No abstract

This review focuses on some aspects of the chemistry involved in the preparation of oxides by sol-gel methods. This field is opening interesting possibilities for molecular chemistry and among those presented herein are: 1) the use of precursors containing functional groups for the preparation of solids with specific chemical reactivity; 2) the non-hydrolytic gelation (NHG) route, a new strate the presence of substructure in the general method for the synthesis of ox-globally amorphous solid; the substrucides that allows the use of oxygen ture greatly depends on the geometry of donors (ethers, alcohols, alkoxides) 0ththe organic moiety. er than water; the mechanism is based on oxygen-carbon bond cleavage; 3) Keywords: materials designmolecular organic-inorganic hybrid solids con-chemistry organic-inorganic hybrid taining covalent bonds for which the compositessol-gel process chemical reactivity is used to demon-R 3. P. Corriu D. Leclercq Dominique Leclercq, born in 1952 in Fourmies, France, obtained his Docteur es Sciences Physiques in 1984.fiom the Universitk de Montpellier II with a thesis on the mechanisms of nucleophilic substitution on organophosphorus compounds. After a postdoctoral position at the Centre de Recherche Rhdne-Poulenc, Aubervilliers, he studied the chemistry of organometallic compounds as precursors to materials. He is currently interested in the preparation of non-oxide ceramics by pyrolysis of polycarbosilanes and polysilazanes as xiell as in synthesis of oxide ceramics by the sol-gel process.

The elaboration of solids from the molecular scale by a kinetically controlled methodology is one of the main challenges of molecular chemistry. In the long term, this should permit the design of solids with desired properties. Here, some examples are given which show a few methods that have been used for the preparation of solids from molecular precursors. The one-pot synthesis of rheologically controlled SiC is described. Access to a new kind of ceramic is obtained by the same methodology using molecular precursors. Mixed ceramics with interpenetrating networks are not accessible by the chemical thermodynamic route. The chemistry of hybrid materials obtained from molecular precursors through inorganic polymerization is presented. This class of materials offers wide perspectives because of 1) the large possibilities opened by the organic unit, 2) the kinetic control, which permits any kind of texture for the solid, and 3) the aptitude of these solids to become nanostructured.

Grignard reagents.Summary A rapid, efficient method for the synthesis of stilbenes and terphenyls is described via reaction between olefinic or aromatic halides and aromatic Grignard Et,0;25 "C reagents activated by a nickel catalyst.The reaction was then extended to substituted aromatic trans-Ph-CH=CH-Br + RMgX _______+ Ni(acac), (02%)