Favoring heterotrimeric boroxine formation using an internal Lewis base: a computational study

Heterotrimeric arylboroxines can be favorably formed by designing one of the arylboronic acid monomers to contain a pendant Lewis base. Using density functional theory (B3LYP//6-311+G*) calculations including Poisson-Boltzmann implicit solvent, we found that AB2 trimeric arylboroxines were thermodynamically favored over A2B, A3, or B3, where A and B are monomeric arylboronic acids with and without a pendant Lewis base, respectively. The most stable AB2 trimers were formed when the B monomer contained electron-withdrawing substituents, particularly halogens in the para-position or pi-acceptors in the meta-position. On the other hand, adding different para-substituents to the A monomer did not significantly change the energetics. Our calculations also suggest that ABC trimers with three different monomers will not be significantly favored over AB2 trimers when making small electronic perturbations, by changing the substituents on each monomer.     

X-ray scattering and density-functional theory calculations to study the presence of hydrogen-bonded clusters in liquid N-methylacetamide

A structural investigation of liquid N-methylacetamide (NMA) is performed by x-ray scattering and density functional theory (DFT). Experimental data are analyzed to yield the total structure function SM(Q) and the pair correlation function g(r). The DFT calculations, using the standard triple zeta valence basis set augmented by a diffuse function for carbon, nitrogen and oxygen atoms, are performed on the one hand to study the structure and stability of the two possible conformers cis and trans. On the other hand, they are meant to examine some possible clusters which may describe the intermolecular arrangement in liquid NMA. Among two series of dimers and trimers associations, the spectra are particularly interpreted in terms of: Trans NMA dimers and trimers which resemble the short-range crystal structure, mixed cis and trans trimers and cis cyclic trimers. The H-bonding parameters and the intermolecular energy for each model are described.     

Anionic Snieckus-Fries rearrangement: solvent effects and role of mixed aggregates

Lithiated aryl carbamates (ArLi) bearing methoxy or fluoro substituents in the meta position are generated from lithium diisopropylamide (LDA) in THF, n-BuOMe, Me2NEt, dimethoxyethane (DME), N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), and hexamethylphosphoramide (HMPA). The aryllithiums are shown with (6)Li, (13)C, and (15)N NMR spectroscopies to be monomers, ArLi-LDA mixed dimers, and ArLi-LDA mixed trimers, depending on the choice of solvent. Subsequent Snieckus-Fries rearrangements afford ArOLi-LDA mixed dimers and trimers of the resulting phenolates. Rate studies of the rearrangement implicate mechanisms based on monomers, mixed dimers, and mixed trimers.     

Synthesis of water-soluble subphthalocyanines

The syntheses of positively and zwitterionically charged subphthalocyanines (SubPcs) are described for the first time. The SubPcs contain alkylated pyridinium substituents located either at the peripheral or at the axial positions of the macrocycle. The compounds were shown to be fairly water soluble.     

Subphthalocyaninato Boron(III) Hydride: Synthesis,Structure and Reactivity

Subphthalocyanine (SubPc) chemistry has been limited so far by their high sensitivity toward strong nucleophiles. In particular, the substitution of the axial chlorine atom by a nucleophilic group in the case of less-reactive SubPcs, such as those bearing electron-withdrawing peripheral substituents, presents some limitations and requires harsh conditions. By taking advantage of the electrophilic character of DIBAL-H, it has been possible to prepare for the first time SubPc-hydride derivatives that exhibit high reactivity as hydroboration reagents of aldehydes. This hydride transfer requires using a typical carbonyl activator (trimethylsilyl triflate) and only one equivalent of aldehyde, affording SubPcs with an axial benzyloxy group in good yield. This transformation has proven to be a useful alternative method for the axial functionalisation of dodecafluoroSubPc, a paradigmatic SubPc derivative, by using electrophiles for the first time. Considering the increasing interest in SubPcs as electron-acceptor semiconductors with remarkable absorption in the visible range to replace fullerene in organic photovoltaic (OPV) devices, it is of the utmost importance to develop new synthetic methodologies for their axial functionalisation.     

Aggregation behavior and non-covalent functionalization of borofullerenes B28, B38, and B40: A density functional theory investigation

Fullerene-like boron clusters (borofullerenes) are rising stars in the field of cluster chemistry. In this work, density functional theory calculations revealed that the recently reported small borofullerenes B_n (n = 28, 38, and 40) are all highly reactive and tend to form dimers and even trimers spontaneously. In addition, the non-covalent modification of these borofullerenes by various cycloparaphenylene nanorings can form stable host-guest systems with substantial intermolecular charge transfer at both ground and excited states. Our results demonstrate that the borofullerenes are versatile platform for exohedral functionalization, and are very promising candidates for the design of novel nanomaterials with desirable properties.     

