Two-Dimensional Co₃S₄ Nanosheetsfor the Visible-Light Photocatalysis of Thioesterification of Alkenesand Thiol–Ene Click Reactions

Recently, photochemistry has enabled the design and development of unique reaction pathways, addressing the increasing demand for efficient, sustainable synthetic methods for diverse organosulfur compounds. Herein, an efficient green solvent-based method for photocatalytic thioesterification and thiol–ene reactions, catalyzed by spinel Co₃S₄ under visible light, has been investigated. This strategy includes a broad substrate scope bearing electron-donating and electron-withdrawing groups with generally high efficiency. The pure-phase spinel Co₃S₄ photocatalyst was synthesized using a deep eutectic solvent (DES) as a solvent and an in situ sulfur source, and cobalt-zeolitic imidazolate framework-9 (Co-ZIF-9) was used as a template and a source of cobalt. The DES offers several advantages, including eco-friendliness, low cost, and tunability, making it an attractive alternative to traditional solvents. The spinel Co₃S₄ has a nanosheet morphology with a direct band gap of 1.79 eV and exhibits thioesterification and thiol–ene reactions under visible-light irradiation with excellent product yields. Electron, hole, and various radical scavenging and time-dependent NMR experiments were performed to support the proposed hole-mediated radical mechanism. The catalyst was readily isolated from the reaction mixture by simple filtration and reused several times without significant degradation in activity. This work provides a promising strategy for developing efficient and sustainable visible-light-driven photocatalysts for organic transformations involving C–S bond formation.