Dimerization iminosilanes

Lithiated Aminofluorosilanes as Precursors for Monomeric and Dimeric Iminosilanes... 

Lithiated aminochlorosilanes are obtained with MejSiCl by a fluorine-chlorine exchange, for example 3 (Figure 2) [2], LiCl is easily eliminated. Monomeric or dimeric iminosilanes are formed [3,4]. 

The last variant requires thermally less drastic conditions for the elimination of lithium chloride, and monomeric or dimeric iminosilanes are formed. 

The first silaethenes and disilenes were synthesized at the beginning of the 1980s, and the first iminosilanes were reported in the mid-1980s. The difference in the electronegativity between Si (1.8) and N (3.0) gives the iminosilanes an ylidic nature, which makes them susceptible to oligomerization and dimerization. 

The formation of the cyclodisilazane ring system can be explained by dimerization of the unstable iminosilane in the cold trap.7... 

The lithium derivative of the aminosilane (Me3C)2SiFNHSiMe(CMe3)2 forms a dimeric LiF adduct of the iminosilane [(Me3C)2SiFLiNSi-Me(CMe3)2]2 associated via Li—F contacts. 

Lithiated aminofluorosilanes are often very stable and can be purified by distillation. Attempts to eliminate LiF lead to dimerization or rearrangement of the polar iminosilane formed. The limits of dimerization have been reached in the dimeric (Me2HC)2Si=N-2,4,6-C6H2(CMe3)3.18-20... 

These molecules can be interpreted as dimers of Li-F adducts of iminosilanes. They react like silylamides as well as like iminosilanes. 

Summary One of the remarkable features of lithiated aminofluorosilanes and dilithiated diaminofluorosilanes with bulky substituents is that they do not undergo the expected substitution on treatment with MesSiCl on the nitrogen atom but instead on the silicon atom to give lithium derivatives of aminochlorosilanes. These salts are far less stable than the analogous fluorine compounds. LiCl elimination leads to the formation of iminosilanes and monomeric and dimeric silaamidides. 

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