| Unbridged cyclidene complexes adopt a variety of conformations, including saddle-shaped, planar and Z-shaped. The conformations preferences of cyclidenes are determined by the macrocycle ring size and by the substitution pattern. 14-membered cyclidenes are consistently flat, 16-membered cyclidenes are predominately saddle-shaped, and 15-membered cyclidenes can adopt either conformation. By utilizing the conformationally switchable behavior of cyclidene platforms, it is conceivable to create “molecular tweezers” with receptors at the periphery.; In this work we present the synthesis and characterization of unbridged Nickel(II) cyclidenes of varied ring size, appended with aminomethyl-2-pyridine, aminomethyl-3-pyridine, aminoethyl-2-pyridine, and dipicolylamine. These polyfunctional metal containing receptors were found to modestly bind dicarboxylic acids. And the binding affinity was dependent on the receptor length and type, and cyclidene macrocyclic size.; Saddle-shaped 16-membered cyclidenes, with the receptors preorganized for substrate binding, have higher binding affinity for substrates than the analogous flat 14-membered cyclidenes. The Z-shaped 15-membered cyclidenes show intermediate binding characteristics.; X-ray structural comparisons, NMR spectroscopy, and synthetic details are also presented in full detail. |
