Multivalent C−H⋅⋅⋅Cl/Br−C Interactions Directing the Resolution of Dynamic and Twisted Capsules |
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Authors: | Radoslav Z Pavlović Dr Lei Zhiquan Dr Murat Güney Remy F Lalisse Ryan G Hopf Dr Judith Gallucci Dr Curtis Moore Han Xie Prof Christopher M Hadad Prof Jovica D Badjić |
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Institution: | 1. Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio, 43210 USA
These authors contributed equally to this work.;2. Department of Chemistry, Science and Art Faculty, Agri Ibrahim Çeçen University, Agri, Turkey
These authors contributed equally to this work.;3. Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio, 43210 USA |
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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. |
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Keywords: | dynamic chirality hydrogen bonds molecular encapsulation stereoselective recognition supramolecular chemistry |
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