Synthesis,Structure, and Properties of O6‐Corona[3]arene[3]tetrazines

O₆‐Corona[3]arene[3]tetraazines, a new class of macrocyclic compounds, were synthesized efficiently in a one‐pot reaction from the nucleophilic aromatic substitution reaction between 1,4‐dihydroxybenzene derivatives and 3,6‐dichlorotetrazine in warm acetonitrile. In the crystalline structure, the resulting macrocycles adopt highly symmetric structures of a regular hexagonal cavity with all bridging oxygen atoms and tetrazine rings located on the same plane with phenylene units orthogonally orientated. The constitutional aromatic rings are able to rotate around the macrocyclic annulus, depending on the steric effect of the substituents and temperature, in solution. The electron‐deficient nature revealed by cyclic voltammetry, differential pulse voltammetry, and characteristic absorbances at a visible region show the O₆‐corona[3]arene[3]tetrazines to be suitable macrocyclic receptors for electron‐rich guests.     

Synthesis of O6‐Corona[3]arene[3]pyridazines and Their Molecular Recognition Property in Organic and Aqueous Media

O₆‐Corona[3]arene[3]pyridazines were synthesized from the one‐pot macrocyclic condensation reaction of 3,6‐dichlorotetrazine with 1,4‐dihydroquinone derivatives followed by the inverse electron demand Diels‐Alder reaction of the tetrazine rings with a cyclopentanone‐derived enamine. Conversion of six ester groups within macrocycle into all sodium acetate moieties afforded a water soluble O₆‐corona[3]arene[3]pyridazine. The coronary macrocycle host formed complexes selectively with organic ammoniums and dinitrile guests in a 1: 1 stoichiometric ratio in organic solvents with association constants ranging from (2.96 ± 0.10) × 10¹ to (2.53 ± 0.33) × 10⁵ L·mol⁻¹. Water soluble O₆‐corona[3]arene[3]pyridazine was also able to complex strongly with organic ammoniums in water to give an association constant up to (2.67 ± 0.21) × 10⁴ L·mol⁻¹. The pseudo‐rotaxane and inclusion structures of the host‐guest complexes were revealed by the X‐ray crystallography.     

Synthesis and Molecular Recognition of Water‐Soluble S6‐Corona[3]arene[3]pyridazines

We report the efficient and scalable synthesis and molecular‐recognition properties of novel and water‐soluble S₆‐corona[3]arene[3]pyridazines. The synthesis comprises a one‐pot nucleophilic aromatic substitution reaction between diesters of 2,5‐dimercaptoterephthalate and 3,6‐dichlorotetrazine followed by the inverse electron‐demand Diels–Alder reaction of the tetrazine moieties with an enamine and exhaustive saponification of esters. The resulting S₆‐corona[3]arene[3]pyridazines, which adopt a 1,3,5‐alternate conformation in the crystalline state, are able to selectively form stable 1:1 complexes with dicationic guest species in water with association constants ranging from (1.10±0.06)×10³ M ^?1 to (1.18±0.06)×10⁵ M ^?1. The easy availability, large cavity size, strong and selective binding power render the water‐soluble S₆‐corona[3]arene[3]pyridazines useful macrocyclic hosts in various disciplines of supramolecular chemistry.     

Synthesis,Structure, and Molecular Recognition of S6‐ and (SO2)6‐Corona[6](het)arenes: Control of Macrocyclic Conformation and Properties by the Oxidation State of the Bridging Heteroatoms

We report herein the synthesis, structure, and molecular recognition of S₆‐ and (SO₂)₆‐corona[6](het)arenes, and demonstrate a unique and efficient strategy of regulating macrocyclic conformation and properties by adjusting the oxidation state of the heteroatom linkages. The one‐pot nucleophilic aromatic substitution reaction of 1,4‐benzenedithiol derivatives, biphenyl‐4,4′‐dithiol and 9,9‐dipropyl‐9H‐fluorene‐2,7‐dithiol with 3,6‐dichlorotetrazine afforded S₆‐corona[3]arene[3]tetrazines. These compounds underwent inverse‐electron‐demand Diels–Alder reaction with enamines and norbornadiene to produce S₆‐corona[3]arene[3]pyridazines. Facile oxidation of sulfide linkages yielded (SO₂)₆‐corona[3]arene[3]pyridazines. All corona[6](het)arenes adopted generally hexagonal macrocyclic ring structures; however, their electronic properties and conformation could be fine‐tuned by altering the oxidation state of the sulfur linkages. Whereas (SO₂)₆‐corona[3]arene[3]pyridazines were electron‐deficient, S₆‐corona[3]arene[3]pyridazines acted as electron‐rich macrocyclic hosts that recognized various organic cations in both aqueous and organic solutions.     

