Loss of phosphorous in silica-phosphate sol-gel films

Phosphosilicate films with 90%SiO₂-10%P₂O₅ molar composition, derived from tetraethoxysilane as SiO₂ precursor and triethylphosphate, triethylphosphite or phosphoric acid as P₂O₅ precursors were prepared using the sol-gel method. The films were deposited on glass and ITO coated glass supports. The influence of the type of P₂O₅ precursor, type of substrate and of the thermal treatment (200, 300 and 500°C) on their structure and properties was studied. By spectroellipsometric and XPS measurements the high vaporization of the phosphorous during the densification of the films by thermal treatment was noticed when alkoxide were used, underlying that the mentioned precursors are not recommended for thin phosphosilicate films preparation. The phosphoric acid that forms chemical bond with silica network during the sol-gel process lead to better incorporation of P in the silica network as compared to the P-alkoxides.     

Metal-template-directed synthesis of diphosphorus compounds through intramolecular phosphinidene additions

Heating the nonchelating cis-bis-7-phosphanorbornadiene-[Mo(CO)4] complex (13) results in the thermal decomposition of one of the 7-phosphanorbornadiene groups. The phosphinidene thus generated adds intramolecularly to a C=C bond of the other ligand to give the novel diphosphorus complex 14. This reaction constitutes a metal-template-directed synthesis. Likewise, the intramolecular phosphinidene addition to the C=C bond of a Mo-phospholene ligand affords the diphos complex 18. Its crystal structure exhibits an extremely small P-Mo-P bite-angle for a five-membered chelate ring. The similar intramolecular 1,2-addition to a C=C bond of a phosphole ligand gives a highly strained, unstable intermediate product. Scission of its P-Mo bond generates a free coordination site, which is then occupied by either CO or a phosphole to yield complexes 22 and 23, respectively. The analogous intermolecular addition of [PhPW(CO)5] to a [phosphole-W(CO)5] complex gives the di-[W(CO)5] complexed adduct 28. The directing effect of the metal on the intra- and intermolecular additions is discussed.     

Polymer–silica hybrids obtained by microemulsion polymerization

The styrene (St), butyl acrylate (BuA), and methyl methacrylate (MMA) polymerization in microemulsion in the presence of sodium dodecylsulfate is studied. This process is conducted in the presence of some comonomers having groups that can participate in sol–gel processes: 3(trimethyloxysilyl) propyl methacrylate (MPTS), triethoxy vinylsilane (VTES), and a comonomer with a sulfate group, styrene sodium sulfonate (StSO₃Na). It has been observed that stabile latexes are obtained by radical polymerization at pH = 7, followed by a sol–gel process in the presence of ammonia. Latex particles sizes and zeta potential grow with MTPS concentration and in StSO₃Na presence. VTES effect depends on its reactivity in St, MMA, and BuA copolymerization. Glass transition temperature and thermal decomposing temperature are influences by functional comonomer concentration and chemical structure. The Fourier transform infrared spectrum and inorganic residue growth after organic part thermal decomposition shows the presence of silica in obtained latexes.     

Synthesis of 1,3-disubstituted bicyclo[1.1.0]butanes via directed bridgehead functionalization

Bicyclo[1.1.0]butanes (BCBs) are increasingly valued as intermediates in ‘strain release’ chemistry for the synthesis of substituted four membered rings and bicyclo[1.1.1]pentanes, with applications including bioconjugation processes. Variation of the BCB bridgehead substituents can be challenging due to the inherent strain of the bicyclic scaffold, often necessitating linear syntheses of specific BCB targets. Here we report the first palladium catalyzed cross-coupling on pre-formed BCBs which enables a ‘late stage’ diversification of the bridgehead position, and the conversion of the resultant products into a range of useful small ring building blocks.

Bicyclo[1.1.0]butanes (BCBs) are valuable precursors to four-membered rings and bicyclo[1.1.1]pentanes, and useful bioconjugation agents. We describe a versatile approach to access 1,3-disubstituted BCBs, which are otherwise challenging to prepare.     

