Synthesis, Structures, and Norbornene Polymerization Behavior of Bis(aryloxide-N-heterocyclic carbene) Nickel Complexes

Treatment of the o-hydroxyaryl imidazolinium pro-ligands (2-OH-3,5-tBu2C6H2)(R)(C3H3N2)+Br− [R = iPr (1a), tBu (1b), Ph (1c), Mes (1d)] with NiL2Cl2 (L = PPh3, Py) or Ni(OAc)2·4H2O afforded the corresponding cis bis(aryloxide-NHC) nickel complexes 2−5. Notably, the products were independent from the pro-ligands/Ni ratios. The same complexes were obtained with the pro-ligands/Ni ratio of 1:1 or 2:1. All the complexes were characterized by 1H and 13C NMR, high-resolution mass spectrometry (HRMS), and elemental analysis. The molecular structures of the aryloxide-NHC-ligated nickel complexes 2−5 were determined by single-crystal X-ray diffraction analysis. With methylaluminoxane (MAO) as cocatalyst, the nickel complexes showed moderate catalytic activities (106 g of PNB (mol of Ni)−1 h−1) in the addition polymerization of norbornene.