title: Frozen Dissymmetric Cavities in Resorcinarene-Based Coordination Capsules.
abstract: By introducing slight structural modifications to a D4-symmetric coordination capsule, we succeeded in isolating the nearly enantiopure capsules (P)- and (M)-2 a(BF4)4. 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(BF4)4, 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.
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan.
authors.forename: Taisuke
authors.initials: T
authors.lastname: Imamura
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Maehara
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Sekiya
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan. haino@hiroshima-u.ac.jp.
authors.forename: Takeharu
authors.initials: T
authors.lastname: Haino
keywords: chirality; host-guest systems; molecular recognition; self-assembly; supramolecular chemistry