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Exploring new directions in homogeneous catalytic (De)hydrogenation chemistry

Latham, Daniel 2022. Exploring new directions in homogeneous catalytic (De)hydrogenation chemistry. PhD Thesis, Cardiff University.
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Abstract

This two-part thesis describes the exploration and development of new routes towards hydrogen transfer chemistry. Initial research focussed on metal-catalysed borrowing hydrogen catalysis, resulting in the development of a one-pot iron-catalysed conversion of allylic alcohols to α-methyl ketones. Overall, this process is referred to as isomerisation-methylation and offers a much greener approach than the one previously known one-pot procedure. The reaction was promoted by a bench stable iron(cyclopentadienyl) complex and employed methanol as alkylating agent. A good substrate scope was exhibited, providing >25 examples up to 84% isolated yield. Mechanistic experiments provided evidence for plausible reaction intermediates and an iron-hydride species in the catalytic process. Other miscellaneous borrowing hydrogen processes were given attention, with an aim to discover further useful and interesting transformations catalysed by earth abundant metal complexes. Firstly, the reactivity of primary allylic alcohols was examined to determine the plausibility for a new route towards δ-methylation using archetypal conditions. Various transformations were observed based on the structural features of the allylic alcohol substrates. Secondly, the regioselective ring opening of terminal epoxides was examined employing various hydrogen donors. A promising result leading to the selective formation of secondary alcohols has the potential to form the basis of a more comprehensive study. Employing methanol as hydrogen donor resulted in the formation of various β-methoxy alcohols. Finally, enantioselective hydrogenation of prochiral substrates, promoted by chiral Frustrated Lewis Pairs (FLPs), was investigated. A range of chiral Lewis bases were tested in combination with Lewis acidic boranes for molecular hydrogen activation and subsequent enantioselective hydrogenation. Attempts were also extended to inverse FLP catalysis, with efforts to synthesise weak Lewis acidic boranes and chiral superbases, to catalyse the same transformation. While some key literature reactions were able to be replicated, the strategy to adopt a chiral phosphine was not effective, nor was a revised strategy employing other chiral Lewis bases.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 17 May 2022
Last Modified: 17 May 2022 15:26
URI: https://orca.cardiff.ac.uk/id/eprint/149815

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