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

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Title
Living Polymerization Caught in the Act: Direct Observation of an Arrested Intermediate in Metathesis Polymerization
Author(s)
Jung-Ah Song; Bohyun Park; Soohyung Kim; Cheol Kang; Dongwhan Lee; Mu-Hyun Baik; Robert H. Grubbs; Tae-Lim Choi
Publication Date
2019-06
Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, v.141, no.25, pp.10039 - 10047
Publisher
AMER CHEMICAL SOC
Abstract
© 2019 American Chemical Society.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[4.2.2.02,5]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
URI
https://pr.ibs.re.kr/handle/8788114/6069
ISSN
0002-7863
Appears in Collections:
Center for Catalytic Hydrocarbon Functionalizations(분자활성 촉매반응 연구단) > Journal Papers (저널논문)
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