Carbon Dioxide Hydrogenation To Formate Catalyzed By A Non-Pincer-Type Mn(I) Complex

In the last decade, there has been a renewed interest in the use of CO2 as synthetic building block, as it can be an abundant, renewable and cheap feedstock for C1 chemical synthesis. Many research groups worldwide have developed selective homogeneous catalysts for the reduction of CO2 to chemicals such as formic acid (HCOOH), formaldehyde (HCHO), methanol (CH3OH), dimethyl ether (CH3OCH3), methane (CH4) and higher hydrocarbons, using milder reaction conditions than those generally required in heterogeneous catalysis. Among the possible products, formic acid can be of interest, as it finds many applications, for example in agriculture for silage, as preservant in food, as strong acid in wood pulping, etc. We have recently jointly developed pincer-type manganese complexes that proved to be suitable and very active catalysts for CO2 hydrogenation and hydroboration. Following on our interest, and with the aim of achieving ligands simplification, we hereby present the results of CO2 hydrogenation to formate in the presence of the well-defined, bench-stable alkylcarbonyl(bisphosphine) Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic data are complemented by a study of the reaction mechanism by DFT calculations, suggesting an unexpected inner-sphere, metal centered mechanism for CO2 activation