Alternative pathways in the ruthenium catalysed hydrogenation of CO to alcohols

CO hydrogenation in [PBu4]Br in the presence of [Ru-3(CO)(12)] gives predominantly methanol, ethanol and propanol with small amounts of 1,2-ethanediol. Using RuO2 as the catalyst precursor, the same products are formed along with higher alcohols (1-butanol-1-heptanol). Reactions carried out using added (CH3OH)-C-13 or (CO)-C-13 show that ethanol and propanol come from homologation reactions of methanol and ethanol respectively, but that the higher alcohols are not formed through the lower alcohols as intermediates.