Arene Ring Research Articles

Friedel-Crafts Acylation for Accessing Multi-Bridge-Functionalized Large Pillar[n]arenes.

Pillar[n]arenes can be constructed using a Friedel-Crafts alkylation process. However, due to the reversible nature of the alkylation, mixture of large pillar[n]arenes (n≥7) are obtained as minor products, and thus laborious purification are necessary to isolate the larger pillar[n]arenes. Moreover, inert methylene bridges are introduced during the alkylation process, and the multi-functionalization of the bridges has never been investigated. Herein, an irreversible Friedel-Crafts acylation is used to prepare pillar[n]arenes. Due to the irreversible nature of the acylation, the reaction of precursors bearing carboxylic acids and electron-rich arene rings results in a size-exclusive formation of pillar[n]arenes, in which the ring-size is determined by the precursor length. Because of this size-selective formation, laborious separation of undesired macrocycles is not necessary. Moreover, the bridges of pillar[n]arenes are selectively installed with reactive carbonyl groups using the acylation method, whose positions are determined by the precursor used. The carbonyl bridges can be easily converted into versatile functional groups, leading to various laterally modified pillar[n]arenes, which cannot be accessed by the alkylation strategy.

Selective C(aryl)-O bond cleavage in biorenewable phenolics.

Biorefining of lignocellulosic biomass via a lignin first approach delivers a range of products with high oxygen content. Besides pulp, a lignin oil rich in guaiacols and syringols is obtained bearing multiple C(aryl)-OH and C(aryl)-OMe groups, typically named phenolics. Similarly, technical lignin can be used but is generally more difficult to process providing lower yields of monomers. Removal of the hydroxy and methoxy groups in these oxygenated arenes is challenging due to the inherently strong C-O bonds, in addition to the steric and electronic deactivation by adjacent -OH or -OMe groups. Moreover, chemoselective removal of a specific group in the presence of other similar functionalities is non-trivial. Other side-reactions such as ring saturation and transalkylation further complicate the desired reduction process. In this overview, three different selective reduction reactions are considered. Complete hydrodeoxygenation removes both hydroxy and methoxy groups resulting in benzene and alkylated derivatives (BTX type products) which is often complicated by overreduction of the arene ring. Hydrodemethoxylation selectively removes methoxy groups in the presence of hydroxy groups leading to phenol products, while hydrodehydroxylation only removes hydroxy groups without cleavage of methoxy groups giving anisole products. Instead of defunctionalization via reduction transformation of C(aryl)-OH, albeit via an initial derivatization into C(aryl)-OX, into other functionalities is possible and also discussed. In addition to methods applying guaiacols and syringols present in lignin oil as model substrates, special attention is given to methods using mixtures of these compounds obtained from wood/technical lignin. Finally, other important aspects of C-O bond activation with respect to green chemistry are discussed.

Исследование кристаллических структур 7-иод-8-оксихинолин-5-сульфонатов алкилтрифенилфосфония [Ph3PAlk][OSO2C9NH4(I-7)(OH-8)], Alk = CH2Ph, CH=CHMe, CH2C≡CH

