Efficient construction of biaryls and macrocyclic cyclophanes via electron-transfer oxidation of Lipshutz cuprates

An efficient method for the homocoupling of aryl halides by electron-transfer oxidation of Lipshutz cuprates (Ar2Cu(CN)Li2) with organic electron acceptors is disclosed. Thus, various types of Lipshutz cuprates are prepared by successive treatment of aryl or heteroaryl bromides with tert-butyllithium and CuCN. The electron-transfer oxidation of Lipshutz cuprates with p-benzoquinones proceeds smoothly to afford the corresponding homocoupling products in moderate to good yields. Furthermore, it can be applied to the construction of either thiophene- or benzene-fused 10-membered ring cyclophanes. For the synthesis of 10-membered cyclophanes, the linear C-Cu-C structure of Lipshutz cuprates should be maintained in the dimetallacyclic intermediates, producing the large ring cyclophanes efficiently. The X-ray analysis of the cyclophanes reveals that the difference in the bridging atoms results in the different conformations of the macrocyclic rings. Thus, the silicon-bridged cyclophane 5a adopts a D2-symmetric structure with a twisted rhombic arrangement of four thiophene rings, whereas the methylene- and oxygen-bridged cyclophanes 5b and 5c possess C2h- and C2-symmetric structures with chair- and boatlike conformations, respectively. The 1H NMR spectrum of C2-symmetric 5c is temperature-dependent, and the activation energy (DeltaG) for the conformational change is 10.1 kcal/mol.     

Novel electron-transfer oxidation of Lipshutz cuprates with 1,4-benzoquinones: an efficient homo-coupling reaction of aryl halides and its application to the construction of macrocyclic systems

The electron transfer reaction from Lipshutz cuprates, which can be easily prepared from aryl bromides, to 1,4-benzoquinones was found to proceed smoothly, affording either the corresponding homo-coupling products, in modest to excellent yields, or macrocyclic products selectively.     

Photocatalytic formation of dimethyllepidopterene from 9,10-dimethylanthracene via electron-transfer oxidation

[Structure: see text] Photocatalytic carbon-carbon bond formation of 9,10-dimethylanthracene (DMA) in chloroform occurs efficiently via the electron-transfer oxidation of DMA with the photoinduced electron-transfer state of 9-mesityl-10-methylacridinium ion (Acr+-Mes), followed by deprotonation from the methyl group of DMA radical cation and the radical coupling reaction between anthracenylmethyl radicals to produce dimethyllepidopterene.     

Melting temperature of Pb nanostructural materials from free energy calculation

The thermodynamic properties of lead, including the entropy, heat capacity, Gibbs free energy, and surface free energy have been studied. Based on bulk thermodynamic properties of lead, Gibbs free energy for nanostructural materials is obtained and used to calculate the size-dependent melting point depression for lead nanostructural materials. The studies indicate that the surface free energy difference between solid phase and liquid phase is a decisive factor for the size-dependent melting of nanostructural materials. The calculated results are in agreement with recent experimental values and the available molecular dynamics simulation data.     

Synthesis of nanostructural electrocatalytic materials on various carbon substrates by ion plasma sputtering of platinum metals

Carbon-supported platinum electrocatalysts for electrochemical systems with a proton-exchange membrane were prepared by ion plasma sputtering in a DC magnetron sputtering unit. Vulcan XC-72, carbon nanotubes, and nanofibers were used as substrates. The starting substrates were occasionally subjected to preliminary chemical treatment or metallization. The synthesized electrocatalyst samples were analyzed by thermogravimetric, X-ray diffraction, and X-ray fluorescent analysis, scanning and transmission microscopy, and cyclic voltammetry. The electrochemical activity of the synthesized Pt/C and Pt-Pd/C materials was studied in a fuel cell, water electrolyzer, and bifunctional fuel cell with a solid polymer electrolyte. Several samples were found to have high specific surface areas (up to 44 m²/g), chemical purity, and electrochemical activity. The qualitative dependences of the characteristics of the catalysts on the parameters of metal deposition and the properties of the starting substrate were found.     

Role of self-assembly in construction of inorganic nanostructural materials

Understanding the evolution process and formation mechanism of nanoscale structures is crucial to controllable synthesis of inorganic nanomaterials with well-defined geometries and unique functionalities. In addition to the conventional Ostwald ripening process, oriented aggregation has been recently found to be prevalent in nanocrystal growth. In this new mechanism, primary small nanocrystals firstly spontaneously aggregate in the manner of oriented attachment, and then the large crystalline materials are formed via the process of interparticle recrystallization. Furthermore, controllable fabrication of the ordered nanocrystal solid materials that has shown specific collective properties will promote the application of inorganic nanocrystal in devices. Therefore, investigation of the mechanism of oriented aggregation is essential to controllable synthesis of nanocrystals and ordered nanocrystal solid materials. In this review, we summarize recent advances in the preparation of nanocrystal materials, which are mostly focused on our work about the role of self-assembly in construction of inorganic nanostructural materials.     

