Nickel(II) cyclidenes with appended ethylpyridine receptor centers as molecular tweezers for dicarboxylic acids.
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. The 14- and 15-membered macrocycles I and II exist in a planar or extended Z-configuration, whereas the 16-membered macrocycle 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 (1)H NMR studies of III in CD(3)CN were conducted (25-65 degrees C), and at room temperature, the interconversion between capping and uncapping is slow on the NMR time scale, resulting in a broad spectrum, whereas at 65 degrees C, interconversion was fast. (1)H NMR binding studies indicated I-III bind unsaturated dicarboxylic acids in a 1:1 stoichiometry with binding constants approaching 400 M(-)(1) in CD(3)CN, 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 the weakest and the 16-membered cyclidene III bound diacids the strongest. The presence of nuclear Overhauser effect spectrometry cross peaks in a 20 mM solution of 1:1 II-maleic acid indicates that the binding mode is ditopic with the guest being encapsulated by the aminoethylpyridine arms above the macrocyclic framework.
Disch
Jeremy S
JS
Department of Chemistry, Tufts University, Medford, Massachusetts 02155, USA.
Staples
Richard J
RJ
Concolino
Thomas E
TE
Haas
Terry E
TE
Rybak-Akimova
Elena V
EV
D003998:Dicarboxylic Acids / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*
D003998:Dicarboxylic Acids; D011725:Pyridines; D009532:Nickel