (m, 3H«). "Pf/H} NMR: 8 -0.74 (s). IR (KBr): 1566, 1448, 1416 (s, py skeletal bands).7 m.pt.: 111-114°C (lit. 115°C). 8 The spectroscopic data agree well with those found in the literature.5'9"12 Figure 2.1 shows the proton-labelling for PN 2 , dpype, and dpypcp. The literature values11 for the UV-Vis spectra of all three PN X ligands are reported in Table 2.1. (a) He py 2P' ? H b H a H a (b) Figure 2.1 Numbering scheme for 2-pyridylphosphines: (a) e.g., PN 2 , (b) P-P ligands. Table 2.1 Literature Values for the UV-Vis Spectra of the PN X ligandsa Ligand ^max [El] ^max [£2] ^max [£3] PNi 308 [1620] 270 [1510] 242 [1400] P N 2 314 [1650] 268 [1540] 248 [1440] PN 3 318 [1520] 268 [1420] 246 [1330] ( f l ) In CH 2C1 2, 2 mM. Taken from ref. 11. 25 Chapter 2 references on page 32 Chapter 2 2.3.4 1,2-Bis[bis(2-pyridyl)phosphino]ethane, dpype The procedure for synthesis of dpype has been published by our research group12 and is identical to that for PN 3 described in the previous Section, except Cl2P(CH2)2PCl2 (6 mL, 40 mmol) is used in place of PC13. The l,2-bis(dichlorophosphino)ethane, which only became commercially available mid-way through this thesis work, was made from C2H4, white phosphorus, and PCI3 according to a literature method13 and was kindly donated by Dr. M . B. Smith of this group. Yield: 10.9 g (68%). Anal. Calcd for C22H20N4P2: C, 65.66; H, 5.01; N, 13.92%. Found: C, 65.56; H, 5.31; N, 13.59%. ! H NMR: 8 2.5 (t, 4H a, 2JRP 4 Hz), 7.10 (dddd, 4H5), 7.41 (m, 4H3), 7.52 (ddd, 4H4), 8.63 (dd, 4^). 3 1P{1H} NMR: 5 -6.1 (s). UV-Vis (CH2CI2, 1 mM): 240 [2330], 268 [2430], 300 [2540], (cf lit. 234, 255-272, solid state for dppe).14 IR (KBr): 1568, 1448, 1417 (s, py skeletal bands).7 m.pt.: 132-133°C. The N M R data agree well with literature data,12 while the LR, UV-Vis, and m.pt. data have not been reported previously. 2.3.5 Racemic l,2-Bis[bis(2-pyridyl)phosphino]cyclopentane, dpypcp The synthetic procedure for dpypcp has been published by our group15 and is identical to that for dpype, described in the previous Section, except fraws-l^fCLP^CsHg (7 mL, 40 mmol) is used in place of PCI3. The l,2-bis(dichlorophosphino)cyclopentane was made from CsHg, white phosphorus, and PC13 according to a literature method16 and was again kindly donated by Dr. M . B. Smith. The final crop was obtained as a cream coloured powder. Yield: 6.64 g (37%). Anal. Calcd for C25H24N4P2: C, 67.87; H, 5.57; N, 12.66%. Found: C, 67.81; H , 5.49; N, 12.54%. ! H NMR: 5 1.74 (qn, 2H a), 1.97 (m, 2Hb), 2.38 (m, 2Hb), 3.90 (ddd, 2 H c ) , 6.49 (dddt, 4H5), 6.87 (dtt, 4 H 4 ) , 7.39 (tt, 4H3), 8.47 (ddt, 4He). 3 1P{1H} NMR: 8 -2.2 (s). UV-Vis (CH 2C1 2, 1 mM): 238 [2330], 268 [2430], 308 [2720]. IR (KBr): 1568, 1446, 1412 (s, py skeletal bands).7 m.pt.: 112-114°C. Again, the NMR data agree well with literature data,15 while the IR, UV-Vis, and m.pt. data have not been reported previously. The compound was obtained as a racemic mixture of R,R and S,S enantiomers, the chirality designators referring to the C a atoms of the cyclopentane backbone. No effort was made to separate the racemate. 2.3.6 l,2-Bis(diphenylphosphino)ethane, dppe The title ligand was prepared by a modification of the literature procedure.17 Liquid N H 3 (65 mL) was collected in a round bottom flask (250 mL) fitted with an ammonia condenser 26 Chapter 2 references on page 32 Chapter 2 apparatus and cooled to -78°C (acetone/C02(s) bath).6 To the NH 3(/) was added Na metal (1.5 g, 65.3 mmol) with stirring for 10 min after which PPh3 (5.7 g, 21.7 mmol) was added with further stirring for 5 min. A mixture of excess 1,2-dichloroethane (6.0 g, 60.6 mmol) in Et 2 0 (2 mL) was added dropwise to the reaction mixture. The reactor was allowed to warm to r.t. to boil off the NH3(/) and the resulting white solid was collected by filtration and washed with H 2 0 (2 x 25 mL) and MeOH (4x2 mL). Recrystallization from hot «-PrOH yielded white crystals which were dried overnight in vacuo. Yield: 2.60 g (64%). Anal. Calcd for C 2 6 H 2 4 P 2 : C, 78.37; H , 6.07%. Found: C, 77.70; H, 6.49%. ! H NMR: 8 2.49 (m, 4H, methylene), 7.35-7.75 (m, 20H, phenyl). 3 1P{ !H} NMR: 8 -13.2 (s). m.pt.: 136-141°C (lit. 140-142°C). 1 7 The spectroscopic data match those found in the literature.18 2.4 Nickel Precursor Compounds The paramagnetic compounds NiX 2(PPh 3) 2 (X = CI, Br, I) and the diamagnetic compounds NiX 2(PPh 3) 2 (X = NCS, N0 3 , CO) were prepared as follows. All 3 1P{ 1H} and X H N M R data were measured at 121.42 and 300 MHz, respectively, at r.t. in ; CDCl 3 . All syntheses, except that of Ni(CO)2(PPh3)2, were conducted aerobically. . 2.4.1 NiCl 2(PPh 3) 2 This compound was prepared following^ a literature method12 which was itself an adaptation of one previously published.19 Bright-green N i C l 2 « 6 H 2 0 (31.2 g, 130 mmol) was dissolved in glacial HOAc (700 mL) to yield a bright-yellow solution. To a second vessel containing glacial HOAc (450 mL) was added PPh3.(73.2 g, 280 mmol); heating at 60°C for 10 min resulted in a colourless solution. A dark-green mixture was obtained instantly upon addition of the PPh3 solution to the NiCl 2 solution. A dark-green powdered solid was isolated via filtration, washed with glacial HOAc (3 x 20[ mL) to remove starting reagents, washed with water (10 x 100 mL) to remove HOAc, and dried in vacuo overnight. Yield: 59.9 g (70%). The complex is susceptible to thermal decomposition if heat is applied in vacuo. Anal. Calcd for C 3 6 H 3 0 Cl 2 NiP 2 : C, 66.09; H, 4.62%. Found: C, 66.10; 4.69%. UV-Vis (CH 2C1 2, 1 mM): 548 [95], 406 [1720], 308 [1710], 266 [1890], 242 [1950], m.pt.: 239-241°C (lit. 247-250).19 The Xmax values are within ± 2 nm of those reported previously, whereas the s values are up to 50% less than those reported previously.11 • 27 Chapter 2 references on page 32 Chapter 2 2.4.2 NiBr2(PPh3)2 This compound was prepared by a literature method.19 The yellow anhydrous NiBr 2 (1.28 g, 5.83 mmol) was dissolved in w-BuOH (10 mL) to yield a dark-green solution. A colourless solution of PPh3 (3.18 g, 12.1 mmol) in w-BuOH (30 mL) was obtained by heating the mixture at 60°C for 5 min. A vibrant light-green mixture was obtained instantly upon addition of the PPh3 solution to the NiBr 2 solution with the concomitant formation of a precipitate. The mixture was stirred for 1 h after which a dark-green solid and bright-green liquor were separated via filtration. A second portion of green solid was obtained upon rotary evaporation of the green liquor. The two portions were then combined and washed with «-BuOH (4x10 mL) and dried in vacuo overnight. Yield: 3.64 g (84%), Anal. Calcd for C 3 6 H 3 0 Br 2 NiP 2 : C, 58.18; H , 4.07%. Found: C, 58.33; H, 3.97%. UV-Vis (C 6 H 6 , 1 mM): 576 [110], 424 [1200], 302 [2920], 256 [810], 236 [970]. m.pt.: 213-217°C (lit. 215°C) . 1 9 The values match those reported previously, but some of the s values are different.11 2.4.3 NiI2(PPh3)2 This compound was prepared following an adaptation of a literature method.19 A mixture of N i I 2 . 6H 2 0 (0.691 g, 1.64 mmol) and PPh3 (0.8600 g, 3.279 mmol) in «-BuOH (20 mL) was heated at 60°C for 5 min, whereupon a purple/black solution was obtained. The flask was cooled to r.t., affording a purple/black precipitate of NiI2(PPh3)2. The solid was isolated via filtration, washed with cold H - B U O H ( 4 X 5 mL), and then dissolved in TFTF (20 mL) in an N2-flushed Schlenk tube to yield a dark-purple solution. This solution was then filtered under N 2 to remove traces of unreacted N i I 2 « 6 H 2 0 and diluted with hexanes (40 mL) to re-precipitate the desired product, which was collected via filtration, washed with hot Et 2 0 (4x5 mL) to remove unreacted PPh3, and dried in vacuo overnight. Yield: 0.623 g (47%). Anal. Calcd for C 3 6 H 3 0 I 2 NiP 2 : C, 51.65; H , 3.61%. Found: C, 51.77; H , 3.85%. UV-Vis (TFTF): 514 [125]. m.pt.: 211-213°C (lit. 218°C) . 1 9 The UV-Vis data differ from those reported (425 [2500], 2-butanone solvent),20 but Xmax is similar to those observed for the NiI2(P-P) species obtained in this current work (Section 3.2.1, p.35). 28 Chapter 2 references on page 32 Chapter 2 2.4.4 trans - Ni(NCS)2(PPh3)2 An adaptation of a literature method was followed.19 Ni(N0 3) 2 • 6 H 2 0 (1.75 g, 6.00 mmol) was dissolved in «-BuOH (125 mL) in a flask equipped with a reflux condenser to yield a bright light-green solution. The solution was then refluxed at 117°C for 2 h upon addition of K S C N (1.75 g, 18.0 mmol). The mixture was cooled to r.t. and then filtered to remove unreacted K S C N and KNO3 by-product, resulting in a green solution of Ni(SCN) 2 (~ 0.48 M assuming 100% yield). To a 20 mL aliquot of the alcoholic Ni(SCN) 2 solution (~ 0.96 mmol) was added a hot solution of PPh3 (0.75 g, 2.86 mmol) in /?-BuOH (20 mL) and the mixture was refluxed for 1 h and then allowed to cool to r.t. overnight. A red, microcrystalline product was isolated via filtration, washed with hot Et 2 0 ( 4 x 5 mL) to remove unreacted PPh3, and dried in vacuo overnight. Yield: 614 mg (91%). Anal. Calcd for C 3 gH 3 0 N 2 NiP 2 S 2 : C, 65.25; H, 4.32; N, 4.01%. Found: C, 65.46; H , 4.28; N, 4.04%. UV-Vis (CHC13, 70 uM): 410 (7790). 3 1P{ !H} NMR. 5 11.2 (s). m.pt.: 211°C (lit. 217°C) . 1 9 There are currently no UV-Vis or NMR data reported in the literature. Rapid cooling of the reaction mixture results in the product being formed as an orange powder. 2.4.5 Ni(N03)2(PPh3)2 A literature method was followed.19 Ni(N0 3 ) 2 -6H 2 0 (1.42 g, 4.90 mmol) was dissolved in glacial HO Ac (40 mL) to yield a pale-green solution. To this was added a solution of PPh3 (2.59 g, 9.90 mmol) in glacial HOAc (40 mL) fdrmed by heating at 60°C for 10 min. The resulting bright-green solution immediately began to precipitate a green, microcrystalline solid. The mixture was stirred overnight and then the solid was isolated via filtration, washed with glacial HOAc (4x5 mL), water (4 x 10 mL), and dried in vacuo overnight. Yield: 3.01 g (87%). Anal. Calcd for C 3 6 H 3 0 N 2 NiO 6 P 2 : C, 61.13; H, 4.28; N, 3.96%. Found: C, 60.92; H , 4.20; N, 3.97%. lH NMR: 8 7.5-7.7 (m, phenyl). 3 1P{1H} NMR: 8 36.72 (br, s). UV-Vis (THF, 3.6 mM): 406 [20], 310 [420], 266 [380]. m.pt.: 227-228°C (lit. 224-227°C) . 1 9 No UV-Vis or N M R data have been published to date. 29 Chapter 2 references on page 32 Chapter 2 2.4.6 Ni(CO) 2(PPh 3) 2 (190) This Ni(0) compound was prepared following a literature method.21 To an N2-flushed Schlenk tube containing NiCl 2(PPh 3) 2 (9.95 g, 15.2 mmol) was added freshly distilled THF (100 mL), this resulting in a dark-green suspension. Zinc dust (1.31 g, 20.0 mmol) was added under a stream of N 2 and then CO was bubbled through the stirred reaction mixture for 2 h via a long syringe needle with use of a venting needle. The solution was then filtered through a frit to remove the zinc dust and ZnCl 2 by-product; this resulted in a bright-yellow solution which was then chilled in an ice/water-bath. A chilled 1:1 EtOH/H 2 0 mixture (50 mL) was then slowly added to the solution, this resulting in the formation of light-yellow, crystalline needles of Ni(CO)2(PPh3)2. This was collected via filtration (in air) and a second aliquot of EtOH/H 2 0 was added to the mother liquor to yield a second crop of product. This process was repeated four times after which time no more product was observed in the mother liquor. The four crops were combined, washed with EtOH/H 2 0 (2 x 10 mL) and Et 2 0 ( 4 x 5 ml), and dried in vacuo overnight. Yield: 9.01 g (93%). Anal. Calcd for C 3 g H 3 0 NiO 2 P 2 : C, 71.39, H, 4.73%. Found: C, 71.13; H, 4.78%. ! H NMR: 8 7.1-7.4 (m, phenyl) (lit. 7.1-7.4).12 "P^H} NMR: 5 32.8 (s) (lit. 32.8).12 IR (CH2C12): 1997, 1936 (s, CO) (lit. 1998, 1932).21 m.pt.: 211°C (lit. 210-215°C) . 2 2 2.5 Growth of Crystals for X-Ray Analysis The setup shown in Figure 2.2 was used to grow crystals of the compounds listed in Sections 2.5.1-2. The inner solvent (A) is relatively volatile (vs. solvent B) and completely evaporates through the vent holes in 3-5 days, while the outer solvent (B) is also quite volatile and diffuses into the inner solvent while evaporating from the chamber at a slightly slower rate than solvent A. Other setups involving layering of solvent B on top of solvent A were only successful for [Ni(PN3)2]Cl2 (see below). 30 Chapter 2 references on page 32 Chapter 2 plastic cap with holes punched through to allow evaporation inner vial (4 mL capacity) with compound dissolved in solvent A (~ 1 mL) outer vial (18 mL capacity) with solvent B (~ 1 mL) Figure 2.2 Crystallization chamber employed in growing crystals of dpypcp and Ni(CO)2(P-P) and NiX2(P-P) complexes aerobically for X-ray analysis; samples of the complex were in the 5-10 mg range. 2.5.1 Ni(CO)2(P-P) complexes Yellow crystals ofNi(CO)2(dpypcp) (Section 4.2.1.6, p.85) were obtained within 5 d from the setup shown in Figure 2.2 with solvent A = CH 2C1 2 and solvent B = hexanes, while yellow crystals of Ni(CO)2(dpype) (Section 4.2.1.5, p.85) were obtained with solvent A = EtOH and solvent B = hexanes although these latter crystals did not diffract well. 2.5.2 NiX2(P-P) complexes Orange, violet, or purple crystals of NiX2(dpypcp) (X = CI, Br, I, respectively; Section 3.2.1, p.35) were obtained within 2 d from the setup shown in Figure 2.2 with solvent A = CH 2C1 2 and solvent B = hexanes. Crystals of the analogous dpype complexes (Section 3.2.1, p.35) were obtained in the same manner but required numerous attempts as solutions of the compounds were highly prone to decomposition prior to crystal growth. 2.5.3 [Ni(PN3)2]Cl2 Violet crystals of the title compound would grow under almost any conditions. Simple evaporation of the 7-BuOH solvent from the reaction mixture (Section 3.2.2.2, p.39) would result in crystals after ~ 1 week. Layering of hexanes over the afore-mentioned mixture consistently resulted in crystals being obtained overnight. 31 Chapter 2 references on page 32 Chapter 2 2.5.4 dpypcp Yellow crystals of this compound were obtained within 2 d from the set-up shown in Figure 2.2 with solvent A = CH 2C1 2 and B = hexanes. 2.6 Deoxygenation of Solvents by N2(g) Sparging Apart from employing standard freeze-pump-thaw techniques, solvents were also occasionally de-oxygenated by bubbling N 2 through them for 30 min using a sparging apparatus, consisting of a Schlenk tube equipped with a glass pipe to which has been fused a high porosity air-stone (Figure 2.3). N 2 glass rod with an air-stone attached at the end solvent to be sparged rubber septum with large bore hole N 2 out to bubbler air-stone Figure 2.3 Apparatus for de-oxygenating solvents by sparging. 2.7 References 1. Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals, 2nd ed.; Oxford: Pergamon, 1980. 2. Isotope Pattern Calculator, v. 1.6.5. L. Arnold, THINK Technologies Inc., 1990. 3. H 2 has a thermal conductivity greater than He, resulting in a negative peak. See HP 5890A Gas Chromatograph Reference Manual, Hewlett-Packard Company, 2086, vol. I, p. 11-39. 32 Chapter 2 references on page 32 Chapter 2 4. Maisonnat, A.; Farr, J. P.; Olmstead, M . M. ; Hunt, C. T.; Balch. A. L. Inorg.Chem. 1982, 21, 3961. 5. Xie, Y.; James, B. R. J. Organomet. Chem. 1991, 417, 277. 6. Gordon, A. J.; Ford, R. A. The Chemist's Companion, New York: Wiley, 1972. 7. Silverstein, R. M . ; Bassler, G. C ; Morrill, T. C. Spectrometry Identification of Organic Compounds, 5th ed., New York: John Wiley & Sons, Inc., 1991. The IR bands for pyridine are reported here and correspond well with those observed for the pyridyl ligands. 8. Mann, F. G ; Watson, J. J. Org. Chem. 1948,13, 502. 9. Jakobsen, H. J. J. Mol. Spectrosc. 1970, 34, 245. 10. Schutte, R. P. Ph. D. Thesis. University of British Columbia, 1995. 11. Baird, I. R. B. Sc. Thesis. University of British Columbia, 1994. 12. Baird, I. R.; Smith, M . B.; James, B. R. Inorg. Chim. Acta 1995, 235, 291. 13. Burt, R. J.; Chatt, J.; Hussain, W.; Leigh, G. J. J. Organomet. Chem. 1979, 182, 203. 14. Frem, R. C. G.; Massabni, A. C ; Massabni, A. M . G.; Maruro, A. E. Inorg. Chim. Acta 1997, 255, 53 15. Jones, N. D.; MacFarlane, K. S.; Smith, M B . ; Schutte, R. P.; Rettig, S. J.; James, B. R. Inorg. Chem. 1999, 38, 3956. 16. Allen, D. L.; Gibson, V. C ; Green, M . L. H ; Skinner, J. F.; Grebenik, P. D.; Bashkin, J. J. Chem. Soc, Chem. Commun. 1983, 895. 17. Hewertson, W.; Watson, H. R. J. Chem. Soc. 1962, 1490. 18. Grim, S.; Briggs, W.; Barth, R.; Tolman, C ; Jesson, J. Inorg. Chem. 1974,13, 1095. 19. Venanzi, L. M . J. Chem. Soc. 1958, 719. 20. Cotton, F. A.; Faut, O. D.; Goodgame, D. M . L. J. Am. Chem. Soc. 1960, 83, 344. 21. Giannoccaro, P.; Sacco, A.; Vasapollo, G. Inorg. Chim. Acta 1979, 37, L455. 22. Gaffhey, T. R.; Ibers, J. A. Inorg. Chem. 1982, 21, 2860. 33 Chapter 2 references on page 32 Chapter 3 CHAPTER THREE The Synthesis, Characterization, Reactivity, and Aqueous Solution Chemistry of Ni(II) 2-Pyridylphosphine Complexes 3.1 Introduction The first Ni(II) phosphine complex prepared was NiCl2(PEt3)2 in 1936.1 As a substantial number of Ni(II) phosphine complexes have been prepared since,2 this brief introduction will focus primarily on NiX2(PPh3)2 and NiX2(dppe) (X = halide). Accordingly, NiX2(PPh3)2 complexes have been used as catalysts for oligomerizations,3'4 living radical polymerizations,5'6 cyclizations,7 transfer hydrogenations,8 Aldol reactions,9 and numerous coupling reactions.10-15 Related Ni(Y)2(PPh3)2 species (Y = mono anion) have also catalyzed oligomerizations,16"21 OO O ^ Ovl O ^ o** polymerizations, ' silylations, and copolymerizations. Various polymerizations, n O Q oo hydroborations, and couplings reactions ' have been successfully catalyzed by NiX2(dppe) complexes. Although coordination chemistry of the PNX ligands is considerably diverse and well established (see Section 1.4.2, p. 7), the chemistry of Ni(II) 2-pyridylphosphine complexes is in its infancy, with most work having originated at UBC, with the preparation of NiBr2(dpype) and NiX2(PNx)2 (X = Cl, Br) type species.30 This Chapter (Section 3.3.1) describes the preparation and characterization (including five X-ray crystal structures) of ten P-coordinated NiX2(P-P) species (X = Cl, Br, I, SCN, and N0 3; P-P = dpype and dpypcp). The aqueous chemistry of these halo species and the NiX2(PNx)2 complexes of Baird et al.30 is examined in Section 3.3.2, along with the preparation of novel [Ni(H20)2(P-P)](PF6)2 species (P-P = dppe, dpype, dpypcp). The formation of tetrahedral, P,7V-chelated NiCl2(PN3).H20 from Ni(CO)2(PPh3)2, and its conversion to octahedral, TV'iV7-chelated [Ni(PN3)2]Cl2 is discussed in Section 3.3.3, along with the X-ray crystal structure and reactivity of the latter species. An examination of the spectroscopic characteristics of dpype and dpypcp, including the X-ray crystal structure of both ligands, is also presented in Section 3.3.1. NiCl2(PN3)2 • 2H20 has also been prepared for the first time. 34 Chapter 3 references on page 76 Chapter 3 3.2 Experimental 3 1P{1H} and ! H NMR spectra were measured at 121.42 and 300 MHz, respectively, in CDC13 at r.t. unless otherwise noted; J are in units of Hz; *H assignments (H a, H b , He, H 3 . 6) are shown in Figure 3.1 (p.47). UV-Vis spectra were measured in CH2CI2 (0.7 mM) unless otherwise noted. All ER spectra were measured as KBr pellets and the assignment of bands will be discussed in Section 3.3.1. 3.2.1 Preparation of Diamagnetic Ni(II) 2-Pyridylphosphine Compounds 3.2.1.1 NiCl2(dpype) (la) To an N2-flushed Schlenk tube containing dpype (10.5 mg, 26.2 pmol) and NiCl 2(PPh 3) 2 (16.5 mg, 25.3 pmol) was added THF (20 mL); the orange solution was stirred for 3 h at r.t. and filtered. The filtrate was reduced in volume to ~ 5 mL in vacuo and hexanes (15 mL) was added to precipitate a bright orange solid, which was collected, washed with hot Et 20 (4x5 mL), and dried in vacuo overnight. Yield: 10.9 mg (81%). Anal. Calcd for C22H2oCl2N4P2Ni: C, 49.69; H, 3.79; N, 10.53%. Found: C, 49.80; H, 3.66; N, 9.98%. T i NMR: 8 2.72 (d, 4H a, 2JHP 14), 7.35 (m, 4H5), 7.75 (m, 4 H 4 ) , 8.45 (m, 4H3), 8.70 (m, 4 H 6 ) . "P^H} NMR: 8 61.8 (s). UV-Vis: 464 [1615]. IR: 1570, 1448, 1421 (s, py skeletal bands).31 EIMS (m/z): 532 [M*] , 496 [M-Clf. m.pt.: ~ 240°C (dec). A M : 148 (MeOH), 230 (H20). The synthesis of la was also attempted via reaction of dpype with NiCl 2 .6H 2 0 in toluene, MeOH, acetic acid, DMSO, or toluene/MeOH (1:1). An uncharacterized dark green solid was obtained in all cases. 3.2.1.2 NiCl2(dpypcp) (lb) The procedure used was as for la, but using dpypcp (34.0 mg, 76.9 umol) and NiCl 2(PPh 3) 2 (46.4 mg, 71.0 pmoi); an orange solid was obtained. Yield: 27.2 mg (67%). Anal. Calcd for C 2 5H 2 4 C1 2 N4P2M: C, 52.48; H, 4.24; N, 9.80%. Found: C, 52.43; H , 4.48; N, 9.49%. ! H NMR: 5 1.40 (m, 2Ha), 1.91 (dm, 4Hb), 3.45 (m, 2Hc), 7.40 (qt, 4H5), 7.82 (dt, 4H3), 8.08 (d, 2H6), 8.72 (d, 4 H 4 ) , 9.02 (d, 2Hfi). 3 1P{1H} NMR: 8 29.3 (s). UV-Vis: 478 [1200]. IR: 1568, 1445, 1419 (s, py skeletal bands). EIMS (m/z): 572 pvf], 536 [M-C1]+. m.pt.: ~ 260°C (dec). A M : 185 (MeOH), 230 (H20). 35 Chapter 3 references on page 76 Chapter 3 3.2.1.3 NiBr2(dpype) (2a) The procedure used was as for la, but using dpype (21.0 mg, 52.1 umol) and anhyd. NiBr 2(PPh 3) 2 (39.4 mg, 53.1 umol); a red/orange solid was obtained. Yield: 26.3 mg (82%). Anal. Calcd for C 2 2 H 2 0 B r 2 N 4 P 2Ni: C, 42.57; H, 3.25; N, 9.03%. Found: C, 42.75; H, 3.14; N, 9.11%. ! H NMR: 5 2.76 (d, 4H a, 2JHP 14), 7.52 (m, 4H5), 7.83 (m, 4FL;), 8.42 (m, 4H3), 8.70 (m, 4He). 3lV{lK) NMR: 5 71.7 (s). UV-Vis: 478 [2100]. IR: 1568, 1446, 1420 (s, py skeletal bands). EIMS (m/z): 620 pvf], 540 [M-Br]+. m.pt.: ~ 240°C (dec). A M : 181 (MeOH), 257 (H20). The NMR data match those reported for 2a -toluene.30 3.2.1.4 NiBr2(dpypcp) (2b) The procedure used was as for la, but using dpypcp (24.1 mg, 54.5 umol) and anhyd. NiBr 2(PPh 3) 2 (39.7 mg, 53.5 umol); a red solid was obtained. Yield: 30.6 mg (87%). Anal. Calcd for C 25H 2 4Br 2N4P 2Ni: C, 45.43; H, 3.66; N, 8.48%. Found: C, 43.77; H, 3.68; N, 7.97%. ! H NMR: 5 1.35 (m, 2Ha), 1.85 (dm, 4Hb), 3.50 (m, 2FL,), 7.41 (m, 4H5), 7.84 (dt, 4H3), 8.05 (d, 2He), 8.72 (t, 4H4), 9.10 (d, 2H 6). 3 1P{1H} NMR: 6 37.1 (s). UV-Vis: 492 [1460]. IR: 1570, 1447, 1420 (s, py skeletal bands). EIMS (m/z): 661 [Nf], 581 [M-Br]+. m.pt.: ~ 260°C (dec). A M : 165 (MeOH), 261 (H20). 3.2.1.5 Nil2(dpype) (3a) The procedure used was as for la, but using dpype (10.6 mg, 26.3 umol) and NiI2(PPh3)2 (21.9 mg, 26.2 umol), a dark-purple solid was obtained. Yield: 17.1 mg (91%). Anal. Calcd for C 2 2 H 2 0 I 2 N4P 2 Ni: C, 36.96; H, 2.82; N, 7.84%. Found: C, 37.10; H, 2.99; N, 7.59%. *H NMR: 5 2.60 (d, 4H a, 2JHP 16), 7.36 (m, 4H5), 7.80 (m, 4 H 4 ) , 8.40 (m, 4H3), 8.67 (m, 4^). ^{'H} NMR: 8 81.8 (s). UV-Vis: 520 [1550]. IR: 1566, 1445, 1420 (s, py skeletal bands). EIMS (m/z): 714 [M+], 588 [M-I]+. m.pt.: ~ 240°C (dec). A M : 182 (MeOH), 250 (H20). 3.2.1.6 Nil2(dpypcp) (3b) The procedure used was as for la, but using dpypcp (17.2 mg, 38.8 umol) and NiI2(PPh3)2 (31.6 mg, 37.8 umol); a dark-purple solid was obtained. Yield: 26.6 mg (93%). Anal. Calcd for C 2 5H 2 4I 2N4P 2Ni: C, 39.77; H, 3.20; N, 7.42%. Found: C, 39.91; H, 3.12; N, 7.19%. lH NMR: 8 1.30 (m, 2Ha), 1.79 (dm, 4Hb), 3.48 (m, 2Hc), 7.43 (dtd, 4H5), 7.84 (dt, 4H3), 8.08 (d, 2H6), 8.74 (dd, 4 H 4 ) , 9.06 (d, 2He). 3 1P{1H} NMR: 8 45.2 (s). UV-Vis: 534 [1630], ER: 1568, 36 Chapter 3 references on page 76 Chapter 3 1445, 1419 (s, py skeletal bands). EJMS (m/z): 754 PVT], 628 [M-I]+. m.pt.: ~ 260°C (dec). A M : 188 (MeOH), 235 (H 20). 3.2.1.7 Ni(NCS)2(dpype) (4a) The procedure used was as for la, but using dpype (20.3 mg, 50.4 pmol) and Ni(NCS)2(PPh3)2 (45.3 mg, 64.7 pmol); a bright-yellow solid was obtained. Yield: 20.2 mg (70%). Anal. Calcd for C 2 4 H 2 0 N 6 NiP 2 S 2 : C, 49.94; H, 3.49; N, 14.56%. Found: C, 49.58; H , 3.44; N, 14.23%. T i NMR: 8 2.86 (d, 4FL, 2JHP 16), 7.50 (td, 4H5), 7.90 (td, 4FL»), 8.22 (m, 4F£3), 8.76 (d, 4H6). ^Pl/H} NMR: 8 63.3 (s). UV-Vis: 440 [2825]. IR: 1568, 1448, 1422 (s, py skeletal bands); 2077 (s, CN); 816 (w, CS). ELMS (m/z): 577 rjVf], 519 [M-SCN] +. m.pt.: ~ 232°C (dec). A M : 165 (MeOH), 215 (H 20). 3.2.1.8 Ni(NCS)2(dpypcp) (4b) The procedure used was as for la, but using dpypcp (43.3 mg, 97.8 pmol) and Ni(NCS)2(PPh3)2 (55.3 mg, 79.1 pmol), a yellow solid was obtained. Yield: 34.9 mg (72%). Anal. Calcd for C 2 7 H 2 4 N 6 NiP 2 S 2 : C, 52.54; H, 3.92; N, 13.61%. Found: C, 51.94; H , 3.92; N, 12.92%. ! H N M R : 8 1.32 (m, 2Ha), 1.88 (dm, 4Hb), 3.46 (m, 2Hc), 7.41 (m, 4H5), 7.98 (m, 4H3), 8.58 (m, 4H0, 8.92 (m, 4H6). ^Pl/H} NMR: 8 30.3 (s). UV-Vis: 452 [1595]. LR: 1567, 1447, 1421 (s, py skeletal bands), 2073 (s, CN), 845 (w, CS). ELMS (m/z): 559 [M-SCN] +. m.pt.: ~ 235°C (dec). A M : 120 (MeOH), 229 (H 20). 3.2.1.9 Ni(N03)2(dpype) (5a) To an N2-flushed Schlenk tube containing dpype (23.6 mg, 58.6 pmol) and Ni(N0 3) 2(PPh 3) 2 (40.5 mg, 57.3 pmol) was added CH 2C1 2 (6 mL) to yield a dark-green solution. After 20 min at 70°C, a yellow precipitate formed; this was collected and more solid formed upon addition of hexanes (9 mL) to the filtrate. A third batch of yellow solid was obtained upon evaporation of the filtrate in vacuo. Yield: 18.4 mg (55%). Anal. Calcd for C 2 2H 2oN60 6NiP 2: C, 45.16; H, 3.45; N, 14.36%. Found: C, 45.33; H, 3.55; N, 13.98%. T i NMR: 8 2.91 (d, 4H a, 2JHP 14), 7.47 (m, 4H5), 7.75-8.08 (m, 8H for H 3 and H 4 ) , 8.70 (d, 4He).  31P{ lrl} NMR: 8 63.2 (s). UV-Vis: 408 [270]. IR: 1569, 1448, 1421, 749 (s, py skeletal bands); 1726, 1693 (w, N0 3 ); 1436, 1382, 984, 699 (s, N0 3). ELMS (m/z): 585 [ M l , 523 [M-N0 3] + . A M : 192 (MeOH), 295 (H 20). 37 Chapter 3 references on page 76 Chapter 3 3.2.1.10 Ni(N03)2(dpypcp) (5b) The procedure used was as for 5a, but using dpypcp (57.2 mg, 129 pmol) and Ni(N03)2(PPh3)2 (79.2 mg, 112 pmol); a yellow solid was obtained. Yield: 34.9 mg (72%). Anal. Calcd for C 2 5 H 2 4 N 6 0 6 N i P 2 : C, 48.03; H, 3.87; N, 13.44%. Found: C, 48.21; H, 3.98; N, 13.12%. 'HNMR: 6 1.36 (m, 2FL), 1.90 (dm, 4Hb), 3.43 (m, 2FL), 7.49 (m, 4H5), 7.92 (m, 4H3), 8.64 (m, 4H4), 8.98 (m, 4He). 31P{XH} NMR: 5 28.4 (s). UV-Vis: 406 [245]. TR: 1571, 1449, 1421, 744 (s, py skeletal bands); 1697, 1671 (w, N0 3); 1433, 1382, 988, 695 (s, N0 3 ) . ELMS (m/z): 625 Pvf], 563 [M-N0 3] + . A M : 184 (MeOH), 277 (H 20). 3.2.1.11 [Ni(H20)2(dpype)](PF6)2 (6a) From NiI2'6H20: To an N2-flushed Schlenk tube containing dpype (26.7 mg, 66.4 pmol) and N i l 2 . 6H 2 0 (30.9 mg, 73.5 pmol) was added reagent grade MeOH (5 mL) to yield a purple solution. Addition of 2 equiv. of KPF 6 (24.7 mg, 134 pmol) and stirring at r.t. for 20 s yielded an orange solution and yellow precipitate. The yellow solid was collected and dried in vacuo overnight. Yield: 21.9 mg (38%). Anal. Calcd for C 2 2H 24N 40 2NiP4Fi 2: C, 33.62; H , 3.08; N, 7.12%. Found: C, 33.47; H, 3.17; N, 6.91%. T i NMR (CD 3OD): 5 3.11 (d, 4H a, 2 JHP 20), 7.80 (m, 4H5), 7.65 (m, 4Ht), 7.75 (m, 4H3), 8.80 (m, 4Hfi). 31V{lU} NMR (CD 3OD): 8 58.2 (s), -141.4 (sept, PF 6); (CDC13): 8 55.6 (s), -141.7 (sept, PF 6); (dmso-fik): 5 62.0 (s), -141.1 (sept, PF 6). TR: 1571, 1448, 1422 (s, py skeletal bands); 837, 558 (m, PF 6); 764, 648 (m, Ni-OH 2). ELMS (m/z): 787 [M+]. A M : 205 (MeOH). From NiCl2(dpype): To an N2-flushed Schlenk tube containing NiCl2(dpype) (14.2 mg, 26.7 pmol) was added CH 2C1 2 (7 mL) to yield an orange solution. Addition of 2 equiv. of aq. KPF 6 (9.98 mg, 54.2 pmol; in 2 mL H 2 0) via a syringe resulted in a yellow organic phase and a colourless aqueous phase after 90 min. The organic phase was extracted via a cannula into a second Schlenk tube and diluted with Et 2 0 (10 mL), when a yellow precipitate formed. The solid was collected, washed with H 2 0 ( 2 x 5 mL) to remove KC1 by-product, and dried in vacuo overnight. The solid was dissolved in CH 2C1 2 and purified by column chromatography (300-mesh silica gel, Fisher) to remove free dpype and dpype oxide impurities by first eluting with Et 2 0/CH 2 C1 2 (1:9); 6a was eluted with MeOH/CH 2 Cl 2 (1:9). Yield: 4.6 mg (22%). ^Pl/H} N M R (dmso-J6): 8 62.2 (s), -141.1 (sept, PF 6); the data match those from the first synthetic method. 38 Chapter 3 references on page 76 Chapter 3 3.2.1.12 [Ni(H20)2(dpypcp)](PF6)2 (6b) The procedure used was as for 6a, but using dpypcp (23.0 mg, 52.0 umol), NiI 2 .6H 2 0 (23.1 mg, 55.0 umol), and KPF 6 (20.2 mg, 110 umol); a yellow solid was obtained. Yield: 18.9 mg (44%). Anal. Calcd for C 2 5 H 2 8 N 4 0 2 NiP4Fi 2 : C, 36.30; H, 3.41; N, 6.77%. Found: C, 36.14; H, 3.22; N, 6.46%. 'H NMR: 5 1.42 (m, 2Ha), 1.79 (dm, 4 H B ) , 3.37 (m, 2IL), 7.49 (m, 4H5), 7.92 (m, 4H3), 8.64 (m, 4 H 4 ) , 8.98 (m, 4 H 6 ) . ^Pj'H} NMR (CD 3OD): 5 35.3 (s), -141.4 (sept, PF 6). IR: 1568, 1445, 1420 (s, py skeletal bands); 836, 558 (m, PF 6); 765, 650 (m, Ni-OH 2). EIMS (m/z): 827 [NT]. A M : 198 (MeOH). 3.2.2 Preparation of Paramagnetic Ni(JX) 2-Pyridylphosphine Compounds 3.2.2.1 NiCl2(PN3).H20 (P^V-coordinated) (7) Method 1: In an N2-flushed Schlenk tube, exposed to standard fluorescent laboratory light, Ni(CO)2(PPh3)2 (18.2 mg, 28.4 umol) and 3 equiv. of PN 3 (23.3 mg, 87.8 umol) were dissolved in CH 2C1 2 (5 mL); after 2 h at 80°C a bright-yellow solution and pale-blue precipitate were obtained. The solid was collected, washed with CH 2C1 2 ( 4 x 5 mL), and dried in vacuo overnight. Yield: 2.80 mg (25%). Anal. Calcd for Ci 5 Hi 2 Cl 2 N 3 PNi + H 20: C, 43.64; H, 3.42; N, 10.18%. Found: C, 43.85; H, 3.58; N, 9.28%. *H NMR (acetone-^): 5 7.35-8.70 (m, br, pyridyl), 2.8 (s, 1 H20). 3 1P{Tl} NMR (acetone-^): 5 -17.0 (br, s). UV-Vis (acetone-of6): 432 [160]. IR: 3364 (m, br, H-OH), 1635, 1621, 1585, 1560, 1458, 1431 (s, py skeletal bands); 1014 (s, py ring breathing). +LSIMS: 414 [M+], 358 [M-C1]+, 323 [M-2C1]+. m.pt.: ~ 330°C (dec.) A M : 139 (MeOH). u e f f: 3.31 B.M. Method 2: To an N2-charged Schlenk tube containing NiCl 2 • 6H 20 (29.5 mg, 124 umol) and PN 3 (32.0 mg, 121 umol) was added 1-BuOH (3 mL); a pale-blue suspension was obtained after 30 min at 65°C. The solid was collected and dried in vacuo overnight. Yield: 41.3 mg (83%). Characterization data match those reported above. 7 can also be prepared as described by Baird et al.30 (see Section 3.2.2.5). 3.2.2.2 [Ni(PN3)2]Cl2 (A/,A/',/Y"-coordinated) (8) Method 1: Method 1 for 7 was repeated and the solution/precipitate mixture was left exposed to standard fluorescent laboratory light for 12 d, when red/orange block crystals of 8 were first observed; no precipitate of 7 was visible after a further 3 d, and so the air-stable crystals 39 Chapter 3 references on page 76 Chapter 3 were collected. Yield: 1.69 mg (9%). The crystals were ground to a powder and dried in vacuo overnight to remove crystallized water molecules. Anal. Calcd for C3oH26Cl2N6P2Ni: C, 54.42; H , 3.96; N, 12.36%. Found: C, 54.31; H, 3.89; N, 11.98%. X H NMR (dmso-fife): 8 7.1-8.6 (m, br, pyridyl). ^Pl/H} NMR (dmso-tf6): no signal. UV-Vis (MeOH): 518 [15], 802 [10]. IR: 1584, 1560, 1459, 1426 (s, py skeletal bands), 1012 (s, py ring breathing). +LSLMS: 588 [M-2C1]+. m.pt.: ~ 205°C (dec). A M : 237 (H 20). peff: 3.20 B.M. 8 can also be prepared as described by Boggess and Zatko;32 see Section 3.3.3 for literature data. Method 2: To an N2-charged Schlenk tube containing NiCl 2 . 6H 2 0 (288 mg, 1.21 mmol) and P N 3 (965 mg, 3.64 mmol) was added 1-BuOH (7 mL); after 3 h at 65°C and upon addition of hexanes (30 mL), a pink precipitate of 8 .H 2 0 was obtained. Yield: 519 mg (65%). The solid was collected and dried in vacuo overnight. Anal. Calcd for C3oH 26Cl 2N 6NiP 2 + H 2 0 : C, 52.98; H, 4.15; N, 12.36%. Found: C, 53.12; H, 4.21; N, 11.87%. TL NMR (acetone-^): 8 7.1-8.6 (m, 24H, pyridyl). 3 1P{1H} NMR (acetone-fife): no signal. UV-Vis: 476 [15]. IR: 3420 (m, br, H -OH), 1583, 1560, 1459, 1426 (s, py skeletal bands). +LSLMS: 588 [M-2C1]+. m.pt.: ~ 70°C (desolvation noted), ~ 195°C (dec. to white solid), ~ 205°C (solid turns pale blue). Red/orange crystals of 8 were grown from a CH2CI2 solution of 8.H 20 with hexanes layered on top. 3.2.2.3 NiCl2(PN,)2.H20 (9a) This compound was prepared as per a literature method.30 To an N2-flushed Schlenk tube containing PNi (70.8 mg, 269 pmol) and N i C l 2 . 6 H 2 0 (31.8 mg, 134 pmol) was added glacial HOAc (3 mL); after 2 h at 40°C, a dark-green precipitate was obtained from the bright-green solution. The solid was collected and dried in vacuo overnight. Yield: 63.2 mg (70%). 3.2.2.4 NiCl2(PN2)2 (9b) The procedure used was as for 9a, but using P N 2 (95.0 mg, 360 pmol) and N i C l 2 . 6 H 2 0 (42.7 mg, 180 pmol); a light-blue/green solid was obtained.30 Yield: 101 mg (85%). 3.2.2.5 NiCl 2(PN 3) 2.2H 20 (9c) The procedure used was as for 9a, but using PN 3 (20.3 mg, 76.5 pmol), NiCl 2 • 6H 2 0 (25.2 mg, 38.2 pmol), and 1-BuOH (5 mL); a light-green solid was obtained. Yield: 9.8 mg (37%). Anal. Calcd for C3oH28N602P2Cl2Ni: C, 51.76; H, 4.05; N, 12.07%. Found: C, 51.88; H , 40 Chapter 3 references on page 76 Chapter 3 4.19; N, 11.88%. This compound has not been reported previously. Use of glacial HOAc instead of 1-BuOH yields 7, as previously observed.30 3.2.2.6 NiBr2(PNi)2.2H20 (10a) This compound was prepared as per a literature method.30 To an N2-flushed Schlenk tube containing a methanolic (3 mL) solution of PNi (77.2 mg, 293 umol) was added a solution of anhyd. NiBr 2 (31.8 mg, 146 umol) in toluene (4 mL). After 90 min at 50°C, a green slurry was obtained from which a lime-green solid was collected and dried in vacuo overnight. Yield: 65.1 mg (57%). 3.2.2.7 NiBr2(PN2)2.2H20 (10b) This compound was prepared as per a literature method.30 To an N2-flushed Schlenk tube containing P N 2 (150 mg, 567 umol) and anhyd. NiBr 2 (61.2 mg, 280 umol) was added 1-BuOH (3 mL); after 30 min at 60°C, and upon addition of hexanes (20 mL), a pale-green solid was obtained. This was collected and dried in vacuo overnight. Yield: 146 mg (67%). 3.2.2.8 NiBr2(PN3)2.2H20 (10c) The procedure used was similar to that of a literature method.30 To an N2-flushed Schlenk tube containing PN 3 (114 mg, 428 umol) and anhyd. NiBr 2 (46.6 mg, 213 umol) was added 1-BuOH (3 mL); after 5 min at 60°C, a purple solution was obtained. A pink precipitate formed on cooling the solution to 0°C, and addition of hexanes (10 mL) increased the yield. The solid was collected and dried in vacuo overnight. Yield: 133 mg (80%). 3.2.2.9 Attempted Preparation of NiI2(PN3)2 (11) To an N2-flushed Schlenk tube containing NiI 2 .6H 20 (20.9 mg, 49.7 umol) and P N 3 (25.3 mg, 95.2 umol) was added 1-BuOH (5 mL); a yellow solution formed within 5 min at 60°C, followed by a pink precipitate 12 h later at r.t. The solid was collected in air and dried in vacuo; this resulted in a beige-coloured solid which became pink again upon exposure to non-dried MeOH or acetone, H 2 0, or the atmosphere. EIMS (m/z) of the pink solid gave a peak at 588, attributable to [Ni(PN 3) 2] 2 + but the solid was not soluble in acetone. Note, 8.H 20 remains pink in vacuo, and is soluble in acetone. Anal. Calcd for C 3 0 H 2 4 I 2 N 6 P 2 Ni: C, 42.74; H, 2.87; N, 9.97%. Found: C, 38.57; H, 2.79; N, 7.77%. 41 Chapter 3 references on page 76 Chapter 3 3.2.3 Preparation of Diamagnetic Ni(II) Phenylphosphine Compounds 3.2.3.1 NiCl2(dppe) (12a) The procedure used was similar to a literature method.33'34 A green, alcoholic (1:2 MeOH/z'-PrOH, 21 mL) solution of NiCl 2 .6H 2 0 (447 mg, 1.63 mmol) was prepared at ~ 50°C in an N2-flushed Schlenk tube. The mixture was then cannulated into a second N2-flushed Schlenk tube containing a hot, z-PrOH (50 mL) solution of dppe (658 mg, 1.65 mmol). A red colour formed instantly, followed by a bright-orange gelatinous precipitate within 1 min. After 1 h, this solid was collected, washed with Et 2 0 (4x10 mL), and dried in vacuo overnight. Yield: 708 mg (82%). 31P{'H} NMR: 6 54.9 (s) (lit. 58.2).35 UV-Vis: 462 [1800] (lit. 463 [1700]).34 3.2.3.2 NiBr2(dppe) (12b) The procedure used was as for 12a, but using anhyd. NiBr 2 (26.0 mg, 119 pmol) in MeOH (1 mL) and dppe (45.9 mg, 115 pmol) in z-PrOH (2 mL); a pale-red solid was obtained. Yield: 61.8 mg (87%). 3 1P{1H} NMR: 5 63.4 (s) (lit. 66.4).35 UV-Vis: 478 [1840] (lit. 481 [1700]).34 3.2.3.3 Nil2(dppe) (12c) The procedure used was as for 12a, but using NiI 2 .6H 2 0 (46.1 mg, 110 pmol) in MeOH (5 mL), and dppe (44.5 mg, 112 pmol) in z-PrOH (5 mL); a dark-purple solid was obtained. Yield: 60.5 mg (78%). 3 1P{1H} NMR: 8 75.3 (s) (lit. 78.2).35 UV-Vis: 526 [2100] (lit. 521 [2000]).34 3.2.3.4 Ni(NCS)2(dppe) (12d) The procedure used was as for 4a, but using dppe (52.3 mg, 131 pmol) and Ni(NCS)2(PPh3)2 (95.6 mg, 137 pmol); a yellow solid was obtained. Yield: 57.2 mg (76%). 3 1P{1H} NMR: 8 57.7 (s). UV-Vis: 442 [2760]. Spectroscopic data have been previously reported for the Pd analogue (8P 69.5),36 but 12d appears to be new. 3.2.3.5 Ni(N03)2(dppe) (12e) The procedure used was as for 5a, but using dppe (44.1 mg, 111 pmol) and Ni(N0 3) 2(PPh 3) 2 (78.7 mg, 111 pmol); a yellow solid was obtained. Yield: 36.6 mg (57%). 3 1P{1H} NMR: 8 52.7 (s). UV-Vis: 406 [296]. This appears to be a new compound. 42 Chapter 3 references on page 76 Chapter 3 3.2.3.6 [Ni(H20)2(dppe)](PF6)2 (13) The procedure used was as for the second route of 6a, but using NiCl2(dppe) (16.7 mg, 31.7 pmol) and KPF 6 (15.0 mg, 81.5 pmol); a yellow solid was collected and dried in vacuo overnight. This was purified by column chromatography as per 6a. Yield: 3.12 mg (13%). Anal. Calcd for C 2 6 H 2 g F 1 2 N i 0 2 P 4 : C, 39.88; H, 3.60%. Found: C, 39.65; H, 3.48%. 31P{XH} N M R (acetone-fife): 8 60.3 (s), -141.3 (sept, PF6); (dmso-fife): 5 58.6 (s), -141.7 (sept, PF 6). UV-Vis (acetone): 462 [1220]. LR: 1437, 1100, 748, 698, 528, 482 (m, dppe); 836, 557 (m, PF 6); 762, 651 (m, Ni-OH 2). ELMS (m/z): 493 [M-2PF6]+, 145 [PF6]+. A M : 242 (H 20). This compound has not been reported. 3.2.3.7 Attempted Preparation of [Ni(H20)2(dppe)](S03CF3)2 (14) I n CH2Cl2: A literature method used for the Pt and Pd analogues was followed.37 Non-dried CF£2C12 (10 mL) was added to an N2-flushed Schlenk tube containing NiCl2(dppe) (15.2 mg, 28.8 pmol), when an orange solution formed. This turned yellow upon addition of 2 equiv. of Ag(CF3S03) (14.8 mg, 57.6 pmol), and.a.yellow precipitate was obtained upon addition of Et 2 0. AgCl contaminant (the by-product) made characterization by microanalysis futile. N M R spectra in the presence of AgCl were "noisy"; whether this resulted from the presence of solid AgCl or the formation of Ag-phosphine species is unknown. In Acetone: Another literature method reported for the Pt and Pd analogues was followed.38 To an N2-flushed Schlenk tube containing NiCl2(dppe) (15.6 mg, 29.6 pmol) was added acetone (8 mL), when an orange suspension was obtained. A yellow solution was obtained upon addition of 2 equiv. of AgCF 3 S0 3 (17.0 mg, 65.9 pmol) in H 2 0 (0.1 mL) and, within 10 min, white AgCl was observed. The mixture was filtered 3 times through Celite 545 on a 10-20 pm glass frit under N 2 to remove AgCl The yellow filtrate was concentrated to 4 mL in vacuo and diluted with Et 2 0 (8 mL); a pale-yellow precipitate was obtained. This was collected, washed with Et 2 0 (3x10 mL), and dried in vacuo overnight, but the resulting violet solid is characteristic of Ag(s) produced via photodecomposition of AgCl(s).3 9 Attempts to completely remove AgCl were thus unsuccessful, and 3 1P{1H} NMR and microanalytic data were again of no value. 3.2.3.8 Attempted Preparation of [Ni(H20)2(dppe)](BPh4)2 (15a) An N2-flushed Schlenk tube containing Nil2(dppe) (11.9 mg, 16.7 pmol), H 2 0 (0.01 mL), 43 Chapter 3 references on page 76 Chapter 3 and acetone (1 mL) was heated with a hot-air blower, and the solution became colourless. Upon addition of NaBPh4 (11.6 mg, 33.8 umol) a brown suspension formed, the solid of which was collected by filtration, washed with H 2 0 (3x10 mL), and dried in vacuo overnight. Anal. Calcd for C 74H5 8B 2Ni0 2P 2: C, 78.54; H, 6.06%. Found: C, 62.21; H, 3.64%. 