Scandium ion-promoted photoinduced electron-transfer oxidation of fullerenes and derivatives by p-chloranil and p-benzoquinone.

In the presence of scandium triflate, an efficient photoinduced electron transfer from the triplet excited state of C(60) to p-chloranil occurs to produce C(60) radical cation which has a diagnostic NIR (near-infrared) absorption band at 980 nm, whereas no photoinduced electron transfer occurs from the triplet excited state of C(60) (3C(60)) to p-chloranil in the absence of scandium ion in benzonitrile. The electron-transfer rate obeys pseudo-first-order kinetics and the pseudo-first-order rate constant increases linearly with increasing p-chloranil concentration. The observed second-order rate constant of electron transfer (k(et)) increases linearly with increasing scandium ion concentration. In contrast to the case of the C(60)/p-chloranil/Sc(3+) system, the k(et) value for electron transfer from 3C(60) to p-benzoquinone increases with an increase in Sc(3+) concentration ([Sc(3+)]) to exhibit a first-order dependence on [Sc(3+)], changing to a second-order dependence at the high concentrations. Such a mixture of first-order and second-order dependence on [Sc(3+)] is also observed for a Sc(3+)-promoted electron transfer from CoTPP (TPP(2-) = tetraphenylporphyrin dianion) to p-benzoquinone. This is ascribed to formation of 1:1 and 1:2 complexes between the generated semiquinone radical anion and Sc(3+) at the low and high concentrations of Sc(3+), respectively. The transient absorption spectra of the radical cations of various fullerene derivatives were detected by laser flash photolysis of the fullerene/p-chloranil/Sc(3+) systems. The ESR spectra of the fullerene radical cations were also detected in frozen PhCN at 193 K under photoirradiation of the fullerene/p-chloranil/Sc(3+) systems. The Sc(3+)-promoted electron-transfer rate constants were determined for photoinduced electron transfer from the triplet excited states of C(60), C(70), and their derivatives to p-chloranil and the values are compared with the HOMO (highest occupied molecular orbital) levels of the fullerenes and their derivatives.     

A small-angle x-ray scattering study of the nanostructural features of high-ash carbon materials

Nanostructured carbon-silica composite materials are prepared from different compounds in one-pot. They are characterized by BET, transmission electron microscopy, X-ray diffraction, and small-angle X-ray scattering. An effective method of the quantitative analysis of the structural dispersed characteristics of the template phase of silica in these composites is proposed.     

Evidence of an electron-transfer mechanism in the peroxynitrite-mediated oxidation of 4-alkylphenols and tyrosine

The mechanism of interaction of the peroxynitrite with some 4-alkylphenols and tyrosine was mainly studied by means of ESR spectroscopy and product analysis. The radical intermediates, detected as spin adducts to the 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), were identified as carbon-centered radicals to the benzene ring. The reaction seems to proceed via an electron transfer process (ET), most likely mediated by a NOx derivative, leading to the intermediacy of a phenoxyl-type radical as proved by the detection of the corresponding Pummerer-type ketone. No evidence of the formation of hydroxyl radicals, due to the homolytic cleavage of the peroxynitrite at physiological pH was obtained, even though DEPMPO hydroxyl spin adducts were detected: the latter most likely arises from the direct attack of the spin trap by the oxidant species. The possible involvement of HCO(3)(-)/CO(2), i.e., the formation of the nitrosoperoxycarbonate, ONOOCO(2)(*)(-), was also investigated.     

Synthesis of mullite from technogenic materials and pyrophyllite

Pyrophyllite introduced into a ceramic batch prepared from the gravity tailings of zircon-ilmenite ore raises the mullite formation temperature by 50–80°C and increases the mullite content of the resulting material. The first stage of the synthesis yields non-acid-resistant mullite. The early formation and rapid buildup of mullite are due to the formation of small amounts of a liquid phase. Large amounts of the liquid phase (>50%) do not favor mullite buildup because they heal lattice defects and thus hamper sintering.     

Synthesis and properties of zirconium-containing materials produced using calcium aluminates

Highly dispersed zirconium-alumocalcium oxide materials were synthesized with calcium aluminates. The phase composition and surface properties of the samples obtained were analyzed in relation to temperature. Texture characteristics and acid properties of the surface of the materials synthesized were examined in relation to the relative amounts of the components.     

