A role of the monomer structure in the mechanism of stereoregulation in the metathesis polymerization of norbornene derivatives

It was shown that, in the metathesis polymerization of norbornene derivativ es catalyzed by the RuCl3H2O system, the ring opening of metallacycles lead s to formation of the closed metal-carbene complexes in which the double bo nd of the terminal monomer unit remains coordinated to the Ru atom. The kin etic scheme of the chain propagation reaction that takes into account the r eaction of the monomers with both the closed and open metal-carbene complex es makes it possible to describe the experimental dependence of the ratio b etween the rates of formation of cis and trans units in the polymers of nor bornene derivatives on the initial concentration of the monomers. The effec t of the monomer structure on the content of tl-ans units in the polymers i s explained by a change in the total energy of cis and trans metallacycles and in the energy barrier to transition of cis and trans metal carbenes fro m the closed to the open structure and by the steric hindrances that appear in the interaction of the monomers with the closed metal-carbene complexes .