Earth-abundant metal catalysed CO2 reduction processes. Highlights and mechanistic diversity

Carbon dioxide (CO2) represents an interesting and abundant renewable C1 feedstock for chemists, upon activation needed to overcome its thermodynamic inertness. Various metal-catalysed CO2 reduction processes have been studied over the years, both under homogeneous and heterogeneous conditions. In the effort of increasing processes cost sustainability, in the last decade earth-abundant metal catalysts have been designed and applied for these processes, in particular under homogeneous conditions, targeting products such as formic acid and formates, and more recently methanol.[1] Highlights of the most efficient systems will be discussed, focusing on the key aspects of molecular architectures and catalytic mechanisms.Manganese, the third most abundant metal in the Earth's crust, is receiving increasing attention for application in catalysis. The results obtained in collaboration with TU Vienna (Austria) on the use of Mn(I) pincer-type PN3P hydridocarbonyl complexes for CO2 hydrogenation to formate,[2] hydrosilylation[3] and hydroboration[4] to silyl- and boryl-protected methanol will be presented. Next, recent results on the use of a class of textbook bench-stable, non-pincer type Mn(I)-alkylcarbonyl complexes in CO2 hydrogenation[5] and hydroboration will be disclosed. It will be shown that, by a combination of experimental NMR data and DFT calculations, outer-sphere MLC-type and inner-sphere metal-centred mechanisms can be in place for CO2 activation, depending on the choice of ancillary ligands coordinating the Mn(I) centre.