Cobalt-Catalyzed C–H Borylation of Alkyl Arenes and Heteroarenes Including the First Selective Borylations of Secondary Benzylic C–H Bonds

A cobalt di-tert-butoxide complex bearing N-heterocyclic carbene (NHC) ligands has been synthesized and characterized. This complex is effective at catalyzing the selective monoborylation of the benzylic position of alkyl arenes using pinacolborane (HBpin) as the boron source. This same cobalt complex enables selective monoborylation of N-methylpyrrole, N-methylpyrazole, and N-methylindole. Catalysis can be achieved with as little as 2–3 mol % of the cobalt precatalyst at 80 °C.