Benzene Complexes Research Articles

Photodissociation Spectroscopy and Photofragment Imaging of the Mg+(Benzene) Complex

Photodissociation Spectroscopy and Photofragment Imaging of the Mg⁺(Benzene) Complex

Effect of coordination mode of thiosemicarbazone on the biological activities of its Ru(II)-benzene complexes: Biomolecular interactions and anticancer activity via ROS-mediated mitochondrial apoptosis

Ru(II)-benzene complexes (P1 and P2) were synthesized using a thiosemicarbazone ligand (L1) in two different coordination modes, monodentate S and bidentate N,S, through carefully adjusted reaction conditions. Comprehensive characterization of the complexes was achieved through single crystal X-ray diffraction, revealing a piano-stool geometry around the Ru(II) ion. To evaluate the binding capabilities of the complexes towards CT DNA and BSA, UV–Vis and/or hydrodynamic methods were utilized. Docking studies further validated the intercalative binding mode with DNA, in agreement with the experimental findings, and identified specific BSA amino acids involved in the binding interactions. Based on the results of binding studies, cytotoxicity of the ligand and complexes was appraised in various cancer and normal cell lines alongside the commercial pharmaceutics. Complexes P1 and P2 displayed a promising activity against MDA-MB-231 [IC50 = 5.11 (P1) and 3.48 μM (P2)] and PANC-1 [IC50 = 7.20 (P1) and 4.85 μM (P2)] cancer cells; with the bidentate system (P2) exhibiting a higher activity than its monodentate congener P1, although both of them showed superior activity than the reference drugs. Various bioassays including Western blot analysis revealed the mode of cell death to be apoptosis, which was further concluded to be via the ROS-mediated mitochondrial signaling pathway.

Biological assays, electrochemical behavior, and theoretical DFT calculations of Ru(II) complexes of chiral phosphinite based based on β-amino alcohols: Transfer hyrogenation of ketones using a HCOOH/Et3N mixture

Synthesis of two phosphinite ligands based on β-amino alcohols, in high yields has been demonstrated. When we treated [Ru(arene)(μ-Cl)Cl]2 {arene:p-cymene,benzene} with chelating phosphinite ligands, we obtained neutral Ru(II)-complexes possessing the general formula [Ru(arene)phosphiniteCl2]. The structure of the ligands and complexes was confirmed using analytical and spectroscopic techniques. The quantum chemical calculations were carried out for the ruthenium complexes at the DFT/CAM-B3LYP level of theory in gas phase. The phosphinite complexes were subjected to cyclic voltammetry studies in order to determine the energies of HOMO and LUMO levels and to estimate their electrochemical and some electronic properties. Organic complex-based memory substrates were immobilized using TiO2-modified ITO electrodes, and the memory functions of phosphinite-based organic complexes were verified by chronoamperometry (CA) and open-circuit potential amperometry (OCPA). In the present study, the antioxidant potentials of ruthenium-based p-cymene and benzene complexes through DPPH radical scavenging, metal chelating, and reducing power activities were also determined. In addition, DNA binding abilities and antimicrobial activities of these complexes against pathogenic bacteria were studied. Finally, the ruthenium complex, (2S)-1-{[(2S)-2-[(diphenylphosphanyl)oxy]propyl][(1R)-1-phenylethyl]amino}propan-2-yldiphenyl phosphinitobis[dichloro(η6-benzene)ruthenium(II)] also catalyzed asymmetric transfer hydrogenation of acetophenone with high conversion (up to 99%) and good enantioselectivity (ee up to 89 %), in the existence of formic acid and triethylamine in dichloromethane medium under air atmosphere.

