Mechanism of di-tert-butylsilylene transfer from a silacyclopropane to an alkene

Tom G. Driver, Keith Woerpel

Research output: Contribution to journalArticle

Abstract

Kinetic and thermodynamic studies of the reactions of cyclohexene silacyclopropane 1 and monosubstituted alkenes suggested a possible mechanism for di-tert-butylsilylene transfer. The kinetic order in cyclohexene silacyclopropane 1 and cyclohexene were determined to be 1 and -1, respectively. Saturation kinetic behavior in monosubstituted alkene concentration was observed. Competition experiments between substituted styrenes and a deficient amount of di-tert-butylsilylene from 1 correlated well with the Hammett equation and provided a p value of -0.666 ± 0.008, using σ p constants. These data supported a two-step mechanism involving reversible di-tert-butylsilylene extrusion from 1, followed by irreversible concerted electrophilic attack of the silylene on the monosubstituted alkene. Eyring activation parameters were found to be ΔH‡ = 22.1 ± 0.9 kcal·mol-1 and ΔS‡ = -15 ± 2 eu. Competition experiments between cycloalkenes and allylbenzene determined cycloalkenes to be more efficient silylene traps (krel =1.3, ΔΔG‡ = 0.200 kcal·mol-1). A summary of the data resulted in a postulated reaction coordinate diagram. The mechanistic studies enabled rational modification of reaction conditions that improved the synthetic utility of silylene transfer. Removal of the volatile cyclohexene from the reaction mixture into an evacuated headspace led to the formation of previously inaccessible cyclohexene-derived silacyclopropanes.

Original languageEnglish (US)
Pages (from-to)10659-10663
Number of pages5
JournalJournal of the American Chemical Society
Volume125
Issue number35
DOIs
StatePublished - Sep 3 2003

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Alkenes
Olefins
Kinetics
Cycloparaffins
Styrenes
Extrusion
Styrene
Experiments
Chemical activation
Thermodynamics
di-tert-butylsilylene
cyclohexene

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Mechanism of di-tert-butylsilylene transfer from a silacyclopropane to an alkene. / Driver, Tom G.; Woerpel, Keith.

In: Journal of the American Chemical Society, Vol. 125, No. 35, 03.09.2003, p. 10659-10663.

Research output: Contribution to journalArticle

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abstract = "Kinetic and thermodynamic studies of the reactions of cyclohexene silacyclopropane 1 and monosubstituted alkenes suggested a possible mechanism for di-tert-butylsilylene transfer. The kinetic order in cyclohexene silacyclopropane 1 and cyclohexene were determined to be 1 and -1, respectively. Saturation kinetic behavior in monosubstituted alkene concentration was observed. Competition experiments between substituted styrenes and a deficient amount of di-tert-butylsilylene from 1 correlated well with the Hammett equation and provided a p value of -0.666 ± 0.008, using σ p constants. These data supported a two-step mechanism involving reversible di-tert-butylsilylene extrusion from 1, followed by irreversible concerted electrophilic attack of the silylene on the monosubstituted alkene. Eyring activation parameters were found to be ΔH‡ = 22.1 ± 0.9 kcal·mol-1 and ΔS‡ = -15 ± 2 eu. Competition experiments between cycloalkenes and allylbenzene determined cycloalkenes to be more efficient silylene traps (krel =1.3, ΔΔG‡ = 0.200 kcal·mol-1). A summary of the data resulted in a postulated reaction coordinate diagram. The mechanistic studies enabled rational modification of reaction conditions that improved the synthetic utility of silylene transfer. Removal of the volatile cyclohexene from the reaction mixture into an evacuated headspace led to the formation of previously inaccessible cyclohexene-derived silacyclopropanes.",
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