Nickel and cationic palladium complexes bearing (imino)pyridyl alcohol ligands: Synthesis, characterization and vinyl polymerization of norbornene

A series of nickel and palladium complexes bearing (imino)pyridyl alcohol tridentate [N,N,O] ligands, 2-(ArNdouble bond; length as m-dashCMe)-6-{(HO)CR2}C5H3N (L1–L4), were synthesized and sufficiently characterized by elemental and spectroscopic analysis along with X-ray diffraction analysis. The X-ray diffraction demonstrated that five-coordinated nickel halide complexes (1a–4a and 1b) and six-coordinated nickel acetate complex (1c) were prepared, and cationic palladium complexes (1d and 2d) formed with the [PdCl4]2− counterion. All these complexes displayed high catalytic activities up to 1.883 × 107 g(PNB) mol−1(cat) h−1 (2d) for the vinyl polymerization of norbornene on treatment with excess methylaluminoxane (MAO), affording the vinyl-type PNBs with high molecular weights and relatively narrow molecular weight distributions. The parameters of reaction conditions, the type of metals and steric effects of coordinative ligands had influences on the catalytic properties.