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

다국어 초록 (Multilingual Abstract)

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 Å3) with small CH2Cl2 (61 Å3) yielding roughly equal population of diastereomeric inclusion complexes. Larger guests, such as CCl4 (89 Å3) and CBr4 (108 Å3), 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 (1H 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 [Nc=d/(rH+rX)=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.
Directing dynamic chirality: Harnessing weak noncovalent interactions is a challenging task, yet the results could pave the way for developing new dynamic materials and functional molecular machines. In this work, it is demonstrated how rarely observed C−H⋅⋅⋅X−C interactions could act in unison to direct dynamic chirality of uniquely shaped and dissymmetric capsules in solution.