Design, Preparation And Catalytic Performance Of Benzimidazole-based Covalent Organic Framework Materials

Covalent organic frameworks（COFs）are an emerging class of porous organic materials.Due to their controllable structure,tunable pore size,and easy modification,they are widely used in catalysis,drug delivery,adsorption,sensing,and gas storage.In particular,covalent organic framework materials also have the characteristics of high thermal stability and insolubility in common organic solvents,which make them widely used in the field of heterogeneous catalysis.COFs have the characteristics of being designable and modifiable,that is,functional groups can be preseted in the precursor structure,or functional groups can be introduced through post-modification strategies to construct functionalized COFs.It is also possible to construct loaded COFs catalysts with COFs as a carrier.Therefore,the development of catalytic systems based on COFs has become a research hotspot in the field of catalysis.This dissertation will focus on three aspects:green preparation method,post-modification functionalization and catalytic performance of benzimidazole-based COFs（COF-BM series）.The main contents are as follows:（1）The benzimidazole-based covalent organic framework material COF-BM was synthesized by room temperature photocatalysis.Using sodium fluorescein as photocatalyst,both 1,3,5-Tris（p-formylphenyl）benzene and 1,2,4,5-phenylenetetramine tetrahydrochloride composed COF-BM by N-arylation reaction which was under blue light at 470 nm.Further,we used the post-modification strategy to prepare the covalent organic framework materials COF-BM-SO₃H with acid-base bifunctionality and acidic ionic liquid-type covalent organic framework materials COF-BM-IL-SO₃H by controlling the amount of 1,3-propane sultone.In this strategy,we used 1,3-propane sultone as the alkylating agent for N atom.The structure,morphology and thermal stability of COFs were tested by FT-IR,SS NMR,SEM,TEM,BET,TGA or other testing instruments.（2）Using acid-base bifunctional covalent organic framework material COF-BM-SO₃H as catalyst,we constructed a catalytic system for tandem decarboxylation Knoevenagel condensation reaction.A series of Knoevenagel condensation products containing C=C double bonds were prepared by catalyzing the reaction between benzaldehyde dimethyl acetal derivatives and active methylene groups at 60°C in the presence of H₂O as solvent.The research results showed that COF-BM-SO₃H had excellent catalytic performance.When the reaction time was 5 h,the product yield reached more than 94%.When COF-BM-SO₃H was used for 10 times,its catalytic activity remained basically unchanged.（3）Using acidic ionic liquid type covalent organic framework material COF-BM-IL-SO₃H as acid catalyst to catalyze the synthesis of 1,8-dioxanthene derivatives under solvent-free conditions at 100℃.The research results showed that the product yield reached more than 91%after 1 h.（4）We constructed the nitrogen-rich benzimidazole-based covalent organic framework material COF-BM-N by function orientation.Using COF-BM-N as a carrier,the covalent organic framework material Pd/COF-BM-N loading palladium catalyst was synthesized.Using sodium fluorescein as photocatalyst,both 1,3,5-tris（2-formylpyridin-5yl）benzene and 1,2,4,5-benzenetetraamine tetrahydrochloride composed COF-BM-N by N-arylation reaction which was under blue light at 470 nm.Further,using COF-BM-N as a carrier,palladium acetate was loaded to prepare Pd/COF-BM-N,which was discussed as a heterogeneous catalyst for Buchwald-Hartwig C-N coupling reaction.The experimental results showed that Pd/COF-BM-N had good substrate adaptability.After 8 catalytic cycles,the activity of Pd/COF-BM-N did not decrease significantly and could be reused.