Hydrogenation of CO<sub>2</sub> to Methanol with Mn‐PNP‐Pincer Complexes in the Presence of Lewis Acids: the Formate Resting State Unleashed
David A. Kuß, Markus Hölscher, Walter Leitner
Abstract
Abstract The hydrogenation of CO 2 to methanol was achieved using a catalytic system comprising metal complexes of the form [Mn(CO) 2 [N(C 2 H 4 PR 2 )] (R= i Pr/Ph, [HN(C 2 H 4 PPh 2 ) 2 ]=MACHO−Ph) together with Lewis acid additives. Mechanistic studies suggest initial CO 2 insertion into a Mn−H bond leads to a formate complex as resting state. By systematically balancing the interaction between the acidic additive and the catalyst, the formate ligand could be removed through esterification to unleash the full catalytic potential. The reaction conditions were optimized on basis of the partial reaction order of relevant compounds. The combination of MACHO−Ph and Ti(O i Pr) 4 was identified as the most active system with a TON of 160 ( p (CO 2 )=5 bar, p (H 2 )=160 bar, T =150 °C). Using methanol as solvent and co‐reagent allows the catalytic conversion of CO 2 /H 2 in a liquid phase process comprising only the substrates and products.