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121.
Palladium 15-20 nm particles stabilized by a Keggin-type polyoxometalate were prepared by reduction of K(5)PPdW(11)O(39) with H(2). The nanoparticles were shown to be effective catalysts for Suzuki-, Heck-, and Stille-type carbon-carbon coupling and carbon-nitrogen coupling reactions of bromoarenes in aqueous media. Chloroarenes were also reactive in reaction media without solvent. [reaction: see text] 相似文献
122.
Ivanovski V Petrusevski VM 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(7):1601-1607
A complete investigation of the phonon mixing in the nu3(SO4(2-)) frequency region was made, under experimental geometry where the reflecting crystal plane and the plane of incidence contain two principal dielectric axes. It was shown that although it is monoclinic, in the frequency region under inspection, gypsum could be treated as an orthorhombic crystal. More sophisticated model dielectric functions were introduced for the explanation of the Evans holes in the reflectance spectra. Using the model dielectric function, an appearance of the shoulder at the higher frequency part of the reflectance band was explained in terms of longitudinal and quasilongitudinal phonons. A possibility for Evans type interaction was encountered between the nu3(SO4(2-)) Au symmetry type mode and probably some of the combination modes. 相似文献
123.
The mechanism of the propylene oxidation by Pd(NOn)Cl2 − m(CH3CN)2 complexes (n = 2, 3; m = 0, 1, 2) in chloroform solutions has been studied by 1H NMR and IR spectroscopy. The main reaction products are acetone and 2-nitropropylene, with their ratio depending on the equilibrium existing in the reaction solutions between palladium complexes containing NOn ligands bonded to a palladium atom via either an oxygen or a nitrogen atom. Reactivities of the oxygen bonded nitrato and nitrito complexes are significantly higher than that of the nitrogen bonded nitro complex. Various new organopalladium intermediates have been observed and monitored in situ. A reversible insertion of the coordinated propylene into the Pd-O or Pd-N bonds results in nitrato-, nitrito- and nitropalladation intermediates, which then decompose via a β-hydrogen elimination. Two isomers of the nitritopalladation intermediate have been detected, i.e., a palladium metallacycle and an open ring complex, with the latter being much more reactive towards the β-hydrogen elimination than the former. The decomposition of the nitrato- and nitritopalladation intermediates results in the organometallic precursor of acetone, i.e., an acetonylpalladium complex, and then in acetone itself. On the other hand, the nitropalladation intermediate originates 2-nitropropylene. In the presence of dioxygen, which re-oxidizes the nitrosyl groups, the acetone formation becomes a catalytic reaction with respect to both palladium and nitrogen. 相似文献
124.
Tatiana Kuznetsova Vladislav Sadykov Lubsan Batuev Ella Moroz Elena Burgina Vladimir Rogov Vladimir Kriventsov Dmitrii Kochubey 《天然气化学杂志》2006,15(3):149-163
For dispersed ceria-zirconia-based solid solutions prepared via the polymerized complex method and annealed at 700℃, effects of bulk doping by Ca, Mn, Co, Bi or Nb cations and surface modification by Mn and Pt on their structural features, surface/bulk oxygen reactivity and catalytic activity in methane combustion are considered. With up to 20 mol% doping, a structural type of homogeneous solid solutions of anion-deficient fluorite with disordered anion vacancies is formed. Doping by transition metal cations or Pt increases the mobility and reactivity of the surface/bulk oxygen. A broad variation in specific rates of methane combustion for the studied systems was observed, suggesting structural sensitivity of this reaction. In general, there is no universal relationship between the oxygen mobility, the reactivity and the catalytic activity in methane combustion, which is explained by the factor of specific methane activation on surface active sites. For the Pt-promoted samples, Pt efficiency in methane activation depends on the Pt-support interaction, and the most favorable ones being mixed Pt/MnOx and Pt/NbOx clusters on the surface of the supports that exhibit high lattice oxygen mobilities. 相似文献
125.
