Arene Species Research Articles

Calix[n]arene/Pillar[n]arene-Functionalized Graphene Nanocomposites and Their Applications.

Calix[n]arenes and pillar[n]arenes, which contain repeating units of phenol and methane, are class of synthetic cyclic supramolecules. Their rigid structure, tunable cavity size, flexible functionalization, and rich host-guest properties make them ideal surface modifiers to construct functional hybrid materials. Introduction of the calix[n]arene/pillar[n]arene species to the graphene may bring new interesting or enhanced physicochemical/biological properties by combining their individual characteristics. Reported methods for the surface modification of graphene with calix[n]arene/pillar[n]arene utilize either covalent or non-covalent approaches. This mini-review presents the recent advancements in the functionalization of graphene nanomaterials with calix[n]arene/pillar[n]arene and their applications. At the end, the future outlook and challenges for the continued research of calix[n]arene/pillar[n]arene-functionalized graphene nanohybrids in the development of applied nanoscience are thoroughly discussed.

Silver-Catalyzed Selective Multicomponent Coupling Reactions of Arynes with Nitriles and Isonitriles.

Pathway selective aryne-based novel multicomponent coupling reactions with isonitriles and nitriles are described. Crucial to these reactions is the formation of a silver-aryne complex, which shows differential reactivity toward isonitriles and nitriles to form two different forms of ortho-nitrilium organosilver arene species. Interception of the nitrilium of an aryne-isonitrile adduct with another isonitrile leads to the formation of benzocyclobutene-1,2-diimines, whereas the nitrilium of an aryne-nitrile adduct renders selective formation of 3H-indol-3-imines or 3-iminoindolin-2-ol depending on the structure of the nitrile employed.

Imine polymers containing chiral nanohoops in the backbone obtained through [2 + 2] cyclocondensation

ABSTRACTA simple method for synthesis of polymers containing shape persistent imine macrocycles as nanohoops in the main chain is studied. It is based on the cyclocondensation reaction carried out in solution and room temperature of triphenylamine‐based tetraaldehyde compounds with (R,R)‐trans‐1,2‐diaminocyclohexane. The pristine polymer P1 bearing long alkyl groups is soluble during the synthesis but becomes insoluble after precipitation due to the strong and multiple CH/π and π‐π stacking intermolecular interactions from arene–arene species and entanglement and interpenetrating of flexible alkyl groups inside of rigid macrocycle hollow. Polymer without any solubilizing groups (P2) separates during the polymerization as an insoluble material. Both polymers are amorphous and have good thermal and environmental stability. They have a low surface area because discrete nanovoids introduced by macrocycles are disconnected in the amorphous polymers and non‐accessible for gas adsorption. Polymers have inherent luminescent properties due to triphenylamine groups and chirality derived from (R,R)‐conformation of the cyclohexane skeleton. In presence of picric acid (PA), the polymer fluorescence in solid state or suspension is strongly quenched, thus the polymers can work as efficient fluorescent probes toward nitrophenolic compounds. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2565–2573

Synthesis and extraction results of new halide terminated 2-alkyl-p-tert-butylcalix[4]arenes bearing phosphine oxides or ketones on the narrow rim

The synthesis of lower rim tetraphosphorylated and tetraketone calix[4]arenes with haloalkyl groups tethered to a single methylene bridge and their utilization as extraction agents for rare earth elements are reported. Synthesis of these new functionalized calix[4]arene species has been achieved in good to modest yields, and extraction of nine lanthanide nitrates has been explored using these novel calix[4]arene species. The tetraphosphorylated calix[4]arenes show better lanthanide extraction efficiency than their ketone counterparts, especially for europium (III). These experiments demonstrate that inclusion of a substituent tethered to the methylene bridge does not significantly reduce the extraction efficiency of these new calix[4]arene ligands as compared to similar unsubstituted ligands in literature, making them important precursors in the development of functionalized stationary phases for separation of lanthanides. Development of similar CMPO-bearing narrow rims and new solid-phase extraction materials for the solid–liquid separation of lanthanides remains the subject of future work.

Binding of an organo-osmium(II) anticancer complex to guanine and cytosine on DNA revealed by electron-based dissociations in high resolution Top-Down FT-ICR mass spectrometry.

