Zirconium phosphonates-supported chiral Mn (III) Salen complexes for the asymmetric epoxidation of unfunctionalized olefins

The mesoporous zirconium phosphonates-supported Mn (III) Salen complexes (1a-e) with the different lengths of alkylsulfonic linkage (n = 2-6) and the loading amount of 0.041-0.059 mmol g (1) (based on Mn) were prepared and used as heterogeneous catalysts in the asymmetric epoxidation of styrene, alpha-methylstyrene and indene. The ee values significantly increased with the linkage length (n) from 2 to 6 only in the case of indene with the m-CPBA/NMO as an oxidant system, in all other shown cases the ee values are not significantly influenced by the linkage length (n). In m-CPBA/NMO system, the comparable ee values to the homogeneous Mn (III) Salen complex 1 were achieved. Due to the confined effect originating from the nanopores of zirconium phosphonates, the heterogeneous Mn (III) Salen complexes (1a-e) gave twice (84-88%ee) as many as ee values of homogeneous Mn (III) Salen complex 1 (49%ee) in the NaClO/PPNO system. (C) 2009 Elsevier B.V. All rights reserved.