Base-Free Borylation\nof Aryl Halides Enabled by Zn-Promoted\nHalide Abstraction

Herein, we report the palladium-catalyzed borylation\nof aryl halides\n(iodides or bromides) under base-free conditions utilizing a commercially\navailable Lewis acidic mediator, Zn(OTf)<sub>2</sub>. Under these\nconditions, an array of electronically and functional-group-diverse\naryl iodides and bromides undergo borylation to afford the corresponding\naryl boronic esters in ≤82% isolated yields. Mechanistic investigations\nare consistent with Zn(OTf)<sub>2</sub> enabling transmetalation between\na cationic Pd(II)–Ar intermediate and B<sub>2</sub>pin<sub>2</sub> via halide abstraction. Furthermore, stabilization of the\ncationic [ArPd<sup>II</sup>]<sup>+</sup> complex with added [BAr<sup>F</sup><sub>4</sub>]<sup>−</sup> significantly improves the\nreaction efficiency with electron-poor arenes.