Using the Lewis Acid Me3 Si-F-Al(ORF )3 To Prepare Phosphino-Phosphonium Cations with the Least-Coordinating Anion [(RF O)3 Al-F-Al(ORF )3 ]

By reaction of two equivalents of Me3 Si-F-Al(ORF )3 1 with an equimolar amount of PPh2 Cl, the salt [Ph2 P-PPh2 Cl]+ [(RF O)3 Al-F-Al(ORF )3 ]- 2 is prepared smoothly in 91 % yield (NMR, XRD). The synthesis of [Ph2 P-PPh3 ]+ [(RF O)3 Al-F-Al(ORF )3 ]- 3 is best achieved by a two-step reaction: firs...

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Published in:Chemistry : a European journal 2017-09, Vol.23 (50), p.12305-12313
Main Authors: Possart, Josephine, Martens, Arthur, Schleep, Mario, Ripp, Alexander, Scherer, Harald, Kratzert, Daniel, Krossing, Ingo
Format: Article
Language:English
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Summary:By reaction of two equivalents of Me3 Si-F-Al(ORF )3 1 with an equimolar amount of PPh2 Cl, the salt [Ph2 P-PPh2 Cl]+ [(RF O)3 Al-F-Al(ORF )3 ]- 2 is prepared smoothly in 91 % yield (NMR, XRD). The synthesis of [Ph2 P-PPh3 ]+ [(RF O)3 Al-F-Al(ORF )3 ]- 3 is best achieved by a two-step reaction: first, two equivalents of 1 react with one PPh3 to give [Me3 Si-PPh3 ]+ [(RF O)3 Al-F-Al(ORF )3 ]- 4 (NMR, XRD), which, upon reaction with PPh2 Cl, yields pure 3 and Me3 SiCl (NMR, XRD). Typically, a stoichiometry of two equivalents of 1 with respect to one equivalent of the chloride donor should be used. Otherwise, the residual strong Lewis acidity of the [(RF O)3 Al-F-Al(ORF )3 ]- anion in the presence of the [F-Al(ORF )3 ]- anion-that forms with less than two equivalents of 1-leads to further chloride exchange reactions that complicate work-up. This route presents the easiest way to introduce the least-coordinating [(RF O)3 Al-F-Al(ORF )3 ]- anion into a system. We expect a wide use of this route in all areas, in which chloride-bond heterolysis in combination with very weakly coordinating anions is desirable. Additionally, we performed calculations on the bond dissociation mechanisms of [R2 P-PMe3 ]+ and the isoelectronic Me2 P-SiMe3 and Me2 Si-PMe3 in dependence of the solvent permittivity. These calculations show, especially for the neutral reference compounds, a heavy influence of the solvent on the dissociation mechanism, which is why we suggest investigating these properties in solution instead of gas phase.
ISSN:1521-3765
DOI:10.1002/chem.201701260