The PhD thesis focuses on understanding the reaction mechanisms involved in the CO2 and H2O reduction reactions catalyzed by first-row transition metal complexes. A systematic study of the electronic effects and KIE studies and DFT modelling in a series of tetradentate pyridylamino Co complexes allowed the identification of the metal-hydride formation as the rate-determining step of the H2O reduction reaction. Later, the same family of complexes activated CO2 at the CoI redox state, generating a CoI-CO thermodynamic sink intermediate and Co-carbonate species identified by in situ FTIR-SEC and ex-situ spectroscopy (XRD, 1H-NMR, XAS). Interestingly, the CO2 to CO electroreduction is boosted with the light. Most likely, this effect is due to the photochemical activation of the Co-CO intermediates.
On the other hand, a highly active MnI(CO)3(bis-NHC) electrocatalyst resulted in an excellent model complex for the in situ detection and chemical generation of an Mn-tetracarbonyl, Mn-hydride and Mn-formate, which are key intermediates in the CO2 reduction to CO and formate. Finally, new Ni complexes based on a C3-symmetric tris(phosphino)alkyl ligand revealed high selectivity for the CO2 reduction to CO through a reduction-first mechanism, as suggested by CPE, CV and computational modelling of the reaction mechanism. Furthermore, FTIR-SEC of the chemically synthesized NiII-CO allowed the formal NiI-CO and Ni0-CO species to be detected.
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