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. η2-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 η2-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-cc-pVDZ//PBE0/SDD level of theory.