Hypersilyl

Since then, several different alkali metal silanide systems have been reported. One of them, the hypersilyl [Si(SiMe3)3] ligand, was first prepared by Gilman and Smith.172, 173 Another ligand includes supersilyl [SPBuJ-prepared in 1975.174-176 Several other variations of the ligand systems are known with the recent addition of [SkB Ph]-, for which several alkali metal derivatives have been prepared and characterized.177,178... 

It is instructive to compare the geometry of the supersilyl with the hypersilyl ligands. The geometry at the supersilyl ligands is clearly less pyramidal with G-Si-G angles frequently in the range of 106-107°. In contrast,... 

Solvent-free hypersilanides have been shown to be useful reagents for the preparation of other especially low coordinated hypersilyl derivatives. The thallium(II) compound 6 [1] or derivatives of divalent tin 7 [3] and lead 8 [3] were synthesized via the reactions of (Me3Si)3SiRb (4) with the bis(trimethylsilyl)amides of thallium(I), tin(II), and lead(II), respectively. 

Here we report the syntheses of solvent-free hypersilyl derivatives of sodium and lithium -(Me3Si)3SiLi (1) and (Me3Si)3SiNa (2) - for the first time. Moreover, we are presenting the crystal structures of unsolvated lithium 1, sodium 2, and potassium 3 derivatives and of two additional solvent adducts of the cesium compound 5. 

Hypersilyl lithium 1 and sodium 2 can be easily synthesized by the reaction of an excess of molten sodium or lithium powder with bis(hypersilyl)zinc in boiling nheptane (Eq. 1). After removal of zinc and sodium by filtration and cooling down the reaction mixtures to room temperature, the less soluble sodium derivative 2 precipitates nearly quantitatively in colorless crystals. A similar procedure has been utilized... 

In hypersilyl sodium and potassium both, infra- and intermolecular M "H-C agostic interactions occur, leading to short M -C distances. Interactions of this type were found in many other alkali metal compounds - a survey is given in reference [5]. In the hypersilyl lithiiun dimers only short znframolecular M--H-C contacts are observed (M "C 239, 245 pm), combined with a significant lengthening of the involved Si-C bonds (191 pm) and a pronounced tilting of the hypersilyl ligands (Fig. 3). 

At the moment we are investigating the influence of different donor ligands on the structural features especially of the rubidium and cesium derivatives. Such adducts are prepared by adding the corresponding ligand to a suspension of hypersilyl rubidium 4 or cesium 5 in npentane until a clear solution is obtained. Although, in some cases side-reactions occur, such as deprotonation (diphenylmethane) or reduction (pyrene, bipyridine). In addition to the toluene solvates 4a and Sa already mentioned above, the only two crystalline derivatives isolated so far are the adducts with THF as a typical cr-donor and with biphenyl as a further Ji-donor (Fig. 6 and Fig. 7). 

Summary The gallium hypersilyl derivatives (TMP)2GaSi(SiMe3)3 and... 

The hypersilyl group allows isolation of stable gallium silyl compounds with tri- and tetracoordinated gallium centres. The GaSi bond seems to be inert to protic reagents. 

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