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

Area of Science:

• Photocatalysis
• Sustainable Chemistry
• Organometallic Chemistry

Background:

• Developing earth-abundant photocatalysts for visible-light-driven aerobic oxidation is crucial for sustainable chemistry.
• Integrating light-harvesting and catalytic functions in a single molecular unit presents a significant challenge.

Purpose of the Study:

• To synthesize and characterize a binuclear cobalt(II) complex (Co2) for visible-light-driven aerobic oxidation.
• To investigate the photocatalytic mechanism and efficiency of the Co2 complex.

Main Methods:

• Synthesis of a binuclear cobalt(II) complex with a polypyridine scaffold.
• Photophysical characterization including absorption spectroscopy and photoexcitation studies.
• Mechanistic studies involving spectroscopic analysis and reaction monitoring of thioether oxidation.

Main Results:

• The Co2 complex exhibits strong absorption below 450 nm and efficient charge separation upon photoexcitation.
• Under blue-light irradiation, the complex facilitates the single-electron reduction of molecular oxygen (O2) to superoxide radical anion (O2•-).
• Co2 selectively oxidizes thioethers to sulfoxides with >95% yield, avoiding over-oxidation to sulfones, and demonstrates high stability over multiple catalytic cycles.

Conclusions:

• The polypyridine scaffold and proximal cobalt sites in Co2 work synergistically to achieve efficient photocatalysis.
• This work presents a design strategy for noble-metal-free, visible-light-driven organic transformations using discrete bimetallic photocatalysts.