Search

Silylboranes with aromatic substituents linked to boron and silicon exhibit an unexpected absorption band in the UV–Vis spectral region. When polar groups were introduced, a marked solvatochromic effect was observed in their fluorescence emission spectra, revealing a strong excited state dipole moment. Semi-empirical MNDO/d and AM1 calculations showed that, upon UV excitation, the polarity of the Si–B bond increased and the aromatic π-electrons migrated toward the Si–B bond, consistent with experimental observations.

A series of organosilylboranes has been investigated by IR spectroscopy and semiempirical calculations (MNDO/d force field methods). Computational studies afforded Si–B stretching wavenumbers in good agreement with the experimental IR bands observed in the range of 480–650 cm −1 . It was shown that these characteristic Si–B bond vibrations depend on the structure of molecules and on the size of substituting groups. Thus, compounds possessing small and medium substituting groups (H, Me) and those having a symmetry element give pure Si–B stretching bands. In the case of silylboranes bearing bulky groups, assignments of bands involving Si–B vibrators were achieved via comparison of experimental and theoretical IR spectra with those of reference molecules containing the parent organosilyl- or organoboryl moieties. An experimental absorption band near 600 cm −1 could reasonably be assigned to ν (Si–B).

Novel stable organosilylboranes possessing dimesityl groups attached to boron were synthesised. They gave an addition reaction with terminal acetylenic hydrocarbons in the presence of a transition metal complex. Thus, (diphenylmethylsilyl)dimesitylborane and (diphenyl-tert-butylsilyl)dimesitylborane reacted in good yields with phenylacetylene and alk-1-ynes in the presence of Pd2(dba)3(etpo)2 as a catalyst. The structures of the products were determined by NMR spectroscopy using INEPT techniques coupled to computational simulation. Various heteronuclear coupling constants J 13 C − H and J 29 Si − H were determined for the first time in this series. The results showed that the dimesitylboryl group added to the terminal acetylenic carbon atom and the organosilyl group to the internal carbon atom, according to a regio- and stereoselective syn-addition.

Using a new procedure, substituted disilylmethanes have been prepared from chlorosilanes, dichloromethane, and magnesium in tetrahydrofuran. Bis(chlorosilyl)methanes can be used as comonomers for the synthesis of polysilacarbosilanes, which are transformed into polycarbosilanes, precursors of silicon carbide.

Polycondensation of 2,4-disilapentane in the presence of titanium or zirconium-based catalysts afforded original poly(2,4-disilapanentane) oligomers useful as ceramic precursors.

A trans-silylation route to 1,3-dichloro-l,3-dihydridodisilazanes, a novel class of polyfunctional disilazane, is described. Thus, heating hexamethyl- or heptamethyl-disilazane under reflux in the presence of an excess of dichlorohydrogenosilane R 1 SiHCl 2 , led to compounds of formula (R 1 ClHSi) 2 NR 2 (R 1 = Me, Et, Vi or Ph and R 2 = H; R 1 = Me and R 2 = Me) in high yield. The exchange of chlorinated organosilicon moieties was strongly facilited by a catalytic amount of ( π Bu 4 N)F. Interpretation of the results and a few chemical properties of these novel disilazanes are reported.

AlCl 3 catalyse la reaction d'echange CH 3 -Cl sur le silicium du poly(dimethylsilylene) methylene(I) (obtenu a partir du tetramethyl-1,1,3,3 disila-1,3 cyclobutane)

In the presence of lithium and in tetrahydrofuran as solvent, trimethylchlorisilane reacts with tetralin to give two new compounds, (I) and (II). The latter when refluxed with acetic acid leads to a new monosilylated olefin (III). The study of the desilylation mechanism leads to envisage an isomerization of allyl- into vinyl-silane.

In the presence of a Lewis acid (AlCl3, InCl3, GaCl3), acyl chlorides react with allyltrimethylsilane to give the corresponding allyl ketones, CH2CHCH2COR, in good yields. Substituted allylsilanes, synthesized by 1,4-disilylation of conjugated dienes, give a similar reaction. The electrophilic substitution of SiMe3 by a COR group occurs with allylic rearrangement and therefore silylated β,γ-ethylenic ketones, , are obtained. In most cases the allylic ketones prepared isomerize easily to the corresponding conjugated ketones; ketones having the formula CH2CHCH2COR lead uniquely to the trans-,propenylketones, MeCHCHCOR.

Thermolysis of linear or cyclic polydimethylsilanes into polycarbosilanes by Yajima's method has been studied by analyzing the gases evolved by means of gas chromatography and mass spectroscopy. About 20% of silicon was eliminated as methylsilanes during the reaction. Furthermore these results suggest some differences in the mechanisms of reactions with and without catalyst, as in the structures of the polycarbosilanes obtained.

Sulphonation by trimethylsilyl chlorosulphonate of various substituted silicon compounds is regiospecific or highly regioselective at the silicon atom, the reaction order is found to be: allyl > α-naphthyl > phenyl > vinyl. Sulphonation of various mono- and di-silylated derivatives leads to trimethylsilylmono- and in some cases to trimethylsilyldisulphonates which by hydrolysis form new sulphonic acids. The orientation of the sulphonation is determined by the position of the silicon atom. The nature of cyclohexyl hinders sulphonation (cyclo-C 6 H 11 Si is much less reactive than MeSi), while cyclopropanyl, due to its π-character, is much more reactive.

The hydroperoxidation of various allylsilanes by singlet oxygen has been studied. The regioselectivity of this reaction compared to those of ethyl azodicarboxylate and 4-phenyl-1,2,4-triazoline-3,5-dione, is discussed. Mechanisms are considered in the general field of the ene reaction applied to allylic organometallic Group IVB compounds. The structures of the new products (alcohols, urazoles, hydrazines) have been determined, directly or after transformations, by NMR spectroscopy.

Polycarbosilane contenant des groupes (methyl et methyldeuteriosilylene. Reticulation terminale. Reduction du poly[(chlorosilylene)methylene]

The action of the Me 3 SiCl/Mg/HMPT system on various acetylenic hydrocarbons leads by a new route, to mono-, di- or poly-silylated compounds. Most of the derivatives synthetized are new. The persilylation of phenylacetylerie led to a heptasilylated derivative with an unexpected structure, whereas the direct monosilylatmon, which leads to PhCCSiMe 3 , can be carried out in satisfactory yields.

The Me3SiCl/Mg/hexamethylphosphorotriamide (HMPT) system permits the silylation of non-conjugated olefins, for the first time in good yields. At 170–200° in an autoclave, the corresponding saturated monosilylated compound is formed in 40–50 % yield, whereas by refluxing the reaction medium and in the presence of catalysts (FeCl3 or TiCl4), the substitution generally accompanied by rearrangement of an allytic hydrogen, is the main reaction which occurs in low yields.

The trimethylchlorosilane/magnesium/hexamethylphosphoric triamide (HMPT) system reacts with some functional polychlorinated compounds (chloral, hexachloroacetone, acetone chloroform) affording a partial reduction accompanied by silylation and leads to new functional silylated derivatives. These reactions exhibit reductive properties of magnesium, in HMPT, towards the CCl bond.