0000000000182265
AUTHOR
Luigi Mandolini
Aromatic Bridged Bis-phenol A Derived Cyclophanes. Synthesis, Molecular Structure and Binding Properties Toward Quats
Three novel polyoxyethylene bridged bis phenol A derived cyclophanes, {\rm 2 -- 4,} with additional aromatic units in the bridge to increase the number of cation–π interactions with guest cations, were synthesized and characterized by means of X-ray crystal structure determinations. The binding properties of these receptors toward tetramethylammonium (TMA), N-methylpyridinium (NMP), acetylcholine (ACh) and N-methylquinolinium (NMQ) salts were evaluated by means of 1H NMR spectroscopy and compared with those of the previously reported receptor 1.
Zinc-salophen complexes as selective receptors for tertiary amines
Zinc-salophen compounds 1-3 incorporating in the given order 1,2-diaminobenzene, 2,3-diaminonaphthalene, and 9,10-diaminophenantrene moieties were synthesised. Their binding properties toward a series of tertiary amines were assessed by UV-Vis and fluorescence spectroscopy in chloroform solution. Unprecedented selectivities of quinuclidine vs. triethylamine higher than 105 were recorded, thereby revealing the dramatic influence of steric effects on axial coordination of tertiary amines. X-Ray diffraction analyses showed that in the solid state compound 2 is dimeric, but its 1 : 1 quinuclidine complex is monomeric. Strong indications were obtained that both free receptors and their amine add…
Ion Pair Recognition of Quaternary Ammonium and Iminium Salts by Uranyl-Salophen Compounds in Solution and in the Solid State
Efficient ditopic receptors for quaternary ammonium and iminium salts have been obtained upon functionalization of the uranyl-salophen unit with conformationally flexible side arms bearing phenyl or beta-naphthyl substituents. Binding affinities in chloroform solution have been measured for a large number of quaternary salts comprising tetramethylammonium (TMA), tetrabutylammonium (TBA), acetylcholine (ACh), N-methylpyridinium (NMP), and N-methylisoquinolinium (NmiQ) cations. Recognition of the anion partner is ensured by coordination to the hard Lewis acidic uranyl center, whereas cation-pi/CH-pi interactions of the quaternary ions are established with the aromatic pendants. The role of th…
Polyether-bridged cyclophanes incorporating bisphenol A units as neutral receptors for quats: synthesis, molecular structure and binding properties
Two novel neutral polyoxyethylene bridged cyclophanes (2a and 2b) incorporating bisphenol A units were synthesized and characterized by means of x-ray crystal structure determination. The binding properties of 2a and 2b toward tetramethylammonium, N-methylpyridinium, and acetylcholine cations were evaluated by means of 1H NMR spectroscopy. Consistent with indications provided by the molecular structure, the cavity in the basket-like cyclophanes is large enough to accommodate the given guest cations conveniently. Circumstantial evidence was obtained that 1,1,2,2-tetrachloroethane is too large to enter the cavity of the smaller cyclophane 2a, but can be included in the cavity of the larger cy…
Recognition of alkali metal halide contact ion pairs by uranyl-salophen receptors bearing aromatic sidearms. The role of cation-pi interactions.
Hard anions have long been known to bind strongly to the uranium of uranyl-salophen complexes. Upon functionalization of the salophen framework with one or two benzyloxy substituents, efficient ditopic receptors for alkali metal ions are obtained. The solid-state structures of complexes formed by the two-armed receptor 1 with CsF and with the chlorides of K+, Rb+, and Cs+ reported here reveal the existence of dimeric supramolecular assemblies in which two receptor units assemble into capsules fully enclosing (MX)2 ion quartets. In addition to the strong coordinative binding of the anion to the uranyl center and to electrostatic cation-anion interactions, stabilizing interactions arise from …
Cation-π interactions between neutral calix[5]arene hosts and cationic organic guests
Abstract The binding properties of the 1,3-bridged calix[5]crowns 1–3 towards a number of quaternary ammonium, phosphonium, and iminium ions have been investigated by 1H NMR in CDCl3 solution, where the sole driving force for association is provided by cation-π interactions. We have found that the cavity of a calix[5]arene fixed in a cone-like conformation provides a fairly efficient, but rather unselective, receptor site for quaternary salts. The conformationally mobile p-tert-butylcalix[5]arene (4) is in general a much less efficient binder than the more preorganized calixcrowns, but displays a remarkable selectivity towards N-methylquinuclidinium ion that is believed to arise from a good…
Specific recognition of fluoride anion using a metallamacrocycle incorporating a uranyl-salen unit
The design and synthesis of a novel fluoride receptor that uses a salen-complexed Lewis acidic uranyl center as the sole binding site is reported here. This receptor binds fluoride anions in DMSO with a high affinity constant (K > 106 M-1) and exhibits a negligible affinity (K < 10 M-1) towards otherwise effective competitors, such as acetate, phosphate and cyanide anions.
Crystal structure of a CsF-uranyl-salen complex. An unusual cesium-chlorine coordination.
Complexation of CsF with the ditopic uranyl-salen receptor results in a solid-state structure, in which the coordination sphere of cesium is filled by ligation to one of the chlorine atoms of the solvent chloroform. This X-ray structure is the first example of chloroform ligation to an alkali-metal ion.