Construction Of N-doped Metal Carbon-based Materials And Their Catalytic Synthesis Of Benzimidazole Derivative

Benzimidazole N-heterocyclic compounds are extensively applied in organic synthesis,but the classical synthetic feed stocks are almost reliy on non-regeneration fossil energy,which further intensify the depletion of fossil resources and environmental depravation.Compared with sustainable resources such as solar,wind,hydrogen,and geothermal energy,biomass is the only sustainable source of carbon that can be used to produce fuels and chemicals for human life.In the context of green chemistry and sustainable chemical conversion,catalytic hydrogen transfer cascade reaction between bioalcohols and nitro compounds to produce benzimidazole nitrogen-containing heterocyclic compounds has attracted wide attention due to its good redox economy and high atom efficiency,but higher requirements for catalysts.In this paper,porous and recyclable nitrogen-doped carbon non-precious metal catalysts were obtained by carbide thermal stability,cavitation adjustable zeolite imidazole framework(ZIFs)precursors in an inert atmosphere,which were used to efficiently catalyze the one-pot synthesis of benzimidazole derivatives from biomass alcohols and substituted 2-nitroanilines in the absence of exogenous hydrogen and alkali through hydrogen self-transfer coupling reaction.This catalytic system overcomes the harsh requirements of hydrogen transfer on catalysts,and has the advantages of green,economic and efficient.The research includes:(1)Nitrogen-doped carbon cobalt metal(Co@NC-T,T is the pyrolysis temperature)catalysts were obtained by pyrolysis of ZIF-67 precursor at different temperatures.It can be seen from the material characterization that the structure and active site distribution of catalyst materials are mainly affected by carbonization temperature.The catalytic activity test showed that the catalytic activity of Co@NC-700 was the best in the hydrogen transfer coupling reaction.After optimization of the catalytic system,86%of the target product of2-phenylbenzimidazole could be obtained after reacting in cyclohexane(2 mL)at a substrate molar ratio of 1:3 at 150℃ for 10 h.Detailed mechanistic studies revealed that the significant synergistic effect of the porous nitrogen-doped carbon with large specific surface area,the significant synergistic effect of the Co-N_x active species double site contributes to the active expression of Co@NC-700,while the excessively high pyrolysis temperature may cause the cleavage of the Co-N bond of the catalyst,thereby reducing its activity.Else,the hydrogen transfer mechanism revealed that the initial dehydrogenation of bioethanols and the cyclization dehydrogenation of condensation intermediates were well correlated with the hydrogenation of nitro.(2)On the exploration of Co@NC-T materials,Co-Znbimetallic catalysts(Co-ZnO@NC-T,T is carbonization temperature)were prepared by metal doping method.The catalytic activity test demonstrated that the Co-ZnO@NC-800 catalyst displaied dramatic catalytic property for the hydrogen transfer coupling reaction.The conversion and yield of o-nitroaniline and 2-phenylbenzimidazole reached 99%and94%,respectively,after reaction in 2 mL chlorobenzene at 150℃ for 9 h.The catalyst characterization showed that the introduction of metallic zinc further reduced the massive aggregation of cobalt nanoparticles,and the cobalt metal was well dispersed in the nitrogen-doped support.Further analysis of the active sites of the catalyst indicated that the introduction of zinc not only hindered the aggregation of cobalt metal,but also contained a small amount of amphoteric oxide zinc oxide species,which was benefical to the condensation of o-phenylenediamine with benzaldehyde.Therefore,the Co-ZnO@NC-T catalyst exhibits better selectivity than the single-metal Co@NC-T catalyst.