Thermo gravimetric analysis of supramolecular complexes of p-tert-butylcalix[6]arene and ammonium cations: crystal structure of diethylammonium complex

Thermo gravimetric analysis of ammonium-p-tert-butylcalix[6]arene salts were carried out to determine the stoichiometry of the inclusion compounds and the temperature of leaving of the ammonium cation, as amine, from the solid phase by a reverse proton transfer reaction to calixarene. The chain length of the amine molecules and their relative basicity order are the main factors which determine the decomplexation temperatures for the ammonium salts of piperidinium, diethylammonium, ethylenediammonium, morpholinium, s-butylammonium, butylammonium, hexylammonium and triethylammonium salts of p-tert-butylcalix[6]arene anion. The solid state structure of bis-diethylammonium-p-tert-butylcalix[6]arene dianion is reported. The calix moiety adopts a 1,2,3 alternate conformation, with one ammonium as exo-calix and other as endo-calix, with an intricate array of hydrogen bonds between phenol, phenolate and ammonium cations.     

Synthesis, characterization, and conformational analysis of new perfunctionalized calix[9]arenes

The synthesis of a series of six new per-substituted p-tert-butylcalix[9]arenes derivatives has been achieved. Functions such as ester, nitrile, or carbonate have been grafted on the phenolic oxygens of calix[9]arene: p-tert-butylcalix[9]arene nona-ethyl acetate, p-tert-butylcalix[9]arene nona-carboxylic acid, p-tert-butylcalix[9]arene nona-cyanopropyloxy, p-tert-butylcalix[9]arene nona-tert-butoxycarbonyle, p-tert-butylcalix[9]arene nona-acetyl, and p-tert-butylcalix[9]arene nona-trifluoroacetyl have been obtained in good yields (from 48% to 78%) and fully characterized. The X-ray structures of p-tert-butylcalix[9]arene nona-tert-butoxycarbonyl and p-tert-butylcalix[9]arene nona-ethyl acetate have been determined. A dynamic NMR study has revealed the high conformational mobility of such structures, even at low temperature.     

Synthesis and Solid-State Conformation of a Calix[8]arene 1,5-Diquinone Derivative

The first example of a calix[8]quinone derivative, hexamethoxy-p-tert-butylcalix[8]-1,5-diquinone 5, has been synthesized from p-tert-butylcalix[8]arene 1by exploiting a protection-deprotection procedure. The structure of the 5·toluene inclusion compound has been determined by a single crystal X-ray diffraction study. The calix[8]arene molecule possesses a crystallographic inversion centre and assumes a ‘pseudo-chair-like’ conformation, with two opposite 3/4-cone moieties, which resembles the previously reported chair-like conformation of p-tert-butylcalix[8]arene. The 4 toluene molecules per unit cell occupy interstitial voids and are released in the temperature range of 30–160 °C.This revised version was published online in July 2005 with a corrected issue number.     

Synthetic and NMR Studies on Calix[n]Arene (n = 4,6,8) Triflates,Mesylates, and Tosylates

Abstract

The synthesis and full characterization of eight new calix[n]arene sulfonate esters including their conformational analysis were carried out. While p-tBucalix[6]arene and p-tBu-calix[8]arene esters are conformationally labile in the temperature interval of 25–100°C, p-tBu-calix[4]arene mono-and diesters were isolated as stable conformers at ambient temperature. Two 1,3-functionalised compounds of these derivatives, p-tert-butylcalix[4]arene ditriflate (5) and dimesylate (6) were shown unexpectedly high conformational stability up to 100°C by dynamic NMR measurements. The NMR measurements confirm the pinched-cone conformation for both derivatives. For the dealkylated calix[4]arene derivatives the partial cone conformer of the triesters have been obtained as major products in all cases.     

Inherently chiral biscalixarene cone–cone conformers consisting of calix[4]arene and calix[5]arene subunits

Inherently chiral biscalixarenes with hetero-cavities were synthesized by a covalent assembly of p-tert-butylcalix[5]arene with a 1,3-substituted calix[4]arene via 1,3-alkylation reaction and subsequent desymmetrization. The racemates were resolved by chiral HPLC method. ¹H NMR spectra, VT-NMR spectra, and theoretical calculations support that the calix[5]arene subunit of the inherently chiral calix[4][5]arene ester adopts a cone-in conformation, with the aromatic ring bearing the CH₂CO₂Et group tilting inward the calix[5]arene cavity. By contrast, such a cone-in structural feature of the calix[5]arene subunit disappears for the corresponding inherently chiral calix[4][5]arene carboxylic acid, due to the intramolecular hydrogen bonding between the carboxyl group and an ethereal oxygen of the glycolic chain.     

