Synthetic Self-Assembly Strategies and Methods

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Nanostructured silica hybrids bearing cationic substructures by liquid crystal templating with anionic surfactants

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i-Silica: Nanostructured silica hybrid materials containing imidazolium groups by hydrolysis-polycondensation of disilylated bis-N,N'-alkyl-imidazolium halides

International audienceWe report the synthesis of silica hybrid materials from the ionic bis-N,N0-(3-triethoxysilyl)propyl imidazolium chloride precursor. This precursor shows very particular behaviour in template directed hydrolysis polycondensation procedures due to its ionic nature. Nanostructured phases were obtained by sol-gel transformation of this precursor in the presence of anionic surfactants. In contrast, hydrolysis- polycondensation under standard reaction conditions using usually applied templating methods with cationic or neutral surfactants led to the formation of amorphous materials. Detailed insight in the hydrolysis polycondensation behaviour of this precursor was obtained via co-condensation reactions of the ionic precursor with a silica network former tetraethoxysilane (TEOS). It appears that the formation of nanostructured phases in the presence of anionic surfactants can be explained by ionic interactions between the template and the organo-cationic substructure of the imidazolium precursor in the hydrolysis polycondensation mixture. These results point a new templating mechanism for the formation of nanostructured silica hybrid materials

Periodic Mesoporous Organosilica containing Imidazolium groups for heterogeneous catalysis

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Bridged silsesquioxanes containing a chiral diphosphine substructure. Catalytic properties in asymmetric hydrogenation.

International audienceBridged silsesquioxanes with asymmetric catalytic properties are described. These new silica-based materials are obtained by the sol-gel hydrolysis of an organosilylated chiral compound bearing rhodium-complexed diphosphine ligands. The incorporation of the organometallic species in various hybrid networks was achieved upon co-hydrolysis of the latter silylated ligands with TEOS or with 1,4-bis(trimethoxysilyl)benzene. These amorphous hybrids have been tested as enantioselective catalysts for the hydrogenation of (Z)a-(acetamido)cinnamic acid to the corresponding aminoacid and the results were compared with that obtained from the complexed precursor in homogeneous medium and related grafted silica. Enantioselectivities slightly higher than for homogeneous reaction were obtained in the case of the heterogeneous catalysts prepared by the direct hydrolysis of the rhodium-complexed diphosphine compound or by its co-hydrolysis with 1,4-bis(trimethoxysilyl)benzene. Conversely, a significant decrease in selectivity was observed when the organometallic species was immobilised in silica or grafted at the surface of silica

Chirality Transcription of Molecular Precursors to Hybrid Silicas

International audienceSilylated racemic, chiral (R,R)- and (S,S)-diureidocyclohexane derivatives have been synthesized in quantitative yields by the reaction of respectively trans racemic, (R,R)- or (S,S)-1,2-diaminocyclohexanes with 3-isocyanatopropyltriethoxysilane. The enantiomeric compounds have the ability to auto-associate through inter-molecular hydrogen bonding owing to the presence of the urea groups. Consequently they formed organic gels in non-polar solvents such as cyclohexane and mesitylene at very low concentration (ca < 10 mg per ml). Such gelating properties were not observed in the case of the racemic mixture. Under acidic aqueous media the controlled hydrolysis-condensation of the (R,R)- and (S,S)-enantiomers led to the hybrid silicates with fibrous structures. Interestingly right- or left-handed helices were respectively observed by Scanning Electronic Microscopy (SEM) images. Conversely, a featureless structure was obtained from the racemic mixture under the same conditions. A significantly reduced wavelength distance ( = 60 cm–1) between the C=O stretching mode and the NH bending mode was observed by FTIR spectroscopy, respectively at 1636 and 1576 cm–1. These results confirm the presence of the H-bonded urea groups in the solid materials. The solid state 13C NMR spectra exhibit in all cases a signal at 160 ppm attributed to the C=O, and a series of chemical shifts at 55, 43, 34, 25 and 10 ppm corresponding to the different sp3 carbon atoms. The preservation of the C–Si bonds was confirmed by the solid state 29Si CP-MAS spectra in which only T2 (–58 ppm) and T3 (–67 ppm) structures, respectively assigned to C—Si(OH)(OSi)2 and C—Si(Si)3, were observed. The formation of the right- and left-handed helical morphologies demonstrates the transcription of chirality from the enantiomers to the hybrid solids

A simple access to ω-aminoalkyltrialkoxysilanes: Tunable linkers for self-organised organosilicas

International audienceA simple route to ω-aminoalkyltriethoxysilanes with variable alkylene chain lengths, (EtO)3Si(CH2)nNH2 (n = 5, 11) is described. These silyl linkers have been used to prepare urea-based compounds with H-bonding and hydrophobic interactions which enable the self-assembly of the molecules. These molecular precursors are suitable for the obtention of nano-structured hybrid silicas

Nanostructured polysilsesquioxanes bearing amine and ammonium groups by micelle templating using anionic surfactants

International audienceWe report the synthesis of new mesoporous nanostructured polysilsesquioxanes by hydrolysis–polycondensation procedures of silylated amine or ammonium precursors. The formation of materials with defined architectures and pore arrangements on a mesoscopic length scale was achieved via soft-templating approaches using anionic surfactants as structure directing agents. For the first time, nanostructured polysilsesquioxanes were obtained with anionic surfactants following a SI+ pathway. Structuring was achieved due to electrostatic interactions between the cationic centers of ammonium precursors and the anionic head group of the sulfate surfactant. This study highlights that specific precursor–surfactant interactions are essential for the formation of nanostructured materials. The obtained new materials are useful for the immobilization of metallic species via the formation of coordination complexes or anion exchange reactions and therefore have high potential as heterogeneous catalysts or adsorbents

Hybrid materials: versatile matrices for supporting homogeneous catalysts

International audienceHybrid materials are increasingly used for supporting homogeneous catalysts. This review describes the various methodologies used to synthesize such hybrid materials or to graft catalysts on inorganic or hybrid supports. Applications of these materials for reactions mediated by supported organometallic or organic catalysts are presented