Edwin Hengge

Mechanistische aspekte zur übergangsmetall-katalysierten dehydrierenden polymerisation von disilanen und höheren silanen

Abstract The dehydrogenative polymerization of 1,2,3-trimethyltrisilane and a mixture of diastereomers of 1,2,3,4-tetramethyltetrasilane showed evidence that besides the “σ-bond metathesis” mechanism a further mechanism is present. We therefore postulate a silylene mechanism. The silylenes are generated from the transition silyl complex intermediate by well-known α-elimination and a proposed new type of β-elimination which involves SiSi bond cleavage, and is designated “β★-bond elimination”.

Dehydrierende polymerisation von methyldisilanen mittels metallocen-katalyse zu den oligomeren Me3Si[Me2Si]nSiMe2H, HMe2Si [Me2Si]nSiMe2H mit n = 3-9, H[MeSiH]nH mit n = 3-14 und hochpolymetem Poly(methylsilan) (MeSiHx)n

Abstract Dehydrogenative polymerization of pentamethyldisilane by means of CP2MMe2 (M  Ti, Zr) afforded a mixture of the oligosilanes Me3Si[Me2Si]2 SiMe2H; 1,1,2,2-tetramethyldisilane reacts to a mixture of the oligosilanes Me2HSi[ Me2Si]nSiHMe2. Dehydrogenative polymerization of 1,2-dimethyldisilane by use of Cp2MR2 (M  Ti, Zr; R  Me, nBu) afforded the new unique cross linked polysilane polymer poly(methylsilane) (MeSiHx)n. The pyrolysis of (MeSiHx)n at 1500°C (argon) gives a ceramic yield (SiC) of 88%. The polymerization progress is observed and investigated by GLC, GC-MS and 29Si-NMR spectroscopy, and the oligomers, formed at the beginning of the polymerization, are identified.

29Si-NMR-Untersuchungen an einigen Cyclosilanderivaten

Abstract29Si-NMR spectras of some new cyclosilane derivatives were measured. First aspects of the dependence of chemical shift on ring size and kind of substituents are given.

Zur elektrochemischen Bildung von Di-, Oligo-und Polysilanen

The electrochemical reduction of halosilanes is presented as a new method for formation of SiSi-bonds. Cathodic reduction of triorganosilanes, usingDME as solvent and tetrabutylammoniumperchlorate as supporting electrolyte, yields the corresponding disilanes in nearly quantitative current efficiency. In contrast, monochloropermethyldisilane and 1,2-dichlorper-methyldisilane do not react to tetrasilanes. Diphenyldichlorosilane gives the cyclic compound (SiPh2)4 besides polymeric products. Trichloromethylsilane and silicontetrachloride react to yellow polymers. The possible reaction mechanisms is discussed.

Darstellung und eigenschaften von heterocyclischen silanen des typs Si4X MIT X = B, N, O

Five-membered heterocycles Si4Ph8X with X = BNMe2, NMe, NEt and O were prepared and characterised with 1H NMR, UV, far IR and Raman spectra. The problem of electron delocalisation in these ring systems containing an electron excess (N) or an electron deficit (B), respectively, is discussed. These measurements suggest that there is no delocalisation.

Dehydrierende copolymerisation zu den neuen polysilan-copolymeren poly(methyl-co-phenylsilan) H[(MeSiH)x(PhSiH)y]nH und Poly(methyl-co-dimethylsilan) H[(MeSiH)x(Me2S)y]nH

Abstract Dehydrogenative copolymerization of PhSiH 3 with MeH 2 SiSiH 2 Me and of Me 2 HSiSiH 2 Me with MeH 2 SiSiH 2 Me by means of Cp 2 MMe 2 (Cp  (C 5 H 5 , M  Ti, Zr) afforded the new polysilane-co-polymers poly(methyl-co-phenylsilane) H[(MeSiH) x (PhSiH) y ] n H and poly(methyl-co-dimethylsilane) H[(MeSi) x (Me 2 Si) y ] n H. The progress of copolymerization is investigated and analyzed by gas liquid chromatography (GLC) and GLC-mass spectrometry (GLC-MS). A variety of new organosilicon compounds, formed at the beginning of the copolymerization, were identified by GLC-MS analysis.

Zur Chemie der Cyclohexasilane

Starting from Si6ph12 (I) the cyclohexasilanes Si6ph6Br6 (II), Si6ph6H6 (III) and Si6Br12 (IV) and a cyclopentasilane, Si5ph8me2, were prepared and characterized by analysis, NMR- and mass spectroscopy. A high stability of the five membered ring in comparison to the other ring sizes is found by chemical investigation and by mass fragmentation. I. r. and Raman spectra were measured and assigned, high coupling effects, mainly in the SiSi region, explain some anomaluos frequencies.

Synthesis, properties and characterization of octadecamethylbicyclo[4.4.O]decasilane

Abstract The title compound 1 was obtained by Wurtz-type dehalogenative coupling of syn -dichlorotetramethyldisilane and trichloromethylsilane under appropriate conditions. Spectroscopic data for 1 are compared with those for bi(undecamethylcyclopentasilanyl) ( 2 ), a possible structural isomer. An X-ray structural study and 29 Si-INEPT-INADEQUATE-NMR spectroscope confirmed that only the trans -isomer of 1 is formed. Several attempts were made to obtain functional derivatives, but monocyclic and catenated oligosilanes were always obtained owing to breakdown of the bicyclic compound. Chemical and electrolytic reduction towards an anion radical was carried out at various temperatures. The ESR signal at 150 K shows an overlap of two distinct species; along with the spectrum of the well known Si 5 Me 10 − radical anion that of a hitherto unknown species was observed.

Zur darstellung von permethylierten cyclosilanylalkalimetall-derivaten

Abstract A simple way for the preparation of undecamethylcyclohexasilanylalkalimetal compounds is described by the reaction of dodecamethylcyclohexasilane with alkalimetal alcoholats in glyme solvents. Reactions of other cyclosilanes are also discussed. Some reactions of undecamethylcyclohexasilanylpotassium with element-halogen derivates and inorganic acids are described.

Dehydrogenative polymerization of disilanes catalysed by titanocene and zirconocene complexes. A novel route to oligo- and poly-silanes

Polymerization of Me3SiSiHMe2, Me2HSiSiHMe2 and MeH2SiSiH2Me takes place readily in the presence of Cp2MR2 catalyst (CP = C5H5; M = Ti, Zr; R = Me, nBu) in the absence of a solvent (“polymerization in bulk”) to give a mixture containing trisilanes, tetrasilanes, pentasilanes, higher oligosilanes and polysilanes. Depending on the reaction conditions different proportions of linear oligo- and poly-silanes are obtained. MeH2SiSiH2Me also yields branched oligo- and poly-silanes. Polymerization of MeH2siSiH2Me “in bulk” in the presence of a catalytic amount of Cp2MR2 (CP = C5H5; M = Ti, Zr; R = Me, nBu) leads to a new type of polysilane polymer, poly(methylsilane), (MeSiHx)n, which is thought to be the first organosilicon “living polymer”. MeH2SiSiH2Me is also polymerized in inert solvents in the presence of Cp2MR2 (CP = C5H5; M = Ti, Zr; R = Me, nBu, Ph) catalysts.