新型多重氮杂杯[4]芳烃衍生物的合成

对叔丁基杯[4]芳烃-1,3-二醛基衍生物1与水杨酰肼、烟酰肼、异烟酰肼反应, 合成了具有开链结构新型杯[4]多重氮杂衍生物2a～2c, 产率分别为88%, 85%和90%. 化合物1与乙二酰肼、丙二酰肼、己二酰肼反应, 得到具有桥联结构的新型杯[4]多重氮杂衍生物3a～3c, 产率分别为86%, 89%和90%. 新化合物的结构经元素分析、质谱、核磁共振谱等表征证实, 杯[4]芳烃单元均为1,3-取代且采取锥式构象.     

p-tert-Butylcalix[4]arene Derivatives Containing Azathiol Receptors and Their Recognition towards Hg(II)

25,27(2,2'-bis(ethoxybenzyl))-1,9-diimine-3,7-dithianonane-p-tert-butylcalix[4]arene (3),25,27(4,4'-bis(ethoxybenzyl))-1,9-diimine-3,7-dithianonane-p-tert-butylcalix[4]arene (4),25,27(2,2'-bis(ethoxybenzyl))-1,8-diimine-3,6-dithianonane-p-tert-butylcalix[4]arene (5) and25,27(4,4'-bis(ethoxybenzyl))-1,8-diimine-3,6-dithianonane-p-tert-butylcalix[4]arene (6) havebeen synthesized by condensation reactions between25,27(2,2'-bis(ethoxybenzaldehyde))-p-tert-butylcalix[4]arene (1) and25,27(4,4'-bis(ethoxybenzaldehyde))-p-tert-butylcalix[4]arene (2) and appropriateamines. Reduction of 3 and 4 withNaBH₄ and subsequent protonation byHCl/CH₃OH resulted in25,27(2,2'-bis(ethoxybenzyl))-1,9-diaza-3,7-dithianonane-p-tert-butylcalix[4]arenedihydrogenchloride (7) and25,27(4,4'-bis(ethoxybenzyl))-1,9-diaza-3,7-dithianonane-p-tert-butylcalix[4]arenedihydrogenchloride (8), respectively. Complexation studies of 7 and 8 withZn(II), Cd(II) and Hg(II) ions were carried out bypotentiometric titration. Compounds 7 and8 selectively form 1 : 1 complexes with Hg(II), andtheir stability constants (log Ks) were estimated tobe 4.47 ± 0.08 and 3.20 ± 0.13, respectively. From spiecies distribution plots, 7 and 8were found to form the highest amount of 1 : 1 complexes with Hg(II) at pH 8.7 and 9.1, respectively.     

Complexation Between (O‐Methyl)6‐2,6‐Helic[6]arene and Tertiary Ammonium Salts: Acid/Base‐ or Chloride‐Ion‐Responsive Host–Guest Systems and Synthesis of [2]Rotaxane

Complexation between (O ‐methyl)₆‐2,6‐helic[6]arene and a series of tertiary ammonium salts was described. It was found that the macrocycle could form stable complexes with the tested aromatic and aliphatic tertiary ammonium salts, which were evidenced by ¹H NMR spectra, ESI mass spectra, and DFT calculations. In particular, the binding and release process of the guests in the complexes could be efficiently controlled by acid/base or chloride ions, which represents the first acid/base‐ and chloride‐ion‐responsive host–guest systems based on macrocyclic arenes and protonated tertiary ammonium salts. Moreover, the first 2,6‐helic[6]arene‐based [2]rotaxane was also synthesized from the condensation between the host–guest complex and isocyanate.     

Preparation and characterisation of thiol functionalised p-tert-butylcalix[4]arene-embedded polymer inclusion membranes: performance and selectivity

ABSTRACT

Here in we report the syntheses of the thiol functionalised p-tert-butylcalix[4]arene from the reaction of p-tert-butylcalix[4]arene-dialkylbromide derivative with thiourea. The structure of the thiol functionalised p-tert-butylcalix[4]arene was determined by using ¹HNMR, ¹³CNMR and elemental analysis techniques. Furthermore, the thiol functionalised p-tert-butylcalix[4]arene, cellulose triacetate (CTA) and 2-nitrophenyl octyl ether (o-NPPE) in dichloromethane were used to make a new calixarene-embedded polymer inclusion membrane (Bu^t-C@PIM). The surface and structure morphology of Bu^t-C@PIM was detected using thermogravimetric analysis, elemental analysis techniques and scanning electron microscopy. The affinity (the percentage of metal ion transferred from the source solution) of a PIM towards a range of divalent cations was found to follow the order Pb²⁺ > Zn²⁺ > Ni²⁺ > Cu²⁺ > Cd²⁺ > Co²⁺. The results also indicated that the transport efficiency of Bu^t-C@PIM was repeatable and may be beneficial in the development of a simplistic and highly influential trace metal recovery method from aqueous solution.     