3.2.3.9 Attempted Preparation of Ni(OH)2(dppe) (15b) The addition of NiCl2(dppe) (50.0 mg, 94.7 umol) to 6 M aq. NaOH in air gave, after 10 min at 80°C, a white precipitate of dppe(0)2, as revealed by 3 1P{1H} NMR spectroscopy and T L C . 3.2.4 Reactivity of [Ni(PN3)2]Cl2 In the hope of obtaining linear or three-dimensional polymers from the N,N',N"-comp\ex [Ni(PN3)2]Cl2, the following reactions were studied (Section 3.3.3): 3.2.4.1 With NiCl2.6H20 or NiCl2(PPh3)2 (16) To an Nrflushed Schlenk tube containing pink [Ni(PN3)2]Cl2 (3.10 mg, 7.9 umol) and green NiCl 2 • 6H 2 0 (1.85 mg, 7.8 umol) was added /-PrOH (3 mL); a blue precipitate was obtained. Dissolving a 1:1 ratio of [Ni(PN3)2]Cl2 and NiCl 2(PPh 3) 2 in CH 2C1 2 resulted in the same coloured product being obtained. The collected solids in CDC13 yielded noisy baseline 3 1P{1H} NMR spectra, typical of paramagnetic species. 3.2.4.2 With Ni(l,5-COD)2 (17) To anN2-flushed Schlenk tube containing Ni(l,5-COD) 2 (2.12 mg, 7.7 umol) and 4 equiv. of [Ni(PN3)2]Cl2 (12.2 mg, 30.9 umol) was added hexanes (5 mL); a white solid, insoluble or poorly soluble in most solvents tested, was obtained. A paramagnetic-type, uninformative 3 1P{1H} N M R spectrum of a CeD6 solution of the solid was obtained. 3.2.4.3 With Ag(CF3S03) (18) To an N2-flushed Schlenk tube containing [Ni(PN3)2]Ci2 (4.21 mg, 10.7 umol) and Ag(CF 3S0 3) (2.77 mg, 10.8 umol) was added CH 2 Cl 2 /MeOH (1:1, 5 mL); a dark-brown precipitate was obtained after 12 h. No 5p signals were observed in CD 3 OD solutions of the solid. 44 Chapter 3 references on page 76 Chapter 3 3.3 Results and Discussion 3.3.1 Dpype, dpypcp, and the NiX2(P-P) Complexes (X = CI, Br, I, N03, NCS) The synthesis of 2-pyridylphosphine ligands is discussed in Section 1.4.1 (p.5), and characterizations of the monophosphines by ^P^H} and lYi N M R , 4 0 m.pt,41 and X-ray crystallography (PNi, 4 2 PN 3 4 3) have been reported elsewhere. Characterization of dpype and dpypcp by UV-Vis, NMR, and IR spectroscopies, and X-ray crystallography will be discussed below, as will the characterization of Ni(II) complexes of dpype and dpypcp. NiX2(dpype) NiX2(dpypcp) X = C1, la X = C1, lb X = Br, 2a X = Br, 2b X = I, 3a X = I, 3b X = NCS, 4a X = NCS, 4b X = N0 3 , 5a X = N0 3 , 5b Complexes 1-5 were prepared in reasonable yield via displacement of PPh3 from NiX 2(PPh 3) 2 by either dpype or dpypcp. This entropically favoured process is typical behaviour of chelating diphosphine ligands, as exemplified by Tolman's work on phosphorus ligand-exchange-equilibria on Ni(0).44 The attempted synthesis of l a via reaction of dpype with N i C l 2 » 6 H 2 0 in various solvents (Section 3.2.1.1) was unsuccessful. All NiX 2(Ph 2P(CH 2)nPPh 2) complexes where n = 1 to 3 are, to date, cis and square-planar in the solid state, while a tetrahedral geometry in both solution and the solid state is reported when n = 4, 5, or 8.2 The former configuration for 1-3 in the solid state was established by X-ray structural analysis of l a , l b , 2a, 2b, and 3b (see below), and presumably also holds for 4 and 5; spectral data (see below) in solution indicate the same cis, square-planar geometry. Some NiX 2 (PR 3 ) 2 and NiX2(P-P) species are known to exist in solution in a dynamic equilibrium of tetrahedral and square-planar forms, when PR 3 is a mixed alkylarylphosphine45 or P-P contains a flexible skeletal backbone (e.g., in NiCl2(dppp)).34 As dpypcp possesses a rigid skeletal backbone, and as no tetrahedral square-planar interconversion has been reported for the NiX2(dppe) complexes,2 no interconversion was expected with 1-5, and none was observed in the 3 1P{1H} NMR spectra. Of note, only 4-coordinate Ni(II) species of the form N1X4 2" possess true Td symmetry, hence the terms "paramagnetic" and "pseudotetrahedral" are more appropriate descriptors for such NiX 2(PR 3) 2 or NiX2(P-P) species. Deviation from Ta symmetry can be quantified by magnetic moment measurements.45 45 Chapter 3 references on page 76 Chapter 3 Characterization of dpype and dpypcp The compounds dpype30 and dpypcp46 have been synthesized previously, and were prepared here in moderate yield (68 and 37%, respectively). Both analyze well by microanalyses (see Section 2.3, p.24) and have sharply defined melting points (132-133 and 112-114°C, respectively). Absorption bands at ~ 240, 268, and ~ 304 nm, with extinction coefficients of ~ 2500, are observed in the UV-Vis spectra. The ER spectra contain three prominent bands at 1566-8, 1446-8, and 1412-7 cm"1, all of which correspond to skeletal stretches of the pyridyl rings;31 bands of lesser intensity are also observed at about 1142, 985, 760, 740, and 527 cm"1. Free ligand and ligand oxide 5P values are listed in Table 3.1. The progressively downfield 5p values for PN X on going from x = 1 to 3 are due to increased deshielding of the P nuclei with increasing number of electron-withdrawing pyridyl N-atoms. The racemic mixture of R,R and S,S enantiomers of the chiral dpypcp yields just one 5p singlet as the enantiomers are chemically and physically identical in achiral solvents.47 All synthetic work in this thesis was conducted with ligands certified by 31P{1H} NMR to be free of oxide impurities. The 5 H values for the ligands and their oxides are given in Table 3.1, while the ! H N M R spectra of dpype and dpypcp are shown in Figure 3.2. Each pyridyl (H3-I-L5) and phenyl (H7-H9) proton displays a complex resonance due to J-couplings with phosphorus, adjacent protons, and other protons in the aryl ring (see the numbering scheme in Figure 3.1); the assignments are based on the work of Jakobsen on PN 3 4 8 The protons within the backbones of the P-P ligands appear at 5 H = 2.50 (t) for the H a methylene protons in dpype, and at 5 H = 174 (qn, Ha), 1.97 (m, Hb), 2.38 (m, Hb), and 3.90 (ddd, Ho) for the cyclopentyl protons of dpypcp. The H3-He resonances of dpype and dpypcp are simplified in a !H{3 1P} NMR spectrum (Table 3.2). The relative downfield 5FE5 from the H 3-H 5 resonances is due to its close proximity to the electron-withdrawing nitrogen.48 Of note, with a change from CDC13 to C 6D 6 , the pyridyl resonances "spread out", and 8H 3 and 8H4 switch relative positions, all this resulting from the anisotropy caused by interaction with the benzene rings of C 6 D 6 . 4 8 The X H and 31P{1H} NMR data in Table 3.1 for P N X , 4 9 dpype,30'50 dpypcp,46'50 dpype(0) 2 , 5 ° and dpypcp(0)246 are similar to those reported elsewhere. 46 Chapter 3 references on page 76 Chapter 3 Table3.1 "PfH} and *H NMR Data for the 2-Pyridylphosphine Ligands and their Oxides Solvent Compound 31pa I V H / H 5 * I V Hg & H 9 b CDCI3 P N / -3.95 7.08 7.56 7.17 8.72 7.38 7.38 P N 2 C -2.62 7.24 7.58 7.18 8.72 7.51 7.40 P N 3 C -0.74 7.39 7.60 7.20 8.71 - -dpype c ' d -6.10 7.41 7.52 7.10 8.63 H a 2.50 (t, 2JHP 4 Hz ) dpypcp c'< * 0.00 7.39 6.87 6.49 8.47 Ha 1.74 (qn),Hb 1.97 (m) H b 2.38 (m), He 3.90 (ddd) CDCI3 O P N / 21.32 8.30 7.88 7.40 8.78 7.88 7.46 O P N / 17.34 8.12 7.81 7.38 8.79 8.12 7.49 om/ 14.56 8.20 7.80 7.38 8.78 - -dpype(0) 2 C 33.14 7.76 8.05 7.34 8.70 H a 2.88 (t) dpypcp(0) 2 C 32.11 8.01 7.62 7.22 8.42 H a 1.72 (m), H b 1.80 (m) ^ 2 . 1 2 ^ X ^ 4 . 0 ^ ) C 6 D 6 PN i c -3.62 7.06 6.85 6.49 8.51 7.53 7.06 P N / -2.02 7.32 6.90 6.50 8.49 7.72 7.09 P N 3 C -0.13 7.47 6.95 6.53 8.50 - -C 6 D 6 O P N / 15.53 8.48 6.97 6.46 8.32 8.19 7.02 O P N / 14.34 8.15 6.91 6.44 8.36 8.69 7.14 O P N 3 / G - 8.30 6.96 6.48 8.40 - -D 2 0 dpype(0) 2 C 34.9 7.70 7.96 7.28 8.64 H a 2.64 (t) dpypcp(0) 2 C 31.9 7.68 7.30 6.69 8.33 H a 1.61 (m),Hb 1.77 (m) H b 2.02 (m), 1^3.86(111) ( f l ) Singlet. {b> Multiplet. ( c ) Measured in this thesis work. w See Section 2.3.4-5, p.26, for multiplicities of H3-H5 ( E ) 2JHP are 9, 8, and 7 Hz for H a , H b , and He, respectively. w Data from ref. 49. fe) Limited solubility. 9 (a) (b) Figure 3.1 Numbering scheme for 2-pyridylphosphines: (a) e.g., PN 2 , (b) P-P ligands. 47 Chapter 3 references on page 76 Chapter 3 H 4 H 5 He W Vt>^ l^*>l»wt>^M l^l^ l»^W* i^•*^M»,'^ yr'•^  H a H a Hb Hb AN (a) (b) 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 ppm Figure 3.2 *H NMR (CDC13) spectra of: (a) dpype, (b) dpypcp. Table 3.2 Changes in Resonance Multiplicities in the *H NMR Spectrum of dpype and dpypcp Upon 3 ^ -Decoupling " X H dpype JH{31P} dpype i *H dpypcp JH{31P} dpypcp H a t S 1 qn t H b - 1 dm t H , - J ddd qt H 3 m dd I tt td H 4 ddd dd i dtt td H 5 dddd ddd 1 dddt ddd He dd d ! ddt dt (a) In CDC13; 500 MHz for J H ; 202.5 MHz for 3 1 P. UV-Vis Spectroscopic Characterization of the Ni(II) Complexes The absorption maximum (Xmax) and extinction coefficients (s) for 1-5, and the dppe analogues 12a-e, are reported in Table 3.3. Ligand field theory states that the greater the field strength of a ligand, the smaller Xmax becomes, due to an increase in energy spacing (10Dq) 48 Chapter 3 references on page 76 Chapter 3 between certain d-orbitals (Figure 3.3). The relative field strengths of the five "X" ligands are, according to the spectrochemical series, I"<Br"<Cr<NCS"<N03";51a the magnitude of Amax for the NiX 2(P-P) complexes is in the exact reverse order, consistent with the series. The 8 values for 1-5 are generally slightly above the range for d-d bands of square-planar complexes with organic ligands (e = 102-103 units);52 tetrahedral complexes (which lack the Laporte-forbidden centre of symmetry) have far more intense absorptions.5lb Although in principle two d-d transitions are expected for low symmetry (e.g., D2h) Ni(II) square-planar complexes, in practice, one of these is usually obscured by ligand charge-transfer bands.2 The solution colour of each complex matches its solid state colour [X = Cl, orange; Br, red; I, purple; SCN and N 0 3 , yellow]. Table 3.3 UV-Vis Data for NiX2(P-P) Complexes a Ligand X ^max (s) •^max (s) A-max (6) Cl la: 464(1615) lb: 478 (1200) 12a: 462 (1800) Br 2a: 478 (2100) 2b: 492 (1460) 12b: 478(1840) I 3a: 520(1550) 3b: 534 (1630) 12c: 526 (2100) NCS 4a: 440 (2825) 4b: 452 (1595) 12d: 442 (2760) N 0 3 5a: 406 (270) 5b: 408 (245) 12e: 406 (296) In CH 2C1 2 (0.7 mM). A™,x are in [nm] and s are in [ M 1 cm"1]. dx2-y2 J H _ - i . ! 0 D q _dz2_ dxz dyz Figure 3.3 Metal d-orbital splitting in a square-planar complex with bonds in the xy plane. 49 Chapter 3 references on page 76 Chapter 3 3 1 P ^ H } NMR Spectroscopic Characterization of the Ni(II) Complexes The 8p values for 1-5 and 12 are reported in Table 3.4. The clean, diamagnetic appearance of the spectra are consistent with these complexes being square-planar in solution; tetrahedral species yield "noisy" (low signal-to-noise ratio), paramagnetic spectra. The large, downfield, coordination shift (A5) relative to 5P for the free ligands is typical of complexes containing 5-membered chelate rings.53 The A8 range for the dpype and dppe complexes (68-88, and 66-89 ppm, respectively) are double that of the dpypcp species (28-45 ppm). Of note, the racemic mixture of R,R and S,S enantiomers of lb-5b gives rise to just one signal, as seen with free dpypcp. The 8P values shift progressively downfield as each halide series is descended. This presumably reflects the relative strengths of X—»Ni a-donation (greatest for CI" and least for I"),51a with the assumption that a constant electron density is maintained at Ni. Accordingly, P-»Ni c-donation should be the least while Ni -»P 7i-back-donation should be the greatest when X = CI, and so the P nuclei of NiCl2(P-P) should be the most shielded and yield the most upfield 8P values. The "constant electron density at Ni" assumption is supported by the fact that the Ni-P bond length decreases on going from 3b to 2b to lb (see below), indicative of an increase in N i - » P K-back-donation induced by the increase in X—»Ni a-donation. Of note, the analogous Pt and Pd species54 and the PdX 2(PNi) 2 5 4 complexes display a progressively upfield shift on descending the halide series (Table 3.5), a trend rationalized in terms of the basicity of the ligands.54'55 Table 3.4 3 1P{1H} NMR Data for NiX2(P-P) Complexesa Ligand X 5P 5P 8P free dpype: -6.1 free dpypcp: 0.0 free dppe: -13.2 CI la: 61.8 lb: 29.3 12a: 54.9 Br 2a: 71.7 2b: 37.1 12b: 63.4 I 3a: 81.8 3b: 45.2 ' 12c: 75.3 NCS 4a: 63.3 4b: 30.3 12d: 57.7 N 0 3 5a: 63.2 5b: 28.4 12e: 52.7 All resonances are singlets; data in CDC13, except for 5a and 5b in CD 3 OD. 50 Chapter 3 references on page 76 Chapter 3 Table 3.5 31P{lH} NMR Data for Pd or Pt analogues of lb-3b and N i X 2 ( P N i ) 2 Complex " 5P Complex " 5P Complexb 5P PdCl2(dpypcp) 38.8 PtCl2(dpypcp) 17.8 PdCl 2 (PNi ) 2 23.4 PdBr2(dpypcp) 36.9 PtBr2(dpypcp) 17.7 PdBr2(PN!)2 20.5 Pdl2(dpypcp) 29.9 Ptl2(dpypcp) 14.4 PdI 2 (PNi) 2 9.6 From ref. 50. (' From ref. 55. 'HNMR Spectroscopic Characterization of the Ni(II) Complexes The crystal structures of lb, 2b, and 3b (see below) show the halo ligands to adopt a cis configuration in the solid state, and the same arrangement must exist in solution for complexes 1-5 as the phosphine is a chelating ligand. Four trends are noted in the *H NMR spectra of 1-5. Firstly, the expected downfield shift of the pyridyl resonances is seen upon complexation of dpype and dpypcp (cf. 5H values in Section 3.2.1 and Table 3.1). Secondly, the multiplicity of F£a in dpype is observed to change from a triplet to a doublet upon complexation within la-5a Thirdly, the multiplicity of the FLj and F£5 resonances in lb-3b change on descending the halide series, with the multiplicity of H 4 changing from (d) to (t) to (dd) on going from X = Cl through Br to I, respectively, while the multiplicity of H 5 changes from (qt) for lb to, eventually, (dtd) for 3b (Figure 3.4). Finally, the multiplet resonance attributed to the four F£6 protons of dpypcp (8.47 ppm) splits into two separate resonances (of equal integrated areas) at 8 ~ 8.1 and ~ 9.1 in lb-3b. The X-ray crystal structures of lb-3b show that one He proton of each of the two Ppy2 units (labeled " F L 5 * " in Figure 3.4) experiences close contact with a halide ligand (FLs*-X distances = 2.91, 3.03, and 3.16 A for lb-3b, respectively; see Appendix A, Tables A. 15, 19, and 23), while the other two FL5 protons do not; this close-proximity to electron-rich halide ligands likely increases the shielding around the FL5* protons, causing them to resonate relatively upfield. 51 Chapter 3 references on page 76 H4 Chapter 3 H4 H 3 _L H 5 _L /A M....A 0.) 9.2 9.0 (C) M l M i i M i i l l l M f f i l M 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2 7.0 ppm Figure 3.4 'H NMR spectra (CDC13) of the pyridyl region of: (or) lb, (b) 2b, (c) 3b. //? Spectroscopic Characterization of the Ni(II) Complexes The pyridyl skeletal bands at 1566-1570 and 1419-1422 cm'1 for 1-5 are shifted slightly from the bands at 1566-8 and 1412-7 cm"1, respectively, for free P-P ligand. The v(Ni-X) and v(Ni-P) stretching bands (400-250 cm"1),56 which can aid in distinguishing between cis and trans geometries, were not observed due to overlap with pyridyl vibrational modes, as reported for Pd/PNX complexes.54 The v(CS) bands of 4a and 4b identify these species as isothiocyanato (TV-bonded) and not thiocyanato (^-bonded) complexes as the values correspond to the ranges reported for TV-bonded Ni(II)/NCS complexes (see Table 3.6).57'58 TV-bonded NCS is common for Ni(II) complexes2 and 52 Chapter 3 references on page 76 Chapter 3 also for M(NCS) 2 L 2 complexes (M = Pd, Pt; L = phosphine).59 The structurally diagnostic, far-IR 8(SCN) and v(MN) or v(MS) bands were not delineated. Table 3.6 Diagnostic IR bands [cm1] for S- vs. JV-terminally bonded SCN ligands to Ni(II) Band S-bonded SCN TV-bonded SCN 4a/4b v(CN) >2100 f l < 2050 2078 b 2077 / 2073 v(CS) 690-720 a 780-860 a , 868 b 816/845 { a ) Ref. 57. ( f c ) For Ni(NCS)2(PPh3)2 (ref. 58). The two weak V1+V4 combination bands for 5a and b (Table 3.7) reveal that NO3 is O-bonded to Ni, as two bands at ~ 1700-1800 cm"1 are typical for such bonding.60'61 [An TV-bonded coordinated NO3 mode is apparently unknown].62 The difference between these bands (33 and 26 cm"1 for 5a and b, respectively) is consistent with N 0 3 being unidentate, as values of ~ 52 cm"1 are reported for bidentate NO3 complexes;57 three X-ray characterized bonding modes (symmetric, asymmetric, and bridging) are known for bidentate N0 3 . 5 7 ' 6 2 The V1+V4 and V3 bands split upon coordination of NO3 as the symmetry of the free ion is lowered from D 3 h to C ^ 6 1 (Table 3.7). The v 4 in-plane, bending band (at ~ 700 cm"1) is also reported57 to split in two upon coordination of NO3 (e.g., 720 and 740 cm"1 for Ni(N03)2[(Me)2Si(PPh2Me)2]).63 A second v 4 band is not assigned for 5 as it likely overlaps with strong pyridyl vibrations (seen at 749 and 744 cm"1 for 5a and b, respectively). The v 2 band was not seen (cf. 820 cm"1 for Ni(N03)2[(Me)2Si(PPh2Me)2]).63 Table 3.7 IR Bands [cm"1] for Ni(N03)2(P-P) Complexes 5a (P-P = dpype) and 5b (P-P = dpypcp) Band 5a 5b Vi v 3 v 4 V1+V4 984 1436 & 1382 699 1693 & 1726 988 1433 & 1382 695 1671 & 1697 53 Chapter 3 references on page 76 Chapter 3 Microanalytic and Mass Spectral Characterization of the Ni(II) Complexes Complexes 1-5 have satisfactory C and H elemental analyses, but all analyses (except for 2a) are somewhat low in N, with those of 4a, 5a, and 5b, and the X-ray characterized la, lb, and 2b low by 0.31-0.55%, while 4b is low by 0.69%; 2a, 3a, and 3b are within 0.3% of the calculated N analysis. Copper oxide was used in an attempt to fully combust the samples. The electron-impact mass spectrometry (EIMS) isotopic distribution patterns for the [M] and [M-X] peaks of 1-5 match those simulated by a computer programme.64 Ligand fragment peaks were also seen. X-ray Structural Analysis of dpype, dpypcp, and the Ni(II) Complexes The molecular structures of P N i 4 0 and P N 3 4 1 have been reported, while that for dpype was recently reported by this group 4 6 The structure of dpypcp was obtained in this thesis work, and its ORTEP and that of dpype are shown in Figure 3.5. Crystals of dpypcp and la-b, 2a-b, and 3b were grown by diffusion of hexanes into a CH 2C1 2 solution of either the ligand or the complex (Section 2.5.2, p.31). The ORTEPs for la and 2a appear in Figure 3.6 and Figure 3.7a, respectively, while those of the S,S enantiomers of lb and 2b, and the R,R enantiomer of 3b, appear in Figure 3.7b, Figure 3.8a, and Figure 3.8b, respectively. Selected bond lengths and angles for dpype and la and 2a are reported in Table 3.8, while the same parameters for dpypcp and lb-3b are listed in Table 3.9. Six selected parameters for dpypcp, the phenyl analogue dpcp,65 and NiX2(dpypcp) complexes lb-3b are presented in Table 3.10 for comparison, while the same six parameters for dpype, the phenyl analogue dppe,66 and NiX2(dpype) complexes la and 2a are listed in Table 3.11. The five Ni complex structures show that 1-3 possess a cis square-planar geometry in the solid state. 54 Chapter 3 references on page 76 Chapter 3 Figure 3.6 ORTEP (50% probability) of the molecular structure of NiCl2(dpype) (la). 55 Chapter 3 references on page 76 Chapter 3 Figure 3.7 ORTEP (50% probability) of the molecular structure of: (a) NiBr2(dpype) (2a), (b) the S,S enantiomer of NiCl2(dpypcp) (lb). 56 Chapter 3 references on page 76 Chapter 3 C(18) C(23) (a) (b) Figure 3.8 ORTEP (50% probability) of the molecular structure of: (a) the S,S enantiomer of NiBr2(dpypcp) (2b), (b) the R,R enantiomer of Nil2(dpypcp) (3b). 57 Chapter 3 references on page 76 Chapter 3 Table 3.8 Selected Bond Lengths and Angles for dpype and the NiX2(dpype) Complexes Bond Lengths (A) Bond la (X = Cl) 2a (X = Br) dpype0 Ni -P(l) 2.162(2) 2.154(5) -Ni - P(2) 2.141(2) 2.164(5) -N i - X ( l ) 2.197(2) 2.349(2) -Ni - X(2) 2.204(2) 2.338(4) -P( l ) -C( l ) 1.823(7) 1.819(3) 1.832(3) P( l ) - C(3) 1.812(7) 1.840(3) 1.846(3) P(l) - C(8) 1.840(6) 1.829(3) 1.850(3) P(2) - C(2) 1.820(7) 1.825(4) 1.832(3) P(2)-C(13) 1.830(7) 1.820(5) 1.846(3) P(2)-C(18) 1.83.7(7) 1.839(6) 1.850(3) C(l)-C(2) 1.518(9) 1.514(2) 1.527(6) N(l)-C(3) 1.360(8) 1.342(6) N(l)-C(2): 1.346(4) N(2) - C(8) 1.327(8) 1.334(6) N(2)-C(7): 1.334(4) N(3) - C(13) 1.331(8) 1.331(6) na, centrosymmetric N(4) - C(18) 1.345(9) 1.339(7) na, centrosymmetric Bond Angles (°) Bond la 2a dpype " P(l)-Ni-P(2) X(l)-Ni-X(2) X(l)-Ni-P(l) X(2)-Ni-P(2) X(l)-Ni-P(2) X(2)-Ni-P(l) P(I>C (3 ) :N(T) P(l)-C(8)-N(2) P ( l)-C ( l)-C (2 ) P(2)-C(13)-N(3) P(2)-C(18)-N(4) P(2)-C(2)-C(l) 86.22(7) 94.29(7) 174.88(8) 176.04(8) 89.49(7) 90.06(7) 114.9(5) 114.6(5) 108.5(5) 112.2(5) 115.7(5) 108.0(5) 86.32(5) 94.47(4) 175.39(6) 174.31(5) 90.12(4) 89.26(4) ii3.4(4) 110.9(4) 106,6(3) 112.7(4) 113.9(4) 106.9(3) P(l) rC(2)-N(l): 112.7(2) P(l)-C(7)-N(2): 119.9(2) P(l)-C(l)-C(l*): 110.4(3) na, centrosymmetric na, centrosymmetric na, centrosymmetric P(l)-Ni-P(2)-C(2) 16.20 12.23 na r";Data for dpype from ref. 46; na•= not applicable.(} Torsion angle. 58 Chapter 3 references on page 76 Chapter 3 Table 3.9 Selected Bond Lengths and Angles for dpypcp and the NiX2(dpypcp) Complexes Bond Lengths (A) Bond ; lb(X = Cl) 2b (X = Br) 3b (X = I) dpypcp N i -P ( l ) 2.1629(8) 2.1618(13) 2.166(2) -Ni - P(2) 2.1619(8) 2.1699(13) 2.166(2) -Ni - X(l) 2.2038(8) 2.3348(8) 2.5225(9) -Ni - X(2) 2.1977(8) 2.3265(7) : 2.5245(7) -P( l ) -C( l ) 1.821(3) 1.832(4) 1.817(6) 1.862(2) P(l) - C(6) 1.827(3) 1.830(5) 1.818(7) 1.850(2) p ( i ) - c r i i ) 1.825(3) 1.823(5) 1.812(8) 1.847(2) P(2) - C(2) 1.832(3) 1.848(5) 1.838(7) 1.863(2) P(2)-C(16) 1.827(3) 1.816(5) 1.806(6) 1.834(2) P(2) - C(21) 1.833(3) 1.810(5) 1.826(6) 1.854(2) N(l) - C(6) 1.354(4) 1.346(6) 1.325(8) 1.344(3) N(2) -C( l l ) 1.341(4) 1.362(6) 1.381(9) 1.332(3) N(3)-C(16) 1.332(4) 1.342(6) 1.387(8) 1.350(3) N(4) - C(21) 1.343(4) 1.374(6) 1.322(8) 1.338(3) C(l)-C(2) 1.523(4) 1.495(7) 1.424(9) 1.545(3) C(2) - C(3) 1.534(4) 1.544(6) 1.514(8) 1.541(3) C(3)-C(4) 1.546(4) 1.535(6) 1.561(9) 1.528(4) C(4)-C(5) 1.561(4) 1.551(6) 1.551(8) 1.521(3) C(5) - C(l) 1.529(4) 1.537(6) 1.543(9) 1.538(3) Bond Angles (°) Bond lb 2b 3b dpypcp P(l)-Ni-P(2) 88.45(3) 88.42(5) 88.13(7) na X(l)-Ni-X(2) 95.49(3) 95.13(3) 94.06(3) na X(l)-Ni-PQ) 171.35(3) 171.37(5) 175.05(6) na X(2)-Ni-P(2) 168.87(3) 168.15(5) 176.87(6) na X(l)-Ni-P(2) 88.23(3) 89.34(4) 88.98(5) na X(2)-Ni-P(l) 89.26(3) 88.49(4) 88.90(5) na P(l)-C(6)-N(l) 116.8(2) 116.4(4) 113.5(4) 119.5(2) P(l)-C(ll)-N(2) 115.1(2) 114.0(3) 118.1(7) 116.63(14) P(l)-C(l)-C(2) 106.9(2) 107.8(3) 111.6(5): 109.01(14) P(2)-C(16)-N(3) 110.5(2) 109.5(4)^  112.8(4) 112.2(2) P(2)-C(21)-N(4) 121.6(2) 112.7(4) 113.0(4) 120.04(15) P(2)-C(2)-C(l) 108.3(2) 107.4(3) 110.6(5) 109.92(14) C(l)-C(2)-C(3) 103.3(2) 103.6(4) 108.5(6) 103.7(2) C(2)-C(3)-C(4) 103.1(2) 101.6(4) 103.5(5) 106.3(2) C(3)-C(4)-C(5) 107.5(2) 109.0(3) 105.8(5) 107.1(2) C(4)-C(5)-C(l) 103.6(2) 102.2(4) 104.0(5) 106.7(2) P(l)-Ni-P(2)-C(2) a 17.79 17.70 10.287 _ H(C1)-C(1)-C(2)-H(C2) a 1.790 1.456 0.212 -Torsion angle . 59 Chapter 3 references on page 76 Chapter 3 Table 3.10 Selected Parameters for lb-3b, dpypcp, and dpcp Parameter lb 2b 3b dpypcp dpcp " C(l)-C(2) bond (A) 1.523 1.495 1.424 1.540 1.544 P(l)-P(2) distance (A) 3.017 3.022 3.012 4.458 4.450 ave. P-C bond (A) * 1.828 1.827 1.830 1.849 1.863 ave. N-C bond (A) 1.343 1.356 1.354 1.341 -ave. C-P-C angles (°) 106.94 107.09 106.03 101.07 na P-C-C-P dihedral angle (°) 50.5 51.4 46.9 15.7 18.2 { a ) Data for dpcp from ref. 65. ( i ) Average of all three (Cback and Cph) P-C bonds. Table 3.11 Selected Parameters for la-2a, dpype, and dppe Parameter la 2a dpype a dppe6 C(l)-C(2) bond (A) 1.518 1.514 1.527 1.521 P(l)-P(2) distance (A) 2.940 2.954 4.453 c 4.434 ave. P-C bond (A) d 1.827 1.828 1.844 1.824 ave. N-C bond (A) 1.341 1.337 1.340 -ave. C-P-C angle (°) 105.47 104.44 99.94 101.55 P-C-C-P dihedral angle (°) 47.5 49.8 0.02 c 0.0 ( a ) Taken from ref. 46; the C(l)-C(2) bond = C(l)-C(l*) bond. { b ) Taken from ref. 66; value for P(l)-P(2) calculated, see Appendix A.9. ( c ) Calculated from atomic coordinate data using SymApps, vl.0 (ref. 67). { d ) Average of all three (Cback and C P h ) P-C bonds. The steric bulk of the cyclopentyl backbone of dpypcp induces steric interaction amongst the 4 py fragments (Figure 3.9c), whereas lack of steric bulk in the ethyl backbone of dpype allows one Ppy2 moiety to rotate by 180° around the C(l)-C(l*) bond with respect to the other Ppy2 moiety to afford maximum spatial separation amongst the 4 py rings (Figure 3.9a). These same Figures show that the two planes defined by the py rings in each Ppy2 of dpype are mutually orthogonal, while in dpypcp one py in each Ppy2 moiety has rotated around the P-C axis so that its plane bisects that of the other py ring. Upon complexation to Ni(II), the py rings of dpype (Figure 3.9b) now bisect each other (as seen for free dpypcp), while the py rings of dpypcp become more coplanar (Figure 3.9d). 60 Chapter 3 references on page 76 Chapter 3 (c) (d) Figure 3.9 Spatial configuration of the pyridyl moieties in: (a) dpype, (b) NiBr2(dpype), (c) dpypcp, (d) NiBr2(dpypcp). These models, generated from SymApps 7 using crystal structure atomic coordinate data, are rotated such that the backbone C-C axis is coming directly out of the plane of the page. Pyridyl protons have been removed for clarity. 61 Chapter 3 references on page 76 Chapter 3 The P-C-C-P dihedral angles (Tables 3.8-9) reveal that the cores of dpype (Figure 3.9a) and dppe are planar, while those of dpypcp (Figure 3.9c) and dpcp are puckered. Upon complexation, all P-C-C-P dihedral angles increase to ~ 50°, thus allowing formation of "the familiar five-membered ring chelate system".65 The intramolecular P-P distances in dpype, dpypcp, and dpcp are virtually identical and, at least for the pyridyl ligands, these decrease ~ 33% upon complexation to Ni(II). The coordination of dpype requires rotation of one Ppy2 fragment around the ligand backbone C-C axis by ~ 180° (Figure 3.9, a—>b), whereas the coordination of dpypcp requires a twist of each Ppy2 fragment around the P-C(l) or C(2) axis (Figure 3.9, c—»d). The backbone C-C bonds of dpypcp and dpcp are marginally longer than those of dpype and dppe. This bond shortens in the Ni(II) complexes, and its general decrease on going from la to 2a, and lb through 2b to 3b, is likely due to a decreasing ligand bite-angle on descending the halide series (see below). The average P-C bond lengths for dpypcp and dpype are almost identical, and differ from those of their phenyl analogues by -0.014 A and +0.020 A, respectively. Meanwhile, the average P-C bond length is practically identical in the five Ni(II) complexes, but ~ 0.02 A shorter than the free ligand values, a shift attributed to changes in P-atom electron density upon ligand coordination to Ni(II). Meanwhile, the average C-P-C bond angles of the free ligands (which are < 109.5° due to the P-atom lone-pair) increase by ~ 5° upon coordination to Ni(II), as the lone pairs are spatially reduced to bonding electron-pairs. The average N-C bond lengths of dpype, dpypcp, la, lb, and 2a are all similar, while those of 2b and 3b are ~ 0.015 A longer. Close to square-planar bond angles about Ni are seen for 1-3 (Tables 3.8-9), while the dihedral angle between the NiP 2 and NiX 2 planes (13.0°, lb; 13.7°, 2b; 4.1°, 3b) quantifies the deviation of the NiX2(dpypcp) cores from planarity. The analogous data are not available for the NiX2(dpype) complexes. The X-Ni-X bond angle in NiX2(dpype) might be expected to be > that in NiX2(dpypcp) as the bite-angle (P-Ni-P) of coordinated dpype is ~ 2° < that of coordinated dpypcp (Tables 3.8-9), but the reverse is observed. Also, the X-Ni-X angles might be expected to increase on descending the halide series to accommodate the larger halide ligand; this was observed for the two NiX2(dpype) complexes, but the opposite is seen for the three NiX2(dpypcp) species. Of 62 Chapter 3 references on page 76 Chapter 3 note, the P-Ni-P bond angle for NiBr2(dpypcp) (88.42°) and NiCl2(dpype) (86.22°) are similar to those of the analogous NiBr2(dpcp)65 (88.33°) and NiCl2(dppe)68 (86.93°) species. The Ni-X bond lengths for all five complexes follow the order of (M-I) > (M-Br) > (M-Cl), a trend attributed to the corresponding increase in size of the halide ligand. The Ni-Cl lengths of la, lb, and NiCl2(dppe) (2.196 and 2.204 A) 6 9 are identical, and the Ni-Br lengths of 2a, 2b, NiBr2(dppe) (2.321 and 2.336A),70 and NiBr2(dpcp) (2.34 A) 6 5 are also very similar. The average Ni-P bond lengths for all complexes are very similar on ascending the halide series (2.159-^2.152 A for 2a->la, and 2.166->2.165->2.162 A for 3b->2b-»lb). The slight differences, if indeed any exist outside of experimental error, are likely due to the increase in Ni->P TC-back-donation as the X—»Ni a-donation increases (see the 3 ,P{ 1H} N M R discussion above). The Ni-P lengths for 2a, 2b, NiBr2(dppe) (2.14 and 2.16 A), 7 0 and NiBr2(dpcp) (2.17 A) 6 5 are similar, while the Ni-P lengths for la and lb are somewhat shorter than those of NiCl2(dppe) (2.195 & 2.205 A). 6 8 The complete listing of bond lengths, bond angles, atomic coordinates, and experimental conditions for all of the X-ray crystal structures obtained in this thesis work can be found in Appendix A. 3.3.2 Aqueous Solution Chemistry of Ni(LT) 2-Pyridylphosphine Complexes The aqueous solution chemistry of 1-3 was examined by NMR spectroscopy and conductivity measurements in their D 2 0 or H 2 0 solutions (Table 3.12). la-3a dissolve fairly readily at r.t. or with mild heating, while dissolution of lb-3b requires higher temperatures (Table 3.12). Of note, lb-3b readily dissolve at r.t. upon acidification of the solution, presumably due to formation of cationic, pyridyl N-atom protonated species, as shown for Ni(CO)2(dpypcp) in Chapter 4. 1-3 in C D C I 3 display unique 8P values, while in D 2 0 only two 5p values are seen (Table 3.12), suggesting dissociation of halide ligands with concomitant formation of a diaquo, dicationic complex of the form [Ni(H20)2(P-P)](X)2. The dicationic nature is confirmed by conductivity data (accepted A M range for 2:1 electrolytic species in H 2 0 is 228-281 units).71'72 Formation of AgCl(s) upon dissolution of AgN03 in the aqueous solutions of la and b is consistent with the presence of free Cl", while the lack of change in pH of the water in which la was dissolved is consistent with formation of a diaquo species. 63 Chapter 3 references on page 76 Chapter 3 The NMR and conductivity samples were prepared in air and measurements were obtained within 2 min of dissolving NiX2(P-P) in D2O. Although the predominant 5p resonance is attributed to [Ni(H20)2(P-P)]2+ (see below), the resonance corresponding to dpype(0)2 (5P = 35.2) or dpypcp(0)2 (5P = 31.3) is also seen in the 31P{?H} NMR spectra of la-3a and lb-3b, respectively. The Ni:bisoxide ratio was -1:1 (based on integration) after 15 min, and only the (O)P-P(O) resonance was detectable after 30 min. The UV-Vis spectrum for the aged N M R sample of la matches that of rNi(H20)6](Cl)2 in H 2 0 (Xmax = 394, 718 nm), indicating that aerial oxidation in H 2 0 converts 1-3 to phosphine oxide and [Ni(H 20) 6] 2 +. Table 3.12 Conductivity and "P^H} NMR Data for 1-3 Compound A M (H 20) a 5(D 2 0) f c 5 (CDCI3) b Soln. Conditions0 NiCl2(dpype) (la) 230 57.42 61.8 r.t NiBr2(dpype) (2a) 257 57.46 71.7 r.t Nil2(dpype) (3a) 250 57.43 81.8 ~ 5 0 ° C NiCl2(dpypcp) (lb) 230 36.61 29.3 100°C NiBr2(dpypcp) (2b) 261 36.57 37.1 100°C Nil2(dpypcp) (3b) 235 36.60 45.2 100°C ( a ) Units are Q"1 cm2 mol"1. < f c ) All 5P resonances are singlets. ( c ) Heating conditions required to dissolve the compound. NMR samples of 1-3 were prepared under anaerobic conditions (N 2 atmosphere, D 2 0 de-oxygenated via 3 freeze-pump-thaw cycles). At t - 2 min, only the resonance corresponding to the dicationic Ni(II) species is seen, while at t = 120 min, the 3 1 P NMR spectra correspond to those obtained at t = 2 min in the aerobic study; after 24 h, complete decomposition to bisoxide was apparent. Aerial oxidation thus causes sample decomposition. Of note, the pyridyl region of the ! H NMR spectrum of la in D 2 0 (under anaerobic conditions at t - 120 min) contains py H resonances attributable to both coordinated dpype and dpype(0)2 (Figure 3.10; prime notation denotes bisoxide protons). Comparison of 5 P for authentic samples of [Ni(H20)2(dpype)]2+ and [Ni(H20)2(dpypcp)]2+ (see below) with values for 1-3 in D 2 0 was used to prove in situ formation of the diaquo species from 1-3. To minimize wastage of dpype and dpypcp, the preparative protocol for the dppe analogue [Ni(H20)2(dppe)]2+ was first determined. 64 Chapter 3 references on page 76 Chapter 3 H4, FL5, FLs 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2 ppm Figure 3.10 lH NMR spectrum of NiCl2(dpype) in D 2 0 at t = 120 min. Synthesis and Characterization of [Ni(H20)2(dppe)f+ Complexes Initial attempts to prepare [Ni(H20)2(dppe)]2+ from NiCl2(dppe) followed the literature method for the synthesis of the Pt and Pd species [M(H20)2(dppe)](S03CF3)2 in CH 2 C1 2 3 7 or wet acetone,38 but it proved impossible to remove AgCl impurity from the product (Section 3.2.3.7). The synthesis of [Ni(H20)2(dppe)](BPh4)2 (15a) was then attempted via reaction of Nil2(dppe) with NaBPli4 in aq. acetone, but the isolated brown solid did not analyze correctly (Section 3.2.3.8). The PF 6 salt of [Ni(H20)2(dppe)]2+ was successfully prepared in a 2-phase system via addition of aq. KPF 6 to a CH 2C1 2 solution of NiCl2(dppe). The procedure allowed for removal of KC1, 7 3 and the yellow product was purified via column chromatography to remove dppe and dppe(0)2 impurities (Section 3.2.3.6). The microanalysis corresponds to rNi(H20)2(dppe)](PF6)2 (13); ELMS peaks at m/z 493 and 145 correspond to [Ni(H20)2(dppe)]2+ and PF6", respectively, and the isotopic splittings for both peaks match simulated ones;64 and conductivity data in H 2 0 are consistent with a 2:1 electrolyte. LR bands at 762 and 651 cm"1 are assigned as rocking A(H 2 0) and wagging y0w(H2O) bands, respectively, of coordinated H 2 0 . 5 7 A diagnostic v(Ni-0) band (~ 405 cm"1)57 could not be assigned, while bands for coordinated dppe, and the PF 6 anion were seen. In the D 2 0 analogue of 13, the pw(D20) band (corresponding to coordinated D 2 0) 5 7 was seen at 459 cm"1. Singlets with 5p values of 58.6 and 60.3 were seen for 13 in &ms,o-d6 and acetone-afe, respectively (plus a septet at 5 ~ -142 for PF6"); there are no corresponding values for 65 Chapter 3 references on page 76 Chapter 3 NiCl2(dppe) in D 2 0 as the complex decomposes to liberate a hydrophobic surface layer of dppe in neutral aqueous media [for NiCl2(dppe) in CDC13, 6P = 54.9]. No coordinated-H20 ! H N M R signal is seen, presumably due to a rapid exchange process with the solvent, as similarly reported for [Pt(H20)2(dppe)](S03CF3)2 in CD 2 C1 2 . 3 7 The [Ni(H20)2(dppe)]2+ species, as in 13, appears to be new. Synthesis and Characterization of [Ni(H20)2(P-P)f+ Complexes (P-P = dpype, dpypcp) The yellow [Ni(H20)2(P-P)](PF6)2 complexes (P-P = dpype, 6a; dpypcp, 6b) were obtained by addition of KPF 6 to a methanolic solution of NiI 2 .6H 2 0 and P-P under N 2 (Sections 3.2.1.11-12). Their identity was established by microanalysis, EIMS (m/z of 787 and 827 corresponding to 6a and b, respectively), and conductivity data. A singlet 8p for 6a is seen at 8 55.6, 58.2, or 62.2 in CDC13, CD 3 OD, or dmso-<4 respectively, while for 6b in CD 3 OD the 8P singlet comes at 35.3; the septet for PF6" is also seen in all solvents at 8 ~ -141. The pt(H20) band is seen at 764 and 765 cm"1 for 6a and b, respectively (cf. 762 cm"1 for 13), while the corresponding yO„,(H 20) band is observed at 648 and 650 cm"1 (cf. 651 cm"1 for 13). As with 13, no coordinated-H20 ! H NMR signal was seen. Of note, the synthesis of [Ni(H20)2(dpype)](PF6)2 (6a) was first achieved via NiCl2(dppe), as for 13 (Section 3.2.1.11), but as this method is more difficult and gives a lower yield, it was not employed for synthesis of 6b. [Ni(H20)2(dpype)]2+ was also prepared in situ upon addition of C D 3 O D to a purple, CDC13 solution of Nil2(dpype) (3a), as indicated by the 8P singlet at 81.1 (diagnostic for 3a) shifting upfield to 8P 55.6 (diagnostic for 6a), along with a solution colour change to yellow. These changes were not reproducible with "dry" CD 3 OD (stored over molecular sieves) until trace H 2 0 was added to the NMR tube. Addition of hexanes to the yellow N M R solution did not precipitate [Ni(H20)2(dpype)]I2 but rather purple Nil2(dpype). Similar fluxional behaviour was reported for the [M(H20)2(dppe)](CF3S03)2 ^ [M(CF3S03)2(dppe)]. 2H 2 0 interconversion (M = Pd,Pt). 3 7 The 8P (CD 3OD) values of 58.2 and 35.3 for isolated samples of [Ni(H20)(dpype)]2+ and [Ni(H20)(dpypcp)]2+, respectively, compare well to the values obtained upon dissolving la-3a and lb-3b in D 2 0 (8 57.4 and 36.6, respectively). This confirms that NiX 2(P-P) complexes 1-3 66 Chapter 3 references on page 76 Chapter 3 convert to [Ni(H20)2(dpype)] and [Ni(H20)2(dpypcp)] in aqueous media. As an aside, note that 8p for [Pt(H20)2(dppe)]2+ is 7.0 ppm < 8p for PtCbXdppe),37 while in this current work, 8P for[Ni(H20)2(dpype)]2+ is 6.2 ppm < 8P for NiCl2(dpype). Aqueous Solution Chemistry of NiX2(PNJ2 Complexes (X= Cl, Br) The NiX 2 (PN x ) 2 complexes (X = Cl, 9; Br, 10; PN X = PNi, a; PN 2 , b; PN 3 , c) have been prepared within this group and NiCl 2(PN 2)2 (9b) and NiBr 2(PN x) 2 (lOa-c) were reported earlier to dissolve in H 2 0 to yield colourless solutions (9a was insoluble).30 These five known NiX 2 (PN x ) 2 species were re-synthesized in this current thesis work as per the literature method,30 while the previously unknown 9c was successfully prepared from NiCl 2 in 1-BuOH medium. The conditions required for dissolution (Table 3.13) suggest that water-solubility increases with the number of pyridyl groups present. Either protonation at the N-atoms to yield quaternized N i X 2 ( « H - P N x ) 2 n + species (as seen in Chapter 4 with [Ni(CO)2(2H-dpypcp)]2+) or dissociation of halide to give [Ni(H 20) 2(PN x) 2] 2 + (see above) may be occurring. The paramagnetic nature of tetrahedral Ni(II) hampered attempts to characterize the in situ species by NMR, although conductivity data suggest formation of 2:1 electrolytic species (Table 3.13). No further work was conducted to determine the identity of the species obtained upon dissolution of 9-10 in H 2 0. Of note, the attempted synthesis of NiI 2(PN 3) 2 yielded a pink precipitate which turns beige when pumped on, and becomes pink again upon exposure to wet solvents. The pink solid shows an ELMS peak corresponding to [Ni(PN3)2]2 +, but is not soluble in acetone. [Pink [Ni(PN3)2]Cl2 (see Section 3.3.3) does not turn beige when pumped on, and is soluble in acetone]. Microanalysis for the pink ppt does not match that calculated for NiI 2(PN 3) 2 or NiI 2(PN 3) 2 »H 20. Table 3.13 Molar Conductivity Data for NiX 2(PN x) 2 Complexes in H 2 0 Compound A M ( H 2 0 ) f l Soln. Conditionsb NiClzfPNOj (9a) na insoluble NiCl 2(PN 2)2 (9b) 261 100°C NiCl 2(PN 3) 2 (9c) 274 ~ 5 0 ° C NiBr 2(PNi) 2 (10a) 207 100°C NiBr 2(PN 2) 2 (10b) 253 ~ 50°C NiBr 2(PN 3) 2 (10c) 277 r.t. { a ) Units are Q"1 cm2 mol"1. { b ) See Table 3.12, footnote (c). 67 Chapter 3 references on page 76 Chapter 3 3.3.3 Synthesis and Characterization of NiCl2(PN3). H 20 (7) and [Ni(PN3)2]Cl2 (8) The preparation of tetrahedral, ^TV-coordinated NiCl 2(PN 3) . H 2 0 (7) from N i C l 2 . 