- Self-assembly of designed oligomeric siloxanes with alkyl chains into silica-based hybrid mesostructures
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A novel self-assembly route to ordered silica-organic hybrids using well-defined siloxane oligomers with alkoxy functionality and covalently attached alkyl chains has been investigated. Various hybrid mesostructures were obtained by hydrolysis and polycondensation without the use of any structure-directing agents. The oligomers 1(Cn), having an alkylsilane core and three branched trimethoxysilyl groups, formed highly ordered lamellar phases when n = 14-18, while those with shorter alkyl chains formed cylindrical assemblies, slightly distorted two-dimensional (2D) hexagonal structures (n = 6-10), and a novel 2D monoclinic structure (n = 12). Furthermore, the mixtures of 1(Cn) with different chain lengths yielded well-ordered 2D hexagonal phases, possibly due to the better packing of the precursors. The hybrids consisting of cylindrical assemblies were converted to ordered porous silica with tunable pore sizes upon calcination to remove organic groups. The liquid-state 29Si NMR analysis of the hydrolysis and polycondensation processes of 1(Cn) revealed a unique intramolecular reaction yielding primarily the oligomer with a tetrasiloxane ring which is a new class of amphiphilic molecule having both self-assembling ability and high cross-linking ability. We also found that the mesostructure (lamellar or 2D hexagonal) was strictly controlled by varying the number of siloxane units per alkyl chain. These results provide a deeper understanding of the present self-assembly process that is strongly governed by the molecular packing of oligosiloxane precursors.
- Shimojima, Atsushi,Liu, Zheng,Ohsuna, Tetsu,Terasaki, Osamu,Kuroda, Kazuyuki
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- SiO2-Supported Rh Catalyst for Efficient Hydrosilylation of Olefins Improved by Simultaneously Immobilized Tertiary Amines
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The simultaneous immobilization of a Rh complex and a tertiary amine on a SiO2 surface afforded a highly active supported catalyst for the hydrosilylation of terminal olefins. The turnover number in the reaction using 0.00005 mol % of the Rh catalyst approached 1 900 000 over 24 h. A broad range of terminal olefins and hydrosilanes acted as good substrates, giving their corresponding hydrosilylation products in excellent yields. CSI-mass analysis of the precursor solution containing the Rh complex and tertiary amine indicated complexation between these two precursors. The resultant close positioning of the Rh complex and amine after attachment onto SiO2 surface led to excellent catalysis.
- Motokura, Ken,Maeda, Kyogo,Chun, Wang-Jae
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p. 4637 - 4641
(2017/07/24)
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- Rh(pph3)3cl/tetrakis(dialkylamino)phosphonium salts as thermoregulated and recyclable catalytic system for hydrosilylation reaction
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Eleven tetrakis(dialkylamino)phosphonium salts have been prepared and were used as "soft" catalyst supports for the hydrosilylation reaction of styrene with triethoxysilane catalyzed by Rh(PPh3)3Cl. Among the Rh(PPh3)3Cl/tetrakis(dialkylamino)phosphonium salts tested, the best catalytic activity and selectivity in favor of the β-adduct were obtained when {[(C4H9) 2N]3[(C8H17)2N]P}PF 6 was used as the support, and Rh(PPh3)3Cl/ {[(C4H9)2N]3[(C8H 17)2N]P}PF6 catalyst system can be reused more than 10 times without noticeable loss of catalytic activity and selectivity. Copyright Taylor & Francis Group, LLC.
- Wang, Diliang,Li, Jiayun,Peng, Jiajian,Bai, Ying,Lai, Guoqiao
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experimental part
p. 2258 - 2266
(2012/03/27)
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- Process for preparing low-chloride or chloride-free alkoxysilanes
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A process for preparing an alkoxysilane with an acidic chloride content of less than 10 ppm by weight, comprising: reacting a chlorosilane with an alcohol in a water-free and solvent-free phase to form a product mixture containing alkoxysilane and residual acidic chloride, with removal of resultant hydrogen chloride from the product mixture, then adding liquid or gaseous ammonia, in an amount corresponding to a stoichiometric excess, based on the content of acidic chloride, to form an ammonia-containing product mixture, treating the ammonia-containing product mixture at a temperature between 10 and 50 DEG C., wherein the ammonia and acidic chloride undergo neutralization, to form a crude product, and optionally, then separating off a salt formed in the course of neutralization, from the crude product, and recovering the alkoxysilane by distilling the crude product.
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- CARBON-SILICON BOND CLEAVAGE OF ORGANOTRIALKOXYSILANES AND ORGANOSILATRANES WITH m-CHLOROPERBENZOIC ACID AND N-BROMOSUCCINIMIDE. NEW ROUTE TO PHENOLS, PRIMARY ALCOHOLS AND BROMIDES
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Alkyl- and aryltriethoxysilanes undergo oxidative carbon-silicon bond cleavage smoothly with m-chloroperbenzoic acid (MCPBA) to afford the corresponding alcohols.Silatranes similarly gave alcohols and bromides with MCPBA and N-bromosuccinimide, respectively.
- Hosomi, Akira,Iijima, Susumu,Sakurai, Hideki
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p. 243 - 246
(2007/10/02)
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