Cobalt-59 NMR relaxation times of symmetric tris(γ-substituted-acetylacetonato)cobalt(III) complexes in benzene

Cobalt-59 NMR relaxation times, T1(59Co), and chemical shifts, δ(59Co), of symmetric tris(γ-substituted-acetylacetonato)cobalt(III) complexes, [Co(acac-X)3], which have chloride, bromide, nitro, and phenyl groups at the methine carbon atoms in the chelate ligands, have been measured in benzene at four temperatures between 284 and 319 K. In view of the viscosity dependence of 1/T1(59Co), the 59Co relaxation is caused by the reorientation of the static electric field gradient at the nucleus in every complex. Assuming that the rotational volume is replaced by the van der Waals volume, the nuclear quadrupolar coupling products, {(1 + ηq2/3)(eQq/h)2}1/2, were obtained for the series of [Co(acac-X)3] complexes in benzene. The negative correlation between {(1 + ηq2/3)(eQq/h)2}1/2 and δ(59Co) was observed for the four complexes [Co(acac)3], [Co(acac-Cl)3], [Co(acac-Br)3], and [Co(acac-NO2)3] except for [Co(acac-Ph)3]. This discrepancy strongly suggests that the rotational volume of the propeller-like [Co(acac-Ph)3] complex with the protruding phenyl groups cannot be simply treated as the van der Waals volume, different from the other almost spherical complexes. Actually, the estimation of the rotational volumes from the distances between the central cobalt and g-substituents gave much better correlation between {(1 + ηq2/3)(eQq/h)2}1/2 and δ(59Co) for all the complexes including [Co(acac-Ph)3].

Main-Group Metal Complexes of Benzene: Predicted Features of Stabilization and Isomerization.

Complexes of metal atoms with organic molecules represent a broad variety of systems with many important applications, e.g., in metal-organic interfaces and organometallic chemistry. One class involves aromatic species like benzene (Bz). Here, such complexes with second-group metals are investigated systematically in terms of structure and shape, stability and isomerization, charge distribution and aromaticity, and polarity and IR spectra. Three groups of isomers are identified, varying from metastable to stable ones, in effect featuring "physisorption" or "chemisorption". In particular, the high polarity of binary complexes and nonadditive stabilization of ternary systems for some isomers are found. Also, the Bz component's shape alteration for different isomers and system sizes and related aromaticity variations are predicted to be considerable. Property evolution for the series of metal components is analyzed.

Weak and strong π interactions between two monomers—assessed with local vibrational mode theory

We introduce in this work a unique parameter for the quantitative assessment of the intrinsic strength of the π interaction between two monomers forming a complex. The new parameter is a local intermonomer stretching force constant, based on the local mode theory, originally developed by Konkoli and Cremer, and derived from the set of nine possible intermonomer normal vibrational modes. The new local force constant was applied to a diverse set of more than 70 molecular complexes, which was divided into four groups. Group 1 includes atoms, ions, and small molecules interacting with benzene and substituted benzenes. Group 2 includes transition metal hydrides and oxides interacting with benzene while Group 3 involves ferrocenes, chromocenes, and titanium sandwich compounds. Group 4 presents an extension to oxygen π–hole interactions in comparison with in-plane hydrogen bonding. We found that the strength of the π interactions in these diverse molecular complexes can vary from weak interactions with predominantly electrostatic character, found, e.g., for argon–benzene complexes, to strong interactions with a substantial covalent nature, found, e.g., for ferrocenes; all being seamlessly described and compared with the new intermonomer local mode force constant, which also outperforms other descriptors such as an averaged force constant or a force constant guided by the electron density bond paths. We hope that our findings will inspire the community to apply the new parameter also to other intermonomer π interactions, enriching in this way the broad field of organometallic chemistry with a new efficient assessment tool.

A Theoretical Study of the Halogen Bond between Heteronuclear Halogen and Benzene.

