Decomposition of Olefin Metathesis Catalysts by Brønsted Base: Metallacyclobutane Deprotonation as a Primary Deactivating Event

Gwendolyn A. Bailey, Justin A.M. Lummiss, Marco Foscato, Giovanni Occhipinti, Robert McDonald, Vidar R. Jensen, Deryn E. Fogg

Research output: Contribution to journalArticlepeer-review

42 Scopus citations

Abstract

Brønsted bases of widely varying strength are shown to decompose the metathesis-active Ru intermediates formed by the second-generation Hoveyda and Grubbs catalysts. Major products, in addition to propenes, are base·HCl and olefin-bound, cyclometalated dimers [RuCl(κ 2-H2IMes-H)(H2C=CHR)]2 Ru-3. These are generated in ca. 90% yield on metathesis of methyl acrylate, styrene, or ethylene in the presence of either DBU, or enolates formed by nucleophilic attack of PCy3 on methyl acrylate. They also form, in lower proportions, on metathesis in the presence of the weaker base NEt3. Labeling studies reveal that the initial site of catalyst deprotonation is not the H2IMes ligand, as the cyclometalated structure of Ru-3 might suggest, but the metallacyclobutane (MCB) ring. Computational analysis supports the unexpected acidity of the MCB protons, even for the unsubstituted ring, and by implication, its overlooked role in decomposition of Ru metathesis catalysts.

Original languageEnglish (US)
Pages (from-to)16446-16449
Number of pages4
JournalJournal of the American Chemical Society
Volume139
Issue number46
DOIs
StatePublished - Nov 22 2017
Externally publishedYes

Bibliographical note

Funding Information:
This work was funded by NSERC of Canada and the Research Council of Norway (project number 262370.

Publisher Copyright:
© 2017 American Chemical Society.

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