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Title: Impact of phosphorus ligand modification on transition metal coordination and homogeneous carbonylation catalysis
Author: Tay Wei Peng, Dillon
ISNI:       0000 0004 9357 0263
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2020
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Subtle changes in phosphorus ligand structure have been known to lead to significant changes in metal-ligand coordination behaviour and subsequent catalytic performance. A combination of both experimental and computational techniques has been employed to study the influence of phosphorus ligand modification on its coordination behaviour and performance in homogeneous olefin carbonylation. The gem-dialkyl effect (also known as the Thorpe-Ingold effect) can be applied to C3-bridged bis(diphenylphosphine) ligands via geminal substitution of two alkyl groups (R) on the central carbon of the C3-bridge. Structurally, the gem-dialkyl effect has been observed to distort 6-membereded chelates formed in diphosphine-palladium(II) chloride complexes from a chair (R = H) to a half-chair (R = Me, Et, iPr) and eventually to a twist-boat (R = tBu) conformation. In terms of catalytic performance, the gem-dialkyl effect favours reductive hydroformylation to directly produce alcohols from olefins during palladium catalysed hydroformylation. The gem-dialkyl effect has also been observed to hinder isomerisation and promote reaction rate in palladium catalysed methoxycarbonylation of terminal olefins. Modification of the C2-linker from ethylene to phenyl in diphobane ligands has resulted in a dramatic shift in chemoselectivity from alcohols to aldehydes in palladium catalysed olefin hydroformylation. The competition between hydroformylation and alkoxycarbonylation in palladium catalysed olefin carbonylation has also been tuned by introducing substituents (X) on phenyl-bridged diphobanes to favour aldehyde (X = H), alcohol (X = OMe, OMe) or ester (X = CF3) products respectively. The testing of a series of ligands in ruthenium catalysed tandem reverse Water-Gas Shift-hydroformylation-reduction of olefins to alcohols has shown that bidentate ligands and higher monodentate ligand-to-metal ratios favour olefin hydrogenation. The choice of solvent has also been found to play a crucial role as high CO2 pressures at reaction conditions can expand the solvent, alter its physical properties and thus influence catalytic activity.
Supervisor: Britovsek, George ; van Meurs, Martin Sponsor: Agency for Science, Technology and Research, Singapore
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral