Azolium-Linked Cyclophanes: A Comprehensive Examination of Conformations by 1H NMR Spectroscopy and Structural Studies

Synthesis, structural studies and computational evaluation of cyclophanes incorporating imidazole-2-selones

We report new cyclophanes containing imidazole-2-selone groups linked by xylylene rings. A set of imidazole-2-selone cyclophanes is synthesized by reaction corresponding to imidazolium cyclophanes with selenium in the presence of K₂CO₃. The structural behavior of the new imidazole-2-selone cyclophanes was determined by ¹H and ¹³C NMR spectra and X-ray diffraction studies. Cyclophanes incorporating o-xylylene or mesitylene-m-cyclophane linked by selone groups were mutually syn in both the solid state and solution, and the cyclophanes showed a conformation similar to the cone conformation of calix[4]arenes. Cyclophanes incorporating p-xylylene or m-xylylene linked by selone groups showed two conformations in the solution: one mutually syn and the other mutually anti. There was no interconversion for both conformations observed on the NMR timescale. In the solid state, three conformations were detected for the p-xylylene-linked cyclophane: one is mutually syn and the other two are mutually anti and partial cone conformations. In the m-xylylene-linked case, only anti-conformation was characterized in the solid state. A density functional analysis was conducted to interpret the stability of the studied compounds and shed light on their origin. The energy preference analysis is in consistent agreement with the observed geometries and their co-existence.

Tetrathiafulvalene-Inserted Diphenoquinone: Synthesis, Structure, and Dynamic Redox Property

A new tetrathiafulvalene (TTF) derivative is synthesized, which is substituted with two phenoxy radicals on one 1,3-dithiole ring, and may have either open-shell diradical or closed-shell extended-quinoidal ground states. X-ray single crystal analysis and NMR measurements prove that this molecule has a closed-shell extended quinoidal structure both in the solid state and in solution. DFT calculations show the donor-acceptor electronic properties of this molecule with a well-separated HOMO-LUMO distribution and a small HOMO-LUMO energy gap. Because of this donor-acceptor character, this molecule gives both the dication and the dianion species by electrochemical oxidation and reduction. Furthermore, during the redox process between the neutral and dication states, this molecule exhibits unique changes in the cyclic voltammogram upon repeating the cycles or varying the scan rate. The observed electrochemical behavior is explained by the conformational changes in the electrochemically generated species, thus indicating that this molecule is classified as a dynamic redox system.

Hybrid Supramolecules for Azolium-Linked Cyclophane Immobilization and Conformation Study: Synthesis, Characterization, and Photocatalytic Degradation

In this paper, one imidazole macrocyclic divalent cation with a flexible configuration was chosen with the aim of the immobilization of its conformation. Six novel organic-inorganic hybrid supramolecules {([syn/anti-did](CdI4)(C2H3N)} (1), {([syn/anti-did](HgI4)(C2H3N)} (2), {([syn/syn-did](Pb2I8)(PbI5)} (3), {([syn/syn-did](Bi2I8)(BiI5)} (4), {([syn/syn-did](Ag4Br6)} n (5), and {([syn/anti-did](Ag2I4)} (6) [did2+ = (12z, 52z)-11H, 51H-1, 5(1, 3)-diimidazol-3-iuma-3, 7(1, 2)-dibenzenacyclooctaphane-13, 53-diium] have been synthesized through the self-assembly reaction of did2+ with different metals under solvothermal reaction. These compounds have been unambiguously confirmed by powder X-ray diffraction, IR, thermogravimetric and X-ray single-crystal diffraction. Crystallographic analysis shows that the anions of compounds 1 and 2 are isostructural with mononuclear anion structure, the anions of compounds 3, 4, and 6 are of binuclear structure, and compound 5 anion is a one-dimensional anionic chain structure. Imidazole cyclophanes of organic cations may exist in a syn/syn-conformation in 3-5 or syn/anti conformation in 1, 2, 6, but tilting angles in compounds 1-6 were different. This article described the photocatalytic degradation of organic dye in waste water and the optical band gap of compounds 1-6. The calculated semiconductor band gap of compounds 1-6 is smaller than that of TiO2, so compounds 1-6 have semiconductor properties. Compound 1 has the smallest band gap value, and the photocatalytic performance is the best.

