Inclusion of p‐sulfonatothiacalix[4]arene and its metal complexes

As a new member of the water‐soluble calixarene family, p‐sulfonatothiacalix[4]arene possesses unique properties resulting from its inherent structural characteristics. In our recent research, we have investigated the self‐assembly of bowl‐like p‐sulfonatothiacalix[4]arenes with or without transition‐metal ions in the presence of suitable guests. We have obtained a series of compounds with different structural motifs, such as capsules, tetranuclear clusters, and molecular clefts. In addition, p‐sulfonatothiacalix[4]arenes show good inclusion abilities and can capture different guests by utilizing their hydrophobic cavities through supramolecular interactions. Even when a cone‐like conformation is fixed, the p‐sulfonatothiacalix[4]arene can also splay its opposite aromatic rings apart to adjust its cone‐like conformations from C_4v to C_2v and even lower symmetries. All of these show that it is a good candidate for the research of inclusion phenomena. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 155–168; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200800033     

New oxacalix[4]arene carboxylate detects viologen in protic media

ABSTRACT

We demonstrate that Ullman fragment-coupling can be used to synthesise an oxacalix[4]arene monocarboxylic acid, which provides easy access to its water-soluble carboxylato derivatives. Crystallographic and computational data suggest that the new carboxyl-substituted oxacalix[4]arene adopts a 1,3-alternate conformation both in the solid-state and in methanol solution. Its water-soluble tetrabutylammonium derivate can detect the herbicide paraquat at neutral pH in aqueous media (K _a = 111 ± 3 M^–1) and in methanol (K _a = 2020 ± 70 M^–1).     

Aminolysis reaction of calix [ 4 ] arene esters and crystal structures and conformational behaviors of calix[4]arene amides

We first make use of aminolysis of calix[4]arene esters to synthesize calix[4]arene amides. When the two ethyl esters of the calix[4]arene esters are aminolysized, the 1, 3-amide derivative is formed selectively. The crystal structures of the calix-[4]arene with two butyl amide (3b) and four butyl amide moieties (4b) were determined. The intermolecular hydrogen bonds make 4b form two-dimensional net work insolid state. The 1H NMR spectra prove that 3b is of a pinched cone conformation, while 4b and tetraheptylamide-calix[4]arene (6b) take fast interconversion between two C2v isomers in solution and appear an apparent cone conformation at room temperature. As decreasing temperature, the interconversion rate decreases gradually and, finally, the interconversion process is frozen at Tc = -10℃, which makes both conformations of 4b and 6b the pinched cone structures. The hydrogen bond improves the interconversion barrier, and the large different values of the potential barrier between 6b and 4b (or 6b) may     

New Efficient Synthetic Pathways to Tetrakis{p‐[(diethylphosphono)methyl]}calix[4]arene

Various operating conditions have been applied on tetrakis[p‐(halogenomethyl)]‐ and tetrakis[p‐(aminomethyl)]calix[4]arene derivatives to improve the synthesis of the 5,11,17,23‐tetrakis[(diethylphosphono)methyl]‐25,26,27,28‐tetrahydroxycalix[4]arene. Two new, high yield, synthetic pathways have been selected, involving, for the first one, the 25,26,27,28‐tetrahydroxy‐5,11,17,23‐tetrakis[(trimethylamino)methyl]calix[4]arene, tetraiodide, DMF, and 10 equiv. of triethyl phosphite ((EtO)₃P), and, for the other one, the 5,11,17,23‐tetra(bromomethyl)‐25,26,27,28‐tetrahydroxycalix[4]arene, CH₂Cl₂, and only 4 equiv. of (EtO)₂P.     

