Group 11 N-heterocyclic carbenes : synthesis, characterisation and catalytic applications
Abstract
As part of a worldwide effort to develop efficient catalysts for use in organic
chemistry and in the synthesis of highly valuable molecules, work performed during
the course of my stay in St Andrews has focused on the design and synthesis of new
group 11 metal complexes for their applications in catalysis. The aim of this work
was to develop new, active and stable, easy to synthesise group 11 complexes and
investigate their catalytic activity as well as to try to understand their mode of action.
Two different types of complexes were explored in order to develop more active
catalysts: the neutral N-Heterocyclic carbene metal complexes and the cationic
derivatives. More than 20 new catalysts were developed and their reactivity studied in
different catalytic reactions.
New hydroxide and tert-butoxide copper(I) or silver(I) complexes were developed
and compared to the common NHC metal systems. Overall, the neutral NHC-metal
catalysts showed to be highly active in a broad range of applications: in the
methylation of amines using CO₂ as a C1 source, in a multicomponent reaction (A³ coupling) and in dual catalysis (hydrophenoxylation). Additionally, mechanistic
studies were undertaken to obtain a greater understanding of these transformations
and to possibly lead to the design of new generations of catalyst.
Regarding the cationic NHC metal complexes, a straightforward methodology was
developed leading to a library of highly stable catalysts. Bis-NHC, mixed NHC/phosphine as well as NHC/pyridine species were efficiently synthesised using thermal
or microwave heating, in high purity and yields. In addition, the effect of the presence
of two different or identical ligands on catalytic reactivity was investigated in the 3+2
cycloaddition and in the alkynylation of ketones.
Insight into the catalytic cycle was obtained via mechanistic studies. These showcased
the release of one ligand during the catalytic cycle and the crucial role of this ligand
displacement in generating the catalytically relevant active species.
The results highlight the importance of understanding the reactivity of catalyst in
order to develop new and improved ones.
Type
Thesis, PhD Doctor of Philosophy
Rights
Creative Commons Attribution-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nd/4.0/
Embargo Date: 2022-03-17
Embargo Reason: Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 17th March 2022
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