Selective epoxidation of unfunctionalized olefins catalyzed by unsymmetric Mn(III)-Schiff base complexes

Abstract

The selective epoxidation of unfunctionalized olefins (styrene, cyclohexene, α-methylstyrene) catalyzed by unsymmetric Schiff base-Mn(III) complexes Mn(CBP-phen-XSal)Cl [X = H, Cl, Br, NO 2, CH 3, OCH 3] 1 and the symmetric analogs Mn(III)(CBP-R-CBP)Y [R = CH 2CH 2, CH(CH 3)CH 2, C 6H 4, Y = Cl, OAc] 2 was investigated under mild conditions with iodosylbenzene as the terminal oxidant. The results showed that: the unsymmetric complexes Mn(III)(CBP-phen-XSal)Cl are effective catalysts in catalytically selective olefin epoxidation, superior to the symmetric analogs; with X = Cl, Br, the catalytic effectiveness was higher, X = strong electron-withdrawing group (NO 2) or electron-releasing (OCH 3) lowered the catalytic effectiveness; the highest percent yields of the three olefins were 73%, 98% and 92%, respectively.