Oxo Bis Research Articles

Kinetics and mechanism of self‐decomposition/reduction of oxo bis (peroxo) pyridine chromium(VI) in nonaqueous solvents

AbstractKinetics of oxidation of phenylmethanol, as a model by the oxo bis (peroxo) pyridine chromium(VI), OPPC, has been studied in different nonaqueous solvents. Decomposition of oxidant in solvents is studied and explained. The probable mechanism of the reaction is expounded and is related to the kinetics data. Furthermore, the data show a hydride abstraction by η2‐peroxo, forming a terminal oxo plus hydroxo ligand. The effects of solvent dielectric constant on the reaction rates are then considered. A formal potential (0.87 V) decomposition of OPPC on the Pt electrode is measured, which is accompanied by a one‐electron transition in determining the reaction. In addition, thermodynamic parameters are calculated and discussed based upon the proposed reaction mechanism.

A Crystallographic and Mo K‐Edge XAS Study of Molybdenum Oxo Bis‐, Mono‐, and Non‐Dithiolene Complexes – First‐Sphere Coordination Geometry and Noninnocence of Ligands

AbstractTen square‐based pyramidal molybdenum complexes with different sulfur donor ligands, that is, a variety of dithiolenes and sulfides, were prepared, which mimic coordination motifs of the molybdenum cofactors of molybdenum‐dependent oxidoreductases. The model compounds were investigated by Mo K‐edge X‐ray absorption spectroscopy (XAS) and (with one exception) their molecular structures were analyzed by X‐ray diffraction to derive detailed information on bond lengths and geometries of the first coordination shell of molybdenum. Only small variations in Mo=O and Mo–S bond lengths and their respective coordination angles were observed for all complexes including those containing Mo(CO)2 or Mo(μ‐S)2Mo motifs. XAS analysis (edge energy) revealed higher relative oxidation levels in the molybdenum ion in compounds with innocent sulfur‐based ligands relative to those in dithiolene complexes, which are known to exhibit noninnocence, that is, donation of substantial electron density from ligand to metal. In addition, longer average Mo–S and Mo=O bonds and consequently lower ν(Mo=O) stretching frequencies in the IR spectra were observed for complexes with dithiolene‐derived ligands. The results emphasize that the noninnocent character of the dithiolene ligand influences the electronic structure of the model compounds, but does not significantly affect their metal coordination geometry, which is largely determined by the Mo(IV) or (V) ion itself. The latter conclusion also holds for the molybdenum site geometries in the oxidized MoVI cofactor of DMSO reductase and the reduced MoIV cofactor of arsenite oxidase. The innocent behavior of the dithiolene molybdopterin ligands observed in the enzymes is likely to be related to cofactor–protein interactions.

Bis(maltolato)-oxovanadium (IV)-induced phosphorylation of PKB, GSK-3 and FOXO1 contributes toits glucoregulatory responses (Review)

Over the last several decades, a large body of evidence has accumulated to suggest that organo-vanadium compounds (OVC) are more potent than inorganic vanadium salts in regulating hyperglycemia and insulin-resistance in rodent models of both type I and type II diabetes. Among these OVC, vanadium (IV) oxo bis(maltolato) (BMOV) was the first to be investigated for its higher potency over inorganic vanadium salts in eliciting insulin-like properties in both in vitro and in vivo systems. While the precise molecular mechanism by which BMOV exerts its insulin-mimetic effects remains poorly defined, studies have shown that BMOV is a potent activator of several key components of the insulin signaling pathways, such as phosphatidyl-inositol 3-kinase (PI3-K), and its downstream effector, protein kinase B (PKB). In addition, BMOV-induced phosphorylation of PKB has also been associated with the enhanced phosphorylation of glycogen synthase kinase-3 (GSK-3) and forkhead box protein 1 (FOXO1). Since PKB is instrumental in mediating the effects of insulin on glucose transport, glycogen synthesis and gluconeogenesis, it is reasonable to suggest that activation of this pathway by BMOV serves as a mechanism for its insulin-like effects.

Theoretical study of olefin oxidation process on a dioxo‐μ‐oxo Mo catalyst

AbstractThe dimeric complex dioxo (μ‐oxo) thiocyanato of molybdenum(VI) bearing a 4,4′‐di‐ter‐butyl‐2,2′‐bipyridine ligand in trans conformation (complex 1) has been used in catalytic reactions of olefins (ethylene) oxidation, giving as intermediate a dimeric complex oxo bis (μ‐oxo) thiocyanato of molybdenum(V) in cis conformation (complex 2). Binding and electronic properties were calculated using the parametric quantum chemistry method for catalytic reactions, CATIVIC. The interaction of an ethylene molecule with complex 3 (cis version of complex 1) leads to the formation of the intermediate named complex 4. This complex is dissociated to form complex 5 plus ethylene oxide. Changes of electronic and bonding properties are analyzed in terms of atomic charge, orbital population, total binding energies, diatomic bond energies, diatomic energies, and Wiberg indexes, and equilibrium bond distances. The energy balance for the complete catalytic process is presented in a schematic way. Results confirm the extraordinary oxo‐transfer abilities of this complex, considering that the whole process is exothermic (−44 kcal/mol). Regeneration of the catalyst is also calculated by the interaction of H2O2 with complex 5. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Organo-vanadium compounds are potent activators of the protein kinase B signaling pathway and protein tyrosine phosphorylation: Mechanism of insulinomimesis

