Photoinduced Perfluoroalkylation Mediated by Cobalt Complexes Supported by Naphthyridine Ligands

Cobalt­(III) and cobalt­(II) perfluoroethyl complexes supported
by
1,8-naphthyridine or its mono- or dimethylsubstituted analogues were
synthesized, and their reactivity has been investigated in light-induced
radical perfluoroethylation of arenes and heteroarenes. Similar to
previously reported NiIII complexes, CoIII naphthyridine-based
complexes show light-induced CoIII–C2F5 bond homolysis to generate the C2F5 radical, while the CoII complex was significantly less
reactive. In the presence of a stoichiometric amount of electron-rich
arene or heteroarene, the products of monoperfluoroethylation by the
cationic [(naphthyridine)2CoIII(C2F5)2]+ complexes were obtained selectively
and with good yields. This reactivity was further enhanced in the
presence of one-electron oxidants or benzoquinone. Moderate catalytic
turnover was obtained when pentafluoroethyl-1,2-benziodoxol-3­(1H)-one (Acid C2F5-Togni reagent) was
used, although the substrate scope and the reactivity remain limited
to electron-rich substrates.