Tris silyllithium

Tetraalkyl- or tetrasilyltetragallium(I) compounds were also obtained by the reactions of the dioxane adducts of Ga2X4 (X = Cl, Br) with bulky alkyl- or silyllithium compounds [Eq. (5)], which were accompanied by disproportionation of Ga(+2) to Ga(+1) and Ga(+3) [44, 45], In particular the yield of the alkyl derivative 21 was very poor and several unknown byproducts were detected by NMR spectroscopy. Furthermore, the reaction requires the employment of a solvent-free lithium compound, which is not readily available. The reaction of tris(trimethylsilyl)silyl lithium yielded the expected product of the disproportionation [(Me3Si)3Si]2GaCl2Li-(THF)2 besides compound 11. 

Silenolates 26, i.e. silicon analogues of enolates, are formed, as shown by Ishikawa and coworkers, when sterically congested tris(trimethylsilyl)acylsilanes 25 are treated with silyllithium compounds (Scheme 10)87a b c The silyllithium reagent does not add to the C=0 bond but exclusively cleaves a Si—Si bond, yielding the corresponding silenolate 26. 

Presumably, a new kind of rearrangement process takes place in the reaction of dicyclopentadienyltungsten dichloride with tris(trimethylsilyl)silyllithium (equation 3473). Silyl complexes formed as intermediates spontaneously rearrange with formation of silylcyclopentadienyl complexes, but the mechanism of this process is not yet clear. 

Tris(trimethylsilyl)silyllithium, which is readily formed upon treatment of tetrakis(trimethylsilyl)silane with methyllithium or triphenylsilyllithium in ether-tetrahydrofuran (63), is useful as the reagent for construction of molecules of an interesting class of highly sterically hindered methyl-polysilanes. The synthesis of hexakis(trimethylsilyl)disilane gives an example (59). 

In agreement with this hypothesis, tetrakis(trimethylsilyl)silane gives tris-(trimethylsilyl)silyllithium when treated with methyllithium or triphenyl-silyllithium in tetrahydrofuran (63). 

Preparation of the branched silane began with the reaction of tris(trimethylsilyl)silane with CHC13 (CC14) and MeLi to afford the peralkylated methyl[tris(trimethylsilyl)]-silane. Subsequent treatment with A1C13 and ClSiMe3 gave the trichlorosilane, which was then reacted with tris(trimethylsilyl)silyllithium yielding the final silane dendrimer. 

A different approach that even obviates the use of a preformed silyllithium reagent takes advantage of the cleavage of the Si-Si bond of a disilane by a copper salt. Hosomi and co-workers185 have reported on the reaction of various enones or enals 250 with hexamethyldisilane or l,l,2,2-tetramethyl-l,2-diphenyldisilane, catalyzed by copper(i) triflate-benzene complex (Scheme 61). The transformation requires heating to 80-100 °C in DMF or DMI and the presence of tri-/z-butylphosphine in order to stabilize the copper catalyst under these harsh conditions. The addition products 251 were obtained with high yield after acidic work-up. The application of the method to alkylidene malonates as the Michael acceptor was recently disclosed.1... 

Similarly, when silene 2a is generated in presence of excess tris(trimethylsilyl)silyllithium, the lithium silanide is added across the silicon-carbon double bond to give an organolithiiun intermediate, which undergoes a rearrangement, a l,3-Si,C-trimethylsilyl migration, resulting in formation of a lithium silanide, which is trapped with chlorotrimethylsilane to yield the polysilane 7. The H-silane 8 is obtained as the protonation product after usual hydrolytic work up (Eq. 4-5). 

Tris(trimethylsilyl)silyllithium, (Me3Si)3SiLi, and its derivatives that contain branched silicon chains are the most extensively investigated species among polysilanyllithiums. 

Trans-l,2-bis[tris(trimethylsilyl)silyl]ethylene 5 was obtained from the reaction of tris(tri-methylsilyl)silyllithium with formic acid methyl ester [7]. The corresponding dianion 6 was obtained as the only reaction product in a fast reaction of 5 with two equivalents of potassium tert-butoxide in the presence of two equivalents of crown ether as the first example of a vinylidene-bridged oligosilyl a,co-dianion (Eq. 3), which is in good analogy with our previously synthesized alkynylidene- and alkylidene-bridged compounds [3,4, 8]. 

