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Published June 26, 2019 | Supplemental Material
Journal Article Open

Living Polymerization Caught in the Act: Direct Observation of an Arrested Intermediate in Metathesis Polymerization


Understanding the stability and reactivity of the propagating species is critical in living polymerization. Therefore, most living olefin metathesis polymerizations require the stabilization of the catalyst by coordination of external ligands containing Lewis basic heteroatoms, e.g., phosphines and pyridines. However, in some cases, chemists postulated that the propagating metal carbene could also be stabilized by olefin chelation. Here, we disclose that stable 16-electron olefin-chelated Ru carbenes play a key role in previously reported living/controlled ring-opening metathesis polymerization of endo-tricyclo[^(2,5)]deca-3,9-diene and cyclopolymerization of 1,8-nonadiynes using Grubbs catalysts. We successfully isolated these propagating species during polymerization and confirmed their olefin-chelated structures using X-ray crystallography and NMR analysis. DFT calculations and van 't Hoff plots from the equilibrium between olefin-chelated Ru carbenes and 3-chloropyridine (Py)-coordinated carbenes revealed that entropically favored olefin chelation overwhelmed enthalpically more stable Py-coordinated Ru carbenes at room temperature. Therefore, olefin chelation stabilized the propagating species and slowed down the propagation relative to initiation, thereby lowering polydispersity. This finding provides a deeper understanding of the olefin metathesis polymerization mechanism using Grubbs catalysts and offers clues for designing new controlled/living polymerizations.

Additional Information

© 2019 American Chemical Society. Received: April 14, 2019; Published: June 13, 2019. This paper is dedicated to Prof. Soon Hyeok Hong on his outstanding contribution to research and education at SNU. This research was supported financially by the Institute for Basic Science in Korea (IBS-R10-A1), Creative Research Initiative Grant, and Creative Material Discovery Program through NRF, Korea. We thank Prof. Soon Hyeok Hong and Mr. Seongyeon Kwon for helpful discussions. The authors declare no competing financial interest.

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Supplemental Material - ja9b04019_si_001.pdf

Supplemental Material - ja9b04019_si_002.cif

Supplemental Material - ja9b04019_si_003.cif


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