6H 2 0 has been reported by this group,30 while the formation of octahedral, tripodally N,N',N"-coordinated [Ni(PN3)2]Cl2 (8) from NiCl 2 • 6H 2 0 is also known.32 Complexes 7 and 8 (Figure 3.11) have now been prepared in a new fashion in this current thesis work. Figure 3.11 Complexes 7 and 8. Complex 7 was obtained in 25% yield on attempting to prepare Ni(CO) 2(PN 3) 2 from Ni(CO)2(PPh3)2 and PN 3 in CH 2C1 2 (Section 3.2.2.1 and Figure 3.12). CH 2C1 2 (under laboratory light conditions) must be the source of chloride; such chloride abstraction from chlorinated solvent has been reported in, for example, the formation of [MCl(PR3)(dppe)]+ (M = Pd, Pt; PR 3 = P"Bu3, PEt 3), 7 4" 7 6 but no example of abstraction to give CI" anions could be found [oxidative addition of CH 2C1 2 to form species such as *ra«s-[Rh(dmpe) 2(Cl)(CH 2Cl)]Cl or [RhCl(dppe)]2(//-C1)2(//-CH2) are also known].77'78 Resonances characteristic of 1,2-C12C2H4 (an expected product from the photolytic decomposition of CH 2C1 2, Eq 3.1) are seen in the ^ NMR spectrum of the filtrate from which 7 was prepared; no such resonances or any traces of 7 were seen within a control reaction carried out for 1 week at 80°C in the dark. Detection of 7 and 1,2-C12C2H4 upon exposure of the control reaction to light supports a reaction such as that shown in Eq. 3.1. [Photolytic decomposition of CHC13 in the presence of H 2 0 / 0 2 similarly yields HC1, Cl 2 CO, and C l 2 by radical processes].79 The GC detection of CO(g) (91 ± 4% of the amount in the Ni(CO)2(PPh3)2 precursor; see Appendix A. 10 for calculations) in the headspace of the reactor in red/orange crystal or pink monohydrated solid (7) (8) 68 Chapter 3 references on page 76 Chapter 3 which 7 was prepared provides support for a required "CO-displacement". CH 2C1 2 — ^ > CH2C1- + Cl- > V2 [1,2-C2H4C12 + Cl 2] (Eq. 3.1) Complex 7 was also prepared from NiCl 2 • 6H 2 0 (Figure 3.12). The use of 1-BuOH rather than glacial H O A c 3 0 resulted in double the reported yield (83 vs. 48%) after a shorter reaction time (V2 vs. 3'/2 h). Attempts to prepare the PNi and PN 2 analogues of 7 via method 2 were unsuccessful and resulted in the low-yield formation of NiCl2(PNi)2 and NiCkfPN^. Of note, P.iV-coordinated PdCl 2(PNi) 8 0 and Ni(CO)2(PNi) are both known.81 C H 2 C 1 2 80°C, 2 h, lablight Ni(CO) 2 (PPh 3 ) 2 + 3 P N 3 - sr • 2 P N 3 and 2 PPh 3 methodl (25% yield) \ 3 3 NiCl 2 (PN 3 ) • H 2 Q (7) N i C l 2 • 6 H 2 0 + 1 P N , 1-BuOH 65°C, 30 min f method 2 (83% yield) Figure 3.12 Synthesis of 7 via novel method 1 and conventional method 2. The synthesis of the cationic "sandwich" complex p i^(PN3)2]Cl2 (8) via conversion of 7 in the presence of excess PN 3 (Figure 3.13) was serendipitous, and red/orange block crystals of 8 were first observed 12 d after leaving a vessel containing 7 and its yellow mother-liquor exposed to light; all traces of 7 disappeared after three more days. Complex 8 was also isolated as a pink monohydrate by a conventional method (Figure 3.13, Section 3.2.2.2). method 1 for 7 15 d Ni(CO) 2 (PPh 3 ) 2 + 3 P N 3 7 and 2 P N 3 N i C l 2 • 6 H 2 0 + 3 P N 3 ( 9 % yield) 1-BuOH, 65°C, 3 h [Ni(PN 3 ) 2 ]Cl 2 (8) (65% yield) 8 H 2 0 + P N q Figure 3.13 Novel and conventional syntheses of 8 and 8 • H 2 0 . 69 Chapter 3 references on page 76 Chapter 3 A speculative pathway for conversion of 7 to 8 is depicted in Figure 3.14. Step (a) is written as ring-opening of the P,TV-chelate at the semi-hard Ni(II) centre;82 this could be followed by rapid TV-coordination of either a pyridyl pendant-arm of the ligated P N 3 moiety (step b) or a second PN 3 molecule. Subsequent TV-coordination of additional pyridyl moieties (c-e) would enhance the hardness of Ni(II), thereby decreasing the probability of P-coordination. The inherent instability of the 4-membered P,TV-chelate likely drives the initial rupture in the proposed mechanism and certainly accounts for the predominance in the literature of monodentate or bridging coordination modes of 2-pyridylphosphine ligands over the mononuclear P.TV-chelate mode (see Section 1.4.2, p.7). The structures of Ru(77 2-PN 1)(CO) 2Cl 2, 8 3 [Pt(7 /-PNi)(?Ni)Cl] + , 8 ° and [Pt(772-PNi)(PNi)Me]+ 8 4 exemplify the ring-strain in a 4-membered P,TV-chelate, with the P-M-N angle compressed from 90 to ~ 68°, and the M-P-C angle compressed from 109.5 to ~ 85°. The ring-strain in Ru(77 2-PNi)(CO) 2Cl 2 is reported to be the cause of its facile conversion to P-coordinated Ru(PNi)2(CO)2(Cl)2 upon addition of 2 equiv. of PNi . 8 3 Figure 3.14 Possible pathway for conversion of 7 to 8. Although complexes of the general type [M(PN 3) 2]X 2 (M = Co, Cu, Fe, Mn, Ni, Ru, Zn; X = C104, C 7 H 7 S 0 3 , N0 3 ) 3 2 , 8 5 " 8 9 are known, and X-ray confirmation of the Tv^TV'-tripodal mode has been obtained for the Ru, 8 5 Zn, 8 6 and Co 8 5 complexes, this thesis work represents the first preparation of a [M(PN 3) 2] 2 + compound via a P,TY-coordinated precursor, albeit in only 9% yield. 70 Chapter 3 references on page 76 Chapter 3 The more conventional reaction of NiCi2»6H20 with 3 equiv. of PN3 (Figure 3.13) proceeded in 65% yield. Note that reaction of NiCl 2 • 6H 2 0 with only 2 equiv. of PN 3 in 1-BuOH yields NiCl2(PN3)2.2H20 (9c). Characterization of 7 The identity of the pale-blue solid has previously been confirmed as NiCl2(PN3). H 2 0 by microanalysis, with ^LSEVIS peaks corresponding to 7 and 7-Cl-H 20, a v(H-OH) band at 3365 cm"1, and p e f f = 3.03 B.M. supporting this formulation.30 In this thesis work, u e f f = 3.31 B.M. , and ^SBVIS peaks corresponding to 7, 7-C1 and 7-2C1 were seen with the correct isotope patterns.64 Aside from the JR pyridyl bands at 1431, 1458, 1560, and 1585 cm"1, two previously unreported py bands were observed at 1635 and 1621 cm"1; these are characteristic of P,TV-coordinated P N 3 8 3 ' 9 0 ' 9 1 as more than four py skeletal stretches between 1440 and 1650 cm"1 indicate the non-equivalence of the pyridyl rings.32'92 Further characterization of 7 was performed in this thesis work. Previous attempts to characterize 7 by 3 1P{1H} NMR at 80.95 MHz were unsuccessful,30 but a broadened singlet at 8 -17.0 was seen at 121.42 MHz. The 16.2 ppm upfield coordination shift vs. free P N 3 (8P = -0.8) is typical for phosphorus ligands that form 4-membered chelate rings53 (e.g., Ru(II) and Pt(II) P.TV-coordinated PN 3 complexes).83'90'93'94 The broadening of the 3 1 P singlet is due to paramagnetic Ni(II), and, in conjunction with the ueff data (cf. 2.83-3.40 B.M. for T d Ni(II) with PPh3 and halide ligands),45 confirms that 7 is tetrahedral. In the synthesis of 7 via method 1 two equiv. of PN 3 and PPh3 are seen by 3 1P{1H} NMR in the yellow reaction filtrate. Conductivity data confirm that 7 is a 2:1 electrolyte in MeOH, and -1.0 moles of H 2 0 per mole of 7 are seen in the ] H NMR spectrum. Attempts to grow crystals of 7 were limited by the fact that, of 25 solvents tested, 7 is only soluble and stable in acetone. Characterization of 8 The red/orange crystals were shown by X-ray analysis (see below) and microanalysis to be [Ni(PN3)2]Cl2 (8) while microanalysis of the pink solid was consistent with the formulation as a monohydate (8.H20). An +LSIMS peak corresponding to 8-2C1 was observed for both species, while ueff (which has not apparently been reported for any paramagnetic [M(PN 3) 2] 2 + complex) 71 Chapter 3 references on page 76 Chapter 3 was 3.20 B.M. , consistent with Oh Ni(II). Coordinated resonances of PN3 are seen in the paramagnetically broadened lH NMR spectrum of 8 (and 8 « H 2 0 ) , but no 3 1 P NMR signal was observed, presumably because of paramagnetic broadening. The LR spectra of 8 and 8 .H 2 0 exhibit only 4 py skeletal vibrations (1584, 1560, 1459, and 1426 cm"1), indicative of the highly symmetrical arrangement of the pyridyl rings.92 [Recall that 6 py bands are seen for asymmetrical 7]. These 4 bands correspond to the ranges 1575-1590, 1550-1565, 1445-1460, and 1425-1430 cm"1 reported for other [M(PN 3) 2] 2 + (M = Cu, Co, Ni, Mn, Zn) complexes.32 The v(H-OH) band is seen at 3420 cm"1 for 8. H 2 0 . The bands seen at 802 (s = 10) and 518 (s = 15) nm in the UV-Vis spectrum of 8 are assigned to vi and v2, respectively, as octahedral Ni(II) normally displays three spin-allowed bands in the ranges of 833-2000 nm (vi), 526-800 nm (v2), and 345-500 nm (v3) for the d-d transitions from the 3 A 2 g ground state [ 3A 2 g(F) -> 3 T 2 g (F) (vi), 3 A 2 g (F) 3Ti g(F) (v2), and 3 A 2 g (F) —» 3T 2 g(P) (v3)].2 The v 3 band for 8 is not observed, and presumably lies under the intense charge-transfer ligand bands which start at ~ 420 nm, as previously reported for [Ni(PN 3) 2]Cl 2. 3 2 The e values are typical for octahedral Ni(II) species.51c Dq for PN 3 is calculated (from the vi band) to be 1247 cm"1, while for [Ni(PN3)2](C104)2 in acetonitrile it is reported to be 1258 cm"1.32 [Dq for [Ni(py)6](N03)295 and Ni(py)4(NCS)2 9 6 is 970 and 1065 cm"1, respectively]. 8 is water-soluble at neutral pH under ambient conditions to yield a 2:1 electrolytic species. Melting point data are presented for characterization. X-ray Crystal Structural Analysis of [Ni(PN3)2]Cl2 The solid-state structure of 8 was determined by X-fay diffraction of a crystal grown via diffusion of hexanes into a 1-BuOH solution of 8. Selected bond lengths and angles are reported in Table 3.14 while the ORTEP appears in Figure 3 15. A complete list of crystallographic data is given in Appendix A.7. 8 resembles a paddle-wheel (C 3 v symmetry) as three planes which are coplanar with the P-Ni-P axis are defined by the six pyridyl rings. The maximum deviation from planarity for any py ring is quantified by the P-C-N-Ni torsion angle of -5.3°. Some [M(PN 3) 2] 2 + complexes resemble propellers rather than paddle-wheels as the P-C-N-M torsion angle can be as great as 40° (Zn complex).89 72 Chapter 3 references on page 76 Chapter 3 Figure 3.15 ORTEP (50% probability) of the molecular structure for the cation in rNi(PN3)2]Cl2 (8). The two P N 3 ligands in 8 are facially bound via the py N-atoms to Ni in a geometry close to O h symmetry, with N-Ni-N angles in the 88.83^91.17° range. The N-Ni-N angles and Ni-N lengths are similar to the average values for [Co(PN3)2](C104) [90.0(1)°, 2.108(7) A], 8 5 but different from those of [Ni(CHpy3)2]2 + which has a shorter Ni-N length [2.069(2) A] and larger N -Ni-N angle [93.5(1)°] due to the smaller size of the bridgehead carbon atom.89 The structure for the known compound [Ni(py)e]2+ has not been reported95 The Ni-N(py) bond length in tetragonal Ni(py)4(NCS)2 [2.033(7) A] 9 6 is shorter than the Ni-N(PN3) bond length. The average P-C bond length of 1.828(3) A is identical to that of the free ligand,43 and may be compared to 73 Chapter 3 references on page 76 Chapter 3 those of 1.823(8) and 1.817(1) A for the Ru 8 7 and Co 8 5 analogues. (These data for the Zn complex were not reported.86) The average C-P-C bond angle is 2.19° less than the average of 101.9° in the free ligand, and also smaller than the average for the R u 8 7 and Co 8 5 analogues [100.24(5)°, 100.78(6)° respectively]. In the unit cell for 8, there are also eight water molecules and two chloride atoms per metal complex; with the closest contacts being 1.98 A (for 0(1)-H(2) of one water to a PN 3 hydrogen) and 2.33 A (for Cl(l)-H(8) of one chloride to a PN 3 hydrogen) (see Appendix A Table A.27). Table 3.14 Selected Bond Lengths and Angles for [Ni(PN3)2]Cl2 Bond Lengths (A) Ni - N(l) 2.119(2) Ni - N(2) 2.102(2) P(l) - C(l) 1.829(2) P(l)-C(6) 1.827(3) N(l) - C(l) 1.358(2) N(2) - C(6) 1.371(3) N(l)-C(5) 1.350(3) N(2) - C(10) 1.335(4) C(l)-C(2) 1.388(3) C(6)-C(7) 1.390(4) C(2) - C(3) 1.377(3) C(7) - C(8) 1.383(5) C(3)-C(4) 1.381(3) C(8) - C(9) 1.385(4) C(4)-C(5) 1.378(3) C(9)-C(10) 1.385(4) Bond Angles (°) N(l)-Ni-N(l) 87.75(9) N(l)-Ni-N(l) 90.25(9) N(l)-Ni-N(l) 180.0 N(l)-Ni-N(2) 88.83(6) N(l)-Ni-N(2) 91.17(6) N(2)-Ni-N(2) 180.0 Ni-N(l)-C(l) 122.08(14) Ni-N(2)-C(6) 121.4(2) Ni-N(l)-C(5) 120.37(12) Ni-N(2)-C(10) 121.1(2) C(l)-N(l)-C(5) 117.3(2) C(6)-N(2)-C(10) 117.5(3) P(l)-C(l)-N(l) 121.4(2) P(l)-C(6)-N(2) 122.1(2) P(l)-C(l)-C(2) 117.17(14) P(l)-C(6)-C(7) 116.7(2) Reactivity of [Ni(PN3)2JCl2 The potential for a P,7V,iVr',iV"-coordination mode exists as there are available two P-atoms in 8. Reaction with another metal centre (such as NiCl 2 , NiCl2(PPh3)2, or Ag(CF 3S0 3)) in a 1:1 ratio could potentially yield a polymeric chain (Figure 3.16), while a 1:2 ratio could produce a capped M-8-M species. Alternatively, reaction of 8 with an M(0) species (such as Ni(l,5-COD) 2) in a 4:1 ratio could result in the formation of a three-dimensional polymeric matrix with tetrahedral Ni(8)4 repeat units. 74 Chapter 3 references on page 76 Chapter 3 (M^^:P(N) 3-Ni-(N) 3P:-^(N!^ n Figure 3.16 Various chain polymers of -[M-8-M]-. The attempted preparation of such polymeric species is described in Section 3.2.4. Blue, white, and brown solids were obtained upon reaction of pink 8 with green NiCl 2 • 6H 2 0 (or NiCl2(PPh3)2), yellow Ni(l,5-COD) 2, and white Ag(CF 3S0 3), respectively. All these solids yielded noisy 31P{'H} NMR spectra, typical of paramagnetic species. No further effort was made to characterize these solids, although the white precipitate was poorly soluble in solvents tested, as is typical for polymeric complexes. 3.4 Conclusion The ten P-coordinated 2-pyridylphosphine NiX2(P-P) species la-5b (X = CI, Br, I, NCS, and N0 3 ; P-P = dpype and dpypcp) were synthesized via displacement of PPh3 from the appropriate NiX 2(PPh 3) 2 precursor, and were characterized by ' H and 3 ,P{ 1H} NMR, UV-Vis, and IR spectroscopies, mass spectrometry, conductivity, melting point, and microanalysis; X-ray structures of dpypcp, la, lb, 2a, 2b, and 3b were also obtained. Novel [Ni(H20)2(P-P)](PF6)2 (6a, 6b, 13) species were prepared and characterized. Comparison of their 5p values to those for 1-3 in D 2 0 suggests that the NiX2(P-P) complexes convert to [Ni(H20)2(P-P)]2 + in aqueous media, with eventual decomposition to [Ni(H 2 0)6] 2 + and the diphosphine bisoxide. 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Nakamoto, K. IR Spectra of Inorganic & Coordination Compounds, 2nd Ed. New York: Wiley Interscience, 1970. 58. Sabatini, A.; Bertini, I. Inorg. Chem. 1965, 4, 1665. 59. Turco, A.; Pecile, C. Nature 1961,191, 66. 60. Eagle, C. T.; Walmsley, F. J. Chem. Educ. 1991, 68, 336. 61. Lever, A. B. P.; Matovano, E. ; Ramaswamy, B. S. Can. J. Chem. 1971, 49, 1957. 62. Addison, C. C ; Logan, N. N.; Wallwork, S. C ; Garner, C. D. Quart. Rev. 1971, 25, 289. 63. Alyea, E . C ; Ferguson, G.; Ruhl, B. L.; Shakya, R. Polyhedron 1987, 6, 1223. 64. Isotope Pattern Calculator, v. 1.6.5, L. Arnold, THINK Technologies Inc., 1990. 65. Allen, D. L . ; Gibson, V. C ; Green, M . L.; Skinner, J. F.; Bashkin, J.; Grebenik, P. D. J. Chem. Soc, Chem. Commun. 1983, 895. 66. Pelizzi, C ; Pelizzi, G. Acta Crystallogr., Sect. B 1979, 35, 1785. 67. SvmApps. v. 1.0. Nedwed, Karl, SoftShell International Ltd., 1996. 79 Chapter 3 references on page 76 Chapter 3 68. Spek, A. L.; van Eijck, B. P.; Jans, R. J. F.; van Koten, G. Acta Crystallogr., Sect. C 1987, 43, 1878. 69. Busby, R ; Hursthouse, M . B.; Jarrett, P. S.; Lehmann, C. W.; Malik, K. M . A.; Phillips, Coral. J. Chem. Soc, Dalton Trans. 1993, 3767. 70. Rahn, J. A ; Delian, A.; Nelson, J. H. Inorg. Chem. 1989, 28, 215. 71. Geary, W.J. Coord. Chem. Rev. 1971, 7, 110. 72. Huheey, J. E. ; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry: Principles and Structure and Reactivity, 4th ed., New York: Harper Collins, 1993. 73. Schrock, R. R ; Osborn, J. A. J. Am. Chem. Soc. 1971, 93, 2397. 74. Fallis, S.; Rodriguez, L.; Anderson, G. K.; Rath, N. P. Organometallics 1993,12, 3851. 75. Oliver, D. L.; Anderson, G. K. Polyhedron 1992, 11, 2415. 76. Anderson, G. K.; Lumetta, G. J. Inorg. Chem. 1987, 26, 1291. 77. Marder, T. B.; Fultz, W. C ; Calabrese, J. C ; Harlow, R. C ; Milstein, D. J. Chem. Soc, Chem. Commun. 1987, 1543. 78. Ball, G. E. ; Cullen, W. R.; Fryzuk, M . D.; James, B. R ; Rettig, S. J. Organometallics, 1991, 10, 3767. 79. 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Polyhedron 1991,10, 1759. 81 Chapter 3 references on page 76 Chapter 4 CHAPTER FOUR The Synthesis, Characterization, Reactivity, and Aqueous Solution Chemistry of Ni(0) 2-Pyridylphosphine Complexes 4.1 Introduction The synthesis of hundreds of Ni(0) complexes of type NiP„ and Ni(CO)„(P) 4 . n (where P is a monodentate tertiary phosphine) has been extensively reviewed1'2 and the impact of these complexes upon both theoretical and catalytic chemistry has been substantial, a prime example being Tolman's landmark work with phosphorus-ligand exchange equilibria on such species which led to a greater understanding of the balance between electronic and steric factors in the formation of metal complexes.3 Examples of contributions towards catalytic chemistry are myriad and it is of historical interest to note that Ni(CO)2(PPh3)2 was the first metal phosphine complex (of any oxidation state) to exhibit rates of catalysis greater than those afforded by non-phosphine containing metal catalysts.4 More recent work with Ni(CO)2(PPh3)2 reports on the silylation of conjugated dienes5 and the double-cycloaddition copolymerization of diynes with maleimides.6 More generally, Ni(0) tertiary phosphine catalyzed reactions are numerous, the best known example being the (cyclo)oligomerization of butadiene by Wilke's group to an array of products.7 Various Ni(0)P4 complexes have also been used in a variety of polymerization and (cyclo)oligomerization catalytic cycles8"11 to produce materials as complex as polypeptides.12 Successful coupling reactions13'14 and various cyclization reactions15 have also been catalyzed by Ni(0)P4 species. Of historical interest, the first M(0) complex prepared was Ni(CO) 4 in 1890.16 This Chapter describes the expansion of the field of Ni(0) 2-pyridylphosphine chemistry with the preparation and characterization of three Ni(CO) 2(PN x) 2 species, two Ni(CO)2(P-P) species and one dinuclear carbonyl species (Section 4.3.1), three Ni(PR 3) 4 species, two Ni(P-P)2 species, and fifteen Ni(0) tertiary mixed-phosphine species (Section 4.3.3), and three trans-Ni(CH3)(I)P2 species (Section 4.3.4). The aqueous solution chemistry of the dicarbonyl complexes is discussed in Section 4.3.2 while the reactivity of the tertiary Ni(0) phosphine 82 Chapter 4 references on page 127 Chapter 4 complexes with various small molecules is examined in Section 4.3.3.3. The synthesis of mono-and bismethylated phosphonium salts of the 2-pyridylphosphine ligands is discussed in Section 4.3.5. Various attempts to prepare the o-acyl complexes Ni(COCH3)(I)Ln, via either carbonylation of /ra«s-Ni(CH3)(i)Ln species or iodomethylation of Ni(CO)2Ln species, is discussed in Section 4.3.6. Note that some of the Ni(0) complexes (19a, 19b, 20b) have already been reported by this group.17 4.2 Experimental ^Pl'H} and J H NMR data were measured at 121.42 and 300 MHz, respectively, at r.t.; J values are in units of Hz. Proton resonance assignments (Ha, H b, Ho, H3.6) are shown in Figure 3.1, p.47). All assignments of pyridyl skeletal IR bands are based on comparison to the IR spectrum of pyridine,18 the free pyridylphosphine ligands (see Sections 2.3.3-5, p.24), or known Ni 2-pyridylphosphine complexes17 (see Section 3.3.1, p.45). 4.2.1 Preparation of Nickel Carbonyl 2-Pyridylphosphine Complexes 4.2.1.1 In Situ Preparation of Ni(CO)2(PNi)2 (19a) This compound was not prepared via the literature method,17 but rather by a modification of the literature method for 19b.17 Accordingly, Ni(CO)2(PPh3)2 (4.2 mg, 6.57 umol) and two equiv. of PNi (3.47 mg, 13.2 umol) were placed in an N2-flushed NMR tube to which acetone-^ (1 mL) was added. A yellow solution was obtained after heating the mixture for 2 h at 60°C. "P^H} NMR (acetone-^): 8 -5.5 (s, free PPh3), -3.6 (s, free PNi), 32.7 (s, Ni-PPh3); a weak AB type signal at 8 35.56 ( 2 J P P 38.5) and 8 37.15 ( 2 J P P 39.6) presumably corresponds to the mixed phosphine species Ni(CO)2(PPh3)(PNi). 8P Ni-PNi was not observed. The in situ preparation of 19a was also attempted in C 6 D 6 with Ni(CO) 2(PPh 3) 2 and two equiv. PNi as above. The mixture was heated for 3 h at 70°C. "P^H} N M R (C 6D 6): 8 -3.4 (s, free PPh3), -3.5 (s, free PNi), 32.6 (s, Ni-PPh3), 31.3 (s, Ni-PNj), weak AB type signal at 8 35.78 ( 2 J P P 36.6) and 8 37.42 ( 2 J P P 37.4). IR (CH2C12): 1941, 2001 (s, CO) (lit. 1946, 1998, KBr) . 1 7 The NMR data have not been previously reported. 83 Chapter 4 references on page 127 Chapter 4 4.2.1.2 In Situ Preparation of Ni(CO)2(PN2)2 (19b) The procedure was as for 19a, using Ni(CO)2(PPh3)2(4.7 mg, 7.35 pmol), P N 2 (3.90 mg, 14.8 pmol), and acetone-c/6 (1 mL). 31V{lH) NMR (acetone-J6): 5 -5.5 (s, free PPh3), -2.0 (s, free PN 2), 32.7 (s, Ni-PPh3); doublets at 8 36.35 ( 2 J P P 85.0) and 8 39.74 ( 2 J P P 114.4) are likely attributable to the mixed phosphine species Ni(CO)2(PPh3)(PN2) as above with the PNi species, but why the 2 J P P values are dissimilar is not known. 8P Ni-PN 2 was not observed. The in situ preparation of 19b was also attempted in CeD6 as for 19a, but using two equiv. PN 2 . 3 1P{ 1H) NMR (C 6D 6): 8 -3.4 (s, free PPh3), -1.9 (s, free PN2), 32.6 (s, Ni-PPh3), 33.1 (s, Ni-PN 2), weak AB type signal at 8 36.23 ( 2 J P P 83.3) and 8 39.68 ( 2 J P P 79.9). LR (CH2C12): 1942, 2003 (s, CO). 19b has been previously prepared, the reported in situ "Pf'H} N M R (CDC13) data being fairly similar [8P Ni-PN 2 = 31.2 and 8P AB signal = 32.9/37.5];17 LR and 2 J P P data were not previously reported. The in situ preparation of 19b was also attempted in dmso-t/6, using two equiv. PN 2 , but only resonances corresponding to free ligands, Ni(CO)2(PPh3)2, and the mixed phosphine species were observed. 4.2.1.3 In Situ Preparation of Ni(CO)2(PN3)2 (19c) The procedure was as for 19a, using Ni(CO)2(PPh3)2 (4.6 mg, 7.20 pmol), two equiv. of P N 3 (3.83 mg, 14.4 pmol), and acetone-rfe (1 mL). 3 1P{1H} NMR (acetone-c/6): 8 -5.5 (s, free PPh3), -0.1 (s, free PN 3), 32.7 (s, Ni-PPh3); doublets at 8 35.92 ( 2 J P P 125.4) and 8 43.29 ( 2 J P P 232.6) presumably correspond to the mixed phosphine species Ni(CO)2(PPh3)(PN3), but again, the reason why the 2 J P P values are dissimilar is not known. 8P Ni-PN 3 was not observed. The in situ preparation of 19c was also attempted in CeD6 as for 19a, using two equiv. PN 3 . 3 1P{ 1H) NMR (C 6D 6): 8 -3.4 (s, free PPh3), -0.09 (s, free PN 3), 32.7 (s, Ni-PPh3), 34.1 (s, Ni-PN 3), weak AB type signal at 8 35.72 ( 2 J P P 113.3) and 8 43.08 ( 2 J P P 116.1). LR (CH2C12): 1943, 2004 (s, CO). 19c has not been previously prepared. 4.2.1.4 [Ni2(CO)4(//-PN2)2]Cl4 (19d) The procedure was similar to that for 19b, but using Ni(CO)2(PPh3)2 (4.2 mg, 6.57 pmol), two equiv. of P N 2 (3.51 mg, 13.2 pmol), and CDC13 (1 mL); heating at 60°C for 90 min resulted 84 Chapter 4 references on page 127 Chapter 4 in a yellow solution and a purple precipitate. The purple product was isolated by column chromatography (300-mesh silica gel, Fisher) using neat acetone to elute PPh3, PN 2 , and Ni(CO)2(PPh3)2, and then a CH 2 Cl 2 /MeOH (20:1) mixture to elute the purple band. Yield: 1.12 mg (38%). Anal. Calcd for C ^ H ^ C L N t O ^ N b : C, 48.00; H, 3.02; N, 6.22%. Found: C, 46.92; H, 2.88; N, 5.46%. ! H NMR (CD 3OD): 7.13 (t), 7.15 (m), 7.20 (m), 7.25 (m), 7.34 (m), 7.45-7.52 (m), 7.56 (t), 7.60 (t), 7.80 (m), 8.20 (tt), 8.79 (dt, He), 9.22 (dt, He). 31P{XH} N M R (CD 3OD): 5 24.1 (s). UV-Vis (MeOH): 572 [122]. IR (CH2C12): 1971 (s, CO). "LSJMS (m/z): 757 PVT]. A M : 429 (MeOH). 4.2.1.5 Ni(CO)2(dpype) (20a) The procedure was as for 20b (see below), using Ni(CO)2(PPh3)2 (12.1 mg, 18.9 umol), dpype (7.81 mg, 19.4 umol), and C 6He (5 mL). Yield: 3.52 mg (36%). Anal. Calcd for C 2 4 H 2 0 N 4 N i O 2 P 2 : C, 55.77; H, 3.90; N, 10.83%. Found: C, 55.66; H, 3.89; N, 10.54%. X H N M R (C 6D 6): 6 2.8 (m, 4Ha), 7.1-8.6 (m,16H, pyridyl). "P^H) NMR (C 6D 6): 5 55.3 (s). UV-Vis (CH2C12): 240 [3270], 268 [3430], dpype bands (cf. bands reported at 240 [2330], 268 [2430], and 300 [2540] in Section 2.3.4 (p.26) for free dpype); 322 [4010], 334 [3875], 352 [3360], probably Ni(e)->CO(7i*) charge-transfer bands.193 IR (CH2C12): 1999, 1937 (s, CO) (lit. 1994, 1939, KBr); 1 7 1569, 1450, 1420 (s, py skeletal bands) (lit. 1559-1577, 1448-1457, 1419-1432, KBr, for PNx-containing species).17'20 m.pt.: ~ 185°C (dec). A M : 0 (MeOH), 3.6 (H 20). 4.2.1.6 Ni(CO)2(dpypcp) (20b) This compound was prepared following a substantial modification of the literature method used for Ni(CO)2(dpype).17 In an N2-charged Schlenk tube, Ni(CO)2(PPh3)2 (185 mg, 290 umol) was dissolved in C e H 6 (40 mL). The mixture was stirred for 10 min at 85°C to give essentially a pale-yellow solution, but then filtered to remove trace, insoluble material. The dpypcp (118 mg, 267 umol) was added under N 2 to the pale-yellow filtrate and the mixture was stirred for 2 h at 85°C. The resulting bright-yellow solution was filtered, reduced in volume to ~ 5 mL, and hexanes (50 mL) was then added to precipitate the product. The pale-yellow solid was collected, washed with cold Et 2 0 (4x5 mL), and dried in vacuo overnight. Yield: 58.9 mg (40%). Anal. Calcd for C 2 7H 2 4 N 4 Ni0 2 P 2 : C, 58.21; H, 4.34; N, 10.06%. Found: C, 58.22; H, 4.43; N, 9.76%. 85 Chapter 4 references on page 127 Chapter 4 lH NMR (C 6D 6): 5 1.59 (m, 2Ha), 2.15 (dm, 4Hb), 3.74 (m, 2Hc), 6.41-8.55 (m, 16H, pyridyl). "Pl/H} NMR (C 6D 6): 6 35.0 (s). UV-Vis (CH2C12): 236 [2365], 268 [2520], dpypcp bands (cf. bands reported at 238 [2330], 268 [2430], and 308 [2720] in Section 2.3.5 (p.26) for free dpypcp); 322 [2910], 344 [2740], 364 [2600], charge-transfer bands (see Section 4.2.1.5). LR (CH2C12): 1997, 1927 (s, CO); 1569, 1450, 1420 (s, py skeletal bands). ELMS (m/z): 500 PVT-2CO]. m.pt.: ~ 205°C (dec). A M : 0 (MeOH), 4.4 (H 20). A crystal was grown that was suitable for X-ray analysis (Section 2.5.1, p.31). 4.2.1.7 Attempted Preparation of Ni(CO)2(P-P) from NiCl2(P-P) The preparations of 20a and 20b were also attempted via the reduction and carbonylation of the appropriate NiCl2(diphosphine) la or lb with Zn dust and CO(g) in THE, as used to synthesize Ni(CO)2(PPh3)2 (see Section 2.4.6, p.30, and ref. 21). This method proved unsuccessful and yielded only the respective starting material la and lb as determined by 3 1P{ !H} NMR spectroscopy. 4.2.1.8 Preparation of Triflate Salts of Protonated Ni(CO)2(dpypcp); [Ni(CO)2(2H-dpypcp)]2+(S03CF3)2 Three experiments were conducted. To a pale-yellow solution of Ni(CO)2(dpypcp) (0.7-1.4 mg, 1.25-2.51 pmol) in C6H6 (2 mL) contained in a Schlenk tube under N 2 was added either 2, 4, or 6 equiv. (22, 83, or 134 pL) of C F 3 S 0 3 H (0.113 M solution in CeHe); this resulted in the the precipitation of a bright-yellow solid within 5 min. The solid was collected and dried in vacuo overnight. All three solids analyzed as bis-triflate salts and gave the same N M R and LR spectra. Anal. Calcd for C 29H 2 6F 6N40gP 2S 2Ni: C, 40.63; H, 3.06; N, 6.54%. Found (for trial with 2 equiv. of C F 3 S 0 3 H added; 4 and 6 equiv. give very similar analyses): C, 40.88; H, 3.29; N, 6.37%. *H NMR (acetone-de): 5 1.39 (m, 2H,), 2.20 (dm, 4Hb), 3.48 (m, 2Hc), 8.08-9.36 (m, 16H, pyridyl), 10.5 (s, 2H, N-H). 3 1P{1H} NMR (acetone-d6): 5 25.5 (s). LR (KBr): 3095 (s, N-H); 2045, 1996 (s, CO); 1522, 1447, 1420 (s, py skeletal bands); 1170, 765 (dpypcp); 1623, 1400, 1277, 1256, 1031, 641 (s, CF3S03"). LR assignments are discussed in Section 4.3.2. 86 Chapter 4 references on page 127 Chapter 4 4.2.1.9 Preparation of Triflate Salts of Proton a ted dpypcp; [2H-dpypcp]2 (S03CF3)2 Three experiments were again conducted. To a solution of dpypcp (6.8 mg, 16.9 umol) in EtOH (0.5 mL) contained in a Schlenk tube under N 2 was added Et 2 0 (3 mL) followed by either 2, 4, or 6 equiv. (3, 6, or 9 uL) of neat CF 3 S0 3 H; this resulted in the formation of a finely divided white precipitate. Note that addition of C F 3 S 0 3 H prior to the addition of Et 2 0 resulted in formation of a pale-yellow oil. The solid was collected and dried in vacuo overnight. All three solids here also analyzed as the bis-triflate salt and gave the same NMR and IR spectra. Anal. Calcd for C 27H 2 6F 6N40 6P 2S 2: C, 43.67; H, 3.53; N, 7.55%. Found (for trial with 2 equiv. of C F 3 S 0 3 H added; 4 and 6 equiv. give very similar analyses): C, 43.49; H, 3.37; N, 7.22%. *H NMR (acetone-Jg): 5 1.44 (m, 2Ha), 2.27 (dm, 4Hb), 3.49 (m, 2FQ, 7.98-9.27 (m, 16H, pyridyl), 10.0 (s, 2H, N-H). ^Pl'H} NMR (acetone-dg): 5 -13.6 (s). IR (KBr): 2690 (s, N-H); 1524, 1447, 1420 (s, py skeletal bands); 1172, 762 (dpypcp); 1623, 1399, 1277, 1259, 1031, 638 (s, CF3S03"). EIMS (m/z): 402 [dpypcp+], 149 [CF 3 S0 3 ] . IR assignments are also discussed in Section 4.3.2. 4.2.2 Preparation of Ni(0) Phosphine Complexes Complexes 21-23, 24b-c and 25 were prepared in situ while 24a and 26 were isolated. All ^Pj1!!} N M R data were collected in C 6 D 6 (with the exception of 24a in CDC13) and are reported in Table 4.13 for 21-23 and 25 (p. 116) and Table 4.12 for 24 and 26 (p. 114). The quantities of each reagent used in the synthesis of 21-23 are listed in Table 4.1. 4.2.2.1 Ni(PR3)2(dppe) [PRa = PPh3, (21a); PNi, (21b); PN2, (21c); PN3, (21d)] To an N2-flushed NMR tube containing Ni(l,5-COD) 2, one equiv. of dppe, and two equiv. of PR 3 were added C 6 D 6 (1 mL); 2 min heating at 60°C resulted in an orange (21a & b), dark-orange (21c), or red (21d) solution. 4.2.2.2 Ni(PR3)2(dpype) [PR3 = PPh3, (22a); PN l 5 (22b); PN2, (22c); PN3, (22d)] The procedure was the same as for 21, with an orange solution obtained in all cases. 4.2.2.3 Ni(PR3)2(dpypcp) [PR3 = PPh3, (23a); PNi, (23b); PN2, (23c); PN3, (23d)] The procedure was the same as for 21, with a red solution obtained in all cases. 87 Chapter 4 references on page 127 Chapter 4 4.2.2.4 Ni(dpypcp)2 (24a) This compound was prepared following a modification of the literature method for Ni(dpype)2.17 On mixing Ni(l,5-COD) 2 (29.3 mg, 107 pmol) and dpypcp (93.4 mg, 211 pmol) in Celts (10 mL) there was a rapid colour change from bright-yellow to orange. After being stirred at 60°C for 3 h the solution was dark red, and upon addition of hexanes (20 mL) a dark-red precipitate was obtained; this was collected, washed with hexanes (4x5 mL), and dried in vacuo overnight. Yield: 84.0 mg (42%). Anal. Calcd for CsoFLsNgNiP^ C, 63.65; H, 5.13; N, 11.88%. Found: C, 63.49; H, 5.03; N, 11.61%. 'HNMR: 5 1.72 (m, 4Ha), 2.13 (dm, 8Hb), 3.89 (m, 4FQ, 6.32-8.51 (m, 32H, pyridyl). "Pf^H} NMR: 8 38.70 (s). UV-Vis (CeH*): 409 [2325]. ELMS (m/z): 942-944 [M"]. m.pt.: 112-115°C (dec). 4.2.2.5 Ni(dppe)2 (24b) This complex has been isolated previously.22 To an N2-flushed: N M R tube containing Ni(l,5-COD) 2 (4.37 mg, 15.9 pmol) and dppe (15:4 mg, 38.6 pmol) was added C 6 D 6 (1 mL); 2 min heating at 60°C resulted in a yellow solution. ^Pf/H} NMR: 8 43.99 (s) (lit. 42.4, toluene-Table 4.1 Amounts of Reagents Used in Preparation of 21-23 " 21a 21b 21c 21d Ni(l,5-COD) 2 4.05 (14.7) 4.01 (14.6) 4.30(15.6) 3.99(14.5) dppe 5.96(14.7) 5.90(14.8) 6.11 (15.3) 5.80 (14.6) PR 3 7.79 (29.7) 8.46(32.1) 8.35(31.6) 7.80 (29.4) 22a 22b 22c 22d Ni(l,5-COD) 2 4.60(16.7) 5.02 (18.2) 5.28 (19.2) ., 5.20(18.9) dpype 7.41 (18.4) 7.83 (19.5) 7.81 (19.4) 7.50(18.6) PR 3 9.75 (37.2) 10.00 (37.9) 10.19(38.6) 10.26 (38.7) 23a 23b 23c 23d Ni(l,5-COD) 2 4.59(16.7) 3.80(13.8) 6.13 (22.3) 5.02(18.2) dpypcp 7.33 (16.6) 5.92(13.4) 9.86 (22.3) 9.46 (21.4) PR 3 8.71 (33.2) 7.04 (26.7) 11.92(45.1) 11.39(42.6) Amounts are given as mg (pmol). 88 Chapter 4 references on page 127 Chapter 4 4.2.2.6 Ni(dpype)2 (24c) The procedure was as for 24b, but using dpype (14.6 mg, 36.2 umol), which resulted in an orange solution. A modification of this procedure has been published.17 3 1P{1H} NMR: 5 55.90 (s) (lit. 55.9, C 6 D 6 ) . 1 7 UV-Vis (C 6D 6): 389 [1970], not reported in ref. 17. 4.2.2.7 Ni(P-P)(P'-P') [P-P = dppe, P'-F = dpype (25a); P'-F = dpypcp (25b); P-P = dpype, P'-F = dpypcp (25c)] The procedure was as for 21 but using 1 equiv. each of Ni(l,5-COD) 2, P-P, and P'-F. All three product solutions were orange. The quantities of each reagent used are listed in Table 4.2. Table 4.2 Amounts of Reagents Used in Preparation of 25a-c a 25a* 25b c 25c d Ni(l,5-COD) 2 3.94(14.3) 3.89(14.1) 5.72 (20.8) P-P 6.06(15.2) 6.51 (16.3) 9.74 (24.2) F - P 7.14(17.7) 6.73 (15.2) 8.62 (24.1) Amounts are given as mg (umol). ( } P-P = dppe; P'-P' = dpype. ( c ) P-P = dppe; P-P 1 = dpypcp. P-P = dpype, P'-P' = dpypcp. 4.2.2.8 Ni(PR3)4 [PR3 = PPh 3 (26a); PNi (26b); PN2 (26c); PN3 (26d)] These compounds were prepared following the literature methods for 26a20 and 26b-d.17 To an Nrflushed Schlenk-tube at 0°C containing Ni(l,5-COD) 2 and 4 equiv. of PR 3 was added chilled hexanes (6 mL). The suspension was stirred for 30 min after which time an orange (26a & c), red (26b), or yellow (26d) precipitate was obtained; this was collected and any remaining 1,5-COD was removed in vacuo. The quantities of reagents used and product yield are reported in Table 4.3. Table 4.3 Amounts of Reagents Used in Preparation of 26a-d a 26a 26b 26c 26d Ni(l,5-COD) 2 9.4 (34.2) 7.2 (26.2) 7.4 (26.9) 6.2 (22.5) PR3 35.9 (137) 27.7 (105) 28.5 (108) 24.0 (90.2) Yield b 34.9 (92) 25.9 (89) 27.3 (91) 22.0 (87) Amounts given as mg (umol). mg yield (%). 89 Chapter 4 references on page 127 Chapter 4 4.2.3 Reactivity of Methyl Iodide with Ni(0) Pyridylphosphine Complexes 4.2.3.1 *rans-Ni(CH3)(I)(PN3)2 (27) To an N2-flushed Schlenk tube at 0°C containing Ni(PN 3) 4 (25.2 mg, 22.5 pmol) was added CeHs (6 mL) to give a dark-yellow solution. One equiv. of CH 3 I (1.4 pL, 22.5 pmol) was added and the reaction solution warmed to r.t. with continual stirring (20 min). The mixture was then heated with stirring for 20 min at 80°C to give a clear red solution and a tan precipitate, that was collected by filtration. Yield: 6.9 mg (42%). Anal. Calcd for C3iH27rN4NiP2: C, 50.93; H , 3.72; N, 11.49%. Found: C, 50.84; H, 3.66; N, 11.17%. ' H N M R (CDCh): 6 0.6 (t, 3H, 3 J P H 6.2, Ni-CFLO, 7.45-9.21 (m, 24H, pyridyl). 3 1P{ !H} NMR (CDC13): 5 31.5 (s). Hexanes (10 mL) was added to the filtrate to yield a reddish-brown solid which was shown by 3 1P{ 1H} N M R spectroscopy to be a mixture of a trace amount of unreacted Ni(PN 3) 4 and ~ 2 equiv. free PN 3 . 4.2.3.2 fra/is-Ni(CH3)(I)(dpype)2 (28) The procedure was as for 27, but using Ni(dpype)2 (68.7 mg, 80.3 pmol) and CH 3 I (5.0 pL, 80.3 pmol); a yellow/orange solid was obtained. Yield: 29.9 mg (37%). Anal. Calcd for C45H43rNgNiP4: C, 53.76; H, 4.31; N, 11.14%. Found: C, 53.91; H, 4.48; N, 10.84%. *H N M R (CDCh): 8 0.9 (qn, 3H, 3 J P H 7.1, Ni-CH 3), 2.7 (t, 8Ha), 7.51-8.78 (m, 32H, pyridyl). 3 1P{ !H} NMR (CDC13): 8 29.0 (s). No free dpype was detected in the filtrate by 3 1P{ 1H} NMR. 4.2.3.3 fra»s-Ni(CH3)(I)(dpypcp)2 (29) The procedure was as for 27, but using Ni(dpypcp)2 (59.32 mg, 69.3 pmol) and CH 3 I (4.3 pL, 69.3 pmol). A yellow solid was obtained. Yield: 34.6 mg (46%). Anal. Calcd for C 5 iH 5 i IN g NiP 4 : C, 56.43; H, 4.73; N, 10.32%. Found: C, 56.58; H, 4.79; N, 10.11%. *H N M R (CDCh): 8 0.7 (qn, 3H, 3 J P H 7.3, Ni-CH 3), 7.22-8.60 (m, 32H, pyridyl), 1.79 (m, 4Ha), 1.91 (m, 8Hb), 2.34 (m, 8Hb), 3.90 (m, 4Hc). 3 1 P{ 1 H} NMR (CDCh): 8 36.5 (s). Again, no free dpypcp was obtained. 90 Chapter 4 references on page 127 Chapter 4 4.2.3.4 Attempted Synthesis of fra#is-Ni(CH3)(I)(dppe)2 (30) The procedure was as for 27, but using Ni(dppe)2 (110.7 mg, 129 umol) and CH 3 I (8.4 uL, 135 umol). The collected off-white solid analyzed by ^P^H} and lH NMR spectroscopy as [(CH3)(dppe)]I. Yield: 10.7 mg (19.7 umol). lH NMR (CDC13): 8 2.41 (t, 2Hai), 3.02 (m, 2H a 2), 3.25 (d, 3H, 2 J P H 15, P-CH 3), 7.15-8.10 (m, 20H, phenyl) (see Figure 4.1 for proton assignments). "Pf/H) NMR (CDCI3): 8 27.41 (d, 3 J P P 44.0), -11.07 (d, 3 J P P 43.7). 3 1P{1H} N M R of the filtrate (CDCU): 6 44.0 (s, Ni(dppe)2), 32.9 (s, dppe(0)2), 28.5 (d, 3 J P P 48.6, dppe(O)), -12.24 (d, 3 J P P 48.6, dppe(O)), -13.0 (s, free dppe). Lit. 8P (CDC13) of dppe(0)2 = 33.1;23 lit. 8P (CDC13) of dppe(O) = -12.2 and 32.6 ( 3 J P P 47).24 After 4 months the Schlenk tube was found to contain a pale-pink precipitate and purple crystals; the latter were identified by T L C and both 3 1P{ !H} NMR and UV-Vis spectroscopies as Nil2(dppe). Characterization by 3 1P{1H} N M R spectroscopy revealed the pale-pink precipitate to be comprised predominantly of the white dppe bisoxide with traces of Nil2(dppe). 4.2.3.5 Attempted Synthesis of *rans-Ni(CH3)(I)(PPh3)2 (31) The procedure was the same as for 27, but using Ni(PPh3)4 (10.0 mg, 9.0 umol) and CH 3 I (0.6 uL, 9.6 umol) in C6H6- An off-white solid was obtained and identified by 3 1P{1H} and ! H NMR spectroscopy as the monomethylphosphonium salt [(CH3)(PPh3)]I. lH N M R (CDC13): 8 2.52 (s, trace free CH3I), 3.46 (d, 3H, 2 J P H 12.9, P-CH 3), 7.60-8.20 (m, 15H, phenyl). 3 1P{1H} N M R (CDCI3): 8 22.2 (s, br). The presence of CH 3I is likely due to inadequate drying of the solid in vacuo. 4.2.4 Preparation of Monomethylated Phosphonium Salts [(CH3)(phosphine)]I The preparation of these salts was attempted as in situ 3 1P{1H} N M R experiments in C 6 D 6 ; these NMR data are reported as "31P{1H} NMR (soln)." The precipitate which eventually formed was collected and re-analyzed by ! H and 3 1P{1H} NMR in CDC13; these N M R data have the label "(ppt)." 32a and 32e were the sole products detected in their respective in situ N M R spectra, whereas traces of free ligand or ligand oxides were also detected in the in situ N M R spectra of 32b-d. Non-pyridyl proton assignments for 32b-d are shown in Figure 4.1 (see Figure 3.1, p.47, for pyridyl protons assignments). 91 Chapter 4 references on page 127 Chapter 4 4.2.4.1 [(CH3)(PN3)]I (32a) To an N2-flushed NMR tube containing PN 3 (23.6 mg, 89.0 pmol) and C 6 D 6 (2 mL) was added excess CH 3 I (15 uL, 169 pmol); a tan precipitate formed. T i NMR (ppt, CDC13): 8 3.29 (d, 3H, 2 J P H 15.0, P-CH 3), 6.85 (t, 3H5), 7.30 (t, 3H4), 7.80 (d, 3H3), 8.82 (d, 3H6). "Pl/H} N M R (ppt, CDC13): 8 10.0 (s, br). 31P{'H} NMR (soln, C 6 D 6 ): 8 10.3 (s, br). For [(CH3)(PNi)]I, 8 P(C 6D 6)= 17.5.25 4.2.4.2 [(CH3)(dppe)]I (32b) The procedure was as for 32a, but using dppe (22.7 mg, 57.0 pmol) and CF£3I (15 pL, 169 pmol); a white precipitate formed. *H NMR (ppt, CDC13): 5 2.41 (t, 2FLi), 3.02 (m, 2FL.2), 3.27 (d, 3H, 2 J P H 13.6, P-CH 3), 7.25-8.15 (m, 20H, phenyl). 3 1P{1H} NMR (ppt, CDC13): 27.41 (d, 3 J P P 44.0), -11.07 (d, 3 J P P 43.7). 3 1P{ !H} NMR (soln, C 6 D 6 ): 8 30.9 (s, dppe(0)2), 26.05 (d, 3 J P P 41.2, [(CH3)(dppe)]I), -12.37 (d, 3 J P P 41.3, [(CH3)(dppe)]I), -12.6 (s, free dppe). He II" H b c ' s ^ H b V I \ I \ I \ I > C H 3 R 2 P ^ H a l H a2 Figure 4.1 Numbering scheme for monomethylated diphosphines. 4.2.4.3 [(CH3)(dpype)]I (32c) The procedure was as for 32a, but using dpype (13.4 mg, 33.3 pmol) and CH 3 I (3.0 pL, 48.2 pmol); a tan precipitate formed. *H NMR (ppt, CDC13): 8 2.57 (m, 2H,i), 3.11 (m, 2Ha2), 3.26 (d, 3H, 2 J P H 13.7, P-CH 3), 7.30 (m, 4H5), 7.60 (m, 4H3), 8.15 (m, 4 H 4 ) , 8.75 (m, 4H«). 3 1P{1H} NMR (ppt, CDC13): 5 21.66 (d, 3 J P P 38.5), -7.98 (d, 3 J P P 38.6). 3 1P{ 1H} N M R (soln, C 6 D 6 ): 8 21.74 (d, 3 J P P 38.5, [(CH3)(dpype)]I), -7.85 (d, 3 J P P 38.5, [(CH3)(dpype)]I), -6.4 (s, free dpype). 92 Chapter 4 references on page 127 Chapter 4 4.2.4.4 [(CH3)(dpypcp)]I (32d) The procedure was as for 32a, but using dpypcp (11.6 mg, 26.2 umol) and CH 3 I (2.0 uL, 32.1 umol); a tan precipitate formed. *H NMR (ppt, CDC13): 5 1.67 (m, H a i ) , 2.00 (m, Ha2), 2.02 (m, 2Hb), 2.46 (m, 2Hb), 3.18 (d, 3H, 2 J P H 13.5, P-CH3), 4.22 (m, 7.31 (m, 4H5), 7.96 (m, 4H3), 8.44 (m, 4H4), 8.70 (m, 4H5). ^Pl'H} NMR (ppt, CDC13): 5 23.55 (d, 3 J P P 15.4), -0.88 (d, 3 J P P 15.6). 31P{'H} NMR (soln, C 6 D 6 ): 5 23.41 (d, 3 J P P 15.3, [(CH3)(dpypcp)]I), -1.07 (d, 3 J P P 15.2, [(CH3)(dpypcp)]I), -0.3 (s, free dpypcp). The multiplets for H a 2 and H b overlap and together integrate for 3H. 4.2.4.5 [(CH3)(PPh3)]I (32e) A white precipitate formed using the procedure described for 32a, but using PPh3 (13.5 mg, 51.5 umol) and CH 3I (4.0 uL, 64.2 umol). X H NMR (ppt, CDC13): 6 3.46 (d, 3H, 2 J P H 13.2, P-CH 3), 7.95-8.15 (m, 15H, phenyl). 31P{XH} NMR (ppt, CDC13): 8 21.8 (s, br), (lit. 22.2, CDC1 3). 2 6 31P{XH} NMR (soln, C 6 D 6 ): 8 21.6 (s, br). 