title: Asymmetric epoxidation of cis/trans-β-methylstyrene catalysed by immobilised Mn(salen) with different linkages: heterogenisation of homogeneous asymmetric catalysis.
abstract: Immobilised Mn(salen) catalysts with two different linkages were studied in the asymmetric epoxidation of cis/trans-β-methylstyrene using NaClO as oxidant. The immobilised Mn(salen) complexes inside nanopores can lead to different catalytic behaviour compared with that of homogeneous Jacobsen catalyst. The rigidity of the linkage was found to be a key factor affecting the catalytic performance of immobilised catalysts. The immobilised catalyst with a rigid linkage exhibited comparable chemical selectivity, enantioselectivity and cis/trans ratio of product formation to that obtained with homogeneous Jacobsen catalysts. In contrast, the immobilised catalyst with a flexible linkage gave remarkably lower chemical selectivity, enantioselectivity and inverted cis/trans ratio compared with the results obtained with the homogeneous Jacobsen catalyst and the immobilised catalyst with rigid linkage. Thus, for immobilised Mn(salen) catalysts, a rigid linkage connecting active centres to the support is essential to obtain activity and enantioselectivity as high as those obtained in homogeneous systems.
authors.affiliation: Chongqing Key laboratory of catalysis science and technology Engineering research centre of waste oil recovery technology and equipment of Chinese ministry of education Chongqing Technology and Business University, Chongqing 400067 (P. R. China), Fax: (+86) 23-62768317. haidongzhang@ctbu.edu.cn.
authors.forename: Haidong
authors.initials: H
authors.lastname: Zhang
authors.forename: Yu
authors.initials: Y
authors.lastname: Zou
authors.forename: Yi-Meng
authors.initials: YM
authors.lastname: Wang
authors.forename: Yu
authors.initials: Y
authors.lastname: Shen
authors.forename: Xuxu
authors.initials: X
authors.lastname: Zheng
keywords: asymmetric catalysis; epoxidation; heterogeneous catalysis; immobilization; supported catalysis; surface chemistry