Joint experimental and theoretical studies of the surprising stability of the aryl pentazole upon noncovalent binding to β-cyclodextrin

Herein, binding of the β-cyclodextrin (β-CD) host to the unstable aryl pentazole guest has been confirmed experimentally and theoretically. After the confinement of aryl pentazole, electron density reorganization was studied by M06-2X dispersion-corrected DFT and further reflected in the characteristic shift in the NMR spectra. Among the host-guest complexes, the inclusion complex is favored with the phenyl ring expectedly encapsulated within the cavity through noncovalent interactions such as hydrogen bonding, C-H⋯π, and the special C_sp²-H⋯H-C_sp³ bonding discovered by the NBO, QTAIM, and NCI-RDG theories. The host-guest binding renders the enhancement of the nitrogen-ring aromatic character; this has been analyzed by employing nucleus-independent chemical shift (NICS)-based profiles. The non-covalent interaction largely enhances the thermal stability of the guest through a change of the decomposition reaction path whether the guest is encapsulated or not by the host. By comparison of the structures of B1-B4, the enhancement could be assigned to the ion-type transition structure stabilized by the C-H bonds of the host.