Ruthenium(II) bis(hydrazone) complexes derived from 1,3,4-oxadiazoles: Synthesis, crystal structure and catalytic application in N-alkylation reactions

Abstract

1,3,4-Oxadiazoles (A–C) were derived via a series of reactions between isoniazid and salicylaldehydes. While reacting the oxadiazoles with [RuHCl(CO)(PPh3)3] in the presence of NaOH, mononuclear ruthenium(II) complexes bearing ‘salen’ type N,N′-bis(salicylidene)hydrazone ligands (1–3) were obtained. The oxadiazoles and ruthenium(II) complexes were characterized by analytical and spectral methods. The single crystal XRD analyses of complexes 1 and 2 suggested an octahedral geometry around ruthenium(II) ions in which the bis(hydrazone) act as mononegative bidentate ligands. It was also observed that the presence of an intramolecular hydrogen bonding between the hydroxyl proton and one of the azomethine nitrogens in all the complexes. Further, the complexes were proved as versatile catalysts for the N-alkylation of amines with alcohols under optimized reaction conditions.