Ruthenium(II) carbonyl complexes containing bidentate 2-oxo-1,2-dihydroquinoline-3-carbaldehyde hydrazone ligands as efficient catalysts for catalytic amidation reaction

The coordination behavior of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde hydrazone ligands in ruthenium(II) and the catalytic activity of newly synthesized complexes have been studied. The complexes [RuCl(CO)(PPh3)2(L1)] (1), [RuCl(CO)(AsPh3)2(L1)] (2), [RuCl(CO)(PPh3)2(L2)] (3) and [RuCl(CO)(AsPh3)2(L2)] (4) were synthesized by reactions of [RuHCl(CO)(EPh3)3] (E = P or As) precursors with hydrazone ligands and characterized by analytical and spectroscopic methods. The molecular structure of complex 2 was identified by means of single-crystal X-ray diffraction analysis. The structural analysis revealed that all the complexes possess a distorted octahedral geometry with the ligand coordinating in a uni-negative bidentate NO fashion. Further, the catalytic efficiency of the complexes have been investigated in the case of direct amidation of alcohols with amines. The influence of base, reaction temperature and catalyst loading in the amidation reaction was also evaluated. Notably, complex 3 was found to be very efficient catalyst towards amidation of alcohols with amine. A variety of aromatic (hetero) amines and alcohols with various functional groups have also been successfully used for amidations.