Coal liquefaction with soluble transition-metal complexes

Several transition-metal complexes were tested for their effectiveness in liquefying coal under very mild conditions. Liquefaction was not observed, probably because interaction with the coal deactivates the catalyst.     

Synthetic resin-bonded transition-metal carbide–carbon hetero-modulus ceramics

Hetero-modulus ceramics (HMC) present an opportunity to combine a ceramic matrix having high Young's modulus with inclusions of a material having a considerably lower value of Young's modulus. The manufacturing method for the powder transition-metal carbide–graphite HMC with synthetic binder was studied. A statistical model for the cured-pressed carbide–carbon powder composition with resin binder was developed employing the statistical fractional factorial experimental design with the 2^5–2 matrix type for several processing parameters. During the subsequent carbonisation of these compacts, the mutual influence between the carbide phase and the phenol–formaldehyde binder leads to the specific transformations in resin-bonded HMC. The pyrolysis reactions in the resin begin at lower temperatures and the products oxidise carbides with the formation of metal oxycarbides and oxides, so the behaviour of HMC depends strongly on the carbide content. The mass gain of carbonised compacts is compensated for by their swelling, so the bulk density in the wide range of contents does not vary after carbonisation. Possessing lower strength, the resin-bonded HMC have better thermal shock/fatigue resistance than materials hot-pressed at high temperatures.     

Development of antimicrobial aminoacid-modified bisphenol-A formaldehyde resin and its transition-metal complexes

A polymeric ligand (BFG), containing glycine moiety was synthesized by the polycondensation reaction of bisphenol-A and formaldehyde with amino acid (glycine) in alkaline medium. The polymer–metal complexes were synthesized with transition metal ions. The polymer and its metal complexes were characterized by elemental analysis and other spectroscopic techniques. The analytical data revealed that the coordination polymers of Cr(III), Co(II), and Ni(II) were coordinated with two water molecules, which are further supported by FTIR spectra and TGA data. The amino acid was found to act as bidentate ligand toward metal ions via the nitrogen of the NH group and carboxyl oxygen of the respective amino acid. The in-vitro preliminary antimicrobial activities of all the synthesized polymers were investigated against some bacteria and fungi. The polymer–metal complexes showed excellent antimicrobial activities against both types of microorganisms. Interestingly the polymeric ligand was found antimicrobial in nature but less effective as compared the polymer–metal complexes. On the basis of the antimicrobial behavior, these polymers hold potential in their application as antifungal and antifouling coating materials in medical devices as well as antimicrobial packaging material.     

固载型过渡金属卟啉催化氧化烷烃的研究进展

对固载型过渡金属卟啉在多相催化体系中氧化烷烃的现状进行综述，重点介绍了有机担体如阴离子交换树脂，无机担体二氧化硅、蒙脱土上固载金属卟啉的方法及催化氧化烷烃的效果。固载金属卟啉容易分离，一定条件下，催化剂的寿命较之液相催化剂有所延长，但是也存在反应诱导期长、催化剂制备复杂及容易从担体流失等缺点。     

Electronic structure and reactivity of three-coordinate iron complexes

[Reaction: see text]. The identity and oxidation state of the metal in a coordination compound are typically thought to be the most important determinants of its reactivity. However, the coordination number (the number of bonds to the metal) can be equally influential. This Account describes iron complexes with a coordination number of only three, which differ greatly from iron complexes with octahedral (six-coordinate) geometries with respect to their magnetism, electronic structure, preference for ligands, and reactivity. Three-coordinate complexes with a trigonal-planar geometry are accessible using bulky, anionic, bidentate ligands (beta-diketiminates) that steer a monodentate ligand into the plane of their two nitrogen donors. This strategy has led to a variety of three-coordinate iron complexes in which iron is in the +1, +2, and +3 oxidation states. Systematic studies on the electronic structures of these complexes have been useful in interpreting their properties. The iron ions are generally high spin, with singly occupied orbitals available for pi interactions with ligands. Trends in sigma-bonding show that iron(II) complexes favor electronegative ligands (O, N donors) over electropositive ligands (hydride). The combination of electrostatic sigma-bonding and the availability of pi-interactions stabilizes iron(II) fluoride and oxo complexes. The same factors destabilize iron(II) hydride complexes, which are reactive enough to add the hydrogen atom to unsaturated organic molecules and to take part in radical reactions. Iron(I) complexes use strong pi-backbonding to transfer charge from iron into coordinated alkynes and N 2, whereas iron(III) accepts charge from a pi-donating imido ligand. Though the imidoiron(III) complex is stabilized by pi-bonding in the trigonal-planar geometry, addition of pyridine as a fourth donor weakens the pi-bonding, which enables abstraction of H atoms from hydrocarbons. The unusual bonding and reactivity patterns of three-coordinate iron compounds may lead to new catalysts for oxidation and reduction reactions and may be used by nature in transient intermediates of nitrogenase enzymes.     

