5 years ago

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

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12Cl11]−
Carsten Jenne, Tobias Borrmann, Simon Grabowsky, Max Grellmann, Jonas Warneke, Markus Rohdenburg, Martin Mayer, Florian Kleemiss, Vladimir A. Azov, Knut R. Asmis
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”.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201702237

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