Catherine Reyé

Activation of silicon-hydrogen, silicon-oxygen, silicon-nitrogen bonds in heterogeneous phase : Some new methods in organic synthesis

Abstract Anionic activation of Si-H, Si-O and Si-N bonds by fluoride ions under heterogeneous conditions is reported: Si-H activated by KF or CsF is a very powerful and selective reducing reagent; the carbonyl group of aldehydes, ketones or esters can be reduced without reduction of other functional groups (CzC, NO2, Br, amido). Furthermore, selective reductions of aldehydes in the presence of ketones and ketones in the presence of carboxylic esters are also possible. CsF in the presence of Si(OR)4 is found to be very efficient in promoting Michael additions of monoketones and arylacetonitriles on different kinds of Michael acceptors such as ⇌, β unsaturated ketones, esters, nitriles and even amides. This constitutes an extension of Michael reaction since the addition occurs even with crowded ketones. N, N bis(silyl)enamines activated by fluoride ions react with carbonyl compounds and provide an interesting route to 2-aza-1, 3 dienes.

Ordered mesoporous hybrid materials containing cobalt(II) Schiff base complex

Immobilisation of Co-salen and Co-fluomine onto ordered mesoporous silica has been achieved through coordination of the cobalt to pyridine or imidazole groups covalently attached to the silica matrix. Two routes have been investigated to obtain mesoporous hybrid materials containing coordinating ligands: post synthesis grafting of 4-[2-(trimethoxysilyl)ethyl]pyridine 1 and N-trimethoxysilylpropylimidazole 2 on hexagonally ordered mesoporous silica via SiOH groups or direct synthesis method i.e. co-hydrolysis and polycondensation of the same functionalised organotrimethoxysilane with a number of equivalents of TEOS in the presence of n-hexadecylamine as structure directing agent. The first method gave rise to hexagonally ordered mesoporous hybrid materials. The second afforded mesoporous hybrid materials with a typically disordered wormhole-like framework structure in which the organic groups are probably regularly distributed. The O2-binding capacity of Co-fluomine immobilized on these materials via the imidazole group was investigated.

Molecular chemistry and nanosciences: on the way to interactive materials

This article is focused on mesoporous hybrid organic–inorganic materials prepared in the presence of structure-directing agents. We attempt to show that they are currently the best supports for exploring polyfunctional materials, which can provide a route to interactive materials. We define interactive materials as nanomaterials of which two properties are in a position to interact with one another. For the purpose of constructing such materials, we describe the functionalization of the channel pores of ordered mesoporous silica, the silica framework and the functionalisation of both, either successively or simultaneously. This last route could allow the preparation of materials coupling two physical properties, located on the nanometric range—one in the channel pores and the other in the silica framework—which could present unexpected interactions. This approach requires a mastery of the chemistry for the preparation of the appropriate precursors as well as of the structure.

Tailored Ru‐NHC Heterogeneous Catalysts for Alkene Metathesis

The introduction of N-heterocyclic carbene ligands (NHC) has led to major breakthroughs in homogeneous catalysis. However, such homogeneous catalysts can still suffer from deactivation and problems related to catalyst cost and recovery, as well as metal separation from the organic substrates. In the case of the very challenging and promising reaction of alkene metathesis, these drawbacks have probably been delaying the development of economical industrial processes. One possible solution would be the development of an efficient heterogeneous catalysts that is highly active (TON and TOF), stable (minimum recycling and leaching) and tolerant to functional groups. Despite numerous efforts in this area (involving permanent grafting of Ru-NHC complexes on various supports or other immobilization strategies), heterogeneous catalysts has not fulfilled the aforementioned requirements. Recently, tailored made organic–inorganic materials have proved to be an alternative and advantageous route towards highly active and well-defined heterogeneous catalysts. In particular, fully characterized well-defined Ir-NHC materials displayed catalytic performances comparable to those of homogeneous homologues. This has been attributed to the careful control of the catalyst preparation: synthesis of materials containing regularly distributed NHC-moieties and subsequent selective functionalization into Ir-NHC species, leading to the “single-site” nature of these catalysts. Here, we describe the preparation of highly active and stable Ru-NHC alkene metathesis catalysts through surface organometallic chemistry on hybrid mesostructured materials (Scheme 1).

