Design And Synthesis Of Chiral Porous Poly(Ionic Liquid)s And The Catalytic Effects On Asymmetric Epoxidation Of Olefins

Chiral epoxides are very important organic synthesis intermediates and have been widely used in the field of drug synthesis.Asymmetric epoxidation of olefin is an important way to synthesize chiral epoxides.Homogeneous chiral ionic liquid catalysts can efficiently catalyze the asymmetric epoxidation of olefin,but there is a problem that the catalyst is difficult to be separated from the catalytic system.The heterogeneous chiral poly ionic liquid catalyst is easy to be separated and recovered,but its catalytic activity is often lower than that of homogeneous chiral ionic liquid due to the fact that its catalytic active center cannot fully contact with the reaction substrate.Therefore,it is of great significance to design and synthesize an efficient and reusable chiral poly ionic liquid catalyst.The chiral Salen Mn（Ⅲ）complex is an efficient catalyst for the asymmetric epoxidation of olefin,and the imidazolium ionic liquid acts as a stable intermediate.In this paper,starting from the chiral porous poly ionic liquid,the chiral Salen Mn（Ⅲ）complex and imidazolium ionic liquid structure were successfully introduced into the polymer structure by Fourier alkylation method and quaternization method,and the chiral porous poly ionic liquid catalyst with high specific surface area and rich active center was prepared.Its application in the asymmetric epoxidation of olefin was also investigated.The main research contents are as follows:1.Preparation of chiral porous poly ionic liquid catalyst by Fourier alkylation methodUsing chiral Salen Mn（Ⅲ）complex,N-methyl imidazole（MIm）and1,4-dichlorobenzyl（DCX）as raw materials,through the method of combining Fourier alkylation reaction and quaternization reaction（Fourier alkylation）,a chiral porous polyionic liquid（CPPILs）containing chiral Salen Mn（Ⅲ）complex has been successfully prepared.The structure,properties and morphology of the chiral porous polyionic liquid were systematically characterized by Fourier transform infrared spectroscopy（FT-IR）,nuclear magnetic resonance spectroscopy（NMR）,X-ray photoelectron spectroscopy（XPS）,thermogravimetric analysis（TG）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The results of N₂adsorption-desorption and inductively coupled plasma（ICP）tests showed that the chiral porous poly ionic liquid had high specific surface area（189-282 m²/g）,abundant micro/mesoporous structures and active centers（Mn content in the range of 0.61-0.25mmol/g）.Moreover,with the increase of DCX component in the structure of chiral porous poly ionic liquid,the specific surface area gradually increases and the content of Mn gradually decreases.This chiral porous poly ionic liquid,which has the structure of chiral Salen Mn（Ⅲ）complex and imidazolium ionic liquid,exhibits excellent catalytic performance in the asymmetric epoxidation of olefin.Among them,the chiral porous poly ionic liquid catalyst CPPIL-4 with high specific surface area and Mn content exhibited similar catalytic activity to the homogeneous chiral Salen Mn（Ⅲ）complex catalyst in the asymmetric epoxidization of styrene.In addition,the chiral porous poly ionic liquid catalyst has good cycling stability,and the catalytic activity does not change significantly after 5 cycles.2.Preparation of chiral porous poly ionic liquid catalyst by quaternizationIn the preparation process of the above chiral porous poly ionic liquid,a large amount of inactive component DCX is needed to stabilize the three-dimensional network structure of the polymer,which will greatly limit the content of chiral Salen Mn（Ⅲ）complex and imidazolium ionic liquid in the active center of the polymer structure.Based on this,a chiral porous poly ionic liquid（Mn-CPOPs）was directly synthesized from chiral Salen Mn（Ⅲ）complex and 2,4,6-tris（1H-imidazole-1-yl）-1,3,5-triazine（TIST）by quaternification reaction.The pore structure and specific surface area of chiral porous poly ionic liquids were modelled by modulating the molar ratio of chiral Salen Mn（Ⅲ）complex and TIST.The chiral porous poly ionic liquid Mn-CPOP-3 of the molar ratio of 3 to the TIST of the chiral Salen Mn（Ⅲ）complex had the highest specific surface area（94 m²/g）.TG results show that the chiral porous poly ionic liquid has excellent thermal stability,and its initial decomposition temperature is as high as 400℃.In the asymmetric epoxidization of styrene,the chiral porous poly ionic liquid Mn-CPOPs showed good catalytic activity,the conversion rate of styrene was more than 90%,and the enantioselectivity reached 39%.