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Coversheet for Thesis in Sussex Research Online A University of Sussex PhD thesis Available online via Sussex Research Online: http://sro.sussex.ac.uk/ This thesis is protected by copyright which belongs to the author. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Please visit Sussex Research Online for more information and further details Synthesis of Novel N- Heterocyclic Carbene- Palladium Complexes and Their Catalytic Activity Daniel P. Guest Supervisor Dr O. Navarro Submitted to the University of Sussex in part fulfilment of the requirements of the degree of Doctor of Philosophy, January 2017 i Declaration I hereby declare that the work presented in this thesis was carried out at the University of Sussex under the supervision of Dr O Navarro between the dates of September 2012 and April 2016. The work presented in this thesis is my own, unless otherwise stated, and has not been submitted in whole or in part form for award of another degree. Daniel P. Guest ii Acknowledgements Firstly I would like to thank Prof. John Spencer for his guidance and constant enthusiasm throughout my Ph.D, also Dr. Oscar Navarro, my supervisor. I would like to thank my fellow research group members past and present Chris Gallop, Irene Malenda, Melvin Ansell and Jose Gascon for their help, support and friendship in the laboratory, which made the Ph.D. a more enjoyable experience. I would like to thank Adam Close, Tom Moore, Oran O'Doherty, Hayley Rand, Gavin Roffe, Rhiannon Jones, Katie Duffell, Jess Dwyer and Dave Neil-Hall for their general support, camaraderie and close friendship. I would like to thank the staff within the chemistry department at University of Sussex. In particular Paul Andrews and Alex Burns for both tolerating my mess in their office when writing up and being generally excellent human beings. Dr. Alaa Abdul-Sada for performing mass spectrometry measurements, Dr. Iain Day for guidance and consultations with NMR spectroscopy. The EPSRC National Mass Spectrometry Service of the University of Swansea and National X-Ray Diffraction Units of the University of Southampton are acknowledged for carrying out HRMS measurements and X-ray crystallographic measurements. I would like to thank my upper school science teacher, Dr J. Maple, for igniting my interest in science, showing how fun and interesting chemistry can be. Last, but by no means least, I would like to thank my family: Mum, Dad, my brother Oliver, grandparents Anna & Ron, and my partner Gemma, for their love and unconditional support throughout this process. iii List of Symbols and Abbreviations OAc acetate, CH3CO AcOH acetic acid, C2H4O2 Bu butyl, C4H9 COD 1,5-Cyclooctadiene CMD concerted metalation deprotonation Cy cyclohexyl d deuterated DCM4 dichloromethane, CH2Cl2 DEA diethylamine, C4H11N DFT density functional theory DME dimethoxyethane, C4H10O2 DMF dimethylformamide, C3H7NO Dppp 1,3-Bis(diphenylphosphino)propane Et ethyl, CH2CH3 equiv equivalent EtOAc ethyl acetate, C4H8O2 EtOH ethanol, C2H6O h hour IPr 1,3-Bis(2,6-Diisopropylphenyl)imidazol-2-ylidene IPr* 1,3-bis[2,6-bis(diphenylmethyl)-4- methylphenyl]imidazole-2-ylidene IMes 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene IPent 1,3-bis(2,6-Di-3-pentylphenyl)imidazol-2-ylidene Me methyl, CH3 MeCN acetonitrile, C2H3N MeOH methanol, CH3OH NHC N-heterocyclic carbene NMR nuclear magnetic resonance iv PEPPSI pyridine enhanced pre-catalyst preparation stabilisation and initiation Ph phenyl, C6H5 py pyridine, C5H5N SIMes 1,3-bis(2,4,6-trimethylphenyl)imidazolidene SIPr 1,3-Bis(2,6-diisopropylphenyl)imidazolidene r.t. room temperature T temperature TBAB tetrabutylammonium bromide TBAC tetrabutylammonium chloride NBu4(OAc) tetrabutylammonium acetate TEA triethylamine, C6H15N THF tetrahydrofuran, C4H8O tol tolyl 4-MeC6H4 ν frequency δ chemical shift σ sigma v Abstract Chapter 1: Gives the reader a background on carbenes paying particular attention to N- heterocyclic carbenes (NHCs). The chapter describes NHC’s electronic and structural properties and their behaviour as ligands. The recent usage of NHC-palladium complexes as catalysts for cross-coupling reactions is explored. Chapter 2: Provides a background on NHC-palladium complexes bearing N-donors as throwaway ligands, highlighting the importance of throw-away ligands on catalytic activity. The chapter describes the preparation of a number of novel NHC-palladium complexes bearing throw-away ligands and the activity of (IPr*)PdCl2(TEA) in Buchwald-Hartwig aminations is explored. Chapter 3: Provides a background on the Mizoroki Heck reaction, focusing on the importance of charged intermediates in the process. Then reviews the