Mechanistic Studies of Water Oxidation Catalyzed by Homogeneous Iron and Ruthenium Complexes and Light-driven Organic Reductions with a Dual Cobalt/Copper Catalytic System

Identifier:  TDX:2980

Handle: https://hdl.handle.net/20.500.11797/TDX2980

Authors:  Casadevall Serrano, Carla

Abstract:
My doctoral work focuses on understanding the mechanisms involved in the application of artificial photosynthesis to store sunlight energy into chemical bonds, as well as developing new greener and sustainable methodologies to produce solar-fuels and fine chemicals. In this regard, the thesis presents: i) the synthesis and characterization of well-defined molecular iron and ruthenium water oxidation (WO) catalysts based on aminopyridine ligands, and ii) the synthesis and characterization of cobalt aminopyridine catalysts with a copper-based photoredox catalyst for the reduction of organic substrates (aromatic ketones, aromatic and aliphatic aldehydes and aromatic olefins) usign light as driving force in aqueous media. In the case of WO, I performed reactivity and mechanistic studies that led to a better understanding of how to access and stabilize the high oxidation states required at the metal centre to form the Oxygen-oxygen bond. In the light-driven organic transformations based on a dual copper-cobalt photocatalytic system, I have found an unprecedented selectivity for the reduction of aromatic ketones in front of aliphatic aldehydes. I have performed mechanistic studies to isolate the intermediates of the catalytic cycle and these together with DFT calculations and spectroscopic techniques (EXAFS and NMR) point out the formation of Co(I) that further yields [Co-H] as the active species. This [Co-H] species can react via Hydride transfer or hydrogen atom transfer depending on the reduction potential of the substrate, rationalizing the observed selectivity.