An opportunity for Mg-catalyzed Grignard-type reactions: direct coupling of benzylic halides with pinacolborane with 10 mol % of magnesium.

Mg in catalytic amounts as the only metal permits the reductive coupling between benzyl halides and pinacolborane. HBpin acts both as an electrophile and as a reducing agent to regenerate an organomagnesium species in situ. An hydride oxidation mechanism is proposed on the basis of DFT calculations.