The characterization and chemical reactivity of powdered wool

Wool powders with various particle sizes have been produced using different milling techniques. Scanning electron microscopy (SEM) showed gradual breakdown of the fibre as it was progressively converted into powder form. Chlorination enhanced the effectiveness of subsequent air-jet milling. X-ray photoelectron spectroscopy (XPS) revealed an increase in the surface concentrations of oxygen and nitrogen, and a decrease in carbon and sulphur on conversion of the fibres into powders, as the cortex became exposed on the powder surface. An increased surface concentration of cysteic acid was observed for the chlorinated powder. Rapid uptake of dye by wool powders was observed in situations where there was virtually no uptake by the original fibre. Hydrophobic dyes were more readily sorbed than were hydrophilic dyes. The chlorination treatment led to a decrease in the sorption of acid dyes. Confocal microscopy, used in conjunction with a fluorescent stain, showed that chemicals were able to penetrate wool particles, even at room temperature. The rate and extent of uptake of dye by the finer powders were comparable to that obtained with activated charcoal, even though the surface area of the charcoal was 100 times greater.     

Synthesis and reactivity of rhenium cluster-supported manganese porphyrin complexes

The first discrete molecules of rhenium cluster-supported Mn(OEP) and Mn(TPP) complexes have been synthesized. The Mn(TPP)-containing rhenium cluster as a heterogeneous catalyst showed a high catalytic activity in the epoxidation of olefins by iodosylbenzene.     

Investigation of the chemical reactivity and stability of c-BNP

Bulk material of cubic boron nitride (c-BN) is commercially achieved via high pressure–high temperature (HPHT) synthesis from h-BN with various catalysts (flux precursors). Since recent investigations indicated c-BN to be the stable modification at standard conditions there is considerable interest to realise a c-BN synthesis at normal or low pressure. Thus growth conditions allowing high mobility for boron and nitrogen atoms have to be found.The interaction of c-BN with various flux precursors used under HPHT conditions was investigated up to 1300 °C at ambient pressure. The reagents were chosen with regard to their ability to stabilize intermediate reaction products. Metals, nitrides and fluorides were applied for the chemical attack. The morphological changes and degradation of the c-BN crystals were examined by scanning electron microscopy (SEM), X-ray diffraction and infrared spectroscopy. SEM studies indicate that the degradation of c-BN depends strongly on the nature of the flux precursors. Those leading to an intermediate phase during the reaction exhibit distinct etching figures on (111)-planes of c-BN, while reagents leading to the formation of several products cause an inhomogeneous decay. Since the degradation of c-BN resembles the reversed growth, the reaction mechanism of the interaction of c-BN with reactive melts allows to establish a growth and degradation model of the cubic phase. The results shall help finding new routes to grow c-BN in a low pressure-melt or chemical vapour deposition process.     

Structural characterization and chemical reactivity of dual doped graphene

Herein, we employed first-principle calculations to study the structure and reactivity of dual-doped graphene. The new materials were derived from graphene by replacing two carbon atoms with one 2p element (B, N or O), and one 3p element (Al, Si, P or S). A total of 12 dual-doped graphenes were used to perform a comparative study and identify the most promising materials for the development of new catalysts and anchoring nanoparticles. The structural analysis indicated that in all cases, except SiB, the dopants prefer to replace a CC bond. Yet, not always the dopants are bonded, presenting an edge-like bonding. As regards chemical reactivity, in general the introduction of two atoms remarkably increases reactivity as compared to graphene. The most prominent examples are Al–O, S–N, P–O and Si–B(para) codoped graphene which present reactivity higher than perfect and monodoped graphenes. This effect was attributed to the strong charge redistribution induced by the dopants. In most cases the heteroatoms are the most reactive sites, but in others the carbon atoms are more reactive, as in Al–O and Si–B codoped graphene. The combination of 2p and 3p dopants offers the possibility of adjusting over a wide range the reactivity of graphene.     

