Base-Free Borylation of Aryl Halides Enabled by Zn-Promoted Halide Abstraction

Herein, we report the palladium-catalyzed borylation of aryl halides (iodides or bromides) under base-free conditions utilizing a commercially available Lewis acidic mediator, Zn(OTf)2. Under these conditions, an array of electronically and functional-group-diverse aryl iodides and bromides undergo borylation to afford the corresponding aryl boronic esters in ≤82% isolated yields. Mechanistic investigations are consistent with Zn(OTf)2 enabling transmetalation between a cationic Pd(II)–Ar intermediate and B2pin2 via halide abstraction. Furthermore, stabilization of the cationic [ArPdII]+ complex with added [BArF4]− significantly improves the reaction efficiency with electron-poor arenes.