A series of tetrahomodioxacalix[4]biscrown-n. Syntheses, crystal structures, and metal binding abilities

A series of novel tetrahomodioxacalix[4]biscrowns with crown-2, crown-3, crown-4, crown-5, and crown-6 units were synthesized. Conformations of each product are dependent on the base used and their conformation stabilities. All conformations were proven by NMR spectra and/or X-ray crystal structures. The 1,3-alternate homodioxacalix[4]biscrown-4 (4b) shows the best selectivity for K+, whereas the 1,3-alternate homodioxacalix[4]crown-5 (5) does for Cs+. Those selectivities are attributable to electrostatic interaction between the metal ion and the crown ring, as well as a pi-metal complexation. However, the C-1,2-alternate conformation does not take the metal ions regardless of the crown species as a result of steric hindrance from the methylene bridge of an ArCH2Ar unit.     

Stilbene-bridged 1,3-alternate calix[4]arene crown ether for selective alkali ion extraction

A series of stilbene-bridged calix[4]arenes was synthesized through an intramolecular reductive McMurry coupling of bisbenzaldehyde calix[4]arene in high yields. Tetra- and pentaethylene glycol chains were tethered to the phenolic groups of calix[4]arene to form stilbene-bridged calix[4]arene crown-5 and crown-6, respectively. The presence of stilbene bridge over the calix[4]arene rim effectively prevented the connection of the polyether chains in the cone conformation resulting in the exclusive formation of 1,3-alternate stilbene-bridged calix[4]arene crown product. Compared to the cone analogues, the 1,3-alternate calix[4]arene crown ethers showed a greater extraction ability and selectivity toward Cs⁺.     

First Synthesis of 1,3-Alternate 25,27-Dialkyloxy-5,17-diarylcalix[4]arenes-crown-6 as New Cesium Selective Extractants by Suzuki Cross-coupling Reaction

The synthesis of new 25,27-dialkyloxy-5,17-diarylcalix[4]arenes-crown-6 1a–f in 1,3-alternate conformation by Suzuki cross-coupling reaction is reported. Their conformation was determined using ¹H, ¹³C, 2D NMR and ROESY analysis, and X-ray crystallography. Extraction experiments using a two-phase solvent method involving sodium, potassium or cesium picrate showed good extraction of the cesium cation. The X-ray crystal structures of 1,3-alternate 25,27-dipropoxy-5,17-diphenylcalix[4]arene-crown-6 ether 1a and its cesium picrate complex were established. Solid-state data were used to determine the complexation behavior of these new ligands. The efficiency of calixarenes 1a–f for cesium ion extraction could be ascribed to the rigidity and flatness linkages caused by the aryl groups at the lower rim of the aromatic moieties in the calixarene skeleton. In addition, the introduction of these aromatic moieties in positions 5 and 17 enhanced the solubility of the metal complexes in organic media.     

Cesium Complex of an Unsymmetrical Calix[4]crown-dibenzocrown-6

An unsymmetrical calix[4]-bis-crown ether having both conventional crown-6 and dibenzocrown-6 rings in a fixed 1,3-alternate conformation was synthesized with good yield by the reaction of a monocyclic calix[4]crown-6 with dibenzodimesylate in the presence of cesium carbonate. The cesium ion selectivity among alkali metal ions increased compared to symmetrical calix[4]-bis-crown-6. The solid state structureof the ligand-cesium complex illustrates a 1:2 complex ratio. On the contrary, insolution, e.g., extraction equilibrium and ¹H NMR experiment gave a 1:1 complex ratio. From the result of the chemical shift change upon metal ion complex, the cesium ion seems to prefer the dibenzocrown loop to the conventional crown-6 ring.     

Silver ion shuttling in the trimer-mimic thiacalix[4]crown tube

Novel 1,3-alternate calix-thiacalix[4]crown trimers bearing crown-5 and crown-6 were prepared. As proven by X-ray diffraction, in a 1:2 mole ratio of ligand to metal ion, the Cs(+) and K(+) ions prefer to be encapsulated in the trimeric thiacalix[4]crown-6 and crown-5, respectively. On the contrary, the Ag(+) ion was found to be entrapped in the central thiacalix spacer as a 1:1 complex confirmed by (1)H NMR spectrosocpy. Variable-temperature (1)H NMR studies for the trimeric thiacalix[4]crown-6 encapsulating the silver ion revealed that the Ag(+) ion oscillates through the central thiacalix spacer with the aid of cation-pi interactions.     