Design of Organoiron Macromolecules Based on Upper Rim Functionalized Calix[4]arenes

The versatility of cationic cyclopentadienyliron complexes is demonstrated for the generation of calix[4]arene‐based dendrimers and polymers. Dendrimers were prepared from a branched organoiron calix[4]arene through subsequent reactions of azo dyes and organoiron complexes. The resulting azo dye‐containing metallocalix[4]arenes were soluble in polar organic solvents and displayed λ_max ranging between 430 and 456 nm. Upon addition of various acids, the λ_max shifted to higher wavelengths (513–535 nm). In the solid state and in solution, the azo dye‐containing metallocalix[4]arenes reversibly changed colour in the presence of acid and base, indicating their potential use as acid sensors. Cyclic voltammetric studies showed that the iron centres of the metallocalix[4]arenes were reversibly reduced at E_1/2 = −1.49 V. When non‐branching organoiron‐based calix[4]arene were reacted with dithiols, polymers containing calix[4]arenes either in their side chains or main chains were obtained. The polymers possessed weight average molecular weights between 35 000 and 53 000. The polymers were determined to be thermally stable with backbone decomposition occurring above 500 °C.

     

Synthesis of Flavin–Calix[4]arene Conjugate Derivatives

The synthesis of two new flavin substituted calix[4]arene derivatives, 9 and 10 , is described. The first flavin substituted calix[4]arene derivative 9 was synthesized by the reaction of 3‐methylalloxazine ( 5 ) with 25,27‐bis(3‐bromopropoxy)‐26,28‐dihydroxy‐5,11,17,23‐tetra(tert‐butyl)calix[4]arene ( 4 ) in high yield (92%). The other derivative 10 was prepared from 3‐methylalloxazine‐1‐acetic acid ( 7 ) and 25,27‐bis(3‐cyanopropoxy)calix[4]arene ( 3 ). All new compounds were characterized by a combination of FT‐IR and ¹H‐NMR spectroscopy, and elemental‐analysis techniques.     

An Indium‐Seamed Hexameric Metal–Organic Cage as an Example of a Hexameric Pyrogallol[4]arene Capsule Conjoined Exclusively by Trivalent Metal Ions

A hexameric metal–organic nanocapsule is assembled from pyrogallol[4]arene units, which are stitched together with indium ions. This indium‐seamed capsule is the first instance of a M₂₄L₆ type hexameric coordination cage held together exclusively by trivalent metal ions. Explicitly, unlike previously reported pyrogallol[4]arene‐based metal‐seamed capsules, the current In³⁺ seamed capsule is entirely supported by O→In coordinate bonds. This work demonstrates the important proof of concept of the ability of pyrogallol[4]arene to react with metals in higher oxidation states to assemble into atomically‐precise hexameric coordination cages. As such, these results open up exciting avenues toward the assembly of previously unanticipated metal–organic capsules, for example offering inspiration for tackling metals exhibiting high valence states such as in the lanthanide and actinide series.     

Liquid chromatographic behavior of two alanine‐substituted calix[4]arene‐bonded silica gel stationary phases

Two new kinds of alanine‐substituted calix[4]arene stationary phases of 5,11,17,23‐p‐tert‐butyl‐25,27‐bis(l ‐alanine‐methylester‐N‐carbonyl‐methoxy)‐26,28‐dihyroxycalix[4]arene‐bonded silica gel stationary phase (BABS4) and 5, 11, 17, 23‐p‐tert‐butyl‐25,26,27,28‐tetra(l ‐alanine‐methylester‐N‐carbonyl‐methoxy)‐calix[4]arene‐bonded silica gel stationary phase (TABS4) were prepared and characterized in the present study. They were compared with each other and investigated in terms of their chromatographic performance by using polycyclic aromatic hydrocarbons, disubstituted benzene isomers, and mono‐substituted benzenes as solute probes. The results indicated that both BABS4 and TABS4 exhibited multiple interactions with analytes. In addition, the commonly used Tanaka characterization protocol for the evaluation of commercially available stationary phases was applied to evaluate the properties of these two new functionalized calixarene stationary phases. The Tanaka test results were compared with Zorbax Eclipse XDB C₁₈ and Kromasil phenyl columns, respectively. BABS4 has stronger hydrogen‐bonding capacity and ion‐exchange capacity than TABS4, and features weaker hydrophobicity and hydrophobic selectivity. Both of them behave similarly in stereoselectivity. Both BABS4 and TABS4 are weaker than C₁₈ and phenyl stationary phases in hydrophobicity and hydrophobic selectivity.     