A [2+3] fragment coupling approach to N,O-bridged calix[1]arene[4]pyridines and their complexation with C60

Functionalized N,O-bridged calix[1]arene[4]pyridines, first examples of the odd-numbered heterocalixaromatics containing mixed heteroatom bridges and mixed aromatic units, have been synthesized from the Pd₂(dba)₃/dppp-catalyzed 2+3 macrocyclic fragment coupling reaction between readily available staring materials. These novel macrocyclic compounds, which adopted distorted 1,3-alternate conformation in solid state, were powerful host molecules able to form 1:1 complex with fullerene C₆₀ in solution, giving binding constant up to 49,494 M⁻¹.     

Construction of π‐Surface‐Metalated Pillar[5]arenes which Bind Anions via Anion–π Interactions

By simple ligand exchange of the cationic transition‐metal complexes [(Cp*)M(acetone)₃](OTf)₂ (Cp*=pentamethylcyclopentadienyl and M=Ir or Rh) with pillar[5]arene, mono‐ and polynuclear pillar[5]arenes, a new class of metalated host molecules, is prepared. Single‐crystal X‐ray analysis shows that the charged transition‐metal cations are directly bound to the outer π‐surface of aromatic rings of pillar[5]arene. One of the triflate anions is deeply embedded within the cavity of the trinuclear pillar[5]arenes, which is different to the host–guest behavior of most pillar[5]arenes. DFT calculation of the electrostatic potential revealed that the metalated pillar[5]arenes featured an electron‐deficient cavity due to the presence of the electron‐withdrawing transition metals, thus allowing encapsulation of electron‐rich guests mainly driven by anion–π interactions.     

Inclusion of diprotonated [2.2.2]cryptand in the cavity of uranyl‐complexed p‐phenyl­tetra­homodioxacalix[4]arene

In the title compound, 4,7,13,16,21,24‐hexa­oxa‐1,10‐diazo­nia­bicyclo­[8.8.8]hexa­cosane dioxo[7,13,21,27‐tetra­phenyl‐3,17‐di­oxa­penta­cyclo­[23.3.1.1^5,9.1^11,15.1^19,23]ditriaconta‐1(29),5,7,9(30),11(31),12,14,19(32),20,22,25,27‐dodeca­ene‐29,30,31,32‐tetra­olato]uranium dimethyl sulfoxide tri­solvate, (C₁₈H₃₈N₂O₆)[U(C₅₄H₄₀O₆)O₂]·3C₂H₆OS, the uranyl ion is bound to the four phenoxide groups of the deprotonated p‐phenyl­tetra­homodioxacalix[4]arene ligand in a cone conformation, resulting in a dianionic complex. The diprotonated [2.2.2]cryptand counter‐ion is located in the cavity defined by the eight aromatic rings of the homooxacalixarene, where it is held by cation–anion, cation–π and possibly C—H⋯π inter­actions. Dimerization in the packing leads to the formation of sandwich assemblages in which two diprotonated [2.2.2]cryptands are encompassed by two uranyl complexes.     

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.     

Density functional theory study of calix[4]arene‐N‐azacrown‐5, calix[4]arene‐N‐phenyl‐azacrown‐5, and their complexes with alkali‐metal cations: Na+, K+, and Rb+

