Oligosilanes synthesis

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. 

Another important aspect is the very simple preparation of the silyltriflates. Systematic investigations of the cleavage of the silicon element bond (Si-E) by CF3SO3H have shown that the reaction rate decreases in the sequence (E=) a-naphthyl > phenyl > Cl > H > alkyl [3]. Therefore especially pure silyltriflates result from protodesilylation of arylsilanes with CF3SO3H. On the basis of these general results the synthesis of a large number of variously substituted silyltriflates [4,5] can be planned. This is of particular interest in the chemistry of oligosilanes. 

Numerous synthetic strategies for "preceramics" based on polysilanes are known, but the synthesis of Si-Si chains with different substituents on the silicon skeleton is difficult. In the following the advantages of the triflate method for the synthesis of special substituted oligosilanes are shown by some examples. 

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. 

Using DME/nheptane in the first reaction step, synthesis of ditungsten substituted oligosilanes is possible within 24 h. The bright yellow product can be separated by fractional recrystallisation from npentane. 

Coupling of photochemically-generated silyl radicals is a useful method for synthesis of branched oligosilanes. An example is given in equation 18. 

Summary Amination of chlorosilanes with dialkylamine allows the synthesis of various chloro- and amino-substituted oligosilanes. The remaining reactive chloro sites enable to bond further hinctionalities as well as other silyl units to the silane. In this procedure the amino group is protecting potentially reactive sites at silicon atoms and can be easily exchanged by chloro substituents. By this route a desired silicon architecture can be built up. 

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