Stereoselective ring-opening metathesis polymerization of 7-tert-butoxy-bicyclo[2,2,1]hepta-2,5-diene by NHC-ruthenium catalysts

摘要

Ru complexes having N-heterocyclic carbene (NHC) ligands, differing in the bulkiness of N-aryl substituents and in the backbone substitution and/or configuration, are utilized in the ring-opening metathesis polymerization (ROMP) of 7-tert-butoxybicyclo[2,2,1]hepta-2,5-diene (7-TBONBD). The activity, regioselectivity, and stereoselectivity of the catalysts are investigated and rationalized considering the influence of the NHC ligand architectures of Ru complexes on the outcome of the polymerization. The reactivity order is influenced by bulky substituents at the nitrogen of the NHC ligand and by NHC-backbone substitution. All of the catalysts give rise to living polymerizations and show high selectivity, producing highly syndiotactic polymers with 100% of anti-units and, surprisingly, an elevated cis-content (up to 88%).