Arene System Research Articles

Haemolytic properties of some water-soluble para-sulphonato-calix-[ n]-arenes

In this paper, we describe the haemolytic effect of parent para-sulphonato-calix-[ n]-arenes and their derivatives bearing one pendant group at the lower rim of calix-arene towards human erythrocytes. A maximum of 30% of haemolysis has been observed for para-sulphonato-calix-[8]-arene for a concentration of 200 mM representing 300 g of calix-arene per liter of human blood, para-sulphonato-calix-[4]-arene and para-sulphonato-calix-[6]-arene show much lower haemolytic effects, 0.5 and 8%, respectively at 200 mM concentration. Coupling of a methoxy-carboxylate function at the phenolic group reduces haemolytic effects in all cases. The presence of an ethoxy-amine function increases the haemolytic behaviour for the calix-[4]-arene and calix-[6]-arene systems, but reduces the effect for the calix-[8]-arene derivatives.

Synthesis of novel rigid triazine-based calix[6]arenes

In this report, the stepwise synthesis of a novel rigid and functionalised macrocycle 2 based on triazine and phenylenediamine linkers, is presented. Poor recognition of the macrocycle 2 for its substrates is observed, which shows experimentally that for the meltriazine based-calix[6]arene system, the binding ability of the melamine moiety gets more benefit from the ring flexibility derived from a xylenediamine linker 1 than from a phenylenediamine linker 2 .

Calixarenes as aryloxides: oligonuclear europium(iii) derivatives

Synthetic and structural studies of europium complexes of calix[8]arene, p-t-Bu-calix[7]arene and p-t-Bu-calix[9]arene are reported. The complex [Eu2(calix[8]arene-6H)(dmso)5] was found to have a similar structure to previously reported p-t-Bu- and p-nitro-calix[8]arene complexes of the lanthanides. Despite being prepared under similar conditions, the complex of p-t-Bu-calix[7]arene was found to be a tetranuclear assembly, formulated as [(HO)2(OCO2)Eu4(p-t-Bu-calix[7]arene-4H)2(dmso)6]. Expanding the ligand to p-t-Bu-calix[9]arene resulted in the isolation of a larger oligonuclear assembly, [(HO)9(H2O)2Eu7(p-t-Bu-calix[9]arene-6H)2(dmso)6]. In contrast to the consistent structural type found with the calix[8]arene system, however, use of a different solvent (acetone) gave rise to a much simpler species, [Eu2(p-t-Bu-calix[9]arene-3H)2(dmso)4].

Synthesis of Highly Functionalized Arene Systems. Novel Selectivities of Intra‐ and Intermolecular Friedel—Crafts Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel tungsten calix[8]arene complexes.

p-tert-Butylcalix[8]areneH8 reacts with WCl6 forming a number of new metallocalix[8]arenes, one of which is reduced to give the first example of a metal-metal triple bond supported by a large calixarene ligand; the degree of metallation and conformations adopted by the newly generated metallocalix[8]arene systems are determined by single crystal X-ray diffraction.

X-Ray Structure of an Inclusion Compound of 5,5'-Biscalix[4]arene-hexabenzoate with Toluene

The structure of the 1:3 complex between 5,5'-biscalix[4]arene-hexabenzoateand toluene has been determined by a single crystal X-ray diffraction study. Thetwo calix[4]arene subunits of the 5,5'-biscalix[4]arene system are related by aninversion center and are joined by an eclipsed biphenyl para-para linkage. Each calix[4]arene moiety displays a 1,3-alternate conformation and includes a toluene molecule within two opposite benzoate groups, while a third toluene molecule lies close to a crystallographic inversion center.

Advances in metal chemistry of quinonoid compounds: new types of interactions between metals and aromatics.

