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

Journal of the American Chemical Society
Gwendolyn A BaileyDeryn E Fogg

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(κ2-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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Citations

Jun 23, 2018·Chemistry : a European Journal·Adrian SytniczukKarol Grela
Mar 1, 2019·Dalton Transactions : an International Journal of Inorganic Chemistry·Maialen Espinal-ViguriMichael K Whittlesey
Jul 6, 2019·Dalton Transactions : an International Journal of Inorganic Chemistry·Yannick D BidalCatherine S J Cazin
Sep 22, 2020·Beilstein Journal of Organic Chemistry·Maximillian Heidrich, Herbert Plenio
Jun 2, 2020·Physical Chemistry Chemical Physics : PCCP·Magdalena JawiczukBartosz Trzaskowski
Aug 16, 2018·Journal of the American Chemical Society·Ka Wing ChanChristophe Copéret
Jul 17, 2020·Journal of the American Chemical Society·Jeffrey C FosterRachel K O'Reilly
Jan 19, 2018·Journal of the American Chemical Society·Carolyn S HigmanDeryn E Fogg
Jun 27, 2018·Journal of the American Chemical Society·Adrian SytniczukKarol Grela
Nov 28, 2019·Journal of the American Chemical Society·Daniel L Nascimento, Deryn E Fogg
Apr 14, 2018·Journal of the American Chemical Society·Gwendolyn A BaileyDeryn E Fogg
Jan 9, 2020·ACS Combinatorial Science·Olivier B C MontyNicholas Simmons
Jul 25, 2019·Accounts of Chemical Research·Christopher P GordonOdile Eisenstein

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