Sequence- and Stereocontrolled Ring-Opening/Cross Metathesis Polymerization

Cascade metathesis polymerization serves as a powerful method to synthesize well-defined polymers with increased structural complexity. Despite recent advances, achieving a sequence-regulated cascade metathesis polymerization of monomers with functional groups that exhibit high metathesis reactivity remains a formidable challenge. Here, we report an asymmetric, cascade ring-opening/cross metathesis polymerization of monomers containing highly ring-strained cyclopropene and highly reactive terminal alkene. The major hurdle lies in the fact that the precision control over the alternating sequences would be compromised by homopolymerization or homodimerization of the two reactive alkenes. By leveraging the 14-electron, chiral cationic Grubbs-type catalyst, both the initiation and chain growth processes include catalytic cycles orchestrated by two sequential metathesis reactions: ring-strain-driven ring-opening metathesis with cyclopropene and subsequent chelation-controlled cross metathesis with terminal alkene. This cascade metathesis polymerization is also characterized by high stereoselectivity, providing polymers with all-cis alkenes and good enantioselectivity at the recurring quaternary stereocenters.