New rare earth metal bis(alkyl)s bearing an iminophosphonamido ligand. Synthesis and catalysis toward highly 3,4-selective polymerization of isoprene

Newrareearth metal bis(alkyl) complexes [(NPNPh)Ln(CH2SiMe3)(2)(THF) (NPNPh:N(Ph)PPh2=NC6H2Me3-2,4,6; Ln = Sc (3a), Ln = Y (3b), Ln = Lu (3c)) and [(NPNPy)Sc(CH2SiMe3)(2)(THF)1 (NPNPY = N(Py)PPh2=NC6H2Me3-2,4,6) (3d)) have been prepared via protonolysis reaction between rare earth metal tris(alkyl)s and the corresponding iminophosphonamines. Complexes 3a-d are analogous monomers of THF solvate. Each metal ion coordinates to a eta(2)-chelated NPN ligand and two cis-located alkyl groups, adopting tetrahedron geometry.

Theoretical studies on the reaction mechanism of oxidation of primary alcohols by Zn/Cu(II)-phenoxyl radical catalyst

The catalytic mechanism for the oxidation of primary alcohols catalyzed by the two functional models of galactose oxidase (GOase), M-II L (M = Cu, Zn; L = N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)1-2-diiminoquinone)), has been studied by use of the density functional method B3LYP The catalytic cycle of Cu- and Zn-catalysts consists of two parts, namely, substrate oxidation (primary alcohol oxidation) and O-2 reduction (catalyst regeneration). The catalytic mechanisms have been studied for the two reaction pathways (route 1 and route 2). The calculations indicate that the hydrogen atom transfer within the substrate oxidation part is the rate-determining step for both catalysts, in agreement with the experimental observation.

Synthesis, crystal structures and spectroscopic properties of copper(I) complexes containing beta-dialdiminato supporting ligands

Two mononuclear neutral copper(I) complexes, Cu(L-1)PPh3 (1), Cu(L-2)(PPh3)(2) (2) ([L-1](-) = [{N((C6H3Pr2)-Pr-i-2,6)C(H)}(2)CPh](-); [L-2](-) = [{N(C6H5)C(H)}(2)CPh](-)) have been synthesized and structurally characterized by X-ray crystallography. In complex 1, the copper(I) atom is in a distorted three-coordinate trigonal planar environment, whereas in complex 2 with the less sterically hindered beta-dialdiminato ligand, the copper(I) atom is the centre of a four-coordinate distorted tetrahedron. At room temperature complexes 1 and 2 in a film of PMMA exhibit green emission at 543 and 549 nm with lifetimes of 5.28 and 5.32 ns, respectively.

Selective hydrogenation of nitrobenzene to aniline in dense phase carbon dioxide over Ni/gamma-Al2O3: Significance of molecular interactions

The selective hydrogenation of nitrobenzene (NB) over Ni/gamma-Al2O3 Catalysts Was investigated using different media of dense phase CO2, ethanol, and n-hexane. In dense phase CO2, the total rate of NB hydrogenation was larger than that in organic solvents under similar reaction conditions; the selectivity to the desired product, aniline, was almost 100% over the whole conversion range of 0-100%. The phase behavior of the reactant mixture in/under dense phase CO2 was examined at reaction conditions. In situ high-pressure Fourier transform infrared measurements were made to study the molecular interactions Of CO2 with the following reactant and reaction intermediates: NB, nitrosobenzene (NSB), and N-phenylhydroxylamine (PHA). Dense phase CO2 strongly interacts with NB, NSB, and PHA, modifying the reactivity of each species and contributing to positive effects on the reaction rate and the selectivity to aniline. A possible reaction pathway for the hydrogenation of NB in/under dense phase CO2 over Ni/gamma-Al2O3 is also proposed.

