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(C₂H₄P ^<i>i</i> Pr₂)₂]] ([HN(C₂H₄P ^<i>i</i> Pr₂)₂] = MACHO- ^<i>i</i> Pr) revealed the best performance, reaching up to turnover number = 4023 and turnover frequency 857 h^-1 in EtOH/toluene as solvent under optimized conditions (<i>T</i> = 150 °C, <i>p</i>(CO/H₂) = 5/50 bar, <i>t</i> = 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 <i>in situ</i>. 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.