From alkyltriphenylphosphonium bromides and 7-iodo-8-hydroxyquinoline-5-sulfonic acid in water, ionic alkyltriphenylphosphonium 7-iodo-8-hydroxyquinoline-5-sulfonates Ph3PAlk][OSO2C9NH4(I-7)(OH-8)], Alk = CH2Ph (1), CH=CHMe (2), CH2C≡CH (3) have been obtained. Crystals 1 [C34H27NO4PSI, M 703.50; monoclinic system, symmetry group P21/c; cell parameters: a = 8.805(4), b = 16.146(10), c = 20.833(11) Å; β = 93.410(17), V = 2956(3) Å3, Z = 4; rcalc = 1.581 g/cm3], 2 [C30H25NO4PSI, M 653.44; rhombic system, symmetry group P212121; cell parameters: a = 9.382(3), b = 14.033(4), c = 21.035(6) Å; a = β = g = 90.00 deg., V = 2769.5(15) Å3, Z = 4; rcalc = 1.567 g/cm3], 3 [C30H27NO6PSI, M 687.46; monoclinic system, symmetry group P21/n; cell parameters: a = 9.426(3), b = 19.239(5), c = 16.088(5) Å; β = 97.296(14) deg., V = 2894.0(15) Å3, Z = 4; rcalc = 1.578 g/cm3]. According to the X-ray diffraction data, the phosphorus atoms in cations 1–3 have a distorted tetrahedral coordination, while the sulfonate anions have a regular geometry with a tetrahedral sulfur atom. The P–C bond lengths vary in the range 1.772(3)−1.815(2) Å; the CPC bond angles take values of 106.08(11)°−112.33(11)°. In the arenesulfonate anions of the complexes, the S–C distances are close to each other [1.781(2)–1.7920(19) Å], the S–O bonds are practically aligned [1.4464(16)–1.4590(17) Å]. In the crystal of hydrate 3 [Ph3PCH2C≡CH][OSO2C9NH4(I-7)(OH-8)] ∙ 2H2O, water molecules participate in formation of a dimeric anion (the O∙∙∙H and N∙∙∙H distances are 1.93 and 2.03 Å, while the arene rings of the sulfonate ligands are almost parallel (the angle between them is 3.24°)). Other water molecules link the dimeric anions into a chain with hydrogen bonds (the O∙∙∙H distances equal 2.12 and 2.15 Å). The structural organization in complexes 1–3 is mainly due to weak intermolecular contacts of the O···H type: 2.04–2.69 Å (1), 2.05–2.69 Å (2), 2.12–2.15 Å (3).

De novo fabrication of higher arene ring incorporated contorted calix[2]phyrin(2.2.1.1.1) and its F- bound complex.

The rational design and synthesis of a novel contorted calix[2]phyrin(2.2.1.1.1) structure has been achieved, utilizing a terphenyl unit as a key building component. This terphenyl unit serves as a segment of the armchair periphery in a π-extended two-dimensional architecture. The resulting molecule exhibits remarkable properties, including the ability to self-assemble into solid-state supramolecular nanotubes. Additionally, it has demonstrated an affinity for complexation with fluoride anions, highlighting its potential for applications in molecular recognition and sensor technology. The incorporation of the terphenyl unit not only enhances the structural rigidity but also contributes to the unique electronic characteristics of the calix[2]phyrin.

Introducing chirality in porous organic cages through solid-state interactions.

Molecular cages contain an internal cavity designed to encapsulate other molecules, resulting in applications in molecular separation, gas storage, and catalysis. Introducing chirality in cage molecules can improve the selective separation of chiral molecules and add new functionalities due to the realisation of chiral photophysical properties. It has recently been shown that solid-state supramolecular interactions between achiral cages can result in the formation of chiral cavities. Here, we develop a computational technique to predict when achiral cages form chiral cavities in the solid-state through the combination of atomistic calculations and coarse-grained modelling to predict the crystalline phase behaviour. Our focus is on the achiral cage B11, which contains rotatable arene rings on the vertices of the cage that can form propeller-like orientations, inducing a chiral cavity. We show that by using dimer pair calculations, we can inform coarse-grained models to predict the packing of the cage. Our results reveal how the supramolecular interactions drive chirality in the achiral cages without the need for a chiral guest. These findings are a first step towards understanding how we can design chirality through supramolecular interactions by using abstract coarse-grained models to inform design principles for targeted solid-state phase behaviour.

Biodiesel from Waste Cooking Oil: Highly Efficient Homogeneous Iron(III) Molecular Catalysts

This article presents an efficient iron(III) molecular catalyst for the production of biodiesel from waste vegetable oils. The approach involved an initial screening of eight salophen complexes with various substituents on the arene rings, leading to the selection of the simplest unsubstituted species as the most active catalyst. Under optimized conditions, this catalyst demonstrated the capability to achieve complete conversion of the oil at a low catalyst loading (0.10% mol/mol) and convenient conditions (160 °C, 20/1 MeOH/oil ratio).

