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Title: Titanium and zirconium permethylpentalene chemistry : ethylene polymerisation and small molecule activation
Author: Fraser, Duncan
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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Chapter One provides an introduction to the chemistry of pentalene and its derivatives encompassing ligand synthesis, organometallic chemistry, and in particular ethylene polymerisation. In the second half, cationic polymerisation is introduced encompassing both main-group and transition-metal initiated polymerisations. The limitations of cationic ethylene polymerisation are highlighted. Chapter Two describes the synthesis of a series of related complexes based on the Pn*MCpR(X) motif for application as ethylene polymerisation catalysts. The products are characterised by NMR spectroscopy, single crystal X-ray diffraction, elemental analysis and, where relevant, EPR spectroscopy. Chapter Three details the application of aforementioned Pn*MCpR(X) complexes as ethylene polymerisation catalysts, tested in solution co-catalysed by methylaluminoxane, and in the slurry phase, immobilised on a variety of inorganic supports. Very high activities are observed for the zirconium congeners of this non-classic polymerisation motif, with the Cp ligand observed to affect activity more dramatically than the "X" ligand. Chapter Four gives an account of mechanistic investigations examining the activity of the Pn*MCpR(X) catalysts. Pre-catalyst activation studies implicate the formation of cationic derivatives, which are rationally synthesised. The unexpected activity of [Pn*ZrCp]+ towards ethylene polymerisation is investigated by in-situ gas uptake measurements and small molecule activation studies, which do not readily accommodate a coordination-insertion mechanism. An alternative cationic initiation mechanism is proposed and explored. Chapter Five describes the synthesis of titanium and zirconium hydride and deuteride complexes. Using either LiAlH4/D4 or H2/D2 as the hydrogen source, trimetallic hydride clusters are synthesised. Preliminary investigations into their reactivity with small molecules is presented. Chapter Six details the synthesis of reduced permethylpentalene titanium complexes. Chlorine atom abstraction, scrambling of the Pn* ligand, and dinitrogen activation was observed depending on the nature of the reducing agent and the stoichiometry employed. Chapter Seven provides experimental details and characterising data for the complexes presented in the preceding five chapters.
Supervisor: O'Hare, Dermot Sponsor: SCG Chemicals
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemistry, Inorganic ; Pentalene ; Permethylpentalene ; Ethylene ; Polymerisation ; Mechanism