Pd-Catalyzed Aerobic Oxidative Coupling of Arenes: Evidence for Transmetalation between Two Pd(II)-Aryl Intermediates

[Image: see text] Pd-catalyzed aerobic oxidative coupling of arenes provides efficient access to biaryl compounds. The biaryl product forms via C–H activation of two arenes to afford a Pd(II)ArAr′ intermediate, which then undergoes C–C reductive elimination. The key Pd(II)ArAr′ intermediate could form via a “monometallic” pathway involving sequential C–H activation at a single Pd(II) center, or via a “bimetallic” pathway involving parallel C–H activation at separate Pd(II) centers, followed by a transmetalation step between two Pd(II)–aryl intermediates. Here, we investigate the oxidative coupling of o-xylene catalyzed by a PdX(2)/2-fluoropyridine catalyst (X = trifluoroacetate, acetate). Kinetic studies, H/D exchange experiments, and kinetic isotope effects provide clear support for a bimetallic/transmetalation mechanism.