Coordination cages containing endohedrally functionalized aromatic cavities are scarce in the literature. Herein, we report the self-assembly of a tetra-cationic super aryl-extended calix[4]pyrrole tetra-pyridyl ligand into a water-soluble Pd(II)-cage featuring two endohedral polar binding sites. They are defined by the four pyrrole NHs of the calix[4]pyrrole unit and the four inwardly directed α-protons of the coordinated pyridyl groups. The efficient assembly of the Pd(II)-cage requires the inclusion of mono- and ditopic pyridyl N-oxide and aliphatic formamide guests. The monotopic guests only partially fill the cage's cavity and require the co-inclusion of a water molecule that is likely hydrogen-bonded to the endohedral α-pyridyl protons. The ditopic guests are able to completely fill the cage's cavity and complement both binding sites. We observed high conformational selectivity in the inclusion of the isomers of α,ω-bis-formamides. We briefly investigate the uptake and release mechanism/kinetics of selected polar guests by the Pd(II)-cage using pair-wise competition experiments.

中文翻译：

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包括极地客体的水溶性内嵌功能化配位笼的自组装

含有内嵌功能化芳香腔的配位笼在文献中很少见。在此，我们报告了四阳离子超芳基扩展的杯[4]吡咯四吡啶基配体自组装成具有两个内嵌极性结合位点的水溶性 Pd( II )-笼。它们由杯[4]吡咯单元的四个吡咯NH和配位吡啶基团的四个向内定向的α-质子定义。Pd( II )-笼的有效组装需要包含单位和双位吡啶基N-氧化物和脂肪族甲酰胺客体。单质客体仅部分填充笼子的空腔，需要共包含一个可能与内嵌 α-吡啶基质子氢键结合的水分子。双色客体能够完全填满笼子的空腔并补充两个结合位点。我们观察到包含 α,ω-双甲酰胺异构体的高构象选择性。我们使用成对竞争实验简要研究了 Pd( II ) 笼对选定极性客体的吸收和释放机制/动力学。