Studies on Properties of Tetra‐p‐nitro‐tetra‐O‐alkylcalix[4]arenes

Ibis paper reports the properties of the novel tetra‐p‐nitro‐tetra‐O‐alkyl‐calix[4]arenes (alkyl= n‐C₄H₉, 1; n‐C₈H₁₇ 2; n‐C₁₂H₂₅, 3; n‐C₁₆H₃₃, 4). X‐ray crystallographic analysis and ¹H NMR revealed that they exist as pinched‐cone conformation in crystal or cone conformation in solution. EFISH experiments at 1064 nm in CHCl₃, indicated that tetra‐p‐nitro‐tetra‐O‐butyl‐calix[4]arene (1) has higher hyperpolarizability β, values than the corresponding reference compound p‐nitro‐phenyl butyl ether, without red shift of the charge transfer band. Compounds 2, 3 and 4 with longer alkyl chains can form monolayer at the air/water.     

Studies on Properties of p—Nitrophenylazo Calix[4]arene Derivatives

The p-nitrophenylazo calix[4] arene derivatives la-ld with nonlinear optical(NLO)properties were prepared by the diazo-coupling reaction of calix[4]arene with p-nitrophenyl diazonium.The diazotization reaction of p-nltroaniline was caried out with isoamyl nitrite as a source of nitrous acid in EtONa/EtOH under refluxing conditon.X-Ray crystallographic analysis and ^1H NMR sptectra reveal that they exist as cone conformation in crystal state or in soution.HRS measurements at 1064 nm in THF indicate that p-nitrophenylazo calix[4]arenes have higher hyperpolarizability βz values than the corresponding reference compound 4-(4-nitrophenylazo)-2,6-dimethyl-phenol,without red shift of the charge transfer band.The tetrakis p-nitropheylazo calix[4]arene(2)with longer alkyl chains can form monolayer aht the air/water interface.     

Synthesis and Structure of Novel Double Flexible Spacer Bridged Biscalix[4]arenes

25, 25′, 27, 27′‐Bis(1,3‐dioxypropane)‐bis(5, 11, 17, 23‐tetra‐tert‐butylcalix[4]arene‐26,28‐diol) (4) and 25, 25′, 27, 27′‐bis(1, 4‐dioxybutane)‐bis (5, 11, 17, 23‐tetra‐tert‐butylcalix‐[4]arene‐26, 28‐diol) (5) were synthesized by the reaction of p‐tert‐butylcalix[4]arene (1) with preorganized 25, 27‐bis(3‐bromoproxyl)calix[4]arene‐26, 27‐diol (2) and 25, 27‐bis(3‐bromobutoxyl)calix[4]arene‐26, 27‐diol (3) in the presence of K₂CO₃ and KI. Compounds 4 and 5 were characterized with X‐ray analysis and the selectivity of 4 and 5 toward K⁺ over other alkali metal ions, alkaline metal ions as well as NH₄⁺ were investigated with an ion‐selective electrode.     