4.2.5 Preparation of Bismethylated Phosphonium Salts [(CH3)2(phosphine)]I2 Attempts to prepare the bismethylated salts 33b-d in situ in C6D6 were unsuccessful (see Section 4.3.5); attempts in CDC13 resulted in a mixture of the mono and bismethyl salts (for 33b and c); 33b, c, and d were prepared as the sole-products in work performed in CD 3 OD, MeOH, or CDC13, respectively. All IR spectra are obtained from KBr discs and all A M are in MeOH. 4.2.5.1 [(CH3)2(dppe)]I2 (33b) A procedure similar to that used for 32b, but using dppe, 5 equiv. of CH 3 I, and CDC13, resulted in the formation of a white precipitate which was found by 31P{XH} N M R (CD 3 OD) to be a ~ 3:1 mixture of the mono and bismethyl salts. This procedure was repeated, but using 20 equiv. of CH 3 I in CD 3 OD and heating the NMR tube at 55°C for 2 h; a white precipitate of pure (by NMR) 32b formed. *H N M R (CD 3OD): 8 3.03 (dm, 4Ha), 3.41 (d, 6H, 2 J P H 5.2, P-CH 3), 7.25-8.15 (m, 20H, phenyl). 3 1P{ 1H} N M R (CD 3OD): 8 26.56 (s) (lit. 26.9, CD 3 OD). 2 7 93 Chapter 4 references on page 127 Chapter 4 4.2.5.2 [(CH3)2(dpype)]I2 (33c) The procedure was as for 33b, but using dpype, 15 equiv. of CH 3I, and CDC13; a cream precipitate formed which was found by 3 1P{1H} NMR (CD 3OD) to be a ~ 1:1 mixture of the mono and bismethyl salts. The synthesis was re-attempted as follows. A solution of dpype (82.2 mg, 204 pmol) in MeOH (10 mL), prepared in an N2-charged Schlenk tube and stirred with 20 equiv. of CH 3 I (254 pL, 4.08 mmol) for 2 h at 55°C, gave a pale-yellow solution. A cream precipitate of 33c, formed on addition of hexanes (25 mL), was collected, washed with hot THF ( 4 x 5 mL), and dried in vacuo overnight. Yield: 58.0 mg (41%). Anal. Calcd for C 2 4H 2 6N4P 2I 2: C, 42.01; H , 3.82; N, 8.16%. Found: C, 42.21; H, 3.84; N, 7.87%. lH NMR (CD 3OD): 5 3.27 (t, 4Ha), 4.45 (d, 6H, 2 J P H 5.7, P-CFL), 7.80 (m, 4H5), 8.15 (m, 4H3), 8.26 (m, 4H4), 8.93 (m, 4Hs). 3 1P{ 1H} N M R (CD 3OD): 8 21.47 (s). LR: 1297 (m, v(P-CH3)), 907 (s, v(P-CH3)), 2944 (m, v(C-H)), 2867 (s, v (C-H)), 1568, 1448, 1417 (s, py skeletal bands). ELMS (m/z): 559 [M-T]. m.pt.: 232-234°C. A M : 210. The assignment of LR bands is discussed in Section 4.3.5. 4.2.5.3 [(CH3)2(dpypcp)]I2 (33d) A solution of dpypcp (24.1 mg, 54.5 pmol) in CDC13 (4 mL), prepared in an N2-charged Schlenk-tube and stirred with 10 equiv. of CH 3I (34 pL, 0.55 mmol) for 6 h at 55°C, gave a pale-yellow suspension. A pale-yellow powder was collected, and dried in vacuo overnight. Yield: 24.5 mg (62%). Anal. Calcd for C27H30N4P2I2: C, 44.65; H, 4.16; N, 7.71%. Found: C, 44.95; H , 4.34; N, 7.58%. T i NMR (CD 3OD): 8 3.40 (d, 6H, 2 J P H 13.2, P-CH 3), 1.52 (qn, 2Ha), 2.48 (m, 4Hb), 5.12 (m, 2H,), 7.56 (m, 4H5), 8.01 (m, 4H3), 8.71 (m, 4H«), 8.78 (m, 4H4). 3 1P{ 1H} N M R (CD 3OD): 8 23.40 (s). LR: 1311 (m, v(P-CH3)), 900 (s, v(P-CH3)), 2965 (m, v(C-H)), 2872 (s, v (C-H)), 1572, 1450, 1424 (s, py skeletal bands). ELMS (m/z): 599 [M-I+], 473 [M-2I+]. m.pt.: 221-224°C. A M : 185. 94 Chapter 4 references on page 127 Chapter 4 4.2.6 Attempted Carbonylation of <ra«s-Ni(CH3)(I)(phosphine)2 Species 4.2.6.1 Attempted Synthesis of Ni(COCH3)(I)(PN3)2 CO was bubbled for 2 h through a solution of zra«5-Ni(CH3)(I)(PN3)2 (27) (30.8 mg, 42.2 umol) in hexanes (6 mL) contained in a Schlenk tube; the tan precipitate that formed was collected by anaerobic filtration and dried in vacuo overnight. Yield: 34.4 mg. lH NMR (CDC13): 8 2.45 (s, free CH3I), 7.4-8.7 (m, pyridyl). nF{l¥L} NMR (CDC13): 8 -0.7 (s, free PN 3), 10.0 (s, br, [(CH3)(PN3)]I), 14.6 (s, OPN3). This procedure was repeated in both CD 3OD and CeD6 with the same results. A similar procedure but with Zn dust added to the solution prior to treatment with CO gave the same tan precipitate. This was dissolved in CDC13, filtered to remove the Zn, and analyzed by 3 1P{'H} NMR spectroscopy as a mixture of free PN 3 , OPN 3, and starting material. 4.2.7 Attempted Methylation of Ni(CO)2(phosphine)2 Species 4.2.7.1 Attempted Syntheses of Ni(COCH3)(I)(PPh3)2 and Ni(COCH3)(CO)(I)(dpypcp) To an N2-flushed NMR tube containing Ni(CO)2(PPh3)2 (7.7 mg, 12.0 umol) and CDC13 (1 mL) was added 4 equiv. of CH 3I (3 uL, 48.2 umol); heating at 55°C for 2 h generated a dark-green solution and an off-white precipitate. The latter was analyzed by 3 1P{XH} NMR spectroscopy (CDC13) to be a mixture of phosphonium salt, OPPh3, free PPh3, and starting material: 8 22.4 (s, br, [(CH3)PPh3]I), 29.4 (s, OPPh3), 32.8 (s, Ni(CO)2(PPh3)2), -5.0 (s, free PPh3). A similar procedure using Ni(CO)2(dpypcp) (1.7 mg, 3.1 umol) and 9 equiv. of CH 3I (1.75 uL, 0.0275 mmol) in CDC13 or CD 3OD gave no reaction. 4.2.8 Reactivity of Ni(0) Tertiary 2-Pyridylphosphine Complexes with Small Molecules 4.2.8.1 Reactivity with Ethylene To an evacuated Schlenk tube containing Ni(PN 3) 4 (26d) (48.8 mg, 43.6 umol) at 0°C was introduced 1 atm C2FLt; addition of C 6 D 6 (2 mL) gave a dark-orange solution. Stirring for 30 min showed no change in colour. Analysis of an aliquot by 3 1P{ 1H} NMR spectroscopy showed just the singlet (8 28.9) of 26d. 95 Chapter 4 references on page 127 Chapter 4 4.2.8.2 Reactivity with Chlorine To an N2-flushed, septum equipped NMR tube containing a red solution of Ni(dpypcp)2 (24a) (6.26 mg, 6.63 pmol) dissolved in C 6 D 6 (1 mL) was added 1 equiv. of C l 2 (150 pL, 6.14 pmol) via a gas-tight syringe; a dark-brown solution was obtained. 3 1P{1H} NMR: 5 -0.4 (s, free dpypcp, 13.3%), 0.95 (d, 3 J P P 41.5, dpypcp monoxide?, 19.2%), 32.53 (d, 3 J P P 41.8, dpypcp monoxide?, 19.2%), 33.19 (s, dpypcp bisoxide, 35.1%), 38.83 (s, 24a, 13.2%). Lit. 5P (CDCh) of dpypcp(0)2 = 32.1.23 4.2.8.3 Reactivity with Oxygen The procedure was the same as for the above C l 2 reaction, but using 24a (3.75 mg, 3.98 pmol) and 1 equiv. of 0 2 (90 pL, 3.69 pmol); a pale-yellow solution was obtained. 31P{'H} NMR: 5 1.12 (s, free dpypcp? 18.2%), 33.11 (s, dpypcp bisoxide, 81.8%). Note that 5P (C 6D 6) of dpypcp in 02-free solution found at -0.4. 4.2.8.4 Reactivity with Water The procedure was the same as above but using 24a (2.50 mg, 2.65 pmol) and 1 equiv. of degassed H 2 0 (0.1 pL, 3.0 pmol); a pale-yellow solution was obtained. 3 1P{1H} NMR: 8 0.93 (s, free dpypcp? 33.0%), 33.05 (s, dpypcp bisoxide, 67.0%). Again, note that 8P (C 6D 6) of dpypcp in 02-free solution found at -0.4. 96 Chapter 4 references on page 127 Chapter 4 4.3 Results and Discussion 4.3.1 Synthesis and Characterization of Nickel(O) Dicarbonyl Phosphine Complexes The complexes synthesized are shown below: PN„ O O " / 1 PN> OC Ni(CO) 2(PN x) 2 X = l 19a X = 2 19b X = 3 19c Ni(CO)2(P-P) P-P = dpype 20a P-P = dpypcp 20b 19 20 The preparation of the MeOH carbonylation catalyst NiRh(PNi) 2(CO)Cl3 from N i ( C O ) 2 (PNi ) 2 2 8 is the only known report in the literature (outside work of this group)17 on 2-pyridylphosphine complexes of Ni. The UBC work17 has documented the preparation of 19a via reduction of NiBr 2 by Zn/CO in a THF solution of P N i , and the in situ preparation of 19b via phosphine-ligand-displacement from Ni(CO)2(PPh3)2; displacement of PPh3 by reaction with two equiv. of P N 2 yielded a mixture of Ni(CO)2(PPh3)2 (henceforth abbreviated as 190), Ni(CO) 2(PN 2) 2, and the mixed-phosphine species Ni(CO)2(PPh3)(PN2) (19b*) (Figure 4.2). Although these complexes have yet to be isolated, this current thesis work examines in situ yields of 19, including formation of the new species 19c (Section 4.3.1.1). Ni(CO)2(PPh3)2 + 2 PN X =^=^ Ni(CO)2(PPh3)(PNx) + PPh3 Ni(CO) 2(PN x) 2 + PPh3 190 19* 19 Figure 4.2 Equilibrium among dicarbonyl species in the in situ formation of Ni(CO) 2(PN x) 2 from Ni(CO)2(PPh3)2 in CDC13. Complex 20a was successfully isolated by Baird et al. via phosphine-ligand-displacement from Ni(CO)2(PPh3)2 in 48% yield. In this current thesis work, both 20a and b have been prepared by a somewhat modified synthetic route (Section 4.3.1.3). 97 Chapter 4 references on page 127 Chapter 4 4.3.1.1 The Ni(CO) 2(PN x) 2 Complexes The in situ NMR experiments using a 2:1 mole ratio of PN X : 1% were repeated under conditions (acetone-fife, 2 h at 60°C) different to those of Baird et al17 (CDC13, 5 d at 20°C for 19b). The 3 1P{1H} NMR spectra contained the singlet of 190 and the two doublets corresponding to the mixed-phosphine species 19* (Table 4.4), but the singlet of the desired Ni(CO) 2(PN x) 2 complex (Table 4.8) was absent. The ratio of 19* to 190 in each system was -2:1 (from integration of the 5P signals), indicating that the equilibrium shown in Figure 4.2 lies in favour of the mixed-phosphine species. This differs from the earlier work in CDC13 where 190 was shown to be the thermodynamically favoured species. Table 4.4 3 1 P NMR Data for Ni(CO)2(PPh3)(PNx) Complexes a Compound 6P Ni(CO)2(PPh3)(PN0, 19a 35.56,37.15 Ni(CO)2(PPh3)(PN2), 19b* 36.35, 39.74 Ni(CO)2(PPh3)(PN3), 19c* 35.92, 43.29 { a ) In acetone-fife. All signals are doublets (see Section 4.2.1 for 2 J P P values). 5P Ni(CO) 2(PPh 3) 2 in acetone-fife = 32.7 (s). Attempts were made to raise the yield of 19, the ratio of 190:19*:19 being calculated from the 3 1P{ 1H) NMR data (Tables 4.5-7). When the reaction is conducted with two equiv. of P N 2 in either dmso-fife or C6D6, equimolar amounts of 190 and 19b* exist in equilibria, whereas in acetone-fife there is twice as much 19b" as 190 (Table 4.5). Of note, 19b is observed only in CeD6, hence this solvent was used in subsequent experiments; dmso-fife was not used in the attempted formation of 19a and c (Section 4.2.1) for this reason. Data reveal that the equilibrium mixture in CeD6 is essentially attained after heating for 12 h (Table 4.6). The yield of 19b approaches 9% (vs. 20% noted in CDC13 by Baird et al),11 while the remaining phosphine-containing species are comprised of an equimolar mixture of 19b* and the starting material. An increase in [PN2] naturally shifts the reaction equilibria in favor of 19b (Table 4.7). The ratios calculated for the 4 h (not shown) and 12 h data sets are identical, indicating that the yield reported for 19b represents 98 Chapter 4 references on page 127 Chapter 4 the mixture at equilibrium. Baird et al. noted a similar increase in the yield of 19b on increasing [PN 2]. 1 7 Table 4.5 Effect of Reaction Medium on the Ratio of 190 to 19b* to 19b Solvent Ni(CO)2(PPh3)219« Ni(CO)2(PN2)(PPh3) 19b* Ni(CO) 2(PN 2) 2 19b dmso-fife 0.53 0.47 C 6 D 6 0.51 0.46 acetone-fife 0.33 0.67 0.00 0.03 0.00 Conditions: 2 equiv. of P N 2 reacted with 190 at 55°C for 4 h. Table 4.6 Effect of Time on the Ratio of 190 to 19b* to 19b Time (h) Ni(CO)2(PPh3)219„ Ni(CO)2(PN2)(PPh3) 19b" Ni(CO) 2(PN 2) 2 19b 4 0.51 0.46 12 0.44 0.48 20 0.43 0.48 0.03 0.08 0.09 Conditions: 2 equiv. of P N 2 reacted with 190 in CeD6 at 55°C. Table 4.7 Effect of Excess PN 2 on the Ratio of 190 to 19b* to 19b Equiv. P N 2 Ni(CO)2(PPh3)2 190 Ni(CO)2(PN2)(PPh3) 19b" Ni(CO) 2(PN 2) 2 19b 2 0.51 0.46 4 0.32 0.54 8 0.07 0.32 0.03 0.14 0.61 Conditions: variable equiv. of PN 2 reacted with 190 at 55°C for 12 h in C 6 D 6 . Baird et al. report that Ni(CO)2(PPh3)2 (190) is the most thermodynamically stable of the three dicarbonyl complexes present in CDC13 in the equilibria shown in Figure 4.2 when two equiv. of PN X are used, and this was rationalized in terms of electronic factors: the relatively strong a-donor/weak 7i-acceptor properties of PPh3 vs. PN X ligands (the latter having the conjugate inductive withdrawal of P-atom electron-density by the pyridyl N-atoms).29'30 The greater a-basicity of PPh3 was assumed to outweigh the contribution from the greater TC-acidity of PN X . However, experiments performed in this current thesis work with two equiv. of PN X 99 Chapter 4 references on page 127 Chapter 4 demonstrate that Ni(CO)2(PPh3)(PNx) can be obtained in either an equimolar amount with, or greater yield than, 190 (depending on solvent), implying that the electronic differences between PPh3 and PN X may be small. In situ 3 1P{ !H} NMR data for the Ni(CO) 2(PN x) 2 complexes and 190 in C 6 D 6 are listed in Table 4.8, along with the two doublets observed for the mixed 19* species. Of interest, the magnitude of 2 J P P for 19a*, 19b* and 19c" (Table 4.8) lies in the order 1.0:2.2:3.1 (relative to 37.0 Hz for 19a"), respectively, closely paralleling the 1:2:3 ratio of N-atoms present in 19a"-c". Also the increase in the separation between the centres of the two doublets (\i-d)) of 19* increases reasonably linearly with the total number of N-atoms present (Figure 4.3). The increases in both 2 J P P and A(d-d) on going from 19a* to 19c* are likely due to the increasing dissimilarity of the electronic environments at the P nuclei of PPh3 and PN X as the N-atom count rises. Table 4.8 3 *P N M R a and LR Data for Ni(CO) 2(PR 3) 2 Complexes Compound dP (s) v(CO) f c 5P c Mixed Species (19*) (2JPP) Ni(CO)2(PPh3)2 190 32.6 1932, 1998 -Ni(CO) 2(PN0 2 , 19a 31.3 1941, 2001 35.78 (36.6), 37.42 (37.4) Ni(CO) 2(PN 2) 2, 19b 33.1 1942, 2003 36.23 (83.3), 39.68 (79.9) Ni(CO) 2(PN 3) 2, 19c 34.1 1943, 2004 35.72(113.3), 43.08 (116.1) In C 6 D 6 . ( 6 ) Thin CH 2C1 2 film on KBr; v s y m = smaller wavenumber; va s y m=larger wavenumber. Upfield doublet assigned to PPh3, and more downfield doublet assigned to PNX; 2 J P P in Hz. The v(CO) values of 19a-c and 190 (Table 4.8) were obtained by placing a thin CH 2C1 2 solution film on a KBr disc. The larger v(CO) values for the pyridyl species vs. Ni(CO) 2(PPh 3) 2 are indicative of the weaker a-donor and/or stronger rc-acceptor properties for the P nuclei of pyridyl ligands relative to that in PPh3. Decreasing the amount of electron density on the metal available for 7i-back-donation into the TC* orbitals of the CO ligands results in a strengthening of the C = 0 bond and hence an increase in v(CO). 1 9 b 100 Chapter 4 references on page 127 Chapter 4 Figure 4.3 Plot of the number of N-atoms in the PN X ligand vs. the separation between the two doublets in the Ni(CO)2(PPh3)(PNx) complexes (19*). 4.3.1.2 Speculative Formation of [Ni 2(CO) 4(//-PN 2) 2]Cl 4 (19d) The reaction of Ni(CO)2(PPh3)2 with two equiv. of P N 2 was also conducted in CDC1 3, as per Baird et al.,11 with the exception that the sample was heated at 60°C. A small amount of purple precipitate 19d was obtained, along with the same yellow solution formed during the in situ preparation of 19b (Section 4.2.1.4). No precipitate was observed under any other reactions conditions. 19d is proposed to be a dimetallic nickel(II) species (Figure 4.4). The dinuelear formulation is suggested by ^LSIMS data as the isotopic splitting pattern of the parent-ion peak (m/z 757) is identical (in the range of 757-765 m/z; see Appendix B, Figure B.l) to the computer-simulated31 mass spectrum of "Ni 204P 2N 4C36H 2 7", which = Ni 2(CO) 4(PN 2) 2 + IH (one mass unit being added for "positive" LSIMS). The 8P singlet at 24.1 implies chemical and magnetic equivalence of the two P nuclei, and requires the PN 2 and CO ligands to be situated symmetrically; the single v(CO) band at 1971 cm"1 suggests that the CO ligands are mutually trans at each metal centre with the PN 2 ligands in a mutally head-to-tail (HT) arrangement. The formulation depicted in Figure 4.4 is further supported by a downfield coordination shift (5P A = +26.7 relative to free PN 2) characteristic of a 5-membered chelate ring.3 2 Of note, if each Ni were P./V-chelated by one P N 2 ligand to yield two 4-membered P.A'-chelate rings, a 8P value similar to that of NiCl2(P,7V-PN3>H20 (7) (8P -17) would be seen (Section 3.3.3, p.68), while if 101 Chapter 4 references on page 127 Chapter 4 monodentate P-coordinated PN2 were present, a 6p value similar to that of 19b (8P 33.1) would be observed. HT and head-to-head (HH) isomers for similar Pd 2X 2(//-PN 2) 2 complexes (X = halogen) can be distinguished by 1 9 5Pt NMR and 2JPIP values.33 4C1" PPhpy N = o-py Figure 4.4 Proposed structure for the purple complex 19d. The two P nuclei for the bridging PN 2 formulation are chiral, and as such, two 5p singlets would be expected for 19d, one arising from the (R,R) and (S,S) set of enantiomers, and the other from the (R,S) species in which the two P nuclei are enantiotopic due to the presence of an inversion centre. The lone singlet detected for 19d at r.t. may be an averaged signal, as reported for Pd 2Cl 2(//-PN 2) 2 complexes where two singlets are observed (8P = 2.0 and 6.0) at -20°C, while at r.t. just one singlet (8P = 5.2) is seen.34 Low temperature studies should be conducted on 19d. The lK NMR spectrum of 19d (Figure 4.5) is far more complex than that of free or P-coordinated PN 2 . The resonances between 8 7.1 and 8.2 (Section 4.2.1.4) are assigned to the H 3 - H 5 protons of the pyridyl groups (TV-coordinated and uncoordinated) and protons of the phenyl groups. The majority of these resonances are similar to those reported for the cluster [Os3(CO)10C"-P,/V-PN2)] (8H = 7.01, 7.19, 7.27, 7.35, 7.41, 7.51, 7.62, 7.81, 7.86, 8.03, 8.12).35 The resonance for FL5 of the uncoordinated pyridyl group is at 8 8.79, while that assigned to H 5 of the TV-coordinated pyridyl group is at 8 9.22; these values are comparable to those of the osmium cluster (8.72 and 9.49 ppm, respectively). A similar downfield shift is reported for (Cp)(CNR)Rh(//-PNi)Pd(CNR)(Cl) (8H 6 = 8.72 and 9.62).36 102 Chapter 4 references on page 127 Chapter 4 H.3-H5, H 3 *-H 5 « , phenyl I , i ' 1 i ' 1 1 1 i 1 1 1 1 i 1 1 1 ' i 1 1 1 1 i 1 1 ' * i 1 1 1 1 i 1 1 1 1 i > < > < i i i i i i •• i i i • i i • i • • ' i 9.4 9.2 9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2 7.0 ppm Figure 4.5 *H NMR spectrum (CD 3OD) of the pyridyl region of 19d; H s protons of non-coordinated pyridyl group, Ft* = protons of coordinated pyridyl group. Conductivity measurements for 19d in MeOH are consistent with the dimeric [Ni(II)]2 4:1 electrolyte formulation, with four chloride counteranions presumably abstracted from the CDCI3 solvent, as observed for formation of 7 and 8 (Ni(II) species) from Ni(CO) 2(PPh 3) 2 (see Section 3.3.3, p.68). The formation of 0.95 mg of AgCl (0.24 mg Cl) upon addition of excess AgN0 3 to 1.55 mg of 19d in MeOH confirms the presence of four chlorides [(0.24/1.55)xl00 = 15.16% Cl; 15.76% theoretical with 4 equiv. of Cl]. Elemental analyses for C, H, and N are low by ~ 1, 0.2, and 0.8%, respectively. 4.3.1.3 Characterization of Ni(CO)2(P-P) Complexes The pale-yellow solids 20a and 20b were characterized by elemental analyses, and 3 1P{ !H} NMR and LR spectroscopies (Table 4.9). The v(CO) stretches for 20a and 20b indicate slightly stronger 71-acceptor/weaker a-donor properties of the dpype ligand vs. dpypcp. The relative order of pyridyl ligand P-atom o-basicity thus appears (in conjunction with the v(CO) data in Table 4.8) to increase in the order PN 3 < PN 2 < PN X < dpype < dpypcp, while pyridyl ligand Tt-acidity increases in the order dpypcp < dpype < PNi < P N 2 < PN 3 . From 3 1P{1H} N M R data, the a-basicity appears to increase in the order dpypcp < PN 3 < P N 2 < PNi < dpype (8P = 0.0, -0.74, -2.62, -3.95, -6.1, respectively, from Table 3.2, p.48). The cause for dpypcp appearing, by 3 1P{1H} NMR, to be the least basic is unknown; it is expected (as seen in the LR-based ranking of ligand basicity) to be the most basic of the pyridyl ligands as it contains the electron-donating cyclopentane fragment. For Ni(CO) 4, v(CO) comes at 2057 cm"1.37 103 Chapter 4 references on page 127 Chapter 4 Table 4.9 Selected 3 1 P NMR and IR Data for Ni(CO)2(P-P) Complexes Compound 5 P a v(CO) b Ni(CO)2(dpype), 20a 55.3 1937, 1999 Ni(CO)2(dpypcp), 20b 35.0 1927, 1997 ( f l ) In C 6 D 6 ; singlet resonances. { b ) Thin CH 2C1 2 film on KBr discs; Ni(CO)2(dppe) v(CO) = 1936, 1997 cm - 1 (in C2H4C12), ref. 38. The data in Table 4.9 match those previously reported for 20a.1' 20b displays a mass spectral peak at 500 m/z corresponding to M-2CO, and being neutral has zero molar conductivity in MeOH. The attempted synthesis of 20a and 20b via the documented Zn/CO reduction of Ni(II) precursors was unsuccessful (see Section 4.2.1.7).17,21 Of note, 20a and 20b are air-stable in the solid-state, whereas many Ni(CO)n(PR3)4-n complexes are not.37 Complexes 20a and 20b were tested as potential catalysts for hydration of maleic acid, the water-gas-shift reaction, and hydrogen transfer (see Chapters 5-7); Ni(CO)2(dppe) has been used for the catalytic dimerization of diquinoethylene to tetraquinocyclobutane (see Appendix B, Figure B.2). 3 9 4.3.1.4 X-ray Crystal Structure of Ni(CO)2(dpypcp) (20b) The solid-state structure of 20b was determined by X-ray diffraction (see Section 2.5.1, p.31). Selected bond lengths and angles are reported in Table 4.10 (see Appendix A.8 for a complete list), while the ORTEP plot showing the R,R enantiomer (C(l) and C(2) of dpypcp are chiral atoms) appears in Figure 4.6. The S,S enantiomer is also present within the unit cell but is not shown here. The core of 20b is considerably distorted from ideal tetrahedral geometry as indicated by the P-Ni-P and CO-Ni-CO bond angles. The former (90.49°) is 19° less than the 109.5° T d angle, and is only 2° greater than the P-Ni-P angle (88.45°) in square-planar NiCl2(dpypcp) (Section 3.3.1, p.45). The P-Ni-P bond angle compression in 20b is attributed to the limited bite of dpypcp as the same angle for Ni(CO)2(PPh3)2 is 117°. 4 0 The electron-rich carbonyl moieties in 20b benefit from the tight P-Ni-P angle by assuming a geometry with less steric interaction (117° CO-Ni-CO angle) than that in Ni(CO)2(PPh3)2 (113° CO-Ni-CO angle).40 Ab initio M O 104 Chapter 4 references on page 127 Chapter 4 calculations suggest that most Ni(CO)2(PR3)2 complexes will be pseudo-Ta, with the ligand o-donor/7C-acceptor properties determining the degree of distortion.41 Figure 4.6 ORTEP (50% probability) of the molecular structure of Ni(CO)2(dpypcp). 105 Chapter 4 references on page 127 Chapter 4 Table 4.10 Selected Bond Lengths and Angles for Ni(CO)2(dpypcp) (20b) Bond Lengths (A) Bond Length (A) Bond Length (A) Ni -P(l) 2.2096(8) P(2) - C(21) 1.831(3) Ni - P(2) 2.2095(7) N(l)-C(6) 1.331(3) Ni - C(26) 1.764(3) N(2)-C(l l ) 1.340(3) Ni - C(27) 1.753(3) N(3) - C(16) 1.344(3) C(26) - 0(1) 1.144(3) N(4) - C(21) 1.338(3) C(27) - 0(2) 1.154(3) C ( l ) - C(2) 1.539(3) P(l) - C(l) 1.832(2) C(2) - C(3) 1.524(3) P(l) - C(6) 1.837(3) C(3) - C(4) 1.566(4) P ( l ) - C ( l l ) 1.835(3) C(4)-C(5) 1.523(4) P(2) - C(2) 1.836(2) C(5)-C(l) 1.534(3) P(2) - C(16) 1.833(3) Bond Angles (°) Bond Angle (°) Bond Angle (°) P(l)-Ni-P(2) 90.49(3) P(l)-C(ll)-N(2) 117.0(2) C(26)-Ni-C(27) 117.09(14) P(l)-C(l)-C(2) 110.7(2) C(26)-Ni-P(l) 108.58(10) P(2)-C(16)-N(3) 113.2(2) C(27)-Ni-P(2) 114.63(9) P(2)-C(21)-N(4) 118.9(2) C(26)-Ni-P(2) 109.40(10) P(2)-C(2)-C(l) 109.9(2) C(27)-Ni-P(l) 113.46(10) C(l)-C(2)-C(3) 102.8(2) Ni-C(26)-0(1) 177.2(3) C(2)-C(3)-C(4) 103.1(2) Ni-C(27)-0(2) 179.2(3) C(3)-C(4)-C(5) 106.9(2) P(l)-C(6)-N(l) 113.2(2) C(4)-C(5)-C(l) 105.1(2) P(l)-Ni-P(2)-C(2)" 10.03(9) H(C1)-C(1)-C(2)-H(C2) 1.97(8) Torsion angle. The Ni-P bonds in 20b are ~ 0.05 A longer than in NiCi2(dpypcp) and ~ 0.01 A shorter than in Ni(CO)2(PPh3)2. The former observation perhaps implies that the Ni-P bonds are weaker between dpypcp and Ni(0) vs. Ni(II). The latter observation, in conjunction with the ER data, where v a s y m (CO) for 20b is 5 cm"1 less than that of Ni(CO)2(PPh3)2, is consistent with the greater 7t-acidity of dpypcp vs. PPh3. The CsO bond lengths in 20b are essentially identical to those of Ni(CO)2(PPh3)2 (1.14 A) 4 0 and Ni(CO) 4 (1.15 A); 4 2 in gaseous CO, the bond length is 1.128 A . 1 9 c The Ni-C bond lengths are also similar to those of Ni(CO)2(PPh3)2 (1.76 A) . 4 0 Pale-yellow crystals of 20a were obtained but they did not diffract properly (see Section 2.5.1, p.31). A search of the Cambridge Structural Database revealed that the X-ray structures of Ni(CO)2(dppe) and Ni(CO)2(dpcp) (phenylphosphine analogue of 20b) have not been reported. 106 Chapter 4 references on page 127 Chapter 4 4.3.2 Aqueous Solution Chemistry of Ni(CO)2(dpypcp) and dpypcp The aqueous solution chemistry of Ni(CO)2(dpypcp) (20b) has been examined. Studies could not be conducted on the Ni(CO)2(PNx)2 complexes 19a-c as they were not isolated; Ni(CO)2(dpype) (20a) is reported to dissolve in water to give a pale-yellow solution.17 The 3 1P{1H} NMR spectrum of 20b (acquired within 5 min of sample preparation) in D 2 0 (containing trace H20) under N2 consists of a singlet at 5P 25.2 and trace singlets attributable to dpypcp bisoxide (5P 31.9)23 and 20b (5p 37.4). The spectrum after a further 5 min displayed only the singlet corresponding to dpypcp(0)2 and a trace singlet at 5p -12.9. Previous work within this group reports that the 3 1P{1H} spectrum of "free" dpypcp in D20/HBF\(aq) shows a singlet at 8P = -13.0, and this was attributed to dpypcp protonated at the pyridyl N-atoms ([wH-dpypcp]n+).23 The data thus suggest that dissolution of 20b in D 2 0 results in the formation of an intermediate species (8P 25.2) which rapidly decomposes to dpypcp(0)2 and [«H-dpypcp] n + . The following discussion establishes via elemental analyses and spectroscopic techniques that the intermediate species is [Ni(CO)2(2H-dpypcp)]2+ (protonated at the N-atoms) while the species at 5 P -12.9 is [2H-dpypcp]2+ (also N-protonated). The above 3 1P{ IH} NMR experiment was repeated in H20/acetone-fi?6 (1:9) and the same results were obtained [5P dpypcp(0)2 = 32.7, 5P 20b = 37.7, 8P «H-dpypcp" + = -13.5, and a singlet at 8P 25.7]. The lH NMR spectrum at t = 5 min revealed, aside from the resonances associated with 20b, a broadened peak at 8 10.25 which, upon integration vs. the two He protons, corresponds to ~ 2 N - H protons (8-10 typical for N-H), 1 8 implying that two of the four pyridyl N-atoms in 20b have been protonated to yield [Ni(CO)2(2H-dpypcp)]2+. This water-soluble dicationic species is considered responsible for the singlet at 8p ~ 25. Examination of a ! H NMR spectrum (acquired at t = 10 min) confirms the conclusion drawn from 3 1P{1H} N M R data as the H3-H6 signals [8 6.70, (m, H 5), 7.28 (m, H4), 7.70 (m, H 3), 8.47 (m, He)] now have values identical to those of dpypcp(0)2 in D 2 0 [8 6.69, (m, H 5), 7.30 (m, H4), 7.68 (m, H 3); He not resolved; Table 3.1] and not of coordinated dpypcp (cf. Figure 3.10, p.65, NiCl2(dpype) in D20), while the broadened N - H peak corresponding to [Ni(CO)2(2H-dpypcp)]2+ has almost completely disappeared. The loss of N-H resonance intensity indicates that the dpypcp(0)2 is not diprotonated, hence the quaternized N-atoms in [Ni(CO)2(2H-dpypcp)]2+ must deprotonate upon 107 Chapter 4 references on page 127 Chapter 4 complex decomposition. The remaining trace N-H peak confirms that the 8P signal at ~ -13 must correspond to N-protonated [2H-dpypcp]2+. Figure 4.7 Diprotonated form of 20b where two protons are shared equally among the four pyridyl N-atoms. The proposed structure for [Ni(CO)2(2H-dpypcp)]2+ is shown in Figure 4.7. The "even distribution" of the two protons among the four pyridyl N-atoms yields a molecule with equivalent P nuclei, as suggested by the sharp 5P singlet. Rapid proton exchange among the N-atoms could also yield a sharp singlet, hence low temperatures studies might help substantiate this possibility. Phosphorus protonation does not occur as no resonances corresponding to P-H protons (typical range of 5H = 0 to -10) were detected;18 TV-protonation occurs prior to P-protonation because of the greater basicity of the N-atom lone-pairs (as valence electrons experience a less effective charge in N than in P). 3 0 IR Spectroscopy of Triflate Salts of [Ni(CO)2(2H-dpypcp)f+ and [2H-dpypcp)f+ Attempts to precipitate [Ni(CO)2(2H-dpypcp)]2+ and [2H-dpypcp]2+ out of solution using trifluoromethanesulfonic acid (triflic acid, CF3SO3H) were unsuccessful because of formation of oils. The following work was thus conducted to provide further evidence that these JV-protonated species are indeed those responsible for the 8P singlets obtained at ~ 25 and ~ -13. Protonated trifluoromethanesulfonate (triflate, OTf) salts of 20b (bright yellow) and dpypcp (white) were prepared by addition of C F 3 S O 3 H to solutions of 20b or dpypcp (see Sections 4.2.1.8-9). The elemental analyses of the solids correspond to the bis-triflate salts of 108 Chapter 4 references on page 127 Chapter 4 diprotonated 20b and diprotonated dpypcp. No v(P-H) LR bands were detected (normal range 2250-2450 cm"1),18 while a v(N-H) band was observed at ~ 2690 cm"1 for [2H-dpypcp](OTf)2 and at 3095 cm'1 for the corresponding salt of 20b. These values are typical of those reported for tertiary amine salts (2250-2700 cm"1)18 and metal complexes containing protonated N-atoms (2950-3150 cm"1).43 The shifts from 1997->2045 and 1927^-1996 cm"1 for the v(CO) bands of 20b upon reaction with triflic acid are a manifestation of the electrophilic N-atoms balancing their positive charge by both decreasing the o-basicity and increasing the 7i-acidity of the P-atoms (see Section 4.3.1.1). A final confirmation of the 7V-protonation of the bis-triflate salt of 20b is yielded by a comparison of the LR spectra of pyridine and pyridinium chlorochromate to the spectra of 20b and its salt. Accordingly, in the former pair, the bands at 1587 and 1149 cm"1 shift by 49 and 17 cm"1, respectively, to 1538 and 1166 cm"1, respectively, upon N- protonation,44 while in the latter pair, similar shifts are observed with the band at 1569 cm'1 shifting to 1522 cm"1 and the band at 1152 cm'1 shifting to 1170 cm"1 upon protonation of 20b. Numerous LR bands attributable to the triflate anion (~ 1630, 1400, 1280, 1256, 1031, and ~ 640 cm"1, as determined from solution TR of CF3SO3H and ref. 18) are also observed for the salts of 20b and dpypcp. If P-protonation were to occur, 20b would likely decompose with release of CO and protonated ligand and no v(CO) bands would be seen. NMR Spectroscopy of Triflate Salts of[Ni(CO)2(2H-dpypcp)f+ and [2H-dpypcp)f+ Microanalyses and TR spectroscopy demonstrate that the triflate salts of 20b and dpypcp are diprotonated at the TV-atoms, and it is these dicationic species that give the 5p 25.7 and -13.5 peaks, respectively, in the 3 1P{1H} NMR spectrum of 20b in H20/acetone-fife, as 5p values of 25.5(s) and -13.6(s) are obtained for the triflate-salts of 20b and dpypcp, respectively (in acetone-tie). Similarly, the ! H NMR spectrum of these salts show the presence of ~ 2 N - H protons at 610.5 and 10.0, respectively, in comparison to the ~ 2 N-H protons seen at 6 10.25 for 20b in H20/acetone-fife. No P-H protons were detected in the lU NMR spectra of the triflate salts. Of note, when 6 equiv. of CF3SO3H were added in situ to acetone-fife solutions of 20b and of dpypcp, 4 equiv. of free CF3SO3H (8H 7.7) were detected in each sample, further supporting the diprotonated formulations. 109 Chapter 4 references on page 127 Chapter 4 From spectroscopic data for the above triflate salts, it is concluded that 20b initially dissolves in aqueous media via quaternization of the pyridyl N-atoms to yield the diprotonated species [Ni(CO)2(2H-dpypcp)]2+. Facile decomposition of this compound in solution subsequently yields a mixture of predominantly dpypcp(0)2 with traces of JV-protonated [2H-dpypcp]2+ (Figure 4.8). Other products of this decomposition are CO, as determined by GO analysis of the headspace of the NMR tube, and [Ni(H 2 0)6] 2 +, as found by UV-Vis (A™* = 396 nm) of the solution (cf. 396 nm for N i C l 2 . 6 H 2 0 in 1:9 H20/acetone). As Ni(CO)2(dpype) is structurally similar to 20b, and has been reported to be water-soluble,17 its decomposition in aqueous media to yield a mixture of dpype(0)2, [2H-dpype]2+, CO, and [Ni(H 2 0 )6] 2 + seems likely. H2o I p 5 min OC OC. CO 2+ 5 min [Ni(H20)6]2' + (O)P-P(O) + [2H-P-P]21" + 2CO Figure 4.8 Proposed fate of Ni(CO)2(P-P) complexes in water. The source of oxygen atoms for the oxidation of P-P is perhaps water, as anaerobic conditions (N2 and de-aerated H 2 0) were employed. Several reports demonstrate (via 1 7 0 NMR with 170-enriched H 2 0) that H 2 0 is the source of O-atoms in the oxidation of phosphine ligands in aqueous media.45'46 In such instances, a redox reaction occurs whereby the phosphine is oxidized while a metal species is reduced. For example, Larpent et al. report that when RJ1CI3 and 1 equiv. of TPPTS (trisulfonated PPh3, see Abbreviations) are dissolved in water under N 2 , 21% of the phosphine ligand is oxidized to the monooxide OTPPTS within 10 min at r.t., the reaction (Eq. 4.1) involving concomitant reduction of Rh(III) to Rh(I).45 TT+ TPPTS RhCl 3 .3H 2 0 + H 2 0 RhCl 2(OH)(H 20) 3 -> "RhCl2(OH)(TPPTS)(H20)" 'RhCl" + OTPPTS + FT CI" <- (Eq. 4.1) 110 Chapter 4 references on page 127 Chapter 4 Similarly, Godfrey et al. report the oxidation of PMe 3 to OPMe 3 upon addition of trace H 2 0 to AuI 3(PMe 3) 2 in Et 2 0 (Eq. 4.2),47 Bond et al. the oxidation of PPh3 to OPPh 3 with the polyoxometalate [S 2Moi 80 6 2] 4" and H 2 0 in acetonitrile (Eq. 4.3),46 Belykh et al. the oxidation of PBu 3 to OPBu 3 using H 2 0 and Pd(acac)2 (Eq. 4.4),48 and Kuntz and Vittori report the oxidation of TPPTS to OTPPTS using an aqueous, alkaline solution of PtCl 2 (Eq. 4.5).49 AuI 3(PMe 3) 2 + xs H 2 0 -», [(Me3PO)2H][AuI2] + HI (Eq. 4.2) 2[S 2Moi 80 6 2] 4" + PPh3 + H 2 0 -> 2[S 2Mo 1 80 6 2] 5" + OPPh3 + 2FT (Eq. 4.3) Pd(acac)2 + 5PBu3 + H 2 0 -> Pd(PBu3)4 + OPBu 3 + 2Hacac (Eq. 4.4) PtCl 2 + wTPPTS + 20H" -> Pt(TPPTS)n.i + OTPPTS + 2C1" + H 2 0 (Eq. 4.5) In contrast, the chemistry depicted in Figure 4.8 involves an overall 6-electron oxidation process (Ni(0)—»Ni(H), and two P(JJf)-»P(V)), and requires a concomitant 6-electron reduction process! The only possibility is that water is acting as the oxidant with concomitant formation of H 2 , which was not looked for. The 6-electron oxidation process could involve the presence of adventitious oxygen, although this is considered unlikely in that every effort was taken to work under anaerobic conditions. The mechanism of the process summarized in Figure 4.8 is worthy of further investigation. I l l Chapter 4 references on page 127 Chapter 4 4.3.3 Synthesis, Characterization, and Reactivity of Ni(0) Tertiary Phosphine Complexes A total of 107 unique P-coordinated tetrahedral Ni(0) complexes can be synthesized by combination of the four PR 3 ligands (PPh3, PNi, PN 2 , PN 3) and the three P-P ligands (dppe, dpype, dpypcp) (Table 4.11). Only the 22 complexes of categories (A), (F), (FT), and (I) were prepared (in situ or isolated) in this thesis work. The prime (') and double-prime (") notations are employed to denote that different PR 3 or P-P ligands are contained within the same complex. Table 4.11 107 Possible Ni(0)L4 Complexes obtained by Combining PR 3 and P-P Ligands " Category Complex Type No. of Complexes A Ni(PR 3) 4 4 B Ni(PR3)3(PR3') 12 C Ni(PR3)2(PR3')2 12 D Ni(PR3)2(PR3,)(PR3") 24 E Ni(PPh3)(PN0(PN2)(PN3) 1 F Ni(PR3)2(P-P) 12 G Ni(PR3)(PR3')(P-P) 36 H Ni(P-P)(P'-P') 3 I Ni(P-P)2 3 ( f l ) PR 3 or PR3' or PR3" = PPh3, PNi, PN 2 , PN 3 ; P-P or P'-P' = dppe, dpype, dpypcp. 4.3.3.1 Synthesis The structures are depicted in Figure 4.9; 21-25 were prepared under N 2 at 60°C in CeD6 or C6H6 from Ni(l,5-COD) 2 while syntheses of 26 were conducted at 0°C in hexanes to prevent complex decomposition (see Section 4.2.2 and Figure 4.10). 21-23 and 25 were only prepared in situ, while 24 and 26 were isolated. The NMR spectra (C 6D 6) of complexes containing PR 3 (21-23 and 26) had to be obtained quickly as decomposition to black "solutions" occurred within 10-30 min, even at 0°C. Complexes 24b,22'50 24c,17 and 26a-d17'51 have been prepared previously. 112 Chapter 4 references on page 127 Chapter 4 . P . v — - p PR3 r ^ " 7 m \ P R 3 R3P 21-23 24-25 26 Ni(PR3)2(dppe) Ni(PR3)2(dpype) Ni(PR3)2(dpypcp) PR 3 = PPh3, 21a PR 3 = PPh3, 22a PR 3 = PPh3, 23a P R 3 = P N 1 ; 21b PR 3 = PNi, 22b PR 3 = PN,, 23b PR 3 = PN 2 , 21c PR 3 = PN 2 , 22c PR 3 = PN 2 , 23c PR 3 = PN 3 , 21d PR 3 = PN 3 , 22d PR 3 = PN 3 , 23d Ni(P-P)2 Ni(P-P)(P'-P') Ni(PR 3) 4 P-P = dpypcp, 24a (P-P)(P'-P') = dppe & dpype, 25a PR 3 = PPh3, 26a P-P = dppe, 24b (P-P)(P'-P') = dppe & dpypcp, 25b PR 3 = PNi, 26b P-P = dpype, 24c (P-P)(P'-P') = dpype & dpypcp, 25c PR 3 = PN 2 , 26c PR 3 = PN 3 , 26d Figure 4 . 9 The 2 2 Ni(0) phosphine complexes synthesized in this thesis work. Ni(PR,)2(P-P) 21-23 2 P P-P 24 Ni(P-P)2 2P -P Ni(l,5-COD) 2 4 P R 3 Ni(PR 3 ) 4 26 P-P P'-P Ni(P-P)(P-P) 25 Figure 4.10 Synthesis of Ni(0) phosphine complexes from Ni(l,5-COD) 2. 113 Chapter 4 references on page 127 Chapter 4 4.3.3.2 Characterization The only new homoleptic complex is Ni(dpypcp)2 (24a) (Section 4.2.2.4), characterized by NMR, UV-Vis and EI mass spectra, microanalysis and a m.pt. As a racemic mixture of R,R and S,S enantiomers of chiral dpypcp was used (Section 2.3.5, p.26), the "Pf^H} NMR spectrum of 24a should yield two singlets, one due to the Ki(RR)2 and Ki(SS)2 set of enantiomers (where the P nuclei are equivalent) and the other due to (RR)-Ni-(SS) (where the P nuclei are enantiotopically related by an inversion centre at Ni). For [M(dpypcp)2]X2 complexes (M = Pd, Pt; X = Cl, PF 6), two 5P singlets separated by < 0.1 ppm have been observed.52 The presence of only one singlet (8p = 38.70) for 24a (Table 4.12) indicates that either only one set of enantiomers is obtained, or, more likely, that the singlets for the two sets of enantiomers are identical. The successful preparation of the other known homoleptic complexes (24b, 24c, and 26a-d) was confirmed by comparison of ^Pl'H} N M R data to that reported (Table 4.12). Of note, Ni(PPh3)4 (26a) has been shown by 31P{"H} N M R to be in equilibria with Ni(PPh3)3 and PPh3 at r.t. in solution, whereas at -80°C it is the sole species present.53 Table 4.12 3 1P{ *H} NMR Data a for Homoleptic Complexes 24 and 26 Compound 5P Compound 5P Ni(dpypcp)2 24a 38.70* Ni(PPh3)4 26a 24.4 e Ni(dppe)2 24b 43.99 c Ni(PN04 26b 16.0/ Ni(dpype)2 24c 55.90 d Ni(PN 2) 4 26c 24.9 8 Ni(PN 3) 4 26d 28.9'' ( a ) In C 6 D 6 . ( 6 ) In CDC1 3 . ( e ) Lit. 5P (toluene-c/8) = 42.4, ref. 22. { d ) Lit. 5P (C 6D 6) = 55.9, ref. 17. ( e ) Lit. 8P (toluene-Jg) = 25.5, ref. 54. w Lit. 8P (C 6D 6) = 16.0, ref. 20; Lit. 8P (solid state) = 32.8, ref. 17; Lit. 5P (toluene-^) = 31.4. ref. 17. fe) Lit. 8P (solid state) = 41.9, ref. 17. w Lit. 5 P (C 6D 6) = 28.9, ref. 17. The characterization of 21-23 and 25 is based solely on 3 1P{1H} N M R data (Table 4.13), with the spectrum shown in Figure 4.11 for Ni(PN3)2(dpype) being representative of that obtained 114 Chapter 4 references on page 127 Chapter 4 for these complexes. The two triplets (columns B and C) arise from coupling of the two P nuclei of one ligand type (L) to the two P nuclei of the other ligand type (L1). The assignment of a triplet to either L or L' is based on the 5p values for the appropriate homoleptic complexes [Ni(L)4 or Ni(L) 2 (Column A) and Ni(L')2 (Column D)]. The 2JPP coupling constants are listed in Column E, while the separation in Hz between each triplet pair (A(t-t)) is listed in Column F. Various 5p signals corresponding to unreacted ligands, ligand oxides, and homoleptic Ni(0) phosphine complexes were also frequently detected. The regions of the 3 1P{1H} NMR spectrum containing the two triplets for 21-23 and 25 are depicted in Appendix B, Figures B.3-6. Of note, the 3 1 P coordination chemical shift (A) for Ni(PPh3)4 (29.0 ppm) is similar to that of the Ni(PN x) 4 complexes 26b and d (29.5 and 26.9 ppm, respectively), whereas that for Pt(PPh3)4 (15.5 ppm)55 differs substantially from those of the Pt complexes Pt(PNi)4 (28.1 ppm),25 Pt(PN2)4 (28.7 ppm),56 and Pt(PN3)4 (29.8 ppm).25 dpype in Ni(PN3)2(dpype) Ni(dpype)2 \ <— PN3inNi(PN3)2(dpype) free P N 3 T — i — i — i — i — r J T—i—I—I—i—|—i—i—I—I—I—r I l l l i I l l l l I ' T — i — i — i — i — r 55 50 45 40 35 30 25 20 15 10 0 ppm Figure 4.11 3 1P{1H} NMR spectrum of Ni(PN3)2(dpype) (22d) in C 6 D 6 . 