Bidentate Urea Derivatives of p-tert-Butyldihomooxacalix[4]arene: Neutral Receptors for Anion Complexation

Abstract

Three new bidentate ureidodihomooxacalix[4]arene derivatives (phenyl 5a, n-propyl 5b, and tert-butyl 5c) were synthesized in four steps from the parent compound p-tert-butyldihomooxacalix[4]arene and obtained in the cone conformation, as shown by NMR studies. The binding ability of these neutral receptors toward spherical, linear, trigonal planar, and tetrahedrical anions was assessed by (1)H NMR and UV-vis titrations. The structures and complexation energies of some complexes were also studied by DFT methods. The data showed that the association constants are strongly dependent on the nature of the substituent (aryl/alkyl) at the urea moiety. In general, for all the receptors, the association constants decrease with decrease of anion basicity. Ph-urea 5a is the best anion receptor, showing the strongest complexation for F(-) (log K(assoc) = 3.10 in CDCl3) and also high binding affinity for the carboxylates AcO(-) and BzO(-). Similar results were obtained by UV-vis studies and were also corroborated by DFT calculations.

Recognition of Anions, Monoamine Neurotransmitter and Trace Amine Hydrochlorides by Ureido‐Hexahomotrioxacalix[3]arene Ditopic Receptors

“…The data (Table ) showed that tert ‐butyl urea 4c , obtained in the partial cone conformation, is a weak receptor displaying very low association constants (log K ass ≤ 1). These results are in line with those obtained with bidentate tert ‐butyl ureido‐dihomooxa receptors,, also having only two urea moieties. The type of substituent (aryl/alkyl) at the urea unit strongly affects the association constants.…”

“…As part of our interest in the study of homooxacalixarenes (calixarene analogues in which the CH 2 bridges are partly or completely replaced by CH 2 OCH 2 groups) we have reported the anion binding affinity of several di‐, and tetra‐substituted (thio)ureido‐dihomooxacalix[4]arenes, in the cone conformation incorporating a four carbon atom spacer. Tetra‐substituted dihomooxa receptors in a partial cone conformation and bearing a propyl spacer were also studied .…”

Site-Specific Description of the Enhanced Recognition Between Electrogenerated Nitrobenzene Anions and Dihomooxacalix[4]arene Bidentate Ureas

“…These macrocycles possess an intermediate size between those of calix [4]-and - [5]arenes. In recent work, 15,16 the binding abilities of dihomooxacalix [4]arene bidentate urea derivatives showed a dependence on both basicity and geometrical features of anions. Also, as expected due to the higher acidity of their NH groups, arylureas showed higher K b values compared with alkylureas.…”

“…However, it is noteworthy that in the case of compounds 9 and 10, only urea-containing residues were considered (Scheme 3), as they provide the specific anionbinding site of the dihomooxacalix [4]arene compounds under study as has been referred in previous work. 15 Theoretical estimates are presented in Tables 2 and 3. (Table 1); this tendency was expected, and it is exemplified using experimental data for the binding with urea compounds 9…”

Calixarenes containing modified meso bridges

“…[22][23][24][25] One should note also heteracalixarenes, i.e. thia-, aza-and homooxa-calixarenes containing S, N and O heteroatoms in their structures, [26][27][28] . They have recently attracted considerable attention due to their easy accessibility and versatile receptor properties.…”