Catalytic oxidation of styrene by dinuclear Mn(III) coordination compound with asymmetric tridentate half-Salen type NNO-donor ligand

Abstract

A new methoxo bridged dinuclear Mn(III) coordination compound, [Mn2(µ-OMe)2(L)2(MeOH)2]Cl2∙2MeOH (1), with tridentate N2O-donor half-Salen ligand was synthesized by the reaction of MnCl2·4H2O and (Z)-3-((2-aminocyclohexyl)amino)-1-phenylbut-2-en-1-one (HL) in methanol and characterized by spectroscopic methods and elemental analysis. The structure of compound 1 was also determined by single crystal X-ray diffraction studies which indicated it is a dinuclear Mn(III) coordination compound. Two Mn(III) are connected together by two methoxo bridges and have distorted octahedral geometry. The coordination compound is ionic and two chloride anions appear as the counter anions which are involved in strong hydrogen bond interactions. The catalytic activity of compound 1 was investigated in oxidation of styrene in the presence of hydrogen peroxide as a green oxidant. The effects of influencing parameters like molar ratio of the reagents, temperature and the presence of different solvents were investigated. The results of catalytic studies indicated the selectivity and activity of this catalytic system considerably depend on the reaction condition. Temperature and molar ratio of oxidant to substrate have high influence on both conversion and selectivity of the oxidation products. The best selectivity toward styrene epoxide was obtained at 40 °C and the best TOF was 66.4 h−1. The results indicate half-salen Mn(III) coordination compound can act as selective and efficient catalyst for oxidation of styrene under mild condition