Oligosilanes linear

Linear Tetrasilanes with Internal Substituents Oligosilanes with Optical Activity... 

Recently a number of linear and branched oligosilane derivatives have been synthesized from easily accessible precursors using mainly organometallic routes [1,2]. Now we are able to report on the first successful synthesis of tetrasilanes of the general formula H3SiSiHXSiHXSiH3 (X = Ph, Cl, Br) bearing internal substituents. 

The cleavage of a Si—Si bond in silacyclic compounds by lithium metal is the most versatile method to prepare linear, a, -dilithiated oligosilanes. The first dilithio compound obtained by Gilman and coworkers in this way was Li(Ph2Si)4Li (equation 29)72. 

FIGURE 1. Schematic representation of the interactions between sp3(Si) hybrid orbitals in linear oligosilanes. (a) Reprinted by permission of The Royal Society of Chemistry, from Reference 33 (b) Reprinted with permission from Reference 17. Copyright 1970 American Chemical Society... 

Many cyclic and linear transition metal-silicon compounds have been obtained by the elimination of alkali halides with the corresponding transition metal salts145,146. The synthesis and reactivity of the Fe-oligosilane systems have been studied in detail by Pannell147-154 and this area has been recently reviewed155. 

An example of the enhanced cross-linking approach involves the pyrolysis of cyclic and linear oligosilane precursors that bear vinyl or acetylenic side groups.34 These are... 

Wurtz coupling reactions of chlorosilanes are the main route to the silicon-silicon bonded compounds. For example, hexamethyldisilane can be prepared by refluxing trimethylchlorosilane with lithium sand in THF (97%). Lithium may be substituted by sodium by using a mixture of HMPA-THF as the solvent. Linear and branched oligosilanes can be prepared by the same method (equations 55-57). 

Similar results are observed in the reaction of a disilanyllithium with a chlorodisilane (28), as shown in Scheme 3. When a mixture of monosilyl and disilanyl anions is introduced to l-chloro-2-phenyltetramethyldisilane, the usual coupling products, 1,3-diphenyltrisilane and 1,4-diphenyltetra-silane, are formed. Alternatively, when the chlorosilane is added into a mixture of the anions, the scrambling processes via the Si-Si bond cleavage occur, to give a mixture of linear and cyclic oligosilanes. These results indicate that the scrambling processes are very fast, but much slower than the coupling of anions with chlorosilanes (see also Section VI-B). 

One of the basic properties of siloxenes is their general insolubility in organic solvents, a fact that strongly impedes physical and structural characterization. As a result, the question arose as to whether structurally better defined siloxene-like polymers with improved solubility can be assembled in a stepwise manner starting from appropriate molecular precursors, and whether the properties of siloxene, such as the intense photoluminescence, can be matched. We thus attempted to rebuild the proposed structure of Kautsky-siloxene by the controlled hydrolysis of cyclic or linear oligosilanes bearing hydrolytically labile substituents followed by the thermal condensation to polymeric siloxanes. The general route is outlined in Scheme 16.1. 

Reaction of LiN(TMS)2 with Linear Oligosilanes SisCls and Si4CIio... 

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