Halogen bonds play an important role in many fields, such as biological systems, drug design and crystal engineering. In this work, the structural characteristics of the halogen bond between heteronuclear halogen XD (ClF, BrCl, IBr, ICl, BrF and IF) and benzene were studied using density functional theory. The structures of the complexes between heteronuclear halogen and benzene have Cs symmetry. The interaction energies of the complexes between heteronuclear halogen XD (ClF, BrCl, IBr, ICl, BrF and IF) and benzene range from -27.80 to -37.18 kJ/mol, increasing with the increases in the polarity between the atoms of X and D, and are proportional to the angles of a between the Z axis and the covalent bond of heteronuclear halogen. The electron density (ρ) and corresponding Laplacian (∇2ρ) values indicate that the interaction of the heteronuclear halogen and benzene is a typical long-range weak interaction similar to a hydrogen bond. Independent gradient model analysis suggests that the van der Waals is the main interaction between the complexes of heteronuclear halogen and benzene. Symmetry-adapted perturbation theory analysis suggests that the electrostatic interaction is the dominant part in the complexes of C6H6⋯ClF, C6H6⋯ICl, C6H6⋯BrF and C6H6⋯IF, and the dispersion interaction is the main part in the complexes of C6H6⋯BrCl, C6H6⋯IBr.

Synergy effect of aluminum complexes during the ring-opening polymerization of ε-caprolactone: Inductive effects between dinuclear metal catalysts

In this study, a series of mononuclear complexes and dinuclear aluminum complexes bridged by 1,3- and 1,4-substituted phenyl ligands were synthesized, and their activities for the ring-opening polymerization (ROP) of ε-caprolactone (CL) were investigated. All the dinuclear aluminum complexes exhibited higher catalytic activity than did the corresponding mononuclear Al complexes (2–6-fold for the kobs values), and most of the dinuclear Al complexes bearing 1,3-substituted phenyl ligands exhibited higher activity than did the corresponding dinuclear Al complexes bearing 1,4-substituted phenyl ligands (1.5–3-fold for the kobs values). The only exceptions were the Al complexes bearing benzothiazole ligands, for which the dinuclear Al complex with 1,4-bis(benzothiazol-2-yl)benzene exhibited higher catalytic activity than did the corresponding 1,3- bis(benzothiazol-2-yl)benzene complex. This higher activity of the dinuclear Al complexes was attributed to one of the Al atoms in the dinuclear Al system being regarded as an electron-withdrawing group. This group influenced the other Al atom through associated aromatic ligands to enhance the catalytic activity for the ROP of CL.

Calculations and measurements for the rotational spectrum and structure of the cyclopentadienyl thallium – benzene complex

Calculations on the structure of the cyclopentadienyl thallium – benzene complex were made using Gaussian-G16 and Spartan programs. Calculations converged to symmetric top and asymmetric top structures. Rotational transition frequencies for the cyclopentadienyl thallium – benzene complex were measured in the 4.5–8.3 GHz range using a Flygare-Balle pulsed beam microwave spectrometer. The basic spectrum from the preliminary experiments exhibited splittings of the observed transitions which would not be expected for a rigid symmetric top molecule. 11 of the measured transitions were assigned to an asymmetric top structure and fit, yielding rotational constants A = 1136.8(11) B = 378.44(11) MHz and C = 375.173(79) MHz.

Dispersion Interactions in Exciton-Localized States. Theory and Applications to π-π* and n-π* Excited States.

We address the problem of intermolecular interaction energy calculations in molecular complexes with localized excitons. Our focus is on the correct representation of the dispersion energy. We derive an extended Casimir-Polder formula for direct computation of this contribution through second order in the intermolecular interaction operator V̂. An alternative formula, accurate to infinite order in V̂, is derived within the framework of the adiabatic connection (AC) theory. We also propose a new parametrization of the VV10 nonlocal correlation density functional, so that it corrects the CASSCF energy for the dispersion contribution and can be applied to excited-state complexes. A numerical investigation is carried out for benzene, pyridine, and peptide complexes with the local exciton corresponding to the lowest π–π* or n– π* states. The extended Casimir-Polder formula is implemented in the framework of multiconfigurational symmetry-adapted perturbation theory, SAPT(MC). A SAPT(MC) analysis shows that the creation of a localized exciton affects mostly the electrostatic component of the interaction energy of investigated complexes. Nevertheless, the changes in Pauli repulsion and dispersion energies cannot be neglected. We verify the performance of several perturbation- and AC-based methods. Best results are obtained with a range-separated variant of an approximate AC approach employing extended random phase approximation and CASSCF wave functions.

