A Selective Cage for Azide Ions

Benzene triimide (BTI) is a planar, electron-deficient, π-conjugated molecule. Due to its three imide groups, it is easy to functionalize and could be a useful building block for larger organic scaffolds.

Qi-Qiang Wang, De-Xian Wang, Beijing National Laboratory for Molecular Sciences, and University of the Chinese Academy of Sciences, Beijing, and colleagues have synthesized a BTI-based cage which can selectively bind anions. The team used three m-xylylene spacers to connect to molecules of BTI. This was achieved by reacting BTI with 1,3-bis(bromomethyl)benzene in the presence of N,N-diisopropylethylamine (DIPEA) as a base.

The resulting cage has an electron-deficient cavity which can bind anions. The team found that it can bind, e.g., N₃^– (azide, pictured), SCN^–, and I^–. Azide is bound particularly strongly and selectively—over 150 and 250 times more strongly than SCN^– and I^–, respectively. The team attributes this to the fact that azide is tightly trapped within the cavity and interacts strongly with the π-electron system.

• Benzene Triimide Cage as a Selective Container of Azide,
  De-Hui Tuo, Yu-Fei Ao, Qi-Qiang Wang, De-Xian Wang,
  Org. Lett. 2019.
  https://doi.org/10.1021/acs.orglett.9b02782

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