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Published September 1995 | public
Journal Article

Group and Site Selective σ-Bond Metathesis Reactions of CH_3ScCH_2CH_3^+ with [2,2-D_2]Propane, [1,1,1,4,4,4-D_6]-n-Butane, [2-D]-Isobutane, and n-Pentane

Abstract

Fourier transform ion cyclotron resonance mass spectrometry has been used to examine the reactions of CH_3ScCH_2CH_3^+ with [D_4]methane, ethane, [2,2-D_2]propane, [1,1,1,4,4,4-D_6]-n-butane, [2-D]isobutane, n-pentane, and [D_12]-n-pentane. CH_3ScCH_2CH_3^+ is not observed to react with methane or ethane, but for propane, n-butane, isobutane, and n-pentane σ-bond metathesis with ethane elimination is the initial and dominant reaction observed, with further dehydrogenation of the resulting products occurring as additional reaction channels. For propane, n-butane, and isobutane, no methane elimination is observed. For n-pentane, methane elimination is a minor reaction channel. For propane, n-butane, and isobutane, the initial σ-bond metathesis involves predominantly the primary C-H bonds of the hydrocarbon. These processes are facile at room temperature and occur with little or no activation energy. Measured total bimolecular rate constants with [2,2-D_2]propane, [1,1,1,4,4,4-D_6]-n-butane [2-D]isobutane, and n-pentane are 0.87 x x 10^(-10), 0.98 x 10^(-10), 1.7 x and 6.4 x 10^(-10) cm^3 s^(-1) molecule^(-1), respectively. With the butanes and pentane a second intramolecular metathesis reaction follows the initial addition to yield a metallacycle product. In accordance with earlier theoretical predictions these metathesis reactions appear to proceed via an allowed four-center mechanism similar to that of a 2_σ + 2_σ cycloaddition. The higher reactivity of the metal-ethyl bond compared to the metal-methyl bond and the observed C-H bond specificity are also in agreement with theoretical predictions.

Additional Information

© 1995 American Chemical Society. Received February 15, 1995. We wish to thank J. K. Perry and Professor W. A. Goddard III for their theoretical work on this system. This work was supported by the National Science Foundation under Grant CHE-9108318, by a grant from AMOCO, and by the Office of Naval Research.

Additional details

Created:
August 20, 2023
Modified:
October 18, 2023