The Os(II) arene anticancer complex [(η(6)-bip)Os(en)Cl](+) (Os1-Cl; where bip = biphenyl, and en = ethylenediamine) binds strongly to DNA. Here we investigate reactions between Os1-Cl and the self-complementary 12-mer oligonucleotide 5'-TAGTAATTACTA-3' (DNA12) using ultra high resolution Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). Identification of the specific sites of DNA osmiation with {(η(6)-bip)Os(en)}(2+) was made possible by the use of Electron Detachment Dissociation (EDD) which produced a wide range of assignable osmiated MS/MS fragments. In contrast, the more commonly used CAD and IRMPD techniques produced fragments which lose the bound osmium. These studies reveal that not only is guanine G3 a strong binding site for {(η(6)-bip)Os(en)}(2+) but, unexpectedly, so too is cytosine C10. Interestingly, the G3/C10 di-osmiated adduct of DNA12 also formed readily but did not undergo such facile fragmentation by EDD, perhaps due to folding induced by van der Waal's interactions of the bound osmium arene species. These new insights into osmium arene DNA adducts should prove valuable for the design of new organometallic drugs and contribute to understanding the lack of cross resistance of this organometallic anticancer complex with cisplatin.

Gilded Chalices: Tetra-aurated Calix[4]arenes

Abstract 5,11,17,23-Tetrakis(trimethylsilylethynyl)-25,26,27,28-tetra-n-propoxycalix[4]arene (1) was synthesised in two steps starting from 25,26,27,28-tetra-n-propoxycalix[4]arene, and the structure of 1 was determined by X-ray diffraction. Compound 1 was desilylated (K2CO3) to give 5,11,17,23- tetrakis(ethynyl)-25,26,27,28-tetra-n-propoxycalix[4]arene (2), which was tetra-aurated under basic conditions (NaOEt, THF) with a series of phosphane-gold chlorides (o-Tol3PAuCl, Ph3PAuCl, Ph2MePAuCl, PhMe2PAuCl, Me3PAuCl, Cy3PAuCl, t-Bu3PAuCl) to afford in good to excellent yields the tetra-aurated tetraethynylcalix[4]arene species 3-9 in one step [with phosphane ligands o-Tol3P (3), Ph3P (4), Ph2MeP (5), PhMe2P (6), Me3P (7), Cy3P (8), t-Bu3P (9)]. All compounds were characterised by 1H NMR and infrared spectroscopy, mass spectrometry and by elemental analyses, additionally 3, 4, 5, 8 and 9 by 13C{1H}, and 3-6, 8 and 9 by 31P{1H} NMR spectroscopy. The molecular structures of complexes 3 and 9 were determined by X-ray diffraction and show pinched-cone conformations, but neither intra- nor intermolecular attractive aurophilic Au···Au contacts. The acceptor ability of complexes 3 and 9 was investigated by complexation attempts with various phosphane-gold chlorides and xenon gas under pressure, but interactions could not be determined experimentally. The formation of a complex between xenon and gilded calix[4]arene could, however, be predicted for fluorine-substituted species and with very small phosphane ligands (PH3) on the basis of quantum-chemical calculations; the energy of formation is 9:6 kJ mol-1. The crystal structure of Ph2MePAuCl was also determined and shows Au···Au-bonded dimers.

Carbon–fluorine bond cleavage in fluoroarenes via a niobium(iii) imido complex: from stoichiometric to catalytic hydrodefluorination

The mechanism of activation of C–F bonds in fluoroarenes using a well-defined niobium(III) imido complex has been investigated. The Nb(III) arene species [BDI]Nb(NtBu)(η6-C6H6), 1, (BDI = β-diketimate), reacts stoichiometrically with fluoroarenes to yield niobium(V) aryl fluorides. Spectroscopic analysis supported by DFT calculations revealed the critical involvement of a Nb(III) fluoroarene-bound species. In contrast to previous reports of related reactivity, we found that perfluorinated arenes (i.e. those normally assumed to bear more ‘activated’ C–F bonds) are, in the present system, much less reactive towards C–F bond cleavage than mono- or difluoro-substituted arenes. In addition to demonstrating stoichiometric hydrodefluorination reactions, we also describe an efficient and mild hydrodefluorination of mono- and di-fluoroarenes that is catalytic in niobium.

New ruthenium(II)-arene complexes bearing hydrazides and the corresponding (thio)semicarbazones of 3- and 4-acetylpyridine: Synthesis, characterization, crystal structure determination and antiproliferative activity

