Study On The Synthesis Of Chiral Salen Mn(Ⅲ) Immobilized Onto Phenoxyl Linker Group Modified ZPS-PVPA By Axial Coordination And The Asymmetric Epoxidation Of Unfunctionalized Olefins

More and more attentions have been paid to the heterogeneous asymmertic catalysis in last decades. Among all these reactions,the heterogeneous asymmetric epoxidation is the most impressive. In this thesis,chiral Jacobsen's catalyst was axially immobilized onto organic polymer-inorganic hybrid support-Zirconium poly (styrene-phenylvinylphosphonate)-phosphate (ZPS-PVPA) by different length phenoxyl linker group. All these immobilized catalysts were characterized by FT-IR,diffusion reflection UV-Vis,AAS,XPS,SEM,TEM and TG-DSC and applied in asymmetric epoxidation unfunctionalized olefins. The various factors influencing the heterogeneous catalysts are also investigated in detail. The main results of the thesis work are described as follows.The heterogeneous catalysts 1a-1d is proved to be poor catalysts in NaClO bi-systems. And the immobilized catalysts show lower ee values and catalytic acitivity for asymmetric epoxidation of unfunctionalized olefins than the homogeneous Salen Mn (III) catalyst. The catalytic activity and selectivity of catalysts la-1d were explored for the asymmetric epoxidation of unfunctionalized olefins using m-CPBA as an oxidant system. Interestingly, the immobilized chiral salen-Mn (III) catalyst shows higher yields and chiral induction in the absence of NMO than that obtained in the present NMO. This stands in contrast to the literatures reported. Especially for the epoxidation of a-methylstyrene (yield%:from 14.3% to 60.9%; ee%:from 29.4% to 73.7%), and the catalyst 1d shows more 21.7% ee values was observed than corresponding homogeneous catalyst, similar pattern was reported in the epoxidation of styrene and indene, which may overcome the last obstacle for the potential industry application of chiral Jacobsen's catalyst.To study the effective and stability of the heterogeneous catalyst during the epoxidation of olefins, we applied catalyst 1d in repeated epoxidation reactions with a-methylstyrene as a model substrate. At the end of each cycle, the catalyst was precipitated from the reaction system by adding hexane and subsequently used in next runs without further purification. The data showed only a slightly decrease in activity and enantioselectivity for the first five runs. Further recycles of heterogeneous catalyst resulted in poor yield. However, still higher enantioselectivity than that of homogeneous counterpart was obtained even after ten times.