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Issue 9, 2019
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Investigations on non-classical silylium ions leading to a cyclobutenyl cation

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Abstract

Instead of yielding the desired non-classical silylium ions, the reactions of different alkenes/alkynes with several [Me3Si]+ sources mostly led to oligomerization, or – in the presence of Me3SiH – hydrosilylation of the alkenes/alkynes. Yet, from the reaction of 2-butyne with ion-like Me3Si–F–Al(ORF)3 (RF = C(CF3)3) the salt of the silylated tetramethyl cyclobutenyl cation [Me4C4–SiMe3]+[alfal]1 ([alfal] = [(RFO)3Al–F–Al(ORF)3]) was obtained in good yield (NMR, scXRD, Raman, and IR). All the experimental and calculated evidence suggest a mechanism in which 1 was formed via a non-classical silylium ion as an intermediate. The removal of the [Me3Si]+ moiety from the cation in 1 was investigated as a means to provide free tetramethyl cyclobutadiene (CBD). However, the addition of [NMe4]F, in order to release Me3SiF and form CBD, led to the unexpected deprotonation of the cation. The addition of 4-dimethylaminopyridine to remove the [Me3Si]+ cation as a Lewis acid/base adduct, led to an adduct with the four-membered ring in the direct neighborhood of the Me3Si group. By the addition of Et2O to a solution of 1, the [F–Al(ORF)3] anion (and Et2O–Al(ORF)3) was generated from the [alfal] counterion. Subsequently, the [F–Al(ORF)3] anion abstracted the [Me3Si]+ moiety from [Me4C4–SiMe3]+, probably releasing CBD. However, due to the immediate reaction of CBD with [Me4C4–SiMe3]+ and subsequent oligomerization, it was not possible to use CBD in follow-up chemistry.

Graphical abstract: Investigations on non-classical silylium ions leading to a cyclobutenyl cation

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Publication details

The article was received on 15 Oct 2018, accepted on 09 Jan 2019 and first published on 10 Jan 2019


Article type: Edge Article
DOI: 10.1039/C8SC04591G
Chem. Sci., 2019,10, 2821-2829
  • Open access: Creative Commons BY-NC license
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    Investigations on non-classical silylium ions leading to a cyclobutenyl cation

    A. Martens, M. Kreuzer, A. Ripp, M. Schneider, D. Himmel, H. Scherer and I. Krossing, Chem. Sci., 2019, 10, 2821
    DOI: 10.1039/C8SC04591G

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