A magnetically recyclable Fe3O4@SiO2/Mn(iii) chiral salen complex as a highly selective and versatile heterogeneous nanocatalyst for the oxidation of olefins and sulfides

Abstract

In this study, a new magnetically recoverable heterogeneous Mn(III) nanocatalyst (MHMC) was developed by covalent grafting of a homogeneous chiral Mn(III) salen complex (HMC) onto the surface of a Fe₃O₄/SiO₂ core–shell. The structural and chemical nature of MHMC was characterized by different techniques. The catalytic activity of the MHMC and comparison with its homogeneous analogue were studied for the enantioselective epoxidation of various alkenes to epoxide compounds using tert-butyl hydroperoxide (TBHP) as an oxidant. The MHMC showed higher enantioselectivity and comparable catalytic reactivity to its homogeneous analogue with benefits such as facile recovery and recycling of the heterogeneous catalyst. The results showed that a higher enantioselectivity and yield were observed in the presence of N-methylmorpholine N-oxide (NMNO). The catalytic activity of this complex was also tested in the oxidation of sulfides using aqueous 30% H₂O₂ in excellent yields. The catalyst was reused for several runs without significant loss in activity and selectivity.