Lithium chlorosilanes

The reductions of chlorosilanes by lithium aluminum hydride, lithium hydride, and other metal hydrides, MH, offers the advantages of higher yield and purity as well as dexibiUty in producing a range of siUcon hydrides comparable to the range of siUcon haUdes (59). The general reaction is as follows ... 

Silylnitronates 1 are prepared14-24,25 by metalation of primary nitroalkanes with lithium diisopropylamide and treatment of the lithionitronates with either chlorotrimethylsilane or (/er/-butyldimethyl)chlorosilane. Nonaqueous workup and distillation gives the silylnitronates in >75% yield as moisture sensitive, but thermally stable, products. (e/7-Butyldimethylsilylni-tronates are more stable than the corresponding trimethylsilyl compounds. 

The chlorosilanes are available from classical synthetic routes [108]. In most cases the products can be obtained from SiCl4 and the lithium salts of the introduced substituents with sufficient selectivity and in high yield. This is particularly true for the alcoholates and the thiolates. The exchange problems R vs. Cl which arise with the t-butylthiochlorosilanes will not be discussed in detail here. These problems are overcome by an appropriate choice of the reaction conditions. 

Terminal alkynes can be converted readily into alkynylsilanes by reaction of the corresponding alkyne anion or its metalloid equivalent with a suitable chlorosilane (/). The reverse reaction, that of liberation of the alkyne, is quite facile, being effected by several reagent combinations, including hydroxide ion, methanolysis, fluoride anion, silver(i) followed by cyanide anion, and methyl lithium-lithium bromide (2). 

Reduction of (alkoxy)chlorosilanes with LDMAN (LDMAN = lithium 1-(dimethylamino)naphthalenide) (Scheme 2.48, A). °°... 

In order to prove the validity of these values, model reactions which are easy to carry out were neccessary. We found such models in the reaction of chlorosilanes and siloxanes with lithium alco-holates or lithium silanolates. 

Wurtz-type couplings have also been observed upon sonication of lithium in the presence of both organic halides (yields 36-73%) (218) and chlorosilanes or chlorostannanes (yields 42-94%) [Eq. (42)] (219). 

The reactions of lithium phosphides with chlorosilanes, which initially seemed so straightforward, turned out to be strikingly many-sided when PH-containing lithium phosphides are present. The formation of pure LiPH2 DME (DME = 1,2-dimethoxyethane) became feasible by coordination of a high boiling point ether (30). This method was employed by Klingebiel and collaborators (31) for the formation of... 

In the reduction of conjugated dienes cis 1,4-addition of trimethyl-chlorosilane to give c -l,4-bis(trimethylsilyl)-2-butene is favored with sodium in THF, lithium naphthalide in THF, and with lithium in diethylether. It appears that the anion radical, which in nonionizing solvents should exist in a cis configuration, leads to the cis 1,4-addition of the silyl groups, whereas the dianions produced by further reduction lead to trans products (140). 

The most convenient method to prepare metalated arylsilanes is the reaction of a chlorosilane with lithium or potassium in polar solvents such as THF or DME (Scheme 2). 

Amino-substituted silyllithium compounds have been prepared by Tamao and coworkers from the corresponding chlorosilanes by treatment with either a dispersion of lithium metal... 

In sharp contrast to the aforementioned lithiated (amino)arylsilanes, 1,3-dilithio compounds 30, which were prepared from the corresponding chlorosilanes 29 by treatment with lithium naphthalenide (equation 42), decompose completely after 3 h at 0 °C91. 

The use of LDMAN as the electron transfer reagent also allows (though a higher temperature of —50 °C is required) the preparation of a di(alkoxy)lithiosilane, (t-BuO)2PhSiLi, from the corresponding chlorosilane45. Alternatively, this compound may be obtained from the chlorosilane by reaction with lithium metal at 0°C96. 

These silylenoid species have been made by lithium-tin exchange from a Si—Sn precursor96, or by reduction of chlorosilanes with lithium l-(dimethylamino)naphthalenide (LDMAN) at —78°C (equations 42 and 43)97. The resulting silyllithium species react as nucleophiles with Mc SiCI to give the corresponding disilanes (equation 44). An... 

In contrast to the ammonolysis of chlorosilanes, the four-membered ring was formed along with the six- and eight-membered rings by heating lithium fluoro-silylamide (Scheme 4).16... 

Carbosiloxane dendrimers with SiH end groups (Fig. 4.48) [92] are generally accessible by hydrosilylation of MeCOCH2CH2CH=CH2 with chlorosilanes to yield Si-Cl terminated compounds and subsequent reduction with lithium aluminium hydride to form the corresponding alcohol with terminal SiH groups. 

Recently silylboronates functionalized on silicon were reported by Suginome and coworkers via the reaction of silyl lithium 379 with borate ester 380 to yield the borosilamide 381. Further transformations on the amine with HC1 furnish the chlorosilane 382, and reaction of SbFs with 382 provide the florosilane 383. The chlorosilanes 382 also react with alcohols or amines to provide the alkoxy or amine substituted silylboronates 384 and 385 respectively (Scheme 61) <20070M1291>. 

When glyoxal diimine is reacted with lithium in THF and in the presence of a chlorosilane, formation of an SMA is not expected. It has been postulated, however, that a l,2-diaza-4-silacyclopentane derivative (SMA) is formed in low yield in addition to the expected product, l,3-diaza-2-sila-4-cyclopentene.178... 

---