Theoretical Study of Light-Induced Crosslinking Reaction Between Pyrimidine DNA Bases and Aromatic Amino Acids

Low-lying electronic excited states and their relaxation pathways as well as energetics of the crosslinking reaction between uracil as a model system for pyrimidine-type building blocks of DNA and RNA and benzene as a model system for aromatic groups of tyrosine (Tyr) and phenylalanine (Phe) amino acids have been studied in the framework of density functional theory. The equilibrium geometries of the ground and electronic excited states as well as the crossing points between the potential energy surfaces of the uracil–benzene complex were computed. Based on these results, different relaxation pathways of the electronic excited states that lead to either back to the initial geometry configuration or the dimerization between the six-membered rings of the uracil–benzene complex have been identified, and the energetic conditions for their occurrence are discussed. It can be concluded that the DNA–protein crosslinking reaction can be induced by the external electromagnetic field via the dimerization reaction between the six-membered rings of the uracil–benzene pair at the electronic excited-state level of the complex. In the case of the uracil–phenol complex, the configuration of the cyclic adduct (dimerized) conformation is less likely to be formed.

Substituent effects on the regium-π stacking interactions between Au6 cluster and substituted benzene.

The regium-π stacking interactions in the Au6···PhX (X = H, CH3, OH, OCH3, NH2, F, Cl, Br, CN, NO2) complexes are studied using quantum chemical methods. The present study focuses on the different effects of electron-donating and electron-withdrawing substituent. The structure and binding strength of the complexes are examined. The interactions between Au6 cluster and various substituted benzene become strengthened relative to the Au6···benzene complex. The interaction region indicator analysis was performed, and the interaction region and interaction between the substituent and Au6 cluster are discussed. It is found that the substituent effects on the regium-π stacking interactions between Au6 cluster and substituted benzene are different from π···π interactions of benzene dimer. Energy decomposition analysis was carried out to study the nature of regium-π stacking interactions, and the substituent effects are mainly reflected on the electrostatic interaction and dispersion.

Hydroamination of Dihapto-Coordinated Benzene and Diene Complexes of Tungsten: Fundamental Studies and the Synthesis of γ-Lycorane.

Reactions are described for complexes of the form WTp(NO)(PMe3)(η2-arene) and various amines, where the arene is benzene or benzene with an electron-withdrawing substituent (CF3, SO2Ph, SO2Me). The arene complex is first protonated to form an η2-arenium species, which then selectively adds the amine. The resulting η2-5-amino-1,3-cyclohexadiene complexes can then be subjected to the same sequence with a second nucleophile to form 3-aminocyclohexene complexes, where up to three stereocenters originate from the arene carbons. Alternatively, 1,3-cyclohexadiene complexes containing an ester group at the 5 position (also prepared from an arene) can be treated with acid followed by an amine to form trisubstituted 3-aminocyclohexenes. When the amine is primary, ring closure can occur to form a cis-fused bicyclic γ-lactam. Highly functionalized cyclohexenes can be liberated from the tungsten through oxidative decomplexation. The potential utility of this methodology is demonstrated in the synthesis of the alkaloid γ-lycorane. An enantioenriched synthesis of a lactam precursor to γ-lycorane is also described. This compound is prepared from an enantioenriched version of the tungsten benzene complex. Regio- and stereochemical assignments for the reported compounds are supported by detailed 2D-NMR analysis and 13 molecular structure determinations (SC-XRD).

