Intramolecular hydrogen exchange among the coordinated methane fragments of Cp2W(H)CH3. Evidence for the formation of a σ complex of methane prior to elimination

R Morris Bullock, Christine E L Headford, Karen M. Hennessy, Susan E. Kegley, Jack R. Norton

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Abstract

NMR examination at 45-50°C of a solution containing appropriate isotopically labeled derivatives of Cp2W(H)CH3 shows intramolecular hydrogen exchange between the hydride and methyl ligands of individual molecules, combined at high concentrations with intermolecular hydride exchange. Because of this intermolecular hydride exchange, methane elimination, although intramolecular, appears to be intermolecular at high concentrations. Comparison of the rate of CH4 elimination from Cp2W(H)CH3 with the rate of CD4 elimination from Cp2W(D)CD3 shows an inverse isotope effect of 0.7 at 72.6°C. The reversible formation of a σ complex of methane as an intermediate in the elimination process is the most plausible explanation for the H/CH3 scrambling and for the inverse isotope effect.

Original languageEnglish
Pages (from-to)3897-3908
Number of pages12
JournalJournal of the American Chemical Society
Volume111
Issue number11
Publication statusPublished - 1989

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Methane
Hydrides
Isotopes
Hydrogen
Ligands
Nuclear magnetic resonance
Derivatives
Molecules

ASJC Scopus subject areas

  • Chemistry(all)

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Intramolecular hydrogen exchange among the coordinated methane fragments of Cp2W(H)CH3. Evidence for the formation of a σ complex of methane prior to elimination. / Bullock, R Morris; Headford, Christine E L; Hennessy, Karen M.; Kegley, Susan E.; Norton, Jack R.

In: Journal of the American Chemical Society, Vol. 111, No. 11, 1989, p. 3897-3908.

Research output: Contribution to journalArticle

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N2 - NMR examination at 45-50°C of a solution containing appropriate isotopically labeled derivatives of Cp2W(H)CH3 shows intramolecular hydrogen exchange between the hydride and methyl ligands of individual molecules, combined at high concentrations with intermolecular hydride exchange. Because of this intermolecular hydride exchange, methane elimination, although intramolecular, appears to be intermolecular at high concentrations. Comparison of the rate of CH4 elimination from Cp2W(H)CH3 with the rate of CD4 elimination from Cp2W(D)CD3 shows an inverse isotope effect of 0.7 at 72.6°C. The reversible formation of a σ complex of methane as an intermediate in the elimination process is the most plausible explanation for the H/CH3 scrambling and for the inverse isotope effect.

AB - NMR examination at 45-50°C of a solution containing appropriate isotopically labeled derivatives of Cp2W(H)CH3 shows intramolecular hydrogen exchange between the hydride and methyl ligands of individual molecules, combined at high concentrations with intermolecular hydride exchange. Because of this intermolecular hydride exchange, methane elimination, although intramolecular, appears to be intermolecular at high concentrations. Comparison of the rate of CH4 elimination from Cp2W(H)CH3 with the rate of CD4 elimination from Cp2W(D)CD3 shows an inverse isotope effect of 0.7 at 72.6°C. The reversible formation of a σ complex of methane as an intermediate in the elimination process is the most plausible explanation for the H/CH3 scrambling and for the inverse isotope effect.

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