Blue-Light-Driven Aerobic Oxidation via ROS-Generating Binuclear Cobalt(II) Complex Photocatalyst

Developing earth-abundant photocatalysts that operate efficiently under visible light remains a central challenge in sustainable aerobic oxidation chemistry. We synthesized a binuclear cobalt(II) structure (Co₂) in which two redox-active metal centers are bridged by a polypyridine scaffold to integrate light-harvesting and catalytic functions within a single low-nuclearity unit. The complex exhibits a strong absorption band below 450 nm, undergoes facile charge separation upon photoexcitation, and channels molecular oxygen (O₂) toward superoxide radical anion (O₂^•-) under blue-light irradiation. Spectroscopic and mechanistic studies indicate that the polypyridine framework governs photon capture and excited-state delocalization, whereas the proximal Co(II) sites mediate the subsequent single-electron transfer to O₂. Driven by this dual-site synergy, Co₂ selectively oxidizes a broad scope of thioethers to the corresponding sulfoxides in yields exceeding 95%, with no over-oxidation to sulfones detected. The catalyst retains its structural integrity over five successive runs without measurable activity loss. By confining complementary photophysical and redox functions within a discrete bimetallic unit, this work establishes a design strategy for noble-metal-free, visible-light-driven organic transformations.