Visible-Light-Induced Phenoxyl Radical-based Metal–Organic Framework for Selective Photooxidation of Sulfides

Phenoxyl radicals originating from phenols through oxidation
or
photoinduction are relatively stable and exhibit mild oxidative activity,
which endows them with the potential for photocatalysis. Herein, a
stable and recyclable metal–organic framework Zr-MOF-OH constructed of a binaphthol derivative ligand has been synthesized
and functions as an efficient heterogeneous photocatalyst. Zr-MOF-OH shows fairly good catalytic activity and substrate compatibility
toward the selective oxidation of sulfides to sulfoxides under visible
light irradiation. Such irradiation of Zr-MOF-OH converts
the phenolic hydroxyl groups of the binaphthol derivative ligand to
phenoxyl radicals through excited state intramolecular proton transfer,
and the excited state photocatalyst triggers the single-electron oxidation
of the sulfide. No reactive oxygen species are produced in the photocatalytic
process, and triplet O2 directly participates in the reaction,
endowing Zr-MOF-OH with wide substrate compatibility
and high selectivity, which also proposes a promising pathway for
the direct activation of substrates via phenoxyl radicals.