2‐Aryl Imidazolium Salts as Potential Bladder Cancer Chemotherapeutic Candidates

AbstractAs potential intravesical exfoliants for the treatment of bladder cancer, four new imdiazolium salts have been prepared. These compounds are modified on the nitrogen positions of the 4,5‐diphenyl‐1H‐imidazole or benzimidazole rings with naphthalen‐2‐ylmethyl groups, and the 2 positions on the azolium cations are occupied by arene rings. The 4,5‐diphenyl‐1H‐imidazole and benzimidazole precursors are produced from 1,2‐phenylenediamine and benzil respectively, and the imidazolium cations are generated from sequential alkylation of the nitrogen positions using 2‐bromomethyl naphthalene. The four imidazolium salts were screened for their chemotherapuetic activity using the NCI‐60 Human Tumour Cell Line Screen, and we observed that the cytotoxicity was more dependent on the identity of the imidazolium group (benzimidazolium versus diphenylimidazolium) rather than on the 2‐aryl position structure.

Syntheses, Structures and Reactivity of Metal Complexes of Trindane, Trindene, Truxene, Decacyclene and Related Ring Systems: Manifestations of Three-Fold Symmetry

The triple condensation of cyclopentanone or indanone to trindane (C15H18) or truxene (C27H18), respectively, provides convenient access to molecular skeletons on which major fragments of the prototypical fullerene C60 can be assembled. In particular, early approaches (both organic and organometallic) towards sumanene, as well as the final successful synthesis, are described. Organometallic derivatives of trindane have been prepared in which Cr(CO)3, Mo(CO)3, [Mn(CO)3]+ or [(C5H5)Fe(CO)2]+ are η6-bonded to the central arene ring. The debromination of hexabromotrindane yields trindene, which forms a tri-anion to which as many as three organometallic fragments, such as Mn(CO)3, W(CO)3Me, or Rh(CO)2, may be attached. Truxene forms complexes whereby three metal fragments can bind either to the peripheral arene rings, or to the five-membered rings, and these can be interconverted via η6 ↔ η5 haptotropic shifts. Truxene also forms a double-decker sandwich with Ag(I) bridges, and decacyclene, C36H18, forms triple-decker sandwiches bearing multiple cyclopentadienyl-nickel or -iron moieties. The organic chemistry of trindane has been investigated, especially with respect to its unexpectedly complex oxidation products, which were only identified unambiguously via X-ray crystallography. The three-fold symmetric trindane framework has also been used as a template upon which a potential artificial receptor has been constructed. Finally, the use of truxene and truxenone derivatives in a wide range of applications is highlighted.

Proton tautomerism and stereoisomerism in 5-[(dimethylamino)methylidene]-4-[3/4-(trifluoromethylphenyl)amino]-1,3-thiazol-2(5H)-ones: synthesis, crystal structure and spectroscopic studies.

5-[(Dimethylamino)methylidene]-4-{[3-(trifluoromethyl)phenyl]amino}-1,3-thiazol-2(5H)-one and the [4-(trifluoromethyl)phenyl]amino derivative, both C13H12F3N3OS, with the trifluoromethyl group substituted at the arene ring at the meta and para positions, were synthesized to study the structural changes associated with proton tautomerism of the amidine system. The studied compounds were found to be in the amine tautomeric form in both the solid and the liquid (dimethyl sulfoxide solutions) phase. In both isomers, the [(trifluoromethyl)phenyl]amino residue assumes a synperiplanar conformation with respect to the thiazolone system, while the 5-[(dimethylamino)methylidene] residue adopts the Z configuration. Density functional theory (DFT) calculations correctly predicted that the synperiplanar arrangement is favoured in both isomers. In the crystal, the whole independent molecule of the para compound is disordered over two alternative positions, with occupancy factors of 0.926 (3) and 0.074 (3).

Synthesis, crystal structure and Hirshfeld surface analysis of 3-(4-fluoro-phen-yl)-2-formyl-7-methyl-imidazo[1,2-a]pyridin-1-ium chloride monohydrate.

