Manganese-Catalyzed Sequential Hydrogenation of CO2 to Methanol via Formamide

Mn(I)-PNP pincer catalyzed sequential one-pot homogeneous CO2 hydrogenation to CH3OH by molecular H-2 is demonstrated. The hydrogenation consists of two parts N-formylation of an amine utilizing CO2 and HD and subsequent formamide reduction to CH3OH, regenerating the amine in the process. A reported air-stable and well-defined Mn-PNP pincer complex was found active for the catalysis of both steps. CH3OH yields up to 84% and 71% (w.r.t amine) were obtained, when benzylamine and morpholine were used as amines, respectively; and a TON of up to 36 was observed. In our opinion, this study represents an important development in the nascent field of base-metal-catalyzed homogeneous CO2 hydrogenation to CH3OH.