Synthesis of Hyperbranched Polymers with Pendent Norbornene Functionalities via RAFT Polymerization of a Novel Asymmetrical Divinyl Monomer

Hyperbranched polymers with numerous pendent norbornene functionalities have been synthesized via the radical polymerization of a novel asymmetrical divinyl monomer hearing a higher reactivity methacrylate group and it lower reactivity norbornene group. Mediated by a rapid reversible addition-fragmentation chain transfer (RAFT) equilibrium, the concentration of polymeric chain radicals is decreased, and thus the gelation did not occur until higher monomer conversions (ca. 90%). An increase in reaction temperature call also significantly promote the formation of the hyperbranched structure owing to the decreased stability of the intermediate radicals derived from the norbornene group, which was confirmed by a model copolymerization system of two single vinyl monomers with similar structures to the vinyl groups in the asymmetrical divinyl monomer. Furthermore, Tri-SEC and conventional Sin-SEC as well as H-1 NMR.

Copolymerizations of ethylene with alpha-olefin-omega-ols by highly active vanadium(III) catalysts bearing [N,O] bidentate chelated ligands

The copolymerizations of ethylene with polar hydroxyl monomers such as 10-undecen-1-ol, 5-hexen-1-ol and 3-buten-1-ol were investigated by the vanadium(III) catalysts bearing bidentate [N,O] ligands (1, [PhN=C(CH3)CHC(Ph)O]VCl2(THF)(2): 2, [PhN=CHC6H4O]VCl2(THF)(2); 3, [PhN=CHC(Ph)CHO]VCl2(THF)(2)). The polar monomers were pretreated by alkylaluminum before the polymerization. High catalytic activities and efficient comonomer incorporations can be easily obtained by changing monomer masking reagents and polymerization conditions in the presence of diethylaluminium chloride as a cocatalyst. The longer the spacer group, the higher the incorporation of the monomer. Under the mild conditions, the incorporation level of 10-undecen-1-ol reached 13.9 mol% in the resultant copolymers was obtained. The reactivity ratios of copolymerization (r(1) = 41.4, r(2) = 0.02, r(1)r(2) = 0.83) were evaluated by Fineman-Ross method. According to C-13 NMR spectra, polar units were located both on the main chain and at the chain end.

Free-Radical Solution Copolymerization of the Ionic Liquid Monomer 1-Vinyl-3-Ethylimidazolium Bromide with Acrylonitrile

Ionic liquid monomer 1-vinyl-3-ethylimidazolium bromide (ViEtIM(+)Br(-)) was first used to copolymerize with acrylonitrile (AN) successfully under various conditions. This was achieved with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The kinetics of this copolymerization were studied. The values of the monomer apparent reactivity ratios were calculated by the Kelen-Tudos method. The apparent reactivity ratios of ViEtIM(+)Br(-) (r(ViEtIM+Br-)) and AN (r(AN)) were similar at polymerization conversions of less than 10%, (r(AN) = 0.954, r(ViEtIM+Br-) = 0.976). The copolymers were obtained with high molecular weights and high hydrophilicides. The copolymers were characterized by H-1-NMR, differential scanning calorimetry, and thermogravimetric analysis. These copolymers may be potentially useful in the preparation of precursor fibers and carbon fibers.

Syndiotactic 1,2-polybutadiene fibers produced by electrospinning

Syndiotactic 1,2-polybutadiene (s-PB) is a typical thermoplastic elastomer with various applications because of its high reactivity. In the past, it is difficult to form s-PB fibers with a diameter below 10 mu m because of the limitation of the conventional method such as melt spinning. Here, we report for the first time on the production of s-PB nanofibers by using a simple electrospinning method. Ultrafine s-PB fibers without beads were electrospun from s-PB solutions in dichloromethane and characterized by environmental scanning electron microscope (ESEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). At 4 wt.% concentration of s-PB, the average diameter of s-PB was about 130 nm. We found that dichloromethane was a unique suitable solvent for the electrospinning of s-PB fibers, and the structure of syndiotactic was changed through the electrospinning process.

C-H activation motivated by N,N '-diisopropylcarbodiimide within a lutetium complex stabilized by an amino-phosphine ligand

A lutetium bis( alkyl) complex stabilized by a flexible amino phosphine ligand LLu( CH2Si(CH3)(3))(2)(THF) (L = (2,6-C6H3( CH3)(2)) NCH( C6H5) CH2P(C6H5)(2)) was prepared which upon insertion of N, N'-diisopropylcarbodiimide led to C-H activation via metalation of the ligand aryl methyl followed by reduction of the C=N double bond.

