Synthesis, Structures and Reactivities of Sterically Hindered A^-Functionalized Transition Metal Alkyl Complexes by Hung Kay LEE A thesis submitted to the Chemistry Division, Graduate School, The Chinese University of Hong Kong in partial fulfilment of the requirements for the degree of Doctor of Philosophy 1995 Thesis Committee: Dr. Kevin W.-P. LEUNG (Supervisor) Dr. Wai-Kee LI Prof. Thomas C.W. MAK Prof. Michael F. LAPPERT (External Examiner, University of Sussex) Prof. Chi-Ming CHE (Additional External Examiner, University of Hong Kong) ‘(9^ k 12 fsi^sj Table of Contents page Table of Contents i Acknowledgements vi Abstracts vii Abbreviations ix CHAPTER L GENERAL INTRODUCTION 1.1 A Brief Review on the Background of Organometallic Chemistry 1 1.2 Stability of Organotransition Metal Complexes 2 1.3 Decomposition Pathways of Transition Metal a Hydrocarbyls .. 5 1.4 Preparation of Transition Metal a-Alkyl Complexes 10 1.5 A Survey on the Use of Functionalized Alkyl and Aryl Ligands in Synthesis of Transition Metal a-Hydrocarbyls 15 L6 2-(TrimethyIsilyl)methyIpyridine (3) and 2-Bis(trimethylsilyl)- methylpyridine (4) as Ligand Precursors 20 1.7 A Brief Review of Previous Results on Synthesis of Metal Alkyl Complexes Using (1) and (2) as Ligands 23 1.8 Objective of This Work 28 L9 References for Chapter I 29 CHAPTER IL SYNTHESIS, STRUCTURES AND REACTIVITY OF IRON(n) AND COBALT(n) DIALKYL COMPLEXES II.l Introduction II.l.l Synthesis of Iron(II) and Cobalt(II) Alkyl Complexes .. 34 ILLl.l Iron(II) Alkyl Complexes 34 II.l.1.2 Cobalt(II) Alkyl Complexes 41 II. 1.2 Reactions of Transition Metal Alkyl Complexes with Protic Reagents and Halogens 45 11.1.3 The Chemistry of Transition Metal Alkoxides and Thiolates 一 A Brief Review 48 IL2 Results and Discussion 11.2.1 Synthesis of Homoleptic Iron(II) and Cobalt(n) Dialkyl ‘ Complexes [M {<：：识乂63)2。5_-2} 2] (M 二 Fe 55，Co 56) 51 11.2.2 Attempted Reaction of [FeCl2(PPh3)2] with [{R2Li}2] . 52 11.2.3 Attempted Synthesis of Monoalkyliron(n) Complexes .. 53 i 11.2.4 Synthesis of Homoleptic Iron(II) and Cobalt(II) Dialkyl Complexes [IS^{(CHSiMe3)C9H6N-8}2] (M = Fe 57, Co 58) 54 11.2.5 Molecular Structures of [M{C(SiMe3)2C5H4N-2}2] (M =Fe 55，Co 56) and [Co{(CHSiMegjCgHsI^-Sh] (58) 56 11.2.6 Spectroscopic and Magnetic Properties of Compounds 55-58 63 11.2.7 Electrochemistry of [Co(R2)2] (56) and [Co(R3)2 (58) ^ 66 11.2.8 Reactivities of [M{C(SiMe3)2C5H4l^-2}2] (M = Fe 55， Co 56) 70 11.3 Experimentals for Chapter II 83 11.4 References for Chapter II 86 CHAPTER m. SYNTHESIS AND STRUCTURES OF DIALKYL COMPLEXES OF NICKEL(n) AND PALLADIUM(n) III. 1 Introduction III. 1.1 Nickel(II) Alkyl Complexes 一 A General Survey . 91 III.1.1.1 T]^-Cyclopentadienylnickel Alkyl and Aryl Complexes 91 III.LI2 Nickel Dialkyls 96 III. 1.2 Palladium(II) Alkyl Complexes — A General Survey 99 III. 1.2.1 Palladium Dialkyls 99 IILl 22 Cyclopalladated Compounds 101 IIL2 Results and Discussion IIL2.1 Synthesis of Nickel(n) Alkyl Complexes 104 1112.1.1 Reactions of [{R^Li(Et20)}2] and [{R^Li}】] with Nickelocenes — Synthesis of 77 ^ - Cyclopentadienylnickelalkyl Complexes (78-80).. 