Aryl Interactions Research Articles

1,8-Bis(phenylethynyl)anthracene - gas and solid phase structures.

1,8-Bis(phenylethynyl)anthracene (1,8-BPEA) was synthesized by a twofold Kumada cross-coupling reaction. The molecular structure of 1,8-BPEA was determined using a combination of gas-phase electron diffraction (GED), mass spectrometry (MS), quantum chemical calculations (QC) and single-crystal X-ray diffraction (XRD). Five rotamers of the molecule with different orientations of phenylethynyl groups were investigated by DFT calculations. According to these, molecules of C2 symmetry with co-directional rotation of the phenylethynyl groups are predicted to exist in the gas phase at 498 K. This was confirmed by a GED/MS experiment at this temperature. The bonding of this conformer was studied and described in terms of an NBO-analysis. Dispersion interactions in the solid state structure and in the free molecule are discussed. In the solid this symmetry is broken; the asymmetric unit of the single crystal contains 3.5 molecules and a herringbone packing motif of π-stacked dimers and trimers. The π-stacking in the dimers is between the anthracene units, and the trimers are linked by π-stacking between phenyl and anthracene units. The interaction between these stacks can be described in terms of σ(C-H)π interactions.

Phase Behavior and Molecular Packing of Octadecyl Phenols and their Methyl Ethers at the Air/Water Interface

Noncovalent molecular interactions, such as hydrogen bonding and van der Waals forces, play an important role in self-assembling to supramolecular structures. To study these forces, we chose monolayers at the air/water interface to limit the possible arrangements of the interacting molecules. Furthermore, monolayers provide useful tools to understand and study interactions between molecules in a controlled and fundamental way. The phase behavior and molecular packing of the phenols 1-(4-hydroxyphenyl)-octadecane (5a), 1-(3,4-dihydroxyphenyl)-octadecane (6), and 1-(2,3,4-trihydroxyphenyl)-octadecane (3) and their methyl ethers in monolayers at the air/water interface have been examined by π/A isotherms, Brewster angle microscopy (BAM), grazing incidence X-ray diffraction (GIXD) measurements, and density functional theory (DFT) calculations. The phenols are synthesized by Friedel-Crafts acylation of methoxybenzenes, hydrogenation of the resulting aryl ketones, and cleavage of the aryl methyl ethers. In the π/A isotherms and in BAM, the phenols show patches of the solid condensed phase at large molecular areas and the monolayers collapse at high pressures. Furthermore, the dimensions of the unit cell obtained by GIXD measurements are compatible with an arrangement of the phenyl rings that allows one aryl ring to interact with four adjacent phenyl rings in an edge-to-face arrangement, which leads to a significant binding energy. The experimental data are in good agreement with DFT calculations of 2D crystalline benzene and p-cresol arrangements. The enhanced monolayer stability of phenol 5a can be explained by hydrogen bonds of the hydroxyl group with water and van der Waals forces between the alkyl chains and aryl-aryl interactions.

Synthesis and Characterization of Cobalt Complexes with Radical Anionic α-Diimine Ligands

Three cobalt complexes, [LCo(μ-Cl)]2·THF·Et2O (1), [LCo(η6-toluene)] (2), and [LCo]2 (3), where L = [(2,6-iPr2C6H3)NC(Me)]2, have been synthesized from reduction of the dichloro cobalt precursor [LCoCl2] by sodium or potassium metal. Single-crystal X-ray diffraction analyses reveal that the complexes display novel structures with the singly reduced form (L•–) of the α-diimine ligand: the dichloro-bridged binuclear complex 1, the mononuclear 2 with an η6-coordinated toluene molecule, and the dimer 3 through Co–aryl interactions of two [LCo] units. The compounds were further characterized by EPR and magnetic studies.

