Synthesis, luminescent, redox and catalytic properties of Ru(II) carbonyl complexes containing 2N2O donors

Abstract

Diamagentic ruthenium(II) complexes [Ru(CO)(B)(L)] (where B = PPh 3, AsPh 3, py (or) pip; L = dianion of tetradentate Schiff bases) were synthesized from the reaction of tetradentate Schiff bases derived from 2-hydroxy-1-naphthaldehyde and the appropriate diamines with monomeric metal precursors [RuHCl(CO)(EPh 3) 2 (B)] (where E = As, B = AsPh 3; E = P, B = PPh 3, py (or) pip). Elemental analyses and spectral (FT-IR, UV–Vis and 1H NMR) studies of all the new synthesized complexes suggest the presence of an octahedral environment around the Ru(II) ion. All the metal complexes exhibit characteristic MLCT absorption and luminescence bands in the visible region. The luminescence efficiency of the ruthenium(II) complexes was explained based on the ligand environment around the metal ion. Cyclic voltammograms of all the complexes display quasireversible oxidations (Ru III/Ru II) in the range 0.76–1.04 V and irreversible reduction peaks (Ru II/Ru I) in the range −0.70 to −0.95 V. The observed redox potentials vary with respect to the size of the chelate ring of Schiff base ligands. Further, the catalytic activity of complex 1 has been found to be high towards the oxidation of primary and secondary alcohols into their corresponding aldehydes and ketones in the presence of N-methylmorpholine- N-oxide (NMO) as co-oxidant. The formation of high valent Ru IV O species as a catalytic intermediate is proposed for the catalytic process.