Synthesis and Complexation Properties towards Alkali Cations of a Photosensitive Azo-modified Calix[4]crown Ether in the 1,3-Alternate Conformation

We report the synthesis and complexation properties towards alkalications of a photosensitive azo-modified calix[4]crown 5 in the1,3-alternate conformation. Selectivity of the cis-isomer towards Cs⁺ andRb⁺ was observed.     

Regioselective complexation of metal ion in chromogenic calix[4]biscrowns

A series of 1,3-alternate chromogenic azo-coupled calix[4]biscrowns in which the crown size varied with crown-5 and crown-6 have been synthesized. From the results of UV/vis band shift upon metal ion complexation, metal ions were entrapped only by the upper crown loop, causing the hypsochromic shift on the UV/vis spectra. Calix[4]bis(crown-5)(crown-6) revealed K(+) ion selectivity while calix[4]bis(crown-6)(crown-6) showed Cs(+) ion selectivity caused by a size complementarity between hosts and guest ions. From the UV band shift of 4 in which the NO(2) group is replaced by the NH(2) group, we observed bathochromic shift upon the metal ion addition, indicating that the metal ion is encapsulated in the lower crown ring because of strengthened pi-cation interaction by introducing the electron-donating NH(2) unit regardless of the steric hindrance between two azo-phenyl groups adjacent to the crown ring.     

新型萃取剂杯[4]冠－6的合成与表征

研究了新型萃取剂1，3－交替构象的二烷氧基杯[4]冠－6化合物系列的合成方 法，对合成的中间体和目标产物进行了详细表征。合成的化合物对铯离子有较高的 选择性。     

Alkaline Earth Metal Template (Cross-)Coupling Reactions with Hybrid Disila-Crown Ether Analogues

Alkaline earth metal iodides were used as templates for the synthesis of novel silicon-based ligands. Siloxane moieties were (cross-)coupled and ion-specific, silicon-rich crown ether analogues were obtained. The reaction of 1,2,7,8-tetrasila[12]crown-4 ( I ) and 1,2-disila[9]crown-3 ( II ) with MgI₂ yielded exclusively [Mg(1,2,7,8-tetrasila[12]crown-4)I₂] ( 1 ). The larger Ca²⁺ ion was then employed for cross-coupling of I and II and yielded the complex [Ca(1,2,7,8-tetrasila[15]crown-5)I₂] ( 2 ). Cross-coupling of I and 1,2,4,5-tetrasila[9]crown-3 ( III ) with SrI₂ enables the synthesis of the silicon-dominant 1,2,4,5,10,11-hexasila[15]crown-5 ether complex of SrI₂ ( 3 ). Further, the compounds [Sr(1,2,10,11-tetrasila[18]crown-6)I₂] ( 4 ), [Sr(1,2,13,14-tetrasila[24]crown-8)I₂] ( 5 ), and [Sr(1,2,13,14-tetrasila-dibenzo[24]crown-8)I₂] ( 6 ) were obtained by coupling I , 1,2-disila[12]crown-4 ( IV ) or 1,2-disila-benzo[12]crown-4 ( V ), respectively. Using various anions, the (cross-)coupled ligands were also observed in an X-ray structure within the mentioned complexes. These template-assisted (cross-)couplings of various ligands are the first of their kind and a novel method to obtain macrocycles and/or their metal complexes to be established. Further, the Si−O bond activations presented herein might be of importance for silane or even organic functionalization.     

Synthesis and Host Properties of (1,3)- p-tert-Butylcalix[5]crown-6 Derivatives Incorporating the 1,1'-Binaphthalene-2,2'-dioxy Subunit

Alkylation of p-tert-butylcalix[5]arene (1) with 2,2'-bis(5-tosyloxy-3-oxa-1-pentyloxy)-1,1'-binaphthalene ((±)-2) in the presence of CsF affords selectively racemic 1,3-bridged calix[5] [5]crown-6-triol 3, along with very small amounts of the (1,2)-bridged regioisomer 4. Compound 3 has been converted into tri-methoxy and tri--picolyloxy derivatives 5 and 6, respectively, by exhaustive alkylation with the appropriate electrophile and base. The direct separation of the enantiomers of racemates 3 and 6 was achieved by HPLC, using a chiral stationary phase (Chiralpak AD). Hosts 5 and 6 are able to selectively form 1 : 1 endo-cavity complexes with the linear RNH₃ ⁺ ions.     

