Manganese and Rhenium Tricarbonyl Complexes Equipped with Proton Relays in the Electrochemical CO2 Reduction Reaction

Abstract

The minireview focuses on the electrochemical CO2 reduction catalysed by manganese and rhenium tricarbonyl complexes with α-diimine ligands having pendant proton relays attached to the α-diimine ligand. Since the pioneering work on [Re(CO)3(Lbpy)Cl], 1Cl, as molecular electrocatalyst in the CO2 reduction reaction in the 80's, some effort has been made to understand the mechanism of the catalytic cycle and to improve the efficiency of the conversion (Lbpy = 2,2'-bipyrdine). Later it was shown that the corresponding Mn complex, [Mn(CO)3(Lbpy)Br], 2Br, is also active in the CO2-to-CO conversion. As the 2 electrons reduction of CO2 is coupled to the transfer of 2 protons, pendent proton relays have been introduced in the ligand framework with the aim to improve the proton management during catalysis, to stabilize intermediates, and to alter the redox and the pH-dependent properties of the catalyst. We summarise in this review the outcome of these studies on the performance of the catalyst, in particular, with regard to the position of the proton relay and thus, its influence on the electronic structure, the reaction steps, and the kinetics.