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, ((Ar)Tpy)Co-(OAc)(2) ((Ar)Tpy = 4'-(4-N,N'-dimethylaminopheny1)-2,2':6',2 ''-terpyridine), is active for the C(sp(2))-H borylation of arenes and heteroarenes with B(2)Pin(2) (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-kappa O-3,O,O] compound has been isolated and characterized by X-ray diffraction and is the result of catalyst deactivation.