1,1,1,2,2,2-Hexamethyldisilane

Trimethylsilyl iodide [16029-98-4] (TMSI) is an effective reagent for cleaving esters and ethers. The reaction of hexamethyldisilane [1450-14-2] with iodine gives quantitative conversion to TMSI. A simple mixture of trimethylchlorosilane and sodium iodide can be used in a similar way to cleave esters and ethers (8), giving silylated acids or alcohols that can be Hberated by reaction with water. 

To a solution of hexamethyldisilane (2.5 mmol) in HMPA (CAUTION— CANCER SUSPECT AGENT) (3 ml) at 0-5 °C was added methyl lithium (2.5 mmol, 1.5 m MeLi.LiBr complex in ether) dropwise. After being stirred for 3 min, the red solution was treated with Cul (2.5 mmol) in Me2S (1 ml), the resulting black reaction mixture was stirred for 3 min. and 2,3-dibromo-propene (1 mmol) was added rapidly via a syringe. The reaction mixture was allowed to warm to room temperature, and was stirred for 1.5 h. It was then poured into pentane (25 ml) and saturated ammonium chloride solution (25 ml, buffered to pH 8 by the addition of ammonium hydroxide), and the mixture was stirred vigorously for 1 h. The aqueous phase was re-extracted with pentane, and the combined organic extracts were dried. Removal of... 

To a solution of potassium methoxide (0.2 mmol) in HMPA (10 ml) (CAUTION—CANCER SUSPECT AGENT), heated to 65°C, was added (E)-oct-4-ene oxide (1.2 mmol), then hexamethyldisilane (1.8 mmol) in HMPA (5ml), and the yellow mixture was stirred at 65°C for 3h. The cooled mixture was poured onto saturated brine, and extracted with pentane (2 x 25 ml). The combined organic extracts were dried and concentrated, to give oct-4-ene (1.15 mmol, 96%, 99 1 (Z) (E) by g.I.c.). 

To a solution of hexamethyldisilane (2.5 mmol) in HMPA (CAUTION— CANCER SUSPECT AGENT) (3 ml) at 0-5 °C was added methyl lithium (2.5 mmol, 1.5 m MeLi.LiBr complex in ether) dropwise. After being stirred for 3 min, the red solution was treated with Cul (2.5 mmol) in Me2S (1 ml), and the resulting black reaction mixture was stirred for 3 min. Ether (6 ml)... 

To a stirred suspension of NaH or KH (20 mmol) in HMPA (CAUTION— CANCER SUSPECT AGENT) was added hexamethyldisilane (10 mmol) slowly with stirring. A clear yellow-brown solution of trimethylsilyl potassium was obtained immediately mild heating at 30-40 °C is necessary to prepare trimethylsilylsodium. 

The decomposition of methyl silane (CH3S1H3) is used to produce an amorphous SiC at 800°C and a crystalline SiC at 900°C.P 1 A two-step growth procedure produces SiC films from hexamethyldisilane and 8% H2/Ar mixture at ambient pressure and low temperature. 

Similar values have been obtained for AHffMesSi ) from two independent studies. The bond dissociation enthalpy DHfMeaSi-SiMea) = 332 +12 kJ moC was obtained from a kinetic study on the very low pressure pyrolysis of hexamethyldisilane and the enthalpy of formation of trimethylsilyl ion, AHf (MeaSi ) = 617.3 + 2.3kJmor, was determined using threshold photoelectron-photoion coincidence spectroscopy (TPEPICO). Both data are related to AHf°(Me3Si ). 

Because aromatic nitro compounds such as nitrobenzene had been reduced by hexamethyldisilane 857 at 240 °C to give azobenzene and aniline [84], we slowly added hexamethyldisilane 857 in THF to a solution of nitrobenzene and 0.05 equivalents of Bu4NF-2-3H20 and obtained, via the probable intermediates 1000-1002, azobenzene in 84% yield [85]. Because azoxybenzene 961 affords azobenzene in 95% yield, azoxybenzene 961 is a probable intermediate in the reduction of nitrobenzene [85] (Scheme 7.26). 

Because reduction of 2-nitrodiphenyl with hexamethyldisilane 857 does not give any carbazole, nitrene intermediates can probably be excluded. The very polar 4-nitropyridine N-oxide 1003 can be reduced by 857 only in the polar solvent N,N-di-... 