Control of coordination chemistry in both the framework and the pore channels of mesoporous hybrid materials

Mesoporous materials containing bridged cyclam moieties inside the framework were prepared by using a neutral templating route. Quantitative formation of bridged CuII-cyclam complexes was obtained by the direct incorporation of CuCl2 inside the hybrid material, showing thus the complete accessibility of cyclam moieties located inside the framework. Grafting of a metal-N-triethoxysilylpropylcyclam complex inside the channel pores followed by the incorporation of another metal salt into the framework gave rise to an hybrid material containing two strongly chelated metal salts, one located inside the framework, the other in the channel pores.

New Inorganic–Organic Hybrid Materials for HPLC Separation Obtained by Direct Synthesis in the Presence of a Surfactant

Nanostructured, mesoporous inorganic–organic hybrid xerogels were reproducibly synthesized by a sol–gel procedure. For the introduction of long alkyl chains into inorganic polymers, trifunctional n-alkyltrialkoxysilanes of the type CH3(CH2)nSi(OR)3 (n = 7, 11, 17; R = CH3, C2H5) were co-condensed with Si(OEt)4 (TEOS). The synthetic pathway involves the employment of n-hexadecylamine as template and catalyst. The xerogels obtained by the present procedure consist of uniform spherical particles with a diameter of about 1 μm. The composition of the new materials was determined by 13C and 29Si cross polarization magic angle spinning (CP/MAS) NMR spectroscopy. In addition, the degree of organization was investigated by small angle X-ray and electron diffraction. In accordance with 13C CP/MAS NMR spectroscopic measurements, the alkyl chains form a crystalline arrangement within the silica polymer. Brunauer–Emmett–Teller (BET) adsorption measurements confirm specific surface areas of up to 1400 m2/g. The material properties prove the xerogels to be suitable as stationary phases in high-performance liquid chromatography (HPLC). These novel mesoporous, nanostructured materials have been successfully employed in HPLC for the first time. Different standard reference materials (SRMs) containing polycyclic aromatic hydrocarbons have been separated with the xerogels described in the present work.

Photoresponsive ordered hybrid materials containing a bridged azobenzene group

This paper describes the synthesis of 4,4′-[(triisopropoxysilyl)propyloxy]azobenzene and the preparation of the ordered hybrid material containing the bridged azobenzene moieties within the framework by using the direct liquid crystal templating approach. We show that a sizable fraction of the azobenzene groups is reversibly photoisomerized though the chromophore is covalently linked to the silica matrix at both ends. In contrast, the photoisomerization did not occur in the corresponding material prepared in the absence of template. This is explained by a regular dilution of the chromophores into silica thanks to the template used for the preparation of the material.

Soft route for monodisperse gold nanoparticles confined within SH-functionalized walls of mesoporous silica

In this paper, we report a soft route leading to small gold nanoparticles confined within the framework of 2D-hexagonal mesoporous SH-functionalised silicas. For that purpose, a hydrophilic bis-silylated precursor containing a disulfide unit was prepared. Framework-functionalised materials were obtained in one step by the “direct synthesis” method which consists of a co-hydrolysis and polycondensation of a bridged organosilica precursor with tetraethylorthosilicate (TEOS) in the presence of a non-ionic triblock co-polymer (P123) as structure-directing agent. Reduction of SS groups leads quantitatively to SH functional groups within the framework of 2D hexagonal mesoporous silicas. All these materials have been characterised by TEM, 13C and 29Si NMR experiments, nitrogen gas adsorption, powder XRD and elemental analysis. The subsequent growth of monodisperse gold nanoparticles of small size (∼2 nm) within the walls of mesoporous materials was studied and is discussed.

Hydrophilic conditions: a new way for self-assembly of hybrid silica containing long alkylene chains

For the first time, hybrid materials with long-range order (lamellar and even 2D hexagonal) were obtained during hydrolysis–polycondensation of α,ω-bis(trimethoxysilyl)alkanes thanks to hydrophobic van-der-Waals type interactions using highly hydrophilic conditions, the nanostructure depending mainly on the alkylene chain lengths.

Intramolecular coordination at phosphorus: donor-acceptor interaction in three- and four-coordinated phosphorus compounds

Abstract The phosphorus derivatives P(X)(O2C6H4−1,2)2[C6H4(CH2NMe2)2−2] (9–11) undergo ready extension of coordination by N → P intramolecular donor-acceptor interaction as shown by 31P NMR and dynamic 1H NMR spectroscopy. This extension of coordination does not occur with P(X)(OEt)2[C6H4(CH2NMe2)2−2] (7 and 8). The ΔG≡ of pseudo-rotation was calculated by dynamic 1H NMR spectroscopy to be 57–58 kJ mol−1 for the three compounds P(X)O2C64−1,2)2[C10H6(NMe2−8)] (19–21).