Mechanism Of Salenco（Ⅲ）-Ⅹ In Conjunction With Quaternary Ammonium Salt For Cycloaddition Of Epoxides With CO₂

Carbon dioxide (CO2) is an important Cl resource, and it can be transformed into various chemical materials and fine chemicals. Among of these, the synthesis of cyclic carbonates via the cycloaddition of CO2to epoxides is one of the important issues, and approaching to the synthesis of optically active cyclic carbonates and the kinetic resolution of epoxides using CO2as a reagent remains challenges. The binary catalyst systems based on chiral SalenCo(Ⅲ)-Ⅹ complexe and quaternary ammonium salt or organic base perform catalytic activity and enantioselectivity for this reaction. Unfortunately, in contrast to very high krel(kinetic resolution coefficient) values in hydrolysis kinetic resolution of aliphatic terminal epoxides, the asymmetric cycloaddition of CO2and racemic epoxides with binary catalyst systems based on chiral SalenCo(Ⅲ)-Ⅹ complex affords a relatively low krel.And, the role of the quaternary ammonium salt in the asymmetric cycloaddition of racemic epoxides with CO2using SalenCo(Ⅲ)-Ⅹ complexes is not clear. Therefore, the present dissertation focuses on exploring the role of the quaternary ammonium salt in the synthesis of optically active cyclic carbonates catalyzed by the binary catalyst system and designing new binary catalyst systems consisted of multichiral SalenCo(Ⅲ)-Ⅹ complexes and quaternary ammonium salts to synthesize optically active cyclic carbonates perfectly.1. In this dissertation, the sequence and molar ratio of polymer/cyclic product in the reaction catalyzed by binary catalyst systems consisted of various molar ratio of quaternary ammonium salt to SalenCo(Ⅲ)-Ⅹ was investigated by in-situ high pressure FT-IR. Cyclic carbonate is formed by the depolymerization of the propagating polycarbonates resulting from consecutive alternating enchainment of epoxide and CO2in the condition of low molar ratio of complex, while with the use of excess quaternary ammonium salt, the production of cyclic carbonate appears via a back-biting pathway of a metal-bound carboxylate.2. Multichiral SalenCo(Ⅲ)-Ⅹ complexs anchored on1,1’-bi-2-naphthol derivative have been developed for the asymmetric cycloaddition. The differences between the results of the kinetic resolution of epoxides using different loading and type of quaternary ammonium salts in the binary catalyst systems were investigated, and the results indicate that the use of excess quaternary ammonium salts or the cocatalyst based on a nucleophilic anion with poor leaving ability and a bulky cation is beneficial for the enantioselectivity. A possible mechanism about the asymmetric cycloaddition reaction catalyzed by binary catalyst systems, effected by the quaternary ammonium salts, was proposed.3. The region-and stereochemistry of styrene oxide was demonstrated. Due to phenyl as the electron-withdrawing group in the molecule, the nucleophilic ring-opening of styrene oxide predominantly occurs at the methane carbon rather than the methylene carbon and this is different from the terminal epoxides with electron-donating groups such as propylene oxide.