current development of anionic NHC-palladium complexes in the literature. An account of the discovery and preparation of novel [(NHC)PdCl3[TBA] complexes and the catalytic activity of [(SIPr)PdCl3[TBA] in Mizoroki-Heck coupling reactions is given. A plausible Amotore-Jutand type mechanism is proposed which is supported by DFT calculations provided by research collaborators. Chapter 4: Provides a background on C-H activation reactions catalysed by palladium compounds with particular focus on acetoxylation reactions. The chapter describes the synthesis of [(NHC)PdCl2X][Y] complexes including the development of [(IMes)PdCl2OAc][TBA] and its performance in acetoxylation reactions. A proposed mechanism for the reaction of [(IMes)PdCl2OAc][TBA] is discussed, using experimental observations. vi Contents 1 Introduction ..................................................................................................................... 1 1.1 Carbenes .................................................................................................................... 1 1.2 Electronic Effects of Substituents on Carbene Multiplicity ..................... 2 1.2.1 Inductive Effects ........................................................................................................ 2 1.2.2 Mesomeric Effects ..................................................................................................... 3 1.3 Steric Effects of Substituents on Carbene Multiplicity .............................. 6 1.4 Persistent Singlet Carbenes: Synthesis and Stability ................................ 6 1.4.1 Phosphinosilyl and Phosphinophosphonio Carbenes ................................. 7 1.4.2 Acyclic Amino Carbenes .......................................................................................... 9 1.4.3 N-Heterocyclic Carbenes ...................................................................................... 11 1.4.4 Cyclic Diphosphinocarbenes ............................................................................... 15 1.4.5 Cyclopropenylidene Carbene .............................................................................. 17 1.5 Bonding of NHCs to Metal Centres ................................................................. 18 1.5.1 Nature of the NHC-metal bond ........................................................................... 18 1.5.2 Abnormal carbenes ................................................................................................. 20 1.5.3 Tuning electronic effects of NHCs as ligands ................................................ 21 1.5.4 Steric impact of NHC ligands ............................................................................... 23 1.6 (NHC)-Palladium Complexes used in Cross Coupling Reactions ........ 27 1.6.1 Suzuki-Miyaura Cross-Coupling ........................................................................ 29 1.6.2 Negishi Reaction ...................................................................................................... 34 1.6.3 Buchwald-Hartwig Aminations .......................................................................... 35 1.6.4 Hiyama Coupling ...................................................................................................... 37 1.6.5 Sonogashira Coupling ............................................................................................ 39 1.6.6 Heck-Mizoroki Cross-Coupling .......................................................................... 42 1.6.7 Kumada-Corriu Cross-Coupling ......................................................................... 45 1.7 References ............................................................................................................. 46 2 N-Donors as Throw-away Ligands ........................................................................ 52 2.1 Background ........................................................................................................... 52 2.1.1 (NHC)PdCl2(Py) complexes ................................................................................. 53 2.1.2 (NHC)PdCl2(Im) complexes ................................................................................. 61 2.1.3 (NHC)PdCl2(TEA) complexes .............................................................................. 62 vii 2.2 Discussion and Results ...................................................................................... 64 2.2.1 Synthesis of novel (NHC) palladium complexes with N donors as throw away ligands. .............................................................................................................................
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