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

Abstract

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.