Nitrosyl ethylenediaminetetraacetato ruthemium(III)-an efficient oxygen atom transfer agent for the oxidation of olefins by molecular O₂ and PhIO through ligand-mediated nitrosyl/nitro couple

Abstract

The complexes [Ru^III(EDTA-H)NO]BF₄ 1 and [Ru^III(EDTA)(NO)] 1a were synthesized and characterised by elemental analysis, IR and UV-Vis spectroscopy, conductivity, magnetic susceptibility, EPR and electrochemical studies. Complex 1a catalyses the oxidation by molecular oxygen of 1-hexene to 2-hexanone and cyclohexene to cyclohexene oxide through the ligand-mediated Ru^III-EDTA-NO 1a/Ru^v-EDTA-NO₂ 2 oxygen atom transfer. The oxidation reactions were studied in 7:3 ethanol-water medium in the temperature range 30-45°C (μ=0.1 M KCl). The oxidation of 1-hexene and cyclohexene proceeds with a turnover number of 50 and 44 moles product per mole catalyst per hour. The rate of oxidation is first order with respect to catalyst concentration and one-half order with respect to molecular oxygen concentration. At higher substrate concentrations, the reaction rate was found to be independent of substrate concentration. ¹⁸O₂ studies indicate that the source of O atom transferred to the substrate is from molecular O₂. The formation of an organometallic metallocyclic intermediate is proposed for the reaction. The rate of oxygenation of cyclohexene by iodosyl benzene catalyzed by 1a was found to be identical with that obtained with O₂ as oxidant. The rate of oxygenation of 1a to 2 was studied independently by an O atom transfer from iodosyl benzene.