Nitrogen-containing Mesoporous Carbon-Supported Copper For Catalyzing N-Arylation Of Nitrogen Heterocycles

Ordered nitrogen-containing mesoporous carbon (NMC) has wide application in many fields, such as adsorption, catalysis, fuel cell and electrochemical etc., because of high surface area, controllable ordered pore structure, large pore size, good hydrothermal stability and excellent conductive properties, as well as the hydrophilic and functionalized surface. Therefore, it is extensively investigated at home and abroad.In this paper, some NMC and CMK-3 materials are prepared by a hard-template method, where the mesoporous silica SBA-15 is used as the hard template, and used as carriers to support coppers to catalyze the C-N coupling. The mesoporous materials and catalysts are characterized by XRD, XPS, SEM and TEM, respectively.The results show that the synthesized NMC and CMK-3 materials have highly ordered mesoporous structure. The copper on NMC has good dispersion; and no aggregated particles of copper are observed on the surface of NMC, when the loading amount is lower than 10%. However, the copper supported on CMK-3 appears serious aggregations. The results suggest that NMC is a much better support of copper than CMK-3.Comapred with on CMK-3, the coppers supported on NMC appear much better performace on catalyzing C-N coupling of bromobenzene and imidazole. Among Cu/NMC catalysts, which copper loading ranges from 2.5% to 20%,10% Cu/NMC shows the best catalytic activity. The lower or higher loading amount causes the active sites to reduce and makes the activity weak. Therefore,10%Cu/NMC catalyst is chosen to optimize the reaction conditions. The optimum reaction condition is: bromobenzene:5mmol, Aryl halide:Imidazole:KOH= 1.0:1.5:2.0, [10%Cu/NMC]/bromobenzene:10mol%,150℃,24h, DMSO/bromobenzene: 5g/5mmol. Yield of 1-Phenylimidazole reachs to 91.3%. The catalyst also exhibits good activity on catalyzing C-N coupling of imidazole with 1,4-bromophenol or 4-Bromoanilines. However, for coupling of some aryls bromides, which contain some electron-withdrawing groups, such as p-Bromoacetophenones, the catalyst shows poor selectivity and the product yield is low. If the reaction condition is optimized further, the yield can increase to 82%. The condition is:Aryl halide:Imidazole:K2CO3= 1.0:4.0:1.1, [10% Cu/NMC]/aryls bromide:10mol%,120℃,24h, DMSO/aryls bromide: 5g/5mmol. And it is also find that for the coupling of different Aryl halide with imidazole and the coupling of bromobenzene with different Nitrogen heterocycle, the catalyst also shows good catalytic activity under different conditions.The catalyst displays good stability, and can be recycled for five times at least without loss of yield and activity. The coupling reactions do not need any ligands to promote, so the products can be purified easily.