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Issue 7, 2013
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The Lewis acidity of fluorophosphonium salts: access to mixed valent phosphorus(III)/(V) species

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Abstract

Oxidative fluorination of the electron-deficient phosphine Ph2P(C6F5) using XeF2, followed by fluoride ion abstraction from the resulting difluorophosphorane Ph2P(F)2(C6F5), produces electrophilic fluorophosphonium salts [Ph2P(F)(C6F5)][X] (X = FB(C6F5)3 or O3SCF3). Variable temperature NMR spectroscopic analysis of [Ph2P(F)(C6F5)][FB(C6F5)3] demonstrates a fluxional process attributed to fluoride ion exchange between B(C6F5)3 and [Ph2P(F)(C6F5)]+, suggesting that these species have comparable Lewis acidities. This exchange can also be illustrated by adding phosphine Ph3P to [Ph2P(F)(C6F5)][FB(C6F5)3] at ambient temperature to produce Ph2P(F)2(C6F5) and Ph3P–B(C6F5)3, while heating this mixture results in thermally induced para-substitution of Ph3P at the C6F5 group of the phosphonium ion to generate [Ph3P(C6F4)P(F)2Ph2][FB(C6F5)3]. Such frustrated Lewis pair reactivity also can be exploited by reacting [Ph2P(F)(C6F5)][O3SCF3] with silylphosphine Ph2PSiMe3 to afford the unique mixed-valent salt [Ph2P(C6F4)P(F)Ph2][O3SCF3], which upon the addition of fluoride is converted to Ph2P(C6F4)P(F)2Ph2. XeF2 reacts with [Ph2P(C6F4)P(F)Ph2][O3SCF3] at ambient temperature, producing equal proportions of the dicationic salt [Ph2P(F)(C6F4)P(F)Ph2][O3SCF3]2 and the bis(difluorophosphorane) Ph2P(F)2(C6F4)P(F)2Ph2, the latter of which can then be quantitatively converted to the former by adding one equiv of Me3SiO3SCF3.

Graphical abstract: The Lewis acidity of fluorophosphonium salts: access to mixed valent phosphorus(iii)/(v) species

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Publication details

The article was received on 13 Nov 2012, accepted on 30 Nov 2012 and first published on 12 Dec 2012


Article type: Paper
DOI: 10.1039/C2DT32711B
Citation: Dalton Trans., 2013,42, 2629-2635
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    The Lewis acidity of fluorophosphonium salts: access to mixed valent phosphorus(III)/(V) species

    L. J. Hounjet, C. B. Caputo and D. W. Stephan, Dalton Trans., 2013, 42, 2629
    DOI: 10.1039/C2DT32711B

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