Directing aryl-I versus aryl-Br bond activation by nickel via a ring walking process

Activation of a strong aryl-Br bond of a halogenated vinylarene by nickel(0) is demonstrated in the presence of aryl-I containing substrates. eta(2)-Coordination of Ni(PEt3)(2) to the C=C moiety of halogenated vinylarenes is kinetically preferable and is followed by an intramolecular aryl-halide bond activation process. This ring-walking process is quantitative and proceeds under mild reaction conditions in solution. Mechanistic studies indicate that the metal insertion into the aryl-halide bond is not the rate-determining step. The reaction obeys first-order kinetics in the eta(2)-Coordination complexes with almost identical activation parameters for Br and I derivatives. The ring-walking process is kinetically accessible as shown by density functional theory (DFT) calculations at the PBE0/SDB-ccpVDZ//PBE0/SDD level of theory.