Alternating Copolymerizations Using a Grubbs-Type Initiator with Unsymmetrical, Chiral N-Heterocyclic Carbene Ligand

摘要

Reports on alternating copolymers prepared by metathesis copolymerization of two different monomers are relatively rare. In 2005, Chen et al. reported on the mechanism-based design of a ROMP (ring-opening metathesis polymerization) catalyst for sequence-selective copolymerization. Here, we report on an alternative system for the synthesis of alternating copolymers based on Grubbs-type initiators containing an unsymmetrical, chiral N-heterocyclic carbene (NHC) ligand. As part of our on ongoing research on ruthenium metathesis catalysts with saturated unsymmetrical NHC ligands initiator 1 was prepared from [RuCl2(PCy3)2-(CHPh)] and 1-mesityl-3-((1'R)-1-phenylethyl)-4,5-dihydro-imidazolium tetrafluoroborate in 90% yield. This initiator was used for the copolymerization of norbornene (NBE) and cyclooctene (COE) using a stoichiometry of 1/NBE/COE of 1:2000:100000.