Mechanochemical Synthesis Of Asymmetric Salen Catalysts And Their Application

Salen-type metal-organic complexes have the advantages of high stability and easy recovery,and high enantioselectivity for catalytic reactions.In this study,a mechanochemical method was proposed to synthesize asymmetric Salen ligands and metal complexes;and based on the Ullmann coupling reaction,bimetallic complexes were also prepared,and the catalytic performance was studied.The specific results are as follows:1 Focusing on the synthesis principle of imines,a mechanochemical method was used to obtain asymmetric Salen-type ligands in good yields with yields of 71-95%.The introduction of a diethylamine group（-N（CH₂CH₃）₂）into the Salen ligand can facilitate purification and improve catalytic efficiency.The chelation effect of asymmetric Salen ligands with Zn,Cu and Co was studied,and the chelation rate of chiral Co-salen complexes was as high as 98%.The catalytic hydrolysis kinetic resolution（HKR）of epichlorohydrin was explored,and the enantioselectivity of the reaction was high（98%ee）.Then,the catalytic asymmetric ring-opening of terminal epoxides and phenols were studied to prepareα-aryloxy alcohols（yields were56-88%）.And the catalytic reaction mechanism was explored:after the catalyst was activated with HOAc,there was a molecular-level interaction between Co（salen）cation and OAc^-in the catalytic process（electrophilic-nucleophilic dual activation mechanism）,which provided better intermediates.hydrogen bond donor capacity.2 Based on the synthesis of asymmetric Salen ligands containing bromine groups,Ullmann coupling reaction with hydroxyl compounds was carried out to form coordination sites for bimetallic complexation.Taking the reaction of bromine-containing Salen-type Schiff base and hydroquinone as an example,the conditions of solvent,temperature,base and reaction time in the reaction process were optimized.The solvent was DMF,the base was Cs₂CO₃,and the catalytic amount was10 mol%Cu Br,the additive 18-crown ether-6,and refluxing for 10 h was the best synthetic route,and the yield was 32-66%.Then,taking phenol and ethylene glycol ligands as special cases,Co（OAc）₂.4H₂O was used for bimetallic complexation,and the yield of aliphatic ligands was even higher as 89%.The catalytic performance of the complex was characterized by studying the yield and recovery of the product catalyzed by the epoxidation of 1-phenyl-1-cyclohexene.The products and intermediates were characterized by NMR,FTIR,HRMS and other means.