New Polyoxometalate Photocatalysts for C-H Functionalisation Reactions

Lead Research Organisation: University of Nottingham
Department Name: Sch of Chemistry

Abstract

Using light to drive chemical reactions via photocatalysis has emerged as a powerful method in the effort to develop greener, more sustainable chemical synthesis. Decatungstate, a photoactive polyoxometalate (POM) compound, has shown great promise as a photocatalyst in organic chemistry as it avoids the use of precious metals common in similar catalysts and is able to mediate a variety of valuable C-H functionalisation reactions. It has also shown applicability in the late-stage functionalisation of complex molecules, which is an emerging strategy for enabling highly efficient derivatization of bioactive molecules.

Despite the interest in and development of decatungstate-mediated H-atom transfer reactions in recent years, there are a number of drawbacks to its use. This photocatalyst is only active in ultraviolet light, which has practical limitations in organic synthesis, and C-H bond selectivities in complex molecules can be limited. These drawbacks need to be mitigated in order to further broaden the scope of this promising catalytic system. Despite the enormous diversity of POM compounds reported in the literature, decatungstate remains the only one in use as a C-H functionalisation photocatalyst in organic chemistry. There is therefore significant scope to further explore the application of POMs as photocatalysts in organic chemistry.

Proposed solution and methodology

The design and synthesis of various 'hybrid' polyoxometalate structures, which have organic ligands attached to the POM cluster, has been investigated extensively by the Newton group. These compounds have similar photochemical characteristics to decatungstate and may therefore be amenable to similar C-H activation chemistry, but with greater tunability due to organic modifications. These organic modifications may allow the energy levels of the POM cluster to be modified to allow for activity in visible light, or allow the addition of supramolecular binding elements that exert greater control over reaction selectivity. These possibilities will investigated in this PhD project.

Previously, tuning of the metal cluster's HOMO / LUMO levels has been demonstrated using phosphonate linkages between the POM and organic ligand. This work will be expanded by designing and synthesizing a range of novel hybrid POM structures that will be fully characterised using a range of techniques including NMR, cyclic voltammetry and UV/Vis spectroscopy. The major goal of the project is to demonstrate the applicability and practicality of hybrid POMs as C-H activation catalysts, and the new catalysts will be therefore be tested in a range of photochemical reactions with the aim over overcoming some of the drawbacks of decatungstate. Alongside this, further novel chemistry using decatungstate will also be explored to expand the scope of this promising photocatalyst.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S022236/1 01/10/2019 31/03/2028
2284777 Studentship EP/S022236/1 30/09/2019 30/09/2029 Elliot Smith