Heteroleptic 1,4‐Diazabutadiene Complexes of Ruthenium: Synthesis, Characterization and Utilization in Catalytic Transfer Hydrogenation

Abstract

Reaction of [Ru(trpy)Cl3] with 1,4-diazabutadienes (p-RC6H4N=C(H)-(H)C=NC6H4R-p; R = OCH3, CH3, H and Cl; abbreviated as L-R) in refluxing ethanol in the presence of triethylamine has afforded a family of complexes, isolated as perchlorate salts, of type [Ru(trpy)(L-R)Cl]ClO4 [depicted as complexes 1 (R = OCH3), 2 (R = CH3), 3 (R = H) and 4 (R = Cl)]. Crystal structures of complexes 1, 2 and 4 have been determined, and structure of complex 3 has been optimized by DFT method. The 1,4-diazabutadiene ligand in each complex is bound to ruthenium as a N,N-donor forming five-membered chelate. Complexes 1–4 catalyze transfer hydrogenation of aryl aldehydes to the corresponding alcohols with high (ca. 106) TON. They are also found to catalyze transfer hydrogenation of aryl ketones to corresponding secondary alcohols, but with much less efficiency. Catalytic transfer hydrogenation of nitroarenes to the corresponding amines has also been achieved.