Ruthenium(II) carbonyl complexes containing ‘pincer like’ ONS donor Schiff base and triphenylphosphine as catalyst for selective oxidation of alcohols at room temperature

Abstract

Reactions of H2L with [RuHCl(CO)(PPh3)3] in toluene gives [Ru(L)(CO)(PPh3)2] (L = binegative tridentate ONS donor ligand derived from salicylaldehyde/4-substituted salicylaldehyde/2-hydroxy-1-naphthaldehyde and o-aminothiophenol) at room temperature. All the complexes were characterized by elemental analyses and UV–Visible, FT-IR, 1H, 13C and 31P NMR spectroscopic methods. 1H–1H COSY and 1H–31P HMBC spectra of [Ru(L4)(CO)(PPh3)2] have been studied. 1H–31P HMBC spectrum established the coupling of phosphorus atoms with azomethine proton. The single crystal X-ray analysis of [Ru(L5)(CO)(PPh3)2] revealed that Schiff base ligand is coordinated to the metal center, via dissociation of the two acidic protons, as a dianionic tridentate ONS donor and that ruthenium(II) ion adopts octahedral coordination with the phosphorus atoms in trans-disposition. Ruthenium complexes have been used in conjunction with N-methylmorpholine-N-oxide (NMO) for the catalytic oxidation of various alcohols at room temperature. Benzylic primary and secondary alcohols are oxidized in good to excellent yields, and aliphatic and cyclic alcohols give carbonyl compounds in moderate yields.