Organo-vanadium compounds (OVC) have been shown to be more effective than inorganic vanadium compounds in ameliorating glucose homeostasis and insulin resistance in rodent models of diabetes mellitus. However, the precise molecular mechanism of OVC efficiency remains poorly defined. Since inorganic vanadium compounds have been found to activate several key components of the insulin signaling cascade, such as protein kinase B (PKB), the objective of the present study was to investigate if stimulation of PKB and its downstream target glycogen synthase kinase-3 (GSK-3), are responsible for the more potent insulinomimetic effects of OVC. Among several vanadium compounds tested, vanadium (IV) oxo bis (acetylacetonate) and vanadium (IV) oxo bis(maltolato) markedly induced the phosphorylation of PKB as well as GSK-3β compared to vanadyl sulfate (VS), an inorganic vanadium salts in Chinese hamster ovary cells overexpressing the insulin receptor (IR). Furthermore, the OVC were stronger inhibitors of protein tyrosine phosphatase (PTPase) activity than VS. The higher PTPase inhibitory potential of the OVC was associated with more robust tyrosine phosphorylation of several cellular proteins, including the IRβ subunit and insulin receptor substrate-1 (IRS-1). In addition, greater IRS-1/p 85α interaction was elicited by the OVC than by VS. These data indicate that the higher PTPase inhibitory potential of OVC translates into greater phosphorylation of PKB and GSK-3β, which, in turn, may contribute to a more potent effect of OVC on glucose homeostasis.

Phosphorus‐containing epoxy resins: Thermal characterization

AbstractThree novel aromatic phosphorylated diamines, i.e., bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl} pyromellitamic acid (AP), 4,4′‐oxo bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AB) and 4,4′‐hexafluoroisopropylidene‐bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AF) were synthesized and characterized. These amines were prepared by solution condensation reaction of bis(3‐aminophenyl)methyl phosphine oxide (BAP) with 1,2,4,5‐benzenetetracarboxylic acid anhydride (P)/3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride (B)/4,4′‐(hexafluoroisopropylidene)diphthalic acid anhydride (F), respectively. The structural characterization of amines was done by elemental analysis, DSC, TGA, 1H‐NMR, 13C‐NMR and FTIR. Amine equivalent weight was determined by the acetylation method. Curing of DGEBA in the presence of phosphorylated amines was studied by DSC and curing exotherm was in the temperature range of 195–267°C, whereas with conventional amine 4,4′‐diamino diphenyl sulphone (D) a broad exotherm in temperature range of 180–310°C was observed. Curing of DGEBA with a mixture of phosphorylated amines and D, resulted in a decrease in characteristic curing temperatures. The effect of phosphorus content on the char residue and thermal stability of epoxy resin cured isothermally in the presence of these amines was evaluated in nitrogen atmosphere. Char residue increased significantly with an increase in the phosphorus content of epoxy network. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2235–2242, 2002

Synthesis and Characterization of O,N-Chelated Vanadium(IV) Oxo Phenolate Complexes: Electronic Effect of Meta and Para Substituents on the Vanadium Center

A series of O,N-chelated vanadium(IV) oxo bis(phenolate) complexes (1a−i) have been prepared from [VOCl2(THF)2] and several ortho-amino-functionalized phenols in the presence of a base. The intermediates in the synthesis of these compounds are mono(phenolato)vanadate complexes, as was shown by the reaction of [VOCl2(THF)2] with 1 equiv of HOC6H2(CH2NMe2)2-2,6-Me-4 in the absence of base. This yielded [VOCl2(OC6H2(CH2NMe2)-2-Me-4-(CH2NHMe2)-6)] (2), in which the second amine function acts as an internal base, assisting in binding the formed equivalent of HCl. Complex 2 exists in the solid state as the dichlorovanadate(IV) species with the protonated amine function forming a three-centered intramolecular hydrogen bridge in which both a chloride atom and the oxygen atom of the phenolate ligand participate. EPR, UV−vis, and cyclic voltammetry analysis of the complexes with meta or para substituents (1a−g) on the aryloxy ring showed the hyperfine coupling constant, the HOMO−LUMO transition, and the oxidation potential, respectively, to be linearly related to the Hammett σ constants of the substituents on the monoanionic aryloxy ring. The oxidation potential shows a large dependence (dEox/dσ = 170 mV (per phenoxy ligand)) on the Hammett constant. Crystal data: 1a, orthorombic, Pbca, a = 9.4321(7) Å, b = 14.1919(14) Å, c = 26.5484(14) Å, V = 3553.8(5), Å3, Z = 8; 2, monoclinic, C2/c, a = 17.9977(15) Å, b = 15.7445(9) Å, c = 14.4986(6) Å, β = 113.206(5)°, V = 3776.0(4) Å3, Z = 4.