Corona[5]arenes Accessed by a Macrocycle‐to‐Macrocycle Transformation Route and a One‐Pot Three‐Component Reaction

Corona[5]arenes, a novel type of macrocyclic compound that is composed of alternating heteroatoms and para ‐arylenes, were synthesized efficiently by two distinct methods. In a macrocycle‐to‐macrocycle transformation approach, S₆‐corona[3]arene[3]tetrazine underwent sequential S_NAr reactions with HS‐C₆H₄‐X‐C₆H₄‐SH (X=S, CH₂, CMe₂, SO₂, and O) to produce the corresponding corona[3]arene[2]tetrazines. Different corona[3]arene[2]tetrazine compounds were also constructed in a straightforward manner by a one‐pot three‐component reaction of HS‐C₆H₄‐X‐C₆H₄‐SH (X=S, CH₂, CMe₂, SO₂, and O) with diethyl 2,5‐dimercaptoterephthalate and 2 equiv of 3,6‐dichlorotetrazine under very mild conditions. All corona[5]arenes adopted 1,2,4‐alternate conformational structures in the crystalline state yielding similar nearly regular pentagonal cavities. Both the cavity size and the electronic property of the acquired macrocycles were fine‐tuned by the nature of the bridging element X.     

Enantioselective Recognition of Calix[4]arene Derivative Bearing Bicyclic Guanidinium for D/L Amino Acid Zwitterions

The p‐tetra‐tert‐butyl calix[4] arene derivatives (3 and 4) with (5,5) chiral bicyclic guanidinium, as the receptors of amino acid zwitterions, have been synthesized via a O‐alkylation reaction of p‐tetra‐tert‐butyl calix [4] arene with cbJoromethyl chiral bicyclic guanidinium 2 in the presence of anhydrous K₂CO₃ in acetonitrile. The results obtained from liquid‐liquid competitive extraction experiments indicate that the two receptors may selectively recognize L‐aromatic amino acids, and that the enantioselective recognizability of the receptor 4 with two chiral bicyclic guanidinium units reachs up to about 90% for L‐Phe.     

Synthesis of （p-Formylphenyl）azo Calix[4]arenes

Five novel azo calix[4]arenes were reported. The p-aminobenzaldehyde was diazotized with sodium nitrite in aqueous hydrochloride solution. Mono-, bis-, tris- and tetrakis(p-formylphenyl)azo calix[4]arenes (including proximal and distal isomers) were obtained respectively by diazo-coupling in different molar ratio to calix[4]arene(1) under pH=7.5--8.5 at 0-5℃. All (p-formylphenyl)azo calix[4]arenes were characterized by ^1H NMR, ^13C NMR, IR, MS (ESIMS) spectroscopies and elemental analysis.     

Influences of Hard Donor on Cation Selectivities Closing to Soft Selenium Donor in Tweezer-like Calix[4]arene Receptors

Three novel 25,27-dihydroxy-26,28-bis(3-benzylselenopropoxy)-5,11,17,23-tetra-tert-butylcalix[4]-arene (2),25,27-dihydroxy-26,28-bis[3-(2-hydroxyethylseleno)propoxy]-5,11,17,23-tetra-tert-butyl-calix[4]arene (3) and 25,27-dihydroxy-26,28-bis(3-propylselenoproppxy)-5,11,17,23-tetra-tert-butyl-calix[4]arene (4) were synthesized for the comparison of their ion-selectivity in ion-selective electrodes (ISE). X-ray structure of the CH/π complex of 4.CH2Cl2 was elucidated. ISEs based on 2-4 as neutral ionophores were prepared, and their selectivity coefficients for Ag (logKAg,M^pot) were investigated against some main group metal ions and transition metal ones using the fixed interference method (FIM). These ISEs showed excellent Ag^ selectivity over most of the interfering cations examined. It is evident that the stronger Hg^2 interference may not be produced while hard donors (hydroxy) are close to the soft selenium donors.     

The Synthesis of Ester and Ketone Derivatives of Azocalix[4]arene Containing Chromogenic Groups

Azocalix[4]arenes were prepared by linking 4-ethylaniline, 4-n-butylaniline, 4-acetamide aniline and 2-aminothiazol to calix[4]arene through a diazo-coupling reaction. A new family of azocalix[4]arenes, L1–L12, have been prepared by the incorporation of acetyl, benzoyl, and methyl ketone units to azocalix[4]arene. Characterization of the synthesized compounds was carried using elemental analyses, UV–Vis, IR and ¹H NMR spectroscopic studies.     

