Influence of exo-adamantyl groups and endo-OH functions on the threading of calix[6]arene macrocycle

Calix[6]arenes bearing adamantyl groups at the exo-rim form pseudorotaxanes with dialkylammonium axles paired to the weakly coordinating [B(ArF)4]- anion. The exo-adamantyl groups give rise to a more efficient threading with respect to the exo-tert-butyl ones, leading to apparent association constants more than one order of magnitude higher. This improved stability has been ascribed to the more favorable van der Waals interactions of exo-adamantyls versus exo-tertbutyls with the cationic axle. Calix[6]arenes bearing endo-OH functions give rise to a less efficient threading with respect to the endo-OR ones, in line with what was known from the complexation of alkali metal cations.