This Account presents an overview of current research activities that focus on novel types of interactions between cationic transition metal complexes and arene systems and on unprecedented quinonoid complexes which result from such interactions. When a negatively charged phenoxy group is present in a position para to the metal in a high oxidation state, intramolecular charge transfer occurs, giving the corresponding metallaquinones or quinone methide complexes. In addition, two types of interactions involving low-valent metal compounds have been observed: methylene arenium complexes which result from positive charge transfer to the aromatic ring and sigma-bonded C-H and C-C agostic complexes of cationic metals. These sigma-complexes are proposed as intermediates in metal-based bond activation processes.

Synthesis of Tetra-3-butenyl-Substituted Metallocenes and the Application of 1,1‘,3,3‘-Tetrakis(1,1-dimethyl-3-butenyl)ferrocene as Core for the Preparation of Polynuclear Compounds

The synthesis of the 1,1‘,3,3‘-tetrabutenyl-substituted metallocenes [C5H3(CMe2CH2CHCH2)2]2M (M = Fe 1, Co 2, Ni 3), their electrochemical properties, and the solid-state structures of 1 and 3 are presented. Hydrosilylation of 1 with dimethylphenylsilane leads to [C5H3(CMe2(CH2)3SiMe2Ph)2]2Fe, 4. The π-coordination ability of the arene system in 4 has allowed the preparation of the pentanuclear complex [C5H3(CMe2(CH2)3SiMe2(η6-C6H5−Cr(CO)3)2]2Fe, 5, containing a ferrocene core and peripherial η6-coordinated Cr(CO)3 moieties. Electrochemical investigations of 5 show a reversible oxidation of the ferrocene unit as well as an independent, noninteracting irreversible oxidation of the Cr centers.

Calix[4]arene-5,17-dicarboxylic acids and their interactions with aliphatic amines. Part 2. A crystal engineering approach

The possible interactions between diacid functionalised conformationally diverse calix[4]arene molecules and simple amines were investigated. The aim was to establish an understanding of the solid state constructions obtained upon crystallising the salts formed between the acids and the amines. Each component of the acid–base system was subject to variations through the degree of chemical substitution and conformational diversity of the calix[4]arene system and through the degree of chemical substitution for the amine system pertaining to primary, secondary and tertiary amines. Unlike the known solution behaviour where tertiary amines behave differently from secondary and primary amines as a group it was found that the solid state behaviour was further differentiated. In the solid state primary amines give rise to salt bridged closed networks whereas secondary amines give rise to open polymeric salt bridged networks and tertiary amines give rise to monomeric salts. Furthermore the patterns that were uncovered from the isolated studies could be used to predict the structural behaviour of a more complex case such as the biological molecule ephedrine for which a calix[4]arene based sensing system was developed in our previous paper.

Structure, Conformational Equilibrium, and Proton Affinity of Calix[4]arene by Density Functional Theory

Density functional theory results for the structure and conformational equilibrium of four calix[4]arene conformers are reported. The results are compared with experiment, force field, and semiempirical molecular orbital calculations. The energy difference between the two most stable conformers of calix[4]arene (cone and partial-cone) is 10 kcal mol-1 at the BLYP/6-31G** level with the geometries optimized at BLYP/6-31G*. For the most stable conformer, results for the protonated structure are also reported. Electrostatic potential surfaces for the cone calix[4]arene and the corresponding tetra-O−H-depleted structure have been calculated. It is suggested that their representation may be of relevance to understand the known ability of calix[n]arene systems to form complexes with charged species in host−guest chemistry.

Epoxide Polymerization and Copolymerization with Carbon Dioxide Using Diethylaluminum Chloride-25,27-Dimethoxy-26,28-dihydroxy-p-tert-butyl-Calix[4]arene System as a New Homogeneous Catalyst

ABSTRACT Previously unknown substituted chelate phenolatoaluminum chloride, (25,27-dimethoxy-p-tert-butylcalix[4]arene-26,28-diolato) aluminum chloride, was derived from the reaction of diethyl-aluminum chloride and 25,27-dimethoxy-26,28-dihydroxy-p-tert-butylcalix[4]arene at reactants 1:1 mole ratio. It was applied successfully for the polymerization of propylene oxide and cyclohexene oxide, and their copolymerization with carbon dioxide, leading to respective oligomers and co-oligomers. The catalyst structure and the structure of the obtained low-molecular-weight polymers and copolymers were studied using NMR spectroscopy. Poly(propylene oxide) obtained in the presence of the studied catalyst appeared to contain isotactic diads predominantly, whereas the obtained poly(cyclohexene oxide) did not exhibit any significantly prevailing sequences of either isotactic nor syndiotactic diads. The polymerization mechanism has been proposed and discussed in view of the obtained results.

