TY - JOUR
T1 - Decomposition of Olefin Metathesis Catalysts by Brønsted Base
T2 - Metallacyclobutane Deprotonation as a Primary Deactivating Event
AU - Bailey, Gwendolyn A.
AU - Lummiss, Justin A.M.
AU - Foscato, Marco
AU - Occhipinti, Giovanni
AU - McDonald, Robert
AU - Jensen, Vidar R.
AU - Fogg, Deryn E.
N1 - 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.
PY - 2017/11/22
Y1 - 2017/11/22
N2 - 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.
AB - 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.
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U2 - 10.1021/jacs.7b08578
DO - 10.1021/jacs.7b08578
M3 - Article
C2 - 29099591
AN - SCOPUS:85034814875
SN - 0002-7863
VL - 139
SP - 16446
EP - 16449
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 46
ER -