Synthesis, structural characterization and catalytic transfer hydrogenation of ruthenium(II) carbonyl complexes bearing N,N,O pincer type benzoylhydrazone ligands

Abstract

The convenient synthesis of four new octahedral ruthenium(II) carbonyl benzoylhydrazone complexes of the general molecular formula [Ru(L)Cl(CO)(PPh3)] (where HL=substituted 2-acetylpyridine benzoylhydrazones; the H represents the dissociable proton) has been described. The characterization of the complexes was accomplished by spectroscopic (FT-IR, 1H NMR, UV–Vis) techniques as well as by elemental (C,H,N) analysis. A single crystal X-ray diffraction study of a representative complex, [Ru(L1)Cl(CO)(PPh3)] (1), confirms a pincer-like N,N,O coordination mode of the benzoylhydrazone ligand via the pyridine N, the azomethine N and the deprotonated amide O atoms, with the formation of two five-membered fused chelate rings, and indicates a distorted octahedral geometry around the ruthenium(II) centre. Further, the catalytic efficiency of complex 1 has been investigated for the transfer hydrogenation of substituted acetophenones to the corresponding secondary alcohols. The influence of base and catalyst loading in the transfer hydrogenation reaction was also evaluated. The complexes were found to be efficient catalysts in the presence of iso-propanol/KOH with conversions up to 99.2%.