Andrej I. Dementev Nikolaj G. Rambidi Vladimir Y.A. Simkin Igor A. Topol Nikolaj F. Stepanov Boris I. Zhilinskii 《Journal of Molecular Structure》1980
The potential surface for the boron(III) oxide (B2O3) ground state has been calculated in restricted HF approximation with a minimal STO—3G basis set. The equilibrium geometry has C2v symmetry; the corresponding structural parameters are as follows: r(Oi—B1)= 1.241 Å; r(Bi—O)= 1.341 Å ; ∠B1QB2 = 142° and ǒO1B1O = 177°. Calculations were also carried out using the SCF-Xα approach for two configurations of B2O3 with C2v and D∞h symmetry. 相似文献
126.
[reaction: see text] For the first time various heteroaromatic compounds with bridgehead nitrogen, including indolizines, bispyrrolopyrimidines, pyrroloquinolines, pyrroloisoquinolines, and bispyrrolopyrazines, were selectively partially reduced under Birch reduction conditions. It was found that the double bond in the fused heterocycles which possesses the highest LUMO density can be selectively reduced under these conditions. Indolizine 6, containing an ester group at C-6, was reductively alkylated to give dihydroindolizines 8 and 9 possessing a quaternary carbon center in good yield. It was found that ambident substrate 12, under Birch reduction conditions, underwent smooth partial reduction to give 4,5-dihydroquinoline 14 as a sole product with no evidence of reduction of the side chain olefin. It was also shown that electron-rich pyrroloisoquinoline 15, which cannot be reduced via catalytic hydrogenation conditions, was efficiently transformed into its dihydrocounterpart 16 by using the Birch reduction protocol. Finally, it was shown that various fused diazines were smoothly and stereoselectively reduced under Birch reduction conditions to give trans-4,5-disubstituted dihydropyrimidines 30 and 32 in virtually quantitative yields. 相似文献
127.
Talgat M. Inerbaev Vladimir R. Belosludov Rodion V. Belosludov Marcel Sluiter Yoshiyuki Kawazoe Jun-Ichi Kudoh 《Journal of inclusion phenomena and macrocyclic chemistry》2004,48(1-2):55-60
In this work, the electronic, structural, dynamic andthermodynamic properties of structure II, H and tetragonalAr clathrate hydrates have been calculated and the effectof multiple occupancy on their stability has been examinedusing first-principles and lattice dynamics calculations.The dynamic properties of these clathrates have beeninvestigated depending on the number of guest moleculesin a clathrate cage. It has been found that selectedhydrate structures are dynamically stable. The calculatedcell parameters are in agreement with experimental data.We also report the results of a systematic investigationof cage-like water structures using first-principles calculations. Ithas been observed that Ar clusters can be stabilized indifferent water cages and the stability is strongly dependenton the number of argon atoms inside the cages. 相似文献
128.
Igor E. Uflyand Andrei G. Starikov Vladimir S. Savostjanov Anatoly D. Pomogailo 《Transition Metal Chemistry》1991,16(1):126-129
Summary The spatial and electronic structures of the complexes [Co(AAm)4(H2O)2](NO3)2 (1), Co(AAm)4Cl2 (2), [Ni(AAm)4(H2O)2](NO3)2 (3) and Ni(AAm)4Cl2 (4), where AAm is acrylamide, and the products of their radical, frontal and post-grafting polymerization have been studied by electronic spectroscopy. The complexes (1), (3) and (4) were found to have pseudooctahedral structures in both the solid and solution phases. A change in the spatial structure of complex (2) was established in going from the crystal (tetragonally distorted octahedral) to solution (tetrahedral). The coordination environment of the metal centre does not change markedly during polymerization of the metal-containing monomers. 相似文献
129.
Remir G. Kostyanovsky Vladimir F. Rudchenko Oleg A. Dyachenko Ivan I. Chervin Aleksandr B. Zolotoi Lev O. Atovmyan 《Tetrahedron》1979,35(2):213-224
trans-Stereospecificity of the amidation of 1-alkoxyisoxazolidine-3,3-dicarboxylic ester (1) has been elucidated. Alkaline hydrolysis of monester 4 yielded the salt 6 which after its ion exchange in the form of S(?) and R-(+)-phenylethylammonium salts was completely separated into the enantiomeric salts (+10 and ?10). Esterification and amidation of these salts afforded antipodes 2 S-( +12) and 2 R-( ?12) containing only a nitrogen asymmetric center. Optical purities of the products were established on the basis of their NMR spectra with shift-reagent. Molecular and crystal structure as well as an absolute configuration of +10 were detected by means of X-ray analysis. 相似文献
130.