Metallacyclic mechanism of the addition polymerization of norbornene involving Ni(I) and Ni(III) complexes

Abstract

The catalytic system Ni(COD)2/BF3·OEt2 is highly active in the addition polymerization of nor-bornene (NB). Its activity, which is up to 1930 (kg NB) (mol Ni)−1 h−1, is higher than the activity of the other known nickel complex catalysts. Another advantage of this system over the latter is that it contains a smaller proportion of a Lewis acid (5 molar parts or below) and no conventional stabilizing organoelement ligands. The activity of this system in NB polymerization has been investigated by Fourier-transform IR spectroscopy. According to EPR data, NB polymerization is accompanied by the formation of low-spin complexes of trivalent nickel, which result from the oxidative addition of the monomer to univalent nickel complexes. A metallacyclic mechanism involving Ni(I) and Ni(III) complexes is suggested for NB polymerization.