Hydrogen adsorption on metal‐functionalized benzene and B‐substituted benzene

Hydrogen storage properties of metal doped benzene complexes vary with positions of boron atom substitution in a benzene ring at MP2/6-311++g(d,p) level. Two carbon atoms of a benzene (C6H6) ring positioned at 1-2, 1-3 and 1-4 are replaced by two boron atoms and the structures named as BB1-2, BB1-3 and BB1-4, respectively. Further, pristine as well as boron substituted benzene complexes are decorated with Li, Be,Ti and Ca atoms. C6H6Li, BB1-2Li, BB1-3Li and BB1-4Li complexes can interact with three, three, two and three H2 molecules, respectively, with 6.64, 6.82, 4.65 and 6.82 wt% H2 uptake capacities. Only one H2 molecule gets adsorbed on each C6H6Be, BB1-2Be, BB1-3Be and BB1-4Be complexes with respective H2 uptake capacity of 2.26, 2.32, 2.32 and 2.32 wt%. One additional hydrogen molecule gets adsorbed on Ti(Ca) decorated boron substituted benzene than C6H6Ti(C6H6Ca) with respective H2 uptake capacity 7.54(7.98) and 6.02(9.46) wt%. Electron density of metal atom gets altered significantly after adsorption of H2 molecules. The averaged H2 adsorption energies with Gibbs free energy correction ΔEG are found to be negative for all Li- and Ca-doped complexes indicates thermodynamically unfavorable H2 adsorption where ΔEG values are positive for all Ti- and Be-doped complexes at room temperature indicating thermodynamically favorable H2 adsorption. Interaction between H2 molecules and Be- as well as Ti-doped complexes is found to be stronger than Li- and Ca-doped complexes. Be-doped complexes considered do not satisfy the target set by DOE regarding H2 uptake capacity. Boron substitution improves molecular hydrogen uptake of Benzene-Ti complex by 1.52 wt% and satisfy the target set by DOE. C6H6Li, BB1-2Li, BB1-3Li and BB1-4Li complexes cannot be used for hydrogen storage since hydrogen adsorption on these complexes is endothermic. Ti-doped boron substituted complexes are found to more promising H2 storage material because of their higher H2 uptake capacity as well as their strong interaction with adsorbed hydrogen molecules than Li-, Be- and Ca-doped complexes.

Complex Formation and Dissociation Dynamics on Amorphous Silica Surfaces.

Benzene complex formation and dissociation dynamics with silanols on the amorphous silica surfaces of nanoporous SiO2, from a benzene/carbon tetrachloride solution, were measured by the growth of off-diagonal peaks in the two-dimensional infrared (2D IR) chemical exchange spectrum of the isolated Si-OD stretch. The presence of two types of isolated silanols, termed type I and II, was revealed, with dissociation time constants of 82 and 4.0 ps, respectively. The type I silanols are associated with the main IR absorption feature in the Si-OD stretching region, while the type II silanols give rise to a broader shoulder to lower frequency. Polarization selective pump-probe (PSPP) measurements provided the vibrational lifetimes and orientational relaxation rates of the two silanols in the CCl4 (free) and benzene (complex) environments. The type II silanols constitute roughly 30% of the isolated silanol population and exhibit a substantially faster rate of vibrational relaxation, making the type I dynamics the dominant contribution to the PSPP and 2D IR signals. From the measured dissociation times, the enthalpies of formation for the two surface complexes were obtained, with the formation of the type I complex being significantly more exothermic. As the type II site is preferentially removed from the amorphous silica surface with increasing activation temperature, the results provide a reasonable explanation for the increased exothermicity of benzene adsorption on silica with increasing activation temperature in previous calorimetry experiments.

A comparative study of interplay effects between the cation-π and intramolecular hydrogen bond interactions in the various complexes of methyl salicylate with Mn+, Fe2+, Co+, Ni2+, Cu+, and Zn2+ cations

The interplay among two important noncovalent interactions involving aromatic ring is studied by means of density functional theory (DFT) calculations on complexes of methyl salicylate with Mn+, Fe2+, Co+, Ni2+, Cu+, and Zn2+ cations. The energetic, geometrical, spectroscopic, topological, and molecular orbital descriptors are applied to evaluate the strength of the cation-π and intramolecular hydrogen bond (IMHB) interactions. These outcomes are compared with the parent molecule of methyl salicylate and the corresponding results of benzene (BEN) complexes with the cited cations as a set of reference points. Based on the energetic conclusions, for the double-charge cations, the simultaneous presence of these interactions enhances the strength of the cation-π, while for the mono-charge cations, the reverse process is observed. On the other hand, for both type of the cations (mono- and double-charge), the coupling of noncovalent interactions reduces the strength of the IMHB in the studied systems. The computations in this study are discussed with the Bader theory of atoms in molecules (AIM), the natural bond orbital (NBO) analysis, and the frontier molecular orbital (FMO) theory.

