Ruthenium(II) complexes encompassing 2-oxo-1,2-dihydroquinoline-3-carbaldehyde thiosemicarbazone hybrid ligand: A new versatile potential catalyst for dehydrogenative amide synthesis

Ruthenium(II) complexes supported by a series of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde substituted thiosemicarbazone ligands have been synthesized and characterized. In addition, the complexes have been found to catalyze the amidation of alcohols with amines in the presence of KtBuO–toluene system. This method has a great potential for the preparation of amides, because it tolerates a wide range of substrates with excellent yield. [Display omitted] •Ru(II) complexes with dihydroquinoline thiosemicarbazone ligands were designed and synthesized.•X-ray studies revealed a distorted octahedral geometry for the new complexes.•The resulting complexes have been evaluated as potential catalysts for amidation of alcohols with amines. Ruthenium(II) complexes (1–6) supported by a series of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde substituted thiosemicarbazone ligands [2-oxo-1,2-dihydroquinoline-3-carbaldehyde thiosemicarbazone (L1), 2-oxo-1,2-dihydroquinoline-3-carbaldehyde N-methyl thiosemicarbazone (L2), 2-oxo-1,2-dihydroquinoline-3-carbaldehyde N-phenylthiosemicarbazone (L3)] have been synthesized and structurally characterized by analytical, spectroscopic methods and X-ray crystallographic technique. The studies revealed that the ligands act as mononegative tridentate in ruthenium(II) complexes and a distorted octahedral geometry has been proposed for the complexes. In addition, the complexes have been found to catalyze the amidation of alcohols with amines in the presence of KtBuO–toluene system. The catalyst 3 displayed higher activity in substrates, including phenyl-, pyridine-, furan-, and thiophene-substituted alcohols with primary and secondary amines. The protocol is highly attractive because of easily available starting materials, high atom efficiency and environmental friendliness.