Mercury silyl anions

Recent years have seen a remarkable development of the preparation, isolation, and characterization of stable silyl radicals. Among these (Me3Si)3Si has gained particular prominence as a popular reagent in organic synthesis [20-26]. In this connection related radicals have been studied to some extent. Following seminal contributions by Matsumoto and coworkers [363-365] key achievements in this development have been made by Sekiguchi and coworkers, which were reviewed only recently [8, 366, 367]. Most stable silyl radicals are trisilylated ones and are commonly prepared either from the respective hydrosilanes, from silyl mercury compounds, by oxidation of silyl anions, or by reduction of silyl halides (Scheme 33) [8]. 

In all examples discussed up to now the radical cation of Qo is involved in the reaction mechanism. However, due to the electronic features reduction of the fullerenes leading to radical anions should be much easier performed. For example, a useful method to synthesize 1-substituted l,2-dihydro-[60]fullerenes is the irradiation of Q0 with ketene silyl acetals (KAs) first reported by Nakamura et al. [216], Interestingly, when unstrained KAs are used, this reaction did not yield the expected [2 + 2]-cycloaddition product either by the thermal, as observed by the use of highly strained ketene silyl acetals [217], or by the photochemical pathway. In a typical reaction Q0 was irradiated for 10 h at 5°C with a high pressure mercury lamp (Pyrex filter) in a degassed toluene solution with an excess amount of the KA in the presence of water (Scheme 11). Some examples of the addition of KAs are summarized in Table 11. 

According to Bard and Merz [108], in MeCN containing TBAP, allyl bromide and allyl iodide interact chemically with a mercury electrode to form allylmercury halides. These allylmercury halides undergo reduction to yield diallylmercury, which is itself electroactive. Allyl bromide and allyl iodide are reduced at platinum in MeCN in a two-electron process to give the allyl anion, and the allyl radical is not involved as an intermediate. Reduction of allyl halides at platinum in DMF containing TEAOTs and in the presence of trimethylchlorosilane results in silylated compounds [100]. 

When bright yellow, solid bis(trimethylsilyl)mercury is treated with trimethylsilyl-lithium in 1,2-dimethoxy ethane (DME), color changes occur and either a three- or a four-coordinated anionic silyl-Hg compound may be isolated according to the stoichiometry ... 

While recent oligosilanyl zinc chemistry was studied by several research groups not much has been done with respect to cadmium. In contrast to this a large variety of oligosilanyl mercury compounds were studied almost exclusively by Apeloig and coworkers, who utilized the unique properties of Si-Hg compounds for the generation of silyl radicals or anions. 

The Apeloig group s most exciting work with silyl mercurials is associated with functionalized sUyl anions and will thus be treated in the respective chapter about this class of compounds. 

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