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Title: Alkali metal alumiate chemistry : advances in hydroelementation catalysis
Author: Pollard, Victoria Alison
ISNI:       0000 0004 7972 262X
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2018
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Applying main group compounds, especially aluminium hydride complexes, as catalysts for hydroelementation reactions is gaining momentum. This project develops the application of heterobimetallic lithium aluminates to the catalytic regime. Five lithium aluminates of general formula (HMDS)₂Al(H)₂Li(donor)x, 1 - 6, were prepared and characterised by X-ray crystallography and multinuclear NMR spectroscopy. Subsequently, 1 - 6 were applied as catalysts for hydroboration of aldehydes and ketones. An alkali metal effect was observed upon changing the donor at lithium, indicating that lithium plays a role in catalysis. A catalytic cycle is proposed whereby the carbonyl substrate is initially hydroaluminated; then the boronic ester product forms, with regeneration of the lithium aluminium hydride complex. A postulated intermediate, (HMDS)₂Al(μ-OCH₂Ph)₂Li(THF)₂, 8, was isolated and characterised. A comparative study between charged bimetallic lithium aluminate complexes and neutral monometallic aluminium counterparts was undertaken. Lithium aluminates were generally observed to exhibit superior catalytic reactivity for hydroboration of aldehydes,ketones, imines and alkynes. A novel catalyst initiation pathway was uncovered for precatalyst iBu₂Al(TMP) via β-hydride transfer from iso-butyl ligands, generating the characterised aluminium benzyloxide complex, [(TMP){Ph₂(H)CO}Al{μ-OC(H)Ph₂}]₂, 15.The reactivity of aluminium compounds towards boranes was examined, to try to uncover potential aluminium catalyst decomposition pathways. Novel structures were crystallographically characterised resulting from cleavage of a B - O bond in pinacolborane resulting in a new aluminium complex. Less active catalytically than the parent aluminium complex, this represents a possible catalyst decomposition product. Finally, the concept of lithium aluminate hydroelementation catalysis was extended to hydrophosphination, representing the first reported example of aluminium catalysed hydrophosphination of alkynes, alkenes and carbodiimides. The active catalyst, lithiumaluminium phosphide, iBu₃AlPPh₂Li(THF)₃, 22, was successfully isolated. Analysis of the reaction mechanism by kinetic studies shows that this reaction is inhibited by excessphosphine. Moreover, postulated intermediates were identified via stoichiometric reactions,and their reactivity probed, further supporting the mechanism proposed.
Supervisor: Mulvey, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral