Photoredox catalysis mediated by transition metal complexes. Towards challenging organic reductions

Identifier:  TDX:4011

Handle: https://hdl.handle.net/20.500.11797/TDX4011

Authors:  Pascual Gascón, David

Abstract:
Photoredox catalysis exploits light as energy source to perform chemical reactions that involve electron transfer processes. Besides, the implementation of water as source of hydrogen equivalents for reductive transformations is essential from a sustainable perspective. Given that transition metals complexes are good candidates to transfer hydrogen equivalents, metallaphotoredox catalysis is a promising platform to reduce organic functionalities. In this thesis, a dual system previously reported in our group has been extended to reduce aryl olefins using visible light as the driving force and H2O/amine as the hydride source. The catalytic system involved a robust cobalt complex with an aminopyridine ligand, and a copper photocatalyst. Based on our mechanistic understanding, evaluation of other photosensitisers and conditions reached a dual Co/Ir system capable of selectively reducing acetophenone versus styrene and vice versa. In parallel, by the utilization of chiral-at-ligand cobalt complexes we explored the asymmetric reduction of aromatic ketones in aqueous media. By means of synthetic modifications in the ligand, we found that the ortho-position of pyridine rings must remain non-substituted, while the meta-substitution could have a positive effect on chirality transfer.