Fast and selective iron-catalyzed transfer hydrogenations of aldehydes

An efficient iron-based catalyst system consisting of Fe(BF)4·6H2O and P(CH2CH2PPh2)3 [tetraphos, (PP3)] is presented for the highly selective transfer hydrogenation of aromatic, aliphatic, and α,β-unsaturated aldehydes. A wide range of substrates including aldehydes with other reducible functional groups gave the corresponding alcohols in good yields. Formic acid is applied as a cheap, environmentally benign and easy to handle hydrogen source. Notable features of the presented methodology are the fast reactions under mild conditions. Advantageously compared to most transfer hydrogenations, no stoichiometric amounts of base additives are required.