Copper-Catalyzed C–B(sp3) Bond Formation through the Intermediacy of Cu–B(sp3) Complex

The vast majority of transition metal (TM) catalyzed borylative transformations rely on TM–B­(sp2) complexes. Contrastingly, the chemistry of TM–B­(sp3) species and their potential in catalytic borylation remain surprisingly underdeveloped, due probably to the lack of suitable boron­(sp3) reagents. Herein, we employ our recently developed sp2-sp3 diboron reagent to successfully enable a copper-catalyzed hydroboration of allenes for C–B­(sp3) bond formation. A comprehensive mechanistic study, including the isolation and structural characterization of a Cu–B­(sp3) complex, substantiates the presence of a Cu–B­(sp3) intermediate in the catalytic cycle.