Cation−π Complexes of Silver Studied with Photodissociation and Velocity-Map Imaging

Ag+(aromatic) ion-molecule complexes of benzene, toluene, or furan are generated in the gas phase by laser vaporization in a supersonic expansion. These ions are mass selected in a time-of-flight spectrometer and studied with ultraviolet laser photodissociation and photofragment imaging. UV laser excitation results in dissociative charge transfer (DCT) for these ions, producing neutral silver atom and the respective aromatic cation as the photofragments. Velocity-map imaging and slice imaging techniques are employed to investigate the kinetic energy release in these photodissociation processes. In each case, DCT produces significant kinetic energy, and evidence is also found for excitation of the internal rovibrational degrees of freedom for the molecular cations. Analysis of the kinetic energy release together with the known ionization energies of silver and the molecular ligands provides new information on the cation-π bond energies.

Experiments and Direct Dynamics Simulations That Probe η2-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes.

Key steps in the functionalization of an unactivated arene often involve its dihaptocoordination by a transition metal followed by insertion into the C-H bond. However, rarely are the η2-arene and aryl hydride species in measurable equilibrium. In this study, the benzene/phenyl hydride equilibrium is explored for the {WTp(NO)(PBu3)} (Bu = n-butyl; Tp = trispyrazoylborate) system as a function of temperature, solvent, ancillary ligand, and arene substituent. Both face-flip and ring-walk isomerizations are identified through spin-saturation exchange measurements, which both appear to operate through scission of a C-H bond. The effect of either an electron-donating or electron-withdrawing substituent is to increase the stability of both arene and aryl hydride isomers. Crystal structures, electrochemical measurements, and extensive NMR data further support these findings. Static density functional theory calculations of the benzene-to-phenyl hydride landscape suggest a single linear sequence for this transformation involving a sigma complex and oxidative cleavage transition state. Static DFT calculations also identified an η2-coordinated benzene complex in which the arene is held more loosely than in the ground state, primarily through dispersion forces. Although a single reaction pathway was identified by static calculations, quasiclassical direct dynamics simulations identified a network of several reaction pathways connecting the η2-benzene and phenyl hydride isomers, due to the relatively flat energy landscape.

Asymmetric Friedel–Crafts Alkylation of Indoles Catalyzed by Chiral Aziridine-Phosphines

Over the course of the present studies, a series of optically pure phosphines functionalized by chiral aziridines was synthesized in reasonable/good chemical yields. Their catalytic activity was checked in the enantioselective Friedel–Crafts alkylation of indoles by β-nitrostyrene in the presence of a copper(I) trifluoromethanesulfonate benzene complex. The corresponding Friedel–Crafts products were achieved efficiently in terms of chemical yield and enantioselectivity (up to 85% in some cases).

Infrared spectra of (H2)1,2-C6D6 and Rg1,2-C6D6 complexes, Rg = He, Ne, Ar

Spectra of dimers and trimers containing C6D6 and He, Ne, Ar, or H2 are observed in the region of the C6D6 ν12 fundamental using a pulsed supersonic jet expansion and a tunable optical parametric oscillator laser source. These are the first reported infrared spectra of hydrogen – benzene complexes. Two bands coupled by anharmonic resonance are studied for each complex: the ν12 fundamental itself (≈2289 cm−1) and the ν2 + ν13 combination band (≈2276 cm−1). Vibrational shifts for the trimers are found to be approximately twice those of the corresponding dimer. Effective intermolecular separations for (H2)1,2-C6D6 are about 3.46 Å, similar to those determined previously from electronic spectra of (H2)1,2-C6H6 and also similar to (Ne)1,2-C6D6.