Synthesis Of N-heterocylic Carbene Functionalized Covalent Organic Framework And Its Catalysis In C-C Coupling Reactions

Covalent organic framework(COFs),a new type of crystalline porous materials,has a wide application prospect in gas adsorption,energy storage,sensing,especially in heterogeneous catalysis due to its special channel structure.However,the reported COFs catalysts had limited application due to the lack of efficient functional site.Because of the outstanding advantage of N-heterocyclic carbene catalysts in catalytic performance,in this paper,we introduced the concept of carbine into COFs,and designed a new stable heterogeneous catalyst named the N-heterocyclic carbene functionalised covalent organic framework with atomically dispersed palladium(Pd@COF-NHC).Then we characterized its structure and studied its catalytic performance in detail.The specific contents are as follows:We synthesized a new type of covalent organic framework using N-heterocyclic carbene dialdehyde and 1,3,5-triaminobenzene(TAB)as building units at room temperature,and made a series of characterizations such as PXRD,SEM,TEM.The results showed that the COFs possesses a regular layered structure with a certain crystallinity.Based on the COF-NHC,we synthesized a stable heterogeneous catalyst with atomically dispersed palladium(Pd@COF-NHC).In this text,we tried to make an in-depth study of the Suzuki-Miyaura coupling reaction for the construction of C-C bonds using Pd@COF-NHC as heterogeneous catalyst.The results were as follow:at room temperature,the yield of the reaction between aryl bromobenzene and aryl boric acid can reach more than 90%for 1 h in air.Moreover,the solvent of this reaction was water,the base was K₂CO₃and the amount of catalyst was only0.5 mol%,which embodied the concept of"green chemistry".More importantly,Pd@COF-NHC could be reused directly for at least eight times in Suzuki-Miyaura coupling reactions without significant loss in catalytic activity.So,the use of the Pd@COF-NHC truly realized the green and high efficient chemical reactions as we advocated.The C-C coupling reaction between aryl halobenzene and aryl bismuth is a type of reaction,which was used in the synthesis of drugs and fine chemicals.Till now,the use of aryl halobenzene in most of reactions was still aryl iodobenzene but there were also some limitations in this reaction such as high reaction temperature,long reaction time,and rigorous anhydrous anaerobic environment.In this essay,we explored the reaction between aryl iodobenzene and aryl bismuth by using the Pd@COF-NHC(2 mol%)and K₂CO₃in ethanol aqueous solution(Et OH:H₂O=4:1)at room temperature for 5 h,which exhibited high yield.We also investigated the reaction between aryl bromobenzene and aryl bismuth,and achieved the same high yield by raising the temperature to 80?.Furthermore,the catalyst can also be reused many times and achieved the green efficiency of reactions.