Two macrocycle-based sensors for anions sensing

Two macrocyclic bis-benzimidazolium salts 2 and 4 (23-membered for 2 and 25-membered for 4) were prepared, and their structures were confirmed by X-ray crystallography, 1H NMR and 13C NMR spectroscopy. The research of anion recognitions using 2 or 4 as hosts were carried out with the methods of fluorescence and ultraviolet spectroscopy, 1H NMR titrations, MS and IR spectra. The experiment results show that 2 can detect acetate anion and 4 can detect nitrate anion with favorable selectivity and sensitivity.

Tracking the absence of anion–π interactions in modified [23](1,3,5)cyclophanes: insights from computation

[2₃](1,3,5)Cyclophanes containing 1,3,5-triazine and 1,3,5-triphosphinine planar rings present different degrees of aromaticity as well as σ-donor and π-acceptor abilities.

Flexible imidazolium macrocycles: building blocks for anion-induced self-assembly

This feature article summarises recent contributions of the authors in the area of anion-induced supramolecular self-assembly. It is based on the chemistry of a set of tetracationic imidazolium macrocycles, specifically the so-called 'Texas-sized' molecular box, cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene) (1⁴⁺), and its congeners, cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,2-dimethylenebenzene) (2⁴⁺), cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,3-dimethylenebenzene) (3⁴⁺), and cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](2,6-dimethylenepyridine) (4⁴⁺). These systems collectively have been demonstrated as being versatile building blocks that interact with organic carboxylate or sulfonate anions, as well as substrates (e.g., neutral molecules or metal cations). Most work to date has been carried out with 1⁴⁺, a system that has been found to support the construction of a number of stimuli responsive self-assembled ensembles. This macrocycle and others of the 'Texas-sized' box family also show the potential to react as carbene precursors and to undergo post-synthetic modification (PSM) to produce new functional macrocycles, such as trans- and cis-cyclo[2]((Z)-N-(2-((6-(1H-imidazol-1-yl)pyridin-2-yl)amino)vinyl)formamide)[2](1,4-bismethylbenzene) (5²⁺ and 6²⁺, respectively). On the basis of the work reviewed in this Feature article, we propose that the imidazolium macrocycles 1⁴⁺-4⁴⁺ can be considered as useful tools for the construction of ensembles with environmentally responsive features, including control over self-assembly and an ability to undergo precursor-specific PSM.

Dinuclear Au(i) N-heterocyclic carbene complexes derived from unsymmetrical azolium cyclophane salts: potential probes for live cell imaging applications

We have synthesized a new series of azolium cyclophanes and used them as precursors of inherently luminescent dinuclear Au(i)-N-heterocyclic carbene (NHC) complexes. The azolium cyclophanes contained two azolium groups (either imidazolium or benzimidazolium), an o-xylyl group, and an alkyl linker chain (either C2, C3 or C4). All of the azolium cyclophanes were characterised by X-ray diffraction studies and VT NMR studies, and all were fluxional in solution on the NMR timescale. The C3- and C4-linked azolium cyclophanes served as precursors of Au2L2(2+) complexes (L is a cyclophane bis(NHC) ligand). Due to the unsymmetrical nature of the azolium cyclophanes, the Au2L2(2+) complexes each existed as cis and trans isomers. X-ray diffraction studies showed that the Au2L2(2+) complexes had short intramolecular AuAu distances, in the range 2.9-3.3 Å, suggestive of an aurophilic attraction, presumably as a consequence of the geometrical constraints imposed by the cyclophane bis(NHC) ligands. The complexes having the shortest AuAu distances (i.e., those based on C3-linked cyclophanes) exhibited intense luminescence in solution. The uptake of one of the dinuclear Au-NHC complexes by tumorigenic cells, and its subsequent distribution and toxicity in the cells, was monitored by luminescence microscopy over 6 h and proliferation measurements, respectively.

Stable AuIII complexes with four N-heterocyclic carbene groups can be prepared in high yield directly from KAuCl4

Au^III complexes bearing four N-heterocyclic carbene groups are surprisingly stable and can be synthesized directly from KAuCl₄ and azolium salts.

Structures of NHC Hg(ii) and Ag(i) complexes and selective recognition of nitrate anion

Eight N-heterocyclic carbene Hg(ii) and Ag(i) complexes were prepared, and the selective recognition of nitrate anion was studied.

Novel iron(iii) catalyst for the efficient and selective coupling of carbon dioxide and epoxides to form cyclic carbonates

“Re-cycling carbon dioxide with iron”. The synthesis of cyclic organic carbonates was accomplished by the coupling of CO₂ and epoxides, using a novel air-stable and easy-to-handle iron(iii) catalyst.

