Easily recyclable polymeric ionic liquid-functionalized chiral salen Mn(III) complex for enantioselective epoxidation of styrene

摘要

A polymeric ionic liquid (IL)-functionalized chiral salen ligand (PICL) was synthesized by covalent polymerization between amino ({single bond}NH_2) group of 1,3-dipropylamineimidazolium bromide with chloromethyl ({single bond}CH_2Cl) group at two sides of 5,5′ positions in the typical chiral salen ligand. Treatment of the synthesized PICL with Mn(OAc)_2?4H_2O and LiCl under aerobic oxidation yielded the corresponding polymeric IL-functionalized chiral salen Mn(III) complex (PICC). The typical IR bands at 1613, 1540, 570, and 412 cm~(-1), as well as the maximum UV-vis absorbed peaks around 433 nm of the PICC were proposed as characteristics of the monomeric salen Mn(III) complex. The PICC was used as a catalyst in the enantioselective epoxidation of styrene. Comparable catalytic activity and enantioselectivity relative to the monomeric chiral salen Mn(III) complex were observed. Furthermore, recovery of the polymeric catalyst was readily accomplished by simple precipitation in n-hexane, and subsequently reused (10 times) without significant loss of reactivity and enantioselectivity.