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Updated: Feb 19, 2026

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry
Published on: October 18, 2019
Decomposition of Olefin Metathesis Catalysts by Brønsted Base: Metallacyclobutane Deprotonation as a Primary
Gwendolyn A Bailey1, Justin A M Lummiss1, Marco Foscato2
1Center for Catalysis Research and Innovation, and Department of Chemistry and Biomolecular Sciences, University of Ottawa , Ottawa K1N 6N5, Canada.
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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