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Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12Cl11]−


It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B12Cl11] spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of “superelectrophilic” dications. [B12Cl11Ng] adducts, with Ng binding energies of 80 to 100 kJ mol−1, contain B−Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B12Cl11] anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B12Cl11CO] and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B12Cl11] results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C6H5]+. This introduces the new chemical concept of “dipole‐discriminating electrophilic anions.”

Unexpected reactivity: The binding of the noble gases Xe and Kr to the anion [B12Cl11] is explained with the exceptional properties of the electric field in the vicinity of the undercoordinated boron atom. Whereas polar nucleophiles such as water face a barrier, neutral unpolar species such as N2 or noble gases are preferred, rendering [B12Cl11] a “dipole‐discriminating electrophilic anion”.

Authors:   Markus Rohdenburg, Martin Mayer, Max Grellmann, Carsten Jenne, Tobias Borrmann, Florian Kleemiss, Vladimir A. Azov, Knut R. Asmis, Simon Grabowsky, Jonas Warneke
Journal:   Angewandte Chemie International Edition
Year:   2017
Pages:   n/a
DOI:   10.1002/anie.201702237
Publication date:   31-May-2017
Facts, background information, dossiers
  • xenon
  • water
  • temperature
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