Carbon-carbon and carbon-nitrogen coupling reactions catalyzed by palladium nanoparticles derived from a palladium substituted Keggin-type polyoxometalate

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]     

The dielectric model function. An evidence for the nu3(SO4-) phonon mixing in gypsum using polarized IR specular reflectance spectroscopy

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.     

Theory of the implementation of the fundamental parameter method for the X-ray fluorescence determination of low-atomic-number elements

The theory of X-ray fluorescence generation in elements with a low atomic number Z is extended to the case of host matrices with high Z. The total contribution of the selective excitation effects is estimated with regard to the cascade K-L transitions. The influence of the elemental composition of the matrix and the excitation conditions on the X-ray fluorescence intensity of the elements in study is assessed. The accuracy of the model of X-ray fluorescence generation in the low-atomic-number elements is confirmed by the agreement of the experimental and calculated intensities of carbon in various carbon-containing compounds.     

Selective partial reduction of various heteroaromatic compounds with bridgehead nitrogen via Birch reduction protocol

[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.     

Synthesis of anodic silicon oxide films in water-organic solutions containing orthophosphoric acid

Variations in electrophysical properties of anodic silicon oxide at the surface of semiconductor silicon are studied as a function of the composition of electrolytic solutions containing orthophosphoric acid and the conditions of reaching the final formation potential. The optimum conditions for the formation of anodic SiO₂ coatings that include phosphorus-containing admixtures are determined, the coatings being intended for application as diffusates in nanoelectronics.     

Metal-containing monomers. Part 1. Spatial and electronic structures of cobalt(II) and nickel(II) complexes with acrylamide and of their polymers

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.     

Asymmetrical nonbridgehead nitrogen-17: Complete separation into antipodes and absolute configuration of chiralic n-alkoxyisoxazolidines

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.     

Synthesis and reactivity of silyl ruthenium complexes: the importance of trans effects in C-H activation,Si-C bond formation,and dehydrogenative coupling of silanes

A series of octahedral ruthenium silyl hydride complexes, cis-(PMe(3))(4)Ru(SiR(3))H (SiR(3) = SiMe(3), 1a; SiMe(2)CH(2)SiMe(3), 1b; SiEt(3), 1c; SiMe(2)H, 1d), has been synthesized by the reaction of hydrosilanes with (PMe(3))(3)Ru(eta(2)-CH(2)PMe(2))H (5), cis-(PMe(3))(4)RuMe(2) (6), or (PMe(3))(4)RuH(2) (9). Reaction with 6 proceeds via an intermediate product, cis-(PMe(3))(4)Ru(SiR(3))Me (SiR(3) = SiMe(3), 7a; SiMe(2)CH(2)SiMe(3), 7b). Alternatively, 1 and 7 have been synthesized via a fast hydrosilane exchange with another cis-(PMe(3))(4)Ru(SiR(3))H or cis-(PMe(3))(4)Ru(SiR(3))Me, which occurs at a rate approaching the NMR time scale. Compounds 1a, 1b, 1d, and 7a adopt octahedral geometries in solution and the solid state with mutually cis silyl and hydride (or silyl and methyl) ligands. The longest Ru-P distance within a complex is always trans to Si, reflecting the strong trans influence of silicon. The aptitude of phosphine dissociation in these complexes has been probed in reactions of 1a, 1c, and 7a with PMe(3)-d(9) and CO. The dissociation is regioselective in the position trans to a silyl ligand (trans effect of Si), and the rate approaches the NMR time scale. A slower secondary process introduces PMe(3)-d(9) and CO in the other octahedral positions, most likely via nondissociative isomerization. The trans effect and trans influence in 7a are so strong that an equilibrium concentration of dissociated phosphine is detectable (approximately 5%) in solution of pure 7a. Compounds 1a-c also react with dihydrogen via regioselective dissociation of phosphine from the site trans to Si, but the final product, fac-(PMe(3))(3)Ru(SiR(3))H(3) (SiR(3) = SiMe(3), 4a; SiMe(2)CH(2)SiMe(3), 4b; SiEt(3), 4c), features hydrides cis to Si. Alternatively, 4a-c have been synthesized by photolysis of (PMe(3))(4)RuH(2) in the presence of a hydrosilane or by exchange of fac-(PMe(3))(3)Ru(SiR(3))H(3) with another HSiR(3). The reverse manifold - HH elimination from 4a and trapping with PMe(3) or PMe(3)-d(9) - is also regioselective (1a-d(9)() is predominantly produced with PMe(3)-d(9) trans to Si), but is very unfavorable. At 70 degrees C, a slower but irreversible SiH elimination also occurs and furnishes (PMe(3))(4)RuH(2). The structure of 4a exhibits a tetrahedral P(3)Si environment around the metal with the three hydrides adjacent to silicon and capping the P(2)Si faces. Although strong Si...HRu interactions are not indicated in the structure or by IR, the HSi distances (2.13-2.23(5) A) suggest some degree of nonclassical SiH bonding in the H(3)SiR(3) fragment. Thermolysis of 1a in C(6)D(6) at 45-55 degrees C leads to an intermolecular CD activation of C(6)D(6). Extensive H/D exchange into the hydride, SiMe(3), and PMe(3) ligands is observed, followed by much slower formation of cis-(PMe(3))(4)Ru(D)(Ph-d(5)). In an even slower intramolecular CH activation process, (PMe(3))(3)Ru(eta(2)-CH(2)PMe(2))H (5) is also produced. The structure of intermediates, mechanisms, and aptitudes for PMe(3) dissociation and addition/elimination of H-H, Si-H, C-Si, and C-H bonds in these systems are discussed with a special emphasis on the trans effect and trans influence of silicon and ramifications for SiC coupling catalysis.     

On the influence of size, zeta potential, and state of motion of dispersed particles on the conductivity of a colloidal suspension

The dependence of the DC conductivity of diluted colloidal suspensions on the size, zeta potential, and state of motion of the dispersed particles is analyzed both theoretically and numerically. It is shown that the simple formula that represents the conductivity as a sum of products: charge times mobility, taken over all the carriers present in the suspension, is only valid for exceedingly low values of the product kappaa. In contrast, the formulation based on the value of the dipolar coefficient of the suspended particles seems to be valid for all the range of particle sizes. This assertion is only true if the dipolar coefficient is calculated taking into account the electrophoretic motion of the particles. For very low values of the product kappaa, the dipolar coefficient of particles free to move can be several orders of magnitude larger than that of immobile particles.     

Chloride ion promoted nucleophilic pentafluorophenylation of imines

Nucleophilic addition of the pentafluorophenyl group from (C₆F₅)₃SiF to non-activated imines affording α-C₆F₅-substituted secondary amines in high yield has been described. The reaction proceeds via simultaneous activation of imines and the silane reagent by means of a proton and chloride ion, respectively.