Anionic or Radical Polymerization Catalyzed by Metal Triflate-Based Lewis Pairs: A Comprehensive Mechanistic Study

Ester and amide enolates are important propagating species in organometallic-mediated polymerization of polar vinyl monomers, but the effects of the transition and main group metallic counterions have not been systematically understood. In this study, various metal triflates along with PPh3 are used to catalyze the Lewis pair anionic polymerization (LPAP) or Lewis pair radical polymerization (LPRP) of (meth)acrylates and acrylamides, and the metallic elements and polymerization solvents determine the dominant propagation mechanism. Specifically, the LPAP and LPRP proceed using early and late transition metal triflates, respectively, and the main group metal triflates catalyze the LPAP in organic solvents and the LPRP on-water. The elementary reactions of LPRP using PPh3/Fe(OTf)3 in organic solvents are kinetically investigated. Notably, the LPRP follows pseudo-second-order kinetics with respect to monomer concentration, which contributes initiation and propagation, whereas the LPAP using PPh3/Sc(OTf)3 proceeds with pseudo-zero-order kinetics. This indicates that the propagating species react with the unactivated free monomer in the LPRP and the Sc-activated monomer in the LPAP. This study demonstrates that metal triflate-based Lewis pairs can generate various new polymerizable metal enolates with distinctive reactivities.