Immobilization of Chiral Manganese(III)-salen Complexes for Enantioselective Epoxidation of Unfunctionalised Olefins

Enantioselective epoxidation of olefins is a useful synthetic route in organic synthesis, as a wide variety of olefins is available and optically active epoxides can be converted into various functionalities with high regio- and stereoselectivity. Chiral manganese(III)- salen catalyst, which is commonly known as the Jacobson-Katsuki catalyst, has been reported as selective and efficient catalyst for the epoxidation of unfunctionalised alkenes in homogeneous phase, using a wide range of oxidants-iodosylbenzene, sodium hypochlorite, mchloroperoxybenzoic acid, hydrogen peroxide, etc. However, this homogeneous catalyst cannot be separated from the reaction media and, subsequently, cannot be recycled. Moreover, it suffers deactivation in homogeneous phase by formation of dimeric μ-oxo-manganese(IV) species, which are inactive in the alkene epoxidation. One way of improving the chemical process, preventing the requirement for a laborious and inefficient extraction processes, is to immobilize the homogeneous catalyst on a solid support. Numerous accounts for salen immobilization using diverse kinds of inorganic materials, organic materials and inorganic-organic hybrid materials have been firstly outlined in this review.