Catalytic photo-induced oxygen atom transfer using metal oxo complexes

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Background: There is a clear need to develop processes that minimise the consumption of limited energy resources and reduce waste detrimental to the environment. In this context, photocatalysis is showing much promise since it allows light energy to be harnessed to drive catalytic reactions via electron or energy transfer. A fundamental chemical reaction that underpins many processes, both in nature and in industry, is oxygen atom transfer. In principle, the cleanest sources of oxygen atoms are water and air. However, industry often uses hazardous peroxides instead or metal oxides that lead to significant waste, primarily because viable catalysts that can use water or air are yet to be sufficiently developed. Objectives: Our aim is to develop oxygen atom transfer (OAT) catalysts using bioinspired metal complexes that can be activated by light. Preliminary work has shown that OAT is very sensitive to the ligand structure and that light is required for more than one fundamental step in the catalytic cycle. This project will investigate details of the mechanism and explore the scope of the OAT reaction for the conversion of useful substrates. Promising photocatalysts will be inserted into protein scaffolds to confer water solubility, biocompatibility and stereoselectivity.Experimental Approach: Metal complex synthesis and photocatalysis will be supported by detailed structural and spectroscopic studies to understand the structure-property relationships that determine thermodynamic and kinetic phenomena that control the OAT process. Metal complex synthesis will include the development of multidentate ligands with photoactive components and the use of transition metals, such as molybdenum, tungsten and rhenium, which can support reactive metal-oxo functionalities. Protein samples will be provided by PDRAs in the group who are developing protein scaffolds for artificial metalloenzymes. Characterisation will include single-crystal X-ray diffraction, NMR, IR, Raman, UV-Vis spectroscopies and electrochemistry. The catalytic mechanism will be studied using time-resolved spectroscopy with the potential to use international facilities for ultrafast studies. In collaboration, mechanistic and photophysical processes will also be studied theoretically using DFT. Novelty: OAT is a fundamental biological process that has not yet been exploited for chemical synthesis. Photocatalytic OAT using water as both benign solvent and oxygen source would be a significant advance that would have immediate impact and potentially wide application for clean oxidations.