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    Chiral ‘Frustrated Lewis Pair’ systems for practical enantioselective hydrogenation and hydrosilylation

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    The chemistry of ‘Frustrated Lewis Pairs’ (FLPs) has been the subject of intense investigation for over a decade now, this activity following the seminal report of Stephan et al. concerning the use of a system capable of reversibly binding hydrogen gas in the absence of a transition metal.1 The explosive development in the field was marked by the discovery of numerous systems which display FLP reactivity and engage in small molecule activation and catalytic reactivity, most notably hydrogenation. To a lesser extent, enantioselective versions of such transformations have also been reported. Perhaps the major limitation which deterred extensive investigation in this area has been the challenging synthesis required to assemble chiral catalysts. This thesis presents efforts towards the development of practical FLP systems for enantioselective hydrogenation and hydrosilylation as follows: Chapter 1 surveys the development of the FLP field, with notable developments in terms of structure, reactivity, and mechanistic understanding being covered. Particular attention is given to enantioselective FLP catalysts and to the work carried out for elucidating mechanisms of chirality transfer. Chapter 2 describes the development of NHC-stabilised borenium ions as catalysts for the FLP hydrogenation and hydrosilylation of N-alkyl ketimines, a poorly explored substrate class. Chapter 3 describes the synthesis of a chiral stannylium ion equivalent and investigations into its catalytic ability in the hydrogenation reaction. Chapter 4 describes the use of BINOL-derived phosphate salts as Lewis bases in FLP hydrogenation.Open Acces
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