Synthesis, Structural Study and Antimicrobial Screening of Substituted Bis-benzothiazole Derivatives

A series of {4-(4-(6-substituted-benzothiazol-2-yl-amino)-3-carboxy-benzyl)-2-carboxy- phenyl}-6-substituted-benzothiazol-2-yl-amines have been synthesized by oxidative cyclization of 1-{4-(4-(3-aryl thiocarbamido)-3-carboxy-benzyl)-2-carboxy-phenyl}-3-aryl thiocarbamides using the solution of bromine in chloroform followed by the basification with dilute ammonium hydroxide solution. Initially 1-{4-(4-(3-aryl thiocarbamido)-3-carboxy-benzyl)-2-carboxy-phenyl}-3-aryl thio- carbamides were prepared by the interaction of different aryl isothiocyanates with 4,4'-methylene- bis-(anthranilic acid). The latter was obtained by treating the mixture of anthranilic acid and concentrated hydrochloric acid with 3% aqueous formaldehyde followed by neutralization with sodium hydroxide. The acetylation of bis-benzothiazoles afforded di-acetyl derivatives. The structures of synthesized compounds have been established on the basis of chemical transformation, elemental analysis, equivalent weight determination and IR, 1 H NMR spectral studies. The title compounds have been assayed for their biological activity against gram-positive as well as gram- negative microorganisms.

ChemInform Abstract: Aryl—Aryl Interactions as Directing Motifs in the Stereodivergent Iron‐Catalyzed Hydrosilylation of Internal Alkynes.

AbstractA well defined and active catalyst is used in the selective synthesis.

Three-Dimensional Network Polymeric Structure of (2-Amino-5 Ammoniopyridinium)[CuCl4]: Crystal Supramolecularity and Magnetic Properties

A single crystal structure determination of the complex (C5H9N3)CuCl4 [henceforth I] has been carried out. It crystallizes in the orthorhombic space group Cmca, with the cell parameters a=6.7053(5) A, b=22.4171(19) A, c=13.4173(9) A, V=2016.8(3) A3, and Z=8. In the complex, the anion is comprised of infinite zigzag chains of monochloro-bridged \(\mathrm{CuCl}_{4}^{2-}\) units ⋯–CuCl3–μ–Cl–CuCl3–μ–Cl–CuCl3–⋯ surrounded by the pyridinium-ammonium cations. The Cu ions are five-coordinate to chloride ions in a distorted square-pyramidal geometry with the zigzag chains formed by corner-sharing polyhedra. The Cu ion is located 0.151 A above the basal plane. In the crystal, there are four intermolecular hydrogen bonding interactions, linking the CuCl chains to the cations to form a 2D-network. The resulting 2D-networks are further linked by aryl⋯aryl (π⋯π) interactions within the cationic chains leading to a 3D-network. Variable temperature magnetic susceptibility data were fit to a one-dimensional S=1/2 antiferromagnetic chain model yielding C=0.44(1) emu-K/mol-Oe and J=−37(1) K.

Interactions in Supramolecular Complexes Involving Arenes: Experimental Studies

The process of learning by doing has fueled supramolecular chemistry and, more specifically, the understanding of noncovalent aromatic interactions in synthetic and natural systems. The preparation of new host molecules and the investigation of their complexations have produced many insights into significant noncovalent binding mechanisms. In this Account, we attempt to discuss significant binding contributions involving aromatic units and their practical applications. We use typical examples from our group and the literature, but this Account is not a comprehensive view of the field. Other than systems with saturated frameworks, host compounds based on arenes offer better controlled conformations and active interactions with many guest molecules. Because of their fluorescent properties, larger aryl systems are particularly suitable for sensors. The noncovalent interactions observed with different supramolecular complexes can be compared and exploited for interactions with biopolymers such as nucleic acids. Complexes formed with cyclophanes have been a constant source of inspiration for understanding noncovalent forces and their use for the design of functional supramolecular systems. Other than cyclodextrins or ionophores, which occur in nature, arene-based macrocycles are synthetic and provide more opportunities for structural variations than other macrocycles. These derivatives allow researchers to study and to exploit an unusually broad variety of binding mechanisms in both aqueous and organic media. Systematic analyses of complexes with different substituents and structures in solution, based also on flat aromatic systems such as porphyrins, can lead to a consistent picture of the noncovalent forces that dominate in these systems. These studies have elucidated attractive interactions between many heteroatoms and π systems including cyclopropanes . Through systematic analysis of the equilibrium measurements one can derive binding free energy increments for different interactions. The increments are usually additive and provide predictive tools for the design of new supramolecular systems, benchmarks for computational approaches, and an aid for drug design. In aqueous media, the major noncovalent forces between different aryl systems or between arenes and heteroatoms of larger polarizibility are dispersive, and hydrophobic forces play a minor role. In several examples, we show that electrostatic forces also contribute significantly if donor and acceptor groups show complimentarity. In early investigations, researchers found cation-π and, to a lesser degree, anion-π interactions with several cyclophanes in systems where the host or the guest molecules bear charges in an orientation that facilitates contact between charged and aryl portions of the molecules. In supramolecular complexes, hydrogen bonding effects are usually only visible in apolar media, but very strong acceptors such as phenolate anions can also work in water. To facilitate potential applications, researchers have primarily developed water-soluble, arene-containing receptors through the implementation of permanent charges. Supramolecular complexes that mimic enzymes can also rely on aryl interactions. Examples in this Account illustrate that the conformation of host-guest complexes may differ significantly between the solid and solution state, and suitable spectroscopic methods are needed to observe and control these conformations.

