Benzene Triimide Cage as a Selective Container of Azide

Benzene triimide (BTI, or mellitic triimide) is a C 3 -symmetric backbone with a highly electron-deficient, extended π surface and three easy functionalization sites. Here, we report the first BTI-based cage composed of two face-to-face BTIs pillared by three m -xylylene spacers and efficient and selective binding of azide through cooperative anion−π interactions. The cage was easily synthesized in two steps from benzene triimide. Crystal structures showed that the two BTI planes can be separated at about 5–6 Å and form a well-defined electron-deficient cavity. Among a series of anions tested, the cage was found able to bind N 3 –, SCN –, and I – . In particular, the binding toward N 3 – is very strong ( K a = 11098 ± 46 M –1 ) and highly selective, over 150 and 250 times higher than SCN – and I –, respectively. The control single BTI, however, showed only very weak binding ( K a < 5 M –1 ). The crystal structure showed that N 3 – is tightly trapped within the cavity through multiple, very short anion−π interactions. The slow enter–release of N 3 – from the cavity was observed in the NMR. The charge-transfer and electron-transfer character of the interactions was also discussed.