Metal-free g-C₃N₄ nanosheets as a highly visible-light-active photocatalyst for thiol-ene reactions

Thiol-ene click reactions are important for the construction of carbon-sulfur bonds. The use of visible-light photoredox catalysis for the formation of C-S bonds has attracted much attention. In this work, two-dimensional metal-free graphitic carbon nitride (g-C₃N₄) nanosheets are prepared through a simple thermal polymerization method and used to catalyze the thiol-ene click reaction under visible light-illumination. This green, atom-economic, and inexpensive approach for the hydrothiolation of alkenes is applicable for structurally different substrates and exhibits superior yields. In air or nitrogen atmosphere, the reaction yield decreases when a hole scavenging agent, CH₃OH, is introduced, which indicates that photogenerated holes in the g-C₃N₄ nanosheets play an important role in the formation of thiyl radicals. The g-C₃N₄ nanosheets still show a good stability and favorable photocatalytic activity after five cycles of the reaction. Moreover, this approach can be scaled up to the gram-scale synthesis of benzyl(phenethyl)sulfane with a yield up to 93%. Our study suggests a good potential of semiconducting g-C₃N₄ nanosheets as a metal-free, efficient photocatalyst for various thiol-ene click reactions and even for other organic reactions.