Cobalt-Catalyzed C(sp<sup>2</sup>)–H Borylation with an Air-Stable, Readily Prepared Terpyridine Cobalt(II) Bis(acetate) Precatalyst

A bench-stable, 4-aryl-substituted terpyridine supported, high-spin cobalt­(II) bis­(acetate) complex, (<sup><i>Ar</i></sup>Tpy)­Co­(OAc)<sub>2</sub> (<sup><i>Ar</i></sup>Tpy = 4′-(4-<i>N</i>,<i>N</i>′-dimethylaminophenyl)-2,2′:6′,2″-terpyridine), is active for the C­(sp<sup>2</sup>)–H borylation of arenes and heteroarenes with B<sub>2</sub>Pin<sub>2</sub> (Pin = pinacolato). Optimization of the catalytic borylation reaction revealed improved performance in the presence of LiOMe and turnover numbers of up to 100 have been observed using all air-stable components. EPR specstroscopy identified formation of inactive cobalt species, promoted by excess HBPin. A high-spin cobalt­(II) bis­[(diacetoxy)­pinacolatoborate−κ<sup>3</sup><i>O</i>,<i>O</i>,<i>O</i>] compound has been isolated and characterized by X-ray diffraction and is the result of catalyst deactivation.