Nickel-catalyzed, silyl-directed, ortho-borylation of arenes via an unusual Ni(II)/Ni(IV) catalytic cycle.

Nickel-catalyzed C-H bond functionalization reactions provide an impressive alternative to those with noble metal catalysts due to their unique reactivity and low cost. However, the regioselective C(sp)-H borylation reaction of arenes accomplished by nickel catalyst remains limited. We herein disclose a silyl-directed ortho C(sp)-H borylation of substituted arenes with a Ni(cod)/PMe/KHMDS catalyst system. Using readily available starting materials, this protocol provides easy access to ortho-borylated benzylic hydrosilanes bearing flexible substitution patterns. These products can serve as versatile building blocks for the synthesis of sila or sila/borine heterocycles under mild conditions. Control experiments and DFT calculations suggest that a catalytic amount of base prompts the formation of Ni(II)-Bpin-ate complex, likely related to the C(sp)-H bond activation. This borylation reaction might follow an unusual Ni(II)/Ni(IV) catalytic cycle.