Density Functional Theory Study of Water Diffusion and Clustering on Pd（111）

1 INTRODUCTION The interaction of water molecules with metal sur- faces plays a vital role in a number of important pro- cesses, such as corrosion, heterogeneous catalysis, electrochemical processes in aqueous solutions, hydrogen production, etc.[1] The structure and pro- perties of water adsorbed on well-defined metal sur- faces have been the subject of numerous experi- mental and theoretical investigations. There have been a number of experimental studies of water on metal surfaces throu…     

Lithiated imines: solvent-dependent aggregate structures and mechanisms of alkylation

We describe efforts to understand the structure and reactivity of lithiated cyclohexanone N-cyclohexylimine. The lithioimine affords complex solvent-dependent distributions of monomers, dimers, and trimers in a number of ethereal solvents. Careful selection of solvent provides exclusively monosolvated dimers. Rate studies on the C-alkylations reveal chronic mixtures of monomer- and dimer-based pathways. We explore the factors influencing reactants and alkylation transition structures and the marked differences between lithioimines and isostructural lithium dialkylamides with the aid of density functional theory calculations.     

Cationic Axial Ligand Effects on Sulfur-Substituted Subphthalocyanines

Herein, we report the synthesis of sulfur-substituted boron(III) subphthalocyanines (SubPcs) with cationic axial ligands. Subphthalocyanines were synthesized by a condensation reaction using the corresponding phthalonitriles and boron trichloride as a template. An aminoalkyl group was introduced on the central boron atom; this process was followed by N-methylation to introduce a cationic axial ligand. The peripheral sulfur groups shifted the Q band of SubPcs to a longer wavelength. The cationic axial ligands increased the polarity and enhanced the hydrophilicity of SubPcs. The effect of axial ligands on absorption and fluorescence properties is generally small. However, a further red shift was observed by introducing cationic axial ligands into the sulfur-substituted SubPcs. This change is similar to that in sulfur-substituted silicon(IV) phthalocyanines. The unique effect of the cationic axial ligand was extensively investigated by theoretical calculations and electrochemistry. In particular, the precise oxidation potential was determined using ionization potential measurements. Thus, the results of the present study provide a novel strategy for developing functional dyes and pigments based on SubPcs.     

Synthesis of thiol-derivatized porphyrin dimers and trimers for studies of architectural effects on multibit information storage

We present the rational design and synthesis of multiporphyrin arrays containing thiol-derivatized linkers for the purpose of multibit molecular information storage. Porphyrin dimers and trimers were synthesized by the Pd-mediated coupling of iodo-substituted and ethynyl-substituted porphyrin building blocks in 5-51% yields. Each porphyrin dimer bears one S-acetylthio group. The architecture of the trimers incorporates a trans-substituted porphyrin (central) bearing two S-acetylthio groups and two diphenylethyne-linked porphyrins (wings) in a trans geometry. The central porphyrin and the wing porphyrins bear distinct substituents and central metals, thereby affording different oxidation potentials. The S-acetylthio groups provide a means for attachment of the arrays to an electroactive surface. The dimers are designed for vertical orientation on an electroactive surface while the trimers are designed for horizontal orientation of the central porphyrin. Altogether seven different arrays were synthesized. Each array forms a self-assembled monolayer (SAM) on gold via in situ cleavage of the S-acetyl protecting group. The SAM of each array is electrochemically robust and exhibits multiple, reversible oxidation waves. In general, however, the trimeric arrays appear to form more highly ordered monolayers that exhibit sharper, better-defined redox features.     

Glyoxal oligomers: A computational study

Ab initio calculations at MP2/6‐311++G(2d,2p) computational level was used to analyze interactions between glyoxal (OCHCHO) dimers and trimers in the gas phase. The structures obtained have been analyzed with the atoms in molecules and natural bond orbital methodologies. Eight minima were located on the potential energy surface of the dimers. Eighteen different structures have been obtained for the trimers. CH···O type of interactions is clustering OCHCHO molecules in studied oligomers. Stabilization energies of dimers and trimers including basis set superposition error and ZPE corrections are in the range 4–8 kJ mol^?1 and 12–19 kJ mol^?1, respectively. Blue shift of CH bond upon complex formation in the ranges between 30–45 and 30–55 cm^?1 was predicted for dimers and trimers, respectively. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Synthesis, structure, and properties of benzoquinone dimer and trimers bearing t-Bu substituents

Highly soluble and stable quinone dimer and trimers were successfully yielded by introduction of t-Bu substituents. In X-ray structure analysis, the dimer quinone moiety was distorted into the boat shape, which was clarified by MO calculations. X-ray and UV/vis studies indicated that the covalently linked quinone moieties bear a large torsional angle. Nevertheless, the reduction potentials rose significantly with the order of monomer < dimer < trimer, indicating that the negative charge was efficiently delocalized within the radical anions.     