104 1112.1.2 Synthesis of the Substituted Nickelocene [Ni{ri^- C^Hs(SiMes)2}2] (SI) 106 I 11.2.1.3 Spectroscopic Properties of Compounds 78-80 ... 107 ii Ill2.1.4 Molecular Structures of [(rj 5 - C^H^)Ni{C(SiMes)2C^H4N-2}] (78) and [{(”、 C^H^)Ni{CH(SiMes)C^H4N-2}}2] (80) 110 III2.L5 Reactions of [{R^Li}2] with NiCl】 and [NiCliL〗] (L2 = TMEDA, 2PPhs) — Synthesis of Nickel Dialkyl Complex [Ni{C(SiMe^)2C5_-2}2] (82) 115 III2.1.6 Molecular Structure of [Ni{C(SiMe^)2C^H4N- 2} 2] (S2) 118 111.2.1.7 Spectroscopic Properties of [Ni(C(SiMes)2C5H4N-2}2] (82) 121 111.2.1.8 Electrochemistry of [Ni{C(SiMes)2C5H4N-2}2] (82) 122 1112.1.9 Reactivities of N.i[C(SiMe姊(82) ... 124 in.2.1.10 Reactions of [{RZU}:] with [NiCl2(diphos)] [diphos = 1,2-bis(diphenylphasphino)ethane] ... 125 in.2.1.11 Molecular Structure of [Ni{C(SiMe^)2C5H4N' 2} {5-(2，-C^H4NC(SiMes)2C3H4N-2 - CH(SiMes)2}Cl] (83) 127 III2 J.12 Reactions of [{R^Li(Et20)}2] and [R^Li] ['R^ 二 -CH2C5H4N-2] withNiCl2 and [NiCl2L2] (L2 二 TMEDA, 2PPhs) 130 III2.1.13 Molecular Structure of [{CH(SiMes)C^H4N- V2] (S6) 136 111.2.2 Synthesis of PaUadium(II) Alkyl Complexes ... 139 III22.1 Reactions of [{R^Li}〗] with [PdXiL〗](L = PPh^, Et2S; X = Cl，Br) — Synthesis of [Pd(R2)2] (88) and [Pd(R^)(PPhs)X] [X 二 Cl 89, Br 90] 139 III.2 2 2 Molecular Structures of Compounds [P'd{C(SiMes)2C 5H 4N-2}2] (8 8)， [Pd{C(SiMes)2C5H在2}(PPhs)Cl] (89)，and [Pd{C(SiMes)2C^H4N-2}(PPhs)Br] (90)…… 140 III.2 2 3 Spectroscopic Properties of Compounds 88-90 146 III.22 A Electrochemistry of [P'd(C(SiMes)2C5H4N-2}2] (88) 147 11• • 1I III22.5 Studies on Stereospecificity of the Reactions between [{R^Li}】] and [PdX2(PPh如]= CI, Br) 150 HI.2.2.6 Attempted Synthesis of [Pd(Rl)2] and [Pd(Rl)(PPhs)Cl] 152 111.2.2.7 Attempted Synthesis of [(Pd(R^)Cl}2] via Intramolecular C-H Activation 153 III.22.8 Molecular Structure of [{CH(SiMe3)2C^H4N- 2}2PdCl2} (91) 154 in.3 Experimentals for Chapter III 157 III.4 References for Chapter III 155 CHAPTER IV. SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF ZIRCONIUM(IV) AND HAFNIUM(IV) ALKYL COMPLEXES IV. 1 Introduction 169 IV. 1.1 Homoleptic and Heteroleptic Complexes 170 IV. 1.2 Organo-Zirconium(IV) and -Hafnium(IV) Compounds Containing Functionalized Alkyl Ligands 177 IV.2 Results and Discussion IV.2.1 Synthesis of Zirconium(IV) and Hafnium(IV) Dialkyl Dichloride Compounds [M(R2)2C12] (M 二 Zr 103, Hf 104) 181 IV.2.2 Attempted Synthesis of Titanium(IV) Alkyl by the Reaction of TiCl4 with [{R2Li}2] 182 IV.2.3 Attempted Synthesis of Zirconium(IV) and Hafnium(IV) Alkyls with "R 1 [= -CH(SiMe3)C5H4N-2] as Ligand 182 IV.2.4 Molecular Structure of [Zr{C(SiMe3)2C5H4N- 2}2Cl2] (103) 183 IV.2.5 Spectroscopic Properties of [W{C(SiMe3)2C5H4N- ’ 2}2Cl2] (M = Zr 103, Hf 104) 187 IV.3 Experimentals for Chapter IV 188 IV.4 References for Chapter IV 190 iv CHAPTER V. COMPARISON