sym-[5.5.5]Heterocyclophanes: structurally well-defined, mixed π/heteroatom-donor macrobicyclic cages

Precedent and Theory Unite in the Hypothesis of a Highly Selective Fluoride Receptor

“…The optimized distances between the center of the cavity of 3, 4 , and 5 and the mean plane of the aromatic ring are calculated to be 2.37, 2.20, and 2.34 Å, respectively. This is consistent with the distance of 2.46 Å found in the crystal structure of 1 (X=NH),16 which shows the effect of repulsion between the electron‐rich cavity and the benzene rings not present in 3 – 5 . When the above values are compared to the modeled equilibrium distances between free chloride or fluoride ions and the respective ring centroid (Table 1), a case for discrimination between the two halides based on the Ar–Ar distance emerges.…”

“…Benzene‐based cyclophanes 1 have been prepared by joining two hemispheres of the cage using the intuitive S N 2 approach or by cyclotrimerization of the appropriately substituted triyne 1. 2, 16 The synthesis of substituted s ‐triazines and cyanuric acids is well‐described in the literature, so sufficient opportunity may exist for the preparation of these cages by analogous methods using materials derived from published sources. Trialkyl boroxines on the other hand can be prepared by the dehydration of alkyl boronic acids by azeotropic distillation with benzene 20…”

Precedent and Theory Unite in the Hypothesis of a Highly Selective Fluoride Receptor

“…This is consistent with the distance of 2.46 found in the crystal structure of 1 (X = NH), [16] which shows the effect of repulsion between the electron-rich cavity and the benzene rings not present in 3-5. When the above values are compared to the modeled equilibrium distances between free chloride or fluoride ions and the respective ring centroid (Table 1), a case for discrimination between the two halides based on the Ar-Ar distance emerges.…”

“…Benzene-based cyclophanes 1 have been prepared by joining two hemispheres of the cage using the intuitive S N 2 approach or by cyclotrimerization of the appropriately substituted triyne. [1,2,16] The synthesis of substituted s-triazines and cyanuric acids is well-described in the literature, so sufficient opportunity may exist for the preparation of these cages by analogous methods using materials derived from published sources. Trialkyl boroxines on the other hand can be prepared by the dehydration of alkyl boronic acids by azeotropic distillation with benzene.…”

Single-Step Synthesis of D3h-Symmetric Bicyclooxacalixarenes

“…The nitrogen atoms point directly into the cavity in a trigonal planar array, with an average distance of 2.74 Å from the nitrogen nuclei to the center of the cavity. Thus, bicycles 6 and 10 − 12 have the potential for inner-cavity metal−cation complexation, although long nitrogen−metal bond lengths and the close spacing of the capping benzene rings (4.49 Å between centroids) may preclude such a complex . Investigations to this effect are ongoing.…”