オルガノコバロキシムの反応と合成への応用

Alkyl- and alkenylcobaloximes are conveniently prepared by the reaction of cobaloxime (I) with alkyl halides, vinyl halides, and acetylenes. The organocobaloximes thus obtained are convenient and versatile radical source for organic syntheses. The cobaloxime group is conveniently transformed into other functions by a variety of radicophiles. The organo radical from organocobaloxime attacks intramolecular or intermolecular olefin in the same manner as a general organo radical. Contrary to the conventional tin hydride method, an organocobaloxime gives not a reduction product but an olefinic product. The olefinic function thus formed is useful for further chemical transformation. The coexisting cobaloxime (II) radical modifies reactivity of the olefinic and arenic part of the organo radical containing sulfur function. The cobaloxime moiety activates an intramolecular diene and arene system to cause cycloaddition and aromatic substitution respectively.

A simple method for the exploration of the conformational space and for the estimation of rotational barriers in calix[4]arene systems

The gradual modification of the z-coordinate(s) of selected atom(s) together with the fixation of the z-coordinates of two or more reference atoms allows the simulation of ring inversion processes in calixarene systems. The energy profile along the reaction pathway is obtained by minimization of all remaining degrees of freedom in each step by means of the MM3(92) force field. The subsequent determination of ground and transition states may be used for the estimation of the activation barriers for ring flip processes. By choosing suitable conditions this coordinate driver method allows not only the simulation of stepwise processes but also the investigation of simultaneous and concerted mechanisms as well as the search of the conformational hypersurface. Five different lower rim substituted calix[4]arenes 1 (X  OH, H, SH, CF 3, NH 2) have been investigated by means of this method and the results are discussed in relation to the available experimental data and compared with previous theoretical studies.

Alkyne–Carbene Chelate Complexes of Chromium: Arrested Intermediates in the Benzannulation Reaction and Precursors of Densely Functionalized Centrosymmetric Chrysenes

AbstractTetracarbonyl‐π2‐alkyne–carbene chromium(0) complexes 3a–c stabilized by a rigid C2‐arene unit bridging the alkyne and the carbene ligands were synthesized from their pentacarbonyl precursors 2a–c by low‐temperature photodecarbonylation. The chelates 3a–c are the first stable alkyne–carbene complexes containing a Group VIB metal carbonyl unit, and can be regarded as arrested intermediates in the chromium‐mediated benzannulation reaction. Comparative X‐ray and 13C NMR studies indicate only weak coordination of the alkyne, both in the solid state and in solution. Decomposition of chelates 3a–c as well as the thermal decarbonylation of their pentacarbonyl precursors 2a–c results in dimerization of the alkynylcarbene ligands to give densely substituted oxygenated chrysene derivatives. A modification of the substitution pattern in the central chrysene rings results in a gradual distortion of the arene system across the central CC arene bond.

A brief overview of the structural determination of cyclopentadienyliron arene complexes

This article constitutes a brief overview of the use of NMR spectroscopy for the determination of the structure of a number of cyclopentadienyliron arene systems. The examples presented here demonstrate the use of one- and two-dimensional NMR techniques in predicting the chemical structure and dynamics of these complexes. The numerous isomers obtained from the hydride addition to mono- and dicyclopentadienyliron arene complexes were identified using 2D HH COSY and CH COSY. The 2D 1H COSY, DQ-COSY and NOE study of the ( η 6-2,6-dimethylphenyl)-phenylsulphonylacetonitrile- η 5-cyclopentadienyliron cation showed that there is restricted rotation about the arene-methine carbon bond. 1D NMR was also used for the determination of the diastereomeric nature of the arene complexes, which arose from their complexation to the cyclopenta-dienyliron moieties, as well as in estimating the number of repeating units in the oligomeric complexes.

