Encapsulation of chiral guests in the dissymmetric capsule 1⋅4 BF4 formed diastereomeric supramolecular complexes G⊂1⋅4 BF4 (G: guest). When chiral guests 2 a-q were encapsulated within the dissymmetric space of the self-assembled capsule 1⋅4 BF4 , circular dichroism (CD) was observed at the absorption bands that are characteristic of the π-π* transition of the bipyridine moiety of the capsule, which suggests that the P and M helicities of the capsule are biased by the chiral guest complexation. The P helicity of diastereomeric complex (S)-2 l⊂1⋅4 BF4 was determined to be predominant, based on CD exciton coupling theory and DFT calculations. The diastereoselectivity was highly influenced by the ester substituents, such that benzyl ester moieties were good for improving the diastereoselectivity. A diastereomeric excess of 98 % was achieved upon the complexation of 2 j. The relative enthalpic and entropic components for the distereoselectivity were obtained from a van't Hoff plot. The enthalpic components were linearly correlated with the substituent Hammett parameters (σp (+) ). The electron-rich benzyl ester moieties generated donor-acceptor π-π stacking interactions with the bipyridine moiety, which resulted in a significant difference in energy between the predominant and subordinate diastereomeric complexes.

By introducing slight structural modifications to a D -symmetric coordination capsule, we succeeded in isolating the nearly enantiopure capsules (P)- and (M)-2 a(BF ) . Chiral guest, dibenzyl 4,4'-diacetoxy-6,6'-dimethyl-[1,1'-biphenyl]-2,2'-dicarboxylate (3) was encapsulated within the dissymmetric cavity of 2 a(BF ) , resulting in a high diastereoselectivity of >99 % de. The encapsulated guest was successfully removed from the complex without racemization through precipitation of the empty capsule. CD spectra confirmed that the chirality of the capsule was maintained in THF and 1,4-dioxane for long periods, whereas a small amount of acetonitrile accelerated racemization of the empty capsule. The activation parameters of the racemization reaction were determined in dichloromethane and 1,2-dichloroethane, resulting in positive enthalpic contributions and large negative entropic contributions, respectively. Accordingly, the racemization fits a first-order kinetic model. Mechanically coupled Cu -2,2'-bipyridine coordination centers were responsible for the high-energy barrier of racemization and led to the unique chiral memory of the dissymmetric cavity, which was turned off by the addition of acetonitrile.

Encapsulation of chiral guests in the dissymmetric capsule 1·4 BF 4 formed diastereomeric supramolecular complexes G&1·4 BF 4 (G: guest). When chiral guests 2 a-q were encapsulated within the dissymmetric space of the selfassembled capsule 1·4 BF 4 , circular dichroism (CD) was observed at the absorption bands that are characteristic of the p-p* transition of the bipyridine moiety of the capsule, which suggests that the P and M helicities of the capsule are biased by the chiral guest complexation. The P helicity of diastereomeric complex (S)-2 l&1·4 BF 4 was determined to be predominant, based on CD exciton coupling theory and DFT calculations. The diastereoselectivity was highly influenced by the ester substituents, such that benzyl ester moieties were good for improving the diastereoselectivity. A diastereomeric excess of 98 % was achieved upon the complexation of 2 j. The relative enthalpic and entropic components for the distereoselectivity were obtained from a vant Hoff plot. The enthalpic components were linearly correlated with the substituent Hammett parameters (s p + ). The electron-rich benzyl ester moieties generated donor-acceptor p-p stacking interactions with the bipyridine moiety, which resulted in a significant difference in energy between the predominant and subordinate diastereomeric complexes.