Alkali Metal, Magnesium, and Zinc Complexes of Bis(chalcogenophosphinoyl)methanide Ligands

AbstractThe complexes [Na{HC(PPh2S)2}] (Na3a), [Na{HC(PPh2Se)2}] (Na3b), [K{HC(PPh2S)2}]∞ (K3a), [K{HC(PPh2Se)2}]∞ (K3b), [Mg{HC(PPh2S)2}2] (Mg(3a)2), [Mg{HC(PPh2Se)2}2] (Mg(3b)2), and [Zn{HC(PPh2S)2}2] [Zn(3a)2] have been prepared in good yields (69–92 %) by treatment of the neutral ligands H2C(PPh2E)2 (1a, E = S; 1b, E = Se) with [Na{N(SiMe3)2}] (Na3a), NaNH2 (Na3b), [K{N(SiMe3)2}] (K3a and K3b), [Mg{N(SiMe3)2}2] [Mg(3a)2 and Mg(3b)2], or Me2Zn [Zn(3a)2] as base in THF/toluene. These compounds were characterized in solution by multinuclear (1H, 13C, 31P, and 77Se) NMR spectroscopy and the X‐ray structures of K3a, K3b, Mg(3a)2, Mg(3b)2, and Zn(3a)2 were determined. In the solid state, the E,E′‐chelated ligands in K3a and K3b also engage in potassium–chalcogen interactions with adjacent molecules to form one‐dimensional ladder structures. With K3a, both sulfur atoms of the ligand are involved in chelation leading to four‐membered K2S2 rings, whereas only one selenium atom is tricoordinated in K3b; significant potassium···aryl interactions are also observed in both structures. In the homoleptic magnesium complexes Mg(3a)2 and Mg(3b)2, the E,E′ chelation by the methanide ligands is supplemented by weak, unequal Mg···C interactions [2.781(10) and 3.199(7) Å for Mg(3a)2; 3.331(8) and 3.217(7) Å for Mg(3b)2]. The zinc complex Zn(3a)2 is isostructural with the previously reported selenium analogue Zn(3b)2. The X‐ray structures of the S,S′‐chelated complex [(TMEDA)Li3a] as well as new polymorphs of 1a and 1b are also reported.

Aryl–aryl interactions as directing motifs in the stereodivergent iron-catalyzed hydrosilylation of internal alkynes

The defined Fe hydride complex FeH(CO)(NO)(Ph(3)P)(2) is highly active as a catalyst for selective hydrosilylation of internal alkynes to vinylsilanes. Depending on the silane employed either E- or Z-selective hydrosilylation products were formed in excellent yields and good to excellent stereoselectivities.

