Silyl anions synthesis

Germyl, Stannyl, and Plumbyl Anions The preparative methods for the synthesis of the germyl, stannyl, and plumbyl anions are essentially the same as those mentioned above for the silyl anions. The most widely used methods are (1) reduction of halides R3EX (R = alkyl, aryl E = Ge, Sn, Pb X = Cl, Br) with alkali metals and (2) reductive cleavage of the E-E bond of R3E-ER3 (R = alkyl, aryl E = Ge, Sn, Pb) with alkali metals or organolithium reagents. Due to the favorable polarization of the (E = Ge, Sn, Pb) bond, the direct metalation... 

The chemistry of metalated organosilicon compounds has been the subject of several reviews1, the most recent ones by Lickiss and Smith13 and Tamao and Kawachilb, which cover the literature up to the year 1994. This chapter will now take into account the developments in the chemistry of metalated silanes up to the middle of 1996 however, for completeness there will be some overlap with former reviews. The emphasis of this review is on the synthesis and structure of these metalated silanes. However, some examples of their utilization for synthetic purposes will also be given where appropriate. For more information about synthetic applications of silyl anions the reader is referred to some leading references in this fieldla,b h k. 

The standard method for synthesis of polysilanes follows the original preparation of (Me2Si) by Burkhard. Diorganodichlorosilanes are treated with finely dispersed sodium metal in an inert diluent, usually above the melting point of sodium. Homopolymers are obtained from single dichlorosilanes, while cocondensation of mixtures of dichlorosilanes yields copolymers (equation 33). Toluene is the most commonly used solvent, but other aliphatic or aromatic solvents are also effective. After completion of the reaction, the mixture is quenched with alcohol and/or water to destroy any excess sodium and silyl anion, then filtered and... 

Colvin, E. Silicon in Organic Synthesis Butterworth London, 1980 Chapter 11. The article is only six pages but gives a good update on silyl anions. 

Certain silyl anions are useful silylating reagents in organic synthesis. Since some leading reviews have covered the synthetic applications Ud,e/,2), only a few typical examples are mentioned here. 

The selective cleavage of one terminal trimethylsilyl group [2] with potassium tert-butoxide is a superior protocol for the synthesis of silyl anions. Also in the case of vinylsilanes, the method proved to be equally selective and efficient (Eq. 2), providing quantitative yield of the first vinylsilyl anions (4a, 4b). 

Some years ago Hengge et al. published a feasible synthesis of KSi6Men (1) and did basic research on the reactivity of this silyl anion including the preparation of transition metal complexes [1-3]. Our group contributed two crystal structures of such compounds [4, 5]. In an effort to get further insight into the reactivity of 1 and the structures of its transition metal conq>lexes, we reacted it with various transition metal conq>ounds. 

Since the preparation of anionic species or organosilicon compounds is largely restricted by its reaction conditions, the synthetic utility of silyl anions for the synthesis of organosilicon compounds is limited. However silyllithiums possessing one or more phenyl groups on a silicon atom are readily prepared by the reductive metallation of the corresponding halosilanes with lithium. Allylsilanes are synthesized by the reaction of allyl acetates with the cuprate prepared from such a reagent (eq (47)) [43]. 

Summary The synthesis of a,(0-bis[tris(trimethylsilyl)silyl] alkanes was achieved by the reaction of ct,(0-ditosylalkanes with tris(trimethylsilyl)silyl potassium. Reaction of these with one equivalent of potassium /er/-butoxide resulted in clean formation of monopotassium silyl anions. Addition of another equivalent of the transmetallating agent led to the formation of the dipotassium compounds in cases where the alkyl spacer contained at least three methylene units. Partial hydrolysis of the dipotassium compounds induced an intramolecular reaction yielding a cyclic silyl potassium compound. 

With substituents like 9-methylfluorene and diphenylmethane, Si-C bonds can be activated for a cleavage under mild conditions. In contrast to the 9-methylfluorenyl-substituted silanes 7a and 7b, diphenylmethyl-substituted tetraorganosilanes of types 10a, 10b and roc-20 have proven to be valuable precursors for the synthesis of silyllithium reagents like 11a, 11b and rac-21 (Eq. 5). Therefore they correspond well to the silyl anion synthons B. Furthermore the bis(diphenylmethyl)-substituted silane 15 allows a sequential synthesis of unsymmetrical trisilanes and thus is a valuable silyl dianion synthon D (Eq. 6). 

Unlike carbanions and silyl anions, boryl anions (BR2"), in the form of boryllithiums, have been unknown until recently. In 2006, Japanese researchers reported the synthesis of a boryllithium via the reduction of a cyclic (diamino)bromoborane with lithium/naphthalene in THF, that is, Li+Np , where Np is the anion radical of naphthalene (Segawa, Y. Yamashita, M. Nozaki, K. Science 2006, 314, 113-115) ... 

Quirk RP, Janoski J, Chowdhury SR. Anionic synthesis of chain-end and in-chain, cyano-functionalized polystyrenes hy hydrosUylation of aUyl cyanide with silyl hydride-functionahzed polystyrenes. Macromolecules 2009 42 494-501. 

Quirk RP, Kim H, Polce MJ, Wesdemiotis C. Anionic synthesis of primary amine functionalized polystyrenes via hydrosUation of allylamines with silyl hydride functionalized polystyrenes. Macromolecules 2005 38 7895-7906. 

Three groups of workers have reported the use of the addition of allyltrimethyl-silyl anion to aldehydes, giving P-hydroxy-silanes, and their subsequent elimination to give dienes. Yamamoto et al. have reported the diastereoselective synthesis of the threo-o coho (209) by the boron- or aluminium-mediated reaction of (208), and of the erythro-dXcohols (210) by using the tin-mediated reaction of (208). A similar approach, using the titanium-catalysed addition... 

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