Electronic structure of tetraaza[1.1.1.1]o,p,o,p-cyclophane and its oxidized states

The smallest macrocyclic oligoarylamine bearing the alternantortho–para-linkage exhibits the unique structural and electronic features.

Ruthenium(ii) complexes of N-heterocyclic carbenes derived from imidazolium-linked cyclophanes

Metal–ligand bonds in ruthenium(ii) complexes of N-heterocyclic carbenes derived from imidazolium-linked cyclophanes with a remarkable covalent character are shown.

Synthesis, structure and dynamics of NHC-based palladium macrocycles

A series of macrocyclic CNC pincer pro-ligands based on bis(imidazolium)lutidine salts with octa-, deca- and dodecamethylene spacers have been prepared and their coordination chemistry investigated. Using a Ag2O based transmetallation strategy, cationic palladium(II) chloride complexes [PdCl{CNC-(CH2)n}][BAr(F)4] (n = 8, 10, 12; Ar(F) = 3,5-C6H3(CF3)2) were prepared and fully characterised in solution, by NMR spectroscopy and ESI-MS, and in the solid-state, by X-ray crystallography. The smaller macrocyclic complexes (n = 8 and 10) exhibit dynamic behaviour in solution, involving ring flipping of the alkyl spacer across the Pd-Cl bond, which was interrogated by variable temperature NMR spectroscopy. In the solid-state, distorted coordination geometries are observed with the spacer skewed to one side of the Pd-Cl bond. In contrast, a static C2 symmetric structure is observed for the dodecamethylene based macrocycle. For comparison, palladium(II) fluoride analogues [PdF{CNC-(CH2)n}][BAr(F)4] (n = 8, 10, 12) were also prepared and their solution and solid-state structures contrasted with those of the chlorides. Notably, these complexes exhibit very low frequency (19)F chemical shifts (ca. -400 ppm) and the presence of C-H···F interactions ((2h)J(FC) coupling observed by (13)C NMR spectroscopy). The dynamic behaviour of the fluoride complexes is largely consistent with the smaller ancillary ligand; [PdF{CNC-(CH2)8}][BAr(F)4] exceptionally shows C(2v) time averaged symmetry in solution at room temperature (CD2Cl2, 500 MHz) as a consequence of dual fluxional processes of the pincer backbone and alkyl spacer.

Simple and versatile selective synthesis of neutral and cationic copper(I) N-heterocyclic carbene complexes using an electrochemical procedure

An electrochemical approach for the preparation of copper(I) N-heterocyclic carbene complexes has been developed to include a diverse range of ligand precursors. Importantly, the method is effective for a ligand precursor that contains several acidic protons and for which traditional methods of carbene formation are not suitable.

Revisit to imidazolium receptors for the recognition of anions: highlighted research during 2006-2009

In this tutorial review we discuss imidazolium receptors for anion recognition and recent contributions between 2006-2009 are reviewed according to target analytes, such as ATP and DNA, as well as structural classification, including cage type imidazoliums, imidazolium calixarenes, ferrocenyl imidazoliums, chiral systems, fluorescent or colorimetric imidazoliums, imidazolium cyclophane, nano assembled structures, bile acid-imidazolium, and tripodal-imidazolium systems.

Review on supermolecules as chemical drugs

Supramolecular medicinal chemistry field has been a quite rapidly developing, increasingly active and newly rising interdiscipline which is the new expansion of supramolecular chemistry in pharmaceutical sciences, and is gradually becoming a relatively independent scientific area. Supramolecular drugs could be defined as medicinal supermolecules formed by two or more molecules through non-covalent bonds. So far a lot of supermolecules as chemical drugs have been widely used in clinics. Supermolecules as chemical drugs, i.e. supramolecular chemical drugs or supramolecular drugs, which might have the excellences of lower cost, shorter period, higher potential as clinical drugs for their successful research and development, may possess higher bioavailability, better biocompatibility and drug-targeting, fewer multidrug-resistances, lower toxicity, less adverse effect, and better curative effects as well as safety, and therefore exhibit wide potential application. These overwhelming advantages have drawn enormous special attention. This paper gives the definition of supramolecular drugs, proposes the concept of supramolecular chemical drugs, and systematically reviews the recent advances in the research and development of supermolecules, including organic and inorganic complex ones as chemical drugs in the area of antitumor, anti-inflammatory, analgesic, antimalarial, antibacterial, antifungal, antivirus, anti-epileptic, cardiovascular agents and magnetic resonance imaging agents and so on. The perspectives of the foreseeable future and potential application of supramolecules as chemical drugs are also presented.