Dioxygen affinities and catalytic epoxidation performance of mono-Schiff base transition-metal complexes with aza-crown or morpholino pendants

Mono-Schiff base CoII complexes, CoL21–CoL26 with aza-crown or morpholino pendants were synthesized. The O2 uptake of these complexes in MeOCH2CH2OMe solution was determined at different temperatures, and the equilibrium constants (KO2) and thermodynamic parameters (ΔH0, ΔS0) for oxygenation were calculated. The corresponding MnIII complexes, MnL21Cl–MnL26Cl, were employed to catalyze epoxidation of styrene at ambient temperature and pressures. Crown ether effects 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 pendants than that by morpholino pendants, and the O2-binding capabilities of CoL21–CoL23 with aza-crown pendants can also be enhanced by adding alkali metal (Li+, Na+ and K+) cations; similarly, the catalytic activities of the MnIII complexes with aza-crown pendants, MnL21Cl–MnL23Cl, are higher than those of the MnIII complexes with morpholino pendants, MnL24Cl–MnL26Cl.