Initiation efficacy of halo-chelated cis-dichloro-configured ruthenium-based second-generation benzylidene complexes in ring-opening metathesis polymerization
The initiation efficacy of eight differently substituted halo-chelated cis-dichloro-configured ruthenium-based second-generation benzylidene complexes was assessed in the ring-opening metathesis polymerization of a norbornene derivative in two solvents and at three temperatures. From the evaluation of the number average molecular masses and the molecular mass distributions of the resulting polymers a conclusion on the level of initiation was possible and it was found that the metathesis-inactive cis-dichloro-configured pre-initiators quickly isomerize to their metathesis-active trans-dichloro isomers leading to remarkably high initiation efficiencies in toluene at 80 °C. Even controlled polymerization is feasible under these conditions. Further, the diverse initiation efficacies of the eight pre-initiators at ambient temperature are discussed with the emphasis to identify whether the position of the cis–trans equilibrium or the speed of the isomerization is responsible for the results obtained in the polymerization experiments.
KeywordsOlefin metathesis Ruthenium Structure–activity relationships Polymerizations
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