Molecular Tectonics. Use of Br•••aryl Supramolecular Interactions for the construction of Organized Networks from 9,9’-spirobifluorene in the Crystalline State

Numerous studies, many based on statistical analyses of structural data from the Cambridge Structural Database (CSD, have highlighted the importance of halogen···aryl interactions. Although the exact value of the binding energy is still a subject of debate, it is generally agreed that such interactions can play an important role in crystal packing. For example, previous work by Desiraju and collaborators has shown that Br···aryl interactions generate characteristic supramolecular motifs, which may be useful for designing molecular solids [2]. With this goal in mind, we set out to use 9,9’spirobifluorene (SBF) or tetrabrominated SBF derivatives as tectons [3] and to see if Br···aryl interactions can be used to build predictable molecular networks. Several features made the SBF core an attractive candidate for this study: 1) SBF has D2d symmetry, is rigid and orients its aromatic rings and their substituents in distinct directions of space; 2) the synthesis of SBF derivatives has been described; and 3) derivatives of SBF tend to crystallize readily, frequently as inclusion complexes, which allows the study of interactions between the network and included guests. In the first part of our work, the two different tetrabromo-SBFs (substituted in the meta and para positions, respectively, relative to the spiro center) were synthesized either by a literature procedure or through a new route. Crystals were grown and the structures were solved. Both structures are close packed, and the molecules are linked together by Br···Ar interactions and also by Br···Br contacts. In the second part of our work, we co-crystallized unsubstituted SBF with small brominated guests that orient 1, 2, 3 or 4 atoms of bromine in distinct directions. The structures of four co-crystals were solved, and analysis reveals the following points: 1) There are at most only a few direct interactions (CH···) between the SBF units themselves; 2) by engaging in Br···aryl interactions, the brominated guests play a role of connector between SBF units; iii) in this way, Br···aryl interactions direct the packing of the crystal structures.

Stabilization of Excited State Using Through-Space Interaction between Independent π-Systems Mediated by a peri-Substituted Hydroxy Group in 1-Arylnaphthalenes: Unexpected Blue Emission of 1,3,5-Tris(peri-hydroxynaphthyl)benzene

Abstract The control of photoluminescence wavelength is important for the design of emitting materials, and compounds bearing aryl–aryl bonds are considered to be useful candidates for the synthesis of these materials. However, the biaryl system lacks an efficient linkage of independent conjugated moieties because of a structure that, rather than planar, is made up of almost perpendicular dihedral angles due to steric effect. In this paper, we report a novel method to link independent π-systems in biaryl compounds. The oxy-substituents at the peri-position in 1-arylnaphthalene systems, which are biaryl compounds, showed interesting and unexpected photophysical properties of a bathochromic shift of emission. In particular, peri-OH-substituted arylnaphthalenes showed a large bathochromic shift that was induced by polarization based on intramolecular OH–aryl interaction. Quantum chemical (TDDFT) calculations accurately reproduced the large bathochromic shifts of peri-OH-substituted arylnaphthalenes. The through-space interaction between the peri-substituted OH and aryl groups generated an unexpected extended conjugation system. The substituting position of OH in 1-arylnaphthalenes is quite critical, because the hydroxy group mediates the independent π-systems to expand conjugation. Based on this concept, 1,3,5-tris(peri-hydroxynaphthyl)benzene had characteristic photophysical properties, giving an unexpected blue emission.

ChemInform Abstract: Pb···π Aryl Interactions as Supramolecular Synthons.

AbstractReview: 64 refs.

ChemInform Abstract: The Use of C3-Symmetric Tripodal Ligands in Crystal Engineering

