(η⁶-Benzene)Ru(II) half-sandwich complexes of pyrazolated chalcogenoethers for catalytic activation of aldehydes to amides transformation

The reaction of [(η⁶-C₆H₆)RuCl(μ-Cl)]₂ with chalcogenoether substituted 1H-pyrazole ligands (L1-L3) in methanol have yielded three novel Ru(II) half-sandwich complexes [(η⁶-C₆H₆)RuCl(L)]PF₆ (1–3) in high yield under the ambient reaction conditions. The NMR, MS and FT-IR analytical techniques were used to identify their structures. The molecular structures of the complexes 2 and 3 were established with X-ray crystallographic analysis and revealed a pseudo-octahedral half sandwich piano-stool geometry around ruthenium in each complex. Complexes 1–3 are thermally robust and were found to be insensitive towards the air and moisture. All the complexes were found to be catalytically active and produced the excellent yields of amides (up to 95%) from corresponding aldehydes. In contrast to the previous reported catalytic systems for aldehyde to amide transformation, the present complexes 1–3 are very efficient and have several advantages in terms of low catalyst loading, reaction time, temperature and wide applicability for various substituted aldehydes. Owing to the stronger σ-donor coordination properties of selenium containing ligands, the complex 2 was found to be more efficient as compare to the sulphur and tellurium analogues.