Synthesis, oxygenation and catalytic properties of ruthenium(III) saloph complexes

Abstract

Synthesis and dioxygen affinities of ruthenium(III)-Schiff base complexes with various appended axial base ligands, [Ru(Saloph)(B)Cl] (where Saloph = bis(salicylaldehyde)-o-phenylenediiminato, B=Cl⁻ 1, imidazole 2, 2-methylimidazole 3 and pyridine 4) are reported. The stoichiometry of dioxygen complexes formed was determined by oxygen uptake measurements. Oxygenation studies of complexes 1-4 reveal a 1:1 dioxygen complex formation. Complexes 1-4 were also studied for their catalytic activity by employing cyclohexene as a substrate for oxidation at 35°C using water-dioxane solvent medium. Kinetics of the oxidation reaction catalysed by complexes 1-4 indicate a first-order dependence with respect to catalyst, substrate and dioxygen concentrations, respectively. The product of oxidation was analysed and identified by GLC as the epoxide. A mechanism is proposed for the conversion of cyclohexene to the epoxide, and a subsequent rate law derived with the help of which were determined the values of the rate and equilibrium constants.