Transfer Hydrogenation and Hydrogenation of Commercial-Grade Aldehydes to Primary Alcohols Catalyzed by 2-(Aminomethyl)pyridine and Pincer Benzo[h]quinoline Ruthenium Complexes

The chemoselective reduction of commercial-grade aldehydes (97–99 %) to primary alcohols is achieved with cis-[RuCl2(ampy)(PP)] [ampy=2-(aminomethyl)pyridine; PP=1,4-bis(diphenylphosphino)butane, 1,1′-ferrocenediyl-bis(diphenylphosphine)] and pincer [RuCl(CNNR)(PP)] [PP=1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane, 1,1′-ferrocenediyl-bis(diphenylphosphine); HCNNR=4-substituted-2-aminomethyl-benzo[h]quinoline; R=Me, Ph] complexes by transfer hydrogenation and hydrogenation reactions. Aromatic, conjugated, and aliphatic aldehydes are converted quantitatively to the corresponding alcohols using 2-propanol with potassium carbonate at substrate/catalyst ratios up to 100 000 by transfer hydrogenation, whereas aldehyde hydrogenation (5–20 atm of H2) is achieved efficiently in MeOH in the presence of KOtBu at substrate/catalyst ratios up to 40 000.