Gérard F. Lanneau

Preparation and optical properties of hybrid sol–gel systems containg doubly anchored oligoarylenevinylenes

The sol–gel transformation of bis-trialkoxysilyl-substituted oligoarylenevinylenes allows the covalent connection of photoluminescent segments into silsesquioxane xerogels.

Studies of the hydrolysis of ethyl and tert-butyl phosphonates covalently bonded to silica xerogels

The mild cleavage of phosphonodiester groups supported on a silica matrix has been investigated. The use of TMSBr (bromotrimethylsilane) with diethyl phosphonates has been revisited, and interactions of phosphonoacids with silicon species are described. An alternative route utilising di-tert-butyl phosphonate group has also been studied and in this case cleavage has been demonstrated in very mild conditions.

Organosilanes cycliques fonctionnels pentacoordonnés O,O disubstitués

Abstract Various pentacoordinated 1,3,2 dioxosilaheterocycles are obtained by dehydrocondensation of diols, diphenols, or more generally bifunctional H-acidic materials with aminoarylhydrosilanes, in neutral conditions. The intramolecular nucleophilic ligands activate the SiH bonds and stabilize the monomeric cyclic pentacoordinated products.

Aminosilylation of heterocumulenes and the intramolecular decomposition of their silyl-functionalized adducts

Abstract Heteroorganic amidosilanes are readily obtained by interaction of CO2, CS2 and other heterocumulenes with pentacoordinated diaminosilanes. A comparison is made with the corresponding reactions of tetracoordinated species. Decomposition of these bifunctional organosilanes gives 2-substituted ureido derivatives and base-stabilized low coordinated silicon species, seemingly by a unimolecular thermal β-elimination.

Silicon-phosphorus analogies. nucleophilic catalysis in the alcoholysis of chlorophosphorus derivatives

Abstract The mechanism of the alcoholysis of chlorophosphonates and chlorophosphates in the presence of nucleophilic catalysts like hexamethylphosphotriamide, pyridine and N-methylimidazole is discussed on the basis of kinetic and stereochemical results. We have proposed a mechanism for the reaction, which is governed by entropy, involving reaction of the alcohol with a pentacoordinated intermediate. This accounts for the differences in the stereochemical outcome and the rate equation which can be derived for the reaction with a variety of substrates in addition to the absence of common ion + solvent effects observed.

SYNTHESIS AND REACTIVITY OF BIS(TRIETHOXYSILYL)METHANE, TRIS(TRIETHOXYSILYL)METHANE AND SOME DERIVATIVES

Abstract Syntheses of new poly(trifunctional-silyl)alkanes, which are potent coupling agents of hybrid organic–inorganic materials have been thoroughly examined. Optimization of the Benkeser reaction using chloroform, trichlorosilane and tri- n -butylamine (respective ratios 1:4.5:3) afforded bis(trichlorosilyl)methane isolated as bis(triethoxysilyl)methane after ethanolysis (overall yield 60%). With nine equivalents of trichlorosilane, tris(trichlorosilyl)methane is preferentially formed, isolated as tris(triethoxysilyl)methane (30% yield). C-Substituted bis(triethoxysilyl) methanes were obtained after metallation of the α -carbon and trapping experiments with the corresponding alkyl halides. In the case of tris(triethoxysilyl)carbanion, only MeI and Br 2 were able to give the anticipated products. Unexpectedly, CO 2 insertion afforded the stable ketene, [(EtO) 3 Si] 2 CCO.

Phosphonate derivatives of pyridine grafted onto oxide nanoparticles

The synthesis of phosphonate derived stilbazole 1 by using a Heck reaction is described. The reactivity of the pyridine moiety is studied. After hydrolysis of the ethyl phosphonate groups, the grafting of phosphonic acid derived stilbazole 5 on metal oxides TiO2 or SnO2 is reported. The accessibility and reactivity of the pyridine moiety at the surface is demonstrated.

Studies of Phosphonic Acids Containing a π-Conjugated Ferrocenyl Unit Grafted on Metal Oxides − Mössbauer and Electrochemical Behaviour

The modification of metal oxide surfaces by π-conjugated ferrocene units has been performed. A phosphonic acid functionality was used to covalently anchor the π-conjugated ferrocene moiety to SnO2 and TiO2 particles. The covalent attachment and the monolayer coverage at the surface of the particles were confirmed by solid-state MAS 31P NMR spectroscopy, microanalysis and electronic microscopy (EDX). The properties of the ferrocene-modified oxides were analysed by cyclic voltammetry, which confirmed the electroactivity of the material, and 57Fe Mossbauer spectrometry, which provided information about the oxidation state and environment of the iron atoms. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthese de cyclodisilanes fonctionnels. Essais d'obtention de disilanes optiquement actifs

Abstract The attempted preparation of asymmetric disilacyclopentanes is reported. Alternative routes are described to prepare functional asymmetric organodisilanes, from which cyclic catenated compounds are obtained by intramolecular reduction. These routes are based on the chemical properties of allylsilanes.

Intramolecular nucleophilic catalysis. Stereoselective hydrosilylation of diketones and α-hydroxyketones.

Abstract Erythro diol skeletons are easily obtained in mild and neutral conditions, through the intra-molecular nucleophilic catalyzed hydrosilylation of diketones and hydroxy-ketones with an aminoaryltrihydrosilane.