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

Abstract

A series of novel bis(imino)pyridine nickel(II) dichloride complexes, with the bis(imino)pyridine ligands containing electron-withdrawing groups (F, Cl, Br, CF 3 ), have been prepared and characterized by elemental analysis and NMR spectroscopy. All complexes exhibit paramagnetically shifted 1 H NMR spectra, indicative of the high-spin ( S = 1) state of the d 8 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 × 10 7 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 ( M w up to 4.5 × 10 6 ). X-ray structures for some of the nickel complexes are reported.