Palladium-Catalyzed Sequential Cross-Coupling/Annulation of -Vinyl Bromobenzene with Aryl Bromide: Bimetallic Pathway versus Pd(II)-Pd(IV) Pathway: A DFT Investigation.

The palladium-catalyzed sequential cross-coupling/annulation of -vinyl bromobenzenes with aryl bromides generating phenanthrenes was characterized by density functional theory (DFT). The Pd(II)-Pd(IV) pathway (Path V) is shown to be less probable than the bimetallic pathway (Path I), the latter proceeding via the following six steps: oxidative addition, vinyl-C(sp)-H activation, Pd(II)-Pd(II) transmetalation, C-C coupling, aryl-C(sp)-H activation, and reductive elimination. The aryl-C(sp)-H activation process acts as the rate-determining step (RDS) of the entire chemical transformation, with an activation free energy barrier of ca.