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Published November 6, 2019 | Supplemental Material
Journal Article Open

Examining the Effects of Monomer and Catalyst Structure on the Mechanism of Ruthenium-Catalyzed Ring-Opening Metathesis Polymerization


The mechanism of Ru-catalyzed ring-opening metathesis polymerization (ROMP) is studied in detail using a pair of third generation ruthenium catalysts with varying sterics of the N-heterocyclic carbene (NHC) ligand. Experimental evidence for polymer chelation to the Ru center is presented in support of a monomer-dependent mechanism for polymerization of norbornene monomers using these fast-initiating catalysts. A series of kinetic experiments, including rate measurements for ROMP, rate measurements for initiation, monomer-dependent kinetic isotope effects, and activation parameters were useful for distinguishing chelating and nonchelating monomers and determining the effect of chelation on the polymerization mechanism. The formation of a chelated metallacycle is enforced by both the steric bulk of the NHC and by the geometry of the monomer, leading to a ground-state stabilization that slows the rate of polymerization and also alters the reactivity of the propagating Ru center toward different monomers in copolymerizations. The results presented here add to the body of mechanistic work for olefin metathesis and may inform the continued design of catalysts for ROMP to access new polymer architectures and materials.

Additional Information

© 2019 American Chemical Society. Received: August 15, 2019; Published: October 25, 2019. W.J.W. gratefully acknowledges the Arnold O. Beckman postdoctoral fellowship for financial support. We thank Dr. David VanderVelde for assistance with NMR experiments, Dr. Michael Takase for assistance with X-ray crystallography, and Dr. Mona Shagholi for assistance with HRMS. We are also indebted to Drs. Tonia Ahmed, Adam Johns, Allegra Liberman-Martin, Chris Marotta, and Mr. Jiaming Li for helpful discussions and assistance with preparing this manuscript. We thank Materia Inc. for the generous donation of Ru metathesis catalysts. We gratefully acknowledge Dr. Jase Gehring for assistance with preparing figures. The authors declare no competing financial interest.

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