Group 13 organometallic chalcogen derivatives: their structures and behavior in solution

The syntheses, structures and equilibria which occur for 13–16 organometallic compounds are reviewed. The organoaluminum thiolates form dimers, trimers, and tetramers with central (AIS)₂, (AIS)₃, and (AIS)₄ rings in the solid state. The structures of the gallium and indium thiolates are dominated by dimers, but a tetramer has been observed for gallium and a trimer for indium. Only dimeric derivatives have been reported for the selenium and tellurium derivatives. In hydrocarbon solutions, the aluminiun thiolates establish equilibria between different aggregates and conformations with dimers and trimers most common. In the dimeric derivatives, [Me₂Al(μ-SME)]₂ and [Me₂Al(μ-SeMe)]₂, syn and anti conformations are observed in solution at low temperature by NMR spectroscopy. In the trimeric derivatives, the chair conformation is observed in the solid state. In solution, a chair to chair inversion occurs with the rate dependent on the substituents bound to the sulfur.     

Infrared and ab initio studies of hydrogen bonding and proton transfer in the complexes formed by pyrazoles

The results of experimental studies and quantum mechanical calculations of vibrational spectra and structure of hydrogen bonded complexes formed by pyrazole (P) and 3,5-dimethylpyrazole (DMP) are presented. IR spectra of pyrazoles in solutions, gas phase, and solid state have been investigated in wide range of concentrations and temperatures. It has been found that in the gas phase both P and DMP reveal the equilibrium between monomers, dimers, and trimers. In solutions the equilibrium between monomers and trimers dominates, no bands, which can be attributed to dimers were detected. DMP retains the trimer structure in solid state, while in the case of pyrazole P, formation of the crystal provides another type of association. Geometrical and spectral characteristics of dimers and trimers, obtained by ab initio calculations, are presented and compared with experimental data.

IR spectra of solutions containing P and DMP with a number of acids (acetic and trifluoroacetic acids, pentachlorophenol, HBr) have been studied in parallel with ab initio calculations. It has been found that pentachlorophenol forms with pyrazoles complexes with one strong hydrogen bond O–HN, while NH pyrazole group remains unbonded. With carboxylic acids DMP forms 1:1 cyclic complexes with two hydrogen bonds. In the case of acetic acid, the complex in CH₂Cl₂ solution reveals molecular structure with OHN and C=OHN bonds, in accordance with results of the calculations. For trifluoroacetic acid, the calculations predict the molecular structure to be energetically more stable in the case of the isolated binary complex (in gas phase), while the experimental spectrum of CH₂Cl₂ solution gives an evidence of the proton transfer with formation of the cyclic ionic pair with two NH⁺O⁻ bonds. The agreement with experimental results can be improved by taking into account the influence of environment in the framework of Onsager or Tomasi models. The shape of proton potential function of the complexes and medium effect on its parameters, resulted from experimental data and calculations, are discussed. It has been found that the number of potential minima and their relative depth depend strongly on the method of calculations and the basic set. Under excess of trifluoroacetic acid, the formation of 2:1 acid–DMP complex has been detected. Spectral characteristics and results of calculations point to the cyclic structure of this complex, which includes homoconjugated bis-trifluoroacetate anion and DMPH⁺ cation. With HBr both studied pyrazoles were found to form ionic complexes including one or two pyrazole molecules per one acid molecule and correspondingly monocation or homoconjugated cation BHB⁺.     

Synthesis of covalently linked porphyrin dimers and trimers

The synthesis of covalently linked porphyrin dimers and trimers is described. Mono- and dihydroxyporphyrins were synthesized by transeslerifying 5,10,15,20-tetra(4-carbomethoxy-phenyl)porphyrin with ethylene glycol. The mixture of transesterified porphyrins were separated by preparative thin layer chromatography. Metal derivatives were made of the mono- and dihydroxyporphyrins and these were reacted with the acid chloride of a monocarboxyporphyrin to yield hybrid dimers and trimers containing one melalloporphyrin and either one or two free base porphyrins. The structures and purity of the dimers and trimers were established by measuring the absorbance spectra, nmr spectra, and molecular weight by gel permeation chromatography.     

