Vinyl Polymerization of Norbornene on Nickel Complexes with Bis(imino)pyridine Ligands Containing Electron-Withdrawing Groups

A series of novel bis­(imino)­pyridine nickel­(II) dichloride
complexes,
with the bis­(imino)­pyridine ligands containing electron-withdrawing
groups (F, Cl, Br, CF3), have been prepared and characterized
by elemental analysis and NMR spectroscopy. All complexes exhibit
paramagnetically shifted 1H NMR spectra, indicative of
the high-spin (S = 1) state of the d8 nickel­(II)
central atom. These complexes have been found to be highly active
catalysts of vinyl-type norbornene polymerization upon activation
with MAO, displaying activities up to 1.16 × 107 g
of PNB (mol of cat.)−1 h–1 (the
highest ever reported for norbornene polymerizations on bis­(imino)­pyridine
nickel complexes) and yielding high-molecular-weight polynorbornene
(Mw up to 4.5 × 106).
X-ray structures for some of the nickel complexes are reported.