Chain propagation kinetics on melt grafting reaction

Graft copolymerization in the molten state is of fundamental importance as a probe of chemical modification and reactive compatibilization. However, few grafting kinetic studies on reactive extrusion have been carried out because of the inherent difficulties, as expected. In this work, we have studied chain propagation kinetics on melt grafting using pre-irradiated linear low density polyethylene (LLDPE) and three monomers, acrylic acid (AA), methacrylic acid (MAA), and methyl methacrylate (MMA), as the model system. We measured the apparent chain propagation rate coefficients of grafting (k(p,g)) and homopolymerization (k(p,h)) at an initial stage for the melt grafting by FT-IR spectroscopy and electron spin resonance spectroscopy. It was observed that the convective mixing affected the rate coefficients. The magnitude of k(p,h) and k(p,g) were in the same order, but k(p,h) was slightly larger than k(p,g) The k(p,g) of the three grafting systems increased in the order: LLDPE/MMA < LLDPE/MAA < LLDPE/AA. These results are explained in terms of phase separation, solubility, and inherent reactivity of the monomer.

Electrogenerated chemi luminescence from Ru(BPY)(3)(2+) ion-exchanged in carbon nanotube/perfluorosulfonated ionomer composite films

The electrochemistry and electrogenerated chemiluminescence (ECL) of ruthenium(II) tris(bipyridine) (Ru(bpy)(3)(2+)) ion-exchanged in carbon nanotube (CNT)/Nafion composite films were investigated with tripropylamine (TPA) as a coreactant at a glassy carbon (GC) electrode. The major goal of this work was to investigate and develop new materials and immobilization approaches for the fabrication of ECL-based sensors with improved sensitivity, reactivity, and long-term stability. Ru(bpy)(3)(2+) could be strongly incorporated into Nafion film, but the rate of charge transfer was relative slow and its stability was also problematic. The interfusion of CNT in Nafion resulted in a high peak current of Ru(bpy)(3)(2+) and high ECL intensity. The results indicated that the composite film had more open structures and a larger surface area allowing faster diffusion of Ru(bpy)(3)(2+) and that the CNT could adsorb Ru(bpy)(3)(2+) and also acted as conducting pathways to connect Ru(bpy)(3)(2+) sites to the electrode. In the present work, the sensitivity of the ECL system at the CNT/Nafion film-modified electrodes was more than 2 orders of magnitude higher than that observed at a silica/Nafion composite film-modified electrode and 3 orders of magnitude higher than that at pure Nafion films.

Phenylthiolate as a sigma- and pi-donor ligand: synthesis of a 3-D organometallic coordination polymer [K2Fe(SPh)(4)](n)

The synthesis and crystal structure of the first mixed-metal organometallic polymer network containing phenylthiolato ligands, [K2Fe(SPh)(4)](n), are investigated. The simple phenyl-thiolate acts as a sigma- and pi-donor ligand to give a 3-D potassium iron coordination polymer with both metal-carbon and metal-sulfur coordination interactions.

Glassy carbon ceramic composite electrodes

A new carbon composite electrode material, based on dispersing glassy carbon (GC) microparticles into methyltrimethoxysilane-derived sol, is described in the present paper. The resulting glassy carbon ceramic composite electrodes (GCCEs) combine the electrochemical properties of GC with the advantages of composite electrodes, and thus offer high electrochemical reactivity, low background current and are easy to prepare, modify and renew. The new material has a low double-layer capacitance and a wide potential window. Scanning electron microscopy (SEM) images indicate significant difference in the structure of GCCE and carbon ceramic composite electrode (CCE). The electrochemical properties and advantages of GCCE should find broad utility in electroanalysis.

Characterization of FeNi3 alloy in Fe-Ni-O system synthesized by citric acid combustion method

Fe-Ni-O samples, with Fe/Ni ratio ranging from 2 to 1/3, were synthesized. Samples synthesized with and without citric acid in the precursor were compared and it was found that the addition of citric acid is the necessary condition for FeNi3 formation; it was found that FeNi3 alloys were formed in these samples even when calcined in an air atmosphere. X-ray diffraction and X-ray photoelectron spectroscopy measurements were used to characterize the samples. Because of the existence of FeNi3 alloys, Fe-Ni-O samples showed strong reactivity to NO and NO + O-2 but were inert to O-2 alone.