Cooperative Lewis pairs in small molecule activation and dehydrocoupling of amine- and phosphine-boranes

This thesis contains a diverse body of work based around the theme of Lewis acid/base chemistry. The reactivity of classical Lewis adducts, such as amine- and phosphine-boranes, has been investigated in addition to the more nascent field of frustrated Lewis pairs (FLPs). Chapter 1 contains a brief overview of the concept of Lewis acidity and basicity whilst also providing a survey of previous work relevant to this thesis. Chapter 2 reports a novel, modular synthetic route to intermolecular Zr/P FLPs with varying steric and electronic properties. The reactivity of these pairs with a plethora of small molecules has been assessed (H2, C02, Phenylacetylene, THF) and is found to be directly related to both the steric and electronic character of the Lewis acid and base employed. The results contained in Chapter 3 build. on those in Chapter 2. by applying the intermolecular Zr/P FLPs as catalysts for the dehydrocoupling of amineboranes. Initial insights into the mechanism of these dehydrocoupling reactions are also provided. Chapter 4 describes preliminary investigations into new directions for the field of transition metal FLP chemistry. Expansion of the intermolecular FLP paradigm to include alternate Lewis acids (Ti(IV) and Ti(III)) and Lewis bases (N-heterocyclic carbenes (NHCs)) has been attempted. Furthermore previously reported intramolecular ZrlP FLPs are shown to be active catalysts for the dehydrocoupling of primary and secondary phosphine-boranes. Finally Chapter 5 details an alternative approach to the synthesis of amine-borane dehydrocoupling products via the deprotonation of amineboronium cations and related species. This methodology has allowed for the synthesis of poly(N-methylaminoborane) in the absence of a transition metal catalyst, whilst also permitting the study of highly reactive primary aminoboranes (RNH=BH2, R = Me or Bu).