Visible light-mediated radical perfluoroalkylation reactions using heterogeneous graphitic carbon nitride

Abstract

Photocatalytic radical fluoroalkylation has become an important approach to prepare valuable organofluorine compounds under mild conditions. Compared to the homogenous photocatalytic fluoroalkylation reactions based on the precious metal complexes or organic dyes, heterogeneous photocatalysis using metal-free carbon nitride catalyst shows cost-effective, easier separation and excellent recyclability. In this work, we report the visible-light-induced photocatalytic perfluoroalkylation of alkynes with perfluoroalkyl iodides (RfI) using heterogeneous cyano-modified graphitic carbon nitride (g-NCNCNx) as the photocatalyst. The mechanism proposed by the experimental and computational studies reveals that the long-lived triplet excited states in photoinduced g-NCNCNx are involved in the initial bimolecular electron transfer process, resulting in the effective activation of RfI and the improvement of sequential photocatalytic reactions. Moreover, the stronger interaction between the substate and surface of catalyst g-NCNCNx can further improve the photocatalytic activity, comparing to the pristine carbon nitride (g-CNx). Through simple variation of the reaction conditions, the photocatalytic addition or coupling reaction can be achieved effectively and selectively. Importantly, the heterogeneous g-NCNCNx photocatalyst can not only show high performance with a wide reaction scope, but also be readily recovered and reused for at least five catalytic cycles with high photocatalytic activity. This work provides a sustainable alternative to the conventional metal-based photocatalysts for organofluorine synthesis.