Conformal Step Coverage of (Ba,Sr)TiO3 Films Prepared by Liquid Source CVD Using Ti(t-BuO)2(DPM)2

We study the application of (Ba,Sr)TiO3 (BST) films prepared by chemical vapor deposition (CVD) method to ∼0.13-µm-scale devices, for example, 4Gbit dynamic random access memories (DRAMs), whose minimum feature size and height of storage nodes are around 0.13 and 0.36 µm, respectively. It is necessary for these devices to obtain a conformal step coverage of the BST films of more than 80% at an aspect ratio of 3–5, along with an equivalent SiO2 thickness (teq) of 0.5 nm. Recently, a new Ti source, Ti(t-BuO)2(DPM)2 [bis (t-butoxy) bis (dipivaloylmethanato) titanium], whose Ti ion is surrounded by four large organic ligands, was developed. It is more stable in THF (tetrahydrofuran; C4H8O) solution and in the vapor phase than conventional Ti sources such as TiO(DPM)2 [oxo bis (dipivaloylmethanato) titanium]. In fact, the step coverages of the BST films using Ti(t-BuO)2(DPM)2 were found to be 80% and 70% at aspect ratios of 3.3 and 5, respectively, which were much better than those of films using TiO(DPM)2. Moreover, the electrical properties of the BST films using Ti(t-BuO)2(DPM)2 were teq =0.44 nm and a leakage current JL of 2.8× 10-8 A/cm2 (+1.1 V) for a film of 24 nm thickness after post-annealing. These characteristics meet the requirements of the 4Gbit DRAM capacitors.

Preparation and reactions of rhenium(VII) trioxo hydrogendiolato complexes and rhenium(VI) oxo bis(diolato) complexes

The compound Re2O7, Re2O7·2H2O or [ReO3(OSiMe3)] reacted with H2diol to form complexes having the general formula [ReO3(Hdiol)] where H2diol = 2,3-dimethylbutane-2,3-diol (H2pin) or 1,1′-bicyclohexane-1,1′-diol (H2bicy). In the case of H2pin the complex [ReO3(Hpin)]·H2pin is formed initially in the reaction of rhenium(VII) oxides with an excess of pinacol. The hydrogen bonded free pinacol molecule can be removed by sublimation. The monomethyl derivative of pinacol, HMepin, reacts in a similar way to form the complex [ReO3(Mepin)]. In the rhenium(VII) compounds the Re atom has a distorted trigonal bipyramidal co-ordination geometry. Pale yellow solutions of [ReO3(Hdiol)] in CH2Cl2 slowly become orange and red crystals having the formula [ReO(diol)2] may be isolated. The reaction of rhenium(VII) oxides with H2diol and PPh3 in the presence of drying agents in CH2Cl2 produced the same compounds in high yield. The crystal structures of the rhenium(VI) complexes reveal that the rhenium(VI) cations have square pyramidal co-ordination geometries. The rhenium(VI) oxo bis(diolato) complexes are thermally stable and do not readily undergo oxidation in dry air.

Binding of a meso-Octaethyl Tris(pyrrole)−Mono(pyridine) Ligand to Titanium(III) and Titanium(IV): A Monomeric Titanium(IV) Oxo Bis(pyridine)−Bis(pyrrole) Complex Derived from the C−O Bond Cleavage of Carbon Monoxide

The reaction of a TiMe species with carbon monoxide occurred with the complete cleavage of the CO bond and formation of the TiO unit, while the [MeC] fragment homologated a pyrrole to a 4-methylpyridine ring within the meso-octaethyl tris(pyrrole)−mono(pyridine) macrocycle.

Poly(Azomethine Sulfones) with Thermotropic Liquid Crystalline Behavior

Abstract New poly(azomethine sulfones) with linear structures containing sulfonyl bis(4-phenoxyphenylene) and oxo bis(benzylideneaniline) or methylene bis(benzylideneaniline) units were prepared in the conventional literature manner by condensing the dialdehyde sulfone monomer (V) with diamines such as 4,4′-oxydianiline (IIIa) and 4,4′-methylenedianiline (IIIb), or by condensing an azomethine biphenol (IX) with 4,4′-sulfonyldichlorobenzene (II). Three model compounds which reproduced the above structures were also synthesized. The resulting polymers were confirmed by IR, 1H-NMR, and elemental analysis, and were characterized by inherent viscosities, thermogravimetric analysis (TGA), and x-ray diffraction. The thermotropic liquid crystalline (TLC) behavior was studied using polarization light microscopy (PLM), thermooptical analysis (TOA), and DSC. A nematic texture was observed only for 4,4′-oxydianiline-units-based polymers. The reaction of polymer VIIIb containing – CH2– links between the mesogens with the model compound IX led to polymer X which exhibited TLC behavior.