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Expansion of the Guerbet Reaction towards group 7 metal catalysts and triglyceride substrates

King, Ashley 2021. Expansion of the Guerbet Reaction towards group 7 metal catalysts and triglyceride substrates. PhD Thesis, Cardiff University.
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This thesis aims to expand the application of the Guerbet reaction towards both new catalysts and substrates. The Guerbet reaction is used to generate longer chain alcohols from their shorter chain analogues through borrowed hydrogen chemistry; the hope being that these long-chain alcohols can find use as both renewable fuels and synthetic lubricants. Substrate scope expansion focussed primarily on triglycerides and methyl esters, as these could be hydrogenated to the corresponding alcohol before Guerbet chemistry was employed. This represented a simple and quick route to the functionalisation of cheap, naturally occurring chemicals. The ruthenium-PNP complex, RuMACHO, showed particularly high activity for this reaction as it was able to catalyse both the hydrogenation and Guerbet step, allowing for a ‘2- step-1-pot’ production of β-methylated alcohols. As such, a variety of different triglycerides, including the readily available coconut oil, have been investigated. Research into the direct coupling of long-chain linear alcohols has also been undertaken, these can be used as synthetic engine oils or be functionalise further to produce surfactants. For this process, a rutheniumdiphosphine bis-chelate complex was found to be most effective with high conversions and moderate yields recorded. Expansion of catalyst scope was centred around investigating the under-utilised group 7 metals for Guerbet chemistry. Investigations focussed on the well-studied production of isobutanol from methanol and ethanol. Here, manganese complexes bearing diphenylphosphinomethane (dppm) ligands were found to be effective over 90 h run times. Substitution of the dppm backbone with electron donating substituents was found to increase catalytic activity. Rhenium complexes bearing both bidentate and tridentate ligands were also tested and broadly showed greater activity than their manganese analogues with shorter run times of 16 h required. Finally, ruthenium half-sandwich complexes bearing ortho substituted dppm ligands were examined, with the hope that this would help stabilise the catalyst under reaction conditions.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 25 October 2021
Last Modified: 03 Aug 2022 01:40

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