Abstract The use of chiral tripodal ligands in the assembly of non-centrosymmetric crystal lattice is illustrated with the triamide ligand tris[ N -( S )-(−)-(α)-methylbenzylcarbamoylmethyl]amine (H 3 1 S -mbz ). In the crystal phase, this tripodal ligand assembles into C 3 -symmetric chiral columns that are stabilized by hydrogen bonds and aryl–aryl interactions. Intercolumnar assembly is driven by the clustering of edge-to-face aryl and methyl-to-aryl interactions. Thrice deprotonation of H 3 1 S -mbz and binding of an Ni(II)–F moiety also produces a non-centrosymmetric lattice which is noteworthy for its six-fold symmetric open framework structure and the alignment of all the molecular Ni–F bonds in the lattice along the crystallographic c -axis. Crystal data: H 3 1 S -mbz crystallizes in the rhombohedral system, space group R 3 with cell dimensions a = b =22.352(5) A, c =4.882(1) A, α = β =90°, γ =120°, and Z =3; [NEt 4 ] 2 [Ni 1 S -mbz (F)] crystallizes in the hexagonal system, space group P 6 3 with cell dimensions a = b =12.0780(1) A, c =18.1231(1) A, α = β =90°, γ =120°, and Z =2.

Probing Substituent Effects in Aryl−Aryl Interactions Using Stereoselective Diels−Alder Cycloadditions

Stereoselective Diels-Alder cycloadditions that probe substituent effects in aryl-aryl sandwich complexes were studied experimentally and theoretically. Computations on model systems demonstrate that the stereoselectivity in these reactions is mediated by differential pi-stacking interactions in competing transition states. This allows relative stacking free energies of substituted and unsubstituted sandwich complexes to be derived from measured product distributions. In contrast to gas-phase computations, dispersion effects do not appear to play a significant role in the substituent effects, in accord with previous experiments. The experimental pi-stacking free energies are shown to correlate well with Hammett sigma(m) constants (r = 0.96). These substituent constants primarily provide a measure of the inductive electron-donating and -withdrawing character of the substituents, not donation into or out of the benzene pi-system. The present experimental results are most readily explained using a recently proposed model of substituent effects in the benzene sandwich dimer in which the pi-system of the substituted benzene is relatively unimportant and substituent effects arise from direct through-space interactions. Specifically, these results are the first experiments to clearly show that OMe enhances these pi-stacking interactions, despite being a pi-electron donor. This is in conflict with popular models in which substituent effects in aryl-aryl interactions are modulated by polarization of the aryl pi-system.

Pb···π Aryl Interactions as Supramolecular Synthons

A survey of lead (Pb) structures containing Pb···π aryl interactions has been conducted. Such contacts usually lead to zero- or one-dimensional aggregates with rare examples of two- and three-dimensional architectures. The Pb···π aryl interactions are found only in crystal structures containing lead(ii) centres and arise as a result of electron donation of the lead-bound lone pair of electrons to the lowest unoccupied molecular orbital of the accepting aryl ring. The prevalence of Pb···π interactions as a supramolecular synthon is relatively low, occurring in ~3% of all structures containing lead and at least one aryl ring, but these are more likely to form compared with Sn···π interactions.

β-Diketiminato Nickel(I) Complexes with Very Weak Ligation Allowing for H2 and N2 Activation

Reaction of [LtBuNiBr] (LtBu = [HC(C(CMe3)NC6H3(iPr)2)2]−) with KC8 in toluene solution yields the complex [LtBuNi(toluene)], 1, where toluene is bound in a η2 mode via a C═C unit of the aromatic ring, as revealed by single-crystal X-ray crystallography and DFT calculations (B3LYP/6-31G*). Performing the same reaction in hexane as the solvent did not lead to a traceable product, so that the β-diketiminato ligand system was changed from LtBu to the less bulky LMe (LMe = [HC(CMeNC6H3(iPr)2)2]−). Reduction of [LMeNiBr]2 with KC8 in diethyl ether led to [LMeNi]2, 2, with intramolecular Ni−aryl interactions, while employment of [LMeNi(μ-Br)2Li(thf)2] as a precursor for a reaction with KC8 in OEt2 led to the complex [LMeNi(μ-Br)Li(thf)2]2, 3. Both complexes 2 and 3 could be fully characterized, also with the aid of XRD, and their reactivity with respect to H2 and N2 was examined. It turned out that they oxidatively add H2 to give the known compound [LMeNi(μ-H)]2, I, while the reaction with N2 provides the dinit...

