Effect of Al cocatalyst in ethylene polymerization using (imido)vanadium(V) complexes containing anionic N-heterocyclic carbenes with a weakly coordinating borate moiety in 4-position (WCA-NHC), [V(N-2,6-Me2C6H3)Cl2(WCA-NHC)] [1; NHC 1,3-bis(2,6-dimethylphenyl)-imidazolin-2-ylidene], have been explored. The activities by 1 upon presence of Al i Bu3 in ethylene polymerization and in the copolymerization with norbornene (NBE) were higher than those in the presence of MAO, and the resultant

more »

... hylene-co-NBE)s prepared by 1-Al i Bu3 catalyst possessed uniform molecular weight distributions and compositions. Formation of vanadium(III) species could be assumed upon presence of Al i Bu3, especially on the basis of both NMR and ESR spectra (silent) and certain significant changes in the V K-edge XANES (pre-edge and edge region) spectrum, whereas no significant changes in the XANES spectrum were observed from the toluene solution containing 1 upon addition of MAO. It is thus suggested that a difference in the catalyst performances between in the presence of MAO and Al i Bu3 should be due to a formation of different catalytically active species with different oxidation states.