Reactions of group III metal alkyls in the gas phase. Part V. The kinetics of the intramolecular elimination of isobutene from tri-isobutylgallium
- 1 January 1971
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc. A
- p. 3603-3606
- https://doi.org/10.1039/j19710003603
Abstract
The gas-phase kinetics and mechanistics of the concerted unimolecular elimination of isobutene from tri-isobutylgallium have been studied in presence of excess of ethylene. For temperatures between 416 and 500 K the unimolecular rate constant k1 for the 4-centre elimination process can be represented (with standard errors) by the Arrhenius relationship: log k1/s–1=(11·57 ± 0·29)–(30·40 ± 0·58)/θ where θ= 2·303 × 10–3RT with T in K and R in kcal mol–1[=(11·57 ± 0·29)–(127·2 ± 2·4)/θ in kJ mol–1]. The activation energy for the back reaction, the addition of isobutene to di-isobutylgallium hydride is estimated at 10 ± 2 kcal mol–1(41·8 kJ mol–1), based on an estimated enthalpy change of 20·5 kcal mol–1 for the title reaction. The reaction is apparently homogeneous and essentially free from side reactions. These data when compared with the activation parameters for the similar reactions with AlBui 3, AlBun 3, and BBui 3 further substantiate the suggested concept of a reasonably tight, quadrupolar four-centre cyclic transition state involved in these reactions.Keywords
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