In the title salt, C15H12FN2O+·Cl-·H2O, the imidazo[1,2-a]pyridin-1-ium ring system of the cation is almostly planar [maximum deviaition = -0.047 (2) Å for the ring C atom with the attached arene ring] and forms a dihedral angle of 61.81 (6)° with the plane of the fluoro-phenyl ring. In the crystal, water mol-ecules form an R 2 4(8) motif parallel to the (100) plane by bonding with the chloride ions via O-H⋯Cl hydrogen bonds. The cations are connected along the b axis via N-H⋯O hydrogen bonds involving the O atoms of water mol-ecules, and C-H⋯O, C-H⋯Cl and π-π inter-actions [centroid-to-centroid distance = 3.6195 (8) Å] form layers parallel to the (100) plane. Furthermore, these layers are connected via π-π inter-actions [centroid-to-centroid distance = 3.8051 (9) Å] that further consolidate the crystal structure.

Crystal structure and Hirshfeld surface analysis of 8-aza-niumylquinolinium tetra-chlorido-zincate(II).

The reaction of 8-amino-quinoline, zinc chloride and hydro-chloric acid in ethanol yielded the title salt, (C9H10N2)[ZnCl4], which consists of a planar 8-aza-n-ium-yl-quinolinium dication and a tetra-hedral tetra-chloro-zincate dianion. The 8-amino-quinoline moiety is protonated at both the amino and the ring N atoms. In the crystal, the cations and anions are connected by inter-molecular N-H⋯Cl and C-H⋯Cl hydrogen bonds, forming sheets parallel to (001). Adjacent sheets are linked through π-π inter-actions involving the pyridine and arene rings of the 8-aza-niumylquinolinium dication. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H⋯Cl (48.1%), H⋯H (19.9%), H⋯C/C⋯H (14.3%) (involving the cations) and H⋯Cl (82.6%) (involving the anions) interactions.

Synthesis, Structure, Spectral, Electrochemical, and Theoretical Studies of Ru(II) Complexes of 3-Pyrrolyl BODIPY-Based Ligands.

3-Pyrrolyl BODIPY having an appended pyrrolyl group at the 3-position of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) and its functionalized derivatives have been used as ligands to prepare one example of Ru(II) complex of pyrrolyl dipyrrin and three unique examples of bichromophoric BODIPY-Ru(II) complexes in good yields. The complexes were characterized by HR-MS, 1D and 2D NMR, X-ray analysis for two complexes, absorption, cyclic voltammetry, and DFT/TD-DFT techniques. The X-ray structure of the Ru(II) complex of pyrrolyl dipyrrin revealed that the geometry around the Ru(II) ion was pseudo-octahedral with an arene unit occupying three coordination sites in η6-fashion and two nitrogen atoms of the dipyrrin ring and one chloro group adopting the "three legs piano-stool" structure. The X-ray structure of the bichromophoric BODIPY-Ru(II) complex revealed that the BODIPY core was planar and the central B(III) was coordinated with two pyrrole nitrogens of the dipyrrin unit and two axial fluoride ions in a tetrahedral geometry, and Ru(II) was bonded to appended pyrrole "N" and "N" of benzimidazole substituent present at the α-position of appended pyrrole, one chloro group, and one arene ring in a pseudo-octahedral geometry. The spectral studies revealed that the electronic properties of the BODIPY unit in BODIPY-Ru(II) complexes were significantly altered, and electrochemical studies indicated that the BODIPY-Ru(II) complexes exhibit one oxidation corresponding to Ru(II) to Ru(III) and one reduction corresponding to the BODIPY unit. The DFT/TD-DFT studies corroborated the experimental observations.

Rhodium-Catalyzed Intramolecular Nitrogen Atom Insertion into Arene Rings.

In this study, we describe the direct insertion of an intramolecular nitrogen atom into an aromatic C-C bond. In this transformation, carbamoyl azides are activated by a Rh catalyst and subsequently directly inserted into the C-C bond of an arene ring to access fused azepine products. This transformation is challenging, owing to the existence of a competitive C-H amination pathway. The use of a paddlewheel dirhodium complex Rh2(esp)2 effectively inhibited the undesired C-H insertion. Density functional theory calculations were performed to reveal the reaction mechanism and origin of the chemoselectivity of the Rh-catalyzed reactions. The novel fused azepine products are highly robust and allow for downstream diversification.

