Nickel(II) Cyclidenes with Appended Ethylpyridine Receptor Centers as Molecular Tweezers for Dicarboxylic Acids

Abstract

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.

Self-Assembled Cagelike Receptor That Binds Biologically Relevant Dicarboxylic Acids via Proton-Coupled Anion Recognition

“…Indeed, there are only a handful of reports of dicarboxylic acid recognition in the literature. [22][23][24][25][26][27] Exacerbating the problem is the need to account for geometric isomers, e.g., maleic acid (Z-isomer) vs fumaric acid (E-isomer). As detailed below, we have prepared a cage-like supramolecular receptor 7•7 via the self-assembly of 7 (cf.…”

“…This makes these dicarboxylic acids important targets for supramolecular chemists. , However, recognition of such species is made challenging due to their characteristic sizes, shapes, p K a profiles, and slightly hydrophilic nature. Indeed, there are only a handful of reports of dicarboxylic acid recognition in the literature. − Exacerbating the problem is the need to account for geometric isomers, e.g., maleic acid ( Z -isomer) vs fumaric acid ( E -isomer). As detailed below, we have prepared a cagelike supramolecular receptor 7·7 via the self-assembly of 7 (cf.…”

Synthesis of Carbonyl‐substituted Tetracyanodihydrotetraaza[14]annulenes

“…Moreover, 14-and 15-membered cyclidene complexes show planar geometry, which -also due to their π-electron rich chemical structures -results in the ability of the compounds to form relatively strong π-π interactions, by acting either as π-acceptors or π-donors, depending on the properties of the exocyclic substituents. [4] The above mentioned features combined with relatively simple synthesis enabled the use of cyclidene rings as some key structural elements of various supramolecular systems, including dioxygen carriers [2] and receptors for alcohols, [8,9] ammonium cations, [10] diacids, [11] amino acids [12] and aromatic systems. [13] The complexes were also used as building blocks in the synthesis of molecular switches, [14,15] and more recently, as polycatenanes, [16] DNA intercalators [17] and DNA analogues for sensing purposes.…”

“…The above mentioned features combined with relatively simple synthesis enabled the use of cyclidene rings as some key structural elements of various supramolecular systems, including dioxygen carriers [2] and receptors for alcohols, [8,9] ammonium cations, [10] diacids, [11] amino acids [12] and aromatic systems [13] . The complexes were also used as building blocks in the synthesis of molecular switches, [14,15] and more recently, as polycatenanes, [16] DNA intercalators [17] and DNA analogues for sensing purposes [18] …”

“…Calcd for C 18 H 10 N 8 O 4 Cu (%): C, 46.41; H, 2.16; N, 24.05; Found: C, 46.33; H, 2.28; N, 24.02; MS (FD, m/z): 464.5 ([C 18 H 10 N 8 O 4 CuÀ e À ] + ); IR (nujol, cm À 1 ): 2221 m (C�N); 1735 s (C=O); 1619 s (C=N). [6,13-Bis(methoxycarbonyl)-2,3,9,10-tetracyano-1,4,8,11-tetraazacyclotetradeca-2,4,6,9,11,13-hexaenato-(2-)-k 4 N 1,4,8,11 ]palladium(II) (ePd). The complex was synthesised according to the same procedure (as for eNi and eCu).…”