Cobalt-Catalyzed C(sp²)–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, (^ArTpy)­Co­(OAc)₂ (^ArTpy = 4′-(4-N,N′-dimethylaminophenyl)-2,2′:6′,2″-terpyridine), is active for the C­(sp²)–H borylation of arenes and heteroarenes with B₂Pin₂ (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−κ³O,O,O] compound has been isolated and characterized by X-ray diffraction and is the result of catalyst deactivation.