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.