Nickel-catalyzed cross-coupling of unactivated alkyl halides using bis(pinacolato)diboron as reductant

The use of bis(pinacolato)diboron as the terminal reductant allows the efficient Ni-catalyzed coupling of unactivated secondary and primary alkyl halides, generating the C(sp(3))-C(sp(3)) coupling products in good yields. The mild catalytic conditions display excellent functional group tolerance, and good chemoselectivities which require only 1.5 equiv. of primary bromides for the coupling with secondary bromides. Preliminary mechanistic studies suggest that an in situ organoborane/Suzuki process is not likely. It was identified that the base and ligand have more profound impact on selecting this reductive coupling pathway. The good chemoselectivity appears to be evoked by the formation of Ni-Bpin catalytic intermediates, which demands matched sizes and reactivities of the alkyl halide coupling partners for optimal coupling efficiency.