115 Chapter 4 references on page 127 Chapter 4 Table 4.13 Selected 31P{XH} NMR Data for Complexes 21-23 and 25 in C 6 D 6 Complex Ligand: L L' column A column B column C column D column E column F L 8p in species: N i L 4 f l NiL 2 L' b L' 5p in species: NiL 2 L' b NiL' 2 a 2T C Jpp A « . t / 21a PPh3 dppe 24.4 31.55 32.18 43.99 19.91 76 22a dpype 24.4 35.17 39.62 55.90 26.62 540 23a dpypcp 24.4 25.55 34.28 38.70 27.69 1059 21b PNi dppe 16.0 33.69 35.09 43.99 23.77 170 22b dpype 16.0 38.19 47.53 55.90 24.53 1133 23b dpypcp 16.0 29.28 35.60 38.70 25.86 767 21c P N 2 dppe 24.9 36.20 39.71 43.99 22.78 427 22c dpype 24.9 42.66 48.39 55.90 23.26 696 23c dpypcp 24.9 32.82 43.57 38.70 25.68 1306 21d PN 3 dppe 28.9 38.27 44.91 43.99 22.19 806 22d dpype 28.9 47.55 49.37 55.90 21.89 221 23d dpypcp 28.9 34.01 49.89 38.70 25.77 1929 25a dppe dpype 43.99 45.17 53.03 55.90 27.46 955 25b dppe dpypcp 43.99 45.10 36.99 38.70 23.24 985 25c dpype dpypcp 55.90 56.12 38.89 38.70 10.26 2092 Singlet. ( } Triplet. ( c ) In Hz. ( i ° Separation between the centre of the two triplets in Hz. 31PfH}NMR Trends: The Chemical Shifts The trend whereby the 8P values for both the homoleptic Ni(PN x) 4 complexes and the triplet assigned to PN X in the Ni(PNx)2(P-P) complexes (Table 4.13, Column B) shift downfield in the order of PNi < P N 2 < PN 3 is likely due to the increased deshielding of the PN X P nuclei as the number of electron-withdrawing N-atoms increases. A linear correlation is observed in plots of the number of N-atoms present in PN X vs. 8P of the corresponding triplet within 21-23 (Figure 4.12a). A similar correlation is observed in plots of N-atom number in PN X vs. 5P of the triplet assigned to P-P (Table 4.13, Column Q in 21-23 (Figure 4.12b). This trend is also likely attributable to increased deshielding of the P-P phosphorus nuclei as the number of electron-withdrawing N-atoms in PN X increases, because the decrease in PN X P-»Ni c-donation may induce a compensating (and deshielding) increase in P-»Ni o-donation from the two P nuclei of the P-P ligand. 116 Chapter 4 references on page 127 Chapter 4 The triplet 8p values for the Ni(P-P)(P'-P') complexes (25) (Columns B and C) are within a few ppm of 5P for the appropriate corresponding homoleptic species (Columns A and D). 50 -r 45 -40 -PH 35 -o to 30 -25 -1 2 3 No. of N-atoms in PNX (a) 5 5 JH 5 0 1EL '5 4 5 -| PH PH 4 0 O c£ 3 5 30 2 0 99X6 o Rz = 0.9988 A R 2 = 0.9959 No. of N-atoms in PN X (b) Figure 4.12 N-atom count for PN X vs. linear increase in 5P of the triplet assigned to: (a) PN X , (b) P-P [o = 21b-d, • = 22b-d, A = 23b-d] 31PfH} NMR Trends: Separation Between the Triplet Resonances The magnitude of the separation between the two triplets (A(t-t)) of the Ni(PR3)2(P-P) complexes (Table 4.13, Column F) must be a manifestation of the differing electronic environments at the different P nuclei, as already noted for the separation observed between the two doublets (A ( d.d )) in the Ni(CO)2(PPh3)(PNx) complexes (Section 4.3.1.1). When the P nuclei of both PR 3 and P-P are ligated by a similar number of either phenyl or pyridyl substituents, A(t.t) is generally smaller then when the same nuclei are ligated by a significantly dissimilar number of such substituents. For example, 21a contains ten P-ligated phenyls groups and A(t-t) is only 76 Hz, in comparison to 806 Hz for 21d where two P nuclei are each ligated by three pyridyls and the other two P nuclei are each ligated by two phenyl groups. Similarly, A(t.t) for 22d (ten pyridyl groups) is 221 Hz, while that for 22b (two pyridyls per P nuclei in dpype and two phenyls and one pyridyl per P nuclei in PNi) is 1133 Hz. This trend is adhered to for nine (21a-d, 22b-d, & 23a-b) of the twelve Ni(PR3)2(P-P) complexes, but not for 22a and 23c-d. The Ni(P-P)(P'-P') complexes (25) also deviate from the general trend, as A(t.t) for 25a and b, both of which contain 117 Chapter 4 references on page 127 Chapter 4 four phenyl and four pyridyl groups, is ~ 1000 Hz whereas that for 25c, which contains only pyridyl groups, is 2100 Hz. slPfH} NMR Trends: 2JPP Coupling Constants The magnitude of 2 J P P between the P nuclei of PR 3 and P-P in the Ni(PR3)2(P-P) complexes 21-23 (Table 4.13, Column E) decreases, with the exception of 21a, in the order PPh3>PNi>PN2>PN3; this decrease is likely due to the reduction in electron density available at the P nuclei of PR 3 for through-bond overlap with the P-atoms of P-P as the number of electron-withdrawing N-atoms increases. This trend also holds for the Ni(P-P)(P'-P') complexes as 25a and b possess only four N-atoms and have 2 J P P = 27.46 and 23.24 Hz, respectively, while 25c contains eight N-atoms with 2 J P P = 10.26 Hz. The phenomenon whereby 2 J P P in 21a is smaller, rather than larger, than those of 21b-d, could possibly be due to 7t-stacking of phenyl rings on adjacent phosphine ligands. In cis-PdCl 2(PN 2) 2, a stacked configuration of two aryl rings causes a weak n charge-transfer interaction between them, resulting in a decrease in electron density around the Pd-P bonds.57 If a decrease in electron density at the Ni-P bonds of 21a were to occur via the same mechanism, then the 2 J P P value could fall below those of PNx-containing species. 4.3.3.3 Reactivity of Ni(0) Tertiary 2-Pyridylphosphine Complexes with Small Molecules Studies on the reactivity of Ni(0) complexes with various small molecules are myriad, as 37 58 59 2 exemplified by the reviews that mention Ni(Y)n phosphine complexes (Y = CO, NO, ' rf-alkene,60 C S 2 , 3 7 N 2 , 6 1 ' 6 2 0 2 , 6 3 S0 2 , 6 3 ' 6 4 and C0 2 6 5 ' 6 6 ) . Reactions of Ni(0) phosphines with HC1, RX, and R C N to afford hydrido halo,37'67 alkyl halo,68'69and alkyl cyano37 Ni(II) phosphine complexes, respectively, are also known. As such, the reactivity of Ni(dpypcp)2 (24a) and Ni(PN 3) 4 (26d) toward small molecules was examined by introducing C2H4, Cl 2 , 0 2 , or H 2 0 to a CeD6 solution of either 24a or 26d contained in an N2-flushed NMR. The reactions with Cl 2 , 0 2 , and H 2 0 resulted in considerable decomposition of the Ni(0) starting material with concomitant release of free ligands and the formation of ligand mono and bisoxides (see Section 4.2.8). Such decomposition upon exposure to 0 2 or H 2 0 is typical of Ni(0) complexes.37 The aqueous solution chemistry of 21-26 was thus not examined. The C l 2 118 Chapter 4 references on page 127 Chapter 4 reaction does not (usually) generate new species,37 although the reaction of X 2 with Ni(CO)2(o-C6H4(PEt3)2) or Ni{(o-C6H4(PEt3)2)}2 to yield NiX2(o-C6H4(PEt3)2) in CeHe has been reported (X = halogen).38 The ligand oxides formed in the reactions with CI2 are presumed to result from O2 impurities in the gas (which was not of analytically pure grade). No reaction was observed between C2H4 and either 24a or 26d. The electronic saturation of these 18-electron species may explain their lack of reactivity as the 16-electron Pt(PNi)3 forms Pt(772-C2H4)(PNi)2 under similar conditions.25 Standard preparations of Ni(0) T -^alkene complexes are carried out under rigorously air-free conditions;37 the initial preparation of Ni(772-C2H4)(PPh3)2 required reduction of an ether solution of Ni(acac)2 and 2 equiv. of PPh3 with AlEt(OEt) 2 under C2H4 at 0°C . 7 0 It was not until later that Ni(C2H4)(PPh3)2 was prepared via addition of C2H4 to the 16-electron Ni(PPh3)3 (which forms upon dissociation of 26a in solution).71 4:3.4 Synthesis and Characterization of <rans-Ni(CH3)(I)(phosphine)2 Species Reactions of Ni(PN 3) 4 (26d), Ni(dpype)2 (20c), and Ni(dpypcp)2 (20a) with CH 3 I resulted in the formation of tan (27) or yellow (28-29) *raws-Ni(CH3)(I)(phosphine)2 species (see Section 4.2.3, Figure 4.13). R 3 P ^ . / C H 3 Ni(PR 3) 4 + CH 3 I *> Y" ! > R 3 + 2PR 3 ( P R 3 = P N 3 2 7 > C H 3 Ni(P-P) 2 + CH 3 I — • ( _NL ) (P-P = dpype 28; dpypcp, 29) V P I P ^ I Figure 4.13 Synthesis of /ra«s-Ni(CH 3)(I)(phosphine) 2 species; species with PR 3 = PPh 3 (31), and P-P = dppe (30) were not successfully synthesized. Singlets were detected in the 31P{XH} NMR spectrum (CDC13) of 27, 28, and 29 at 5 31.5, 29.0, and 36.5, respectively. These singlets are close, but not identical, to those known for 26d (5 28.9, in C 6 D 6 ) , and dpype(0)2, dpypcp(0)2, and 20a (6 33.1, 32.1, and 38.7, respectively, in CDC13). Detection of ~ 2 equiv. of PN 3 in the 3 1P{1H} NMR spectrum of the filtrate from the 119 Chapter 4 references on page 127 Chapter 4 reaction of 26d with CH3I is consistent with 27 possessing two PN3 ligands. The absence of dpype and dpypcp in filtrates from the syntheses of 28 and 29 is consistent with the complexes containing two dpype and dpypcp ligands, respectively. The ! H NMR spectrum of 27 shows a triplet ( 3JP H = 6.2 Hz) at 8 0.6, while the ! H NMR spectra of 28 and 29 show quintets at 8 0.9 ( 3 J P H = 7.1 Hz) and 0.7 ( 3 J P H = 7.3 Hz), respectively. These signals integrate to ~ 3 H in all three cases, and are assigned to Ni-CHj (5H for free CH 3I = 2.1). Similarly observed is the report of a triplet at 8 0.05 ( 3 J P H = 5.7 Hz) being assigned to Pt-CH.3 in /raHS-Pt(CH3)(I)(PN3)2 2 5 The multiplicity of these signals provides evidence for 27 being a bis-PN3 species, and 28 and 29 being bis-P-P species; these formulations were confirmed by elemental analysis. The d8, square-planar structure for 27 in solution is implied by the diamagnetic appearance of the NMR spectra, while an octahedral geometry for 28 and 29 is likewise suggested by the "noisy", paramagnetic appearance of the 3 IP{'H} NMR spectra. Of note, the *H NMR spectra of 28 and 29 were diamagnetic in appearance, even though they are d8 octahedral complexes. Such behaviour is known for Ni(II) species (e.g., the ! H NMR spectrum of trans-Ni(p-CH3C6H4NC)2(acac)2 in CDCI3 is sharply resolved and 8CH3 is 2.38 vs. 2.02 for uncoordinatedp-CH3C6H4NC), and is attributed to the favorable electron relaxation time of octahedral Ni(II). ' The trans formulation for 27-29 is suggested by the observance of just one singlet in the 3 1P{ !H} NMR spectrum of each complex. A fast dynamic cis^ trans equilibrium (on the NMR time-scale)27 is unlikely and would require rapid fluctuation of the chelating P-P ligands between mono and bidentate states during molecular rearrangement. Nevertheless, low temperature NMR studies should be conducted to exclude this possibility. No phosphonium salts were detected in the 3 1P{ !H} NMR spectra of either 27-29 or the solutions in which they were prepared (see Section 4.3.5). There appears to be no report on fra«5-Ni(CH3)(I)(dppe)2 (30) or trans-Ni(CH3)(I)(PPh3)2 (31) (the phenyl analogues of 27-29) being prepared from Ni(dppe)2 or Ni(PPh3)4, respectively. The preparation of various aryl6 8'6 9 or acyl73 halide frzws-Ni(R)(X)(PR3)2 complexes via oxidative addition of organohalide to Ni(PR3)4 in CeHs has been reported, but PR 3 120 Chapter 4 references on page 127 Chapter 4 is either PEt3 or PCy 3. A patent has described the use of Ni(CH3)(Cl)(PPh3)2 as an olefin dimerization catalyst.74 The attempted synthesis of 30 and 31 (Sections 4.2.3.4-5, p.91) resulted in the isolation of the off-white solids [(CH3)(dppe)]I and [(CH3)(PPh3)]I, respectively (see Section 4.3.5). Analysis of the reaction solutions from which these compounds were obtained (Figure 4.13) revealed the presence of starting material, free ligand, and sometimes ligand oxides. Electronic differences between pyridyl and phenyl groups are presumably responsible for the success and failure, respectively, in preparing 27-29, and 30-31. Of interest, the Schlenk tube used in the attempted synthesis of 30 was found four months later to contain purple crystals of Nil2(dppe) (12c) (see Section 4.2.3.4). 4.3.5 The Phosphonium Salts, [(CH3)(phosphine)]I and [(CH3)2(phosphine)]I2 Some mono and bismethyl phosphonium salts of PN 3 , dpype, dpypcp, PPh3, and dppe were prepared (Figure 4.14); 32e,26 33b,27 and the PN] analogue25 of 32a are known. The 32b-d salts are also depicted in Figure 4.1 (p.92). Ligand Monomethyl Salt Bismethyl Salt ^ — PN 3 32a - ( N dppe 32b 33b \ / dpype 32c 33c 0 _ . ® / \ ® . A -I'IJ R2(Me)P, P(Me)R2 dpypcp 32d 33d PPh3 32e - ° " D " a j Figure 4.14 Labelling scheme for the mono and bismethyl phosphonium ligand salts. 21" The monomethyl salts were prepared in situ by addition of excess CH 3 I to free ligand in CeD6 (see Section 4.2.4). The monomethyl salts 32a and e display one 31P{1Ff} N M R singlet while an A X pattern of two doublets is seen for 32b-d (Tables 4.14-15); 3 J P P coupling is between the P nuclei of P R / and PR 3, whose assignments are based on comparison with the 8P singlets for the appropriate bismethylated (Table 4.16) and free ligands, respectively. No bismethyl salts were detected even though excess CF£3I was employed in these experiments. 121 Chapter 4 references on page 127 Chapter 4 Table 4.14 3 1P{ Ti} NMR Data for the Monomethylphosphonium Salts 32a-e in C 6 D 6 a Salt of: 5P PRt+ P-atom (3JP P) 5P PR 3 P-atom (3JP P) P N 3 32a 10.3 -PPh3 32e 21.6 -dppe 32b 26.05 (41.2) -12.37(41.3) dpype 32c 21.74(38.5) -7.85 (38.5) dpypcp 32d 23.41 (15.3) -1.07(15.2) ( a ) Singlets for 32a and 32e; doublets for 32b-d; J values in Hz. Table 4.15 NMR Data for the Monomethylphosphonium Salts 32a-e in CDC13 " Salt of: 5P P R / P-atom (3JPP) 5P PR 3 P-atom (3JP P) | 8 C H 3 (2JP H) PN 3 32a 10.0 s 6 - 3.29 d (15.0) PPh3 32e 21.8 s 6 - 1 3.46 d (13.2) dppe 32b 27.41 d (44.0) -11.07 d (43.7) 3.27 d (13.6) dpype 32c 21.66 d (38.5) -7.98 d (38.6) 3.26 d (13.7) dpypcp 32d 23.55 d (15.4) -0.88 d (15.6) 3.18 d(13.5) ( o ) J values in H z . ( 6 ) Lit. 5P (CDC13) for 32e = 22:2, ref. 26, and for [(CH3)(PN0]I = 17.5, ref. 25. Precipitates which formed within an hour in all five NMR samples were collected and identified as 32a-e by NMR in CDC13 (Table 4.15). The doublet in the ! H N M R spectrum assigned to the phosphorus-ligated methyl group (P-CH3) arises from 2 J P H coupling. Attempts to prepare in situ bismethylated 33b-d in CeD6 with excess CH 3 I were unsuccessful because of precipitation of the monomethyl salts. Such behavior is known for ditertiary bisphosphines and has been exploited to ensure the quantitative formation of ligand monoxides (vs. bisoxides) upon alkaline hydrolysis of the insoluble monophosphonium salt (Figure 4.15);75"77 bisphosphonium salts decompose to mixtures of R3P(0)-Y-(0)PR3, OPR 3, PR 3, and Y under these same conditions.78 C 6 H 6 R 2 P - Y - P R 2 + R'X — Figure 4.15 Hydrolysis of monoalkyl salts of ditertiary bisphosphines to yield the monoxide quantitatively. R R 2 P - Y - P R 2 © X BO\aq) -(R'X + H+f O R 2 P - Y - P R 2 122 Chapter 4 references on page 127 Chapter 4 A precipitate composed of mono and bismethylated dppe (3:1) was obtained by reaction of dppe with 5 equiv. of CH 3I in CDC13, as determined by 3 1P{1H} NMR (CD 3OD) (see Section 4.2.5). A similar reaction of dpype with 15 equiv. of CH 3 I resulted in a 1:1 mixture, while bismethylated dpypcp (33d) was obtained as the sole-product upon addition of 10 equiv. of CH 3 I to dpypcp in CDC13; 33b and c were obtained as the sole-products upon heating a mixture of 20 equiv. of CH 3 I and ligand in MeOH at 55°C for 2 h. NMR data for 33b-d are reported in Table 4.16. Table 4.16 NMR Data for the Bismethylphosphonium Salts 33b-d " Parameter: dppe, 33b dpype, 33c dpypcp, 33d 26.56* 21.47 23.40 5CH3 ( 2 J P H ) 3.41 (5.2) 4.45 (5.7) 3.40(13.2) ( a ) In CD 3 OD; singlets for 5P, doublets for 5CH 3 ; J values in Hz. ( f c )Lit. 8P (CD 3OD) = 26.9, ref. 27. The LR bands assigned to v(P-C) stretches (lit. 890-973 and 1278-1330 cm"1)18 were observed at 907 and 1297 cm"1 for 33c, and at 900 and 1311 cm"1 for 33d, while those assigned to the v a s y m (CH 3 ) and v s y m (CH 3 ) C-H stretches were detected at 2944 and 2867cm"1, respectively, for 33c, and at 2965 and 2872 cm"1, respectively, for 33d. Fragmentation ELMS peaks with isotopic splitting patterns corresponding to 33c-I, 33d-I, and 33d-2I, were observed at 559, 599, and 473 m/z, respectively, for the two bismethyl salts. Molar conductivity values in MeOH for 33c and 33d were 210 and 185 Q"1 cm2 mol"1, respectively (cf. values of 160-220 for 2:1 electrolytic species in MeOH), 7 9 while melting points ranges of 232-234°C (33c) and 221-224°C (33d) are indicative of high purity. Acceptable elemental analyses were obtained for 33c and d. lH NMR Features of Interest The conversion of mono to bismethylated dpypcp (over ~ 4 h) can be monitored by observing the decrease in intensity of the doublet assigned to P-CH 3 in 32d (8H 3.18) with concomitant increase in intensity of the P-CH 3 doublet of 33d (5H 3.40) (Figure 4.16). The collapse of the doublet upon phosphorus-decoupling (TH^P}, 500 MHz 1 H , 405 MHz 3 1P) confirms the 2 J P H coupling with an appropriate magnitude.27 123 Chapter 4 references on page 127 Chapter 4 The pyridyl ! H resonances shift downfield on going from the neutral to mono to bismethylated compounds, likely attributable to increased deshielding of the ! H nuclei with increasing charge. The shifts are depicted in Figure 4.17 for the pyridyl protons ( H 3 - H 6 ) , while the shifts for H3-FL5 in both dpype and dpypcp are reported in Table 4.17. An COSY experiment of the sample associated with Figure 4.17b was required to facilitate assignment of the pyridyl protons (Appendix B, Figure B.7). A similar COSY spectrum was obtained for a mixture of dpype and [(CH3)(dpype)]I (Appendix B, Figure B.8). 33d 3.5 3.4 3.3 3.2 3.1 3.0 ppm Figure 4.16 ' H NMR spectrum (CDC13) of the 8CH 3 region of the methylphosphonium salts of dpypcp: (a) monomethyl salt, (b) mono and bismethyl salt, (c) bismethyl salt. Table 4.17 Total Downfield Shift of lH NMR Signals of P-P Ligands Upon Bismethylation Ligand A a 8H 3 A8FL, A 8 H 5 A8H6 dpype 0.75 0.76 0.70 0.33 dpypcp 0.62 1.91 1.07 0.24 ( a ) A = [8H (bismethylated compound) - 8H (compound)]. H a of dpype and FL of dpypcp shift downfield by 0.58 and 1.68 ppm, respectively, upon bismethylation. 124 Chapter 4 references on page 127 Chapter 4 125 Chapter 4 references on page 127 Chapter 4 4.3.6 Attempted Preparation of Acyl Ni(II) Phosphine Species The preparation of Ni(COMe)(I)Ln o-acyl complexes via either carbonyl insertion into the Ni-Me bond of Ni(Me)(I)Ln species or methyl migration to a Ni-CO bond of Ni(CO)2L„ species (Figure 4.18) would demonstrate potential use of the compounds as catalysts for cycles requiring such steps. Ni(COCH3)(I)(PMe3)2 has been prepared via carbonylation of Ni(CH 3)(I)(PMe 3) 2. 8 0 CO C H I Ni(CH3)(I)Ln > Ni(COCH 3)(I)Ln < Ni(CO)2L„ Figure 4.18 Possible routes to formation of acyl Ni(II) phosphine complexes. Neither carbonylation of fra«s-Ni(CH3)(I)(PN3)2 (27) (see Section 4.2.6), or iodomethylation of Ni(CO)2(PPh3)2 (190) or Ni(CO)2(dpypcp) (20b) (see Section 4.2.7) was successful: 27 generated CH 3I, [(CH3)(PN3)]I, PN 3 , and OPN 3 , while 190 generated PPh3, OPPh 3, and [(CH3)(PPh3)]I. The synthesis of acyl Ni(II) phosphine species probably requires a more basic phosphine ligand, as in Ni(COCH 3)(I)(PMe 3) 2. 8 0 4.4 Conclusions The known P-coordinated Ni(CO) 2(PN x) 2 species 19a-c have been prepared in situ via displacement of PPh3 from Ni(CO)2(PPh3)2 (190), and the effects of solvent, time, and ligand stoichiometry upon the equilibrium between 190, Ni(CO)2(PNx)(PPh3), and 19 have been examined. The P-coordinated Ni(CO)2(P-P) species 20a-b have been synthesized and well characterized, including a crystal structure for Ni(CO)2(dpypcp). [Ni(CO)2(2H-dpypcp)](CF3S03)2 and [2H-dpypcp](CF3S03)2 have been prepared and characterized. Comparison of their ^P^H} NMR spectra to those obtained by dissolving 20b in D 2 0 or H20/acetone-cfe shows that Ni(CO)2(P-P) species dissolve in aqueous media via protonation of two of the pyridyl N-atoms to yield [Ni(CO)2(2H-P-P)]2+. Subsequent decomposition in H 2 0 via an unknown process yields [Ni(H 20) 6] 2 +, [2H-dpypcp]2+, CO, and ligand bisoxide. The species [Ni2(CO)4(//-PN2)2]Cl4 (19d) has also been isolated and tentatively characterized. The in situ preparations and 3 1P{1H} NMR characterization of 16 new Ni(0) phosphine complexes (21-23, 24a, and 25) and 6 known homoleptic Ni(0) phosphine complexes (24b-c and 126 Chapter 4 references on page 127 Chapter 4 26a-d) have been achieved. Various 3 1P{1H} NMR spectroscopic trends have been noted for the Ni(0) phosphine species. Ni(dpypcp)2 (24a) was also isolated and well characterized. Ni(dpypcp)2 and Ni(PN 3) 4 were unreactive toward C2H4 and decomposed upon reaction with O2, H 2 0, or Cl 2 , while reaction of Ni(PN3)4, Ni(dpype)2, and Ni(dpypcp)2 with CH 3 I resulted in the formation of novel *ratts-Ni(CH3)(I)(PN3)2 (27), ^a«5-Ni(CH3)(I)(dpype)2 (28), and trans-Ni(CH3)(I)(dpypcp)2 (29), respectively, as determined by NMR spectroscopy and microanalysis. Attempts to prepare /rara-Ni(CH3)(I)(PPh3)2 and *raro,-Ni(CH3)(T)(dppe)2 were unsuccessful. The mono (32a-e) and bismethyl (33b-d) phosphonium salts of PPh3, PN 3 , dppe, dpype, and dpypcp were prepared and well characterized by NMR spectroscopy. Attempts to prepare Ni(COCH 3)(I)L n via iodomethylation of Ni(CO)2Ln with CH 3I, or carbonylation of trans-Ni(CH3)(I)Ln with CO, were unsuccessful. 4.5 References 1. McAuliffe, C. A. Transition Metal Complexes of Phosphorus, Arsenic, and Antimony Ligands. London: McMmillan, 1973. 2. Eller, P. G ; Bradley, D. C ; Hursthouse, M . B.; Meek, D. W. Coord. Chem. Rev. 1977, 24, 1. 3. Tolman, C. A. J. Am. Chem. Soc. 1970, 92, 2956. 4. Reppe, W.; Schweckendiek, W. J. Annalen 1948, 560, 104. For olefinic and acetylenic polymerization. 5. Jzang, T. T.; Liu, C. S. Main Group Met. Chem. 1987,10, 373. 6. Tsuda, T.; Mizuno, H.; Takeda, A ; Tobisawa, A. Organometallics 1997, 16, 932. 7. Jolly, P. W.; Wilke, G. The Organic Chemistry of Nickel, Vol. 2. New York: Wiley, 1975. 8. Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry. Mill Valley: University Science Books, 1987. 9. Furman, D. B.; Ivanov, A. O ; Morozova, L. N.; Kustov, L. M . ; Elev, I. V. Metalloorg. Khim. 1990, 3, 264, as cited in Chem. Abstr. 1991 113, 39969. 127 Chapter 4 references on page 127 Chapter 4 10. Furman, D. B.; Kudryashev, A. V.; Ivanov, A. O.; Pogorelov, A. G.; Yanchevskaya, T. V.; Bragin, O. V. Izv. Akad. NaukSSSR, Ser. Khim. 1990, 3, 512, as cited in Chem. Abstr. 1991, 113, 39870. 11. 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IR Spectra of Inorganic & Coordination Compounds, 2nd ed. New York: Wiley Interscience, 1970. 44. Pouchert, C. J. Ed. The Aldrich Library of Infrared Spectra, 3rd ed. Milwaukee: The Aldrich Chemical Company, Inc. 1981. 45. Larpent, C ; Dabard, R.; Patin, H. Inorg. Chem. 1987, 26, 2922. 46. Bond, A. M . ; Eklund, J. C ; Tedesco, V.; Vu, T.; Wedd, A. G. Inorg. Chem. 1998, 37, 2366. 129 Chapter 4 references on page 127 Chapter 4 47. Godfrey, S. M . ; Ho, N.; McAuliffe, C. A.; Pritchard, R: G. Angew. Chem., Int. Ed. Engl. 1996, 35, 2344 48. Belykh, L. B.; Dmitrieva, T. V.; Shmidt, F. K. Russ. J. Coord. Chem. 1999, 25, 494, as cited in Chem. Abstr. 2000, 131, 199809. 49. Kuntz, E . G.; Vittori, O. M . J. Mol. Catal. A: Chemical 1998,129, 159. 50. van Hecke, G. R.; Horrocks, Jr., W. D. Inorg. Chem. 1966, 5, 1968. 51. Ittel, S. D. Inorg. Synth. 1977,17, 117. 52. Jones, N. D.; MacFarlane, K. S.; Smith, M . B.; Schutte, R. P.; Rettig, S. J.; James, B. R. Inorg. Chem. 1999, 38, 3956. 53. Mynott, R.; Mollbach, A.; Wilke, G. J. Organomet. Chem. 1980, 199, 107. 54. Fisher, K. J.; Alyea, E . C. Polyhedron, 1989, 8, 13. 55. Sen, A ; Halpern, J. Inorg. Chem. 1980, 19, 1073. 56. Rastar, G. M.Sc. Thesis. University of British Columbia, 1989. 57. Newkome, G. R.; Evans, D. W.; Fronczek, F. R. Inorg. Chem. 1987, 26, 3500. 58. Caulton, K. G. Coord. Chem. Rev. 1975, 14, 317. 59. Enemark, J. H.; Feltman, R. D. Coord. Chem. Rev. 1974,13, 339. 60. Malatesta, L. ; Cenini, S. Zerovalent Compounds of Metals. London: Academic, 1974. 61. Chatt, J.; Kilworth, J. R.; Richards, R. L. Chem. Rev. 1978, 78, 589. 62. Jolly, P. W.; Jonas, K.; Kruger, C ; Tsay, Y. H. J. Organomet. Chem. 1971, 33, 109. 63. Vaska, L. Acc. Chem. Res. 1976, 9, 175. 64. Moody, D. C ; Ryan, R. R. Inorg. Chem. 1979,18, 223. 65. Palmer, D. A.; Van Eldik, R. Chem. Rev. 1983, 83, 651. 66. Yaneff, P. V. Coord. Chem. Rev. 1977, 23, 183. 130 Chapter 4 references on page 127 Chapter 4 67. Sacconi, L. ; Orlandi, A.; Midollini, S. Inorg. Chem. 1974, 13, 2850. 68. Tsou, T. T.; Kochi, J. K. J. Am. Chem. Soc. 1979,101, 6319. 69. Hidai, M . ; Kashiwagi, T.; Ikeuchi, T.; Uchida, Y. J. Organomet. Chem. 1971, 30, 279. 70. Ashley-Smith, J.; Green, M . ; Stone, F. G. A. J. Chem. Soc. A. 1969, 3019. 71. Tolman, C. A ; Seidel, W. C ; Gerlach, D. H. J. Am. Chem. Soc. 1972, 94, 2669. 72. Horrocks, Jr., W. D.; Taylor, C. R.; LaMar, G. N. J. Am. Chem. Soc. 1964, 86, 3031. 73. Otsuka, S.; Naruto, ML; Yoshida, T.; Nakamura, A. J. Chem. Soc, Chem. Comm. 1972, 396. 74. Zuech, E. A. U. S. Pat. 3,485, 881. 1969, as cited in Chem. Abstr. 1970, 72, P99989a. 75. Abatjoglou, A. G., Kapicak, L. A. Eur. Pat. Appl. EP 72,560 1983, as cited in Chem. Abstr. 1983, 98, P198452p. 76. Brassat, I.; Englert, U.; Keim, W.; Keitel, D. P.; Killat, S.; Suranna, G-P.; Wong, R. Inorg. Chim. Acta 1998, 280, 150. 77. Bonderenko, N. A.; Rudomino, M . V.; Tsvetkov, E. N. Synthesis 1991, 125. 78. Brophy, J. J.; Gallagher, M . J. Aust. J. Chem. 1969, 22, 1385. 79. Geary, W.J. Coord. Chem. Rev. 1971, 7, 81. 80. Carmona, E. ; Gonzales, F.; Poveda, M . L.; Atwood, J. L. ; Rogers, R. D. J. Chem. Soc, Dalton Trans. 1980, 2108. 131 Chapter 4 references on page 127 Chapter 5 CHAPTER FIVE Catalysis of the Water-Gas-Shift Reaction and Attempted Olefin Hydration using Nickel 2-Pyridylphosphine Complexes 5.1 Water-Gas Shift Catalysis 5.1.1 Introduction The production of hydrogen gas rose sharply during World War II as many countries sought to convert local non-petroleum carbon sources (such as coal and coke) to hydrocarbon fuels via Fischer-Tropsch (FT) type syntheses (Figure 5.1).1 Previously, the main source of H 2 was steam-reformation of methane (Eq. 5.1),1 which was itself a scarce commodity in many countries interested in the FT-synthesis of hydrocarbon fuels. A needed alternate route to H 2 was soon found in the "water-gas" reaction, which involves the treatment of carbon (from coal) with water at high temperatures and pressures to produce a mixture of H 2 0 , C 0 2 , H 2 , and CO (Eq. 5.2); removal of H 2 0 and C 0 2 yields "synthesis-gas" (H 2/CO) for the FT production of hydrocarbon fuels. The H 2 content of synthesis gas can be increased by recycling the CO product to react with water to produce H 2 and C 0 2 in the water-gas-shift reaction (WGSR) (Eq. 5.3). The separation of H 2 from C 0 2 is then achieved by scubbing the product stream with an aqueous solution of monoethylamine.2 The loss of CO to recycling in the WGSR is acceptable as CO can be readily obtained from other sources (Table 5.1)3 to yield, upon combination with H 2 , the synthesis-gas used in FT chemistry. H 2 + CO > alkanes Co cat. „,0,,. / 2H 2 + CO > C H 3 O H Co or Zn/Cu cat. ^ Q ^ ' ^ Q ^ ^ 3H 2 + CO < > CH4 + H 2 0 Ni cat. alumina-supported catalyst Figure 5.1 Fischer-Tropsch synthesis of organics using catalysts supported on alumina (Al203) or metal oxides. CH4 +H 2Ofe) « Ni catalyst CO +3H 2 (Eq.5.1) < 700-1000 °C 132 Chapter 5 references on page 149 Chapter 5 catalyst 4H 2 0 + 2C » H 2 0 f e ) + C 0 2 + 3H 2 + CO (Eq. 5.2) catalyst H 20(g) + CO ^ W H 2 + C 0 2 A H ° 2 9 8 = - 42 kJ mol"1 (Eq. 5.3) Table 5.1 Various Industrial CO Sources Reactants Products A H ° 2 9 8 (kJ mol"1) c + co2 2CO + 173 C + H 2Ofe) CO + H 2 + 131 C + V2O2 CO - I l l CH4 + H 2Ofe) CO +3H 2 + 206 CH4 + ,/2o2 CO +2H 2 - 36 Table 5.2 Equilibrium Constant (KP) of the WGSR vs. Temperature a Temperature (°C) K P Reference 127 1450 4 200 227.9 3 327 26.9 4 400 11.70 3 800 1.105 3 (a)ForH 2Ofe). The WGSR reaction is reversible with the equilibrium constant (KP) decreasing as the temperature is raised (Table 5.2). The industrial production of H 2 via the WGSR should thus ideally be conducted at low temperatures. Current industrial WGSR proccesses, however, employ heterogeneous metal oxide catalysts at high temperatures, with the pre-eminent system utilizing a Fe304/Cr203 mixture operating at 350°C in gaseous water;5 the K P at this temperature allows only 85% of the CO to be shifted to H 2 . 6 A more effective catalyst mixture based on Cu 133 Chapter 5 references on page 149 Chapter 5 with ZnO operates at 200°C in liquid water (under pressure), and the larger K P value allows for a 95% shift. Unfortunately, this Cu/ZnO system is highly susceptible to poisoning by trace sulfur impurities present in industrial CO streams (prior to any costly purification).3 The Fe304/Cr203 catalyst is, however, highly tolerant of sulfur impurities, and the two systems have been combined in some plants in a two-step, two-catalyst process with the Fe/Cr catalyst removing the sulfur and the Cu/ZnO catalyst "completing" the WGSR. 6 The combined systems also offer the advantage of performing the "final shift" in a liquid water medium which results in a large positive change in AS° on going from H 20(g) to H 20(/) (Table 5.3).7 This results in considerable cost savings and more than compensates for the mildly endothermic nature of the WGSR when run in H 20(/). Table 5.3 Thermodynamic Parameters for the WGSR Using Either H 20(/) or H 20(g) H 2 0 state A G ° 2 9 8 (kJ mol"1) A H 0 2 9 8 (kJ mol"1) AS° 2 98 (kJ mol"1 K"1) gas -28.53 -41.17 -42.3 liquid -19.92 +2.85 +76.6 The catalyst system employed must be active enough to promote the WGSR but not so active for catalysis of other undesirable reactions (e.g., Figure 5.2).3 CO + 3F£2 > CH4 + H 2 0 AH° = - 206 kJ mol"1 2CO > C + C 0 2 AH° = -173 kJ mol'1 Figure 5.2 Other possible product mixtures from the WGSR. The Kp and thermodynamic data reveal that the optimum conditions for WGSR require a liquid water medium and an operation temperature of 27°C as the equilibrium of the CO to H 2 shift then approaches 100%. These conditions naturally favour homogeneous catalysis as heterogeneous catalysts generally do not operate at low temperatures. Interest is thus high in the development of homogeneous WGSR catalysts which are sulfur-tolerant6 and research in this field 134 Chapter 5 references on page 149 Chapter 5 is substantial as 1081 publications from 1986-1999 contain the phrase "water gas shift", as revealed by a computerized Chemical Abstracts search. Historically, homogeneous catalysis of the WGSR was first discussed by Reppe in 1953 when Fe(CO)5 and Ni(CO)4 were used as catalysts for the production of hydrogenated organic substrates and C 0 2 from water, CO, and an unsaturated organic.8 However, it was not until 1970 that the homogeneous catalysis of the WGSR strictly for H 2 and C 0 2 production was first reported (using Group 8-10 metals, Group 15 ligands (P, As, Sb), and inorganic bases).6 Since then, scores of transition-metal complexes have been found to catalyze the WGSR under differing conditions, thereby resulting in a variety of possible catalytic cycles. These are typically classified by their lack or presence of a cocatalyst (acidic or basic) and by whether CO or H 2 0 activation occurs in the primary step;6 to date the majority of catalysts fall into the "basic medium/CO activation" category.3 Unfortunately, only a few transition-metal catalysts have shown significant potential.9 The catalytic cycles have been reviewed by Laine and Crawford,6 and are presented here in a single diagram (Figure 5.3). In general, once CO has coordinated to a metal, the reactivity of the carbonyl towards H 2 0 , OH", or HT is determined by the electron density (e.d.) available at the metal for back donatation to CO. Accordingly, when e.d. is low (i.e., high metallic oxidation state or overall "+" charged complex), weakly nucleophilic H 2 0 can react with the coordinated CO (Route I). When e.d. is high (i.e., good electron-donor ligands, neutral metal, or overall negatively charged complex), the strongly nucleophilic OH" can react with coordinated CO (Route H). Alternatively, an electron-rich metal carbonyl can become protonated under acidic conditions and subsequently react with H 2 0 (as e.d. decreases upon complex protonation; Route i n ) . In rare cases, with metals that are high in both e.d. and coordinative unsaturation (e.g., Pt(P'Pr3)3 or W(CO)3(PCy3)2), oxidative addition of H 2 0 to the metal is preferential over CO coordination (Route IV), as greater reduction of the high e.d. and coordinative unsaturation is attained with H 2 0 . 6 In all cases, the production of H 2 and C 0 2 is attained via either a metallocarboxylic acid (MC0 2 H), hydridometallocarboxylic acid (HMC0 2 H), metalloformate (M0 2 CH), or hydridometalloformate (HM0 2 CH) intermediate. 135 Chapter 5 references on page 149 Chapter 5 Figure 5.3 Various catalytic cycles for the WGSR. Many factors affect homogeneous catalysis of the WGSR, as revealed by examination of the conditions and results for the various systems tabulated in Laine and Crawford's review.6 Either neat water or an aqueous organic solvent has been used traditionally, and changing the aqueous component from acetone to THF can result in an 8-fold increase in H 2 production.10 136 Chapter 5 references on page 149 Chapter 5 The water content can also be important: one study reports maximum activity at 25% v/v H 2 0 - M e O H , u another at 10% v/v H 2 0-MeOH (with a minimum at 50% v/v),7 and yet another at 99% v/v H 2 0 - M e O H . 1 2 Increasing addition of inorganic base cocatalysts (e.g., NaOH, KOH) typically results in increased activity,13 while organic nitrogen bases (such as pyridine, NMe3, NEt3, and en) are also popular cocatalysts.3 A shift from 300 to 5700 turnovers h"1 was observed on changing from pyridine to NMe3,6 and differences are also observed with acid cocatalysts (i.e., HC1, Et 3 NHCl, C5H5NHCI, or H 2 S0 4 ) . 1 4 Some catalysts have been shown to be active at high or low p H . 1 4 , 1 5 Some systems experience a change in mechanism at a certain temperature,16 others undergo catalyst decomposition at relatively low temperatures,14 others go through a temperature-dependent activity-maximum,17 and still other systems display increasing activity with increasing temperature with no upper-limit found.13 Yet another factor is the loading pressure of CO (Pco), with some studies showing a decrease in activity as Pco rises,7 others reporting high activity at high Pco,12 and still other reports describing a maximum activity at sub-atmospheric pressures (~ 0.5 atm).14 Catalyst concentration is naturally important, and in most cases saturation kinetics are obtained with increasing catalyst concentration.12 Table 5.4 Examples of Homogeneous WGSR Catalyst Systems Catalyst Pco° Temp. * Solvent Base/Acid T O F c Ref. Rh(H)2(02COH)[P(/-Pr)3]3" 20 100 pyridine(a<7) py 36 4 Pt[P(/-Pr)3]3 d 20 153 H20/acetone - 19.2 10 Pt(PPh3)3 d 20 153 H20/acetone - 0 10 [Ru(bpy)2(CO)Cl](PF6)e 20 150 H 2 0 KOH(aq) 21 13 NiCl 2 (PMe 3 ) 2 / 1 , 160, , EtOH(a?) pyridine 48 14 Ru 3 (CO) 1 2 * 1 100 diglyme(a6*) H 2 S 0 4 1.4 15 Ru 3 (CO)i 2 * 1 100 ethoxyethanol KOH(aq) 0.1 15 Rh dimer' 1 90 H 2 0 / « -PrOH - 2.5 17 RhCU* 0.9 100 pyridine(a6*) pyridine 4 18 Rh4(CO)i2* 1 80 pyridine(a<7) pyridine 172 19 CuCl 2 • H 2 0 * 1.9 120 pyridine^) pyridine 0.25 20 Ru 3 (CO) 1 2 y 24 100 THE NEt3(a<7) 330 21 IGPtCVSnCU k 0.5 88 acetic acid(a<7) HOAc 1.0 22 rRh(CO)2I2"T 0.5 90 acetic acid(a<7) HCl(aq) 0.4 23 <a) Atm. { b ) ° C . ( c ) TOF = turnover frequency = mol H 2 • mol cat/1 • h" 1, ( d ) 14 m M , ( e ) 3.3 mM, OT 0.1 mM, te) 10 mM, ( h ) 20 mM, w 1.6 mM of [Rh2(p.-H)(p.-CO)(CO)2(p.-dpm)2]+, w 50 mM, with 10 atm propylene in Reppe-style hydroformylation to yield C4 aldehydes and C4 alcohols, ( k ) 1:30 ratio. 137 Chapter 5 references on page 149 Chapter 5 Some of the better known literature examples for homogeneous WGSR catalysis are shown in Table 5.4, and demonstrate how the factors mentioned above can result in both similar and disparate outcomes. Although not listed in the table, WGS catalysis has been observed with RI1/PN3 complexes.24 Some of the Ni 2-pyridylphosphine complexes prepared in this thesis work were tested for catalysis of the WGSR as they are water-soluble and, in general, cheaper than the catalysts listed in Table 5.4. 5.1.2 Experimental 5.1.2.1 Set-Up for Ambient CO Pressure Work All work conducted under ambient CO pressure was accomplished by charging a thick-walled Schlenk tube (90 mL), equipped with a Kontes-valve and a Teflon-coated magnetic stir-bar, with de-oxygenated (via N 2 sparging, see Section 2.6), pH 7, deionized water (10.0 mL) or de-oxygenated EtOH(a^) (10% v/v H 2 0 , 10.0 mL), and 0.47 mM of the complex to be tested. The reaction solution was then saturated under a stream of CO via a cannula for 10 min prior to sealing the reactor vessel under an atmosphere of CO and placing it at 100°C (for neat water experiments) or 75°C (for aqueous EtOH experiments) for 24 h. A sample of the gas headspace was then analyzed by GC. For the experiments conducted under basic conditions, the reactor was also charged with an appropriate amount of either KOH(s) or pyridine to obtain 0.2 M KOH(a<7) or 1.2 M C 5 H 5 N , respectively. The pH of the K O H reaction solutions was lowered to 6.2 with 2M HC1 prior to GC analysis to release any C 0 2 that may have been converted to C03 2 ~/HC03~ (pKa 10.25 and 6.37, respectively).25 For the experiments conducted under acidic conditions, the reactor was also charged with an appropriate amount of HCl(a<7) to yield an acid : nickel ratio of 0.5. The complexes tested under ambient CO pressure were Ni(CO)2(PPh3)2, Ni(CO)2(dpypcp), Ni(CO)2(dpype), NiCl 2(PN 2) 2, NiCl2(dpype), and [Ni(PN3)2]Cl2. 5.1.2.2 Set-Up for High CO Pressure Work A glass tube (31 mL) contained within a Parr model 4843 stainless-steel autoclave, mounted on an electrical heater and equipped with a programmable temperature control unit and a mechanical stirrer, was charged with 0.47 mM of NiCl 2(PN 2) 2 and the same water or EtOH(a^) solvents used in the ambient pressure work. In some cases the reactor was also charged with 0.2 138 Chapter 5 references on page 149 Chapter 5 M K0H(a(7), 1.2 M C 5 H 5 N , or UC\(aq) (0.5 mol acid per mol Ni). After being degassed by three 40 atm (588 psi) pressurization/depressurization cycles with CO, the autoclave was pressurized to 40 atm with CO and heated at 100°C for 24 h. Actual gauge pressures at reaction temperature were in the range of 44 to 48 atm. The gas headspace was then slowly released from the autoclave via a needle-valve exit-tap into an evacuated Schlenk-tube until the pressure inside the Schlenk was 1 atm. The headspace of the Schlenk-tube was analyzed by GC. The set-up used did not allow for neutralization of KOH(aq) reaction mixtures prior to GC analysis. 5.1.2.3 GC Analysis The aliquots of the headspace gases were analyzed by gas chromatography for H 2 , CO, and C 0 2 content (see Section 2.2.5 for instrumentation). Instrument settings were as follows: oven temperature, 50°C; injector temperature, 115°C; detector temperature, 200°C; column head pressure, 40 kPa. Standard retention times (min) obtained from authentic gas samples were: tR(H2) 1.55 (inverted peak),26 tR(CO) 6.64, tR(C0 2) 7.38. 5.1.3 Results and Discussion In this current work six nickel complexes were tested for WGSR activity in neat water, with the addition of K O H and a change of CO pressure (1 to 40 atm) being the only factors varied. The results (Table 5.5) show that no H 2 or C 0 2 was detected in any system under 1 atm of CO in neutral water, fairly common behaviour as the majority of WGS catalysts function under basic, and not neutral, conditions.3'14 Ni(CO)2(PPh3)2 (Table 5.5) has been previously tested for WGS catalysis, when 0.95 total turnovers of H 2 production were reported for an aqueous 2 mM HC1 system at 150°C over 8 h under 1 atm of C O . 