Dergi makalesi Açık Erişim

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

2019    Pavlovic, Radoslav Z.; Lei Zhiquan; Guney, Murat; Lalisse, Remy F.; Hopf, Ryan G.; Gallucci, Judith; Moore, Curtis; Xie, Han; Hadad, Christopher M.; Badjic, Jovica D.

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 (Delta G(189K)(not equal)=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 angstrom(3)) with small CH2Cl2 (61 angstrom(3)) yielding roughly equal population of diastereomeric inclusion complexes. Larger guests, such as CCl4 (89 angstrom(3)) and CBr4 (108 angstrom(3)), however, formed M-1(-)subset of CX4 at the expense of M-1(+)subset of CX4 in circa 3:1 ratio. To account for the observation, theory (DFT:M06-2X/6-31+G*) and experiments (H-1 NMR spectroscopy) were used to deduce that CX4 guests become localized inside the twisted cage of the capsule by forming a C-X...pi 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(-)subset of 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(+)subset of 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.