Synthesis and structure of the silylated benzene radical anion salts [K([18]crown-6){C6H4(SiMe3)2-1,4}] and [K([18]crown-6)(THF)2][C6H2(SiMe3)4-1,2,4,5]

The crystalline compound [K([18]crown-6){C₆H₄(SiMe₃)₂-1,4}] (1) was prepared by the low-temperature reduction of the para-disilylated benzene with K/[18]crown-6 in toluene followed by recrystallisation from the same solvent. Reduction of 1,2,4,5-tetrasilylated benzene with 2(K/[18]crown-6) in toluene produced a hydrocarbon-insoluble powder identified as the dianionic derivative [K([18]crown-6)]₂[C₆H₂(SiMe₃)₄-1,2,4,5)] (2), which upon crystallisation from THF/Et₂O yielded [K([18]crown-6)(THF)₂][C₆H₂(SiMe₃)₄-1,2,4,5] (3). An X-ray diffraction study revealed that 1 comprised a contact ion pair with the crown-encapsulated K cation η⁵-connected to the planar ring of the substituted benzene radical anion, while 3 contained a well separated cation and anion.     

The associations of macrocyclic ethers with cations in 1,4-dioxane/water mixtures; potentiometric Na+ and K+ binding measurements and computational study

This paper deals with the study of different degrees of association constants of Na⁺ and K⁺ ions with macrocycles of [12]crown-4, [15]crown-5, [18]crown-6, and Diaza[18]crown-6 in (1:1)dioxane/water mixture using the sodium and potassium ion selective electrodes (ISE). The gas phase molecular mechanical and quantum chemical calculations of [18]crown-6 and diaza[18]crown-6 were performed at MM+, AM1, MINDO/3, HF/6-31G(d), and B3LYP/6-31G(d) levels with the help of Gaussian03 program. Conformational abilities were compared with the ion binding results of ISE measurements. The results were also discussed in terms of oxygen charges and enthalpy stabilized association mechanism.     

Potassium Sensing Calix[4]arene Crown Ethers

1,3-Alternate calix[4]arene crown-5 (1) and corresponding biscrown-5 (2) were synthesized and the complexation behavior with alkali metal ions examined. For both 1 and 2, potassium ion was selectively extracted from aqueous phase into organic phase over other alkali metal ions based on two phase extraction experiment. The complexation ratio between calix[4]arene biscrown-5 (2), in which two crown cavities connect to the calix[4]arene framework by 1,3-alternate fashion and potassium metal ion is found to 1:1 by proton NMR spectroscopy and extraction equilibria. Association constants (logK_a) for 1 and 2 were determined to give 2.51 and 3.49, respectively.     

The cation binding of benzo crown ethers in acetonitrile using fluorescence spectroscopy

The effects of Na⁺, K⁺ and Li⁺ cations on the fluorescence spectra of benzo[15]crown-5, benzo[18]crown-6 and dibenzo[18]crown-6 were investigated in acetonitrile. The alkali cation role observed was usually the complexation-enhanced quenching fluorescence effect (CEQF) in acetonitrile due to the increased fluorescence quenching rate of the complexed fluoroionophore. The association constants for 1 :1 stoichiometry InK _a have been obtained using the relationship 1/K _a[L ₀] = (1 –P)²/P. It was shown that the preferential interaction rule of compatibility of cationic radii and macrocyclic ring size is in excellent agreement with the association constants obtained by fluorescence spectroscopy. The order of InK _a found for benzo[15]crown-5 complexation was Li⁺ > Na⁺ > K⁺ and K⁺ > Na⁺ > Li⁺ for benzo[18]crown-6 in acetonitrile.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August, 1995.     

Ion Complexation Properties of Calix[6]Arene Derivatives: I. 1,4-Calix[6]Crown-4 Derivatives

Abstract

A series of 1,4-p-tert-butyl-calix[6]crown-4 tetraesters, tetraamides, tetraacids with defined conformation have been synthesized, and their complexation properties towards metal ions and alkyl ammonium ions were investigated systematically. It was found that 1,4-p-tert-butyl-calix[6]crown-4 tetraethylester (3a) and 1,4-p-tert-butyl-calix[6]benzocrown-4 tetramethyl-ester (4b) show high selectivity towards Na⁺, Li⁺, respectively and all of them exhibit high complexation abilities towards Et₂NH₂ ⁺ cation.     

