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S TU D IE SOF Pt METALCOMP LE XESW IT H LIG

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S TU D IE SOF Pt METALCOMP LE XESW IT H LIG 1. STUDIES OF Pt METAL COMPLEXES W ITH LIGANDS CONTAINING C, Si, Ge and Sn. By Victor Christou B.Sc., A.R.C.S.. A thesis submitted in partial fulfilment of the requirements for the awards of Doctor of Philosophy of the University of London and Diploma of Imperial College Inorganic Chemistry Laboratories, Department of Chemistry, Imperial College of Science,Technology and Medicine, London SW7 2AY. December 1990. Mum -for all the times I promised to go home but never quite made it - This is what I was doing Jbergekumene tsores iz gut tsu dertselyn . Troubles overcome are good to tell. — Yiddish Proverb. 4. A bstract. In order to evaluate the influence of N-donor ligands in neopentylplatinum(II) reactivity, a series of heteroaromatic N-donor complexes, Pt(CH2CMe 3 )2L2 , has been prepared by ligand displacement from the corresponding diene complex Pt(CH2CMe3)2(nbd). These complexes have been fully characterised by and 13C N.M.R., infrared and electronic spectroscopy. In homogeneous solution, the phenanthroline complexes are thermolytically inert to temperatures in excess of 120*C, whereupon they decompose gradually via a complex series of competing or sequential steps generating metallic platinum {inter alia). In contrast, at 90*C, Pt(CH2CMe3)2(bipy) generates an insoluble oligomeric bipyridylplatinum complex, concomitant with formation of neopentane. The nature of this product is discussed and compared with other similar bipyridylplatinum(II) species. The effect of substituent electronic effects on the rates of reductive arene elimination during metallacyclisation of neophylpladnum is also studied, using a range of mixed aryl-neophylplatinum complexes, Pt(CH2CMe2Ph)(4-C6H4R)L2 [R = H, CH3, lBu, CF3]. The most suitable ancillary ligand for this reaction is triphenylphosphinee, although corresponding triethylphosphine and 2,2'-bipyridyl derivatives have also been synthesised and fully characterised. Triphenylphosphine derivatives invariably rearrange to form &/r-phosphineplatinaindans and CgH4R exclusively. Detailed study of these elimination reactions by 31P N.M.R. show first order kinetic characteristics. Kinetic isotope effects and activation parameters for the rearrangement are reported and a mechanistic pathway where dissociation of one phosphine ligand is an essential, but non rate-limiting, step is proposed. It is shown that electron withdrawing groups retard the rate of rearrangement, whereas, electron donating groups facilitate cyclometallation relative to R = H. From the activation parameters it appears that the transition state resembles the reaction product more than the parent complex. When L is triethylphosphine, thermolysis of the sample results in the formation of three new species; in addition to platinaindan, cis- and rratts-&/s-(aryl)platinum species are observed. Formation of all products is a first order process, as is decay of the parent; Pt(CH2CMe2Ph)(C6H5)(PEt3). It is postulated that all products occur from the same intermediate. Studies of PtCCI^GeMe^L^ [L = PPh3, PPh2Me] show that this complex undergoes (3-Ge-C bond activation to form, via an 0i2-germene)platinum intermediate, the complex Pt(CH2GeMe2CH2GeMe3)(Me)L2. This species has been characterised by !H, 13C and 31P N.M.R. spectroscopy. An ADEPT study provides conclusive proof of Ge-C connectivity. Thermolysis of Pt(CH2SnMe 3 )2 (PPh 3 )2 does not result in formation of Pt(CH2SnMe2CH2SnMe3)(Me)(PPh3)2, but produces several organotin species which are shown to occur via (r|2-stannene)platinum type intermediates. Similarly, Pt(CH2GeMe3)2(cod) is thermolytically unstable at temperature above 60°C, resulting in formation of carbogermane products which are postulated to occur via (T|2-germene)platinum intermediates. The study of the reaction preferences of various silicon substituted alkyl and arylplatinum species is also reported. Reaction preferences depend heavily upon the ancillary ligand. When L is a monodentate phosphine Pt(CH2SiMe2Ph)(Ph)L2 rearranges readily at 100°C and forms an asymmetric trinuclear platinum cluster as the major reaction product, in stark comparison to the cyclometallation reactions of its carbon bearing analogue. If is a bidentate phosphine , such as dppe, rearrangement is reluctant even at 180°C and no evidence for cluster formation is seen. Thermolysis of Pt(SiMe3)2(dcpe) at 180°C in benzene results in formation* of carbosilane species with 1 - 4 Si atoms. These species have been characterised by G.C./M.S. and are purported to occur by a complex series of intra- and intermolecular rearrangements. 