1 4 No activity was expected for Ni(CO)2(PPh3)2 as it is insoluble in neutral H 2 0 . The experiments performed in alkaline media under 1 atm of CO showed similarly disappointing results for most of the complexes tested. Trace amounts of C 0 2 were detected in the experiments with Ni(CO)2(dpype) and Ni(CO)2(dpypcp), but the absence of H 2 indicates that the C 0 2 was not generated via the WGSR. Formation of 0.05 mL C 0 2 per mmole of Ni (with no H 2 ) was reported when NiCl 2(PPh 3) 2 was heated in aqueous EtOH (5% v/v H 2 0) for 8 h at 130°C under 1 atm C O , 1 4 but this results from a well established redox type reaction shown in Eq 5.4. A similar redox reaction likely accounts for the Ni(CO)2(P-P) results as Ni(CO)2(dpypcp) has been 139 Chapter 5 references on page 149 Chapter 5 shown in Chapter 4 to decompose in H 2 0 to Ni(II). Production of C 0 2 via reaction of CO with trace 0 2 is ruled out as 0 2 was not detected before or after the 24 h heating period. It should also be noted that H 2 , 0 2 , CO, and C 0 2 all had almost identical response factors to detection by GC/TCD. NiCl 2(PPh 3) 2 + 3CO + H 2 0 > Ni(CO)2(PPh3)2 + C 0 2 + 2HC1 (Eq. 5.4) Table 5.5 H 2 and C 0 2 Production Using Ni Complexes in the Water-Gas-Shift Reaction Gaseous Products Obtained " Complex 1 atm CO, 1 atm CO, 40 atm CO, neutral H 2 0 0.2 M KOH(a<7) 0.2 M KOH(a<7) Ni(CO)2(PPh3)2 none none n.t. Ni(CO)2(dpypcp) none n o H 2 / 5 . 4 x l 0 " 3 C O 2 6 n.t. Ni(CO)2(dpype) none noH 2/5.4x 10" 3 CO 2 6 n.t. NiCl2(dpype) none none n.t. NiCl 2(PN 2) 2 none 9.5 x 10' 4H 2and C 0 2 c 2.43 (± 0.09) H 2 and C 0 2 [Ni(PN3)2]Cl2 none none n.t. ( f l ) Reported as TOF = mol H 2 • mol cat."1 • h"] ; n.t. = no test conducted. Conditions: 0.47 mM complex in H 2 0 (10.0 mL), T = 100°C, reaction time = 24 h . ( 6 ) ± 0.24 xlO' 3 . ( c ) + 1.3 xlO"4. The experiment with NiCl 2(PN 2) 2 yielded equimolar amounts of H 2 and C 0 2 , thereby suggesting successful WGSR catalysis, albeit at a marginal, low turnover frequency. The amounts of H 2 and C 0 2 generated by the NiCl 2(PN 2) 2/H 20/KOH(a#) system at 40 atm CO increased by a factor of ~ 2600 to a turnover frequency of 2.43 h"1. Previous work with NiCl 2(PPh 3) 2 and NiCl 2(PMe 3) 2 in EtOH has reported a decrease in catalyst activity at higher CO pressures.14 As NiCl 2(PN 2) 2 was the most active species for WGS catalysis under the conditions noted in Table 5.5, the conditions were varied further (Table 5.6). A 10-fold increase in H 2 yield was observed upon changing from water to aqueous EtOH (10% v/v water), trials (iv) and (viii). The TOF of 27 becomes significant in comparison to the range of activities reported more generally (Table 5.4). The production of C 0 2 without any concomitant H 2 in trial (vii) presumably occurs via Eq. 5.4.14 Attempts to catalyze the WGSR in aqueous EtOH with no added base were 140 Chapter 5 references on page 149 Chapter 5 unsuccessful (trials (v) and (vi)), while use of 1.2 M pyridine in place of 0.2 M K O H in aqueous EtOH was equally effective (trials (viii) and (x)). Table 5.6 H 2 Turnovers Obtained With NiCl 2(PN 2) 2 Under Varying Conditions a Trial Solvent Base/Acid Pco (atm) T O F * /'. H 2 0 - 1 0 ii. H 2 0 - 40 0 iii. H 2 0 0.2 M K O H 1 9.5 (± 1.3) x 1 0 " 4 H 2 & C O 2 iv. H 2 0 0.2 M K O H 40 2.43 (+ 0.09) H 2 & C 0 2 v. EtOH (aq) - 1 0 vi. EtOH (aq) - 40 0 vii. EtOH (aq) 0.2 M K O H 1 0.27 (+ 0.007) C 0 2 viii. EtOH (aq) 0.2 M K O H 40 27.1 ( + 0 . 8 ) H 2 & C O 2 ix. EtOH (aq) 1.2 M pyridine 1 0 x. EtOH (aq) 1.2 M pyridine 40 27.0 (+ 0.8) H 2 & C 0 2 xi. EtOH (aq) H C I C 1 0 xii. EtOH (aq) H C I C 40 0 ... d Xlll. EtOH (aq) 0.2 M K O H 40 0 xiv. d H 2 0 0.2 M K O H 40 0 ( f l ) 0.47 mM NiCl 2(PN 2) 2, 100°C, 24 h , { b ) TOF = mol H 2 • mol cat."1 • h"\ ( c ) 0.5 mol HCl/mol Ni, w Blank experiment; no Ni(II) species present. In trials (xi) and (xii) the cocatalyst was changed from a base to HC\(aq). As Giannoccaro et al. found that with NiCl2(PMe3)2 the greatest activity was obtained with an HCl(a<7): Ni ratio of 0.5,14 the same ratio of HCl(a^) was used here. No activity whatsoever was observed with NiCl 2(PN 2) 2 under acidic conditions at either 1 or 40 atm CO at 100°C; a TOF of 26 h"1 was reported for NiCl 2(PMe 3) 2 in aq. EtOH (5% v/v water) with 1 atm CO at 130°C. 1 4 Two "blanks" confirmed that no catalytic activity was observed in the absence of a Ni complex (trials (xiii) and (xiv)). NiBr 2, shown to be an active catalyst precursor for various transfer hydrogenation reactions (see Chapters 6 & 7), was inactive under the conditions noted in trial (viii) of Table 5.6. As previously mentioned, most WGSR work is conducted in basic media as OH" promotes the reaction (see Figure 5.3). As C 0 2 reacts with OH" to produce bicarbonate (HC03", pK a = 141 Chapter 5 references on page 149 Chapter 5 6.37) and carbonate (CO32", pK a = 10.25) (Eq. 5.5),27 the reaction solution should be acidified to below pH ~ 6 prior to GC analysis by the addition of HCl(a<7) to release any sequestered CO2 back into the gas headspace. In work conducted at 1 atm CO, this acidification was achieved by addition of 2 M HC1. This acidification was not done with the experiments conducted at 40 atm CO as there was no means by which to inject the acid into the autoclave while it was still under high pressure. The equimolar production of H 2 and C 0 2 [i.e., H 2 / C 0 2 = 1] in trials (/V), (viii), and (JC) was thus of interest as C0 3 2"/HC0 3" sequestering and C 0 2 solubility (see below) can result in H 2 / C 0 2 >1. There are, however, many reports in the literature of equimolar H 2 / C 0 2 production over a catalyst solution which has not been acidified prior to sampling (Table 5.7). The thermal decomposition of either formate13'20'28 or bicarbonate18'27 (Eqs. 5.6-5.7) was proposed to generate the required C 0 2 , and such processes could be operating in trials (iv), (viii), and (x). Of note, CO can react with OH" to produce formate (HC02", pK a = 3.74) (Eq. 5.8).13 C 0 2 + OH" HCO3" ^ C 0 3 2 ' + F f (Eq. 5.5) HC0 2 " + H 2 0 => H 2 + C 0 2 + OH" (Eq. 5.6) 2HC0 3" 4 C 0 2 + CO32" + H 2 0 (Eq. 5.7) CO + OH" HC0 2 " (Eq. 5.8) Table 5.7 Catalytic WGSR Systems Where H 2 / C 0 2 ~ 1 Without Acidification Treatment Catalyst Base Solvent Temp. a CO b T O F c H 2 / C 0 2 Ref. RhCl 3 4-picoline H 2 0 110 0.9 -200 1.0 18 C u C l 2 . 2 H 2 0 py H 2 0 120 1.9 0.13 1.0 20 [Ru(bpy)3]Cl2 K O H H 2 0 150 20 16 1.07 13 NiCl 2(PMe 3) 2 py aq. EtOH 110-150 1 13-39 1.00 14 (H) x (M) y (CO)/ K O H aq. 2-EtOEtOH 110 0.9 0.04-0.1 0.91-1.12 27 Ru 3(CO)i 2 KOH, aq. 2-EtOEtOH 100 1 na 0.86 28 Ru 3(CO)i 2 py aq. DMSO 100 0.5 5 1.0 29 FeRu2(CO)io(PPh3)2 py H 2 0 100 0.4 35 1.0 30 (a) o C (6) A t m (c) M o l H 2 . m o l c a t -1 . h-i (d) C o m p l e x e s a r e Fe(CO)5, Ru3(CO)i2, (H) 2Ru4(CO)i3, and (H)4Ru4(CO)i2. "na" = not reported. 142 Chapter 5 references on page 149 Chapter 5 It should be noted that the high solubility of CO2 (~ 40 times that of H 2 in neutral H 2 0 at r.t.25) can lead to a discrepancy in the ratio of H 2 to C 0 2 (i.e., >1) generated by the WGSR. 7 Ishida et al. have determined that, after running WGS experiments (in 0.2 M aq. K O H with 20 atm CO), up to 30% by weight of the C 0 2 product can remain dissolved in solution upon releasing the pressure,13 while King et al. report that C 0 2 is ten times more soluble in H 2 0 / M e O H (1:4) than H 2 . 1 1 5.1.4 Conclusion Of the six nickel complexes tested for WGSR catalysis, only NiCl 2(PN 2) 2 was shown to be effective, the activity in EtOH(a#) with K O H or pyridine cocatalysts falling within the range of many reported homogeneous catalytic systems. However, the TOF observed is unremarkable when compared to the activities attained with the current industrial heterogeneous catalysts. Perhaps the most telling statement on homogeneous WGSR catalysis was made by Laine et al. in 1977 when they commented that "comparing [our] activity [TOF 0.05 h"1] to that of a standard heterogeneous catalyst - principally Fe304 - under similar conditions we estimate that at 110°C under 1 atm CO the heterogeneous system would produce several orders of magnitude more H 2 per gram mole of the catalyst per unit time."28 Although homogeneous WGSR catalysts have since yielded turnover frequencies at least 5 orders of magnitude greater6 than the 0.05 value, a similar increase in catalytic activity has been attained for heterogeneous systems. 143 Chapter 5 references on page 149 Chapter 5 5.2 Olefin (Maleic Acid) Hydration 5.2.1 Introduction The hydration of olefins to alcohols is an industrially important process with the potential of being catalyzed by a transition-metal complex capable of activating either water or olefin in what is an overall thermodynamically favoured reaction.31'32 This potential exists because when olefins (which are normally nucleophilic) are coordinated to an appropriate metal centre through the C=C bond, they lose electron-density from the rc-orbitals of the double bond to the metal d-orbitals via a cr-M-olefm bond and thereby become susceptible to nucleophilic attack by OH" at the double bond. In the case of maleic acid, this susceptibility is further enhanced by the presence of the electron-withdrawing carboxylic groups on either terminus of the C=C bond. The hydration of maleic acid (Figure 5.4) has been attempted previously within this group by Xie 3 3' 3 4 using Pt(PNx)4 and *raHS-PtH(Ci)(PNi)2 as catalyst precursors, and by Schutte using [RuCl(PN3)3]Cl, [RuCl(PN2)3]Cl, and [RuCl(PPh3)(PN3)2]Cl.35 Unfortunately, none of these complexes promoted the hydration of maleic acid over that observed in the "blank" experiments. Nevertheless, Xie successfully prepared Pt(PNx)2( ^ -maleic anhydride) and Pt(PNx)2(/^-olefin) complexes (olefin = diethyl maleate and diethyl fumarate), thus demonstrating that olefins can coordinate to the water-soluble Pt(0) PNX complexes.34 There has been very limited success in homogeneous catalytic hydration of maleic acid and, in general, other olefins. H H u r H H H COOH W " ), < + W / \ H20,A „_ / VCOOH / \ HOOC COOH 2 HOOC H HOOC H maleic acid malic acid fumaric acid (hydration product) (isomerization product) Figure 5.4 Hydration and isomerization of maleic acid to malic and fumaric acid, respectively. Two plausible mechanisms for catalytic olefin hydration to give alcohols are shown in Figure 5.5.36"38 The pathway on the left-hand-side involves initial oxidative addition of water (7a) with subsequent olefin coordination (lb), migratory insertion of the olefin into the M-OH bond to yield an alkylhydrido complex (7c), and finally, reductive elimination of the alcohol with 144 Chapter 5 references on page 149 Chapter 5 concomitant regeneration of the M L 2 catalyst. The right-hand-side pathway involves initial olefin coordination (2a) and continues with subsequent nucleophilic attack of OH" on the coordinated olefin to yield an anionic alkyl complex (2b), oxidative addition of water to yield an alkylhydrido complex (2c), and again, reductive elimination of the alcohol in the final step (2d). Alternatively, the anionic alkyl complex formed in step 2b could be directly protonated by FT to yield the alcohol and M L 2 . Figure 5.5 Possible mechanistic pathways for maleic acid hydration with an M L 2 catalyst. Bzahasso and Pyatnitskii39 first observed the catalytic hydration of maleic acid in 1967, using CrCl 3 .6H 2 0 at elevated temperatures (170°C), and two years later reported similar catalysis with Al(III) compounds;40 hydration with CrCl 3 • 6H 2 0 was also examined by Xie. 3 3 In 1969 James and Louie reported the hydration of the fluorinated olefins 1,1-difluoroethylene and vinyl fluoride to acetic acid and acetaldehyde, respectively, using a chloromthenate(n)/HCl(aG») catalyst.41 James and Rempel reported in that same year the hydration of acetylene using acidic aqueous solutions of Rh (III) chlorides and explored the dependence of the reaction on complexed water ligands.42 This followed the previous work of Halpem et al. in 1961 when acidic aqueous solutions of Ru(II) chlorides were used to hydrate acetylene, methylacetylene, ethylacetylene, and phenylpropiolic acid to acetaldehyde, acetone, methyl ethyl ketone, and acetophenone, respectively.43 The spectrophotometric characterization of a Ru(II)-maleic acid R H L, 145 Chapter 5 references on page 149 Chapter 5 complex intercepted in the hydrogenation of maleic acid to succinic acid was also reported in 1961 using the cWoromthenate(II)/HCl(a<7) catalyst system.44 The slow isomerization of maleic acid to fumaric acid promoted by chlororuthenate(II) species was reported in 1966, along with the formation of dimethyl maleate complexes of Ru(II).45 In 1978, Otsuka's group observed the hydration of the olefinic nitriles acrylonitrile (CH 2=CHCN) and crotonitrile (CH 3CH=CHCN) to yff-cyanoethanol and /?-cyanopropanol, respectively, using Pt(PCy)2 and Pt(PR3)3 complexes (R = Et, 'Pr) in water.36 Two years later, Arnold and Bennett reported hydration of these same olefins using Pt(II) methyl and phenyl bis(tertiary phosphine) hydroxo complexes.46 In 1986 Jensen and Trogler also reported hydration of acrylonitrile and 1-hexene using fra«5-PtH(Cl)(PR3)2 (R = Me, Et) and isolated the catalytic intermediate species [PtH(H20)(PEt3)2]+, [PtH(N=CCH3)(PEt3)2]+, and PtH(NHC(0)Me)(PEt 3) 2. 3 7 Unfortunately, this catalysis work on the 1-hexene substrate appears to be irreproducible.47 An automated search of the Chemical Abstracts between 1986 and 1999 with the keywords "olefin hydration", "alkene hydration", or "maleic acid hydration" yielded scores of papers and patents. Unsuccessful attempts at olefin hydration with Pt(PNx)3 and Pt(PNx)4,34 and fr-<ms-PtH(Cl)(PMe3)2,47 were reported, while the addition of dimethyl maleate to cis-Pt(OH)(Me)(phosphine)n complexes with subsequent release of dimethyl malate upon treatment of the complex with acid was also reported.48 Successful olefin hydrations were reported using: Pd clusters,49 [Ti(BH 3) 4], 5 0 organoboranes,51 ZnCBFL,) supported on silica gel or A1P0 4, 5 2' 5 3 Co and Pd supported on Nb 2 0 5 , 5 4 MH(Cl)(PMe3)2 (M = Pt, Pd, Ni), 5 5 sulfonic acid group-containing polysiloxanes,56 an aqueous solution of PdCl 2, OPPh3, and HC1, 5 7 aqueous mixtures of olefin and "Na +", 5 8 aqueous solutions containing Cu + , sulfolane, and polymers having sulfo groups,59 aqueous alcoholic solutions containing Co(II)(diketonato)2 complexes, 0 2 , and a reductant (such as triethylsilane, 'PrOH, or phenylsilane),60 and photochemical tandem addition of water and oxygen.61 The search of the Chemical Abstracts also yielded 56 references on catalytic olefin hydration using zeolites,6217 references on the use of heteropolyacid solutions,63 14 references on hydration with ion-exchange-resin systems,64 and three references to the fermentative manufacture of optically pure D-(+)-malic acid from maleic acid using various microorganisms.65 Catalytic homogeneous hydration of olefins is an area in which much more work is 146 Chapter 5 references on page 149 Chapter 5 needed. This Section describes attempts to catalytically hydrate maleic acid using several nickel complexes prepared in this current work. 5.2.2 Experimental 5.2.2.1 Set-Up A thick-walled Schlenk tube (90 mL) equipped with a Kontes-valve and a Teflon-coated magnetic stir-bar was charged with de-oxygenated, pH 7 deionized water (10.0 mL, see Section 2.6), maleic acid (115.8 mg, 0.9975 mmol), and 0.01 mmol of the nickel complex to be tested (Table 5.8). The reactor was then sealed under N 2 and heated at 100°C. Aliquots (1.0 mL) of the mixture were withdrawn usually after 24, 48, 72, and 96 h, dried by rotary evaporation to yield a white residue, and further dried in vacuo overnight. This procedure is similar to that reported.35 5.2.2.2 ! H N M R Analysis Relative amounts of maleic, malic, and fumaric acid were calculated by integration of the appropriate peaks in a *H NMR spectrum (300 MHz, acetone-ofe, 20°C) of the residue [maleic acid, 8 6.40 (s, 2H, CH=CH); fumaric acid, 5 6.80 (s, 2H, CH=CH); malic acid (Figure 5.6), 8 4.52 (dd, 1H, CHa(OH)), 2.75 (ddd, 2H, CH>FL).33'35 The results are presented in Section 5.2.3. C O O H C O O H Figure 5.6 Fischer projection of malic acid showing the ! H NMR assignments. The three acids have a relatively low solubility in acetone, and so solubility limits were determined so as to ensure the reliability of the ! H NMR data. This was accomplished by dissolving a weighed amount of acid in acetone-fife (1 g) and then back-calculating the amount found experimentally by comparison of the integrated area of the acid peaks in the 'H NMR spectrum with that of an internal standard (PPh3). When a difference of > 1% was found between the actual and experimentally determined acid mass, the solubility limit was deemed to have been reached; this limit was ~ 13 mg of acid per gram of acetone-fife. Three other samples were then 147 Chapter 5 references on page 149 Chapter 5 prepared for *H NMR analysis with each one containing an equimolar mixture of the three acids (~ 4 mg of each). Maleic, malic, and fumaric acid were experimentally found to be present in a 1.01 : 0.98 : 1.00 ratio (average), respectively. This agreement demonstrates that reliable percent conversions may be obtained from *H NMR spectroscopy when the sample concentration is < 12 mg of acid per gram of acetone-fife The withdrawal of 1.0 mL aliquots from the reaction mixture ensured that the total mass of acids present in theanalyte was ~ 12 mg. 5.2.3 Results and Discussion The catalytic hydration of maleic acid was attempted using the six Ni(II) and three Ni(0) potential catalyst precursors listed in Table 5.8; three of the complexes are square-planar (trials viii, ix, x), five are tetrahedral (trials /'/, iv, v, vi, vii), and one is octahedral (trial iii), while two of the complexes (trials ii, v) contain monophosphine P-donor ligands, five contain diphosphine P-donor ligands (trials vi through x), one contains a P,TV-coordinated ligand (trial iv), and one contains an Ar,JV7,JV7'-coordinated ligand (trial iii). All of these Ni species dissolved in the acidic aqueous media, but many (trials vi-x) are assumed to have become [Ni(H20)6]2 + after 96 h as both Ni(CO)2(dpypcp) and NiX2(P-P) have been shown to decompose within 24 h to this species in aqueous media (see Sections 4.3.2 (p. 107) and 3.3.2 (p.63)). Table 5.8 Reaction Mixture Distribution in the Attempted Hydration of Maleic Acid " Trial Complex Maleic Acid (%) Malic Acid (%) Fumaric Acid (%) /'. Blank* 85.6 8.8 5.6 ii. NiBr 2(PN 2)2 91.6 2.8 5.6 iii. [Ni(PN3)2]Cl2 92.7 3.1 4.2 iv. NiCl 2(PN 3) • H 2 0 92.7 3.1 4.2 v. Ni(CO)2(PPh3)2 92.5 3.1 4.4 vi. Ni(CO)2(dpype) 85.5 3.6 10.9 vii. Ni(CO)2(dpypcp) 88.4 3.3. 8.3 viii. NiCl2(dpype) 87.6 3.6 8.8 ix. NiCl2(dppe) c 96.1 2.2 1.7 X. NiBr2(dpypcp) d 79.8 9.8 10.4 ( f l ) 1 mM Catalyst, 0.1 M substrate, T = 100°C, Reaction time = 96 h . ( i ) No metal complex. ( c ) Reaction time = 48 h. { d ) Reaction time = 196 h. 148 Chapter 5 references on page 149 Chapter 5 After 96 h at 100°C, the blank sample yielded 8.8% conversion to malic acid via hydration, and 5.6% conversion to fumaric acid via isomerization. The greatest amount of hydration attained by any of the Ni systems tested after 96 h was 3.6% conversion for both Ni(CO)2(dpype) and NiCl2(dpype). All of the complexes tested thus appear to "inhibit" rather than enhance the conversion of maleic to malic acid observed in the blank sample. As the substrate is present in a 100-fold excess over the metal complex, this implies that the Ni complexes perhaps catalyze dehydration of malic acid! [Complexing of the malic acid as malate could account for a maximum of 3% formation of the hydration product]. However, an experiment conducted as per trial (viii), but using malic acid, showed no formation of maleic acid. Similar inhibition was observed by Schutte in experiments conducted with Ru/PNX complexes.35 Fumaric acid was detected in all of the trials and in three instances (vi, vii, and v/7'/') the amount present was greater than that observed in the blank trial. This suggests possible coordination of maleic acid to Ni via the C=C bond in a side-on fashion with subsequent rotation of the terminal carboxylic groups about the C-C axis of reduced bond order to yield the isomerization product. Again, such behaviour has been observed previously by both Schutte35 and Xie 3 4 with maleic acid, and by other workers with other olefins.46'66 Of note, the ratio of fumaric to malic acid in all but one of the trials with nickel is > 1 whereas in the blank trial and trial ix, the ratio is < 1. 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Ger. Offen. D E 3801275 A l 1989, as cited in Chem. Abstr. 1990, 112, 7032. (d) Latimer, E. G. U.S. Pat. US 4956506 A 1990, as cited in Chem. Abstr. 1990, 113, 214267. (e) Butt, M . H. D.; Waller, F. J. U.S. Pat. US 5094995 A 1992, as cited in Chem. Abstr. 1992, 116, 195946. (f) Nigam, S. C ; Bannore, S. N.; Subbarao, H . N.; Dev, Sukh Proc. Int. Congr. Essent. Oils, Fragrances Flavours, 11th, Vol. 5, 113-18. Ed. Bhattacharyya, S. C ; Sen, N.; Sethi, K. L. New Delhi: Oxford & JJBH, 1989, as cited in Chem. Abstr. 1992, 117, 171704. (g) Hattori, A.; Nakamura, K.; Washiyama, T.; Kato, T.; Saito, T.; Arai, S. Eur.Pat.Appl. EP 579153 A2 1994, as cited in Chem. Abstr. 1994, 121, 60203. (h) Inoe, K.; Iwasaki, M . ; Ueda, N. Jpn. Kokai Tokkyo Koho JP 07165640 A2, 07165641 A2 1995, as cited in Chem. Abstr. 1996, 124, 8232, and 8233. (i) Widdecke, H. ; Dettmer, M . ; Reith, W. Ger. Offen. D E 4425216 A l 1996, as cited in Chem. Abstr. 1996, 124, 177915. (j) Chaplits, D. N.; Stolyarchuk, V. I; Pilipenko, I. B.; Pautov, P. G.;Kazakov, V. P.; Bubnova, I. A.; Lazaryants, E. G ; Sobolev, V. M.;Vernov, P. A.; 155 Chapter 5 references on page 149 Chapter 5 Perlin, L. Ya.; Yakovlev, B. Z.; Sakhapov, G. Z.; Sozinov,G. A.; Savin, Yu. I.; Svirskaya, K. I.; Abaev, G. N.; Korotkevich, B. S.;Yureva, L. I. U.S.S.R. SU 588729 A l 1996, as cited in Chem. Abstr. 1997, 726, 330424. (k) Inoue, Y.; Watabe, Y. Jpn. Kokai Tokkyo Koho JP 09268145 A2 1997, 127, 346118. (1) Linnekoski, J. A ; Krause, A. Outi I.; Struckmann, L. K. Appl. Catal., A. 1998, 170, 111, as cited in Chem. Abstr. 1998, 129, 43043. (m) Kobayashi, N.; Shimura, M. ; Asaoka, S. Jpn. Kokai Tokkyo Koho JP 10287602 A2 1998, as cited in Chem. Abstr. 1998,129, 275635. 65. (a) Nakayama, K.; Kobayashi, Y. Jpn. Kokai Tokkyo Koho JP 07143891 1995, as cited in Chem. Abstr. 1995, 123, 141892. (b) van der Werf, M . J.; van den Tweel, W. J. J.; Hartmans, S. Eur. J. Biochem. 1993 217, 1011, as cited in Chem. Abstr. 1993, 119, 220328. 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Syn., Florence, Italy, 1989, PSI-60, as found through reference 34. 156 Chapter 5 references on page 149 Chapter 6 CHAPTER SIX Transfer Hydrogenation of Cyclohexanone Catalyzed by Ni(II) Compounds 6.1 Introduction Stoichiometric hydrogenation of ketones has been achieved for over a century by the use of reducing agents such as LiAlFL, and NaBHt, or, in the last 50 years, aluminum isopropoxide (Meerwein-Ponndorf-Verley reduction).1 More recently, the reduction of ketones has been realized catalytically by both heterogeneous hydrogenation systems (such as H2/Raney Ni) 2 and homogeneous hydrogenation systems (such as H2/[Rh(H)2(PPhMe2)2(acetone)2]+).3 Unfortunately, practically all standard commercial H2-hydrogenation systems employ severe reaction conditions (such as high pressures and temperature) which consequently plague the industry with safety, engineering, and economic concerns.1-5 In recent decades, there has been an increased interest in catalysis performed by systems that transfer hydrogen-atoms from a donor solvent to a substrate. Typically, the use of alcohols as both cheap and plentiful hydrogen-sources allows for much milder reaction conditions (atmospheric pressure and the solvent's reflux temperature), thus making transfer hydrogenation an attractive alternative to the standard H 2 -hydrogenation of unsaturated functional groups.6 All transfer hydrogenation systems require a hydrogen-donor and, although the use of donors such as formic acid,7"9 amines,10 cyclic ethers,10'11 aldehydes,7 1-phenylethanol,12'13 and MeOH 4 is known, the vast majority of work has been conducted using /-PrOH. 1 ' 5 ' 7 ' 1 0 ' 1 4 " 3 2 Most catalytic systems also require the use of a base cocatalyst to "activate" the system, and as such, NaOH, 1 ' 6 , 1 9 ' 2 3 K O H , 5 ' 9 ' 1 6 ' 1 3 ' 2 1 ' 2 5 " 2 7 ' 2 9 ' 3 0 ' 3 3 /-PrONa, 3 2 /-PrOK, 6 ' 2 4 N a O C H 3 , 1 7 and sodium enolates11 are the most frequently used bases. A recent report34 on the use of NiCl2(PPh3)2, NaOH, and /'-PrOH to catalyze the transfer hydrogenation of various ketones and aldehydes (Eq. 6.1) inspired the testing of various Ni(II) 2-pyridylphosphine complexes, synthesized in this thesis work, as potential catalysts for the transfer hydrogenation of cyclohexanone (Eq. 6.2). 157 Chapter 6 references on page 187 Chapter 6 0 OH 1 NiCl2(PPh3)2, NaOH T (Eq. 6.1) R ^ ^ R z-PrOH, reflux R ' ^ R ' OH , > Q =0 + u Catalyst, Base cocatalyst / \ ^ . H ^ II (Eq 6 2) ,1 \ / ^N/-\TT ^ reflux \ / T)H This Chapter explores various aspects of the work performed on the transfer hydrogenation of C 6 H i 0 O by catalytic systems incorporating a Ni(II) catalyst, NaOH cocatalyst, and /'-PrOH hydrogen-donor/solvent (hereafter abbreviated as the NiNa'P system). In Section 6.3.1, the activity of ten different Ni(II) species is examined, while in Section 6.3.2, *H N M R spectroscopy is used to confirm that CeHnOH is the hydrogenation product. The necessity of each of the components in the NiNa'P system is verified in Section 6.3.3, and the NiNa'P system is shown to be homogeneous in Section 6.3.4. The kinetic order of the reaction with respect to [NaOH] and [Ni] for the NiBr 2 system is determined in Sections 6.3.5 and 6.3.6, respectively, along with the effect of using other bases as cocatalysts. In Section 6.3.7, the kinetic dependence of the activity of the NiNa'P system on [H-acceptor] and [H-donor] is examined, while in Sections 6.3.8-9 the effects of adding acetone, cyclohexanol, H 2 0 , H 2 , X", and PPh3 to the reaction mixture are discussed. The deactivation of the catalyst with repeated use is examined in Section 6.3.10. Section 6.3.11 discusses the steric-effect of placing a methyl group at various sites around the cyclohexanone ring, and finally plausible mechanisms for the transfer hydrogenation of CeHioO by NiBr 2, NaOH, and /-PrOH are considered in Section 6.3.12. 6.2 General Experimental Chapter 6 is organized differently from the preceding Chapters in that only a few general experimental details are reported in this Section. The amounts of substances employed in each individual experiment, along with reaction temperatures and times, are reported in figure captions, table footnotes, or the actual body of the text. 158 Chapter 6 references on page 187 Chapter 6 6.2.1 Typical Set-Up for Catalytic Transfer Hydrogenation Experiments Most catalytic trials were performed with the set-up shown in Figure 6.1. 35 mL screw-capped test tube thermometer oil-bath vacuum « • N2fe) wide-bore Schlenk tube (a) (b) Figure 6.1 Experimental set-up for transfer hydrogenation catalytic trials: (a) positioning of reactor vessel within oil-bath to enable use of the upper portion of the test-tube as an air-cooled condenser, (b) charging of reactor vessel within a Schlenk tube with the reaction components while under an N 2 stream. A screw-capped, thick-walled test-tube (35 mL capacity) equipped with a Teflon-coated magnetic stir-bar was loaded into a wide-bore Schlenk tube (Figure 6.1b) and typically charged with metal complex, base cocatalyst, and z-PrOH solvent. The test-tube was then sealed with a screw-cap under N 2 after three vacuum-evacuation/N2-purge cycles, removed from the Schlenk tube, and heated in an oil-bath (95°C) until all solid material had dissolved to yield (in the cases with NiBr 2) a clear pale-green solution. The test-tube was then cooled in an ice/water-bath, returned to the wide-bore Schlenk tube, charged with CeHioO, re-evacuated and N2-purged, and re-capped under N 2 . Once all of the test-tubes for a particular set of experiments had been prepared, they were lowered simultaneously (to ensure identical reaction times) into the oil-bath 159 Chapter 6 references on page 187 Chapter 6 (Figure 6.1a) to a depth just sufficient to immerse the reaction mixture (-3.0 mL), thereby allowing the remainder of the test-tube to serve as an air-cooled condenser to ensure that a safe internal pressure was maintained. Unless otherwise noted, the oil-bath temperature was maintained at 95 ± 1°C; /-PrOH refluxes at 83°C. By use of the set-up shown, ten vessels could be loaded into an oil-bath simultaneously. No loss of sample volume was observed in any experiment, even over extended periods of time (e.g., 24 h). The test-tubes were thoroughly washed after each experiment by: (a) sonication in a hot soapy solution, (b) overnight soaking in an EtOH/KOH bath, and (c) overnight soaking in an aqua-regia bath (3:1 HN03/HC1). 6.2.2 Analysis of the Hydrogenation Products As injection of solution samples containing NaOH or metal complexes into a GC unit tends to damage the column, aliquots of the reaction mixture were first vacuum distilled to extract the solvent, substrate, and product from the inorganic residue prior to GC analysis (Section 2.2.5, p. 22) [C 6 HioO and C 6 HnOHboil at 155 and 161°C, respectively].35 Injected sample volumes were 0.1 uL and all analyses were performed isothermally with an FED detector. The injector and detector were heated to 220°C, the oven was set at 100°C, and the column pressure was maintained at 42 kPa with He carrier gas. Retention times (tR) for samples of /'-PrOH, C 6 H i 0 O , and C 6 H n O H are 2.77, 5.88, and 4.95 min, respectively, while tR(min) for samples of 2-Me-C 6H 9 0, 4-Me-C 6H 9 0, 2-Me-C 6 Hi 0 OH, and 4 - M e - C 6 Hi 0 O H (used in Section 6.3.11) are 5.57, 5.57, 6.48, and 6.85. The data reported in most experiments are the average obtained from 2-3 injections per sample, with a GC error of ± 0.4%. Initial rates and % conversions are generally reported to 3 significant figures. 160 Chapter 6 references on page 187 Chapter 6 6.3 Results and Discussion 6.3.1 Transfer Hydrogenation of Cyclohexanone by Various Ni(H) Species The activities of ten Ni(II) species and a base-only system are summarized in Table 6.1. Table 6.1 Transfer Hydrogenation of Cyclohexanone to Cyclohexanol With Various Ni(II) Catalyst Precursors Species a Trial Ni(II) Species % Conversion * Sampling Time c r 0, x lO^Ms" 1 ' /'. none e 4.21 / 14.1 A 11.7 ii. NiCl 2(PPh 3) 2 13.9/46.2 A 38.6 iii. NiBr 2(PPh 3) 2 24.0 / 99.7 B 66.7 iv. NiBr 2(PN 3) 2 36.0/99.9 B 100 v. NiBr 2(PN,) 2 36.3 /99.9 B 101 vi. Nil2(dppe) 41.3/99.9 C 115 vii. Nil2(dpypcp) 39.9/99.9 C 111 viii. Nil2(dpype) 27.8 / 99.9 C 77.2 ix. NiCl 2 • 6H 2 0 17.0/97.6 A 47.2 X. NiBr 2 (anhyd) 90.1 /99.9 A 250 xi. Nil 2 • 6H 2 0 90.3 /99.9 A 251 ( a ) 4.0 xlO'3 M Ni (in 0.3 mL /-PrOH), 0.34 M NaOH, 1.0 M C 6 H 1 0 O , T = 9 5 ° C . ( 6 ) From C 6 Hi 0 O to CeHnOH after 1 & 24 h . ( c ) "A" = 1 & 24 h; "B" = 1, 2, 3, 4, 5, 6, 7, 8, 17, and 24 h; "C" = 1, 2, 3, 4, 5, 6, 7, 8, 11, 15, 18, and 24 h . { d ) Calculated from t = 1 h data; r0= [C 6H nOH]/3600 s. ( e ) Blank trial, only NaOH, /'-PrOH, and C 6 Hi 0 O present. Trial (/') reveals that hydrogenation can be achieved in metal-free, basic alcohol (see Section 6.3.5), albeit at a lower initial rate (r0) than in the presence of a Ni(II) species (ii-xi). Trials (/'/) and (ix) show dichloro Ni(II) species to be inferior to the dibromo and diiodo species, hence no more experiments were performed with chloro species. Trials (///)-(v) reveal that the two dibromo PN X complexes are more active than the PPh3 analogue by a factor of - 1.5, while trials (vi)-(yiii) show that Nil2(dppe) and Nil2(dpypcp) are slightly more active catalyst precursors than NiBr 2(PR 3) 2. The overall similarity of the results obtained with the dibromo and diiodo Ni(II) phosphine catalyst precursors is depicted in Figure 6.2 (see Appendix C, Table C l ) ; 90+ % 161 Chapter 6 references on page 187 Chapter 6 conversion to C 6 H n O H has been attained in most cases by ~ 8 h, with complete reduction within 24 h. The data for NiBr 2(PNi) 2 are almost identical to that of the PN 3 analogue. Figure 6.2 Transfer hydrogenation of CeHioO by: (a) monodentate phosphine Ni(II) complexes; • = NiBr 2(PN 3) 2 , 0 = NiBr2(PPh3)2, (b) bidentate phosphine Ni(II) complexes; • = Nil2(dpypcp), 0 = Nil2(dppe), A = Nil2(dpype). The similarity of rQ in trials (iii)-(viii) suggests that the active catalytic species might be phosphine-free, while experiments with NiBr 2 (anhyd) and Ni l 2 • 6H 2 0 salts (trials x and xi) could support this hypothesis as r0 increases ~ three-fold. The lower r0 values in trials (ii)-(viii) might thus possibly result from some phosphine-dissociation pre-equilibrium step, although no inhibition was seen upon addition of PPh3 to the NiBr 2 system (Section 6.3.9). As 90% conversion to CeHnOH was attained in trials (x) and (xi) after only 1 h (cf. ~ 8 h for trials iii-viii), all further work reported in this Chapter was conducted with NiBr 2 (hygroscopic Ni l 2 • 6H 2 0 was not used as it was more difficult to work with). Of note, all r0 values mentioned in this Chapter are not true "initial rates" due to the complications mentioned in Section 6.3.7 (p. 175), and could all potentially be of a greater magnitude than that reported. The % conversion data for NiBr 2 (trial x, t = 1 h) correspond to 3.8 turnovers min"1. In a second experiment where [NiBr2] = 4.0 xlO"4 M , [NaOH] = 0.26 M , and [C 6Hi 0O] = 0.80 M (see Appendix C, Table C.2 and Figure 6.3), turnover and initial turnover frequencies of 30 and 82 162 Chapter 6 references on page 187 Chapter 6 min"1 (measured at t = 60 and 5 min, respectively) are observed. These two values exceed the corresponding turnover (15 min"1) and initial turnover (30 min"1) frequencies reported, for example, for the transfer hydrogenation of CeHioO by a RuCl2(PPh3)2/NaOH/z-PrOH system.1 Time (min) Figure 6.3 Transfer hydrogenation of CeHioO with NiBr 2. Conditions: 4 xlO"4 M NiBr 2, 0.26 M NaOH, 0.8 M C 6 Hi 0 O, T = 95°C. kobs = 8.45 xlO"4 s"1 Reaction Order With Respect to [CJIioO] The reaction curves shown above (Figures 6.2 and 6.3) are typical for first-order with respect to [substrate], and this is common for hydrogen transfer hydrogenation systems.1 ,7 ,10 ,11'16'20'21 The half-lives method36'37 was used to confirm this kinetic dependence for trials (iii)-(viii) and for the experiment depicted in Figure 6.3 (see Appendix C.2). Rate constants (kobs) and half-lives were calculated for these experiments from first-order plots of log [substrate] vs. time over the first two half-lives of the reaction (see Appendix C, Tables C.3 and C.4, and Figures C.2b and C.3). The similarity of the six k0bs values in Table C.4 also suggests that the active catalytic species might be phosphine-free. Colour Changes The colour of the reaction solution that is associated with the data of Figure 6.3 progresses from pale-green (NiBr2 in z-PrOH, t = 0 min), to pale yellow (t = 5 min, 21% conv.), to yellow (t = 15-35 min, 53-81% conv.), to yellow/orange (t = 40 min, 85% conv.), to orange (t = 60 min, 90% conv.), and finally to brown-black (t = 120 min, 97% conv). In all other experiments reported in this Chapter, the colour of the reaction solution similarly progresses from 163 Chapter 6 references on page 187 Chapter 6 pale-green through to dark brown-black with increasing conversion. Similar colour changes as a function of time/conversion have been reported, for example, in the homogeneous transfer hydrogenation of acetophenone by Ru and Rh complexes in alkaline / -PrOH, 2 5 ' 2 6 ' 3 8 but these have not been discussed. 6.3.2 *H NMR Spectroscopy and CeHioO Transfer Hydrogenation A typical reaction mixture was distilled and the third fraction was diluted in CDCU (first fraction is acetone, b.p. 56°C; second fraction is /-PrOH, b.p. 83°C; third fraction is a mixture of CeHioO, b.p. 155°C, and C 6 HnOH, b.p. 161°C). The ! H NMR spectrum (Figure 6.4) corresponds to the reported 5H values for CeHioO and C 6 H n O H (~ 2:1 mixture).39 a 1"' • 1 1 1 1 11 1 1 1 11" " 1 1 " 1 1 1 " 1 1 " 1 1 1 1 " 1 1 " " 1 1" 11" " 1 1" 1 1 1 1 1 1 1 1 1 " 1 1 1" 1" " 1" " 1 1 1 1 11" 1 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 ppm Figure 6.4 ! H NMR spectra of a typical catalytic run showing both CeHioO and CeHnOH resonances. 6.3.3 Blanks A study was conducted where the Ni, NaOH, and /-PrOH components of the NiNa'P system were systematically eliminated to verify that all are required for the reduction of CeHioO (Table 6.2). Cyclohexanone is not thermally converted to CeHnOH (trial /), nor is it reduced upon exposure to a hydrogen-atom source (trial /'/'). Minimal conversion is seen in base-free, alcoholic NiBr 2 (trial /'/'/'), and Ni-free, alcoholic NaOH (trial iv), whereas activity is attained when all four components of the NiNa'P system are present (trial v). No hydrogenation is seen in the absence of /-PrOH (trials vi-vii). 164 Chapter 6 references on page 187 Chapter 6 Although the use of base cocatalysts is common in transfer hydrogenation experiments (see Section 6.1), few groups report the activity achieved in their systems with "base-only" blanks.1'11'14 Table 6.2 Effect of Systematic Exclusion of Reaction Components ("Blank" Trials) a Reaction Components Present: Trial CeHioO 6 *-PrOH c N i B r / N a O H 6 Conversion (%) f i. Y - - - 0.0 ii. Y Y - - 0.0 iii. Y Y Y - 0.2 iv. Y Y - Y 1.9 v. Y Y Y Y 27.2 vi. Y - - Y 0.0 vii. Y - Y Y 0.0 («) T = 9 5 o C ; t = 2 h; "Y" = component present, "-" = component absent. ( ) 3 mL, 28.8 mmol. ( c ) 3 mL, 63.6 mmol. { d ) 25.2 mg, 0.12 mmol. ( e ) 115 mg, 2.88 mmol. w To C 6 H n O H . 6.3.4 Test for Homogeneity of the NiNa'P System Hg(0) poisons completely heterogeneous or colloidal catalysts (by either blocking the pores/reactive sites of solids or by forming amalgams with colloidal metal particles) but has no drastic effect on homogeneous catalysts.21'40"42 This phenomenon was used to probe the NiNa'P system. Two vessels (charged with 5.6 xlO"3 M NiBr 2 in 3.0 mL /-PrOH, 0.47 M NaOH, and 1.41 M C6HioO), one containing a drop of Hg(0) (0.137 g, 684 umol), were heated at 95°C for 30 min. The conversions to C 6 H n O H were 68.1 and 63.3%, for the Hg(0)-free and Hg(0)-systems, respectively. As a decrease of 5-15% is typical upon addition of Hg(0) to proven homogeneous systems,41 the NiNa'P system behaves in a homogeneous manner. 6.3.5 Kinetic Dependence of CeHioO Transfer Hydrogenation on Base The promotion of /-PrO" formation is cited as the chief role played by base in catalytic transfer hydrogenation.24 The kinetic dependence of the NiNa'P system on NaOH was determined by two series of experiments, the first at a constant ionic strength (p) of 0.05 M with [NaOH] = 165 Chapter 6 references on page 187 Chapter 6 0.00-0.04 M , and the second at u = 0.60 M with [NaOH] = 0.00-0.60 M (Table 6.3). A constant u was maintained by the addition of variable amounts of KF to ensure that changes in r0 were not simply a manifestation of the increasing ionic strength of the reaction solution (see Appendix C.3 for discussion on constant ionic strengths and why KF was chosen to maintain a constant u). Note that although ion-pair formation will occur at u = 0.60 M , the second series of experiments was both conducted and analyzed as though ion-pair formation had not occurred, as most of the work performed in Chapters 6 and 7 was done at 0.47 M NaOH. Table 6.3 Dependence of Initial Rate (ra) of Formation of Cyclohexanol on [NaOH] a [NaOH] M u M 6 [Cyclohexanol] mM ^ x l O ^ M s " 1 ' 0.00 0.05 0.00 0.00 0.01 0.05 1.00 0.560 0.02 0.05 6.40 3.56 0.03 0.05 11.4 6.33 0.04 0.05 19.3 10.7 0.00 0.60 0.00 0.00 0.10 0.60 58.9 32.7 0.20 0.60 131 72.8 0.30 0.60 330 183 0.40 0.60 655 364 0.50 0.60 753 418 0.60 0.60 211 117 ( f l ) 5.6 xlO"3 MNiBr 2 ( in 3.0 mL /-PrOH), 1.41 M C 6 H 1 0 O , T = 95°C, t = 30 min. ( 6 ) Using KF to maintain a constant u. { c ) r0= [C6HuOH]/1800 s. The curved lines obtained in plots of [NaOH] vs. r0 for the two series of experiments (Figure 6.5a and Figure 6.6a) suggest a second-order dependence of r0 on [NaOH]. This is confirmed by plots of log r0 vs. log [NaOH] ("initial-rate method")36'37 which give slopes of 2.1 (Figure 6.5b) and 1.7 (Figure 6.6b), and by the reasonable linearity of a plot of r0 vs. [NaOH]2 for both sets of data at up to ~ 0.5 M NaOH (Figure 6.7a). The sharp drop in r0 at [NaOH] > 0.5 M (Figures 6.6a and 6.7b) presumably results from the solubility limit of NaOH in refluxing /-PrOH, (as suggested by the visual detection of undissolved white particles). 