Disilane hydrolysis

The dry compound explodes on impact or heating [1], This polymeric product of hydrolysis of hexahalo- or hexaethoxy-disilane decomposes with more or less violence if heated in air (when it ignites) or in a test tube (when it explodes) [2],... 

Enones are also bis-silylated. Asymmetric 1,4-bis-silylation of the enone 505 catalyzed by Pd-BINAP afforded the silyl enol ether 507, and the keto alcohol 509 with 87% ee was obtained after hydrolysis and oxidation of 508 [195]. In this case, the unsymmetric disilane 506 should be used. 

Detailed investigations of the hydrolysis of disilanes to form heterocyclic compounds were carried out by Kumada et al.360) (for more details, see Chapter 9.2 Heterocyclic Silanes). 

Although the reactions with water and methanol yield the expected 1,2-addition products 43 and 44, the addition of methyllithium to the Si=Si bond, which is expected to give the disilane 45 after subsequent hydrolysis, has not yet been observed. Haloalkanes react to furnish compounds 46 (X = Cl, Br). In contrast, those haloalkanes in which halide abstraction is impaired react to form the disilanes I R Si—SiR2X preferentially this is also observed in the reactions of 9 with benzyl chloride and 2-chloro-2-methylpropane70. 

The hydroxyl ions again act catalytically, and it has been proposed10 that they do so by preliminary co-ordination to the covalently unsaturated silicon atoms. The complete hydrolysis of disilane in alkaline solution therefore produces seven equivalents of hydrogen and leaves only hydrated silica as a residue ... 

On the other hand, hydrolysis with aqueous alkalis is complete, producing hydrogen and silicates. Silyl iodide gives a Wurtz-type reaction with sodium, wliich affords a useful path to disilane ... 

Based on material testing and other laboratory work, TCS DPR is not to be considered pyrophoric. This is primarily because of the absence of SiH-containing disilanes. However, these streams can form shock-sensitive hydrolysis products, which can be an ignition source for flammable atmospheres in the vicinity of the gel. 

Employing a hot-atom technique shows that SiCl4 reacts with xs Li vapor to give SiLi. Hydrolysis of the product gives SiH. (12%) and no disilane... 

The formation of an asymmetric silyllithium reagent by lithium cleavage of the silicon-silicon bond of an optically active disilane 10 (eq. [7]) has been reported (26). Hydrolysis of the silyllithium reagent 11 yielded an optically active silicon hydride. This result demonstrates that silyllithium has considerably enhanced optical stability relative to acyclic alkyllithium compounds. 

We have observed that the disilane R HBrSi-SiBrHR (R = SiHR 2), generated according to Scheme 7.4 from the silane R SiH2Cl (obtained by the action of SiH2Cl2 on NaR and Na via the disilane R K Si-SiH R, reacts with supersilyl sodium NaR in THF at -78 °C to form mainly the disilene R HSi=SiHR (3) besides the cyclotetrasilene R Si H (20). The hydrolysis-and air-sensitive disilene 3, which is in fact the first silicon compound with hydrogen atoms bound to unsaturated silicon atoms that has been isolated as a pure substance ( Si NMR for >Si= d of d at S = 141.32 ppm with = 149.9 and Vjjjj = 0.9 Hz), decomposes slowly at room temperature 3 h) with formation of the colorless isomer 19 (Scheme 7.4), and adds MeOH with formation of the colorless compound R HSi-SiH(OMe)R. Unfortunately, crystals of 3 suitable for an X-ray structure analysis have not yet been obtained. 

Metallodisilanes LnM-SiX2-SiX3 (X = H, Cl) represent interesting model compounds for the study of the transition metal effect , because these species contain both a transition metal substituted- as well as a metal-ffee Si-X unit in the same molecule. EtsN-assisted hydrolysis of the ferrio-pentachlorodisilane Cp(OC)2Fe-Si2Cl5 yields exclusively the ferriodichloro-trihydroxy-disilane 10, demonstrating the reduced susceptibility to nucleophilic attack at the silicon in the a-position to the transition metal atom. ... 

The 1,4-disilylation of a,p-unsaturated ketones usinga disilane with a palladium BINAP catalyst has also been achieved with good enantiomeric excess. For example, with a,p-unsaturated ketone (2.157), the initially formed product (2.158) can be converted into the P-silyl ketone (2.159) by addition of methyllithium followed by hydrolysis. However, quenching the intermediate lithium enolate (formed on addition of MeLi) with an alkylating agent leads to an a-substituted product... 

Palladium complexes carrying chiral BINAP ligands catalyze the addition of disilanes to a,)8-unsaturated ketones these are subsequently converted into either j8-silylketones or -hydroxyketones (Scheme 29). Silylketones are obtained in up to 92% ee. Complexes made in situ from [(COD)RhCl]2 and the new chiral ligands (42) (R = H, Me) catalyze the reaction of Ph2SiH2 with aromatic ketones to give, after hydrolysis, chiral secondary alcohols in good optical yields (>80% ee). 

As initial products containing the Si Si unit we used 1,2-dichlorotetramethyldisilane, 1,1,2,2-tetra-chlorodimethyldisilane, hexachlorodisilane and the previously unknown tetramethyldisilane-1,2-diol, which we just synthesized by cautious hydrolysis of 1,2-dichlorotetramethyldisilane. Both chloromethyldisilanes are available starting from the so-called disilane fraction of the direct chloromethylsilane synthesis (Huls-Silicone) by methods already described in the literature [7, 8] and partly improved by us. 

The product mixture from a typical MCS reaction is subjected to several distillation and isolation steps. The product mixture can be roughly divided into monomers and residue. The monomers are separated from the residue stream by distillation the residue contains siloxanes and disilanes. Some monomers can be recovered by various redistribution reactions of the residue mixture (15). The individual monomers are separated by distillation where the separation of Di from Tri is difficult. With Di as an example, equation 3 shows the hydrolysis and condensation to form linear and cyclic polysiloxanes. Another useful material is hexamethyldisiloxane (MM) which forms from hydrolysis/condensation of Me3SiCl (mono), equation 4. 

Organosilyllithium compounds react, over extended periods, with decaphenylcyclopentasilane to give disilanyllithium compounds, which have been used to prepare a variety of organic substituted disilanes. For example, triphenylsilyllithium reacts to give a 79% yield of pentaphenyldisilane (45) after acid hydrolysis. Methyldiphenylsilyllithium and... 

---