Authors
Rakesh Puttreddy, Ngong Kodiah Beyeh, S Maryamdokht Taimoory, Daniel Meister, John F Trant, Kari Rissanen
Publication date
2018/7/10
Journal
Beilstein Journal of Organic Chemistry
Volume
14
Issue
1
Pages
1723-1733
Publisher
Beilstein-Institut
Description
Host–guest complexes of C-hexyl-2-bromoresorcinarene (BrC6) with twelve potential aromatic N-oxide guests were studied using single crystal X-ray diffraction analysis and 1 H NMR spectroscopy. In the solid state, of the nine obtained X-ray crystal structures, eight were consistent with the formation of BrC6-N-oxide endo complexes. The lone exception was from the association between 4-phenylpyridine N-oxide and BrC6, in that case the host forms a self-inclusion complex. BrC6, as opposed to more rigid previously studied C-ethyl-2-bromoresorcinarene and C-propyl-2-bromoresorcinarene, undergoes remarkable cavity conformational changes to host different N-oxide guests through C–H··· π (host) interactions. In solution phase CD 3 OD/CDCl 3 (1: 1 v/v), all twelve N-oxide guests form endo complexes according to 1 H NMR; however, in more polar CD 3 OD/DMSO-d 6 (9: 1 v/v), only three N-oxides with electron-donating groups form solution-phase endo complexes with BrC6. In solid-state studies, 3-methylpyridine N-oxide+ BrC6 crystallises with both the upper-and lower-rim BrC6 cavities occupied by N-oxide guests. Computational DFT-based studies support that lower-rim long hexyl chains provide the additional stability required for this ditopic behaviour. The lower-rim cavity, far from being a neutral hydrophobic environment, is a highly polarizable electrostatically positive surface, aiding in the binding of polar guests such as N-oxides.
Total citations
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