Synthesis and characterization of nanostructural polymer-silica composite: positron annihilation lifetime spectroscopy study

The swelling of poly(TRIM) spherical particles in TEOS is assessed as a potential way for obtaining polymer-silica nanocomposite materials. Silica deposition was achieved by simply stirring of swollen polymer particles in acidic hydrochloric-water solution. This procedure leads to spherical composite particles with dispersed silica gel within the polymer matrix. The resulting material exhibits the same morphology as the initial polymer. Nanocomposite particles are silica rich (about 17 wt.%). Characterization of the nanocomposites was performed using scanning electron microscopy, FT-IR spectroscopy, (29)Si CP MAS NMR spectroscopy and thermogravimetry. Moreover, the use of positron annihilation lifetime spectroscopy PALS to characterize the structural properties of the nanocomposites is presented. This technique gave more realistic pieces of information about the pore structure of the investigated samples in contrast to nitrogen adsorption studies.     

Computation of equilibrium oxidation and reduction potentials for reversible and dissociative electron-transfer reactions in solution

Equilibrium free-energy cycles relating oxidation and reduction potentials in solution to ionization potentials and electron affinities in the gas phase are constructed and the utilities of various levels of theory for computing particular free-energy changes within these cycles are discussed within the context of several examples. Emphasis is placed on the use of quantum-mechanical continuum solvation models to compute free energies of solvation. Key systems discussed include quinones, substituted anilines, substituted phenols, and reductive dechlorination reactions.Dedicated to Prof. Jean-Louis Rivail, whose pioneering efforts in developing and exploiting continuum solvent models were critical in making quantum chemistry more applicable to solution phenomenaProceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail     

Synthesis and photoinduced electron-transfer process of a novel triphenylamine-substituted polyfluorene-C60 triad

The photoinduced electron-transfer process of a newly prepared, soluble, pi-conjugated poly[9,9-bis(4-diphenylaminophenyl)-2,7-fluorene] (PDPAF), covalently bridged, C60 triad (C60-PDPAF-C60) is described. The molecular orbital calculations revealed that the majority of the highest occupied molecular orbital (HOMO) is located on the polyfluorene entity, while the lowest unoccupied molecular orbitals (LUMO) are found to be entirely on the C60 entity. The excited-state electron-transfer processes were monitored by both steady-state and time-resolved emission as well as by transient absorption techniques in toluene and benzonitrile. By excitation of the polyfluorene moiety, fluorescence quenching of the singlet excited state of polyfluorene moiety was observed. The nanosecond transient spectra in near-IR region revealed the charge-separation process from the polyfluorene moieties to the C60 moiety through the excited singlet states of polyfluorene. The lifetimes of the charge separated states were evaluated to be 20-50 ns, depending on the solvent polarity.     

Evaluation of ferryl formation by electrocatalytic oxidation of alkene using luminol chemiluminescence

Electrochemical formation of ferryl porphyrin was examined by electrocatalytic oxidation of alkene by measuring luminol chemiluminescence using a flow-injection method. Emission was observed both below the reduction potential of Fe(III)TMPyP (-0.08 V at pH 11, -0.02 V at pH 7 and 0.15 V at pH 3) and above the oxidation potential (0.6 V at pH 11, 0.75 V at pH 7 and 1.1 V at pH 3). However, both anodic and cathodic emissions were inhibited significantly by the addition of alkene (cyclopent-2-ene-1-acetic acid) solutions downstream of the working electrode. Further, the spectra at both anodic and cathodic sides shifted to the longer wavelength (>424 nm) compared to the original spectrum of Fe(III)TMPyP (422 nm), which was not observed with the addition of alkene solution. Therefore, the results suggest that the electrochemically generated oxo-ferryl species have been engaged in catalytic oxidation of alkene before the flow reaches the observation cell.     

Crater formation in oxidic materials generated by using ion- and laser beams

Summary The etch rate of material due to ion bombardment is the amount of material removed per unit time at a given set of beam parameters. Usually the etch rate is given in units of length/time. The length is measured as the depth of the craters formed by the ion/laser beam. With insulating materials a dependence was obtained of the etch rate on charging effects. Crater formation is also influenced by charging, i.e. walls are built around the craters. These effects were studied in different oxidic materials, (yttrium-iron-garnets (YIG) and gadolinium-gallium-garnets (GGG)).     

The preparation of hindered cuprates from aldehyde tosylhydrazones

Copper reagents react with secondary and tertiary aldehyde tosylhydrazones to give unique, hindered cuprates which are alkylated in a one-flask procedure.