Solution and X-Ray Crystal Structures of the Di- and Tetra-allyl Ether of tert- utylcalix[4]arene

The di- and tetra-allyl ethers of tert-butylcalix[4]arene 1 and 2 have been prepared by alkylation of tert-butylcalix[4]arene with allyl bromide and K₂CO₃ using different reaction times. Solution ¹H NMR measurement of the di-allyl ether 1 and X-ray crystal structures of the complexes of 1 with chloroform (1a) or methanol (1b) indicate the cone conformation of 1 in which intramolecular hydrogen bonding can be maximized. The crystalline state conformers 1a and 1b are distorted in different grades depending on the solvent. While methanol is incorporated in the macrocycle, chloroform molecules do not occupy the cage. The solution ¹H NMR spectra of tetra-allyl ether 2 show the co-existence of the cone and partial cone conformation. The partial cone conformer of 2 was investigated by X-ray crystallography. In this compound hydrogen bonding is not existent. The conformer distribution is likely affected by steric and template effects.     

Synthesis of Oligomer and Styrene Polymer-supported Calix[4]arene Derivatives and Selective Extraction of Fe3+

Five new polymeric compounds containing more than one calix[4]arene have been synthesized by reacting an oligomer with 5,11,17,23-tetrakis[(diethylamino)methyl]-25,26,27,28-tetrahydroxycalix[4]arene (L1), 25,27-dimethyl-26,28-dihydroxy-p-tert-butylcalix[4]arene diketone (L2), and p-nitrocalix[4]arene (L3), and chloromethylated polystyrene with 25,27-dimethyl-26,28-dihydroxy-p-tert-butylcalix[4]arene diketone (L4) and p-nitrocalix[4]arene (L5). These compounds were studied by the selective extraction of Fe³⁺ cation from the aqueous phase into the organic phase and was carried out by using compounds L1–L5. It was observed that the polymer support attached to the lower rim of p-nitrocalix[4]arene was the most efficient carrier of Fe³⁺ in the extraction process.     

Calixarenes 11. Crystal and molecular structure ofp-tert-butylcalix[8]arene

Monoclinic prisms were obtained by slow evaporation of a pyridine solution ofp-tert-butylcalix[8]arene: space groupP2₁/c,a=20.312(3),b=23.020(2),c=20.006(6) ; =113.05(2)⁰;V=8707.6 ų;Z=4. Refinement led to anR value of 0.166 for 4231 reflections which, although high, is sufficient to establish the conformation of the molecule as a pleated loop in which the eight hydroxyl groups are arranged in a slightly undulating, almost planar, intramolecularly hydrogen bonded cyclic array. The possible inferences for the conformation ofp-tert-butylcalix[8]arene in solution are discussed. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82019.     

Conformational properties of propargyloxy-calix[4]arene tricarboxamides: NMR and DFT studies on the O-through-the-annulus rotation

The size limit of substituents allowing O-through-the-annulus rotation of substituted calix[4]arenes was further extended to the propargyloxy group in 24-propargyloxy-25,26,27-tris(N,N-dimethylcarbamoylmethoxy)-p-tert-butylcalix[4]arene by demonstrating its free but slow motion affording equilibrium between the partial cone and 1,2-alternate conformers. The effect of solvent and upper rim substituents R¹ on the conformational inversion was investigated by means of ¹H NMR. The rotational isomerisation of the parent (R¹ = H) analogue could not unambiguously be detected. The experimental results were supported by comprehensive density functional theory studies.     

Thermodynamic and electrochemical aspects ofp-tert-butylcalix[n]arenes (n=4, 6, 8) and their interactions with amines

Attention is drawn to the need of detailed thermodynamics in calixarene chemistry. The reasons for increasing efforts in this area are underlined and suggestions for new issues to be addressed are given. The solution thermodynamics ofp-tert-butylcalix[n]arenes (n=4, 6, 8) is discussed with particular reference to transfer Gibbs energies which reflect the selective solvation that the tetramer and the octamer undergo in the various solvents. This is followed by recent solution studies on amine-p-tert-butylcalix[n]arene (n=4, 6, 8) in nitrobenzene and in benzonitrile at 298.15 K which indicate the lower acidic character of the tetramer relative to the hexamer and the octamer in these solvents. As an implication of these results, very low conductivities are observed in studies involving the interaction of the former with amines. Thus, thermodynamic studies suggest thatp-tert-butylcalix[4]arene interacts with triethylamine in benzonitrile and in nitrobenzene through hydrogen bonding or ion-pair formation. A thermodynamic cycle is used to investigate the effect associated with the interaction of the amine with the tetramer in these solvents.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

