Cationic four- and five-coordinate nickel(II) complexes: Insights into thenickel(II)-catalyzed copolymerization of ethylene and carbon monoxide

Using the dppp-derived Ni(II) catalyst system 2, several four- and five-coo rdinate intermediates relevant to the alternating copolymerization of ethyl ene and carbon monoxide have been characterized. In addition, the activatio n barriers for the migratory insertion steps corresponding to chain growth have been determined to be at or below ca. 10 kcal/mol, indicating that a s trongly stabilized catalyst resting state is most likely responsible for th e low activity of 2 for copolymerization.