Triptycene-Derived Calix[6]arenes: Synthesis, Structures, and Their Complexation with Fullerenes C60 and C70

Two pairs of novel triptycene-derived calix[6]arenes 4a,b and 5a,b have been efficiently synthesized through both one-pot and two-step fragment-coupling strategies starting from 2,7-bis(hydroxymethyl)-1,8-dimethoxytriptycene 1. Subsequent demethylation of 4a,b and 5a,b with BBr3 in dry dichloromethane gave the macrocyclic compounds 6a,b and 7a,b. Treatment of either 4a or 6a with AlCl3 resulted in the same debutylated product 8, while 9 was similarly obtained from either 5a or 7a. Structural studies revealed that all of the macrocycles have well-defined structures with fixed conformations both in solution and in the solid state owing to the introduction of the triptycene moiety with a rigid three-dimensional (3D) structure, making them very different from their classical calix[6]arene counterparts. As a consequence, it was found that all of these the triptycene-derived calix[6]arenes could encapsulate small neutral molecules in their cavities in the solid state. Moreover, it was also found that the macrocycles 4b and 5b showed highly efficient complexation abilities toward fullerenes C-60 and C-70, forming 1:1 complexes with association constants ranging from (5.22 +/- 0.20) x 10(4) to (8.68 +/- 0.30) x 10(4) M-1.