Operation of the boomerang mechanism in olefin metathesis reactions promoted by the second-generation Hoveyda catalyst

Jennifer M. Bates, Justin A.M. Lummiss, Gwendolyn A. Bailey, Deryn E. Fogg

Research output: Contribution to journalArticlepeer-review

Abstract

A long-standing question in olefin metathesis centers on whether the "release-return" (boomerang) mechanism contributes to the productivity of Hoveyda-class catalysts. According to this mechanism, a molecule of o-isopropoxystyrene (A) is liberated during catalyst initiation, but recaptures the active catalyst following metathesis. The relevance of this pathway for the second-generation Hoveyda catalyst HII was assessed in metathesis of 1,1-and 1,2-disubstituted olefins. Crossover studies with 13C-labeled A*, as well as competition experiments involving ring-closing or cross metathesis (RCM, CM) in the presence of A (equimolar with HII) indicated rapid reuptake of styrenyl ether. The crossover studies indicated highly efficient catalyst initiation, with the entire catalyst charge being activated before metathesis was complete. In a comparative study involving CM of anethole with methyl acrylate, sustained activity was shown for HII, whereas the second-generation Grubbs catalyst GII was rapidly deactivated. These data demonstrate that the release-return mechanism is indeed operative for HII in these demanding metathesis reactions, and that facile shuttling from a protected recapture cycle into the productive metathesis cycle contributes to the superior performance of HII relative to GII.

Original languageEnglish (US)
Pages (from-to)2387-2394
Number of pages8
JournalACS Catalysis
Volume4
Issue number7
DOIs
StatePublished - Jul 3 2014
Externally publishedYes

Keywords

  • boomerang mechanism
  • homogeneous catalysis
  • Hoveyda catalysts
  • olefin metathesis

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