Investigations on non-classical silylium ions leading to a cyclobutenyl cation† †Electronic supplementary information (ESI) available: Experimental details, procedures, weights, and 1D- and 2D-NMR spectra of the reactions are displayed. Details of the quantum chemical calculations are given together with crystallographic details. CCDC 1868136–1868138. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8sc04591g

Autor: Martens, Arthur, Kreuzer, Marvin, Ripp, Alexander, Schneider, Marius, Himmel, Daniel, Scherer, Harald, Krossing, Ingo
Jazyk: angličtina
Rok vydání: 2019
Předmět:
Zdroj: Chemical Science
ISSN: 2041-6539
2041-6520
0000-0000
Popis: The formation of simple non-classical silylium ions from [Me3Si]+ sources and alkenes or alkynes was investigated, but mainly oligomerization was observed. Yet, the reaction with MeC 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 CMe led to a room temperature stable cyclobutenyl cation. DFT calculations suggest that a non-classical silylium ion intermediate was formed on the way to this product.
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]+[al–f–al]–1 ([al–f–al]– = [(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 [al–f–al]– 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.
Databáze: OpenAIRE
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