166 Chapter 6 references on page 187 Chapter 6 o o y = 2 .1175x- 1.9631 R = 0.9809 (a) Figure 6.5 0.01 0.02 0.03 [NaOH] M 0.04 -2.0 -1.8 -1.6 -1.4 -1.2 ( b ) log [NaOH] Dependence of: (a) initial rate on [NaOH] at u = 0.05 M , (b) plot of log rQ vs. log [NaOH] where the slope of the line = order of reaction with respect to NaOH. © 60 -3.2 -3.4 -3.6 -3.8 -4.0 -4.2 -4.4 -4.6 y= 1.6878x-2.8496 R = 0.9756 (a) Figure 6.6 0.1 0.2 0.3 0.4 0.5 [NaOH] M 0.6 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 ( b ) log [NaOH] Dependence of: (a) initial rate on [NaOH] at u = 0.60 M , (b) plot of log r0 vs. log [NaOH] where the slope of the line = order of reaction with respect to NaOH. 500 -r 400 -'in 300 -o 1—1 X 200 -o !k 100 - 1814.8x +8.8501 500 o x 0.3 0.0 0.1 0.2 0.3 0.4 0.5 0.6 (b) [NaOH] M Figure 6.7 Dependence of initial rate for both sets of data (Figures 6.5 and 6.6) on: (a) [NaOH]2, and (b) [NaOH]. 167 Chapter 6 references on page 187 Chapter 6 Based on the extrapolated best-fit line of this graph, all experiments should be performed at [NaOH] = 0.47 M to ensure maximum catalytic activity. Although this concentration is high, concentrations as high as 1.0 M in z-PrOH (with use of a phase transfer catalyst) have been reported in the transfer hydrogenation of CeHioO.19 Effect of Changing from NaOH to Other Bases A series of experiments was performed to determine the activity of the NiNa'P system when bases other than NaOH were used (Table 6.4). The results reveal that activity may be a function of the pK b of the base, and that the inorganic hydroxide bases are more active cocatalysts than the amine bases (anomalous "LiOH data" are attributed to low solubility in z'-PrOH). The results obtained at other reaction times (t = 1, 3, 6, 10 min) with the hydroxide bases are tabulated in Appendix C, Table C.5. Table 6.4 Transfer Hydrogenation of CeHioO with Various Base Cocatalysts 0 Base Cocatalyst p K b f e Conversion (%)c Conversion (%)d NaOH <0.0 75.0 99+ K O H <0.0 20.0 99+ L i O H e 0.20 0.20 2.0 [(CH 3) 4N]OH (25 wt% in H 2 0) 1.75 2.50 55 Piperidine 2.88 0.20 -Triethylamine 2.99 0.03 -2,4-Dimethylaniline 3.27 0.02 -4-Methoxy aniline 8.66 0.00 -( a ) 5.6 xlO - 3 M NiBr 2 (in 3.0 mL z-PrOH), 0.47 M Base, 1.41 M C 6 H i 0 O , T = 95°C. { b ) From ref. 35. ( c ) At t = 30 min. ( d ) At t = 24 h; not measured for the amine bases.(e) Poor solubility. 6.3.6 Kinetic Dependence of C 6H 1 0O Transfer Hydrogenation on [NiBr2] The reaction order with respect to [NiBr2] was determined by a series of experiments with varying [NiBr2]. Initial rates (A-0) of conversion to C 6 H n O H (Table 6.5) are plotted vs. [NiBr2] in Figures 6.8a and b; the data reveal a first- to zero-order dependence with increasing [NiBr2] up to ~ 10"4 M , the rates then becoming essentially independent of [NiBr2] at higher concentrations. 168 Chapter 6 references on page 187 Chapter 6 Table 6.5 Effect of Varying [NiBr2] on Transfer Hydrogenation of CeHioO " [NiBr2] (M) r0, xlO - 6 M s"1 0.00 (base only) 3.00 3.5 xlO"6 21.6 7.0 xlO"6 34.5 3.5 xlO"5 40.9 7.0 xlO - 5 45.9 3.5 xlO"4 46.4 7.0 xlO"4 46.8 3.5 xlO"3 45.9 7.0 xlO"3 44.6 ( f l ) 0.47 M N a O H (in 3.0 mL /-PrOH), 0.1 M C 6 Hi 0 O, T = 95°C, t = 30 min. o o Figure 6.8 2 4 6 [NiBr2] x 10' 3M 00 o f—I 20 40 60 [NiBr2] x 10"6M (b) 80 Initial rate of C 6 H i 0 O transfer hydrogenation vs. [NiBr2] at: (a) 3.5 xlO' 6 to 7.0 xlO"3 MNiBr 2 , (b) 3.5 x 10"6 to 7.0 xlO"5 MNiBr 2 . The zero-order kinetic dependence on NiBr 2 at > ~ 10"4 M could result from catalytically inactive multinuclear species forming at these higher concentrations, as reported for other transfer hydrogenation systems with Ru, 1 1 although there is no direct experimental evidence for this. If a monomelic catalyst is involved (see below), and at higher concentration aggregation to inactive species occurs according to the process «Ni ^  Ni„, then the kinetic dependence on total Ni concentration will become (w)"1 at higher concentrations (e.g., half-order for formation of a 169 Chapter 6 references on page 187 Chapter 6 dinuclear species, one-third-order with a trinuclear species, etc.). Over the experimental 100-fold increase in [NiBr2] in Figure 6.8a (7.0 xlO"5 to 7.0 xlO"3 M), an essentially zero-order in Ni dependence would require n to be large (e.g., for n = 50, the rate should increase by about one-tenth for a 100-fold increase in [Ni]). A UV-Vis study at r.t. (Figure 6.9b, Appendix C, Table C.6) reveals that Beer's law is obeyed at 432 nm at least up to ~ 8 xlO"4 M , implying that up to this concentration range, there is: (a) no change in the nature of the Ni species present, and (b) no precipitation of a Ni species. [The absorption maximum for all data points in this study was 432 nm; an example is shown in Figure 6.9a]. Whether these conclusions are valid at the reaction temperature of 95°C is uncertain; certainly no precipitate was visible at the numerous experiments described in this Chapter at 5.6 xlO"3 M NiBr 2. The possible deviation from Beer's law at higher concentrations (~ 10"3 M) could result from precipitation of a Ni species (although none was seen), or the afore-mentioned nucleation process. 0.40 0.30 % 0.20 CA 0.10 0.00 200 400 600 Wavelengh(nm) 2.0 1.5 •e L O o 3 0.5 0.0 y = 0.1507x + 0.0141 R 2 = 0.9900 oo 2 4 6 8 10 12 [NiBr2] x 10'4 M (a) (b) Figure 6.9 (a) UV-Vis spectra of 1 xl0"4 M NiBr 2 and 0.47 M NaOH in i-PrOH at r.t. using a 1 cm pathlength cell, (b) Absorbance at 432 nm vs. [NiBr2]. The overall first- to zero-order kinetic dependence on [NiBr2] (Figure 6.8) shows a marked fall off from first-order behaviour even at the low concentration of ~ 10"5 M (Figure 6.8b), and this was not accompanied by any evident precipitation of Ni species. This encouraged 170 Chapter 6 references on page 187 Chapter 6 measurement of the UV-Vis spectrum at 1.0 xlO"5 M when a new absorption maximum at 582 nm was observed (Figure 6.10, s = 3100); this peak was not evident in the (1-10) xlO"4 M range, and perhaps suggests that it is associated with the catalytically active Ni species. This could be monomeric and be the dominant species present in solution over the approximately first-order kinetic range (i.e., up to ~ 7 xlO"6 M). At 1.0 xlO"5 M Ni, the absorption maximum at ~ 430 nm was still evident at an intensity in the range calculated via the Beer's law data of Figure 6.9. As a very speculative suggestion, the kinetic dependence on [NiBr2] might thus be consistent with monomeric Ni (A™,x 582 nm) being the active catalyst at low concentrations, this then aggregating to larger size, less active species at higher concentrations. Strong evidence against colloidal activity is the "Hg addition" test in Section 6.3.4. Clearly, more extensive studies are needed in attempts to elucidate the nature of the catalyst. 0.40 T 0.30 -1 -| 0.20 -0.10 -0.00 -200 400 600 800 Wavelength (nm) Figure 6.10 UV-Vis spectra of 1 xlO"5 M NiBr 2 and 0.47 M NaOH in /-PrOH at r.t. using a 5 cm pathlength cell. The maximum initial rate (418 xlO"6 M s"1) obtained in Section 6.3.5 (where [NiBr2] = 5.6 xlO'3 M and [NaOH] = 0.50 M) differs from that seen in Figure 6.8a (~ 45 xlO"6 M s"1) at about the same [NiBr2] and [NaOH], as the former experiment was conducted at 1.41 M C 6 H i 0 O , whereas the latter was at 0.1 M C 6 H i 0 O (see Section 6.3.7 for the kinetic dependence on CeHioO). Note also that although the maximum activity for CeHioO reduction occurs at ~ 7.0 xlO"4 M NiBr 2 (Table 6.5), most of the work in this Chapter was conducted at 5.6 xlO"3 M NiBr 2. 171 Chapter 6 references on page 187 Chapter 6 6.3.7 Kinetic Dependence of C 6 H i 0 O Transfer Hydrogenation on Hydrogen-Atom Acceptor and Donor Two series of experiments were conducted to determine the kinetic dependences on the concentrations of hydrogen-acceptor (C 6 Hi 0 O) and donor (z-PrOH). Twelve samples at 0.1-4.0 M CeH ioO and 9 M z-PrOH were examined in the first series (Figure 6.11), while 15 samples at 0.035-13 M z-PrOH (neat z-PrOH = 13.07 M) and 0.1 M C 6 H i 0 O were examined in the second series (Figure 6.12). All samples were charged with NiBr 2, NaOH, and enough ?-BuOH to maintain a total volume of 3.0 mL (see Appendix C.8 for factors leading to the use of ?-BuOH as an inert diluent and Tables C.7-8 for tabulated ra values). [ C 6 H 1 0 O ] M Figure 6.11 r0 vs. [CeHioO] for the transfer hydrogenation of C 6 H i 0 O . 0 2 4 6 8 10 12 14 [/-PrOH] 0 Figure 6.12 r0 vs. [z-PrOH] for the transfer hydrogenation of C 6 Hi 0 O. 172 Chapter 6 references on page 187 Chapter 6 The kinetic dependences over certain concentration ranges were determined from the slope of the line of plots of log rQ vs. log [C 6 Hi 0 O] o and plots of log r0 vs. log [z-PrOH]0, respectively (see Appendix C, Tables C.7-8 and Figures C.4-5). The two CeHioO plots (made over 0.1-1.41 and 1.41-2.5 M) show the reaction is first-order in C 6 H i 0 O up to 1.41 M and roughly inverse second-order from 1.41-2.50 M ; at 3-4 M , there is no hydrogenation. The four z'-PrOH plots (made over the arbitrarily selected ranges of 0.035-0.5, 0.5-3.0, 3.0-9.0, and 9.0-13.0 M) have slopes of 0.84, 0.24, -0.26, and -0.56, respectively; visual inspection of Figure 6.12 shows a first- to zero-order dependence with increasing [z'-PrOH] up to ~ 3 M . The existence of maxima in plots of r0 vs. [H-atom donor] or [H-atom acceptor] for transfer hydrogenation reactions, as seen in Figure 6.12 and Figure 6.11, respectively, are known. For example, Beaupere et al. report an activity maximum at 1.0 M 1-phenylethanol in a plot of rQ vs. [1-phenylethanol] for the reduction of 0.25 M cyclohexenone catalyzed by RhH(PPh3)4 in 1-phenylethanol.12 Imai et al. similarly report maximum activity at 0.4 M cycloheptene in a plot of r0 vs. [cycloheptene] for the reduction of cycloheptene by Pd/C and 0.5 M indoline.7 In both cases, a competition between the donor and the substrate for the catalyst is suggested, with an optimal balance between these attained at initial donor : acceptor ratios of 4 (1.0 M / 0.25 M ) 1 2 and 1.25 (0.5 M / 0.4 M), 7 respectively. The competition between H-atom donor (D) and H-atom acceptor (A) for the catalyst (C) has been extensively investigated by Beaupere et al.12'43"45 This group reports that the initial rate of hydrogenation for various ketones can vary depending on the order in which the reactants are combined. For example, if RhH(PPh3)4 (C) and 1-phenylethanol (D) are first heated together, followed by addition of cyclohexanone (A), rD = 1.25 xlO"4 M s"1 for a given set of conditions. However!, when C and A are first heated together, followed by addition of D, r0 = 0.29 xlO"4 M s"1. These two scenarios, labeled as "Process I" and "Process II" in Figure 6.13, were invoked and indicated that the CD species formed in Process I more readily bound A and was susceptible to H-atom-extraction by A, whereas the C A species formed in Process II did not readily bind D. These differences were thus attributed to C 6 H i 0 O (A) binding more strongly to RhH(PPh3)4 than does 1-phenylethanol (D). When benzalacetone (4-phenyl-3-buten-2-one) was used in place of cyclohexanone, r0 values of 6.50 xlO"5 and 5.00 xlO"5 M s"1 were obtained for Process I and II, respectively, and the data were thought to indicate that benzalacetone and 1-phenylethanol 173 Chapter 6 references on page 187 Chapter 6 coordinate with similar strength to RhH(PPh 3) 4. 4 3 Imai and workers similarly attributed their observed decrease in rQ with increasing [acceptor] to the competitive formation of inactive Ru-acceptor vs. active Ru-donor species.10 Process I C + D = = = C D = ^ C D A -ProcessII C, A H 2 , and D - H 2 D C A D = = = C A = ^ C + A Figure 6.13 Process I and II mixing orders. The activity maxima seen in this thesis work might thus also be due to competition between the donor and acceptor for the catalyst, with coordination of /-PrOH to Ni inhibited if [CeHioO] is too high (i.e., > 1.41 M , Figure 6.11), and coordination of C 6 H i 0 O to Ni inhibited if [/-PrOH] exceeds a certain value (i.e., ~ 3.0 M , Figure 6.12). The following experiments confirm that a competition between CeHioO and /-PrOH for Ni can exist, at least in a mixed /-PrOH/r-BuOH medium. Mixing-Order Experiments Processes I (CD+A) and II (CA+D) were tested on the NiNa'P system as follows. To two vessels (charged with NiBr 2, NaOH and r-BuOH) was added /-PrOH (first vessel) and C 6 H i 0 O (second vessel), respectively (see Figure 6.14). Both vessels were heated for 30 min at 95°C, after which time CeHioO was added to the first vessel and /'-PrOH to the second vessel (final volume = 3.0 mL for both). The heating of both reactors at 95°C was continued, and samples were removed every minute (for 7 min) for GC analysis. The [CeHnOH] measured is reported in Appendix C, Table C.9, while the number of turnovers attained per minute vs. time is plotted in Figure 6.14. The reduction of CeHioO via Process I begins at ~ 0.9 turnovers (TONi) in the first minute, whereas only ~ 0.2 turnovers (TONn) are observed via Process II at this same time (Figure 6.14). This difference would result from CeHioO being added (in Process I) to a solution where the catalyst has been bound up by /'-PrOH to form CD species from which subsequently coordinated CeHioO can effectively extract H-atoms, whereas when /-PrOH is added to a solution containing C A species, a less effective Process II occurs. 174 Chapter 6 references on page 187 Chapter 6 0 1 2 3 4 5 6 7 8 Time (min) Figure 6.14 Turnovers per minute vs. time for two different mixing orders. Conditions: 5.6 xlO"3 M NiBr 2 (in 3 mL solution, of which 1.4 mL is /-BuOH), 0.47 M NaOH, 0.1 M C 6 H 1 0 O , 7 M /-PrOH, T = 95°C. The decline in TONi after t = 2 min could be attributed to the free competition between A and D for C once the first cycle is completed, with the less reactive C A species preferentially forming over the more reactive CD species; the data would imply that CeHioO binds more strongly to Ni than does /'-PrOH. T O N n does not decrease with time as the less reactive C A species is present throughout. After 7 min, TONi approaches the value of TONn. The NiNa'P system (with the added /-BuOH) is thus sensitive to the order of addition of the reactants, implying a competition between the donor and acceptor for the catalyst. The kinetics discussed generally in this Chapter were determined under the conditions of Process I, i.e., the substrate (A) was added to a pre-mixed /-PrOH solution of the NiBr 2 and NaOH. The data in Figure 6.14 imply a possible serious limitation to the measured kinetics as the r0 (so-called initial rate) values were determined by measuring conversion over 30 min; Figure 6.14 shows that the initial rate is far from linear even over the first 5 min (but note, the NiNa'P system does not contain 7-BuOH). This limitation becomes apparent when comparing different experiments in this Chapter as, upon "normalization" to the same reactant concentrations (i.e., converting the data in Tables 6.1, 6.3, 6.5-8, C.2, C.7 and C.8 to 1.41 M C 6 H i 0 O and 0.47 M NaOH set-up conditions), rQ values ranging from 418-843 xlO"6 M s"1 are seen for "repeat" experiments. 175 Chapter 6 references on page 187 Chapter 6 IR Spectroscopy Experiments Three solution LR samples (in Figure 6.15) were prepared by adding either /-PrOH, C 6HioO, or both to 0.01 M NiBr2(PPh3)2 in C6He (final solutions are 0.2 M in each additive). [The use of NiBr 2 in aqueous solvents was considered impractical] 100 4000 3600 3200 2800 2400 2000 1600 1200 800 400 80 , , 4000 3600 3200 2800 2400 2000 1600 1200 800 400 Wavenumber (cm'1) Figure 6.15 LR spectrum of 0.01 M NiBr2(PPh3)2 in CeHe with: (a) 0.2 M /-PrOH; (b) 0.2 M CeHioO ; (c) 0.2 M /-PrOH and 0.2 M C 6 H 1 0 O . (• = /-PrOH, o = C 6 H i 0 O , * = Ni-/-PrOH complex, * - Ni-CeHi 0O complex). 176 Chapter 6 references on page 187 Chapter 6 The spectra consist predominantly of C 6 H 6 peaks. The bands at 3597 and 2893 cm"1 in Figure 6.15a arise from /-PrOH, 4 6 while the band at 3257 cm"1 is tentatively assigned to a Ni-z'-PrOH species. Beaupere et al. have reported a 3392 cm"1 band attributed to a Rh-z'-PrOH species formed when 0.2 M RhH(PPh3)4 was added to 0.2 M /-PrOH in C 6He. 4 3 The bands at 1714 and 3690 cm"1 in Figure 6.15b belong to C 6 H i 0 O , 4 6 and the peak at 2863 cm"1 is tentatively assigned to a Ni-CeHi 0O species. In the third spectrum (Figure 6.15c), the only band observed that is attributable to a Ni species is that of the possible Ni-CeHi 0O complex at 2863 cm"1. The absence of the 3257 cm"1 band shows that CeHioO coordinates more powerfully than /'-PrOH to Ni(II), albeit within a NiBr2(PPh3)2 precursor. 6.3.8 Effect of Acetone and Cyclohexanol on the Transfer Hydrogenation of C 6 Hi 0 O Acetone The products from the transfer hydrogenation of CeHioO by /-PrOH are a ketone/alcohol pair, hence concomitant catalysis of the back-reaction might occur (Eq. 6.3), and indeed this is known to be a reversible equilibrium.33 The complete conversion of C 6 H i 0 O to C 6 H n O H seen in most experiments implies that the reverse process does not happen, presumably because the acetone co-product (b.p. 56°C) is forced into the gas headspace of the reactor by the 95°C temperature of the solution, although some acetone must remain in solution in a sealed vessel due to vapour-liquid phase equilibria [thick-walled test-tubes were used as full conversion of 1.41 M CeHioO in 3.0 mL /'-PrOH produces ~ 4.3 atm acetone(g) in the headspace]. Sasson and Blum note that the metal hydride formed by hydride-transfer from an alkoxy ligand to metal (e.g., z'-PrO" - » Ni) will attack whichever ketone has the higher reduction potential, hence the larger A E 0 ^ is between the two ketones, the more irreversible the reaction.11 As the E°% values for CeHioO and acetone are 162 and 129 mV, respectively,47 and as the equilibrium constants (K) for the reduction of C 6 H i 0 O and acetone by 2 H-atoms are 2.97 xlO 5 and 2.28 xlO 4, respectively, (as calculated from In K = «FE°/RT), near complete transfer hydrogenation of C 6 H i 0 O would be expected if a Ni hydride species were present. Ni CeHioO + (CH 3 ) 2 CHOH — C 6 H n O H + (CH 3) 2C=0 (Eq. 6.3) 177 Chapter 6 references on page 187 Chapter 6 The effect of removing acetone from the product was examined. Two vessels (charged with 5.64 xlO"3 M N i B r 2 , 0.47 M N a O H , 1.41 M C 6 Hi 0 O, and 3.0 mL /-PrOH), one of which was left open to the atmosphere, were heated for 30 min at 80°C; the temperature was lowered from 95°C to prevent boiling off all solvent from the unsealed vessel. Initial rates of 500 and 430 xlO"6 M s"1 for the open and sealed,reactors, respectively, indicate that removal of acetone perhaps shifts Eq. 6.3 to the right-hand side. The effect of adding acetone to the system was also examined. To four vessels (charged with 3.1 xlO"3 M NiBr 2, 3.0 mL /-PrOH, 0.27 M NaOH, 0.78 M C 6 H 1 0 O , and /-BuOH) were added the amounts of acetone listed in Table 6.6, these corresponding to mole ratios of 10, 100, and 1000 : 1 vs. NiBr 2, respectively. A total volume of 4.0 mL was maintained by addition of /-BuOH, and the solutions were heated at 95°C for 24 h and analyzed by GC after 1 and 24 h. Although increasing amounts of acetone slowed the hydrogenation at t = 1 h, complete conversion of C 6 H i 0 O is seen in all four trials by 24 h. Table 6.6 Transfer Hydrogenation of C 6 H i 0 O vs. Amount of Acetone Added Acetone added (uL) % Conversion (sampling time) 0 66.3 (1 h), 99.9 ( 24 h) 7 65.7(1 h), 99.9 (24 h) 69 57.1 (1 h), 99.9 (24 h) 690 30.9 (1 h), 99.7 (24 h) Cyclohexanol The addition of C 6 H n O H to a typical catalytic run might decrease the activity of the NiNa'P system as the equilibrium of Eq. 6.3 will be shifted towards the left-hand side. To six vessels (charged with 5.6 xlO"3 M NiBr 2, 0.47 M NaOH, 9 M /'-PrOH, and r-BuOH) was added enough CeHnOH to yield the initial concentrations (calculated for a total reaction mixture volume of 3.0 mL) shown in Table 6.7. Once the solutions reached 95°C, 0.1 M C 6 H i 0 O was added to each vessel, and heating was continued for 30 min. The amount of CeHnOH produced from the initial 0.1 M CeHioO is calculated by subtracting the initial amount of C 6 H n O H added to the solution from that detected by GC (Table 6.7). A decrease in activity upon addition of CeHnOH 178 Chapter 6 references on page 187 Chapter 6 is observed, but the effect is small and is certainly not evident in the first-order type conversion plots such as that shown in Figures 6.2 and 6.3, at least for the first two half-lives. Table 6.7 Transfer Hydrogenation of 0.1 M C 6 H i 0 O at Various Added [ C 6 H u O H ] [C 6HiiOH] Added (M) [C 6 H n OH] Detected (M) [C 6HnOH] Due to % Conversion b Conversion of CeHioO (M) " 0.00 0.0938 0.0938 93.8 0.01 0.0978 0.0878 87.8 0.03 0.1180 0.0880 88.0 0.05 0.1373 0.0873 87.3 0.08 0.1664 0.0864 86.4 0.10 0.1811 0.0811 81.2 ( a ) [C 6 H„OH] Detected - [C 6 H u OH] Added. ( 6 ) O f the initial 0.1 M C 6 H 1 0 O to C 6 H u O H . 6.3.9 Effect of Water, H 2 , Halide, and PPh3 on the Transfer Hydrogenation of C 6Hi 0O Water c .2 I - I o U v/v H 2 0 • 0.0% n o . i % • 1.0% • 10.0% 3 10 30 Time (min) Figure 6.16 Transfer Hydrogenation of CeHioO with various amounts of water added. Increasing the H 2 0 content of a transfer hydrogenation system can decrease its catalytic activity.16 Exposing the NiNa'P system to H 2 0 in the following manner also resulted in a decrease in activity. To three of four vessels (charged with 5.6 xlO"3 M NiBr 2 in /-PrOH, 0.47 M NaOH, 179 Chapter 6 references on page 187 Chapter 6 and 1.41 M C 6 H i 0 O ) was added enough water to yield 0.1, 1.0, and 10.0% v/v H 2 0 / / ' -PrOH solutions, respectively (total volume = 3.0 mL). The vessels were heated at 95°C and sampled at various times (Figure 6.16 and Appendix C , Table C . 10). Although 0.1% v/v H 2 0 diminished the yield from 56 to 47% (t = 30 min), complete conversion to C 6 H n O H was nevertheless attained in the 0.1 and 1.0% H 2 0 trials within 15 h. However, only 9.7% conversion was attained after 15 h with the 10% H 2 0 trial (Table CIO); a separate experiment with 50% v/v H 2 0 (3.0 mL total volume) afforded only 0.7% conversion after the same time. Hydrogen The effect of H 2 upon the transfer hydrogenation of CeHioO by the NiNa'P system was examined as follows. Two vessels (charged with 5.6 xlO"3 M NiBr 2 in 3!0 mL z-PrOH, 0.47 M NaOH, and 1.41 M CeHi06) were evacuated and charged with 1 atm of N 2 or H 2 , and then heated at 95°C for 30 min. As the conversions to C 6 H H 6 H were 82.8 and 80.5% for the N 2 - and H 2 -charged reactors, respectively, H 2 is considered to have no effect upon the reduction of C 6 H i 0 O by the NiNa'P system. Halides A decrease in catalytic activity upon addition of halide ions (X") to hydrogen transfer hydrogenation systems has been reported in some cases,48'49 To four of five vessels (charged with 5.64 xlO"3 M NiBr 2 in 3.0 mL /-PrOH, 0.47 M NaOH, and 1.41 M C6Hi06) was added 0.5 M of either NaF, NaCl, NaBr, or Nal. The vessels were heated at 95°C for 30 min and then sampled (see Appendix C, Table C. l l ) . The observed poisoning effect of X" upon the hydrogenation increases on descending the halijde/series (as noted by others49). The slight increase in activity reported in Appendix C.3 upon addition of 0.05 M KF to the "NaOH-only" blank is likely attributable to the increase in ionic strength of the solution. Experiments were also conducted with variable amounts of NaBr. To two of three vessels (charged with 3.11 xlO"3 M NiBr 2 in 3.0 mL /-PrOH, 0.47 M NaOH, and 1.41 M C 6 Hi 0 O) was also added 0.03 or 0.3 M NaBr. The vessels were heated at 95°C and samples were withdrawn after 1 and 24 h. The conversion to CeHnOH after 1 h was 65.7, 60.3, and 59.8 %, respectively, for the blank, 0.03, and 0.30 M NaBr samples, while after 24 h the corresponding values were t. ,:• \ t * . i < 180 Chapter 6 references on page 187 Chapter 6 99 A, 99.2, and 91.8 %, respectively. As the ten-fold increase in [Br"] at t = 1 h yielded a decrease in activity of only - 1 % conversion, and as the molar conductivity of NiBr 2 in /'-PrOH (20.5 Q"1 cm2 M" 1; in the absence of CeHioO) is in the accepted range (16-22 units) for 1:1 electrolytes in /'-PrOH, 5 0 complete dissociation of all Br" from NiBr 2 apparently does not occur in the NiNa'P system. This, along with the fact that Ni(OH) 2 does not dissolve in refluxing /'-PrOH, shows that the active catalytic species is not Ni(OH)2. Phosphines Addition of PPh3 to transfer hydrogenation systems can increase,51 decrease,52'53 or not effect10'54'55 the activity of the system. The effect of PPh3 on the NiNa'P system was examined as follows. To three of four vessels (charged with 3.11 xlO"3 M NiBr 2 in 3.0 mL /-PrOH, 0.26 M NaOH, and 0.78 M C 6 Hi 0 O ) was added enough PPh3 to afford either 0.03, 0.30, or 3.00 M (in PPh3) solutions. The vessels were heated at 95°C and sampled at 1 and 24 h. The results show that PPh3 has no effect on the activity of the NiNa'P system (Table 6.8). The addition of PPh3 to NiBr 2 in /'-PrOH readily yielded the green NiBr2(PPh3)2 species (?wx (C 6He) = 576 nm), but formation of this species was prevented by the addition of 0.4 M NaOH to the NiBr2//'-PrOH mixture prior to addition of PPh3, as indicated by the clear and colourless appearance of the final mixture; correspondingly, /-PrOH solutions of NiBr2(PPh3)2 turned colourless on addition of NaOH. The data tend to suggest that the NiBr2(PPh3)2 system in NaOH likely involves some dissociation of the complex into the more active NiBr 2 system (see Table 6.1). Table 6.8 Effect of PPh3 on the Transfer Hydrogenation of C 6 H i 0 O [PPh3] M % Conversion (sampling time) 0.00 65.7 (1 h), 99.4 (24 h ) 0.03 65.8 (1 h), 99.4 (24 h) 0.30 65.6 (1 h), 99.4 (24 h) 3.00 65.8 (1 h), 99.2 (24 h) 6.3.10 Catalyst Deactivation A vessel (charged with 5.6 xlO"3 M NiBr 2 in 3.0 mL /-PrOH, 0.47 M NaOH, and 1.41 M CeHioO) was heated at 95°C until 95.9% conversion to C 6 H n O H was attained (2 h). The brown 181 Chapter 6 references on page 187 Chapter 6 solution was then passed through an ultrafine filter (0.22 p Millex - G V filter) to trap any solid particles, although none were seen visually. Molecules in solution would not be removed by such a filter.42 The filtrate was then distilled (to remove CeHioO, C 6 HnOH, /-PrOH, and acetone) and the inorganic residue was redissolved in fresh C 6 H i 0 O and /-PrOH. The full heating/filtration/distillation/recharging cycle was repeated twice and the time required to attain 95.2 and 92.1% conversion was 3 and 7 h, respectively, while the fourth trial was terminated at t = 3 h (62.8% conversion) (Figure 6.17 and Appendix C, Table C.12). Deactivation of the catalyst is thus seen over four cycles, but the data certainly imply that the catalyst is a solution soluble species, either a molecular entity or possibly colloidal Ni(0). However, the experiment with added mercury rules out the latter, and also colloidal catalysts, unless "stabilized", tend to aggregate with re-use to inactive, heterogeneous metallic species.56 0 6 i 11 I6I 111116 6 1111 0 2 4 6 8 10 12 14 16 Time (h) Figure 6.17 Recharging of NiBr 2/NaOH residue with C 6 H i 0 O and /'-PrOH at total reaction times of 2, 5, and 12 h. 6.3.11 Effect of Steric Hindrance upon the Transfer Hydrogenation of Substituted CeHioO Incorporation of a methyl substituent ortho to the carbonyl moiety of CeHioO can create steric interference between the active site of the catalyst and the carbonyl group. Thus, Shibagaki et al. report that C 6 Hi 0 O, 4 -MeC 6 H 9 0 , and 2- M e C 6 H 9 0 were reduced by ZrO/z'-PrOH with rate constants of 7.2, 7.0, and 1.1 xlO"4 s"1, respectively,18 and Mestroni et al. report H2-uptakes of 14, 10, 11, and 12 mL min"1 for C 6 Hi 0 O, 2-Me-, 3-Me-, and 4-Me-C 6 H 9 0 , respectively (with 182 Chapter 6 references on page 187 Chapter 6 [Rh(bipy)2Cl2]C1.2H20/NaOH/MeOH/H2). Lin and Zhou, however, report similar values of 24 vs. 23 turnovers h"1 in the transfer hydrogenation of 4-Me- vs. 2-Me-C 6 H 9 0 by Ru(H) 4(PPh3)3//-PrOH. 2 0 Data in this thesis work for vessels charged with NiBr 2, NaOH, /-PrOH and either CeH ioO, 2-Me-CeH 90, or 4-Me-CeH 90 are shown in Table 6.9; coordination of substrate to catalyst via the carbonyl group seems highly likely. [Note, v(CO) for CeH ioO and 2-Me-C 6 H 9 0 were found to be almost the same (1718 vs. 1715 cm"1 in CCU), and electronic factors are considered unimportant.] Table 6.9 Transfer Hydrogenation of C 6 H i 0 O , 2-Me-C 6H 90, and 4-Me-C 6H 90 a Substrate % Conversionb CeHioO 74.5 4-Me-C 6H 9 0 78.1 2-Me-C 6H 9 0 20.6 ( f l ) 5.64 xlO"3 M NiBr 2 (in 3.0 mL /-PrOH), 0.47 M NaOH, 1.41 M substrate, T = 95°C, t = 30 min. { b ) To cis- and/or trans- 2-Me- or 4-Me-C 6Hi 0 OH. 6.3.12 Possible Mechanism for the Transfer Hydrogenation of CeHioO by the NiNa'P System The hydrogenation of cyclohexanone within a single experiment analyzes for a first-order dependence on its concentration, at least for two half-lives (Figure 6.3), and this is substantiated by the close to linear dependence of the "initial rate" (r0) as a function of initial [CeHioO] , at least up to ~ 1.4 M (Figure 6.11). This kinetic dependence, as well as those ori [NiBr2] and [NaOH], were carried out in essentially neat (~ 13 M) /-PrOH, in the region where the reaction is close to zero-order in the /-PrOH (Figure 6.12); in any case, the [/-PrOH] is essentially constant within a single experiment. There are clearly complications at higher [CeHioO] and lower [/-PrOH] (Figures 6.11 and 6.12) and these are attributed to a competition between the ketone and alcohol for a Ni catalysis site; these dependences, and some experiments in which the order of the addition of the reaction components was varied, imply that the ketone binds more strongly. However, it is impossible to analyze quantitatively the "competition data" (Process I vs. Process II, Section 6.3.7) because the processes cannot be occurring under conditions where the equilibria to give 183 Chapter 6 references on page 187 Chapter 6 CD and C A are established "rapidly" (otherwise the order of addition of reagents would be irrelevant). The kinetics were determined generally under the Process I conditions in that the acceptor ketone substrate was added after equilibrium between the catalyst and the donor /'-PrOH had been established. The limitations in the kinetic data because of this procedure (i.e., uncertainties in r0 as it is not linear even over the first 5 min) have been mentioned (Section 6.3.7), but nevertheless as a first approximation the reaction (in the region of the first-order in [C 6Hi 0O] and independence of /-PrOH) is second-order in [NaOH] (Figures 6.5-6). It is difficult to imagine how the rate-determining step can involve directly a NaOH molecule. The essential steps almost certainly involve, at some stage, /i-hydride migration from a coordinated alkoxide to a coordinated ketone; Figure 6.18 shows a generalized and often postulated mechanism for H-transfer from /'-PrOH to a ketone.1'16'33 "Ni" Me2CHO~Na (a) Me 2 CO R 2CH(OH) N i - 0 = C M e 2 (e) (fast) R 2 CO Ni—OCHMe 2 — 1 • (b) N i - 0 = C M e 2 R 2CHO 4 (d) Ni—OCHMe 2 R 2 C = 0 (c) H N i - 0 = C M e 2 R2C=6 Figure 6.18 Generally proposed mechanism for transfer hydrogenation of CeHioO, exemplified by the NiNa'P system (charges omitted). A direct first-order dependence on [NaOH] could result from a rapid pre-equilibrium involving formation of the isopropoxide needed for step (a) with K i being small (Eq. 6.4); the isopropoxide would then have to bind to the metal centre via again a small value equilibrium K 2 (Eq. 6.5). 184 Chapter 6 references on page 187 Chapter 6 Me 2CH(OH) + NaOH ^=L= M ^ H C - 0 " N a + + H 2 0 (Eq. 6.4) "Ni" + Me 2CHO" , Ni-OCHMe^ (Eq. 6.5) If any of steps (b)-(e) were rate-determining, none would realize a further first-order dependence on [NaOH]. For example, if (b) were rate-determining with a kb step, rate = -_d[R2CO] = /cb[Ni-OCHMe2][R2CO] - /cbK1K2["Ni"]T[R2CO][/-PrOH][NaOH] (Eq. 6.6) dt [ H 2 0 ] where ["Ni"]T = total nickel with unspecified ligands. One possible source for the "second" [NaOH] dependence could result from a pre-equilibrium involving the Ni species, for example, Eq. 6.7 (the Ni site will almost certainly have coordinated /-PrOH molecules, but these are not included inEqs. 6.5, 6.7, and 6.8). "Ni-Br" + O H " . "Ni-OH" + Br" ' (Eq. 6.7) NiBr 2 + OH" , ^ 3 - NiBr2(OH)" (Eq. 6.8) If the reaction involved reaction of "Ni-OH" formed via Eq. 6.7, then a direct inverse dependence on [Br] would be predicted, whereas addition of Br" has essentially no effect (Section 6.3.9). Thus, an equilibrium such as shown in Eq. 6.8 could be invoked. In this case, with K 3 again being small, the rate law could be modified to rate = k^K2K3[NiBr2][R2CO][/-PrOH][NaOH]2 (Eq. 6.9) [ H 2 0 ] The numerator of the rate equation (Eq. 6.9) is at least qualitatively consistent with the observed first-order dependence on R 2 CO (cyclohexanone), first-order dependence on /'-PrOH (at least at lower [/-PrOH]), and second-order in [NaOH]. There is also an experimental inverse dependence on [ H 2 0 ] (Section 6.3.9), but the effect is much smaller than the predicted direct inverse order; 185 Chapter 6 references on page 187 Chapter 6 however, varying the concentration of H 2 0 would almost certainly effect the nature, and the distribution, of the Ni species present, and the activity may well result from contributions from more than one. [The formation of Ni(OH) 2 as a precursor catalyst is not invoked in the catalytic cycle as the hydroxide is insoluble in refluxing /-PrOH.] Of note, step (b) was randomly chosen as rate-determining; however, if steps (c) or (d) were rate-determining, the "same type" of rate law as shown in Eq. 6.9 would result as long as step (b) was now a rapid pre-equilibrium for binding of the R 2 C O substrate (again with a small equilibrium binding constant, so that the kinetic dependence on [R2CO] remains as unity). All of the above speculative discussion requires that the dominant Ni species present in solution contains no liganded isopropoxide or cyclohexanone; the kinetically significant species would be 1, 2, or 3, respectively, depending on whether step (b), (c), or (d) is rate-determining. The studies aimed at elucidating the nature of the dominant (and likely precursor catalyst) Ni species in solution are non-conclusive. The LR data show that /-PrOH and C 6 H i 0 O can both bind to NiBr 2(PPh 3) 2 in benzene (Figure 6.15), but whether this pertains to the strongly basic /-PrOH medium (in the absence of PPh3) is unclear. [Of note, the lack of formation of NiBr 2(PPh 3) 2 from NiBr 2 in the NaOH/z-PrOH medium, and the dissociation of NiBr 2(PPh 3) 2 in the same medium (Section 6.3.9), implies that the active catalyst in the reported H-transfer using NiCl 2(PPh 3) 2 3 4 likely contains no phosphine]. The kinetic dependence data on the [NiBr2], coupled with the UV-Vis Beer's law studies, are very difficult to rationalize as they suggest the presence of both colloidal Ni and at least two different Ni species (with absorption maxima at 432 and 582 nm, respectively), but the test with added mercury seems to rule out colloidal Ni (Section 6.3.4). Clearly, more extensive studies are needed in attempts to elucidate the nature of the catalyst. 6.4 Conclusion It has been shown in this Chapter that the Ni(II) species listed in Table 6.1 are capable of catalyzing the transfer hydrogenation of C 6 H i 0 O to C 6 H n O H using alkaline /'-PrOH, and that the halide salts NiBr 2 and Ni l 2 are the most active catalyst precursors. The order of the reaction with respect to CeHioO has been found to be first-order up to ~ 2 half-lives. The kinetic dependence of the reaction on the various reaction components has been determined to be fairly complex, with 186 Chapter 6 references on page 187 Chapter 6 the second-order dependence on NaOH being the only constant parameter. The kinetic dependence on NiBr 2 is first-order up to 7.0 xlO"6 M , while at higher concentrations it becomes zero-order. The kinetic dependences on H-atom donor and H-atom acceptor go through activity maxima at ~ 3.0 and ~ 1.4 M , respectively, and are only first-order over the ranges of 0.035-0.50 M /-PrOH and 0.1-1.41 M CeHioO, respectively. These activity maxima have been suggested to result from a competition between CeHioO and /-PrOH for the active catalyst site. A second-order dependence on NaOH was observed over concentration ranges in which the hydroxide was soluble. The effect of various additives (acetone, CeHnOH, H 2 0 , H 2 , halides, and PPh3) upon the activity of the NiNa'P system has been investigated. The catalytic system was: (a) determined to most likely be homogeneous, (b) shown to decrease in activity over four cycles, and (c) found to be effected by steric factors. Plausible mechanisms are considered, and corresponding rate laws are given which are at least qualitatively consistent with the observed kinetic dependences on each of the reaction components at certain concentration ranges. 6.5 References 1. Chowdhury, R.; Backvall, J. J. Chem. Soc, Chem. Commun. 1991, 1063. 2. Morrison, R. T.; Boyd, R. N. Organic Chemistry, 5th ed., London: Allyn and Bacon, Inc. 1987, p. 774. 3. Schrock, R. R.; Osborn, J. A. J. Chem. Soc, Chem. Commun. 1970, 567. 4. Prati, L . ; Rossi, M . ; Gargano, M . ; Ravasio, N. Gazz. Chim. Ital. 1992,122, 221. 5. Upadhya, T. T.; Katdare, S. P.; Sabde, D. P.; Ramaswamy, V.; Sudalai, A. J. Chem. Soc, Chem. Commun. 1997, 1119. 6. Sammakia, T.; Strangeland, E. L. J. Org. Chem. 1997, 62, 6104. 7. Imai, H.; Nishiguchi, T.; Hirose, Y.; Fukuzumi, K. J. Catal. 1976, 41, 249. 8. Gordon, E. M . ; Gaba, D. C ; Jebber, K. A.; Zacharias, D. M . Organometallics 1993,12, 5020. 187 Chapter 6 references on page 187 Chapter 6 9. Puntener, K.; Schwink, L.; Knochel, P. Tetrahedron Lett. 1996, 37, 8165. 10. Imai, H.; Nishiguchi, T.; Fukuzumi, K. J. Org. Chem. 1976, 41, 665. 11. Sasson, Y.; Blum, J. J. Org. Chem. 1975, 40, 1887, and references cited therein. 12. Beaupere, D.; Nadjo, L.; Uzan, R.; Bauer, P. J. Mol. Catal. 1983, 20, 195. 13. Kvintovics, P.; James, B. R.; Heil, B. J. Chem. Soc., Chem. Commun. 1986, 1810. 14. Mezzitti, A.; Consiglio, G. J. Chem. Soc, Chem. Commun. 1991, 1675. 15. Farnetti, E. ; Gulati, N. V.; Graziani, M . Gazz. Chim. Ital. 1993,123, 165. 16. de Bellefon, C ; Tanchoux, N. Tetrahedron: Assymetry 1998, 9, 3677. 17. Jiang, Y. T.; Jiang, Q. Z.; Zhu, G. X.; Zhang, X. M . Tetrahedron Lett. 1997, 38, 215. 18. Shibagaki, M . ; Takahashi, K.; Matsushita, H. Bull. Chem. Soc. Jpn. 1988, 61, 3283. 19. Jothimony, K.; Vancheesan, S. J. Mol. Catal. 1989, 52, 301. 20. Lin, Y. G ; Zhou, Y. F. J. Organomet. Chem. 1990, 381, 135. 21. Marcec, R.; Raza, Z.; Sunjic, V. J. Mol. Catal. 1991, 69, 25. 22. Inada, K.; Shibagaki, M. ; Nakanishi, Y.; Matsushita, H. Chem. Lett. 1993, 1795. 23. Jalon, F. A.; Otero, A ; Rodriguez, A.; Perez-Manrique, M . J. Organomet. Chem. 1996, 508, 69. 24. Barbaro, P.; Bianchini, C ; Togni, A; Organometallics 1997,16, 3004, and references cited therein. 25. Gladiali, S.; Chelucci, G.; Chessa, G ; Delogu, G.; Soccolini, F. J. Organomet. Chem. 1987, 327, C15. 26. Spogliarich, R.; Kaspar, J.; Graziani, M . J. Catal. 1985, 94, 292. 27. Krause, H. W.; Bhatnagar, A. K. J. Organomet. Chem. 1986, 302, 265. 28. Gargano, M . ; D'Orazio, V.; Ravasio, N.; Rossi, M . J Mol. Catal. 1990, 58, L5. 