Group chemical composition of coal batch and reactivity of coke 1. Determining coke reactivity

With a view to finding correlations between coke reactivity and the coal batch employed, methods of determining coke reactivity are considered—in particular, the standard and pulsed methods. The kinetic equation fundamental to all methods of assessing the coke reactivity from the gasification rate constant is presented. The possibility of combining data obtained by different methods of estimating the coke reactivity is established.     

4-氨基吡啶的合成技术进展及其应用

评述了4-氨基吡啶的合成研究进展,重点介绍了硝基氮氧化吡啶法工艺。概括介绍了4-氨基吡啶在医药、农药、染料等领域的应用状况以及在国内外的生产现状。指出4-氨基吡啶合成工艺的难点在于降低生产成本,提高反应收率以及减少环境污染。建议从催化加氢还原或电化学还原过程中找到一条合乎国情的工艺路线,以推动我国吡啶系列产品的研发工作。     

Correlation of reactivity to hydrogenation and chemical structure of lignites

Three North Dakota lignites with almost the same percentage carbon have been used to determine the relation between chemical structure and reactivity to hydrogenation. Average structural indices of the lignites were estimated using the pyridine-soluble products after alcohol-alkali treatment, the structural indices obtained at various reaction times being extrapolated to zero reaction time. Hydrogenation was influenced by the average structure, with the lignite having higher aromaticity, higher molecular weight of the pyridine extract from the alcohol-alkali reaction product, larger aromatic ring size and lower content of aliphatic structure, showing a smaller degree of conversion.     

Insoluble poly(akylarylphosphine)siloxanes and their application as supports for catalytic transition-metal complexes

Light induced addition of diphenylphosphine (DPP) to methylvinylcyclotetrasiloxane (MVS) yielded poly(2-diphenylphosphinoethyl) cyclotetrasiloxane (DPPS). Similar treatment of allyldiphenylphosphine (ADPP) with linear poly(methylhydrogenosiloxane)-co-hexamethyldisiloxane (PMS) led to formation of poly(3-diphenylphosphinopropyl)methylsiloxane-co-hexamethyldisiloxane (PPMS). DPPS and PPMS were condensed by acid treatment to give insoluble rubbery phosphine bearing materials P₁ and P₂, respectively. Iridium and rhodium complexes were immobilized on P₁ and P₂. The ability of a high molecular weight substrate (PMS) to migrate to active catalytic centers within support matrix was examined. The effect of varying metal: phosphine ratio and total percentage metal on the support were examined during catalysis of O-silylation of ethanol with PMS and triethoxysilane (TES).     

