[V(N-2,6-Cl2C6H3)(CHSiMe3)(OC6X5)(NHC)] [X = F (1), Cl (2), NHC = 1,3-bis-(2,6-dimethylphenyl)-imidazol-2-ylidene], exhibited remarkable catalytic activities [TOF = 133-193 sec-1 (1), 90.9-126 sec-1 (2)] for ring opening metathesis polymerisation (ROMP) of norbornene (NBE) at 25 ºC to afford ring-opened polymers not only with high cis- (93-98 %) selectivity, but also with exclusive syndiotactic stereo-regularity. These polymerisations proceeded in a living manner under optimised conditions. The activity improved at 50 ºC with decreasing in the cis specificity. Synthesis and the structural analysis of the fluorinated alkoxide complexes, [V(N-2,6-X2C6H3)(CHSiMe3)(NHC)] [X = F (3), Cl (4)] have been studied, and the difluorophenylimdo complex (3) exhibited comparable catalytic activities for ROMP of NBE. The cis selectivities in the resultant polymers prepared by 3 were low (88 %) and the selectivities in the ring-opened poly(tetracyclododecene) (TCD) were low (61-66 %) compared to those in poly(NBE)s. The resultant ring opened poly(TCD) possessed syndiotactic stereo-regularity confirmed by DSC thermogram of the hydrogenated polymers.

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