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Isolation of crystalline carbene-stabilized P2-radical cations and P2-dications

Abstract

The discovery in 1900 by Gomberg that the trityl radical (Ph3C·) exists at room temperature is often considered to be the beginning of radical chemistry. Since then, persistent and even room-temperature stable radicals based on second-row and heavier elements have been synthesized. However, few of them have been characterized crystallographically, because they are either too reactive or dimerize in the solid state. Here, we show that a P2 fragment, capped with two bulky, strongly electron-releasing singlet carbenes (dicoordinate carbon compounds with only six valence electrons), can undergo one-electron oxidation, giving rise to room-temperature stable radical cations. Moreover, when N-heterocyclic carbenes are used, two-electron oxidation can also be performed, producing the corresponding stable dicationic diphosphene, which has to be regarded as a P22+ fragment coordinated by two carbenes. These results reveal a new application of stable singlet carbenes, the stabilization of paramagnetic species and electron-poor fragments.

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Figure 1: Preparation of bis(carbene)–P2 adducts 2 (ref. 19) and 4 (ref. 18), according to reported procedures, and their resonance forms.
Figure 2: Electrochemical behaviour of compounds 2 and 4, and spectroscopic characterization of products of their oxidation.
Figure 3: Selected molecular orbitals for 2 and 4, and products of their oxidation.

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Acknowledgements

The authors gratefully acknowledge financial support from the National Science Foundation (CHE-0924410), the Alexander von Humboldt Foundation (fellowship to P.P.) and Deutsche Forschungsgemeinschaft. Thanks are also given to D. Borchardt for the EPR part of this paper.

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Contributions

O.B. performed the chemical experiments, B.D. performed the X-ray diffraction studies, and P.P. carried out the calculations. G.F. and G.B. co-wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Guy Bertrand.

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The authors declare no competing financial interests.

Supplementary information

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Supplementary information (PDF 501 kb)

Supplementary information

Crystallographic data for the radical cation of compound 2 (CIF 32 kb)

Supplementary information

Crystallographic data for the radical cation of compound 4 (CIF 38 kb)

Supplementary information

Crystallographic data for the dication of compound 4 (CIF 20 kb)

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Back, O., Donnadieu, B., Parameswaran, P. et al. Isolation of crystalline carbene-stabilized P2-radical cations and P2-dications. Nature Chem 2, 369–373 (2010). https://doi.org/10.1038/nchem.617

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