Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University , Jinju 660-701, Korea.
Department of Chemistry, The University of Texas at Austin , 105 E. 24th, Street-Stop A5300, Austin, Texas 78712-1224, United States.
J Org Chem. 2018 Mar 2;83(5):2686-2693. doi: 10.1021/acs.joc.7b03135. Epub 2018 Feb 19.
The binding interactions between the azide anion (N) and the strapped calix[4]pyrroles 2 and 3 bearing auxiliary hydrogen bonding donors on the bridging moieties, as well as of normal calix[4]pyrrole 1, were investigated via H NMR spectroscopic and isothermal titration calorimetry analyses. The resulting data revealed that receptors 2 and 3 have significantly higher affinities for the azide anion in organic media as compared with the unfunctionalized calix[4]pyrrole 1 and other azide receptors reported to date. Single crystal X-ray diffraction analyses and calculations using density functional theory revealed that receptor 2 binds CsN in two distinct structural forms. As judged from the metric parameters, in the resulting complexes one limiting azide anion resonance contributor is favored over the other, with the specifics depending on the binding mode. In contrast to what is seen for 2, receptor 3 forms a CsN complex in 20% CDOD in CDCl, wherein the azide anion is bound only vertically to the NH protons of the calix[4]pyrrole and the cesium cation is complexed within the cone shaped-calix[4]pyrrole bowl. The bound cesium cation is also in close proximity to a naphthobipyrrole subunit present in a different molecule, forming an apparent cation-π complex.
通过核磁（NMR）光谱和等温热滴定分析，研究了带辅助氢键给体的支载杯[4]吡咯 2 和 3 中的叠氮阴离子（N）与 strapped calix[4]pyrroles 之间的结合相互作用，以及未功能化的杯[4]吡咯 1 的结合相互作用。结果表明，与未功能化的杯[4]吡咯 1 和迄今为止报道的其他叠氮受体相比，受体 2 和 3 在有机介质中对叠氮阴离子具有更高的亲和力。单晶 X 射线衍射分析和使用密度泛函理论的计算表明，受体 2 以两种不同的结构形式结合 CsN。从度量参数判断，在得到的复合物中，一个限制的叠氮阴离子共振贡献者比另一个更受青睐，具体取决于结合模式。与 2 不同，受体 3 在 20% CDOD 与 CDCl 的混合物中形成 CsN 复合物，其中叠氮阴离子仅垂直结合到杯[4]吡咯的 NH 质子上，而铯阳离子则与杯[4]吡咯碗内配位。结合的铯阳离子也与存在于不同分子中的萘并联吡啶亚基非常接近，形成明显的阳离子-π 络合物。