OF BONDING PARAMETERS AMONG METAL ALKYL COMPLEXES WHICH CONTAIN ALKYL LIGANDS -R2 193 References for Chapter V 201 APPENDIX I A. General Procedures 202 B. Physical and Analytical Measurements 202 APPENDIX II Magnetic Moment Measurements 205 APPENDIX III Table A-1. Selected Crystallographic Data for Compounds 55, 56, 58，and 63 207 Table A-2, Selected Crystallographic Data for Compounds 78, 80, 82 and 83 208 Table A-3. Selected Crystallographic Data for Compounds 86, 88, 89 and 90 209 Table A-4. Selected Crystallographic Data for Compounds 91 and 103..… 210 V Acknowledgements I wish to express my deepest gratitude to my supervisor, Dr. Kevin W.-P. Leung, for his invaluable guidance, continuous enthusiasm and encouragement throughout the course of my work and the preparation of this thesis. I would also like to thank Prof. Thomas C.W. Mak, Prof. Z.-Y Zhou, Prof. J.C. Wang, and Prof. B.-S. Luo for their skillful determination of crystal structures. I am indebted to Prof. Sunney 1. Chan and Dr. Wai-Kee Li for very useful discussions and suggestions. Thanks also go to Mr. Y.H. Law，K.W. Kwong, and Ms. W.P. Chung for their assistance in measuring all mass spectra and some ^H and ^^C NMR spectra. Financial support from the Chinese University of Hong Kong in the form of Postgraduate Studentship is gratefully acknowledged. December, 1994 Hung Kay LEE Department of Chemistry The Chinese University of Hong Kong .) . VI Abstract The work presented in this thesis focuses on two areas: (1) synthesis and characterization of A^-functionalized transition metal alkyl complexes by employing sterically demanding ligands, and (2) studies on the reactivities of these metal alkyl complexes towards protic reagents such as phenol and thiophenoL Chapter 1 begins with a brief introduction to the general background of organometallic chemistry. Decomposition pathways and common synthetic methods for organo-transition metal compounds are briefly discussed. A brief review of previous results on the synthesis of metal alkyl complexes involving the bulky A^-functionalized alkyl ligand "R^ = -C(SiMe3)2C5H4N-2 concludes Chapter 1. Chapter 2 describes synthetic and structural studies leading to novel homoleptic iron(n) and cobalt(II) dialkyl complexes [M(R")2] ["R^ = -C(SiMe3)2C5H4N-2，M = Fe (55)，Co (56); -R3 = -CH(SiMe3)C9H6N-8，M = Fe (57)，Co (58)]. Complexes 55， 56 and 58 have been fully characterized (including X-ray diffraction studies). Cyclic voltammetry of 56 and 57 is also reported. In addition, reactivities of complexes 55 and 56 towards a variety of protic reagents and Lewis bases have also been studied. Compound 55 reacts with the bulky thiophenol ArSH (Ar = 2’4,6」Bu3C6H2) and the bulky phenol Ar^eOH (ArMe = 4-Me-2,6」Bu2C6H2) to give the corresponding neutral monomeric iron(II) dithiolate [Fe(SAr)2(R^H)] (63) and diaryloxide [Fe(OArMe)2(R2H)] (66), respectively. A free molecule of R^H was found to be bound intact to the iron(II) center through iV-coordination.