X-ray crystal structure of a p-hydroxycalix[6]arene derivative

The first molecular structure of a p-hydroxycalix[6]arene 6 has been determined by a single crystal X-ray diffraction study. The calix[6]arene molecule assumes a 1,2,3-alternate conformation with all OH groups at the upper rim engaged in H-bonds with pyridine molecules. The stacking of molecules of p-hydroxycalix[6]arene 6 along the a and c axes gives rise to a solvent pseudo-cylindrical cavity at the centre of the cell.     

Synthesis and conformation studies of multiple bridged p-tert-butylcalix[7]arene diphosphates

p-tert-Butylcalix[7]arene reacting with phosphorus pentachloride and then with water afforded two stereoisomers p-tert-butylcalix[7]arene diphosphates 2a and 2b, representing the first phosphorus multiple bridged calix[7]arene. The more accurate structure of 2a was investigated with the aid of Gaussian03 calculations.     

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.     

Stereochemical control of calixarenes useful as rigid and conformationally diversiform platforms for molecular design

Stereochemical problems and related functions of calix[4]arenes, calix[6]arenes and their chiral derivatives have been reviewed. In p-tert-butylcalix[4]arene (1H₄) and its mono-, di-, tri-, and tetra-O-alkyl derivatives (1H₃R, 1H₂R₂,1HR₃, and 1R₄, respectively), 23 different homologues can exist (including 1H₄). We found that the OH group in the unmodified phenol unit is permeable through the calix[4]arene ring. Thus, several conformational isomers become equivalent after the ‘oxygen-through-the-annulus’ rotation of the OH group and the number of possible homologues is reduced to 13 (including 1H₃). We report in this paper the syntheses of all of these possible conformational isomers using a protection-deprotection method with a benzyl group and metal template effects. On the other hand, all possible chiral isomers that can be derived from calix[4]arene by modification of the OH groups have been systematically classified. Molecular asymmetry can be generated not only by different substituents but also by conformational isomerism. The numbers of chiral isomers are 17 for tetra-O-substituted calix[4]arenes, 9 for tri-O-substituted calix[4]arenes, 3 for di-O-substituted calix[4]arenes, and 0 for mono-O-substituted calix[4]arenes. Chiral calix[4]arenes can also be designed by the introduction of a substituent into the m-position of a phenol unit or by the use of a dissymmetric ‘stapling reaction’ in proximal phenol units. In p-tert-butylcalix[6]arene, the conformational behaviour is totally different from that in p-tert-butylcalix[4]arene. A large degree of conformational freedom remains in the framework, and both ‘oxygen-through-the-annulus rotation’ and ‘para-substituent-through-the-annulus rotation’ can take place. However, when metal cations are bound to calix[6]aryl esters, the conformation is changed to a cone type. Bridging and capping are powerful methods to immobilize the conformation of calix[6]arenes. In addition, definitive evidence for ring immobilization was obtained from the absence of racemization in the chiral calix[6]arene. A successful example of chiral recognition for α-amino acid derivatives was achieved by using chiral homooxacalix[3]arene which has ‘pseudo C₂ symmetry’. These examples indicate that calixarenes serve as rigid and conformationally diversiform platforms for the design of novel functional supramolecules.     

Selectively formylated and bridged calix[6]arene derivatives at the upper rim

The strategy of bridging the anisole units at the upper rim of calix[6]arene has been applied to strain the conformations of calix[6]arene. Based on the selective formylation of the 1,3,5-tri-p-tert-butylcalix[6]arene, several new calix[6]arene derivatives with different 1,3-bridged chains or a 1,3,5-tripod bridge at the upper rim have been prepared with moderate yields. The ¹H NMR spectra indicate that these calix[6]arene derivatives adopt a cone conformation, which has also been confirmed by the theoretical calculation at AM1 level. X-ray crystal structure of 1,3,5-tripod bridged compound 5 discloses that the calix[6]arene host stands in a cone conformation with approximate C_3v symmetry, and that a methanol molecule is enclosed in its hydrophobic cavity and stabilized by multi hydrogen bonds.     

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 mol h^-1) found until now with dihomooxacalix[4]arene derivatives.