Computational characterization of a complete palladium-catalyzed cross-coupling process: the associative transmetalation in the Stille reaction

[reaction: see text] The species presumably involved in the associative ligand substitution mechanism for the Stille cross coupling of vinyl bromide and trimethylvinyl stannane with Pd(PMe(3))(2)/PMe(3) as catalysts in DMF (as ligand and solvent) have been structurally and energetically characterized. The cyclic four-coordinate transition state for the rate-determining transmetalation step explains the retention of configuration in the Stille coupling of chiral nonracemic alkyl stannanes.     

Approximation properties of the generalized Szasz operators by multiple Appell polynomials via power summability method

In this paper some properties of the generalized Szasz operators by multiple Appell polynomials are given, using into consideration the power summability method. In the first section are given some direct estimation related to the generalized Szasz operators by multiple Appell polynomials, including Korovkin type theorem. In the second section, we give some results related to the weighted spaces of continuous functions and Voronovskaya type theorem. In the third section, we have proved some results related to the statistical convergence of the generalized Szasz operators by multiple Appell polynomials, using into consideration the A− transformation. At the end of the paper are given some illustrative computational examples which make such summability methods (for example, power series method) more useful and fruitful for applications of functional analysis in approximation theory.     

Soft set theory and uni–int decision making

We firstly redefine the operations of Molodtsov’s soft sets to make them more functional for improving several new results. We also define products of soft sets and uni–int decision function. By using these new definitions we then construct an uni–int decision making method which selects a set of optimum elements from the alternatives. We finally present an example which shows that the method can be successfully applied to many problems that contain uncertainties.     

Computational study and analysis of the kinetic isotope effects of the rearrangement of cis-bicyclo[4.2.0]oct-7-ene to cis,cis-cycloocta-1,3-diene

[reaction: see text] On the basis of KIE experiments, the ring opening of cis-bicyclo[4.2.0.]oct-7-ene has been suggested as an anti-Woodward-Hoffmann reaction candidate. We hereby report the results of a high-level computational study of the alternate reaction pathways which proves that the energy profiles show a clear preference for the conrotatory (W-H allowed) ring opening followed by double-bond isomerization. Computed KIE values for the aforementioned mechanism are in good agreement with the experimental values.     

Electrochemical and electrophoretic coatings of medical implants by nanomaterials

Journal of Solid State Electrochemistry - The demand for medical implants has rapidly increased over the last decades. These artificial devices should possess various properties such as...     

Determination of pesticides in water by cone-shaped membrane protected liquid phase microextraction prior to micro-liquid chromatography

A new sample pre-treatment technique termed cone-shaped membrane liquid phase microextraction (CSM-LPME) was developed and combined with micro-liquid chromatography (micro-LC) for the determination of selected pesticides in water samples. Four pesticides (hexaconazole, procymidone, quinalphos and vinclozolin) were considered as target analytes. Several important extraction parameters such as types of extraction solvent, agitation rate, pH value, total exposure time and effect of salt and humic acids were optimized. Enrichment factors of > 50 folds were easily achieved within 20 min of extraction. The analytical data demonstrated relative standard deviations for the reproducibility of the optimized CSM-LPME method ranging from 6.3 to 7.5%. The correlation coefficients of the calibration curves were at least 0.9995 across a concentration range of 2-100 microg/L. The detection limits for all the analytes were found to be in the range of 1.1-1.9 microg/L.     

Synthese und Kristallstrukturen der Phosphaniminato-Komplexe [AlCl2(NPEt3)]2, [GaI2(NPEt3)]2 und [GaI2(NPPh3)]2

Synthesis and Crystal Structures of the Phosphoraneiminato Complexes [AlCl₂(NPEt₃)]₂, [GaI₂(NPEt₃)]₂, and [GaI₂(NPPh₃)]₂ [AlCl₂(NPEt₃)]₂ ( 1 ) is made according to the known method by reaction of aluminium trichloride with the silylated phosphaneimine Me₃SiNPEt₃ in acetonitrile; it is isolated as colourless, moisture sensitive crystals. The phosphoraneiminato complexes [GaI₂(NPEt₃)]₂ ( 2 ) and [GaI₂(NPPh₃)]₂ ( 3 ), on the other hand, are obtained by redox reactions as pale yellow crystals; ( 2 ) of “gallium(I) iodide” with Me₃SiNPEt₃ in toluene and ( 3 ) of gallium with N-iodine triphenylphosphaneimine, INPPh₃, in tetrahydrofuran. 1 and 3 are characterized spectroscopically and by crystal structure determinations; 2 is characterized only crystallographically. 1 : Space group Pbca, Z = 4; lattice dimensions at –70 °C: a = 1232.6(2), b = 1341.1(2), c = 1393.4(3) pm, R₁ = 0.0315. 1 forms centrosymmetric molecules in which the Al atoms are linked via Al–N bonds of the two (NPEt₃^–) groups; with 185.0 and 184.4 pm these bonds are of almost the same lengths. 2 : Space group Pbca, Z = 4; lattice dimensions at –80 °C: a = 1380.0(1), b = 1311.0(1), c = 1429.1(1) pm, R₁ = 0.0273. 2 crystallizes isotypically with 1 . The gallium atoms of the centrosymmetric Ga₂N₂ four-membered ring are connected with Ga–N distances of equal length (190.9 pm). 3 · THF: Space group P2₁2₁2₁, Z = 2; lattice dimensions at –140 °C: a = 1494.6(1), b = 1536.3(1), c = 974.6(1) pm, R₁ = 0.0382. 3 forms dimeric molecules in which the gallium atoms are linked via the N atoms of the (NPPh₃^–) groups to form a non-planar Ga₂N₂ four-membered ring of C₂ symmetry with Ga–N bonds of equal lengths – within standard deviations – of 194.7 pm. The phosphoraneiminato groups are arranged in a synperiplanar way.     

