Helic[1]triptycene[3]arene: Synthesis, Complexation, and Formation of [2]Rotaxane Shuttle

A new
macrocyclic arene, helic[1]­triptycene[3]­arene H, was
conveniently synthesized in 37% yield by a one-pot reaction
starting from 2,6-dimethoxyl-3,7-dihydroxymethyltriptycene. Macrocycle H showed fixed conformation in solution and could form 1:1
complexes with a series of neutral guests, secondary ammonium salts,
and tertiary ammonium salts in both solution and solid states. The
association constants between H and the neutral guests
were between (1.23 ± 0.10) × 102 and (4.70 ±
0.47) × 103 M–1, while the association
constants between H and the ammonium guests were between
(1.35 ± 0.12) × 103 and (1.59 ± 0.14) ×
105 M–1. Moreover, H showed
bigger association constants with secondary ammonium salts than those
with tertiary ammonium salts possibly because of the steric hindrance
effect and multiple intermolecular interactions. The stimuli-responsive
complexation between H and the ammonium salts could be
controlled by the addition and removal of acids and bases as well.
Based on the host–guest complexation between H and the secondary ammonium salt, [2]­rotaxane was further synthesized,
and its shuttling motion could be efficiently controlled by an acid
and base.