Metal‐Free Phosphorus‐Directed Borylation of C(sp2)−H Bonds

Abstract Spectacular progress has recently been achieved in transition metal‐catalyzed C−H borylation of phosphines as well as directed electrophilic C−H borylation. As shown here, P‐directed electrophilic borylation provides a new, straightforward, and efficient access to phosphine–boranes. It operates under metal‐free conditions and leverages simple, readily available substrates. It is applicable to a broad range of backbones (naphthyl, biphenyl, N ‐phenylpyrrole, binaphthyl, benzyl, naphthylmethyl) and gives facile access to various substitution patterns at boron (by varying the boron electrophile or post‐derivatizing the borane moiety). NMR monitoring supports the involvement of P‐stabilized borenium cations as key intermediates. DFT calculations reveal the existence and stabilizing effect of π‐arene/boron interactions in the (biphenyl)( i ‐Pr) 2 P→BBr 2 + species.