Pyridine and benzonitrile adducts of bis(4-nonafluorobiphenyl)zinc

Treatment of (Ar F′) 2Zn(OEt 2) 2 (Ar F′ = 4-C 6F 5C 6F 4) with 2 equiv. of benzonitrile, 4-(phenyl)benzonitrile, 4-(pyrrolyl)benzonitrile, pyridine, 4-(phenyl)pyridine or 4-(pyrrolyl)pyridine in dichloromethane afforded the corresponding adducts (Ar F′) 2ZnL 2 in near quantitative yield. The 2,2′-bipyridine adduct was prepared similarly. Multinuclear NMR spectroscopy indicated that zinc′s four-coordinate character was maintained in solution. The pyridine complex crystallized from dichloromethane with a solid-state structure free of face-to-face aryl–aryl interactions. In contrast, the 4-(pyrrolyl)pyridine adduct crystallized from both dichloromethane and 1,2-difluorobenzene, with solvent of crystallization, but otherwise essentially identical supramolecular architectures assembled through aryl–aryl synthons, including a face-to-face pentafluorophenyl–pyrrole interaction.

Origin of substituent effects in edge-to-face aryl–aryl interactions

Substituent effects in the edge-to-face configuration of the benzene dimer have been studied using modern density functional theory. An accurate interaction potential energy curve has been computed for the unsubstituted dimer using ab initio methods with large basis sets. The recommended binding energy for the edge-to-face benzene dimer is 2.31 kcal mol−1, estimated at the counterpoise-corrected CCSD(T)/aug-cc-pVTZ level of theory. For both edge-ring and face-ring-substituted dimers, interaction energies correlate with σm for the substituents, indicating that substituent effects can be understood qualitatively in terms of simple electrostatic effects, although in the latter case dispersion results in some scatter in the data. In contrast to prevailing models of substituent effects in benzene dimers, polarization of the π-system of the substituted ring does not induce substituent effects. For edge-ring-substituted dimers, substituent effects arise from differential electrostatic interactions between the hydrogens on the substituted ring and the π-cloud of the face ring and direct interactions of the substituents with the unsubstituted ring. For face-ring-substituted dimers, substituent effects arise from direct electrostatic and dispersion interactions of the substituents with the edge ring. Substituents with σm > 0.12 favour edge ring substitution while for σm < 0.12 substitution on the face ring is preferred.

A structural survey of metal⋯π heteroaromatic supramolecular synthons for metal = tellurium, tin, and gold

A survey of tellurium, tin and gold structures containing metal⋯π heteroaromatic interactions has been conducted, and their occurrence correlated with previously described metal⋯π aryl interactions. Metal⋯π heteroaromatic interactions are found for all three metals when the heteroaromatic ring was a pyridine/pyridine-derivative, and these contacts lead usually to 0-D or 1-D aggregates with rare examples of 2-D and 3-D architectures. For each of tellurium and tin, metal⋯π aryl interactions are more likely to form over metal⋯π pyridine interactions, while the reverse is true in the case of gold. These observations are readily correlated with the influence of increasing electron density in the pyridine compared with an aryl ring. In the case of tellurium and tin, for which the metal⋯π interaction involves a metal-based lone pair of electrons being donated to the LUMO of the aryl group, increasing the electron density of the aromatic ring naturally decreases the probability of forming this type of interaction. In the case of gold, where the metal⋯π interaction involves the donation of electron density from the aromatic ring to the gold centre, increasing the electron density of the aromatic ring favours such an interaction. At least for the metals surveyed, metal⋯π interactions are observed in a significant number of their crystal structures, for example up to 6% of all tellurium structures feature Te⋯π aryl interactions as a supramolecular synthon.

Silver⋯X–aryl (X = I and Br) interaction in a network assembly with a flexible polynuclear silver–ethynide supramolecular synthon

In a series of five new silver(I) ethynide complexes, the invariable appearance of the μ4 and μ5 ligation modes of the ethynide moiety affirms the general utility of the supramolecular synthon p-X–C6H5OCH2C≡C⊃Agn (X = I, Br; n = 4, 5) in the assembly of coordination networks, in which the silver⋯halogen–aryl interaction plays an important role.