Cyclisierende Polymerisation von Acetylen I Über Cyclooctatetraen

The chemistry of silicon is mainly based on silicon(IV), whereas that of silicon(II) is still in its infancy. Silylene (R2Si:) is a molecule with a divalent neutral silicon atom having a lone pair of electrons. Silylenes are key intermediates in various photochemical, thermal, and metal reduction reactions of organosilicon compounds. Therefore, silylenes play a vital role in the field of silicon chemistry. Until 1994, silylenes were generally considered to be very reactive unstable species that decompose or polymerize readily at temperatures above 77 K. This situation changed when West et al. reported the first N-heterocyclic silylene that is stable at room temperature. Since then, a fair number of cyclic silylenes and a dialkyl silylene have been reported. Only one example of a monochlorosilylene that is stable at room temperature has been published, and it was characterized by X-ray diffraction; no dihalosilylenes that are stable at room temperature have been reported to date. Gaseous dichlorosilylene has been known for many years; at room temperature, it condenses to polymeric (SiCl2)n. Its properties were already studied by Schmeisser and Schenk in 1964. Some reactions of condensed SiCl2 with acetylene and with benzene were carried out by Timms in 1968, and resulted in brown polymeric products of unknown composition. A literature survey reveals that there have been few reports on the synthesis and properties of cyclic and linear polydichlorosilanes. A polymeric perchloropolysilane (SiCl2)n was reported by West et al. in 1998 and was studied by single crystal Xray diffraction. However, access to dichlorosilylenes that are stable at room temperature and with electronic structure and properties are quite similar or close to those of unstable examples, such as SiCl2, is still a challenge. Of course, efforts of making a stable version of a very reactive species may cause a change of its behavior. How an unstable species can be stabilized is a matter of keen interest for the scientific and industrial community. Addition reactions of HSiCl3 with different organic compounds in the presence of various tertiary amine bases were reviewed by Benkeser, and the existence of the trichlorosilyl anion as an intermediate was postulated. Moreover, Jung et al. reported the trapping of dichlorosilylene, which was generated by the reaction of HSiCl3 in the presence of phosphonium chloride in a stainless steel cylinder at 150 or 180 8C, by conjugated dienes and by an alkyne. In their proposed mechanism, species of dichlorosilylene or the trichlorosilyl anion as intermediates were discussed but not isolated. In 1995, Kuhn et al. prepared N-heterocyclic carbene (NHC) adducts of SiCl4. We have used N-heterocyclic carbenes as dehydrochlorinating agents for the preparation of germylene and metal hydroxides. Very recently, Robinson and co-workers reported a Lewis base stabilized low-valent silicon compound in which the silicon atom is present in the formal oxidation states + 1 or zero, but no dichlorosilylene was isolated. Almost all silylenes or low-valent silicon compounds reported to date were prepared by reductions of their parent compounds using strong reducing agents, such as potassium metal or KC8. Herein, we report the synthesis of the first basestabilized dichlorosilylene that is stable at room temperature, LSiCl2 (1; L 1 = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). This compound is formed under mild reaction conditions by reductive elimination of HCl from trichlorosilane in the presence of the NHC (L; Scheme 1), and was

Lewis Base Stabilized Dichlorosilylene

The aqueous geochemistry of gallium, germanium, indium and scandium

Silicon molecular beam epitaxy

Polarized and depolarized Raman spectra of alkali germanate glasses are given, together with Raman powder spectra of the crystalline compounds Li2O · 2 GeO2; 3 Li2O · 8 GeO2; 2 Li2O· 9 GeO2; Li2O · 7 GeO2; 2 Na2O · 9 GeO2; K2O · 2 GeO2; K2O · 4 GeO2 and K2O · 8 GeO2.

The alkali germanate glasses: xA2O (1−x) GeO2 are studied in the composition range 0 < x < 0.333. The vibrational modes observed in the high energy range of the Raman spectra of the crystalline compounds are interpreted in terms of symmetrical and antisymmetrical O-Ge-O and Ge-O− stretch vibrations. The molecular structure of the germanate glasses is deduced from a comparison of the Raman spectra of the glasses with those of the crystalline compounds, together with a study of the polarization properties of the glass spectra.

It is observed that 6-coordinated Ge atoms occur in a network structure which resembles the structures occurring in the crystalline compounds 2 Li2O · 9 GeO2 and 2 Na2O · 9 GeO2.

In the region of 0.18 < x < 0.33 it is found that tetrahedra with one non-bridging oxygen atom are formed. These tetrahedra are probably present in a network as occurs in the crystalline digermanates Li2O · 2 GeO2 and K2O · 2 GeO2.

The structure of lithium, sodium and potassium germanate glasses, studied by Raman scattering

1. Bei der Zersetzung der gesattigten Silane in der stillen und in der elektrodenlosen Ringentladung entstehen hochpolymere feste Hydride von nngesattigtem Charakter, deren Zusammensetzung je nach den Versuchsbedingungen zwischen SiH1,2 und SiH1,7 schwankt. Die Eigenschaften dieser Hydride werden beschrieben.

Über ungesättigte Siliciumhydride

Über Ein Siliciumchlorid der Formel Si10Cl22

Die Peroxydhydrate der Titangruppe wurden betreffs des Gehalts an aktivem Sauerstoff und an Hydratwasser untersucht. Das Verhaltnis Oxyd : akt. O : H2O ergab sich beim Titan, Zirkon, Hafnium und Cerium ubereinstimmend als 1:1:2. Die Peroxydhydrate sind als Peroxyorthosauren vom Typus Me(OOH)(OH)3 zu formulieren. Fur das Thorperoxyd wurde die Formel Th2O7·4H2O gefunden.

Über die Peroxyde des Titans, Zirkons, Hafniums und Thoriums

Zur Kenntnis der Kieselsäuren (III.)

Bei der thermischen Zersetzung des Si10Cl20H unter Normaldruck bei 300° entsteht in einer inerten Gasatmosphare ein fester, gelber Korper von blattriger, amorpher Struktur. Die Analyse ergibt ein Atomverhaltnis von Si : Cl wie 1,00:1,00. Bei der Zersetzung mit Kalilauge lost sich der gelbe Korper unter sturmischer Wasserstoffentwicklung vollstandig auf. Die Reaktion verlauft nach 






.

Einige neue Halogenide des Siliziums. IV. Über ein Siliziumchlorid der Formel SiCl

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