Theoretical studies of 1,3‐alternate‐25,27‐bis(1‐methoxyethyl)calix[4]arene‐azacrown‐5 ( L₁ ), 1,3‐alternate‐25,27‐bis(1‐methoxyethyl)calix[4]arene‐N‐phenyl‐azacrown‐5 ( L₂ ), and the corresponding complexes M⁺/ L of L₁ and L₂ with the alkali‐metal cations: Na⁺, K⁺, and Rb⁺ have been performed using density functional theory (DFT) at B3LYP/6‐31G* level. The optimized geometric structures obtained from DFT calculations are used to perform natural bond orbital (NBO) analysis. The two main types of driving force metal–ligand and cation–π interactions are investigated. The results indicate that intermolecular electrostatic interactions are dominant and the electron‐donating oxygen offer lone pair electrons to the contacting RY* (1‐center Rydberg) or LP* (1‐center valence antibond lone pair) orbitals of M⁺ (Na⁺, K⁺, and Rb⁺). What's more, the cation–π interactions between the metal ion and π‐orbitals of the two rotated benzene rings play a minor role. For all the structures, the most pronounced changes in geometric parameters upon interaction are observed in the calix[4]arene molecule. In addition, an extra pendant phenyl group attached to nitrogen can promote metal complexation by 3D encapsulation greatly. In addition, the enthalpies of complexation reaction and hydrated cation exchange reaction had been studied by the calculated thermodynamic data. The calculated results of hydrated cation exchange reaction are in a good agreement with the experimental data for the complexes. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Polymer Supported Calix[4]arene Schiff Bases: A Novel Chelating Resin for Hg2+ and Dichromate Anions

This article describes the synthesis and characterization of two new calix[4]arene Schiff bases and their polymeric resins. The extraction properties of these “proton switchable extractants” with alkali, transition, post transition metal cations and for dichromate anions are reported. The two new calix[4]arene based Schiff bases (5 and 6) have been synthesized from 5,17‐diformyl‐25,27‐dipropoxy‐26,28‐dihydroxycalix[4]arene (4) by treatment with 3‐amino‐methylpyridine and 1,8‐diaminooctane in two separate reaction flasks following the same procedure. Compounds 5 and 6 have been appended to a polymeric resin by treatment with Merrifield resin through a nucleophilic substitution reaction. The receptor compounds (3 and 5–8) do not extract alkali metal cations, but show some selectivity toward transition metal cations, and a particularly high selectivity to Hg²⁺ and Pb²⁺. The protonated forms of all of the calixarene‐based receptors are good extractants for transferring Cr₂O₇ ^2?/HCr₂O₇ ^? anions from an aqueous into a dichloromethane layer.     

Polymorphic crystals of oxacalix[4]arene with 1,3‐alternate conformations of S4 and C2 symmetry

Calix[4]arene and oxacalix[4]arene derivatives have eight possible conformations in the up and down directions of their four aromatic rings from the mean plane of a bridged central ring, the conformations of which determine the functionality of the host frameworks. Despite being a known compound for five decades, oxacalix[4]arene, C₂₄H₁₆O₄, has not been characterized previously by crystallographic methods. It crystallizes from hexane/CH₂Cl₂ solution to give two polymorphs, i.e. prismatic and block‐shaped crystals as twisted 1,3‐alternate structures with S₄ and C₂ symmetry, respectively. These were previously suggested as the prefered stable conformations by density functional theory (DFT) calculations.     

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.     

A new nano‐Fe3O4‐supported organocatalyst based on 3,4‐dihydroxypyridine: an efficient heterogeneous nanocatalyst for one‐pot synthesis of pyrazolo[3,4‐b]pyridines and pyrano[2,3‐d]pyrimidines

A simple and practical strategy for the synthesis of a novel nano‐Fe₃O₄‐supported organocatalyst system based on 3,4‐dihydroxypyridine (Fe₃O₄/Py) has been developed. The prepared catalyst was characterized using Fourier transform infrared spectroscopy, transmission and scanning electron microscopies, X‐ray diffraction, vibrating sample magnetometry and energy‐dispersive X‐ray analysis. Accordingly, the Fe₃O₄/Py nanoparticles show a superparamagnetic property with a saturation magnetization of 61 emu g^?1, indicating potential application in magnetic separation technology. Our experimental results reveal that the pyridine‐functionalized Fe₃O₄ nanoparticles are an efficient base catalyst for the domino condensation of various aromatic aldehydes, Meldrum's acid and 5‐methylpyrazol‐3‐amine under very mild reaction condition and in the presence of ethanol solvent. Moreover, the synthesized catalyst was used for one‐pot, three‐component condensation of aromatic aldehydes with barbituric acid and malononitrile to produce 7‐amino‐2,4‐dioxo‐5‐phenyl‐2,3,4,5‐tetrahydro‐1H‐pyrano[2,3‐d]pyrimidine‐6‐carbonitriles. All reactions are completed in short times and all products are obtained in good to excellent yields. Also, notably, the catalyst was reused five times without significant degradation in catalytic activity and performance. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Desymmetrized Leaning Pillar[6]arene