Metal semicarbazone and thiosemicarbazone complexes have attracted much attention due to their diverse biological activities. Because of the ability of ruthenium(II)-arene species to coordinate to different classes of ligands, they are suitable for fine-tuning chemical and pharmaceutical properties. Ruthenium(II) arene-complexes containing different types of ligands: namely caprylic hydrazide (a hydrazide with a long hydrocarbon chain), isonicotinic acid hydrazide (a hydrazide with an aromatic pyridine ring), thiosemicarbazones and semicarbazones (derived from the reaction of 3- and 4-acetylpyridine with either thiosemicarbazide or caprylic hydrazide), were obtained in the reaction of [(η6-p-cymene)RuCl2]2 with the corresponding ligands in a 1:2 or 1:2.2 molar ratio in methanol, ethanol or isopropanol with mild heating. The complexes were characterized by elemental analysis, mass spectrometry, IR and NMR spectroscopies. The structure of complex 1 was determined by X-ray crystallography. Antiproliferative activity of the investigated complexes, determined for three human cancer cell lines (HeLa, A549 and LS-174) revealed moderate activity without significant influence on the matrix metalloproteinases (MMP-2 and MMP-9) activity.

Negishi coupling reactions as a valuable tool for [11C]methyl-arene formation; first proof of principle

The Negishi coupling reaction between arylzinc halide reagents and (11)CH3I has been used to synthesise (11)C-methylated arene species via a palladium-mediated process. The metabotropic glutamate receptor subtype-5 radiotracer [(11)C]MPEP has been radiolabelled using this technique.

New potential prodrugs of aciclovir using calix[4]arene as a lipophilic carrier: synthesis and drug-release studies at the air–water interface

Two tetra-p-tert-butyl-calix[4]arene species bearing one or two anti-HSV aciclovir units tethered via carbodiester linkages at the lower rim were synthesized as possible antiviral prodrugs. The amphiphilic properties of these derivatives were studied using Langmuir balance at the air–water and air–carbonate buffer interfaces; the monolayers formed were stable on both subphases. Monolayers formed with these molecules on a carbonate buffer subphase at pH 10 and 37 °C were then used for monitoring hydrolysis of the diester linkage. The release of free aciclovir of around 30% in 3 days was observed with both derivatives, as shown with HPLC.

Organosoluble calixarene-based quinolone carriers: syntheses, evaluation and model hydrolytic studies at the air–water interface

Two tetra-p-tert-butyl- and two tetra-p-H-calix[4]arene species integrating one or two propylnalidixate esters at the lower rim have been synthesized as possible antibacterial prodrugs. As they display amphiphilic behavior, their properties at the air–water interface were evaluated using the Langmuir balance technique. It has been shown that the two tert-butyl analogues form stable monolayers. The two tert-butyl analogues were then studied at 20 and 37 °C on carbonate buffered subphases at pH 10.0, before being engaged in hydrolytic studies on “production” of monolayers so as to allow a simple treatment, a HPLC survey of nalidixate release. The latter was found to be effective at 37 °C, with formation of free nalidixate in 13% yield for the bisnalidixate derivative, and 10% yield for the mononalidixate after 3 days.

Silylium–Arene Adducts: An Experimental and Theoretical Study

The solvent-coordinated [Me(3)Si·arene][B(C(6)F(5))(4)] salts (arene = benzene, toluene, ethylbenzene, n-propylbenzene, isopropylbenzene, o-xylene, m-xylene, p-xylene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene) are prepared and fully characterized. As an interesting decomposition product the formation of bissilylated fluoronium ion [Me(3)Si-F-SiMe(3)](+) was observed and even cocrystallized with [Me(3)Si·arene][B(C(6)F(5))(4)] (arene = benzene and toluene). Investigation of the degradation of [Me(3)Si·arene][B(C(6)F(5))(4)] reveals the formation of fluoronium salt [Me(3)Si-F-SiMe(3)][B(C(6)F(5))(4)], B(C(6)F(5))(3), and a reactive "C(6)F(4)" species which could be trapped with CS(2). Upon addition of CS(2), the formation of a formal S-heterocyclic carbene adduct, C(6)F(4)CS(2)-B(C(6)F(5))(3), was observed. The structure and bonding of substituted [Me(3)Si·arene][B(C(6)F(5))(4)] with arene = R(n)C(6)H(6-n) (R = H, Me, Et, Pr, and Bu; n = 0-6) is discussed on the basis of experimental and theoretical data. X-ray data of [Me(3)Si·arene][B(C(6)F(5))(4)] salts reveal nonplanar arene species with significant cation···anion interactions. As shown by different theoretical approaches (charge transfer, partial charges, trimethylsilyl affinity values) stabilizing inductive effects occur; however, the magnitude of such effects differs depending on the degree of substitution and the substitution pattern.

