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Frozen Dissymmetric Cavities in Resorcinarene‐Based Coordination Capsules
Author(s) -
Imamura Taisuke,
Maehara Takeshi,
Sekiya Ryo,
Haino Takeharu
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201505183
Subject(s) - racemization , enantiopure drug , chemistry , acetonitrile , chirality (physics) , resorcinarene , dichloromethane , capsule , solvent , stereochemistry , organic chemistry , catalysis , molecule , enantioselective synthesis , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , quark , botany , biology
By introducing slight structural modifications to a D 4 ‐symmetric coordination capsule, we succeeded in isolating the nearly enantiopure capsules ( P )‐ and ( M )‐ 2 a (BF 4 ) 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 (BF 4 ) 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.