A similar reduction of nitrobenzene with (Me3Si)2Hg to give azobenzene and azoxybenzene has been described [86]. The dehydration of tetrabutylammonium fluoride di- or trihydrate by hexamethyldisilane 857 is discussed in Chapter 13. 

Trans-4-Octene oxide 1885 (1.2 mmol), then hexamethyldisilane 857 (1.8 mmol) in 5 mL HMPA, are added, at 65 °C under argon, to 0.2 mmol potassium methox-ide in 10 mL anhydrous HMPA. After 3 h stirring at 65 °C and cooHng to room temperature saturated aqueous NaCl solution is added to the reaction mixture, which is then extracted with pentane. The pentane extracts are combined and dried with Na2S04 and analyzed by vapor phase chromatography (VPC) to reveal the formation of 99% cis 4-octene 1887 [103] (Scheme 12.71). 

As described in Section 7.4, hexamethyldisilane 857 reduces, analogously, pyridine, quinoline and isoquinoline N-oxides to the free bases [17] and converts aromatic nitro groups to azo compounds [12]. Likewise, as already discussed allyltti-methylsilane 82 and benzylttimethylsilane 83 will gradually dehydrate and activate BU4NF-2-3H20 in situ to catalyze the addition of 82 and 83 to pyridine, quinoline, and isoquinoline N-oxides [13] (cf Section 7.2). 

Hexamethyldisilane, Tetrabutylammonium fluoride Vorbrueggen, H. et al Tetrahedron Lett., 1983, 24, 5337... 

Slow addition of hexamethyldisilane in THF to pyridine iV-oxide and tetrabutylammonium fluoride in THF effected smooth reduction to pyridine, while addition of undiluted fluoride led to an explosion on two occasions. 

Pyridine iV-oxide, Tetrabutylammonium fluoride See Pyridine /V-oxidc Hexamethyldisilane, Tetrabutylammonium fluoride See other alkylsilanes... 

The distance-dependent Pauling bond orders range from 1.00 in hexamethyldisilane with a SiSi bond of 235 pm in length (Fig. 4 standard d(l)) to 0.26 for hexakis(rert.butyl)disilane with an extremely elongated spacer distance of 270 pm between its bulky Si(C(CH3)3)3 half-shells [6b]. To rationalize the sometimes considerably weakened SiSi bonds - hexakis(rm.butyl)disilane does not dissociate into two radicals -, it has been proposed [6b,7] that additional attractive van der Waals interactions within the hydrocarbon wrapping contribute to the bonding within the respective organosilicon molecules. This assumption is further supported by the structure of hexakis(trimethylsilyl)disilane (Fig. 2), in which (presumably due to the considerable polarization Si -C5e-H5 calculated [5b]) extremely short non-bonded C(H3)-- (H3)C distances of only 352 pm are found. 

Trimethylsilyl iodide can be substituted for the trimethylsilyl triflate catalyst in the reactions of aliphatic aldehydes. TMSI can be generated conveniently in situ either from trimethylsilyl chloride and sodium iodide in acetonitrile314 or from hexamethyldisilane and iodine in dichloromethane334 or pentane.338 It is noted that neither triisopropylsilane nor PMHS is an effective reducing agent for this purpose when used with TMSI under these conditions.314,334... 

Compound 14 is diamagnetic and represents the first tetrasodium-dication cluster that is stabilized by two sterically congested silyKflu-orosilyl)phosphanide counterions (see Section II,D). It has been also independently synthesized through sodium consumption of 13 in the presence of styrene as catalyst in 24% yield. The electron reservoir of the Na) cluster can serve for reduction processes, that is, it reduces Me3SiCl to hexamethyldisilane (see Section II,F). The fact that 14 is intensely yellow, and not red or blue as observed for Na-loaded zeolites (28), suggests that the residual metal electrons are probably much less delocalized. 

Since compound 14 bears two equivalent Na atoms, which can bring about reduction, its reactivity toward Me3SiCl has been investigated (27). Indeed, the reaction of 14 with 4 molar equivalents of MesSiCl furnishes hexamethyldisilane, with reductive Si-Si bond formation, and the corresponding formation of trisilylphosphane (Eq. 8). 

The reactions of salts of nitro compounds (113) (Scheme 3.95) with silylated thiols (308), hexamethyldisilathiane (308, 309), and hexamethyldisilane (310) afford oximes (114), thiohydroxamates (115), or thiohydroxamic acids (116) as final products depending on the structures of the starting nitronates and the reagents used. 

---