Transition metal-carboryne complexes: synthesis, bonding, and reactivity

The construction and transformation of metal-carbon (M-C) bonds constitute the central themes of organometallic chemistry. Most of the work in this field has focused on traditional M-C bonds involving tetravalent carbon: relatively little attention has been paid to the chemistry of nontraditional metal-carbon (M-C(cage)) bonds, such as carborane cages, in which the carbon is hypervalent. We therefore initiated a research program to study the chemistry of these nontraditional M-C(cage) bonds, with a view toward developing synthetic methodologies for functional carborane derivatives. In this Account, we describe our results in constructing and elucidating the chemistry of transition metal-carboryne complexes. Our work has shown that the M-C(cage) bonds in transition metal-carboranyl complexes are generally inert toward electrophiles, and hence significantly different from traditional M-C bonds. This lack of reactivity can be ascribed to steric effects resulting from the carboranyl moiety. To overcome this steric problem and to activate the nontraditional M-C(cage) bonds, we prepared a series of group 4 and group 10 transition metal-carboryne complexes (where carboryne is 1,2-dehydro-o-carborane), because the formation of metallacyclopropane opens up the coordination sphere and creates ring strain, facilitating the reactions of M-C(cage) bonds with electrophiles. Structural and theoretical studies on metal-carboryne complexes suggest that the bonding interaction between the metal atom and the carboryne unit is best described as a resonance hybrid of the M-C σ and M-C π bonds, similar to that observed in metal-benzyne complexes. The nickel-carboryne complex (η(2)-C(2)B(10)H(10))Ni(PPh(3))(2) can (i) undergo regioselective [2 + 2 + 2] cycloaddition reactions with 2 equiv of alkyne to afford benzocarboranes, (ii) react with 1 equiv of alkene to generate alkenylcarborane coupling products, and (iii) also undergo a three-component [2 + 2 + 2] cyclotrimerization with 1 equiv of activated alkene and 1 equiv of alkyne to give dihydrobenzocarboranes. The reaction of carboryne with alkynes is also catalyzed by Ni species. Subsequently, a Pd/Ni co-catalyzed [2 + 2 + 2] cycloaddition reaction of 1,3-dehydro-o-carborane with 2 equiv of alkyne was developed, leading to the efficient formation of C,B-substituted benzocarboranes in a single process. In contrast, the zirconium-carboryne species, generated in situ from Cp(2)Zr(μ-Cl)(μ-C(2)B(10)H(10))Li(OEt(2))(2), reacts with only 1 equiv of alkyne or polar unsaturated organic substrates (such as carbodiimides, nitriles, and azides) to give monoinsertion metallacycles, even in the presence of excess substrates. The resultant five-membered zirconacyclopentenes, incorporating a carboranyl unit, are an important class of intermediates for the synthesis of a variety of functionalized carboranes. Transmetalation of zirconacyclopentenes with other metals, such as Ni and Cu, was also found to be a very useful tool for various chemical transformations. Studies of metal-carboryne complexes remain a relatively young research area, particularly in comparison to the rich literature of metal-benzyne complexes. Other transition metal-carborynes are expected to be prepared and structurally characterized as the field progresses, and the results detailed here will further that effort by providing easy access to a wide range of functionalized carborane derivatives.     

Intrinsic defects,Mo-related defects,and complexes in transition-metal carbide VC: A first-principles study

Intrinsic defects and Mo-related defects in vanadium carbide VC, as well as the defect complexes between vacancies and Mo defects were investigated by means of first-principles calculations within the framework of density functional theory. In addition, Mo diffusion in VC was also studied using LST/QST method. The formation energies of defects have clearly shown that except C vacancy (V_C) all other point defects are not energetic favorable compared to perfect VC. V_C can exist in the lattice forming nonstoichiometric carbide VC_x (x < 1), and also can stabilize the Mo-related defects (S_Mo-V, S_Mo-C, and T_Mo). Free Mo atoms have the strong tendency to enter the already formed V_V and occupy the lattice position of V atoms. Meanwhile, Mo atom in C lattice (S_Mo-C) and interstitial Mo (I_Mo) atom can also enter the V_V position stabilizing the lattice structure. S_Mo-C + V_V will transform into S_Mo-V + V_C and I_Mo + V_V will transform into S_Mo-V during optimization, and large binding energy makes Mo atom tend to exist in the interstitial position. From the perspective of energy, Mo atom tends to diffuse through the interstitial position.     

Self-organised synthesis of Rh nanostructures with tunable chemical reactivity

Nonequilibrium periodic nanostructures such as nanoscale ripples, mounds and rhomboidal pyramids formed on Rh(110) are particularly interesting as candidate model systems with enhanced catalytic reactivity, since they are endowed with steep facets running along nonequilibrium low-symmetry directions, exposing a high density of undercoordinated atoms. In this review we report on the formation of these novel nanostructured surfaces, a kinetic process which can be controlled by changing parameters such as temperature, sputtering ion flux and energy. The role of surface morphology with respect to chemical reactivity is investigated by analysing the carbon monoxide dissociation probability on the different nanostructured surfaces.     

Role of mineral matter in the chemical reactivity of coal

Previous work showed that the solvent extraction yield of coal increased as a result of chemical reactions such as formylation, reductive acylation, acylation, amidomethylation, alkylation, reduction and depolymerization. In the work described in this Paper, dmmf coal obtained after demineralization with mixed HF-HCI acids was used for solvolytic extraction studies after depolymerization, alkylation, acylation, amidomethylation, reductive acylation and reduction reactions. In comparison with the original coal, mineral matter free coal showed less increase in extractability as a result of these reactions indicating that mineral matter present in the original coal was acting as a promoter for these reactions.