Disilanes properties

Figure 4. shows the route from the high boiling residue of the direct synthesis to silicon carbo-nitride fibers. Methylchlorodisilanes and trichlorosilanes as additives are mixed in a specific ratio and react with methylamine and a small amount of ammonia to form an aminodisilane/oligosilazane. The subsequent polycondensation reaction of this mixture by heating to 250 °C yields a soluble and melt spinnable polysilazane. In comparision with the polysilane the properties of the polysilazane depend on the ratios of the disilanes/silanes and methylamine/ammonia and also on the reaction conditions. 

Stabilizing SISHA interactions were invoked to account for the unusual properties of the chelate complexes [Ru(H)2 (ri -HSiR2)2X (PCy3)2] (141). These compounds were prepared by disilane additions to [Ru(H)2(ri -H2)2(PCy3)2]... 

The proton NMR spectral data of organopolysilanes have often been published incidental to preparative studies (51, 54, 62, 74, 108, 119, 177, 187, 190). Only recently has a systematic investigation to determine the chemical shifts and coupling constants in linear and cyclic permethylated polysilanes, and to study the effects of substituents on the NMR properties of methyl derivatives of disilane and trisilane been reported (see Table V-VII) (206). 

The most important results that throw light on the Si-Si bond are summarized in this review. It deals first with the hydrogen and halogen compounds having Si—Si bonds, describes the preparation and properties of organic substituted disilanes and oligosilanes, and discusses the physicochemical properties of the Si—Si bond. 

The possibilities of synthesis are limited by the general properties of the Si-Si bond to a small number of reaction types. Disilane derivatives were usually synthesized by a Wurtz-like reaction of monosilane halide derivatives with alkali or alkaline-earth elements. Some pyrolysis reactions that have yielded disilane derivatives are also known. Often, new disilane derivatives were prepared from common derivatives by an exchange of substituents. Some rearrangements have been observed in recent years. 

The NMR data for most disilane derivatives are known. However, only a small number of studies have been published relating NMR data to the properties of the Si-Si bond. The chemical shift of the protons of Si2me6 shows only a very small difference in comparison with Sime4 (Si2me6 9.963 0.02 ppm59)), indicating the small influence of the Si-Si bond. 

Abedini, M., and A. G. MacDiarmid Preparation and properties of some new nitrogen and fluorine derivatives of disilane. Inorg. Chem. 2, 608 to 613 (1963). 

The results show that branehed silanes are the preferred products determining the properties of the final oolysilanes. The disproportionation of the disilane mixture gives similar results, whereas the nonsymmetric trichlorodimethyldisilane reacts under abstraction of DMS. Comparing the oligosilane... 

Thermal Properties, Silanes have less thermal stabflity than hydrocarbon analogues. The C—H bond eneigy in methane is 414 kj / mol (98.9 kcal/mol) the Si—H bond energy in silane is 3781 /mol (90.3 kcal/mol) (10). Silane, however, is one of the most thermally stable inoiganic silanes. Decomposition occurs at 500 0 in the absence of catalytic surfaces, at 300°C in glass vessels, and at 180°C in the presence of charcoal (11). Disilanes and other members of the binary series are less stable. Halogen-substituted silanes are subject to disproportionation reactions at higher temperatures (12). 

The Si-Si bond is quite different from the C-C bond and actually resembles more the C = C bond in its chemistry and properties. For example, disilanes readily undergo electrophilic cleavage by the same reagents that add to olefins by cleavage of the tt bond. 

Silicon-based polymers form a dimensional hierarchy from disilanes, to crystal silicon, and through polysilanes, ladder polymers, siloxenes, polysilane alloys, clusters, and amorphous silicons and include unsaturated systems, such as polysilenes, hexasilabenzenes, and so on. Their properties depend basically on the network dimensions and can vary from conducting (metallic) and semiconducting to insulating. 

Summary The stable silylene 1 reacts with halocarbons like dichloro-, trichloro-, and tetrachloromethane at room temperature under formation of the disilane 3. The mechanism of this reaction is still unknown. Results of recent ab initio calculations do not agree with the experimental observations. In this investigation we have studied the photochemical behavior of the stable silylene 1 in a diluted ai]gon-tetrachloromethane matrix at 10 K as well as the thermal properties of 1 in pure solid CCU in the temperature range of 10 - 200 K. The formation of a trichloromethyl radical in both types of experiments indicates that electron transfer may play an important role in these processes. 

Conformational Properties of 1,1,2,2-Tetrakis(trimethylsilyl)disilanes and of Tetrakis(trimethylsilyl)diphosphine a Comparative Vibrational Spectroscopic and ab initio Study... 

Summary An investigation of the conformational properties of the title compounds is presented. Energy profiles for rotation around the central bonds were computed at HF level. Frequency calculations for the optimized geometries were carried out. Temperature-dependent Raman spectroscopy was utilized to revise the cmnputed results. While the results of the ab initio calculations predict up to four minima on the potential energy surfaces (PES), Raman spectroscopy gives unambiguous evidence for more than one rotamer for tetrakis(trimethylsilyl)disilane only. 

Y. Yan, J. Verbiest, P.D. Hulsters, and E.F. Vansant, Modification of Mordenite Zeolites by chemisorption of Disilane and its Influence on the Adsorption Properties. Part 1. - A Modification Parameter Study. J. Chem. Soc., Faraday Trans. 1, 1989, 85, 3087-3094. 

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