材料期刊网

使用不同空间位阻的苯氧链接手臂修饰的聚(苯乙烯基-苯乙烯膦酸)-磷酸氢锆轴向固载手性MnI I(Salen)催化剂(Cat1-Cat3)，随后在间氯过氧苯甲酸(m-CPBA)为氧化剂的体系中考察了固载催化剂的催化性能.同时，在相同氧化体系下测试了一系列均相催化剂类似物(Cat4-Cat6).结果表明，在非均相条件下，可调变苯氧链接手臂的邻位取代基对催化剂活性起着重要作用，环氧化产物的对映选择性随着取代基位阻的增加而增大，但产物转化率有一定程度下降.此外，非均相催化剂即使在没有轴向助剂的参与下(通常需要添加，为了增大催化活性)仍然表现出非常高的催化活性，尤其对α-甲基苯乙烯反应，其对映选择性从6.8%增加到76.8%，转化率从19.8%上升到90.7%.制备的非均相催化剂11次的循环使用实验表明，在前5次使用后催化剂活性与对映选择性没有明显变化.

We have developed a series of chiral MnI I(Salen) (chiral Jacobsen’s catalyst) catalysts that were axially supported onto zirconium poly(styrene-phenylvinylphosphonate)-phosphate through tunable phenoxyl linkers of varying steric hindrance, and evaluated their perfor-mance as catalysts (Cat1-Cat3) for the epoxidation of unfunctionalized olefins using m-chloroperbenzoic acid as an oxidant. The corresponding non-supported analogues (Cat4-Cat6) were also prepared and tested under similar conditions. The results demon-strated that the incorporation of substituents at the ortho-positions of the tunable phenox-yl linkers had a critical effect on the catalytic activity. Furthermore, the enantioselectivity increased as the steric hindrance imposed by the linker increased, although this also led to a decrease in the conversions under the same reaction conditions, especially for heteroge-neous epoxidation. The heterogeneous system also displayed high ee values and conver-sions in the absence of the axial additive N-methylmorpholine N-oxide, which is commonly required to improve the catalytic activity of epoxidation reactions, especially for the epox-idation ofα-methylstyrene. The reusability of the catalyst was also evaluated over 11 cata-lytic cycles, with no significant reduction observed in the catalytic activity or enantioselec-tivity after five runs.