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Issue 43, 2013
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P-oxidation of gem-dicationic phosphines

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In spite of the general oxophilic character and λ5 valence state accessibility of phosphorus centers, the oxidation of phosphanes bearing proximal positive charges remains challenging, in particular for dicationic representatives. Previously described diimidazolo- and diimidazolio-phosphane substrates were first resumed in the P-phenylated series, where the reported absence of coordinating ability of the N,N-dimethylated dication towards a neutral Rh(I) center is here confirmed towards a promoted oxygen atom. By contrast, the P-tert-butylated homologue is shown to undergo P-oxidation to give a stable gem-dicationic phosphine oxide (in 91% yield with m-CPBA). The latter could also be obtained by N,N-dimethylation of the neutral diimidazolo-phosphine oxide precursor. The strict covalent vs. dative character of the N2C–P bond in dicationic systems (N2C+)2P(X)R (R = Ph, tBu; X = lone pair, :O) has been investigated by DFT calculations on a model series where (N2C+) = 1,3-dimethyl-1H-imidazolio-2-yl. The relative magnitude of Gibbs free energies of the homolytic and heterolytic dissociation modes shows that diamidinio-phosphines and corresponding P-oxides are not N2C → P donor–acceptor adducts (as mono(amidinio)phosphines are), but rather true gem-dicationic phosphines and phosphine oxides in the strict sense, respectively.

Graphical abstract: P-oxidation of gem-dicationic phosphines

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Publication details

The article was received on 11 Jul 2013, accepted on 16 Aug 2013 and first published on 16 Aug 2013

Article type: Paper
DOI: 10.1039/C3RA43563F
Citation: RSC Adv., 2013,3, 20391-20398

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    P-oxidation of gem-dicationic phosphines

    C. Maaliki, Y. Canac, C. Lepetit, C. Duhayon and R. Chauvin, RSC Adv., 2013, 3, 20391
    DOI: 10.1039/C3RA43563F

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