Insights into the Self‐Filling Effects of Branched Isopropyl Groups on the Conformational and Supramolecular Properties of Isopropoxyprism[6]arene

In this work, the direct macrocyclization of a prism[6]arene macrocycle bearing branched alkyl chains on the rims is reported. Isopropoxyprism[6]arene adopts in solution and in the solid state a cuboid D-2-conformation in which four isopropyl groups are folded inside the cavity, to give C-H center dot center dot center dot pi interactions and filling the internal void. The conformational features of isopropoxyprism[6]arene have been studied by dynamic H-1 NMR experiments. The presence of branched isopropyl chains on the prism[6]arene rims, stabilizes the cuboid D-2-conformation to a greater extent than ethyl or propyl groups in PrS[6](Et) and PrS[6](nPr). The higher resistance of PrS[6](iPr) to open its cuboid D-2 conformation, with respect to PrS[6](Et) and PrS[6](nPr), also affected its binding abilities. In fact, alkylammonium-based endo-cavity complexes of PrS[6](iPr) show lower binding constant values than the analogous propoxy/ethoxy-prism[6]arene complexes.