Phosphoraneiminato Complexes of Manganese and Cobalt with Heterocubane Structure

The phosphoraneiminato complexes [MnBr(NPEt₃)]₄ ( 1 ) and [M₄Br₅{NP(NMe₂)₃}₃] with M = Mn ( 2 ) and M = Co ( 3 ) are prepared by melting reactions from the anhydrous metal dibromides with the silylated phosphaneimines Me₃SiNPR₃ (R = Et, NMe₂) in the presence of potassium fluoride. All complexes are characterized by crystal structure analyses. 1 forms an only slightly distorted Mn₄N₄ heterocubane skeleton with an approximate T_d symmetry and short Mn…Mn distances of average 295.7 pm. In the structures of 2 and 3 one μ₃-NPEt₃ ligand of 1 is replaced by one bromine atom with μ₃-function. This leads to the novel heterocubane type M₄N₃Br with approximate C₃ symmetry. The deformation of the cubic skeleton leads to metal-metal distances of different lengths, i. e. 292.7 and 323.6 pm in 2 and 274.4 and 306.2 pm in 3 . Temperature dependent magnetic susceptibility measurements between 300 and 5 K on 1 have shown that strong antiferromagnetic coupling exists between the Mn(II) ions with S = 5/2, with a large negative Weiss constant of Θ = –694 K.     

Die Kristallstrukturen der silylierten Phosphanimine Me3SiNP(c-C6H11)3 und (Me3SiNPPh2)2CH2

Crystal Structures of the Silylated Phosphaneimines Me₃SiNP(c-C₆H₁₁)₃ and (Me₃SiNPPh₂)₂CH₂ The crystal structures of Me₃SiNP(c-C₆H₁₁)₃ ( 1 ) and (Me₃SiNPPh₂)₂CH₂ ( 2 ) are determined by X-ray diffraction at single crystals. In both compounds the PN distances correspond to double bonds, the SiN distances to single bonds. With 149.8° the SiNP bond angle in 1 is noticeably large, while it is only 138.5° in 2 , which shows C₂ symmetry. 1 : Space group P2₁/n, Z = 4, lattice dimensions at –70 °C: a = 1143.0(1), b = 1743.0(2), c = 1152.5(1) pm, β = 90.42(1)°; R = 0.0677. 2 : Space group I4₁/a, Z = 8, lattice dimensions at –60 °C: a = b = 1959.7(1), c = 1695.8(1) pm, R = 0.0433.     

Application of continual injection liquid‐phase microextraction method coupled with liquid chromatography to the analysis of organophosphorus pesticides

A liquid‐phase microextraction coupled with LC method has been developed for the determination of organophosphorus pesticides (methidation, quinalphos and profenofos) in drinking water samples. In this method, a small amount (3 μL) of isooctane as the acceptor phase was introduced continually to fill‐up the channel of a 1.5 cm polypropylene hollow fiber using a microsyringe while the hollow fiber was immersed in an aqueous donor solution. A portion of the acceptor phase (ca. 0.4 μL) was first introduced into the hollow fiber and additional amounts (ca. 0.2 μL) of the acceptor phase were introduced to replenish at intervals of 3 min until set end of extraction (40 min). After extraction, the acceptor phase was withdrawn and transferred into a 2 mL vial for a drying step prior to injection into a LC system. Parameters that affect the extraction efficiency were studied including the organic solvent, length of fiber, volume of acceptor and donor phase, stirring rate, extraction time, and effect of salting out. The proposed method provided good enrichment factors of up to 189.50, with RSD ranging from 0.10 to 0.29%, analyte recoveries of over 79.80% and good linearity ranging from 10.0 to 1.25 mg/L. The LOD ranged from 2.86 to 82.66 μg/L. This method was applied successfully to the determination of organophosphorus pesticides in selected drinking water samples.