Promoting effect of cyano groups attached on g-C3N4 nanosheets towards molecular oxygen activation for visible light-driven aerobic coupling of amines to imines

Abstract

Molecular oxygen activation shows a great potential for a wide range of applications in organic transformations, but remains a challenge owing to the high inertness from its high energy electrons. In this work, we firstly report the dramatically promoting effect of cyano groups on visible light-driven molecular oxygen activation over cyano-decorated g-C3N4 nanosheets (DCNNS) fabricated by a facile and green thermal post-treatment approach from g-C3N4 nanosheets (CNNS). Experimental studies and theoretical calculation reveal that the homojunction-like structure is constructed in DCNNS owing to the introduction of cyano-groups, which can facilitate the generation of hot carriers, and thus promotes the O2− production. The optimized DCNNS exhibits 2.4 times higher activity than pristine CNNS for the visible light-driven oxidative coupling of benzylamine to imine, an industrially important transformation as a probe reaction. The discovered cyano groups-promoting visible light-driven molecular oxygen activation strategy has been extended to coupling of various amines to their corresponding imines. The present work could open a new horizon for designing highly efficient g-C3N4-based catalysts for diverse organic transformations via molecular oxygen activation.