Aminofluorosilanes

The lithium derivative of the Ph-substituted aminofluorosilane crystallizes from THF as a monomeric LiF adduct of an iminosilane, (THF)3LiF (CMe3)2Si=NSiPh(CMe3)3.2I... 

In general, almost all lithiated aminofluorosilanes—the LiF adducts of iminosilanes—react like iminosilanes.18 Only exceptional reactions are mentioned here.18... 

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... 

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

Summary Lithiated aminofluorosilanes can often be regarded as LiF adducts of iminosilanes on account of their structures. They are suitable precursors to iminosilanes after fluorine-chlorine exchange. 

Essentially three factors determine the structural make up of the lithium derivatives of aminofluorosilanes ... 

Aminofluorosilanes 679 are formed in the reaction of difluorosilanes with lithiated amines. 679 can then be metalated by RLi (R = Me, Bu) to give the corresponding lithium salts (e.g. 680a). The structure of salts 680 depends on the basicity of the nitrogen atom and on the solvent. Representative structure types (680a-c) will be discussed in the subsection dedicated to structural features. The thermal elimination of LiF leads to silanimine dimers (e.g. 682 from 680c), if sterically possible (equation 223), or to rearrangements. 

The lithiated aminofluorosilane f-Bu2Si—N—Si(OSiMc3)Pr-/2 FiF 2 809 behaves in the same way, and its cycloadduct with benzaldehyde decomposes into the respective imine and cyclotrisiloxane above 105 °C354. 

The reaction of equation 14 probably occurs stepwise, and it is a complex process involving substitution reactions and/or homo- and heterofunctional condensations. Numerous cyclodi-, tri- and tetrasilazanes (76) are obtained in the reactions of aminofluorosilanes (74) with lithium organyls via thermal LiF elimination of lithium aminofluorosilane derivatives (75) (equation 18)69-75. The primary products of such condensations in the reaction of fluorosilanes with lithium amide have been synthesized in order to study the mechanisms of their formation. An (R2SiFNLiH) compound was characterized by X-ray diffraction8,76 77. 

Cyclotrisilazanes are obtained in the ammonolysis of dichlorosilanes (equation 14), LiF elimination from lithiated aminofluorosilanes (equation 18) and MejSiHal elimination from trimethylsilylaminohalosilanes (equation 19). In the reaction of the dilithiated tert-butyldimethylsilylamine and SiF4 the only known hexafluorocyclotrisilazane (100) was isolated beside a four-membered ring 99 (equation 26). The cyclotrisilazane is the first Si—N six-membered ring which crystallizes in a twist conformation. 

Summary Lithiated aminofluorosilanes can often be regarded as LiF adducts of iminosilanes on account of their structures [1], They are suitable precursors to iminosilanes after fluorine-chlorine exchange followed by elimination of lithium chloride [1,2]. This synthesis shows the following features (a) the method is a general one in the sense that it can be applied to differently substituted aminosilanes (b) the iminosilanes are obtained, either as THF adducts or as free imines in good yield (c) the tedious and sometimes complicated synthesis of aminochlorosilanes as precursors is avoided, since the fluorine-chlorine exchange takes place in one step in the lithium derivative. 

Lithiated aminochlorosilanes are obtained in reactions of lithiated aminofluorosilanes with Me3SiCl by a fluorine-chlorine exchange. LiCl is easily eliminated, and monomeric or dimeric iminosilanes are formed. 

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. 

Aminofluorosilanes have NH- and SiF-fiinctional groups. Lithiation of the NH-flinction makes either intramolecular elimination of lithium fluoride or fluorine-chlorine-exchange by MesSiCl possible... 

Intra- and intermolecularly stabilized iminosilanes are obtained by using heteroaromatic substituted aminofluorosilanes. For example, the bicyclic system 3 is obtained in an insertion reaction of the iminosilane into a polar C-H bond of the pyrrole substituent. Using smaller substituents the [2+2] cycloaddition product 4 is obtained [6]. 

The substitution of the hydroxyl H-atom of H2NOH by fluorosilanes results from the reaction of NF120H-HC1 with aminofluorosilanes 1. If the substituents of the fluorosilanes are small the product cannot be isolated, because it polymerizes on removal of the solvent. However, when bulky substituents are used the product can be distilled at reduced pressure. These fluorosilylhydroxylamines 2 show no tendency to condense. 

Cyclodisilazanes are obtained in the reactions of aminofluorosilanes with organolithiums via thermal LiF elimination of Li aminofluorosilanes - ... 

Substitution products are obtained with the aminofluorosilanes with the monolithiated ring , and four-membered rings are formed in a further reaction as well as with the dilithium salt and the aminofluorosilanes in a 1 2 mole ratio. 

In the mid-1980s the first stable iminosilanes were prepared by two independent routes by Wiberg et al. and our group [1]. We discovered that lithium derivatives of bulky aminofluorosilanes which react with MeaSiCl by a fluorine-chlorine exchange in the presence of the Lewis base THF are suitable precursors of iminosilanes because they allow subsequent LiCl elimination (Scheme 1). The unsaturated Si=N compounds can be purified by distillation in vacuo. 

For a further understanding a great number of crystal structures of lithiated aminofluorosilanes was examined by X-ray structure determination and a great variety of structural types was found [2]. 

The products of the reaction of lithiated aminofluorosilanes with AICI3 were the first reported unsaturated silicon compounds [7-9] they form four-membered rings with bridging chlorine atoms as exemplified in Fig. 4 (12). In a similar reaction with BF3 OEt213 is formed (Fig. 5). 

For further data on lithiated aminofluorosilanes see Reference 305. For further data on silaamidides see Reference 346. 

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