An inherently chiral calix[4]crown carboxylic acid in the 1,2-alternate conformation

For better understanding of the structure/property relationship of inherently chiral calixarenes in the 1,2-alternate conformation, we designed and synthesized an inherently chiral calix[4]crown-4 carboxylic acid 1,2-alternate conformer. Resolution of the racemates was effected by condensation with (S)-BINOL as a chiral auxiliary and separation of the resultant diastereomers via preparative TLC plates, followed by hydrolysis of the isolated diastereomers to afford enantiopure antipodes of the title compound. Preliminary property study revealed that the title compound has the ability to enantioselectively discriminate 2-phenylglycinol by ¹H NMR spectroscopy.     

Regioselective intramolecular bridging of p-tert-butylcalix[10]arene

The synthesis and characterization of a series of regioselective intramolecular bridging of calix[10]arene are described for the first time. Reacting p-tert-butylcalix[10]arene with tri-ethylene glycol ditosylate using K₂CO₃ as a base in toluene, 1,2-calix[10]crown-4 2a, 1,4-calix[10]crown-4 2b and 1,6-calix[10]crown-4 2c were obtained in yields of 9%, 14% and 7%, respectively. While using Cs₂CO₃/acetone instead of K₂CO₃/toluene, the 1,4-calix[10]crown-4 2b was obtained selectively in good yield up to 50%.     

Potassium ion-selective membrane electrodes based on 1,3-alternate calix[4]crown-5-azacrown-5

A series of 1,3-alternate calix[4]azacrown ethers for which the monoaza and unsymmetrical crowned-azacrown with different side arms were examined as an ionophore for ion-selective polymeric membrane electrode toward potassium ion. Among them, the electrode based on calix[4]crown-5-azacrown-5 with a phenyl group exhibited near Nernstian response for K⁺ ions over a wide concentration range (1×10⁻⁵ to 1×10⁻¹ M) with a limit of detection of 2×10⁻⁶ M. It has a fast response time of approximately 2-3 s and can be used for at least 2 months without observing any major deterioration. Selectivity coefficients indicated that interference from all common alkali, alkaline and transition metal ions was very small.     

Synthesis of a phloroacetophenon[4]arene consisting of four isomers via the one-pot,acid-catalysed condensation of phloroacetophenone with benzaldehyde

A phloroacetophenon[4]arene (3) consisting of four isomers was synthesised for the first time via the condensation of phloroacetophenone and benzaldehyde in a one-pot reaction with refluxing toluene in the presence of catalytic amounts of TsOH·H₂O for a maximum yield of 64%. The conformational elucidation of four isomers (3a–d) by ¹H NMR spectroscopy and X-ray crystal structure analysis showed them to be cone, partial cone, 1,3-alternate and 1,2-alternate types of conformations, respectively.     

Synthesis and Cesium Binding Affinity of New 25,27-Bis(alkyloxy)calix[4]arene-crown-6 Conformers in Relation to the Alkyl Pendent Moiety

The preparation of new 25,27-bis(alkyloxy)calix[4]arenes-crown-6 in the cone, partial-cone and 1,3-alternate conformation is reported. We have also investigated the alkylation of the cone monoalkylated calix[4]arene-crown-6 achieved using Cs 2 CO 3 . This reaction afforded a mixture of cone and partial-cone calix[4]arenes-crown-6 having an alkyl chain anti or syn to the polyether ring. Conformations have been probed using 1 H, 13 C, 2D-NMR and NOESY analysis, and using X-ray crystallography. Extraction experiments using a two-phase solvent method involving cesium picrate were performed for these newly synthesized conformers. They reveal and confirm the strong preference for the 1,3-alternate conformers. The affinity of 1,3-alternate calixarenes for Cs + has been assessed by complexation measurements (log g ) using a spectrophotometric technique. No significant Cs + extraction difference was observed in relation to the nature of the alkyl chains on the aromatic rings. 1 H NMR studies of the 1,3-alternate calixarene Cs + complexes confirms the cation's spacial position between the two aromatic rings, due to cation- ~ interactions.