Ruthenium(II) carbonyl complexes containing pyridoxal thiosemicarbazone and trans-bis(triphenylphosphine/arsine): Synthesis, structure and their recyclable catalysis of nitriles to amides and synthesis of imidazolines

Abstract

Pyridoxal N(4)-substituted thisemicarbazone hydrochloride ligands (L1–3) were synthesized and reacted with the ruthenium(II) starting complexes [RuHCl(CO)(EPh3)3] (EP or As). The resulting complexes [Ru(CO)(L1–3)(EPh3)2] (1–6) were characterized by elemental analyses and spectroscopic techniques. The molecular structure of complex 5 was identified by means of single crystal X-ray diffraction analysis. The catalytic activity of the new complexes was evaluated for the selective hydration of nitriles to primary amides and also the condensation of nitriles with ethylenediamine under solvent free conditions. The processes were operative with aromatic, heteroaromatic and aliphatic nitriles, and tolerated several substitutional groups. The studies on the effect of substitution over thiosemicarbazone, reaction time, temperature, solvent and catalyst loading were carried out in order to find the best catalyst in this series of complexes and favourable reaction conditions. A probable mechanism for both the catalytic reactions of nitrile has also been proposed. The catalyst was recovered and recycled in the hydration of nitriles for five times without any significant loss of its activity.