P. Mazerolles

Synthèses et réactivités comparées de sila- et germacyclopentanes fonctionnellement β-substitués

Abstract The synthesis and the chemical reactivity of 1-sila- and 1-germa-3-cyclopentenes (I), 6-oxa-3-sila and -3-germabicyclo[3.1.0]hexanes (II) and 1-sila- and 1-germa-3-cyclopentanols (III) are closely dependent upon the heteroatom M and its Σ substituents. Thus, bromine adds to ethylenic cycles (I) (3,4-dibromo-1-sila- and -1-germacyclopentanes stable for MSi, ΣMe, Ph and MGe, ΣBr, Ph are so obtained) and gives simultaneously ring opening reactions for MGe, ΣPh, Me. In the same way, concentrated halogen hydrides react on epoxides (II) and lead to cyclic halohydrins, stable for MSi, ΣPh and to linear products of β-decomposition for MSi, Ge; ΣMe. 1-Oxa-2,2-diphenyl-2-sila- and -2-germacyclopentanes (IV) are synthesised by oxidation of alcohols (III). Interpretation of experimental results accounts for different chemical behaviour of isologous Σ-alkyl-, aryl- and halosilicon and -germanium compounds.

α- et β-silacyclopentanols

Abstract 1,1-Dimethyl-1-silacyclopentan-3-ols are synthetised by hydroboration—oxidation or epoxidation—reduction of the corresponding silacyclopent-3-enes. In acidic media, β-silacyclopentanols give ring opening reactions. Secondary sila-β-alcohols are rearranged by Raney nickel on warming to give 1-oxa-2-sila-cyclopentanes. Thermal dehydration of tertiary β-alcohols gives a mixture of cyclenic isomers from which α-silacyclopentanols can be prepared. Silacyclopentane-3,4-diols are obtainable from the acidic cleavage of the epoxidic ring of oxasilabicyclohexanes.

X-ray photoelectron spectroscopy and Raman spectroscopy investigations of amorphous SixC1x(H) coatings obtained by chemical vapour deposition from thermally labile organosilicon compounds

Abstract Thermal decomposition of organosilicon molecules was carried out in order to obtain amorphous coatings with variable silicon and carbon contents. We selected four molecules: two cyclic molecules, sila-5-spiro[4.4] nona-2,7-diene (I A ) and dimethyl-2,7-sila-5-spiro[4.4]nona-2,7-diene (I B ), and two non-cyclic molecules, tetrapropargylsilane (II A ) and tetraethynylsilane (II B ). Classical chemical vapour deposition (CVD) apparatus was used and the nature of various influences was studied. The coatings were investigated by X-ray photoelectron spectroscopy and micro Raman spectrometer analysis. The coatings have the general formula Si x C 1− x (H), where x varies from 0.24 to 0.82 (depending on the molecule and the decomposition temperature). The binding energies of the core electrons in the Si 2s and C 1s levels ( E b (Si 2s) ≈ 152.4 eV; E b (C 1s) ≈ 284.2 eV) are shifted relative to those for an SiC standard sample ( E b (Si 2s) = 151.6 eV; E b (C 1s) = 283.7 eV). Nevertheless, the Raman spectra display two peaks (800 and 960 cm −1 ) corresponding to SiC after annealing of the deposits. The correlations between the properties of the solid phase (coating) and the gas phase (decomposition byproducts) in the CVD reaction permit an understanding of the decomposition. The coating composition is related to the structure of the starting molecule.

Sultones organométalliques : IV. Réactions de sulfonation en série silacyclobutanique

Abstract The behaviour of some substituted silacyclobutanes with respect to sulfur trioxide and other sulfonating agents (SO 3 /dioxane, trimethylsilyl chlorosulfonate) is studied. The 1,1-dialkylated derivatives of silacyclobutane, 2-methylsilacyclobutane and 3-methylsilacyclobutane as well as the spiranes of the type (CH 2 ) n Si(CH 2 ) 3 ( n = 4 or 5) react with sulfur trioxide to give 4-sila-1,4-butanesultones. On the other hand, the alkoxylated or dialkylaminated derivatives fix SO 3 via the functional group, thus giving silacyclobutanyl sulfates or amidosulfates of the type XSO 2 O(R)Si(CH 2 ) 3 (X = OR′, NR′ 2 ). The sulfonation of 1-methyl-1-phenylsilacyclobutane leads mainly to 1-methyl-1-silacyclobutylbenzenesulfonate, besides the expected sultone. The structure of the insertion products of SO 3 in the SiC, SiN, SiO and SiCl bonds is deduced from their infrared and protonic resonance spectra. Reaction mechanisms, permitting to ascertain the role of the substituents on the mode of insertion of sulfur trioxide and the reactivity of the cyclobutane SiC bond, are considered.