Synthesis and Structure of Functionalized Zigzag Hydrocarbon Belts

Described in this paper are the synthesis and structure of novel and edge‐functionalized zigzag hydrocarbon belts. A stepwise “fjord‐stitching” strategy featuring repetitive intramolecular acylation reactions of a resorcin[4]arene derivative as the key steps afforded a biscarbonyl‐functionalized octahydrobelt[8]arene product. Facile ketone reduction with NaBH₄ and nucleophilic addition with n‐butyllithium produced secondary and tertiary alcohol‐containing molecular belts, respectively. Selective oxidation reactions of biscarbonyl‐bearing octahydrobelt[8]arene with m‐CPBA and (PhSeO)₂O furnished the corresponding lactone‐ and 1,4‐quinone‐embedded molecular belts. Depending on the functional groups on the edges, the acquired belt molecules adopt different shapes such as square prism, truncated cone, and elliptical cylinder.     

High-performance Liquid Chromatography Study of the Nitration Course of Tetrabutoxycalix[4]arene at the Upper Rim:Determination of the Optimum Conditions for the Preparation of 5,11,17-Trinitro-25,26,27,28-tetrabutoxycalix[4]arene

A selective nitration of calix[4]arene at the upper rim in one pot process was described by monitoring the time dependence of the distribution of products by high‐performance liquid chromatography (HPLC). The discrimination of five nitrated products was accomplished by molecular symmetry considerations and ¹H NMR analysis. As a result, unusual 5,11,17‐trinitrocalix[4]arene ( 2d ) was obtained in 57% isolated yield. 5,11‐Dinitro‐calix[4]arene ( 2b ) and 5,11,17‐trinitrocalix[4]arene ( 2d ) with tetranitrocalix[4]arene 2e were further characterized by crystal X‐ray diffraction analysis. Furthermore, as an example of potential application, trinitrocalix[4]arene 2d could be converted to triaminocalix[4]arene 3d conveniently.     

Improvement of selective d-cation binding by tetrathiacalix[4]arene hydrazides: synthesis and extraction properties

New de-tert-butyltetrathiacalix[4]arenes with acetylhydrazide substituents in cone and 1,3-alternate conformations have been synthesised with good yield by the hydrazinolysis of calix[4]arene ester derivatives. The recognition ability of synthesised macrocycles towards transition and alkali metals has been investigated by the picrate extraction method. The stoichiometry of complexes and the extraction constants have been determined. It has been found that tetrahydrazides do not extract alkali metal ions, but show an excellent affinity towards transition and heavy metal cations. The 1,3-alternate conformer of de-tert-butyltetrathiacalix[4]arene has revealed a remarkable selectivity for Ni²⁺ and Ag⁺ in the row of d-elements and for Cd²⁺ ion among the toxic heavy metals. The experimental data show that the removal of tert-butyl groups from tetrathiacalix[4]arene framework leads to the drastic improvement of extraction efficiency and selectivity of new tetrahydrazides.     

Ab initio and density functional studies of cooperative hydrogen bonding in calix[4]-and calix[6]arenes

The cone conformation of C ₄ symmetry is shown by the Hartree-Fock method (3-21G basis) to be the predominant conformer of calix[4]arene; the compressed cone of C ₂ symmetry is the major conformer of calix[6]arene. Using quantum chemical methods we calculated hydrogen bond cleavage energies for calix[4]-(ab initio and density functional methods) and calix[6]arene (ab initio), and also for the complex of calix[4]arene with carbon disulfide. These energies along with structural data point to the cooperative effect of hydrogen bonds. The results of these studies provided an explanation to the greater conformational lability of calix[6]arene compared with calix[4]arene molecules. It is also predicted that the nucleophilic substitution reaction involving calix[6]arene in the presence of weak bases and in aprotic solvents, as well as in the gas phase, will occur via diastereomeric transition states.