As eries of in situ formed alkenyl diboronate complexes from alkenyl Grignard reagents (commercially available or prepared from alkenyl bromides and Mg) with B 2 Pin 2 (bis(pinacolato)diboron) react with diverse alkyl halides by aR up hotocatalyst to give various gem-bis-(boryl)alkanes.A lkyl radicals add efficiently to the alkenyl diboronate complexes,and the adduct radical anions undergo radical-polar crossover,s pecifically,a1,2-boryl-anion shift from boron to the a-carbon sp 2 center.T his transformation shows good functional-group compatibility and can serve as ap owerful synthetic tool for late-stage functionalization in complex compounds.M easurements of the quantum yield reveal that aradical-chain mechanism is operative in whichthe alkenyl diboronates acts as reductive quencher for the excited state of the photocatalyst.