Ruthenium(ii) carbonyl complexes containing benzhydrazone ligands: synthesis, structure and facile one-pot conversion of aldehydes to amides

Convenient synthesis of a series of eight octahedral ruthenium(II) carbonyl complexes having the general molecular formula [Ru(L)(CO)Cl(AsPh3)2] (where HL = thiophene aldehyde benzhydrazone ligand) has been described. The substituted benzhydrazone ligands behave as monoanionic bidentate N and O donors (L) and coordinate to the ruthenium(II) ion via the azomethine nitrogen and deprotonated amide oxygen. The compositions of the complexes have been established by elemental analysis, spectral methods (FT-IR, UV-Vis, 1H NMR) and X-ray crystallography. The crystal structure of two of the complexes, viz., [Ru(L1)(CO)Cl(AsPh3)2] (1) and [Ru(L5)(CO)Cl(AsPh3)2] (5) have been solved by single crystal X-ray crystallography and it indicates the presence of a distorted octahedral geometry in these complexes. The complexes were demonstrated as efficient catalysts for the one-pot conversion of various aldehydes to their corresponding primary amides using NH2OH·HCl and NaHCO3. The effects of solvent, base, reaction temperature and catalyst loading on the catalytic activity of the most active ruthenium(II) carbonyl benzhydrazone complex were also investigated.