Disilanes synthesis

Wrackmeyer B, Milius W, Badshah A (2002) Hexa(l-alkynyl)disilanes. Synthesis, structure and 1,1-ethylboration. J Organomet Chem 656 97... 

Grogger C, Fallmann H, Fiirpass G, Stiiger H, Kickelbick G (2003) The [Cp(CO)2Fe] (Fp) group as a donor in donor/acceptor substituted disilanes synthesis, structure and electronic properties of Fp-Si2Me4-CgH4CH C(CN)2. J Organomet Chem 665 186... 

Recently, this work has been extended and further developed by Brown-Wensley into a preparative method for the synthesis of disilanes. The results of competitive reactions with several silanes allow insight into the reaction kinetics, in particular the relative rates of disilane formation versus hydrosilation (Table 5a, b) [61]. 

The Miiller-Rochow-Synthesis [16,17] (direct synthesis of methylchlorosilanes) provides as byproduct a high boiling fraction consisting essentially of 1,1,2-trimethyltrichlorodisilane and 1,2-dimethyltetrachlorodisilane [18]. Starting with these disilanes Wacker-Chemie has developed different ways to produce silicon carbide [19, 21] and silicon carbonitride [22] fibers. 

Figure 4. shows the route from the high boiling residue of the direct synthesis to silicon carbo-nitride fibers. Methylchlorodisilanes and trichlorosilanes as additives are mixed in a specific ratio and react with methylamine and a small amount of ammonia to form an aminodisilane/oligosilazane. The subsequent polycondensation reaction of this mixture by heating to 250 °C yields a soluble and melt spinnable polysilazane. In comparision with the polysilane the properties of the polysilazane depend on the ratios of the disilanes/silanes and methylamine/ammonia and also on the reaction conditions. 

Chloro-hydrogen disilanes H6 nClnSi2 are obtained by chlorination of Si2H6 or by reaction of phenylated disilanes with HCI/AICI3. The synthesis of these compounds in a pure form is difficult because of equilibration reactions and the formation of azeotropic mixtures with the solvents. Eq.(3) shows all disilanes formed from 1,2-diphenyl-disilane and HCI/AICI3 [8]. 

Palladium-catalyzed bis-silylation of methyl vinyl ketone proceeds in a 1,4-fashion, leading to the formation of a silyl enol ether (Equation (47)).121 1,4-Bis-silylation of a wide variety of enones bearing /3-substituents has become possible by the use of unsymmetrical disilanes, such as 1,1-dichloro-l-phenyltrimethyldisilane and 1,1,1-trichloro-trimethyldisilane (Scheme 28).129 The trimethylsilyl enol ethers obtained by the 1,4-bis-silylation are treated with methyllithium, generating lithium enolates, which in turn are reacted with electrophiles. The a-substituted-/3-silyl ketones, thus obtained, are subjected to Tamao oxidation conditions, leading to the formation of /3-hydroxy ketones. This 1,4-bis-silylation reaction has been extended to the asymmetric synthesis of optically active /3-hydroxy ketones (Scheme 29).130 The key to the success of the asymmetric bis-silylation is to use BINAP as the chiral ligand on palladium. Enantiomeric excesses ranging from 74% to 92% have been attained in the 1,4-bis-silylation. 

Kunai and Ishikawa et al. have reported that electrolysis of monochloro-silanes in 1,2-dimethoxyethane using a platinum cathode and a mercury anode gives disilanes in high yield (Scheme 40) [84]. Silver can also be used as an excellent anode material in place of mercury. The electrolysis of a mixture of two different monochlorosilanes produces unsymmetrical disilanes. Trisilanes can also be synthesized by the electrolysis of a mixture of monochlorosilanes and dichlorosilanes. They also reported that the use of copper electrodes is effective for the synthesis of disilanes, trisilanes, tetrasilanes, and pentasilanes [85]. 

Shono and Kashimura et al. have reported the elegant electrochemical synthesis of disilanes from chlorosilanes by using magnesium for both the anode and the cathode and by alternating the direction of the current at some interval... 

The use of sacrificial aluminum electrodes is also effective for the eleetrore-ductive synthesis of disilanes and polysilanes from monochlorosilanes and dichlorosilanes, respectively as reported by Nonaka et al. and Dunogues et al. independently [88],... 

The direct silylation of arenes through C—H bond activation provides an attractive route for the synthesis of useful aromatic compounds [64]. Vaska s complex was the first of the iridium catalysts to be reported for activation of the C—H bond in benzene by Si—H of pentamethyldisiloxane to yield phenylsubstituted siloxane [65]. However, a very attractive method for the aromatic C—H silylation with disilanes has been recently reported by the groups of Ishiyama and Miyaura [66-68]. 

Direct Synthesis reaction, 6 393-408 Discrete monomeric anions, halogenocuprate and halogenorgenate(I) ions, 37 2-6 Disilacyclohexadienes, 29 12-13 Disilacyclohexanes, 29 12 Disilanes... 

Silylated triphosphanes and triphosphides, synthesis, 31 188-194 yields, 31 194 Silylenes, 29 2-6 addition reactions, 29 4-6 to butadiene, 29 4 to ethylene, 29 4 to hexadienes, 29 5 mechanism, 29 4 nitric oxide scavenging, 29 4 complexes, 25 37, 51, 116, 118 as catalyst intermediates, 25 118 extrusion from disilanes, 25 114, 118 halides, 3 225 from hydridosilanes, 25 14 insertion into element-hydrogen bonds, 29 3-4... 

The 1,3-silyl shift in aryl disilanes is suppressed when the aromatic ring is ortho-substituted144. An attempted silylene synthesis from 1,3-dimesitylhexamethyltrisilane 259, however, led to low yields of silylene trapping products (ca 30% generation of Me2S ). The major pathway is the homolytic cleavage of the trisilane, followed by disproportionation of the radicals 260 and 261 to the silene 262 and the disilane 263 (equation 65). 

The disilane fraction refers to a fraction boiling over the range of about 150°-l 60° C which is obtained by fractionation of the higher boiling fraction of methylchlorosilanes produced by the so-called direct synthesis (141, 214). It is composed mainly of 1,1,2-trichlorotrimethyldisilane and 1,1,2,2-tetrachlorodimethyldisilane, somewhat contaminated by siloxanes (6, 22, 27, 114,125,126, 134). 

Another important method for synthesis involves the disproportionation of methoxy-substituted disilanes, which will be discussed in the next section. 

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