Synthesis and characterization of gold complexes with pyridine-based SNS ligands and as homogeneous catalysts for reduction of 4-nitrophenol

Abstract

Three gold complexes with pyridine-based SNS type ligands, 2,6-bis(1-methylimidazole-2-thione)pyridine (Bmtp), 2,6-bis(1-ethylimidazole-2-thione)pyridine (Betp) and 2,6-bis(1-isopropylimidazole-2-thione)pyridine (Bptp) have been synthesized and characterized. Reactions of HAuCl₄·H₂O with three pyridine-based SNS ligands result in the formation of the complexes [(L)AuCl₂]Cl (L = Bmtp (1); L = Betp (2) and L = Bptp (3)). All compounds are investigated by elemental analysis, NMR, MS and UV-Vis as well as IR spectral analysis. The molecular structure of 3 has been confirmed by X-ray crystallography. Moreover, all gold complexes are efficient homogeneous catalysts and catalyze the reduction of 4-nitrophenol (4-NP) to 4-nitroaniline (4-AP) in the presence of NaBH₄ reducing agent in water. And complex 3 exhibits an exceptionally high turn over frequency (TOF) of 1.20 min⁻¹ for the reduction of 4-NP.