| Abstract
| - (2-Pyridyl)ethylamino-appended cyclidenes with varied platform sizes (I, x, y = 0; II, x = 0, y = 1; III, x, y = 1) were crystallography characterized and display planar, Z-configuration, and saddle shapes, respectively. Cyclidenes I−III were evaluated for dicarboxylate binding in CD3CN solution using 1H NMR. Binding constants approached 400 M-1 in CD3CN, and the binding affinity was dependent on the shape of the cyclidene.
- A series of 14-, 15-, and 16-membered nickel(II) cyclidene macrocycles appended with 2-aminoethyl(2-pyridine)receptors I−III, respectively, were prepared and characterized by X-ray crystallography and NMR techniques. The14- and 15-membered macrocycles I and II exist in a planar or extended Z-configuration, whereas the 16-memberedmacrocycle III was saddle shaped and had two asymmetric configurations in the unit cell (IIIa in a “capped”configuration and IIIb in an “open” configuration). Variable-temperature 1H NMR studies of III in CD3CN wereconducted (25−65 °C), and at room temperature, the interconversion between capping and uncapping is slow onthe NMR time scale, resulting in a broad spectrum, whereas at 65 °C, interconversion was fast. 1H NMR bindingstudies indicated I−III bind unsaturated dicarboxylic acids in a 1:1 stoichiometry with binding constants approaching400 M-1 in CD3CN, and the binding strength was dependent on the shape of the macrocyclic cyclidene platforms,whereas monocarboxylic acids were not bound. Generally, the planar 14-membered cyclidene I bound diacids theweakest and the 16-membered cyclidene III bound diacids the strongest. The presence of nuclear Overhausereffect spectrometry cross peaks in a 20 mM solution of 1:1 II−maleic acid indicates that the binding mode is ditopicwith the guest being encapsulated by the aminoethylpyridine arms above the macrocyclic framework.
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