Calix(8)arene LB superlattices: pyroelectric molecular baskets

Carboxyl and amino groups have been inserted into calix(8)arene rings to yield two materials which, when processed as alternate-layer Langmuir-Blodgett assemblies, exhibit the pyroelectric effect. Such a temperature-dependent electric polarisation arises partially from proton transfer between the acid and amine groups. The calix(8)arene system has been selected because of the extreme thinness of each monolayer (~1.0 nm), the resulting high density of acid-amine pairs and the very high thermal stability exhibited by calixarenes (typically, melting point above 200°C).

Nucleophilic addition to di- and poly-iron arene complex cations

Hydride and cyanide addition to a series of di- and polycyclopentadienyliron arene complex cations with etheric bridges is described. Reaction of the di-iron complexes with sodium borohydride resulted in the formation of a number of adducts.p-Methyl- and o,o-dimethylphenoxybenzene cyclopentadienyliron complexes were used as models in this study to allow for the characterization of the analagous di-iron complexes. The use of HH COSY and CH COSY NMR techniques enabled us to identify the isomeric nature of these adducts. The hydride addition results indicated that the etheric substituent had the predominant effect over the methyl group, leading to a higher addition ratio to the meta-, followed by the ortho-, then the para-positions. It was also clear that in the di-iron system, the hydride addition to each complexed arene ring took place independently. The addition of the cyanide anion to di- and poly-iron arene systems was more selective than that of the hydride anion. Reaction of sodium cyanide with p-methyl- or o-methyl-substituted arene complexes led to the formation of one adduct, with the cyanide being added to the meta position to the etheric bridges. However, cyanide addition to the di-iron complex, with a methyl substituent attached at the meta position of each complexed arene, led to the formation of a mixture of adducts. Cyanide addition to the poly-iron system with p-substituted arenes proved to be very selective, allowing for the formation of one adduct. Oxidative demetallation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) produced the uncomplexed polyaromatic ethers with cyano groups in a very good yield. Key words: cyclopentadienyliron, arene, nucleophilic addition, hydride, cyanide.

ChemInform Abstract: Neighboring Rotor Substituents on Arene Systems. Part 3. Axially Chiral 2‐(Dialkylamino)benzamides. Barriers to Rotations, Determined by NMR and by Racemization.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

On the mechanism of the stereo- and regioselective ether-ring opening of 1,2,3,4-tetrahydro-1β,4β-epoxy-2α,3α-carbonyldioxy arene systems with boron tribromide

Stereo- and regioselective formation of bay-region bromo alcohols observed during etherbridge opening of the titled systems with boron tribromide has been rationalized, on the basis of AM1 calculations, by the intramolecular same-face delivery of the bromide ion from the intermediate borate group and the relative stability of the bay-region versus non-bay-region benzylic cations, respectively.

Axially chiral 2‐(dialkylamino)benzamides. Barriers to rotations, determined by NMR and by racemization (neighboring rotor substituents on arene systems, part 3)

AbstractThe title compounds (Scheme 1, Y = NMe2) were investigated by variable‐temperature NMR and/or by racemization of enantiomers enriched by liquid chromatography on microcrystalline triacetylcellulose. For several reasons, a dialkylamino and a dimethylcarbamoyl group were used, for the first time, as neighboring rotor substituents on a benzene ring. Barriers to rotations about their aryl‐nitrogen and/or aryl‐carbon bonds were determined and assigned (Table I). Correlated or uncorrelated motions of these groups are possible for amides 11 and 19 bearing in their 3‐positions tert‐butyl substituents which hinder the aryl‐nitrogen rotation. Uncorrelated rotations have been found for amide 15 (Figure 2) and thioamide 8 which have the less voluminous bromine atom in their 3‐position.