Crystallographic and spectroscopic characterization of two 1-phenyl-1H-imidazoles: 4-(1H-imidazol-1-yl)benzaldehyde and 1-(4-meth-oxy-phen-yl)-1H-imidazole.

The title compounds, C10H8N2O, (I), and C10H10N2O, (II), are two 1-phenyl-1H-imidazole derivatives, which differ in the substituent para to the imidazole group on the arene ring, i.e. a benzaldehyde, (I), and an anisole, (II). Both mol-ecules pack with different motifs via similar weak C-H⋯N/O inter-actions and differ with respect to the angles between the mean planes of the imidazole and arene rings [24.58 (7)° in (I) and 43.67 (4)° in (II)].

Fluxionality Modulating the Magnetic Anisotropy in Lanthanoarene [(ηCnRn)2Ln(II/III)] (n = 4-8) Single-Ion Magnets.

Lanthanoarenes have emerged as the best bet for the futuristic application of single-ion magnets in information storage devices. While dysprosocenium molecules with various substituents at the arene ring exhibit a very large blocking temperature, the corresponding Er(III) analogues do not, and this is reversed if the size of the arene ring is eight. Using a combination of ab initio CASSCF and DFT-based molecular dynamics (MD) study, we have explored 25 Dy(III)/Er(III)/Ho(II)/Tb(II)/Dy(II) arene complexes with the ring size varying from 4 to 8 to understand the differences observed and decipher the correlation of structure to the spin dynamics behavior. Among the oxidation state of +2 complexes studied, Tb(II) exhibits the highest barrier, with the Cp-Tb-Cp angle being linear. Further, one of the four-membered arene model studied exhibits a very large barrier of 1442 cm-1, suggesting a potential high-blocking SIM. While bulky substituents at the arene ring help increase the axiality and the CR-Ln-CR angle, this also fetches several agostic C-H···Ln interactions, which injects transverse anisotropy. Furthermore, MD coupled with the CASSCF study reveals that the fluxional behavior of the arene ring generates several rotational conformers that are even accessible at lower temperatures offering a shortcut to the magnetization relaxation process. The importance of structural fluctuations in controlling the magnetic anisotropy by choosing apt metal-ion/ring partners and the corresponding substituents has been highlighted to offer clues to the futuristic SIM design.

Isolation and Structures of Polyarene Palladium Nanoclusters.

We report that surrounding coordination of neutral six-membered arene rings affords molecularly well-defined organotransition metal nanoclusters. With the use of [2.2]paracyclophane as the face-capping arene ligand, we have isolated two polyarene palladium nanoclusters, one consisting of a hexakis-arene ligand shell and a hexagonal close-packed Pd13 anticuboctahedron trichloride core, and the other consisting of an octakis-arene ligand shell and a non-close-packed Pd17 square gyrobicupola dichloride core, both with Pd-Pd direct bonding. The μ4-facial coordination mode of arene was discovered through the structural characterization of the Pd13 cluster. Their Pd13 and Pd17 cores, which are distinct from the previously identified face-centered-cubic Pd13 core surrounded by seven-membered cycloheptatrienyl, are explained by stereochemical and theoretical analyses.

Crystal structures, Hirshfeld analysis, and energy framework analysis of two differently 3'-substituted 4-methylchalcones: 3'-(N=CHC6H4-p-CH3)-4-methylchalcone and 3'-(NHCOCH3)-4-methylchalcone.

Two crystal structures of chalcones, or 1,3-diarylprop-2-en-1-ones, are presented; both contain a p-methyl substitution on the 3-Ring, but differ with respect to the m-substitution on the 1-Ring. Their systematic names are (2E)-3-(4-methylphenyl)-1-(3-{[(4-methylphenyl)methylidene]amino}phenyl)prop-2-en-1-one (C24H21NO) and N-{3-[(2E)-3-(4-methylphenyl)prop-2-enoyl]phenyl}acetamide (C18H17NO2), which are abbreviated as 3'-(N=CHC6H4-p-CH3)-4-methylchalcone and 3'-(NHCOCH3)-4-methylchalcone, respectively. Both chalcones represent the first reported acetamide-substituted and imino-substituted chalcone crystal structures, adding to the robust library of chalcone structures within the Cambridge Structural Database. The crystal structure of 3'-(N=CHC6H4-p-CH3)-4-methylchalcone exhibits close contacts between the enone O atom and the substituent arene ring, in addition to C...C interactions between the substituent arene rings. The structure of 3'-(NHCOCH3)-4-methylchalcone exhibits a unique interaction between the enone O atom and the 1-Ring substituent, contributing to its antiparallel crystal packing. In addition, both structures exhibit π-stacking, which occurs between the 1-Ring and R-Ring for 3'-(N=CHC6H4-p-CH3)-4-methylchalcone, and between the 1-Ring and 3-Ring for 3'-(NHCOCH3)-4-methylchalcone.