6. Acknowledgments. Firstly I would like to thank Brent for his excellent support and supervision during the three years of my PhD. His introduction to the subtleties of postgraduate life, the informal atmosphere he encouraged in the group and the wonderful group outings, all made working with him a pleasure. The receipt of awards from the Science and Engineering Research Council and the Society of Chemical Industry is gratefully acknowledged. I would also like to thank all the members of the GBY group past and present, particularly Bemadeta, Katie, Rob, Steve, Dave, Pan Yi, Andy and Mike, who saved my sanity in the last few days of the preparation of this thesis; members of the GW group and other resident of the sixth floor, particularly Andreas, Phil, Chih, Caroline, Niki, Jon, Danny, Peter, Simon and Penny, other people at college including Fitzy, Yogi, Paul, the two "crazy French chicks" and Edie who brightened up my day...literally. I am extremely grateful to Dick Shepherd and Sue Johnson for all their N.M.R. assistance. Without the help of Dick this thesis would never have been completed and I’m sorry for all the late nights of work I made him endure. Thanks also to Roger Tye for G.C./M.S. measurements and John Bilton for useful discussions. The technical assistance of Colin Robinson and Roger Lincoln has been greatly appreciated. Out of college I would like to thank Monisha, Sarah, Agent, Angie and Tony for making me laugh, Jenny for all the culture she has given me and Neill for being a scally; everyone at Andrews Restaurant, for housing and feeding me for the past five years especially the chefs, Maria (for tirelessly running up and down the stairs for my phone calls) and Rita "for the crack". Also I would like to thank Bill Mason and all the other people at the boat club, especially Joey and Russell and the Villas Boys and Girl, where I whiled away most of my "free time". Thanks for all the blisters. I would like to thank Sara for her friendship over the last year and for starting her thesis a month earlier than I did, thereby encouraging me to start writing. Not a moment too soon! Colin, Giles and Matilda also deserve a mention for their friendship and tales of far flung distant places which have given me itchy feet. A special mention must go out to the "Losers Club", Brian, Vahe, Robin and Greg. Their friendship at college over the past three years has certainly made all the difference to the time I've spent as a postgraduate. Stefan also, whose constant encouragement during the last few weeks of this thesis spurred me on. I've finished now. I must also mention my family, my mum for being so understanding and supportive and my brother Chris whose impeccable musical taste has annoyed so many people in the chemistry department and whose money lending capacity knows no bounds. Thanks also to Andrew whose friendship has lasted all my time at university and who has certainly made my life outside college much more entertaining and cosmopolitan than it otherwise would have been. Thanks to Primo Levi for the quote, Bob and Maree for buying such lovely bread on the Isles of Scilly and encouraging me to drop hives full of bees and Debbie and John for cooking vegetarian Christmas dinners. Finally I would like to thank Sally most of all, for all her support during the most difficult times of the last three years and for being there. Cheers! s. Contents. Page. Abstract. 4 Acknowledgements. 6 Contents. 8 List of Figures. 12 List of Schemes. 15 List of Tables. 17 Abbreviations. 19 SECTION ONE: Distal C-H Bond Activation. 21 CHAPTER 1: Introduction 22 CHAPTER 2 Synthesis and characterisation of &/s-(neopentyl)platinum(II) complexes with bidentate heteroaromatic nitrogen donor ligands. 32 2.1. Synthesis of 6/.y-(neopentyl)platinum(n) complexes with nitrogen donor ligands. 33 2.2. Conventions. 33 2.3. Spectroscopic studies of Z?/5-(neopentyl)platinum(II) complexes with nitrogen donor ligands. 34 2.3.1 !H N.M.R. Spectroscopy. 34 2.3.2 13C N.M.R. Spectroscopy. 36 2.3.3 Infrared Spectroscopy. 42 2.3.4 Electronic Spectroscopy. 42 2.4. Experimental. 44 2.4.1 General. 44 2.4.2 Syntheses. 44 CHAPTER 3: Synthesis and characterisation of neophyl(aryl)platinum(II) complexes with phosphorus and nitrogen donor ligands. 48 3.1. Syntheses of neophyl(aryl)platinum(II) complexes with phosphorus 49 and nitrogen donor ligands. 3.2. Conventions 49 3.3. Spectroscopic studies of neophyl(aryl)platinum(II) complexes. 50 3.3.1 *H N.M.R. Spectroscopy. 50 3.3.2 13C N.M.R. Spectroscopy. 56 3.3.3 31P N.M.R. Spectroscopy. 62 9. Page. 3.3.4 Infrared Spectroscopy. 63 3.4. Experimental. 64 3.4.1 General. 64 3.4.2 Syntheses. 64 CHAPTER 4: Mechanisms of rearrangement of some neophyl and neopentylplatinum(II) complexes. 70 4.1. Introduction. 71 4.2. Results and discussion. 74 4.2.1 Mechanistic studies of 6fr-(neopentyl)platinum(II) complexes with N-donor ligands. 74 4.2.2 Mechanistic studies of c/.s-neophyl(aryl)(2,2'-bipyridyl)- platinum(II). 76 4.2.3 Mechanistic studies of ris-neophyl(aryl)-Z?/s-(triphenylphosphine)- platinum(II).
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