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Facile and systematic access to the least-coordinating WCA [(RFO)₃Al–F–Al(ORF)₃]− and its more Lewis-basic brother [F–Al(ORF)₃]− (RF = C(CF₃)₃)

Martens, A., Weis, P., Krummer, M.C., Kreuzer, M., Meierhöfer, A., Meier, S.C., Bohnenberger, J., Scherer, H., Riddlestone, Ian and Krossing, I. (2018) Facile and systematic access to the least-coordinating WCA [(RFO)₃Al–F–Al(ORF)₃]− and its more Lewis-basic brother [F–Al(ORF)₃]− (RF = C(CF₃)₃) Chemical Science, 9 (35). pp. 7058-7068.

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By reaction of the Lewis acid Me3Si–F–Al(ORF)3 with a series of [PF6]− salts, gaseous PF5 and Me3Si–F are liberated and salts of the anion [F–Al(ORF)3]− ([f–al]−; RF = C(CF3)3) can be obtained. By addition of another equivalent of Me3Si–F–Al(ORF)3 to [f–al]−, gaseous Me3Si–F is released and salts of the least coordinating anion [(RFO)3Al–F–Al(ORF)3]− ([al–f–al]−) are formed. Both procedures work for a series of synthetically useful cations including Ag+, [NO]+, [Ph3C]+ and in very clean reactions with 5 g batch sizes giving excellent yields typically exceeding 90%. In addition, the synthesis of Me3Si–F–Al(ORF)3 has been optimized and scaled up to 85 g batches in an one-pot procedure. These anions could previously only be obtained by difficult to control decomposition reactions of [Al(ORF)4]− or by halide abstraction reactions with Me3Si–F–Al(ORF)3, generating relatively large countercations that are unsuited for further use as universal starting materials. Especially [al–f–al]− is of interest for the stabilization of reactive cations, since it is even weaker coordinating than [Al(ORF)4]− and more stable against strong electrophiles. This bridged anion can be seen as an adduct of [f–al]− and Al(ORF)3. Thus, it is similarly Lewis acidic as BF3 and eventually reacts with nucleophiles (Nu) from the reaction environment to yield Nu–Al(ORF)3 and [f–al]−. This prevents working with [al–f–al]− salts in ethereal or other donor solvents. By contrast, the [f–al]− anion is no longer Lewis acidic and may therefore be used for reactions involving stronger nucleophiles than the [al–f–al]− anion can withstand. Subsequently it may be transformed into the [al–f–al]− salt by simple addition of one equivalent of Me3Si–F–Al(ORF)3.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Chemistry
Authors :
Martens, A.
Weis, P.
Krummer, M.C.
Kreuzer, M.
Meierhöfer, A.
Meier, S.C.
Bohnenberger, J.
Scherer, H.
Krossing, I.
Date : 1 August 2018
DOI : 10.1039/c8sc02591f
Copyright Disclaimer : © The Royal Society of Chemistry 2018. Open Access Article. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.
Depositing User : Clive Harris
Date Deposited : 20 Jun 2019 08:53
Last Modified : 20 Jun 2019 08:53

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