Silyl—Alkali-Metal Reagents

Formation of Silicon-Transition and Inner Transition-Metal Bond 243 S.8.3.4. from Silyl-Alkali Metal Reagents... 

Silyl-alkali-metal reagents with Al metal and organoaluminum halides lead to silyl-Al compounds. The best results are, e.g., using K[SiHj] with n-BujAlCl in... 

Besides the elimination of alkali halides in the reaction between the silyl and metal reagents, several types of reactions in which other simple molecules are liberated have been widely employed. These methods, which include elimination of hydrogen, oxidative eliminations and ligand displacement reactions, are often interrelated. 

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... 

Deprotection of silyl ethers can be accomplished by using a variety of reagents such as TBAF, BF3-OEt2, alkali metal tetrafluoroborate and HF. Here, PPTS is used to distinguish the TBS from the TPS group. Thus, the rearranged 27 cleaves selectively the least bulky silyl group to form mono-protected 8.12... 

Route (a) is severely limited by the availability of the silyl alkali reagents. KSiH3i4>, LiSiph3a> 27> 50> 155>1S6), LiSimeph262,64), LiSime2ph64>, and KSiph3129 have been used in the synthesis of Ti-, Zr-, Hf-, Fe-, Pt-, and Au-Si compounds. The reactions are carried out in cooled etheral solvents, the yield of the silyl metal derivative varying between 13 (Eq. (1)) and 90% (Eq. (2)) ... 

The use of monoglyme and THF follows from their involvement in the synthesis of the alkali-metal-silyl reagent. 

The alkali metal hydrides NaH and KH are also effective as metalating reagents for hydrosilane and disilane to give trialkylsilyl anions in an aprotic solvent such as THE, DME, or HMPA 8) (Scheme 4) (for the mechanism, see Section III-A-2). The reaction of disilane with 2 equivalents of metal hydride converts both silyl groups into silyl anions in two steps, in contrast to the reaction with MeOM described earlier. 

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. 

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