Reversible, solvent-induced chirality switch in atrane structure: control of the unidirectional motion of the molecular propeller.

Here we demonstrate that atrane-hemicryptophane molecular cages exhibit a reversible change in chirality uniquely controlled by the solvent, thus establishing the feasibility of a new mode of stimulation for atrane-based molecular switches. The oxidovanadium(V) complexes of hemicryptophane molecules exist as diastereomeric mixtures because of the P or M handedness of the cyclotriveratrylene unit and the chiral ether groups with the S configuration. The Δ/Λ propeller-like arrangement of the atrane moiety introduces a new local dissymmetry because of the conformationally restricted helical structure. (1)H NMR experiments provided significant data for the Δ ⇆ Λ interconversion process, where the solvent profoundly influences the chirality sense of the propeller motion, making control of the chirality by the choice of solvent possible. The reversible chirality inversion process is induced by alternating changes of solvent from CDCl(3) to C(6)D(6). The ratio of the rates of the clockwise and anticlockwise tilting motions of the atrane structure shows that the solvent directs the rotational motion of the vanatrane moiety, so the propeller sense of the motion can be considered as unidirectional.