Multivalent C-H⋅⋅⋅Cl/Br-C Interactions Directing the Resolution of Dynamic and Twisted Capsules

In this work, we report a mechanism by which stereoisomeric and twisted capsules P/M-1 direct their dynamic chirality in the presence of haloalkane guests. The capsule comprises a static, but twisted, cage that is linked to a dynamic tris(2-pyridylmethyl)amine (TPA) lid at its top. From the results of experimental (NMR spectroscopy and X-ray crystallography) and computational (DFT) studies, the TPA lid was shown to assume clockwise (+) and counterclockwise (-) folds with diastereomeric (but racemic) capsules M-1(+) and M-1(-) interconverting at a rapid rate (ΔG^≠ _189K =9.1 kcal mol^-1 ). The relative stability of the capsules was found to be a function of guest(s) residing in their interior (243/262 ų ) with small CH₂ Cl₂ (61 ų ) yielding roughly equal population of diastereomeric inclusion complexes. Larger guests, such as CCl₄ (89 ų ) and CBr₄ (108 ų ), however, formed M-1(-)⊂CX₄ at the expense of M-1(+)⊂CX₄ in circa 3:1 ratio. To account for the observation, theory (DFT:M06-2X/6-31+G*) and experiments (¹ H NMR spectroscopy) were used to deduce that CX₄ guests become localized inside the twisted cage of the capsule by forming a C-X⋅⋅⋅π halogen bond [N_c =d/(r_H +r_X )=0.91-0.92] with the benzene "floor" while encountering electrostatic repulsions with closer naphthalimide boundaries. At last, the TPA lid used its central methylene hydrogens to establish, within the M-1(-)⊂CX₄ , three stabilizing C-H⋅⋅⋅X-C interactions with the guest. The same C-H⋅⋅⋅X-C interactions, however, became weaker (or possibly vanished) after the conformational reorganization of the lid and the formation of less stable M-1(+)⊂CX₄ complex. On individual basis, C-H⋅⋅⋅X-C intermolecular contacts are weak and hardly detectable in the solution phase. In the case of capsule P/M-1, however, these contacts were multivalent and altogether strong enough to direct the host's dynamic chirality.