J. L. C. Pereira

p-tert-Butyldihomooxacalix[4]arene/p-tert-Butylcalix[4]arene: Transition and Heavy Metal Cation Extraction and Transport Studies by Ketone and Ester Derivatives

The binding properties of two phenylketones (2a and 3a) and two ethylesters (2b and {3b) derived from p-tert-butyldihomooxacalix[4]arene or from p-tert-butylcalix[4]arene, in the cone conformation, towards transition (Ag+, Ni2+, Cu2+, Co2+, Zn2+, Fe2+ and Mn2+) and heavy (Cd2+, Hg2+ and Pb2+) metal cations have been determined by extraction studies with metal picrates and liquid membrane transport experiments with the same salts. The affinity of these ligands for Ag+ has also been investigated by 1H NMR spectroscopy. Both ketones are better extractants than the esters, and show a strong preference for Ag+, while Cu2+ is the most extracted cation with the esters. 1H NMR titrations with AgSO3CF3 indicate 1 : 1 complexes for all ligands, those with ketones are more stable, on the NMR time scale, than those with esters. Both esters are good carriers for Ag+, and 2b exhibits the highest transport rate (4.7 μmol h-1) found until now with dihomooxacalix[4]arene derivatives.

Complexation and transport of alkali, alkaline earth, transition and heavy metal cations by p-tert-butyldihomooxacalix[4]arene tetra(diethyl)amide

The binding properties of the tetra(diethyl)amide (2) derived from p-tert-butyldihomooxacalix[4]arene, in the cone conformation, towards alkali, alkaline earth, transition (Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) and heavy (Ag+, Cd2+, Hg2+ and Pb2+) metal cations have been established by extraction studies of metal picrates from an aqueous solution into dichloromethane, transport experiments with the same salts through a dichloromethane membrane and stability constant measurements in methanol. Results concerning the calorimetric study of Na+ and K+ complexes in methanol are presented. The affinity of 2 for some cations (Na+, K+, Ba2+, Ag+ and Zn2+) has been investigated by 1H NMR spectrometry, as well. The results are compared to those obtained with the analogous calix[4]arene tetraamide derivative 3. Amide 2 displays a preference for the alkali cations (mainly Na+ and K+) in contrast to amide 3 that prefers the alkaline earth cations. Ag+ and Cd2+ soft Lewis acids are also strongly bound by both amides. 1H NMR titrations confirm the formation of 1∶1 complexes between 2 and all cations studied, also suggesting that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. 2 shows transport rates that do not follow the same trends as the stability constants or extraction percentages; it can therefore be characterized as a selective receptor.

NMR conformational studies of tetraalkylated dihomooxacalix[4]arenes

Abstract Four tetraethers (methyl, ethyl, allyl and benzyl) of p - tert -butyldihomooxacalix[4]arene were synthesized and their conformational behaviour studied by means of variable temperature 1 H NMR, including the determination of coalescence temperatures and ΔG + . It was shown that the methyl ether still has some conformational monility at −100 °C, the ethyl ether displays a fixed conformation at −20 °C and the other two derivatives are conformationally rigid at room temperature. The conformations obtained are the 1,2-alternate B and cone, depending on the derivative formed.

Alkali and alkaline-earth metal cation complexation and transport properties by tetraphenyl ketone ofp-tert-butyldihomooxacalix[4]arene

The tetraphenyl ketone of p-tert-butyldihomooxacalix[4]arene (2) was synthesized for the first time. This derivative possesses the cone conformation in solution at room temperature, which was confirmed by NMR measurements (1H, 13C and NOE 1D). Extraction studies with metal picrates from neutral aqueous solution into dichloromethane, transport experiments with metal picrates through a dichloromethane membrane and stability constant measurements by UV absorption spectroscopy in methanol and acetonitrile were performed to evaluate the binding ability of ketone 2 towards alkali and alkaline earth metal cations. The tetraphenylketone of p-tert-butylcalix[4]arene (3) was also studied, and the results for the two derivatives were compared. Compound 2 shows a preference for K+ and Ba2+ cations, being selective only in the alkaline earth metal cation series. Compound 3 is a stronger binder than 2, but is a weaker extractant. Both show transport rates that are not proportional to complex stability or to extraction efficiency. Ketone 2 can be characterized as a selective receptor. Copyright