188 Chapter 6 references on page 187 Chapter 6 29. Botteghi, C ; Chelucci, G.; Cheesa, G.; Delogu, G.; Gladiali, S.; Soccolini, F. J. Organomet. Chem. 1986, 304, 217. 30. Matsumura, K.; Hashiguchi, S.; Ikariya, I.; Noyori, R. J. Am. Chem. Soc. 1997,119, 8738. 31. Hanaoka, T.; Kubota, Y.; Takeuchi, K.; Matsuzaki, T.; Sugi, Y. J. Mol. Catal. A: Chem. 1995, 157. 32. Sariego, R.; Martinez, M. ; Carkovic, I.; Contreras, R ; Moya, S. A. J. Mol. Catal. 1989, 51, 67. 33. Haack, K.; Hashiguchi, S.; Fujii, A ; Ikariua, T.; Noyori, R. Angew. Chem. Int. Ed. Engl. 1997, 36, 285. 34. Iyer, S.; Varghese, J. P. J. Chem. Soc, Chem. Commun. 1995, 465. 35. Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 72nd ed., Boston: CRC Press, 1991. 36. Levine, I. N. Physical Chemistry, 3rd ed., New York: McGraw-Hill Book Co., 1988, p. 524. 37. Birk, J. P. J. Chem. Educ. 1976, 53, 704. 38. MacFarlane, K. M.Sc. Thesis, The University of British Columbia, 1989. 39. Pouchert, C. J.; Campbell, J. R. The Aldrich Library of NMR Spectra, Milwaukee: The Aldrich Chemical Company, Inc. 1974. 40. Hassan, M . Z.; Untereker, D. F.; Bruckenstein, S. J. Electroanal. Chem. Interfacial Electrochem. 1973, 42, 161. 41. Whitesides, G. M . ; Hackett, M. ; Brainard, R. L.; Lavalleye, J. P.; Sowinksi, A. F.; Izumi, A. N.; Moore, S. S.; Brown, D. W.; Staudt, E. M . Organometallics 1985, 4, 1819. 42. Anton, D. R ; Crabtree, R. H. Organometallics 1983, 2, 855. 43. Beaupere, D.; Nadjo, L.; Uzan, R ; Bauer, P. J. Mol. Catal. 1983,18, 73. 44. Beaupere, D.; Nadjo, L.; Uzan, R ; Bauer, P. J. Mol. Catal. 1983, 20, 185. 45. Beaupere, D.; Nadjo, L.; Uzan, R ; Bauer, P. J. Mol. Catal. 1982,14, 129. 189 Chapter 6 references on page 187 Chapter 6 46. Pouchert, C. J. Ed. The Aldrich Library of Infrared Spectra, 3rd ed. Milwaukee: The Aldrich Chemical Company, Inc. 1981. 47. Adkins, H.; Elofson, R. M . ; Rossow, A. G.; Robinson, C. C. J. Am. Chem. Soc. 1949, 71, 3622. 48. Baltzly, R. J. Org. Chem. 1976, 41, 920. 49. Baltzly, R. J. Org. Chem. 1976, 41, 928. 50. Taniewska-Osinka, S.; Piekarska, A.; Bald, A.; Szejgis, A. J. Chem. Soc; Faraday Trans. 1 1989, 85, 3709.. 51. Sharf, V. Z.; Freidlin, L. Kh.; Krutii, V. N. Izv. Akad. NaukSSSR, Ser. Khim. 1977, 4, 735, as cited in Chem. Abstr. 1977, 87, 38552. 52. Imai, H.; Nishiguchi, T.; Fukuzumi, K. J. Org. Chem. 1974, 39, 1622. 53. Imai, H.; Nishiguchi, T.; Fukuzumi, K. J. Org. Chem. 1977, 42, 431. 54. Imai, H.; Nishiguchi, T.; Fukuzumi, K. J. Org. Chem. 1976, 41, 2688. 55. Nishijuchi, T.; Fukuzumi, K. J. Am. Chem. Soc. 1974, 96, 1893. 56. Matijevic, E . "Colloid" in McGraw-Hill Encyclopedia of Chemistry, 2nd. ed., Parker, S. P., Ed., New York: McGraw-Hill, Inc., 1993. 57. Mestroni, G.; Spogliarich, R.; Camus, A.; Martinelli, F.; Zassinovich, G. J. Organomet. Chem. 1978, 157, 345. 190 Chapter 6 references on page 187 Chapter 7 CHAPTER SEVEN Transfer Hydrogenation of Various Functional Groups by Ni(II) Systems 7.1 Introduction Having successfully demonstrated the catalytic transfer hydrogenation of cyclohexanone to cyclohexanol using NiBr 2 as a catalyst, NaOH as a cocatalyst, and z'-PrOH as the hydrogen-donor/solvent (Chapter 6), it was decided to examine the use of this NiBr2/NaOH/z-PrOH system (hereafter abbreviated as NiNa'P) in the attempted transfer hydrogenation of other substrates. As such, three ketones (2-butanone, 2-pentanone, and acetophenone), two aldehydes (1-heptanal and benzaldehyde), five unsaturated hydrocarbons (1-octene, zrans-2-octene, cyclooctene, 1,5-cyclooctadiene, and benzene), two nitriles (acetonitrile and benzonitrile), two a, /3-unsaturated ketones (cyclohex-2-ene-l-one and 3-buten-2-one), two diketones (2,4-pentanedione and 2,5-hexanedione), and three other compounds (nitrobenzene, 4-nitrobenzaldehyde, and propionic acid) were examined as substrates for transfer hydrogenation. 7.2 Experimental 7.2.1 Set-up for Catalytic Trials The experimental set-up for all of the substrates tested (except acetonitrile) involved the use of screw-capped, test-tube reactor vessels placed in a hot oil-bath equipped with a magnetic stirrer as depicted in Figure 6.1. Two reactor vessels were used for each substrate tested and were charged with identical concentrations of the substrate, z-PrOH (3 mL), and NaOH. One of the two vessels was also charged with NiBr 2 and in all cases the ratio of NiBr 2 : NaOH : substrate was approximately 1:85:250. Upon being sealed, both vessels were heated at 95°C with aliquots withdrawn for either J H NMR or GC analysis after varying times. The amounts of NiBr 2 and substrate used in each experiment, along with the reaction times at which aliquots were withdrawn, are shown below in Table 7.1. 191 Chapter 7 references on page 211 Chapter 7 The tests involving acetonitrile were conducted in thick-glass-walled Schlenk tubes for safety as the high vapour pressure of any ethylamine product (boiling point 17°C) may render the regular test-tube reactor vessels unsafe; after reaction, the vessel was chilled at 0°C to condense any amine product. Table 7.1 Amounts of Catalyst and Substrate Used and Sampling Times Substrate [NiBr2] (x 10"3 M) Substrate, uL (M) Sampling Time (h) 2-butanonea 2.36 159 (0.590) 2, 24 2-pentanone 6 2.36 190 (0.590) 24, 48 acetophenone0 1.92 168 (0.480) 4, 22 1-heptanal d 1.71 179 (0.428) 4 benzaldehyde a 1.37 104 (0.343) 0.5 1-octenec 0.69 81 (0.173) 0.5 trans-2-octene " 0.69 81 (0.173) 0.5, 24 cyclooctene 6 5.60 547(1.40) 24 1,5-cyclooctadienea 5.64 550(1.41) 24 benzenee 4.62 309 (1.16) 12, 24 acetonitrilee 3.87 152 (0.968) 24 benzonitrile^ 4.21 322(1.05) 24 cyclohex-2-ene-l-one a 5.63 422(1.41) ~ 0.2 to 48 s 3-buten-2-one6 2.71 165 (0.678) 24 2,4-pentanedione0 3.51 271 (0.878) 24 2,5-hexanedione6 3.62 318 (0.905) 2 nitrobenzene^ 4.40 337(1.10) 0.5, 48 4-nitrobenzaldehydee 4.42 0.501 g (1.11) 24 propionic acid e 3.87 217 (0.968) 24 Chemicals obtained from: ( f l ) Aldrich,Eastman, ( c ) M C B , { d ) Merck, ( e ) Fisher, OT BDH. fe) Samples taken from 3 mL /"-PrOH solution at 10, 22, 30, and 42 min, and at 1, 2, 6, 12, 20, 40, and 48 h. 192 Chapter 7 references on page 211 Chapter 7 7.2.2 *H NMR Analysis of Reaction Mixture The majority of the reaction mixtures obtained from the transfer hydrogenation experiments were first analyzed by lH NMR spectroscopy to determine if any resonance signals corresponding to the desired hydrogenated product were present. NMR samples were prepared by diluting the organic components (i.e., substrate, product, /'-PrOH, acetone) of the reaction mixture in CD 3 OD (1 mL) (components obtained by vacuum distillation of a 1 mL aliquot of the reaction mixture). If traces of product were detected, then a determination of the parameters and machine settings required for analysis by GC was made. The *H NMR resonances characteristic of 14 substrate/product pairs are shown in Table 7.2, along with those of /-PrOH and acetone. Table 7.2 *H NMR Resonances of Substrate/Hydrogenated Substrate Pairs " Compound 'H Chemical Shift (ppm) Compound *H Chemical Shift (ppm) /-PrOH 1.15(d), 3.95(s), 4.92(s) 1-octene 0.9(m), 1.3(m), 2.0(m), acetone 3.30(qn), 4.78(s) 5.0(m), 5.5-6.2(m) 2-butanone l.l(t), 2.1(s), 2.5(qt) «-octane 0.9(m), 1.3(m) 2-butanol 0.9(s), 1.1(d), 1.2(d), 1.8(s), cyclooctene 1.5(d), 2.2(s, br), 5.5(m) 7.8(t) cyclooctane 1.5(s) , 3-buten-2-one 2.3(s), 5.9(qt), 6.4(t) 1,5-COD 2.5(s), 5.5(s) 2-pentanone 0.9(t), 1.3-1.8(qt), 2.2(s), 2.4(t) benzene 7.4(s) 2-pentanol 0.8-1.0(m, br), 1.2(d), 7.2(s), cyclohexane 1.35(s, br) 3.6-4.0(m) acetonitrile 2.04(s) acetophenone 2.7(s), 7.5(m), 8.0(m) ethylamine l.l(t), 1.65(8), 2.75(qt) 1-phenylethanol 1.4(d), 1.9(s), 4.6(qt), 7.3(s) benzonitrile 7.5-8.0(m) 1-heptanal 0.8(t, br), 1.5(s, br), 2.5(t), benzylamine 1.5(s),3.9(s), 7.3(s) 9.8(t) propionic acid 1.2(t),2.5(qt), 7.2(s) 1-heptanol 0.8(m), 1.5(s), 2.2(s), 3.5(t) propanol 0.9(qt), 1.5(sx), 3.1(s), 3.5(t) benzaldehyde 7.1-8.2(m) nitrobenzene 7.3-7.6(m), 8.0-8.2(dd) benzyl alcohol 1.8(s), 4.7(s), 7.3(s) aniline 3.6(s, br), 6.7(m), 7.1(m) { a ) Data obtained from the Aldrich Library of NMR Spectra (ref. 1); all spectra in CDC13 at r.t. 193 Chapter 7 references on page 211 Chapter 7 7.2.3 G C Analysis of Reaction Mixture All reaction mixtures that contained traces of product when analyzed by *H N M R spectroscopy were subsequently analyzed by GC to accurately determine percent conversions. A few of the reaction mixtures which had not been analyzed by *H NMR spectroscopy were also analyzed by GC, and all analyses were performed using the instrumentation described in Section 2.2.5. Accurate calculation of percent conversion values requires a high degree of resolution among the substrate, product, solvent, and acetone co-product peaks,2 and so the necessary machine settings were determined using authentic samples of the compounds. Of the 15 different reaction mixtures analyzed by GC, 11 different groups of machine settings were required and these are listed in Table 7.3, along with the retention time (tR) for the /-PrOH solvent; the machine settings used and the retention times for the substrate and product(s) of the 15 reaction mixtures are given in Table 7.4. Three GC runs were performed for each reaction mixture analyzed and a spread of approximately ± 0.4% conversion exists for all conversions reported in this Chapter. Table 7.3 GC Settings Used Group Oven Temp (°C) Injector & Detector Temp (°C) Pressure (kPa) tR /-PrOH (min) I 35 150 15 10.05 II 35 150 35 6.75 III 150 235 50 3.50 IV 100 190 50 3.33 V 150 220 50 3.33 VI 75 220 40 2.62 VII 35 150 20 6.23 VIII 100 220 108 1.77 IX 160 220 108 1.83 X 100 220 50 3.37 XI 220 220 108 1.98 194 Chapter 7 references on page 211 Chapter 7 Table 7.4 Settings and Retention Times (IR) for the Reaction Mixtures Analyzed by GC " Substrate Group IR Substrate Product tR Product(s) 2-butanone I 8.65 2-butanolb 14.02 2-pentanone II 7.45 2-pentanolc 16.00 acetophenone III 5.39 1-phenylethanol d 6.92 1-heptanal IV 4.18 1-heptanol d 7.65 benzaldehyde V 4.65 benzyl alcohol * 7.95 1-octene II 5.19 w-octane d 5.40 zraws-2-octene II 7.23 w-octane d 5.40 cyclooctene VI 6.16 cyclooctane6 6.71 1,5-cyclooctadiene VI 6.16 cyclooctene Vcyclooctanee 6.71/8.03 benzene VII 6.30 cyclohexane b 4.39 cyclohex-2-ene-1 - VIII 5.07 cyclohexanone ^/cyclohexanol^/ 3.34/4.46 one cyclohexen-l-ole 9.81 3-buten-2-one I 9.83 2-butanone 72-butanol6 8.65/14.02 2,5-hexanedione IX 2.55 2,5-hexanediol0 4.28 nitrobenzene X 19.1 anilinee 21.2 4-nitrobenzaldehyde XI 4.69 4-aminobenzaldehyde (4-AB) b 8.69 4-nitrobenzyl alcohol (4-NBA) b 17.57 4-aminobenzyl alcohol (4-ABA) b 19.43 ( a ) HP-17 20M column, He carrier gas, FID detection, tR given in units of min. Product samples obtained from:(b) Fisher, (c ) Eastman,{d) B D H , ( e ) Aldrich, w Mallinckrodt. 7.3 Results and Discussion 7.3.1 Transfer Hydrogenation of Ketones and Aldehydes 2-Butanone, 2-pentanone, acetophenone and 1-heptanal were reduced to the corresponding alcohols via the NiNa'P system (Figures 7.1-2, Table 7.5). O 4 OH Me-C-R + NiBr2, NaOH w 95 °C OH O Me-CH-R + Figure 7.1 Transfer hydrogenation of ketones; R = Et, n-Pr, Ph. 195 Chapter 7 references on page 211 Chapter 7 jl J T ^NiBf2, NaOH fc H ^ . R + II ^ \ 95 °C ^ ^ Figure 7.2 Transfer hydrogenation of aldehydes; R = n-hexyl [with benzaldehyde, benzyl alcohol was formed, but by the base-catalyzed Cannizzaro reaction]. Table 7.5 Percent Conversions for the Transfer Hydrogenation of Ketones and Aldehydes to the Corresponding Alcohols Substrate Trial a % Conversion (sampling time) 6 2-butanone /. Ni/NaOH 55.0 (2 h), 97.2 (24 h) ii. NaOH 8.4 (2 h), 18.5 (24 h) 2-pentanone iii. Ni/NaOH 31.0 (24 h), 99.9 (48 h) iv. NaOH 12.2 (24 h), 27.8 (48 h) acetophenone v. Ni/NaOH 50.1 (4 h), 99.4 (22 h) vi. NaOH 70.4 (4 h), 98.8 (22 h) 1-heptanal vii. Ni/NaOH 92.2 (4 h) viii. NaOH 83.0 (4 h) benzaldehyde ix. Ni/NaOH ~ 50 (0.5 h) X. NaOH -50(0.5 h) (°) "Ni/NaOH" represents the experiments run with NiBr 2 and NaOH, while "NaOH" represents the experiments run with only NaOH present. { b ) % Conversion to hydrogenated product. 2-Butanone was tested primarily because the data obtained could be used in conjunction with those obtained from experiments on the a /^j-unsaturated ketone 3-buten-2-one (Section 7.3.4). Only a minor amount of base-catalyzed hydrogenation occurs (trial ii) in comparison to the metal/base system (trial /') which promotes almost complete reduction to 2-butanol after 24 h. The activity exceeds that reported by Jothimony and Vancheesan who observed 20% conversion after 3 h using a [HFe3(CO)n]" (0.5 mM)/NaOH (1 M)//-PrOH system in what appears to be the only literature example for transfer hydrogenation of 2-butanone using /'-PrOH.3 With the 2-pentanone reduction, - 30% of base-catalyzed hydrogenation occurs (trial iv), while addition of NiBr 2 results in a tripling of the product yield (trial /'/'/', 48 h). The degree of hydrogenation attained by this system is not as great as that observed by Shibagaki and workers 196 Chapter 7 references on page 211 Chapter 7 (81% after 10 h) for the only other transfer hydrogenation of 2-pentanone using /'-PrOH that is reported in the literature (with granules of hydrous ZrO as the catalyst).4 With a change of substrate from aliphatic to an aromatic ketone, markedly different results are obtained. With acetophenone, the 4 h-activity observed for the base-only catalyzed system (trial v/') is superior to that observed for the metal/base system (trial v), implying inhibition by NiBr 2! Numerous papers have been published on acetophenone transfer hydrogenation from /'-PrOH and a paper by Barbaro et al. mentions about a dozen recent examples.5 Of seven papers published on this topic since 1987, three report rates of hydrogenation which are less than those observed with the NiNa'P system. As such, Shibagaki et al.4 obtained a conversion of 77% after 6 h with their granulated hydrous ZrO catalyst, Chowdhury and Backvall6 obtained a conversion of 75% after 6 h using a RuCl2(PPh3)3 (1 mM)/NaOH (24 mM) system, and Jothimony and Vancheesan3 achieved only 36% conversion after 3 h using [HFe3(CO)n]"(0.5 mM)/NaOH (1 M). The NiNa'P results can not, however, compete with the work of other groups. A remarkable paper by Puntener et al.7 details conversions of >95% and enantiomeric excess (e.e.) values ranging from 60-80% after 1.5 h at r.t. to 4 h at -14°C using a catalyst mixture of a chirally modified aminoferrocene (1 mM, see Appendix D.3) and [Ru(/?-cymene)Cl2]2 (0.25 mM) in the absence of base. Haack et al. obtained 98% conversion with 97% e.e. after 10 h using a [RuCl2(776-arene)]2 (0.5 mM)/KOH (1 mMy/'-PrOH/^^-TsDPEN (0.5 mM, see Appendix D.3) system,8 while Zhang's group report 72% conversion and 79% e.e. after 12 min using a [RuCl2(776-C6H6)]2 (1 mM)/NaH (30 mM)//-PrOH system with a chiral NPN-type ligand (see Appendix D.3).9 Gladiali and workers report 93% conversion and 31% e.e. after 1 h with [Rh(l,5-C0D)C1]2 (0.6 mM)/KOH (6 mM) and a chiral 1,10-phenanthroline ligand (1.2-15 mM, see Appendix D.3). 1 0 Previous work within our group on acetophenone using a [RhCl(l,5-hexadiene)]2 (5 mM)/KOH (25 mM)//-PrOH/(5)-AMSO (10 mM, see Appendix D.3) system gave 45% conversion and 63% e.e. after 10 h. 1 1' 1 2 Although six of the above examples utilize a base cocatalyst, only one paper reports performing blank runs with only base present (49% conversion of acetophenone after 8 h with metal/base vs. 7% with base-only).12 The ten-fold greater base-only conversion of acetophenone after 4 h in this current work (trial vi) may be due to the use here of - 0.5 M NaOH vs. 0.025 M K O H in the previously cited work.12 197 Chapter 7 references on page 211 Chapter 7 The results for 1-heptanal (Table 7.5) reveal that the metal/base system (trial vii) is only marginally more active than the base-only system (trial viii). The conversion to 1-heptanol is greater than that observed by Shibagaki and workers (93% after 6 h) with a granulated hydrous ZrO catalyst in the absence of base in what appears to be the only known publication describing the transfer hydrogenation of 1-heptanal using /-PrOH. 4 Benzaldehyde appears, by GC analysis, to be almost fully reduced to benzyl alcohol (BzOH) with, or without, NiBr 2 (trials ix and x) after 30 min. This insensitivity towards NiBr 2, however, suggests that the nickel is not involved in the reaction, hence reduction of benzaldehyde is likely occurring via the Cannizzaro reaction, whereby aldehydes that do not contain any a-hydrogen atoms undergo self-oxidation-and-reduction in the presence of concentrated alkali to yield the alcohol and a salt of the carboxylic acid.13 Sodium benzoate (not detectable by GC analysis) must thus also be present in equimolar amounts with BzOH, hence the conversion to BzOH is reported in Table 7.5 as ~ 50%. The conversion from this seemingly purely base-catalyzed system is far more rapid than that observed by Shibagaki et al.4 (98% after 6 h) for what appears to be the only report on transfer hydrogenation of benzaldehyde using /-PrOH as the hydrogen-donor (with granulated hydrous ZrO as the catalyst and in the absence of base). As an aside, it is interesting to note that Gordon and workers found that use of a household microwave oven versus an electric heating mantle for a RuCl(CO)(H)(PPh3)3/formic acid/benzaldehyde mixture resulted in an increase in turnovers to 6700/h from 890 for benzaldehyde hydrogenation.14 The influence of NiBr 2 in the reduction of acetophenone and 1-heptanal to the corresponding alcohols is also minimal or negative. The observed reduction can not result from the Cannizzaro reaction as these two compounds contain a-hydrogen atoms. 7.3.2 Transfer Hydrogenation of Unsaturated Hydrocarbons The unsaturated hydrocarbons 1-octene, /ra«s-2-octene, cyclooctene, 1,5-COD, and benzene were tested for conversion to the corresponding saturated hydrocarbons via the NiNa'P system as described in Section 7.2 (Figure 7.3, Table 7.6). 198 Chapter 7 references on page 211 Chapter 7 1-octene, OH O frans-2-octene, I NiBr2, NaOH w-octane cyclooctene + - 9 5 o c cyclooctane + 1,5-cyclooctadiene y j Figure 7.3 Transfer hydrogenation of alkenes to alkanes. Table 7.6 Percent Conversions for the Transfer Hydrogenation of Unsaturated Hydrocarbons to the Corresponding Saturated Hydrocarbons Substrate Trial ' Sampling Time (h) % Conversion 1-octene / . Ni/NaOH 0.5 99.9 ii. NaOH 0.5 0.0 zraws-2-octene iii. Ni/NaOH 0.5, 24 0.0, 0.0 iv. NaOH 0.5, 24 0.0, 0.0 cyclooctene v. Ni/NaOH 24 3.7 V/'. NaOH 24 0.4 1,5-cyclooctadiene vii. Ni/NaOH 24 0.24* viii. NaOH 24 0.0 benzene ix. Ni/NaOH 24 0.0 x. NaOH 24 0.0 See footnote (a) in Table 7.5. No cyclooctene detected. The NiNa'P system was remarkably active in transfer hydrogenation of 1-octene with complete conversion to w-octane attained after 30 min, while no hydrogenation was observed for the base-only system (Table 7.6). Gessner and Heesing15 have achieved homogeneous transfer hydrogenation of this substrate (22% conversion after 3 h) with RhCl(PPh3)3 (0.02 M) and 1,2-dihydronaphthalene as the hydrogen-donor, while Nishiguchi and co-workers report 47% conversion after 1 h at 90°C over Pd/C using indoline as the hydrogen-donor.16 Neither the metal/base or base-only system was active for hydrogenation of trans-2-octene. The same is so for cyclooctene with a maximum conversion of only 3.7% after 24 h. 199 Chapter 7 references on page 211 Chapter 7 An experiment was conducted under the same conditions as in trial (i), but using a 1:1 mixture of 1- and zra/?s-2-octene (0.173 M each); 27% conversion of 1-octene, and 0% conversion of /ra«s-2-octene to //-octane was observed. 1,5-Cyclooctadiene was not effectively converted to either cyclooctene or cyclooctane after 24 h using either the metal or metal-free system. Hanaoka et al. have achieved moderate success in photochemically catalyzed conversion of 1,5-COD to cyclooctane (18% at 6 h, 42% at 11 h) through the cyclooctene intermediate (82% at 6 h, 58% at 11 h) with a hydrogen-transfer system containing colloidal Rh generated photochemically from Rh4(CO)i2 and / -PrOH. 1 7 Benzene was tested as a substrate as interest remains high in hydrogenation of aromatics.18 One interest within our group and the pulp-and-paper industry is the hydrogenation of lignin aromatic moieties to eliminate the yellowing of paper products.19'20 Another application is the synthesis of ligands such as tricyclohexylphosphine (PCy3) by direct hydrogenation of PPh 3 . 2 1 The most common industrial processes for CeH; hydrogenation are conducted using Raney nickel or Ni /Al 2 0 3 catalysts,22 and there has been only limited success with homogeneous hydrogenation catalysts. A recent review (by Rothwell) on hydrogenation of aromatics details the use of niobium and tantalum hydrido aryloxide catalysts to hydrogenate a wide range of arenes and arylphosphines.18 Data for the current NiNa'P system were difficult to obtain. GC analysis can only be used to identify qualitatively cyclohexane formation because of minimal resolution between benzene and /'-PrOH (which have very similar boiling points: benzene, 80°C; /'-PrOH, 83°C). •H N M R spectroscopy does not give sufficient resolution between cyclohexane (5 1.35 br) and /-PrOH (8 1.20 br) signals to allow for calculation of conversion based on the integration of CeHs vs. CeHn resonances.  l H NMR spectroscopy can thus only be used to observe a relative decrease in the amount of benzene. 1 3 C NMR spectroscopy is also limited by similar resolution problems (8 C 6 H , 2 : 26.4, 8 /-PrOH: 24.2, br). In any case, the GC trace showed no cyclohexane, and the J H N M R spectrum of the reaction mixture after 24 h shows no changes from that of the original reaction mixture. Thus, no more effort was made to find a better analytical method. 200 Chapter 7 references on page 211 Chapter 7 7.3.3 Transfer Hydrogenation of Nitriles Neither acetonitrile nor benzonitrile undergoes any transfer hydrogenation via the NiNa'P system as described in Section 7.2. Indeed, there is no mention in the literature of transfer hydrogenation of nitriles, regardless of the hydrogen-source. Heterogeneous and homogeneous catalytic systems for H2-hydrogenation of nitriles are well documented.23"27 7.3.4 Transfer Hydrogenation of a,B -Unsaturated Ketones Two a;/i-unsaturated ketones (cyclohex-2-ene-l-one and 3-buten-2-one) were tested for reduction via the NiNa'P system as described in Section 7.2. Transfer Hydrogenation of Cyclohex-2-ene-l-one Possible hydrogenation products are cyclohexen-l-ol, cyclohexanone, and cyclohexanol (Figure 7.4). The initial GC results indicated that both the ketone and alcohol products were obtained (path ,4), and so a reaction profile was generated by analyzing samples taken over 10 min to 48 h (see Table 7.1, footnote g, and Appendix D.l) (Figure 7.5). A rapid conversion of cyclohex-2-ene-l-one to cyclohexanone, followed by reduction to cyclohexanol, is observed during the first hour of the reaction. Subsequently, a gradual partial conversion of the ene-one to alcohol is observed with trace amounts of ketone always present. There were no detectable traces of the path B intermediate cyclohexen-l-ol, implying that path A is followed exclusively, yet another example of the often observed hydrogenation of C=C bonds prior to C=0 bonds within a,/?-unsaturated ketones.28"31 The conversions after 48 h clearly demonstrate the superior activity of the metal/base system versus the base-only system (Table 7.7, trial /' vs. ii). Cyclohexen-l-ol Figure 7.4 Possible products from the transfer hydrogenation of cyclohex-2-ene-1 -one. 201 Chapter 7 references on page 211 Chapter 7 With NiBr2(PPh3)2/NaOH as the catalyst, the species distribution after 48 h was almost identical to that obtained using the NiBr 2 catalyst over 42 min, with the same degree (20%) of hydrogenation to alcohol (Table 7.7, iv vs. iii). Other data indicate that the addition of PPh 3 inhibits the rate of hydrogenation to alcohol by ~ 3V£ (Table 7.7, iv vs. i). The transfer hydrogenation of cyclohex-2-ene-l-one by RuCl2(PPh3)3 (1 mM)/NaOH (24 mMYz-PrOH has been reported by Chowdhury and Backvall6 to give 71% conversion to cyclohexanone and 29% conversion to cyclohexanol after 1 h, whereas the corresponding values in this current system are 9 and 35%, respectively. Table 7.7 Transfer Hydrogenation of Cyclohex-2-ene-1 -one a Species Present in the Reaction Mixture: Trial alcohol (%) ketone (%) ene-one (%) NiBr 2 /NaOH b 71 2 27 ii. NaOH b 16 4 80 iii. NiBr 2/NaOH c 20 19 61 iv. NiBr 2(PPh 3) 2/NaOH b 20 20 60 ( a ) No ene-ol detected.{b) After 48 h . ( c ) After 42 min. 0.0 0.5 1.0 1.5 2 0 5 10 15 20 25 30 35 40 45 50 Tuns(h) Time(h) Figure 7.5 Transfer hydrogenation of cyclohex-2-ene-1 -one by the NiNa'P system ( • = cyclohex-2-ene-l-one, 0 = cyclohexanone, O = cyclohexanol). 202 Chapter 7 references on page 211 Chapter 7 Transfer Hydrogenation of 3-Buten-2-One (methyl vinyl ketone, MVK) Possible hydrogenation products are shown in Figure 7.6. O 3-Buten-2-one pathB 2-Butanone OH 3-Buten-2-ol OH 2-Butanol Figure 7.6 Possible products from the transfer hydrogenation of 3-buten-2-one. After 24 h no GC peaks corresponding to any hydrogenated product were detected but there was a slight decrease (~ 0.4%) in the amount of substrate present. Coupled with the knowledge that this NiNa'P system readily catalyzes the reduction of 2-butanone to 2-BuOH (Section 7.3.1), this decrease in substrate led to an inquiry as to the fate of the M V K . Imai and co-workers had very low yields of «-butyl alcohol and w-butyraldehyde on attempting the transfer hydrogenation of 2-butenal (CH 3-CH=CH-CHO) with Ru(H)2(PPh3)4/ benzyl alcohol/CeHsBr in the absence of base; they reported that the "low conversion of 2-butenal may be due to the stabilization by resonance between C=C and C = 0 bonds and/or to the coordination [of 2-butenal] to Ru(H)2(PPh3)4 as a bidentate ligand blocking the coordination of hydrogen donor."32 The formation of a stable nickel metallacyclic complex with M V K (e.g., Figure 7.7) could thus account for the observed decrease in the amount of substrate present. NiBr2 + O NaOH,/-PrOH Br. Br V Figure 7.7 Plausible reaction of NiBr 2 with 3-buten-2-one to form a nickellacycle. 203 Chapter 7 references on page 211 Chapter 7 The formation of 7/"4-MVK transition-metal complexes is known and the preparation of M(/7 4-MVK) 3 (M = W, Mo) via reaction of M(CO) 3(MeCN) 3 with M V K in boiling hexanes is the first known example.33'34 Since then, Jia et al. reported Ru(triphos)(774-MVK) prepared from Ru(H)(BH4)(triphos), M V K , and pyridine in C6H„ (triphos = PhP(CH 2 CH 2 CH 2 PPh 2 ) 2 ), 3 5 Andersson et al. prepared a tetrameric Cu/rf-MVK complex by simply mixing M V K with CuCl in EtOH at -50°C, 3 6 Nesmeyanov et al. described reaction of M V K with Fe 3 (CO)i 2 in refluxing CeFLs to afford Fe(CO) 3(/7 4-MVK), 3 7 Kovalev et al. synthesized [Rh(PMe3)3(74-MVK)]Cl in solution from RhCl(PMe3)3 and M V K in acetone/MeOH,38 Deeming et al. observed an [Os3(H)(CO)9(MVK)] cluster where the M V K ligand was T^-bound to one Os nucleus,39 and Cenini et al. reported Pt(PPh3)2(774-MVK) prepared from Pt(PPh3)3 and M V K in hexanes.40 The synthesis of Ni(7/"4-MVK)(bipy) from Ni(Et)2(bipy) and M V K by Yamamoto et al. is the only known literature on aNi(7 4 -MVK) complex.41 A "stoichiometric" reaction was also conducted with 540 mg of NiBr 2 (2.47 mmol), 200 uL of M V K (2.46 mmol), and 32.8 mg of NaOH (0.82 mmol) in refluxing /-PrOH (25 mL) for 3h under N 2 . Analysis of the reaction solution by TLC (Figure 7.8) reveals an unidentified product along with the spots corresponding to 2-butanone, 2-BuOH, and trace amounts of the M V K substrate. Based on the attempted catalytic hydrogenation of M V K , the formation of the reduced products was unexpected, and GC analysis revealed the presence of both 2-butanone and 2-BuOH (and also acetone co-product). An aliquot of the reaction solution (minus NaOH and NiBr 2 components, see Section 7.2.2) was analyzed by lH NMR spectroscopy in CDC13 (Figure 7.9) and found to contain resonances corresponding to 2-butanone and 2-BuOH, the unidentified product being insoluble. There seems to be complete conversion of the substrate under "stoichiometric" conditions to semi- and fully-hydrogenated products. No attempts have been made to characterize the insoluble product. The results from these experiments conducted under "catalytic" vs. "stoichiometric" conditions suggest that the excess of substrate used in the former case results in all of the Ni present being bound up in an inactive form (i.e., as a Ki/rf-MVK complex), hence no hydrogenation of M V K occurs; lack of excess substrate in the latter case allows some Ni to remain available as "free Ni" catalyst, hence the observed hydrogenation of M V K . 204 Chapter 7 references on page 211 Chapter 7 unidentified product (nickellacycle ?) • • • • • a b e d Figure 7.8 Thin-layer chromatogram (CH 2 Cl 2 /MeOH 95:1) of: (a) the stoichiometric NiBr 2 /MVK reaction mixture solution, (b) M V K , (c) 2-butanone, (d) 2-BuOH. i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 i • 1 1 1 i 1 • 1 1 i 1 1 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 ppm Figure 7.9 *H NMR spectrum (CDC13) of the reaction mixture obtained from the stoichiometric reaction of NiBr 2 with M V K . Peak assignments: 2-butanone a, b, e; 2-BuOH c, d,f, g; O H signal not seen at 8 7.8. /-PrOH peaks removed by digital subtraction of the FED of /-PrOH/CDCl3 from the FED of the reaction mixture. Smith and Maitlis have reported transfer hydrogenation of M V K to 2-butanone (52% conversion after 5 h at 150°C) using [(Cp*Rh)2(^-OH)3]Cl (5 mmol), with MeOH as the hydrogen-donor,42 while Beaupere et al. observed a corresponding reduction (~ 30% conversion after 15 min) using RhH(PPh3)3 (0.01 M) with 1-phenylethanol as the hydrogen-donor at 4 0 ° C . 4 3 205 Chapter 7 references on page 211 Chapter 7 7.3.5 Transfer Hydrogenation of Diketones The diketones 2,4-pentanedione and 2,5-hexanedione were tested as substrates for hydrogen transfer reduction via the NiNa'P system, (e.g., Figure 7.10). O H O H I I Q Q O H H 3 C - C H - ( C H 2 ) „ - C H - C H 3 N II NiBr 2,NaOH H 3 C - C — ( C H 2 ) „ - C - C H 3 + A. = ^ \ 95 °C y - „ (n = 1, 2) H 3 C - C H - ( C H 2 ) „ - C - C H 3  c O H 0 1 0 Figure 7.10 Transfer hydrogenation of diketones. With 2,4-pentanedione, both with the NiNa'P and NaOH-only system, white crystalline needles precipitated out during reactions. Characterization by melting point (222-225°C) suggested that deprotonation of an a-hydrogen of 2,4-pentanedione by NaOH may have occurred to yield sodium acetylacetonate (see Figure 7.11), which is white and crystalline with a melting point of 2 3 0 ° C . 4 4 This identity was confirmed by elemental analysis (Anal. Calcd for CsH 7 0 2 Na: C, 49.19; H, 5.78%. Found: C, 49.47; H, 5.77%), J H NMR (CD 3OD) (5 2.05 s, br, 6H, C H 3 ; 5 2.25 s, 1H, CH) (lit. 5 2.05 s, 2.25 s),1 and 1 3 C NMR (CD 3OD) (5 26.6 s, C H 3 ; 5 101.5 s, CH; 5 193.6 s, C = 0 ) (lit. CDC13, 5 24.8, 101.1, 192.6).45 Formation of the green trans-[Ni(acac)2(H20)2] (m.pt. 228°C) 4 4 ' 4 6 is ruled out. The GC trace of the reaction mixture showed no peaks, thus suggesting complete conversion of 2,4-pentanedione to the Na salt. .Na. NaOH • H /-PrOH + H 2 0 H Figure 7.11 Formation of sodium acetylacetonate in basic media. Complete reduction of the dione to the diol (S,S, e.e. >99%) using [RuCl2(PPh3){(5)-biphemp}] (0.5 mmol, see Appendix D.3) with 100 atm H 2 at 50°C for 15 h in the absence of base has been reported, along with use of the same catalyst in transfer hydrogenation of this substrate to the diol both in the presence and absence of an unspecified base with /'-PrOH. 4 7 206 Chapter 7 references on page 211 Chapter 7 With 2,5-hexanedione as substrate, no GC peaks corresponding to 2,5-hexanediol or 5-hydroxy-2-hexanone were observed, but conversion to a product (28% for the metal/base system and 20% for the base-only system) with tR 9.35 min was seen. This peak corresponds to what is presumably the aldol condensation product 5-methyl-5-undecen-2,7,10-trione (Figure 7.12) (see Appendix D.2). Figure 7.12 Formation of 5-methyl-5-undecen-2,7,10-trione from 2,5-hexanedione. Matsushita and co-workers also observed aldol condensation while attempting transfer hydrogenation of various ketones and aldehydes over hydrous zirconium oxide, but complete suppression of this undesired reaction and formation of high yields of the desired alcohol products was obtained by supporting the zirconium catalyst on silica.48 Brunner et al. were able to obtain modest yields of the diol (20%) and 5-hydroxy-2-hexanone (58%) with a heterogeneous, NaBr-modified, Ni system with H 2 . 4 9 7.3.6 Transfer Hydrogenation of Miscellaneous Functional Groups The transfer hydrogenation of nitrobenzene, 4-nitrobenzaldehyde, and propionic acid by the NiNa'P system was attempted. Aliquots of the product mixture obtained from the experiments with nitrobenzene and propionic acid were found to contain J H N M R signals characteristic of a reduced product in only the former case (aniline). GC results for the mixtures from the two nitro-containing substrates (Figures 7.13, 7.14) are shown in Tables 7.8 and 7.9. O O O 207 Chapter 7 references on page 211 Chapter 7 Transfer Hydrogenation of Nitrobenzene Figure 7.13 Transfer hydrogenation of nitrobenzene to aniline. Table 7.8 Percent Conversions for the Transfer Hydrogenation of Nitrobenzene to Aniline Trial 3 % Conversion (sampling time) 6 i. Ni/NaOH 14.1 (0.5 h), 19.2 (48 h) ii. NaOH 4.0 (0.5 h), 14.0 (48 h) { a ) A b ) See footnotes (a) and (b) of Table 7.5. The results shown in Table 7.8 reveal that the initial activity of the metal/base system is more than triple that of the base-only system. However, after 48 h, the conversions to aniline of both systems are similar with a maximum of ~ 20%. No other products (aside from the acetone co-product), such as azobenzene (PhN=NPh) or azoxybenzene (PhN(0)=NPh), were observed in the GC traces. Early work on nitrobenzene hydrogenation includes Knifton's use of RuCl 2(PPh 3) 2 (3 mM) 5 0 or Fe(CO)3(PPh3)2 (2 mM) 5 1 with 80 atm H 2 at 130°C in 1:1 (v/v) CeHe/EtOH with K O H (0.14 M) to afford 100% PhN0 2 conversion to either 96% (after 45 min)50 or 87% aniline (after 8 h).5 1 More recently, under only 1 atm H 2 , Belousov et al. attained 22% conversion to aniline after 5 h with Re 2(//-S) 2L 8 (4.5 mM; L = CI, H 2 0 , thiourea) in DMF at 100°C. 5 2 Sariego et al. used the transfer hydrogenation system [Rh(NBD)L2]+ (40 mM)//-PrONa (20 mM)//-PrOH (L = PPh3, P(p-tol)3) to afford complete reduction to aniline, azoxybenzene, and azobenzene (70, 18, and 12% selectivity, respectively) after 16 min.53 Reviews by Bulatov et al.54 and Downing et al. 55 cover more recent work on homogeneous nitroaromatic hydrogenation. 208 Chapter 7 references on page 211 Chapter 7 Transfer Hydrogenation of 4-Nitrobenzaldehyde OH N 0 2 (4-NB) NiBr2, NaOH 95 °C O. / = \ HO / = \ HO ) " ^ - ^ H H ^ \ _ y ~ ™ ° 2 H H ^ V ^ f + A C 6 t 0 n e 4-aminobenzaldehyde 4-nitrobenzyl alcohol 4-aminobenzyl alcohol (4-AB) (4-NBA) (4-ABA) Figure 7.14 Transfer hydrogenation of 4-nitrobenzaldehyde to observed products. Table 7.9 Transfer Hydrogenation of 4-Nitrobenzaldehyde to Various Products' Species Present in the Reaction Mixture: b Trial 4-ABA (%) 4-NBA (%) 4-AB (%) 4-NB (%) i. Ni/NaOH 10.5 21.9 5.5 62.1 ii. NaOH 3.6 7.4 1.5 87.5 ( a ) 24 h reaction time. ( ) See Figure 7.14 for abbreviation definitions. As benzaldehyde is effectively (50%) reduced, even by base alone via the Cannizzaro reaction (Section 7.3.1), and nitrobenzene is reduced to some degree by the NiNa'P system, 4-nitrobenzaldehyde was used as a substrate for potential transfer hydrogenation. The GC results (Table 7.9) reveal that the partially reduced products 4-NBA and 4-AB and the fully reduced product 4-ABA were obtained. The activity of the metal/base system is about triple that of the base-only system in terms of the production of 4-NBA, 4-ABA and 4-AB (the product distribution obtained in the two trials is similar). Some production of 4-NBA could result in conjunction with sodium-4-nitrobenzoate from the Cannizzaro reaction (Section 7.3.1), the salt not being detectable by GC. Transfer hydrogenation reactions must also be occurring within this NiNa'P/4-NB system, however, as the observed reduction of the N 0 2 group in 4-NB and 4-NBA 209 Chapter 7 references on page 211 Chapter 7 to the N H 2 group in 4-AB and 4-ABA, respectively, can not proceed via the Cannizzaro reaction. The detection of acetone further supports a hydrogen transfer mechanism. Note that the N O 2 group has a negative effect upon reduction of the CHO fragment as the reaction mixture (trial /) is comprised of - 68% RCHO species after 24 h whereas 50% "reduction" of PhCHO to PhCH 2 OH was observed after only 30 min (Table 7.5). The CHO group does not appear to have much effect upon the reduction of the N O 2 group, as 16% of the reaction mixture is comprised of R N H 2 species after 24 h (trial /'), while ~ 19% of PhN0 2 has been converted to PhNH 2 (Table 7.8, trial /') after 48 h. The literature on nitroaromatic hydrogenation is substantial.54'55 Nevertheless, only one report was found on nitrobenzaldehyde hydrogenation and this work describes autoclaving a mixture of 2-nitrobenzaldehyde and Raney Ni in MeOH at 60°C under 8.4 atm H 2 for 5 h to afford 97.7% conversion to 2-aminobenzyl alcohol.56 Of note, 4-nitroacetophenone can be chemoselectively transfer hydrogenated to the nitro-alcohol by a RuCl2(PPh 3) 2/HCOOH/NEt3 system, whereas H2-hydrogenation by RuCl2(PPh 3) 3 yields the amino-ketone.55 Transfer Hydrogenation of Propionic Acid No reduction of 2-propionic acid was observed. Organic acids are normally reduced to the corresponding alcohols via more conventional methods (i.e., reduction with LiAlFL,) and no reports on transfer hydrogenation of propionic acid were found. A few examples of H2-hydrogenation are known in the patent literature. Kitson and Williams report hydrogenation of propionic acid in the vapor phase to w-PrOH at elevated temperatures and H 2 pressures over a Pd/Re catalyst on a carbon surface,57 while Moy employed CuO on a ZnAl204 support at 275°C and 34 atm H 2 . 5 8 A patent by Maki et al. mentions the hydrogenation of propionic acid over Z r 0 2 with H 2 at 3 5 0 ° C . 5 9 Bianchi et al. achieved 75% conversion of propionic acid (220 mmol) to various products (10% «-PrOH) with a Ru4(H)4(CO)8(PBu3)4 catalyst (0.02 mmol) and 130 atm of H 2 at 200°C for 48 h. 6 0 There is a substantial body of literature on the hydrogenation of acid anhydrides.61 210 Chapter 7 references on page 211 Chapter 7 7.4 Conclusion The NiBr2/NaOH/z'-PrOH system has been shown to promote catalytically the transfer hydrogenation of 2-butanone, 2-pentanone, and 1-octene at rates which are both useful (i.e., ~ 99 % after 48 h) and significantly greater than those obtained by the base-only catalyzed system. The selective hydrogenation of 1-octene over trans-2-oc\ene, was observed. A certain amount of hydrogenation was also seen for cyclohex-2-ene-l-one and 4-nitrobenzaldehyde at rates greater than that of the base-only system. The system under investigation displayed activity similar to that of the base-only system in the hydrogenation of acetophenone, 1-heptanal, and benzaldehyde and the slow hydrogenation of nitrobenzene. Note, however, that the reduction of benzaldehyde to BzOH must occur via the Cannizzaro reaction and not transfer hydrogenation. Experiments with 2,4-pentanedione resulted in the conversion of the substrate to sodium acetylacetonate while tests with 2,5-hexanedione resulted in formation of the aldol condensation product and not the desired diol. No activity was observed in the attempted catalytic hydrogenation of trans-2-octene, cyclooctene, 1,5-cyclooctadiene, benzene, acetonitrile, benzonitrile, propionic acid or 3-buten-2-one. 7.5 References 1. Pouchert, C. 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