Synthesis and anti-HIV evaluation of water-soluble calixarene-based bithiazolyl podands

Nine anionic water-soluble calix[4]arene species, incorporating sulfonate, carboxylate or phosphonate groups, six of them incorporating two 2,2′-bithiazole subunits in alternate position at the lower rim, have been synthesised and evaluated as anti-HIV agents on various HIV strains and cells of the lymphocytic lineage (HIV-1 III B/MT4, HIV-1 LAI/CEM-SS, HIV-1 Bal/PBMC), using AZT as reference compound. A toxicity was detected for a minority of compounds on PBMC whereas for the others no cellular toxicity was measured at concentrations up to 100 μM. Most of the compounds have an antiviral activity in a 10–50 μM range, and one of them, sulfonylated, displays its activity, whatever the tropism of the virus, at a micromolar concentration.

Synthesis and Structures of an Unusual Germanium(II) Calix[4]arene Complex and the First Germanium(II) Calix[8]arene Complex and Their Reactivity with Diiron Nonacarbonyl

The protonolysis reaction of the germanium(II) amide Ge[N(SiMe3)2]2 with calix[4]arene and calix[8]arene furnishes the two germanium(II) calixarene complexes {calix[4]}Ge2 and {calix[8]}Ge4, respectively, which have been crystallographically characterized. The calix[4]arene complex contains a Ge2O2 rhombus at the center of the molecule and is one of the only four germanium(II) calix[4]arenes that have been structurally characterized. The calix[8]arene species is the first reported germanium calix[8]arene complex, and it exhibits an overall bowl-shaped structure which contains two Ge2O2 fragments. The latter complex reacts with Fe2(CO)9 to yield an octairon compound, which has also been structurally characterized and contains four GeFe2 triangles arranged around the macrocyclic ring. The germanium(II) centers are oxidized to germanium(IV) in this process, with concomitant reduction of the neutral diiron species to Fe2(CO)(8)2- anions.

The first 4,1,10-MC2B10 supraicosahedral metallacarboranes and a route to previously inaccessible 4,1,12-ruthenium arene species

Reduction of 1,12-closo-C2B10H12 or its C,C-dimethyl analogue with sodium in liquid ammonia followed by metallation with {CpCo}2+, {(arene)Ru}2+ or {(dppe)Ni}2+ fragments affords the first examples of 4,1,10-MC2B10 species; thermolysis of these yields the appropriate 4,1,12-MC2B10 isomers, unavailable for (arene)Ru metallacarboranes by similar thermolysis of known 4,1,6-MC2B10 compounds.

Mononucleotide recognition by cyclic trinuclear palladium(II) complexes containing 4,7-phenanthroline N,N bridges.

Reaction of [(dach)Pd(NO3)2] entities (dach = (R,R)-1,2-diaminocyclohexane, (S,S)-1,2-diaminocyclohexane) and 4,7-phenanthroline (phen) providing, respectively, 90 and 120 degrees bond angles, leads to the formation of two novel positively charged homochiral cyclic trinuclear metallacalix[3]arene species [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2b). These species have been characterised by 1)H NMR and X-ray diffraction methods (2b), showing that they possess accessible cavities suited for supramolecular recognition processes. We prove, indeed, from 1H NMR studies the inclusion of mononucleotides inside the cavity of the trinuclear species [(ethylenediamino)Pd(phen)]3(6+) (1), [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2b) in aqueous solution. Association constants (K(ass)) range from 85 +/- 6 M(-1) for the interaction between [(ethylenediamine)Pd(phen)]3(6+) and adenosine monophosphate to 37 +/- 4 M(-1) for the interaction between [(1,2-diaminocyclohexane)Pd(phen)]3(6+) and thymidine monophosphate. We invoke the synergy of electrostatic, anion-pi and pi-pi interactions to explain the recognition of mononucleotides inside the cavity of the metallacalix[3]arenes.

Synthesis and ring-opening metathesis polymerization of eight-membered unsaturated lactams and related monomers

Novel eight-membered ring unsaturated lactams were synthesized and tested as monomers for the ruthenium-catalyzed ring-opening metathesis polymerization (ROMP). The reaction of a N-protected cyclic alkeneamine was also investigated. The Grubbs’ benzylidene complexes RuCl 2(=CHPh)(PCy 3) 2 or RuCl 2(=CHPh)(PCy 3)(IMesH 2) and selected ruthenium–arene species bearing either phosphine or stable Arduengo-type N-heterocyclic carbene ligands served as catalyst precursors. In most cases, isomerization of the starting materials took place and only 1-benzyl-1-aza-2-ketocyclooct-5-ene afforded a polymeric product. This polyamide was characterized by numerous analytical techniques.

Evidence for the formation of a tantalum(IV) arene species from arene-alkyl complexes of tantalum(III)

Evidence for the formation of a tantalum(IV) arene species from arene-alkyl complexes of tantalum(III)