Alcohol-Assisted Hydrogenation of Carbon Monoxide to Methanol Using Molecular Manganese Catalysts

Abstract Alcohol-assisted hydrogenation of carbon monoxide (CO) to methanol was achieved using homogeneous molecular complexes. The molecular manganese complex [Mn(CO)2Br[HN(C2H4PiPr2)2]] ([HN(C2H4PiPr2)2] = MACHO-iPr) revealed the best performance, reaching up to turnover number = 4023 and turnover frequency 857 h–1 in EtOH/toluene as solvent under optimized conditions (T = 150 °C, p(CO/H2) = 5/50 bar, t = 8–12 h). Control experiments affirmed that the reaction proceeds via formate ester as the intermediate, whereby a catalytic amount of base was found to be sufficient to mediate its formation from CO and the alcohol in situ. Selectivity for methanol formation reached >99% with no accumulation of the formate ester. The reaction was demonstrated to work with methanol as the alcohol component, resulting in a reactive system that allows catalytic “breeding” of methanol without any coreagents.