Corannulene-Based Coordination Cage with Helical Bias.

We report here the first corannulene-based molecular cage, constructed via metal-induced self-assembly of corannulene-based ligands. In sharp contrast to those assembled via the planar π-conjugated analogues of corannulene, at ambient and elevated temperatures, the molecular cage exists as an ensemble of four stereoisomers (two pairs of enantiomers), all of which possess a D5-symmetric (regardless of the counteranions) and inherently helical structure. Decreasing the temperature shifts the equilibrium between different pairs of enantiomers. At low temperature, only one pair of enantiomers is present. Helical bias for the cage could be efficiently achieved by inducing asymmetry with enantiopure anions. When nonenantiopure anions are used, the asymmetry induction abides by the "majority rule", i.e., the major enantiomer of the chiral anions controls the bias of helical sense of the cages.