In this work, a novel version of macrocyclic arenes, namely leaning pillar[6]arenes, was discovered and it can be considered as a tilted version of a pillar[6]arene with two hydroxy/alkoxy functionalities removed. Through a facile two‐step synthetic approaches, in conjunction with a diversity of post‐modification possibilities, a series of leaning pillar[6]arenes, with good cavity adaptability and enhanced guest‐binding capability, was synthesized, and their self‐assembly in single‐crystal states is presented. DFT calculations demonstrated that the lower rotational barrier of unsubstituted phenylene rings, the uneven electron density centered at the leaning phenyl rings, and the polarization effect along the edge generated by the hydrogen‐bond‐induced orientation of hydroxy groups greatly affected the host‐guest properties, and meanwhile provided an intuitive explanation for the pillar‐like and rigid structure of traditional pillar[6]arenes. Significantly, the crystal structure of cyclo‐oligomeric quinone was obtained by direct oxidation of leaning pillar[6]arenes.     

Selective functionalization at the small rim of calix[6]arene. Synthesis of novel non-symmetrical N3, N4 and N3ArO biomimetic ligands

Eight novel calix[6]arene-based biomimetic ligands for transition metal ions have been synthesized. They display a non-symmetrical N₃, N₄ or N₃ArO binding core that mimics enzyme active sites presenting histidine and tyrosine residues. The key step for their synthesis is the mono-alkylation at the small rim of the C_3v symmetrical trimethyl ether derivative of tBu-calix[6]arene with N-Boc-2-chloroethylamine to yield a novel calix[6]arene synthon. Its combined O-alkylation with a chloromethyl aromatic amine and N-deprotection or alkylation or reductive alkylation with a salicylaldehyde derivative yielded the calix[6]arene-based ligands with mixed N/O donors.     

Molecular Recognition Properties of Biphen[4]arene

Biphen[n]arenes (n=3, 4) are a new family of macrocyclic hosts. Here, we describe the molecular recognition behavior of hydroxylated biphen[4]arene (OHBP4) for the first time. A series of cationic guests with different sizes and shapes, including quaternary ammonium salts ( 1? PF₆ and 2? PF₆), pyridinium‐based guests ( 3? 2 PF₆– 6? 2 PF₆), and cobaltocenium hexafluorophosphate ( 7? PF₆), were chosen as model guest molecules. OHBP4 exhibits good selectivity towards the 2,7‐dibutyldiazapyrenium bis(hexafluorophosphate) ( 4? 2 PF₆) axle to form a [2]pseudorotaxane‐type complex. In contrast, hydroxylated biphen[3]arene (OHBP3) cannot bind with this big guest. In addition, OHBP4 strongly interacts with adamantane derivative 2? PF₆ and cobaltocenium 7? PF₆, which have tridimensional shape and relatively large size. The association constant of the 7 ⁺?OHBP4 complex in 1:1 (v/v) [D₆]acetone/CD₂Cl₂ solution is up to 3100±300 m ^?1.     

Naphth[4]arene: Synthesis,Conformations, and Application in Color-Tunable Supramolecular Crystalline Assemblies

Although the chemistry of macrocyclic arenes has seen rapid development in recent years, the synthesis of new macrocyclic arenes from aromatic rings with no directing groups remains a challenge. In this work, a new macrocyclic arene, naphth[4]arene (NA[4]A), composed of four naphthalene rings bridged by methylene groups, was synthesized using macrocycle-to-macrocycle conversion. NA[4]A shows 1,3-alternate and 1,2-alternate conformations in the solid state, which can be selectively obtained. By supramolecular co-assembly of NA[4]A and 1,2,4,5-tetracyanobenzene (TCNB) in different concentrations and temperatures, two conformation-dependent crystalline luminescent co-assemblies 1,2-NTC and 1,3-NTC can be selectively prepared. Interestingly, the two charge-transfer crystalline assemblies containing NA[4]A with different conformations show bright yellow and green fluorescence, and also display high photoluminescence quantum yields (PLQYs) of 45 % and 43 %. Furthermore, they exhibit color-tunable two-photon excited upconversion emission.     

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     

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.