Photocatalytic cyclization of nitrogen-centered radicals with carbon nitride through promoting substrate/catalyst interaction

The use of metal-free carbon nitride and light to drive catalytic transformations constitutes a sustainable strategy for organic synthesis. At the moment, enhancing the intrinsic activity of CN catalysts by tuning the interfacial coupling between catalyst and substrate remains challenging. Herein, we demonstrate that urea-derived carbon nitride catalysts with the abundant -NH2 groups and the relative positive charged surface could effectively complex with the deprotonated anionic intermediate to improve the adsorption of organic reactants on the catalyst surface. The decreased oxidation potential and upshift in its highest occupied molecular orbital position make the electron abstraction kinetics by the catalyst more energetically favorable. The prepared catalyst is thus utilized for the photocatalytic cyclization of nitrogen-centered radicals for the synthesis of diverse pharmaceutical-related compounds (33 examples) with high activity and reusability, which shows competent performance to the homogeneous catalysts. Carbon nitride catalysts with positively charged surfaces and abundant -NH2 are found to be effective photocatalysts for dihydropyrazole synthesis. A surface-mediated mechanism where deprotonated intermediates interact with the surface is proposed.

Automated summary

The use of metal-free carbon nitride and light for catalytic transformations is a sustainable strategy for organic synthesis. In this study, urea-derived carbon nitride catalysts with positively charged surfaces and abundant -NH2 groups were found to improve the adsorption of organic reactants on the catalyst surface, resulting in enhanced activity. The prepared catalyst was successfully utilized for the synthesis of various pharmaceutical-related compounds through photocatalytic cyclization of nitrogen-centered radicals, demonstrating high activity and reusability.