π-Extension of the Tribenzotriquinacene Framework: Efficient Vinylene and Arylene Bay Bridging Based on a New C3 -Symmetric Key Derivative.

1,5,9-Tribromo-2,3,6,7,10,11-hexamethoxy-4b1 -methyltribenzotriquinacene, a C3 -symmetric TBTQ derivative, can be prepared conveniently and with high regioselectivity from readily available starting materials. It is a versatile key compound for the synthesis of other chiral 1,5,9-trifunctionalized TBTQ derivatives and π-extended congeners in which the bays of the TBTQ skeleton are bridged by vinylene and 1,2-arylene units. X-ray crystal structure analysis and UV-vis spectroscopy show that vinylene bay-bridging enables better π-conjugation with the arene rings of the TBTQ core than 1,2-arylene bay-bridging does.

Ruthenium(II)–Arene Complexes with Glycosylated NHC-Carbene Co-Ligands: Synthesis, Hydrolytic Behavior, and Binding to Biological Molecules

Ruthenium(II) complexes with a three-legged piano-stool structure based on an arene ring, an N-heterocyclic carbene (NHC)-carbene ligand with a peracetylated glucose moiety and two chlorides or one bidentate ligand, were prepared and characterized by spectroscopy and crystallography. In one case, the sugar substituent is replaced by an ethyl. The chirality of the sugar results in the formation of two diastereomers that interconvert through rotations around the Ccarbene–Ru and Carene–Ru bonds. In water, the complexes undergo a series of equilibrium hydrolysis steps involving the Ru–Cl bonds. The Ru–arene bond and the sugar acetyls are also partially hydrolyzed, and the selectivity of the process is governed by the nature of the arene and the pH of the solution. The reactivity of the compounds was studied against model nucleophiles and biological macromolecules. In the former case, mass experiments demonstrated a variety of binding modes with a trend reflecting the stability in aqueous environment. In the latter case, protein crystallography was used to characterize the preferential binding sites of one of the complexes. The X-ray structure of the adduct formed upon reaction of one representative complex with hen egg white lysozyme contains a Ru center, which retains the carbene ligand, close to the side chain of Asp119. In the adduct with bovine pancreatic ribonuclease, there are two protein molecules in the asymmetric unit. In one molecule, two Ru centers are located close to the side chains of His105 and of His119, which is the protein active site. In the second molecule, only one Ru center was found in the proximity of the side chain of His105. The Ru complexes also interact with calf-thymus DNA, although without displacing the intercalating probe EB. Finally, the complexes are essentially inactive against the human ovarian carcinoma A2780 cells, the cisplatin-resistant A2780cis cells, and the human embryonic kidney HEK293T cells.

Crystal structure and Hirshfeld surface analysis of N-[2-(5-methyl-furan-2-yl)phen-yl]-3-nitro-N-[(3-nitro-phen-yl)sulfon-yl]benzene-sulfonamide.

In the title compound, C23H17N3O9S2, C-H⋯O hydrogen bonds link adjacent mol-ecules in a three-dimensional network, while π-π stacking inter-actions, with centroid-centroid distances of 3.8745 (9) Å, between the furan and an arene ring of one of the two (3-nitro-phen-yl)sulfonyl groups, result in chains parallel to the a axis. The Hirshfeld surface analysis indicates that O⋯H/H⋯O (40.1%), H⋯H (27.5%) and C⋯H/H⋯C (12.4%) inter-actions are the most significant contributors to the crystal packing.