Heterogeneous organophotocatalytic HBr oxidation coupled with oxygen reduction for boosting bromination of arenes.

Developing mild photocatalytic bromination strategies using sustainable bromo source has been attracting intense interests, but there is still much room for improvement. Full utilization of redox centers of photocatalysts for efficient generation of Br + species is the key. Herein we report heterogenous organophotocatalytic HBr oxidation coupled with oxygen reduction to furnish Br 2 and H 2 O 2 for effective bromination of arenes over Al 2 O 3 supported perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). Mechanism studies suggest that O-vacancy in Al 2 O 3 can provide Lewis-acid-type anchoring sites for O 2 , enabling unexpected dual-electron transfer from anchored photoexcited PTCDA to chemically bound O 2 to produce H 2 O 2 . The in-situ generated H 2 O 2 and Br 2 over redox centers work together to generate HBrO for bromination of arenes. This work provides new insights that heterogenization of organophotocatalysts can not only help to improve their stability and recyclability, but also endow them with the ability to trigger unusual reaction mode via cooperative catalysis with supports.