Synthesis, NMR conformational analysis, complexation and transport studies of an inherently chiral dihomooxacalix[4]arene triester

Abstract The synthesis of the inherently chiral triethyl ester monomethyl ether of p-tert-butyldihomooxacalix[4]arene (3) is reported. A distorted cone conformation in solution at room temperature has been established for triester 3 by NMR measurements (1H, 13C, NOE 1D and 2D). The extracting and complexing properties of 3 towards the entire alkali and alkaline earth cation series have been assessed by picrate extraction and stability constant determinations. Transport experiments with metal picrates through a CH2Cl2 membrane have also been performed. Comparison is made with tetraethyl ester of p-tert-butylcalix[4]arene (4) described in literature and also studied by us. 3 is a poor phase transfer agent and binder. In contrast, it is a good carrier, mainly for the alkali cations and displays a selective transport for Ba2+.

Synthesis and conformational analysis of p-tert-butyldihomooxacalix[4]arene derivatives containing the carbonyl group

Abstract Three novel tetraketones (methyl, adamantyl and tert -butyl) and the first tetraamide (diethylamide) derived from p - tert -butyldihomooxacalix[4]arene were obtained and their conformations established by NMR studies. Tetramethylketone was isolated in two different conformations, partial cones A and B, respectively, and the other derivatives were all obtained in the cone conformation. The conformational behaviour of the tetramethylketone conformers was studied by means of temperature dependent 1 H-NMR.

Inherently Chiral Calixcrowns Derived from p-tert-Butyldihomooxacalix[4]arene

Abstract The synthesis of the first calixcrowns derived from p-tert-butyldihomooxacalix[4]arene is reported. Both are, in solution at room temperature, in the cone conformation, which is shown by NMR studies. Their inherently chirality is also evident from 1H NMR experiments.

Synthesis, conformational behaviour, alkali and alkaline-earth metal cation extraction and transport studies of p-tert-butyldihomooxacalix[4]crowns

Abstract 1,3-Dimethoxy- p - tert -butyldihomooxacalix[4]arene-crown-6 ( 4 ) was synthesized for the first time. 4 was isolated in a partial cone A conformation in solution at room temperature, as established by NMR measurements ( 1 H, 13 C, COSY and NOESY). Conformational behaviour of 4 and p - tert -butyldihomooxacalix[4]-crown-5 ( 2 ) and crown-6 ( 3 ) was studied by dynamic 1 H NMR and by MD/MM calculations. Two-phase (water/CH 2 Cl 2 ) picrate extraction studies and transport experiments with the same salts through a CH 2 Cl 2 membrane were performed to evaluate the binding properties of these ligands towards alkali and alkaline earth metal cations. 2 and 3 are poor phase transfer agents for all cations, while 4 is a reasonable extractant for the alkali cations, showing preference for Cs + . However, all three calixcrowns are good carriers for the alkali cations and display a very selective transport for Ba 2+ .

Synthesis and NMR Conformational Studies of p‐tert‐Butyldihomooxacalix[4]arene Derivatives Bearing Pyridyl Pendant Groups at the Lower Rim

Direct O-alkylation of p-tert-butyldihomooxacalix[4]arene (1) with 2-(chloromethyl)pyridine hydrochloride and NaH in DMF provided six of the nine possible (2-pyridylmethoxy)dihomooxacalix[4]arene conformers in the cone conformation. Mono- and tetrasubstituted derivatives were obtained, as well as all four (1,2-, 1,3-, 1,4- and 2,3-) types of disubstituted compounds. The conformations and the substitution patterns were established by NMR spectroscopy (1H, 13C, COSY, NOESY and TOCSY 1D). From the same reaction, another tetrasubstituted derivative (6) in a 1,2-alternate A conformation was also isolated and characterised. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis and NMR conformational studies of p-tert-butyldihomooxacalix[4]-arene derivatives

Abstract The tetramethyl (2) and tetraethyl (3) ethers, and the tetraacetate (4) derivatives of the p-tert-butyldihomooxacalix[4]arene were prepared. The mobility of these compounds studied by temperature-dependent 1H NMR spectroscopy. For the tetraacetate derivative, at room temperature, 1,2- or 1,3-alternate conformations are suggested. Those conformations were confirmed by NOE difference and COSY spectra for the tetraethyl ether derivative in CDCl3 at -20°C.