Synthesis and reactions of terminal osmium and ruthenium complexed phosphinidenes [(eta6-Ar)(L)Md=PMes*

Novel, very stable ruthenium and osmium containing terminal phosphinidene complexes [(eta(6)-Ar)(L)M=Mes*] (Ar=benzene, p-cymene; L=PR(3), CO, and RNC) have been prepared by dehydrohalogenation of novel [(eta(6)-Ar)MX(2)(PH(2)Mes*)] complexes in the presence of a stabilizing ligand. Xray crystal structures are reported for [(eta(6)-C(6)H(6))(PPh(3))Rud=PMes*] (9) and [(eta(6)-pCy)(PPh(3))Os=PMes*] (4). Dehydrohalogenation in the absence of a stabilizing ligand resulted in the new P-spiroannulated Ru(2)P(2)-ring structure 16. Dehydrohalogenation in the presence of but-2-yne gave a novel phosphaallyl complex [(eta(6)-Ar)Ru(eta(3)-R(2)PC(Me)CHMe)] 26, for which an X-ray crystal structure is reported. The mechanism by which 16 and 26 are obtained is presumed to involve the intermediate formation of the 16-electron (eta(6)-benzene)Rud=PMes* phosphinidene complex.     

Benzimidazolium surfactants for modification of clays for use with styrenic polymers

Nanocomposites of polystyrene (PS), acrylonitrile-butadiene-styrene copolymer (ABS) and high impact polystyrene (HIPS) were prepared with two new homologous benzimidazolium surfactants used as organic modifications for the clays. The morphology of the polymer/clay hybrids was evaluated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing good overall dispersion of the clay. The thermal stability of the polymer/clay nanocomposites was enhanced, as evaluated by thermogravimetric analysis. From cone calorimetric measurements, the peak heat release rate of the nanocomposites was decreased by about the same amount as seen for other organically-modified, commercially available clays.     

Strained, stable 2-aza-1-phosphabicyclo[n.1.0]alkane and -alkene Fe(CO)4 complexes with dynamic phosphinidene behavior

The synthesis of highly strained bicyclic phosphirane and phosphirene iron-tetracarbonyl complexes, that is, complexes with 2-aza-1-phosphabicyclo[n.1.0]alkanes and -alkenes (n = 3-5), is explored by using intramolecular cycloaddition of an in situ generated electrophilic phosphinidene complex, [R(iPr)NP=Fe(CO)(4)], to its C=C- and C[triple chemical bond]C-containing R substituent. Saturated bicyclic complexes 7 a-c with n = 4-2 are remarkably stable, as illustrated by the X-ray crystal structure for 7 b (n=3), yet all readily undergo retroaddition to react with phenylacetylene. Shuttling of the phosphinidene iron complex between two equivalent C=C groups is demonstrated for a 1-butene-substituted 2-aza-1-phosphabicyclo[3.1.0]hexane by selective (1)H NMR magnetization transfer from the phosphirane protons to the olefinic protons. Even the more strained unsaturated bicycles 17 a,b (n = 4,3) are surprisingly stable as illustrated by the X-ray crystal structure for 17 a (n = 4), but the smaller phosphabicyclo[3.1.0]hex-5-ene (17 c, n = 2) dimerizes to tricyclic 19 with a unique ten-membered heterocyclic ring; an X-ray crystal structure is reported. Like their saturated analogues also the bicyclic phosphirenes readily undergo retroaddition as shown by the reaction of their phosphinidene iron moiety with phenylacetylene.     

Transport numbers from hydrogen concentration cells over different oxides under oxidising and reducing conditions

Partial hydrogen ion conductivity in acceptor doped CaTiO(3), BaCeO(3) and ZrO(2) and nominally undoped BaTiO(3) and TiO(2) has been investigated by transport number measurements using the hydrogen concentration cell/EMF method in wet atmospheres as a function of pO(2)(10(-20)-1 atm) at 800 or 1000 [degree]C. All oxides investigated, except ZrO(2), show minor proton conductivity in oxidising atmospheres. Earlier indications of apparent negative charge transport by hydrogen under reducing conditions and high temperatures in SrTiO(3) samples have been reproduced for all the investigated oxides including ZrO(2).