Photo-Induced -C-H Borylation of Arenes through In Situ Generation of Rhodium(II) Ate Complexes.

Photoinduced "oxidation" of half-sandwich metal complexes to "high-valent" cationic metal complexes has been used to accelerate catalytic reactions. Here, we report the unprecedented photoinduced "reduction" of half-sandwich metal [Rh(III)] complexes to "low-valent" anionic metal [Rh(II)] ate complexes, which facilitate ligand exchange with electron-deficient elements (diboron). This strategy was realized by using a functionalized cyclopentadienyl (Cp) Rh(III) catalyst we developed, which enabled the basic group-directed room temperature -C-H borylation of arenes.