Metal silyl halides

Salt Elimination Reaction of an Alkali Metal Silyl with a Transition Metal Halide... 

These precursors are generally prepared by alkane elimination (Equation (7a)) or—especially useful with bulkier substituents—the coupling of metal chlorides with lithium pnictides or silyl arsines (Equation (7b)) or salt elimination or silyl halide elimination reactions (Equation (7c)) ... 

Strictly speaking, a catalyst is some species directly involved in the catalytic cycle and, in the reactions discussed here, these species are usually low-valent, coordinatively unsaturated transition metal complexes. Metal halides, e-.g., chloroplatinic acid, PdCl, etc., although often claimed as catalysts are more properly catalyst precursors, since in the presence of silyl hydrides the metal halides are reduced. If no stabilizing ligands, e.g., olefins, phosphines, etc. are present, the reduction normally proceeds to a finely divided form of the metal or to insoluble metal silyl/hydride clusters which may act as heterogeneous catalysts. 

Z ) From silyl halides. Since disilanes are usually prepared from Wiutz eoupling of chlorosilanes, so metallation of silyl halides is accomplished with potassium or lithium in ether solvent. 

Use of main-group metal silyls to prepare transition-metal silyls appears to be a generally applicable method that is primarily limited by the availability of suitable starting materials, since these silyl anion reagents are sometimes rather difficult to obtain. Typically an alkali-metal silyl is generated in solution and then treated with the appropriate transition-metal halide. Displacement of halide by the silyl anion, with salt elimination, then leads to product (equations 17-19)46 49. The lithium silyl in equation... 

Early transition-metal silyl compounds have received much less attention, largely due to the fact that general, straightforward synthetic routes have not been available. Syntheses based on oxidative additions are less applicable, given the more electropositive character of the early metals. Particularly for d° silyl complexes, most syntheses are based on nucleophilic displacement of halide by a silyl anion reagent, usually an alkali metal derivative. 

Halide ligands in early transition-metal silyl complexes are readily displaced with nucleophilic reagents (equation 39) to introduce a variety of functionalities cis to the silyl... 

Beryllium-silicon bonds are a recent development. They are likewise prepared by the reaction of the metal halide with alkali metal silyls, but unlike the Mg analogues, both of the well-characterized Be examples are base-free. While [(te/T-Bu3Si)BeCl] is oligomeric, the molecular structure of (tert-Bu3Si)2Be features a perfectly linear Si-Be-Si unit. CpBe(SiMe3), prepared from CpBeCl and trimethylsilyllithium in pentane, exhibits an intriguing thermal chemistry. The identity of the primary thermolysis products, Scheme 14, implies the participation of silylene intermediates, a contention supported by DFT/NBO (density functional theory/natural bond order) analysis. ... 

The salt elimination route is also a useful method, relying on the reaction between a silyl halide and a transition metal anion, for example, equation (40). " The IR spectra of such compounds are informative values of 2141,2136, and 2132 cm for the disilyl compound and 2142 cm for the silyl compound are found for the Si-H stretching frequencies. 

This was accomplished by coupling either an amine or a phosphide with a silyl halide, followed by metalation. In the case of the obtained aminosilane, the subsequent metalation proceeded smoothly resulting in a stable aminosilylanion. In the case of phosphorus, we observed the formation of the phosphinosilyl anion by NMR, but the compound was not stable under the reaction conditions and rearranged to give the potassium phosphide. 

As an alternative to enolization and addition of a silyl halide or trillate, silyl enol ethers may be prepared by the 1,4-hydrosilylation of an a,3-unsaturated ketone. This can be done by using a silyl hydride reagent in the presence of a metal catalyst. Metal catalysts based on rhodium or platinum are most effective and provide a regiospecific approach to silyl enol ethers (1.25). 

Besides the metallocene group 4 metal silyl compounds already discussed, substances which do not contain the cyclopentadienyl ligand are also of interest [7]. Remaricably, the seemingly most straightforward synthetic route, namely the reaction of silyl anions with group 4 tetrahalides, has not been reported so far. The reason for this seems to be connected to the highly Lewis acidic character of the metal halides, which causes ether cleavage and other side reactions. 

Silylene complexes have been prepared by coordination of free silylene, extrusion of dihydrogen from a dihydrosilane, a-hydrogen elimination from a hydrosilyl complex, extraction of hydride, halide, or pseudo-haUde from a metal-silyl complex, and photoextrusion of silylene from a disilanyl complex. Examples of these reactions are shown in Equations 13.39-13.45. 

Many routes to 0x0 and imido compounds have been developed. Transition metal-oxo complexes are coimnonplace and, in many cases, are the most stable form of an element in air. Some imido compoimds, including the first imido complex, have been prepared from metal-oxo complexes (Equation 13.50). The reactions of some of the later metal-oxo compounds with a primary amine generate an imido species by extrusion of water. In other cases, metal-imido complexes are prepared from 0x0 complexes by the reaction of phosphmimines (Equation 13.51) or from 0x0 or halo complexes by the reactions of silylamines (Equations 13.52 and 13.53). The driving force for these reactions is the formation of phosphine oxide, silyl ethers, or silyl halides. 

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