Ruthenium(II)furoic hydrazone complexes in effective catalytic transfer hydrogenation of aldehydes to alcohols

A series of [Ru(ɳ⁶-p-cymene)(Cl)(L^1-3)] complexes based on three different furoic hydrazone ligands (HL^1-3) were developed for the catalytic application in the effective and simple methodology for the synthesis of benzyl and aliphatic alcohols through transfer hydrogenation of benzaldehyde or aliphatic aldehydes, respectively. The solid-state molecular structures of the three ruthenium complexes were determined by single-crystal X-ray diffraction revealing pseudo-octahedral three-legged piano-stool geometries. Complex [Ru(ɳ⁶-p-cymene)(Cl)(pyrene-furoichydrazone) showed the higher catalytic performance over others due to the hyperconjugation effect of the pyrene moiety that facilitates the transfer hydrogenation reaction. The catalytic experiments afforded the desired products in good to excellent yields and were performed through an effective methodology using isopropanol as solvent, using a 1 mol% of catalyst loading under room temperature. The catalyst demonstrates a wide range of substrate scope being able to catalyze the transfer hydrogenation of 17 different substrates that includes aromatic, heterocyclic and aliphatic aldehydes with electron donating and/or withdrawing substituent groups.