Preparation Of Polymers Based On Bulky N-Heterocyclic Carbene And Its Catalytic Performance In Suzuki-Miyaura Reaction

Palladium-catalyzed Suzuki-Miyaura cross-coupling reaction is one of the C-C coupling widely apllied in advanced materials,electronics,pharmaceuticals and other fields.N-heterocyclic carbenes?NHCs?have been extensively discussed and studied as the ligand of palladium catalysts.In recent years,the emergence of self-supported catalyst with plenty of active centers provides a new idea.However,there is less research on self-supported palladium catalysts with large steric hindrances,and the synthesis process of self-supported palladium catalysts is complicated.This paper focuses on the preparation of polymers based on bulky N-heterocyclic carbenes and the catalytic performance of the corresponding palladium complexes for the Suzuki-Miyaura reaction:?1?We designed two synthetic routes,and explored a simple and effective synthetic scheme for the preparation of N-heterocyclic carbene polymer.Using 2,6-diisopropylaniline and formaldehyde as raw materials,we explored the synthesis scheme of N-heterocyclic carbene polymer and optimized the reaction conditions,and obtained the optimum conditions?solvent:tetrahydrofuran;the amount of formic acid:70?L;the ratio of aldehyde to amine:1:1.05;the reaction temperature:25 ^oC and the reaction time:48 h?.Theof poly-imine?P-imine?can reach 1.3�10⁴ g mol^-1.The imidazolium-based polymer?P?b-NHC�HCl??with excellent thermal stability was successfully prepared.?2?Based on the above studies,we obtained two self-supporting palladium catalysts C 1&C 2 with large steric carbenes by complexing polycarbene with stable palladium trichloropyridine,and explored the catalytic performance of the catalysts in the Suzuki-Miyaura cross-coupling reaction.Catalyst C 1 is a green and efficient self-supporting palladium catalyst based on bulky N-heterocyclic carbenes polymer.Its palladium loading is up to 1.35 mmol g^-1.Catalyst C 1 exhibits good catalytic activity and substrate suitability for Suzuki-Miyaura reaction of aryl bromides and aryl chlorides,and it can be recycled 6 times.In this paper,catalysts C 1 with different palladium loadings were prepared and compared,and the optimal palladium loading was found to be 0.8 mmol g^-1.However,applying the phenyl-modified catalyst C 2 to the Suzuki-Miyaura reaction,the results show that it exhibits good catalytic activity for brominated substrates,but not for chlorinated substrates.In addition,catalyst C 2 can only be recycled 3 times.We compare the catalysts C 1 to C 2,and find that the presence of benzene rings is detrimental to the catalytic ability of the self-supporting palladium catalyst based on bulky N-heterocyclic carbenes polymer.