The insertion of phenyl(bromodichloromethyl)mercury-derived dichlorocarbene into the SiC(ring) and βCH bonds of the cis and trans isomers of 1,3-dimethyl-1-n-butyl-1-silacyclobutane

Abstract Reaction of n-butylmagnesium bromide with a 1/1 cis/trans mixture of 1,3-dimethyl-1-chloro-1-silacyclobutane gave a 1/1 cis/trans mixture of 1,3-dimethyl-1-n-butyl-1-silacyclobutane and reaction of n-butyllithium with a 4/1 cis/trans mixture of 1,3-dimethyl-1-tert-butoxy-1-silacyclobutane resulted in a 4/1 mixture of the (presumed) cis and trans isomers of 1,3-dimethyl-1-n-butyl-1-silacyclobutane. Both of these isomer mixtures were treated with phenyl(bromodichloromethyl)mercury in benzene at 80° to give a mixture of the β CH dichlorocarbene insertion product. 1,3-dimethyl-1-n-butyl-3-(dichloromethyl)-1-silacyclobutane (major product) and the SiC insertion product, 2,2-dichloro-1,4-dimethyl-1-n-butyl-1-silacyclopentane. The NMR spectra of these products showed that both were formed as a mixture of cis and trans isomers, with the isomer ratios being very similar to those of the starting silacyclobutane. It was concluded that these stereoselective CCl2 insertion processes proceed with overall retention of configuration.

Stereochemistry of reactions in the 1,2-dimethylsilacyclopentane ring system. II. Stereoselective transformation

Abstract Preparations, separations of geometric isomers, and structural assignments based on nmr and on chemical evidence are described for a number of 1-substituted 1,2-dimethylsilacyclopentanes. A number of stereospecific reactions have been observed, and the stereochemistry is in all cases the same as that observed for acyclic silanes. A discussion of the role of ring strain in determining stereochemical outcome and reaction rates is presented.

Germacycloalcanes à quatre et cinq chaînons

Resume Une nouvelle synthese du germacyclopentane, et de ses derives substitues, a partir du diphenyldibromogermane est decrite. Les germacyclobutanes sont prepares par la methode de cyclisation monomoleculaire par le sodium des derives 1,4-dihalogenes du type R 2 Ge(X)-(CH 2 ) 3 X. La structure de ces nouveaux composes est demontree par une etude physique, et par leur grande reactivite chimique comparee a celle des germacycloalcanes a cinq et six chainons.

Synthese du dimethyl-1,1 silole

Abstract The first synthesis of a monomeric C-unsubstituted silole is described. Photo-oxygenation of 1,1-dimethyl-1-silacyclopent-3-ene leads to an allylic hydroperoxide with a shifted carobon—carbon double bond (ene reaction) which, upon treatment with a reducing agent (NaBH 4 ) gives 1,1-dimethyl-1-silacyclopent-4-ene-3-ol. Catalytic vacuum-flow dehydration of this alcohol gives monomeric 1,1-dimethylsilole, which is characterized by its PMR spectrum at room temperature and by its Diels—Alder adducts.

Influence du Solvant sur une Reaction d'Heterocyclisation a Partir des Dichlorosilanes: Synthese de Nouveaux Sila-1 Cyclopentenes-3

Abstract The reaction between dichlorosilanes and conjugated dienes is closely dependent upon the metal and the solvent. New 1-silacyclopent-3-enes, with various substituents at the heteroatom, are prepared in good yield with Mg, THF and butadiene. For isoprene and dimethylbutadiene, a THF-HMPT mixture must be generally used to increase the ring closure reaction and to limit the competitive reaction of polymerisation to a low value.

Synthese et reactivite de sila-1 cyclopentanols-2: formation d'oxa-1 sila-2 cyclohexanes par reaction d'extension de cycle

Abstract Three 1-silacyclopentan-2-ols, representative members of a new class of compounds, were prepared from the corresponding 1-silacyclopent-3-enes. These silacyclopentanols can, in particular, give rise to 1-oxa-2-silacyclohexanes by a ring expansion reaction.