Efficient Synthesis of Aryl Boronates via Cobalt-Catalyzed Borylation of Aryl Chlorides and Bromides

An efficient catalytic system based on a Co(II)-NHC precursor has been developed for the cross coupling of bis(pinacolato)diboron with aryl halides including aryl chlorides, affording the aryl boronates in good to excellent yields. A wide range of functional groups are tolerated under mild reaction conditions. The reaction shows excellent chemoselectivity for bromide over chloride. Preliminary mechanistic investigations show that the catalytic cycle may rely on a cobalt(I)-(III) redox couple.