The chemocatalytic processing of the greenhouse gas CO2 into valuable chemicals and biofuels has gained broad appeal in recent years. Among the approaches described, the N-formylation of CO2 with an amine is of great importance due to its versatility in the construction of N-containing linear and cyclic frameworks. Here, a stable N-heterocyclic carbene-carboxyl adduct (NHC-CO2) was prepared in a simple manner, which can be used as a recyclable zwitterionic catalyst for efficient CO2-reductive upgrading either via N-formylation or further coupled with a cyclization under mild conditions (25 ° C.) Could be used, 1 atm CO2) using hydrosilane as the hydrogen source. More than 30 different alkyl and aromatic amines could be converted into corresponding formamides or benzimidazoles with remarkable yields (74% -98%). It was found that the electronic effect of the introduced substituents on NHC-CO2 obviously influences the thermostability and nucleophilicity of the zwitterionic catalyst, which correlates directly with its catalytic activity. In addition, NHC-CO2 could deliver CO2 through in situ decarboxylation at a specific temperature that depends on the type of substituent introduced. Experimental and computational studies showed that carboxyl species on NHC-CO2 were not only a nucleophilic center but also a C1 source by rapidly capturing or replacing CO2 from the environment during hydrosilylation. In addition, a simple and environmentally friendly conceptual process for product cleaning and catalyst recycling with good small-scale feasibility was developed.


Please enter your comment!
Please enter your name here