Moni Chauhan

Hydrosilylation of alkynes catalyzed by platinum on carbon

Hydrosilylation of terminal and internal alkynes with chlorosilanes, alkylsilanes, and alkoxysilanes catalyzed by platinum on carbon are discussed. The yields of the isolated vinylsilanes are high and the selectivity of the product depends on the silane used. Hydrosilylation of alkynes with chlorosilanes produced the β-trans vinylsilanes, while alkyl and alkoxysilanes produced two or three vinylsilane isomers. The selectivity of the catalyst platinum on carbon is similar to Karstedts catalyst in the reaction of phenylacetylene with triethylsilane or triethoxysilane. High resolution electron microscopy showed colloidal platinum to be present in these reactions.

MORE INFORMATION ABOUT THE EXISTENCE OF SILICONIUM IONS

Abstract We confirm that compounds 2 bearing a SiH bond are siliconium ions. In contrast we show that the non-functional cationic compounds 4–7 exist as silylammonium ions or siliconium ions depending on the counteranion and on the solvent.

Crystallographic evidence of hexacoordination at phosphorus via intramolecular coordination of donor groups on phosphane and phosphane sulphide

Abstract The X-ray structure analysis of bis(8-dimethylamino-l-naphthyl)phenylphosphane ( 3 ) and of the corresponding sulphide 4 has revealed hexacoordination at phosphorus in both cases, the N … P separations being less than the sum of the van der Waal radii. Furthermore, in both cases the overall geometry corresponds to a distorted bicapped tetrahedron. The optimum geometry calculated for 4 via the Hyperchem program developed by Autodesk (MM + method) suggests that the structure of the molecule is a function not only of steric requirements but also of electronic effects.

HEXACOORDINATE PHOSPHONIUM SALTS InCORPORATING TWO (8-DIMETHYLAMINO)-1-NAPHTHYL LIGANDS. STRUCTURE AND REACTIVITY

Abstract New hexacoordinate phosphonium salts Ar2RZP+ X-[ar=(8-dimethylamino)-1-naphthyl] with two N→P intramolecular coordinations are described. NMR studies of these salts and the X-ray structure of one of them, 5 (R=Ph, Z=H, X=Br) show that they have a dissymmetric structure with the two Me2N groups coordinated at the phosphorus centre. Salts 4 (R=Ph or Me, Z=CH2CO2Et) react slowly with PhCHO under Wittig conditions probably because of the steric hindrance around the phosphorus atom. This is confirmed by the higher reactivity of the less hindered pentacoordinate phosphonium salts ArR2PCCH2C02Et X− 11 (R=Ph or Me) which are also much more reactive than Ph3P+CH2CO2Et Br−. This study points out the increase of reactivity of these salts due to the N→P interaction.

Influence of the solvent and of the counteranion on the structure of silyl cations stabilized by a terdentate aryldiamine ligand

Abstract Solution NMR studies of silyl cations [ArSiMe2]+X− (X = I, CF3SO3) incorporating the terdentate aryl diamine ligand Ar - C6H3− 2,6-(CH2NMe2)2 have been carried out in a protic solvent (methanol-d4) and in an aprotic solvent (CD2Cl2). This study has shown that the structure of these silyl cations is highly dependent on the solvent. In CD2Cl2, the silyl cation is five-coordinated owing to the coordination of one NMe2 group and of the anion to the silicon centre which gives rise to a dissymmetric structure. On the other hand, in CD3OD there is no coordination of the anion, but the silyl cation is also probably five-coordinated due to the coordination of the solvent to the silicon atom which is supported by the X-ray analysis of the compound 9. With the weakly nucleophilic anion BPh4− in CD2Cl2, in addition to the silyl cation previously described, another five-coordinated silyl cation resulting from the coordination of both NMe2 groups to the Si centre was postulated.

A new catalyst for exclusive β-hydrosilylation of acrylonitrile

Abstract Acrylonitrile and 2-chloroacrylonitrile react with trichlorosilane in the presence of cobalt chloride and an amine to give the β-adduct in 75–95% yields under mild conditions.

First Example of Monomeric Hydrosilane Stabilized Redispersible Silver Nanoparticles

The direct production of silver nanoparticles in organic media is achieved via a simple one pot protocol using long chain hydrosilanes both as reducing and stabilizing agents. This synthetic strategy leads to highly efficient production of stable yet reactive silver nanoparticles. This synthesis is unique in terms of stabilization mechanism, where a very weak passivation is used to produce dispersible but highly active nanoparticles. The effect of hydrosilane alkyl chain length on the growth mechanism, reactivity, dispersibility and stability of the nanoparticles are also investigated.

Controlled Fabrication of Self-Assembled Arrays of Silver Nanoparticles

A simple one pot, highly efficient method to produce self-assembled arrays of functional silver nanoparticles is presented. In this strategy, a combination of tris[3-(trimethoxysilyl)propyl] isocyanurate (TTPI) and trioctylamine (TOA) play the dual role of reducing and stabilizing agents. In situ self-polymerization of TTPI, after attachment with self-assembled nanoparticles provides unique silicon nucleated soluble nanocomposites.