Keywords Reaction Intermediates / Tris(trimethylsilyl)silyllithium / Lithium Silyl Cuprates / Disilagermirane... 

The reaction of tris(trimethylsilyl)silyllithium with AICI3 at -78°C yields the aluminate [Li(THF)4][AlCl3Si(SiMe3)3] [10], This Lewis base adduct can be interpreted as an LiCl-containing intermediate of the reaction towards [(MesSOsSiAlCL]. As a building block this intermediate makes soluble alumosilicates feasible that can be used in homogeneous catalysis. 

The application of tris(trimethylsilyl)silyllithium to stabilize reactive intermediates and to form small rings of group 14 elements are summarized in Scheme 1. 

Preparation and Structure of Tris(tetrahydrofuran)tris(trimethylsilyl)silyllithium... 

Following the original 1968 recipe of Gilman and Smith [2] a white crystalline product (1) is obtained in 69% yield. The crystal structure of this compound [12] (Fig. 1) revealed it to consist of 2 equiv. of the desired tris(trimethylsilyl)silyllithium which cocrystallized with 1 equiv. of the starting material tetrakis(trimethylsilyl)silane. 

As expected the structure of the lithiated component in 1 is almost identical to the structure of the pure tris(trimethylsilyl)silyllithium 2. Interestingly, the lengths of the Si-C and Si-Si bonds are almost unaffected by the lithiation compared to those of the starting material [12]. The average Si-Li bond length of 266 pm is consistent with other Si-Li bond lengths previously reported [13]. 

Unfortunately, in all of the known cases reductive cyclization with, e.g., lithium naphtalide was necessary to obtain the products. With this route the synthesis of three-membered rings containing various group 14 metals is limited and yields are poor. In contrast, reaction of 2 equiv. of tris(trimethylsilyl)silyllithium with GeCb at -78 C yields (Me3Si)2Si 2Ge(SiMe3)2 (3) in a straightforward way [9] (Fig. 4). 

As a product of the reaction between tris(trimethylsilyl)silyllithium and AICI3 at low temperature the aluminate 4 was isolated [10] (see Fig. 5). 

Methoxy-bis[tris(trimethylsilyl)silyl]methane (4) - the first compound bearing two hypersilyl groups at a carbon atom - was synthesized by the reaction of tris(trimethylsilyl)silyllithium (1) with dichloromethyl methyl ether in a yield of 35 % In view of the extreme bulkiness of the two hypersilyl substituents, the ease of the formation of 4 is really surprising. But the reaction pathway is easily understood as a consecutive replacement of the two chlorine atoms of the dichloromethyl methyl ether by the silanide 1 (Eq. 1). 

Hoffmann, D., Reinke, H., Oehme, H. The reaction of tris(trimethylsilyl)silyllithium with dibenzosuberenone. J. Organomet Chem. 1996,... 

The preparation of a variety of higher polysilanes using silylmetallic reagents has been described (4, 5, 14). More recently, silylmetallics have been successfully employed in the synthesis of branched polysilanes. Treatment of silicochloroform with either triphenyl- or dimethylphenyl-silyllithium gives the corresponding tris derivatives. 

An enlargement of the silicon skeleton is possible by coupling reactions with lithium metal or silyllithium reagents [4-6]. The homocoupling of tris(diethylamino)-l-chloro-l,2-dimethyldisilane results in the linear hexakis(diethylamino)-l,2,3,4-tetramethyltetrasilane [7]. After treatment with HCl the hexachloro compound could be obtained. By the reaction of aminochlorophenylsilanes with... 

Summary The synthesis of derivatives of the type [(Me3Si)3Si]2CHR (R = OH, OCH3, 0C(0)H, 0C(0)Me, NMe ) proved to be surprisingly facile and was achieved by the reaction of tris(trimethylsilyl)silyllithium (1) with suitable Ci building blocks. The results of the X-ray analyses and reactions of these di(hypersilyl) compounds are described in this paper. 

In 1968, Gilman and Smith showed that tetrakis(trimethylsilyl)silane can be cleaved by methyllithium to generate tris(trimethylsilyl)silyllithium (A in the reaction below), sometimes also called supersilyllithium (J. Organomet. Chem. 1968,14, 91) ... 

As might be expected in such types, the compounds tend to be high-melting, with high volatility, and enhanced thermal stability. A novel and very reactive type directly derivable from the parent type, is tris(trimethyl-silyl)silyllithium. 

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