Evaluation of two- and three-coordinate copper(I) NHC complexes as photocatalysts
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Date
14/06/2023Author
Supervisor
Grant ID
EP/L016419/1
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This thesis explores the design, synthesis, optoelectronic properties, and photocatalytic testing of copper(I) complexes with a two- or three-coordinate geometry bearing N-heterocyclic carbene
ligands. Our design strategies aim to avoid the failings of four-coordinate copper(I) complexes
which are prone to Jahn-Teller distortion in the excited state.
The first chapter provides an overview of the fundamental photophysical properties of transition
metal complexes and an introduction to bimolecular energy and electron transfer processes. A
mini-review of Earth-abundant photocatalysts is presented. Special attention will then be devoted
to describing the design principles of copper(I) based photocatalysts (PCs). We begin by
describing the photophysical and electrochemical properties of four-coordinate copper(I)
complexes, followed by the design and applications of copper(I) complexes as PCs. Next, we
provide a summary of the development of two- and three-coordinate copper(I) complexes,
describing their photophysical properties and applications.
Chapter 2 describes the synthesis, characterisation and optoelectronic properties of seven three-coordinate copper(I) N-heterocyclic carbene (NHC) complexes bearing N^N ligands, of the form of [Cu(IPr)(N^N)]PF₆ (where IPr is 1,3-Bis(2,6-diisopropylphenyl)imidazolium, and N^N is phen = 1,10-phenanthroline, bpy = 2,2’-bipyridine, dpa = 2,2’-dipyridylamine, mdpa = N-methyl-2,2’-dipyridylamine, dpym = di(pyridin-2-yl)methane, phdpym = 2,2'-(phenylmethylene)dipyridine, fludpym = 2,2'-(9H-fluorene-9,9-diyl)dipyridine). Six complexes
underwent successful preliminary photocatalytic testing in two mechanistically distinct
photocatalysis reactions: an Atom Transfer Radical Addition (ATRA) photoinduced electron
transfer (PET) reaction between an alkyl halide and an alkene; and photoinduced energy transfer
(PEnT) reaction of a vinyl azide to a vinyl nitrene, which subsequently rearranges to form a
pyrrole. The complex [Cu(IPr)(phen)]PF₆ performed best in the ATRA reaction (77% NMR
yield) out of six complexes tested, while complex [Cu(IPr)(phdpym)]PF₆ performed best in the
PEnT reaction (59% NMR yield vs 66% obtained with [Cu(dmp)(BINAP)]BF₄).
Chapter 3 reports the synthesis, characterisation and optoelectronic properties of a series of three-coordinate copper(I) NHC complexes bearing a dpa ligand, of the form [Cu(NHC)(dpa)]PF₆.
Three complexes underwent preliminary photocatalytic testing, however their performance as
PCs was poor.
Chapter 4 reports the first example of a neutral linear two-coordinate Cu(I) complex
Cu(IPrBIAN)(Cz) bearing an IPrBIAN NHC ligand, and after investigation of its optoelectronic
properties, it was successfully applied as a PC in a proof-of-concept PET ATRA reaction (52% NMR yield). Cu(IPrBIAN)(Cz) also exhibited interesting dual emission properties in solution;
this is seen as separate emission depending on excitation source for most solvents, and is
especially strong in chloroform solution. The synthesis, characterisation, and optoelectronic
properties of further derivatives of this complex bearing 3,6-substituted carbazolate ligands were
also investigated.
The final conclusions chapter summarises the results of each chapter and brings focus to the
overarching aims and themes of the thesis. This chapter identifies key areas for future work in the field of two- and three-coordinate copper(I) complexes as photocatalysts, specifically the need to improve PC stability, investigate reaction mechanisms, and correlate structure-property relationships with photocatalytic performance. A need for standardisation of photocatalysis reaction set-ups is identified as a requirement for reproducibility of results within the field of photocatalysis.
Type
Thesis, PhD Doctor of Philosophy
Rights
Creative Commons Attribution-NonCommercial 4.0 International
http://creativecommons.org/licenses/by-nc/4.0/
Embargo Date: 2025-01-18
Embargo Reason: Thesis restricted in accordance with University regulations. Restricted until 18th January 2025
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