Switchable organocatalysts: Highly efficient reductive functionalization of CO2 to benzimidazoles under mild conditions

Chemocatalytic of CO2 as a low-cost C1 feedstock to produce valuable fine chemicals was considered as a green and environmental approach. Among the reported strategy, the cyclization of o-phenylenediamines with CO2 is of great significance due to their broad application in the industry and medicine. Hence, we reported the switchable organocatalysts-catalyzed synthesis of benzimidazoles via cyclization of o-phenylenediamines with CO2 and hydrosilane as a hydrogen source under mild conditions (60 ℃, 0.5 MPa). It was found that imidazolium hydrogen carbonate ionic liquids ([CnCmIm][HCO3]) was not only used as recyclable organic pre-catalysts for N-heterocyclic carbenes, but also served as a multifunctional catalyst in which could activate o-phenylenediamines, CO2, and hydrosilane. So, up to 99% conversion of o-phenylenediamines could be achieved for 8 h at 60 ℃ and the reactivity of the catalyst remained nearly unchanged after three cycles. This protocol provides a feasible methodology for fixing CO2 into valuable benzimidazoles.