Recyclable porphyrin photocatalyst for highly efficient visible-light-driven aerobic oxidation of sulfides

Abstract

Herein, we report a highly efficient, environmentally benign, and sustainable photocatalytic system for aerobic sulfide oxidation, employing a porphyrin-based catalyst in green solvents under visible light irradiation at room temperature. Synergistically modulating the photostability, solubility, and photoactivity of porphyrins by tailoring their peripheral substituents enabled both high catalytic efficiency and facile recovery. Notably, porphyrins bearing carboxyl groups (tetrakis (4-carboxyphenyl) porphyrin, TCPP) exhibited superior catalytic activity and recyclability, and could be easily reused for at least eight cycles with consistent performance. This method delivers sulfoxides with excellent selectivity (>99%) and high isolated yields (86-99%) within exceptionally short reaction times (15-40 min) and a low catalyst loading (0.1-1.0 mol%). In addition, the protocol exhibits broad substrate scope across various sulfide skeletons (30 examples), encompassing alkyl aryl sulfides bearing strong electron-withdrawing groups (-CN, -NO2) as well as notoriously oxidation-resistant diaryl sulfides, and can be successfully scaled up to the gram scale within 40 min. Mechanistic studies reveal that the oxidation proceeds mainly via an energy transfer pathway, with singlet oxygen identified as the reactive oxygen species. This work opens a new avenue for developing practical visible-light-initiated oxidations and serves as an inspiration for the design of recyclable organic photocatalysts.