Control The Reactivity Of Chiral Mn(Ⅲ) Salen Catalysts For Asymmetric Epoxidation By Ion Exchange

In recent years, efficient asymmetric catalysis has become an important challenge in the fields of green chemistry and chemical engineering. The chiral schiff-base (salen) metal complexes as an efficient catalyst have been widely applied and showed excellent asymmetric induction in various organic reactions, such as asymmetric addition reaction, asymmetric hydrogenation reaction, cyclopropanation reaction, Diels-Alder reaction, asymmetric epoxidation of olefins, and hydrolytic kinetic resolution of epoxides and so on. Chiral salen complexes have attracted considerable attention due to their easily tunable stereochemical properties, which readily create effective chiral environments around the metal centers, resulting in more efficient enantioselectivity in asymmetric catalysis. So we can change the physical and chemical properties by modifing its structure. Moreover, the asymmetric reaction using the chiral salen metal complexes as catalyst has many advantages, such as the mild reaction conditions, broad substrate scope, green and efficient. So this kind of catalyst has important research and application value. To further improve its reactivity and enantioselectivity, we synthesize a series of chiral catalysts [salen-Mnm][X] X"=Cl-, OAc-, NO3-, BF4-, CF3SO3-, OCH2CH3-) by simple ion change. Further more, the catalytic performance of these complexes were in-depth studied in the asymmetric epoxidation of olefins.This thesis consists of four parts:1. Giving a brief introduction on chiral salen metal catalysts, and summarizing the application of the catalysts in various asymmetric reactions, as well as the basic process, reaction mechanism and influence factors in the asymmetric epoxidation of olefins.2. A series of chiral catalysts [salen-Mn(Ⅲ)][X] X-=C1-, OAc-, NO3-, BF4-, CF3SO3-, OCH2CH3-) were synthesized. The structure of the complexes were confirmed by NMR, elemental analysis, mass spectrometry, infrared spectroscopy, UV-Vis spectroscopy optical test and TGA.3. Through the theoretical calculation method, optimizing the structure of Mnv=O (salen) active intermediates and studying the influence of the axial anions on both the electronic structure and steric configuration.4. Based on the theoretical calculation, the reactivity and enantioselectivity of these catalysts with different axial anions were explored in the asymmetric epoxidation of olefins. Its Mnv=O active intermediate were carefully investigated by UV-Vis. Meanwhile, we systematically studied the influence factors on the catalytic performance, such as oxidizing agent, solvent, temperature. Extending the substrate scope and trying to use the catalyst with large ion KB(C6F5)4 instead of Cl- for the asymmetric epoxidation under the optimized conditions.Overall, The obtained results indicated that (1) a simply changing on the axial anions can result in chiral Mn(Ⅲ) salen complexes with different electronic structure and steric configuration; (2) the influence of axial anions is dependent on the reaction substrate and solvent. It shows a simple, economic, efficient method to control the reactivity and enantioselectivity of these chiral Mn(Ⅲ) salen complexes.