Synthesis, photophysical, electrochemical, and electrogenerated chemiluminescence studies. Multiple sequential electron transfers in BODIPY monomers, dimers, trimers, and polymer

Synthesis of the C(8) BODIPY monomers, dimers, and trimers, a C(8) polymer, and N(8) aza-BODIPY monomer and dimer was carried out. Methyl and mesityl C(8)-substituted monomers, dimers, and trimers were used. Dimers, trimers, and polymer were formed chemically through the β-β (2/6) positions by oxidative coupling using FeCl(3). A red shift of the absorbance and fluorescence is observed with addition of monomer units from monomer to polymer for C(8) dyes. The aza-BODIPY dye shows red-shifted absorbance and fluorescence compared with the C(8) analogue. Cyclic voltammetry shows one, two, and three one-electron waves on both reduction and oxidation for the monomer, dimer, and trimer, respectively, for the C(8) BODIPYs. The separation for the reduction peaks for the C(8) dimers is 0.12 V compared with 0.22 V for the oxidation, while the trimers show separations of 0.09 V between reduction peaks and 0.13 V for oxidation peaks. The larger separations between the second and third peaks, 0.25 V for the oxidation and 0.2 V for the reduction, are consistent with a larger energy to remove or add a third electron compared with the second one. The BODIPY polymer shows the presence of many sequential one-electron waves with a small separation. These results provide evidence for significant electronic interactions between different monomer units. The aza-BODIPY dye shows a reduction peak 0.8 V more positive compared to the C(8) compound. Aza-BODIPY dimer shows the appearance of four waves in dichloromethane. The separation between two consecutive waves is around 0.12 V for reduction compared with 0.2 V for oxidation, which is comparable with the results for the C(8) dyes. Electrogenerated chemiluminescence (ECL) of the different species was obtained, including weak ECL of the polymer.     

Effect of substitution on the optical properties and HOMO-LUMO gap of oligomeric paraphenylenes

A series of dialkyl amino benzophenone dimers with various alkyl chain lengths is presented. Gaussian B3LYP/6-31G(d) calculations show that the band gap decreases within the dimer series as a function of the donor group efficiency. Theoretical calculations show that the interaction between phenyl-phenyl rings is more important than simple donor-acceptor effects. We report the experimental and electro-optical properties of one of these dimers, N,N-(dibutyl)-4-amino-benzophenone. The experimental and theoretical results enabled us to design a new dimer. Altogether, side chain substituents reported herein tune the theoretical band gap of paraphenylene based dimers by over 8.86 eV.     

A combined computational and experimental approach for investigating a hydrogen‐bonded supermolecular compound comprising benzimidazole and malonic acid

A hydrogen‐bonded tetramer supramolecular motif of 2:2 benzimidazole (BIZ) and malonic acid (MLA) has been synthesized and characterized by elemental analysis, infrared (IR), and X‐ray single crystal diffraction. Thermal stability analyses demonstrate that this supramolecular adduct is a new material and it is not the ordinary superposition of the original monomers. Density function theory (DFT) calculations for the models of dimers, trimers, and tetramer comprising BIZ and MLA have been carried out at B3LYP/6‐31G* and PBE1PBE/6‐31G* levels of theory, respectively. By comparing the calculated results with the experiments (single crystal structure, IR spectra, and thermal analysis) and based on the statistic thermodymnamic calculations, it is concluded that the dimers cannot exist at room temperature and the tetramer can simulate the title supramolecular complex better than the two trimers. Further studies on the model of tetramer indicate that the hydrogen bond of N···H? O is stronger than that of O···H? N. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Ce（SO4）2-mediated Oxidative Coupling of Primary Aromatic Amines in Water

The oxidative coupling of primary aromatic amines was investigated. Ce(SO4)2 can mediate the oxidative coupling of primary aromatic amines in water to dimers, trimers and/or tetramers, which depended on the substituents of primary aromatic amines. When 2,6-dimethylaniline or 2,6-diethylaniline was used as substrate, dimer, and tetramer were formed as major products. When 2,6-diisopropylaniline or 2,6-dihaloanilines was used as substrate, dimer, and trimer were formed. The mechanistic aspect was also investi...