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) 2 Br[HN(C 2 H 4 P i Pr 2 ) 2 ]] ([HN(C 2 H 4 P i Pr 2 ) 2 ] = MACHO- 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 ( T = 150 °C, p (CO/H 2 ) = 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.

Hydrogenation of CO2 to Methanol with Mn‐PNP‐Pincer Complexes in the Presence of Lewis Acids: the Formate Resting State Unleashed

“…In line with the catalytic activity of Mn–MACHO complexes for CO hydrogenation, [12,16] 3 shows a high tolerance towards the presence of CO (Table 2, Entry 7). Even with additional 5 bar of CO, a high yield of methanol was obtained.…”

“…Most recently, we found that complex 1 was highly active for the hydrogenation of carbon monoxide (CO) to methanol [12] . The reaction proceeds via formate ester intermediates formed under the basic reaction conditions from ROH and CO.…”

“…Most recently, we found that complex 1 was highly active for the hydrogenation of carbon monoxide (CO) to methanol. [12] The reaction proceeds via formate ester intermediates formed under the basic reaction conditions from ROH and CO. Initial attempts in our laboratories to use a similar strategy starting from CO 2 , H 2 and ROH gave no or only marginal yields of MeOH, however.…”

Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

“…Recently the Leitner group reported the alcohol assisted CO reduction to methanol using the Mn pincer complex ( Mn2 ) resulting in a TON of 4023 and a TOF of 857 h –1 in EtOH/toluene as solvent under p (CO/H 2 ) = 5/50 bar at 150 °C ( Scheme 61 b). 393 …”

Thermodynamic Trends for Reduction of CO by Molecular Complexes

“…In contrast, catalytic reduction of CO by molecular catalysts is much less developed, which hinders the development of tandem processes that utilize CO as an intermediate. Some molecular complexes have been reported to catalytically reduce CO via hydrogenation, − electrocatalysis, , or photocatalysis; , unfortunately, these catalysts typically require harsh reaction conditions and afford low conversion.…”