Catalytic epoxidation performance and dioxygen affinities of unsymmetrical Schiff base transition–metal complexes with pendant aza-crown or morpholino groups

Abstract

Unsymmetrical Schiff base CoII complexes (CoL1–CoL6) and Schiff base MnIII complexes (MnL1Cl–MnL6Cl) with pendant aza-crown or morpholino groups were synthesized according to the literature. The oxygen uptake of Schiff base CoII complexes in MeOCH2CH2OMe solution was determined at different temperatures, and the equilibrium constants (KO2) and thermodynamic parameters (∆H 0, ∆S 0) for oxygenation were calculated. The corresponding MnIII complexes, MnL1Cl–MnL6Cl, were employed to catalyze epoxidation of styrene at ambient temperature and pressures. The effects of crown ether on the modulation of O2-binding capability and the catalytic oxidation of styrene are discussed. The results indicate that the dioxygen affinities of the CoII complexes are much more enhanced by aza-crown pendant group than that by morpholino pendant group, and the O2-binding capabilities of CoL1–CoL3 with aza-crown pendant group can also be enhanced by adding alkali metal cations (Li+, Na+, and K+); similarly, the catalytic activities of the MnIII complexes with aza-crown pendant group, MnL1Cl–MnL3Cl, are higher than those of the MnIII complexes with morpholino pendant group, MnL4Cl–MnL6Cl. Catalytic epoxidation performance and dioxygen affinities of unsymmetrical Schiff base transition–metal complexes with pendant aza-crown or morpholino groups. Jian-zhang Li*, Bin Xu, Wei-dong Jiang Key Laboratory of Green and Technology, Department of Chemistry, Sichuan University of Science & Engineering, Zigong, Sichuan 643000, People’s Republic of China Bo Zhou, Wei Zeng, Sheng-ying Qin Department of Chemistry, Sichuan University, Chengdu, Sichuan 610064, People’s Republic of China The oxygen uptake of Schiff base CoII complexes in MeOCH2CH2OMe solution was determined at different temperatures, and the equilibrium constants (KO2) and thermodynamic parameters (∆H 0, ∆S 0) for oxygenation were calculated. The corresponding MnIII complexes, MnL1Cl-MnL6Cl, were employed to catalyze epoxidation of styrene at ambient temperature and pressures. The effects of crown ether on the modulation of O2-binding capability and the catalytic oxidation of styrene are discussed.