Olefin metathesis by Grubbs−Hoveyda complexes: computational and experimental studies of the mechanism and substrate-dependent kinetics

Ian W. Ashworth, Ian H. Hillier, David J Nelson, Jonathan M Percy, Mark A. Vincent

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

The potential energy surfaces for the activation of Grubbs−Hoveyda-type precatalysts with the substrates ethene, propene, 1-hexene, and ethyl vinyl ether (EVE) have been probed at the density functional theory (DFT) (M06-L) level. The energetically favored pathway of the reaction leading to a 14e Fischer carbene and styrene starts with an initiation step in which the incoming substrate and outgoing alkene ligand are both clearly associated with the ruthenium center.
For these substrates, with the exception of ethene, the rate determining step is predicted to be the formation of the metallocyclobutane (MCB). We have taken the initial reactant to be a weak van der Waals complex between substrate and
precatalyst. This model yields good agreement between the computed activation parameters for both the parent Grubbs−Hoveyda and Grela complex with EVE substrate, and the experimental values, reported here. The alternative model which takes the initial reactant to be two isolated molecules requires an estimate of the entropy loss on formation of the initial complex in solution which is difficult to evaluate. Our estimate of this quantity yields a barrier for the rate determining step for the interchange mechanism which is close to the value we find for the alternative mechanism in which the rate determining step is the initial dissociation of the precatalyst. The relative energetics of these two mechanisms involving different initiation steps but with similar activation barriers, could well be dependent upon the precatalyst and substrate in line with the recent experimental findings of Plenio and co-workers.
LanguageEnglish
Pages1929-1939
Number of pages11
JournalACS Catalysis
Volume3
Early online date12 Jul 2013
DOIs
Publication statusPublished - 2013

Fingerprint

Alkenes
Olefins
Kinetics
Substrates
Chemical activation
Ethers
Potential energy surfaces
Styrene
Ruthenium
Interchanges
Propylene
Density functional theory
Entropy
Ligands
Molecules

Keywords

  • olefin metathesis
  • reaction mechanism
  • potential energy surface
  • Grubbs-Hoveyda type complexes
  • Fischer carbene
  • density functional theory
  • kinetic studies

Cite this

Ashworth, Ian W. ; Hillier, Ian H. ; Nelson, David J ; Percy, Jonathan M ; Vincent, Mark A. / Olefin metathesis by Grubbs−Hoveyda complexes : computational and experimental studies of the mechanism and substrate-dependent kinetics. In: ACS Catalysis. 2013 ; Vol. 3. pp. 1929-1939.
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Olefin metathesis by Grubbs−Hoveyda complexes : computational and experimental studies of the mechanism and substrate-dependent kinetics. / Ashworth, Ian W.; Hillier, Ian H.; Nelson, David J; Percy, Jonathan M; Vincent, Mark A.

In: ACS Catalysis, Vol. 3, 2013, p. 1929-1939.

Research output: Contribution to journalArticle

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AB - The potential energy surfaces for the activation of Grubbs−Hoveyda-type precatalysts with the substrates ethene, propene, 1-hexene, and ethyl vinyl ether (EVE) have been probed at the density functional theory (DFT) (M06-L) level. The energetically favored pathway of the reaction leading to a 14e Fischer carbene and styrene starts with an initiation step in which the incoming substrate and outgoing alkene ligand are both clearly associated with the ruthenium center.For these substrates, with the exception of ethene, the rate determining step is predicted to be the formation of the metallocyclobutane (MCB). We have taken the initial reactant to be a weak van der Waals complex between substrate andprecatalyst. This model yields good agreement between the computed activation parameters for both the parent Grubbs−Hoveyda and Grela complex with EVE substrate, and the experimental values, reported here. The alternative model which takes the initial reactant to be two isolated molecules requires an estimate of the entropy loss on formation of the initial complex in solution which is difficult to evaluate. Our estimate of this quantity yields a barrier for the rate determining step for the interchange mechanism which is close to the value we find for the alternative mechanism in which the rate determining step is the initial dissociation of the precatalyst. The relative energetics of these two mechanisms involving different initiation steps but with similar activation barriers, could well be dependent upon the precatalyst and substrate in line with the recent experimental findings of Plenio and co-workers.

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