Disilane

It was found that the pressure rise was preceded by an induction period . The decomposition then accelerated to a stage in which it was approximately first order. Later on it was retarded, probably due to inhibition by the hydrogen formed. From the variation of the first-order rate coefficient 

In spite of the complexity of the pyrolysis, a first-order rate law was found to fit the experimental results at least for the greater part of the reaction time. Stokland s first-order rate coefficients were consistently higher than those of Emel6us and Reid76, this can be understood in the light of the relation between decomposition and pressure change. They could be represented formally by an Arrhenius expression for the overall coefficient 

Chemical Name Synonyms Chemical Formula CAS number Molecular Weight Boiling point Melting point Absolute density Solubility in water DOT classification DOT label UN Number 

NFPA hazard identification Exposure limits Target effects 

Shut off ignition sources. Use water spray from a distance to reduce potential flammable cloud dispersal. Caution, resulting fumes (HCl) are corrosive and can react violently. If possible contain in exhausted cabinet and direct to suitable scrabbing medium. 

Chemical vapor deposition of Si02 or SiN and growth of epitaxial or polycrystalline silicon. 

Acute exposure may be irritating to the mucous membranes of the respiratory tract, headache and nausea may be factors. There is no data available for chronic exposure. 

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The SiH radical physisorbs on tlie a-Si H surface and recombines tliere witli anotlier SiH radical to fonn disilane Si2 Hg, or abstracts H from tlie surface to fonn a dangling bond and SiH. The film growtli is detennined by tlie chemisoriDtion of tlie SiH radical on a free dangling bond site by fonnation of a Si-Si bond. The cross-linking of... 

Silicon, unlike carbon, does notiorm a very large number of hydrides. A series of covalently bonded volatile hydrides called silanes analogous to the alkane hydrocarbons is known, with the general formula Si H2 + 2- I uf less than ten members of the series have so far been prepared. Mono- and disilanes are more readily prepared by the reaction of the corresponding silicon chloride with lithium aluminium hydride in ether ... 

Substituted aroyl- and heteroaroyltrimethylsilanes (acylsilanes) are prepared by the coupling of an aroyl chloride with (Me3Si)2 without decarbonylation, and this chemistry is treated in Section 1.2[629], Under certain conditions, aroyl chlorides react with disilanes after decarbonylation. Thus the reaction of aroyl chlorides with disilane via decarbonylation is a good preparative method for aromatic silicon compounds. As an interesting application, trimel-litic anhydride chloride (764) reacts with dichlorotetramethyidisilane to afford 4-chlorodimethylsilylphthalic anhydride (765), which is converted into 766 and used for polymerization[630]. When the reaction is carried out in a non-polar solvent, biphthalic anhydride (767) is formed[631]. Benzylchlorodimethylsilane (768) is obtained by the coupling of benzyl chloride with dichlorotetramethyl-disilane[632,633]. 

Disilanes add to conjugated dienes by splitting their Si—Si bond. 1.1.2.2-Tetramethyl-1.2-disilacyclopentane (82) reacts with butadiene at 100 C to give l,l,5,5-tetramethyl-l,5-disilacyclotrideca-7,l 1-diene (83) in 8330 yield[77]. The six-membered carbodisilanes undergo a similar reaction to give 14-membered compounds. 

Arylsilylation of conjugated dienes to give 88 takes place at 80 °C by the reaction of a diene, disilane, and benzoyl chloride, which undergoes facile decarbonylation at 80°C[83]. 

The reaction of l,4-bis(trimethylsilyl)-l,3-butadiyne (174) with disilanes, followed by treatment with methylmagnesium bromide, produces i,l,4,4-tetra(-trimethylsilyl)-l,2,3-butatriene (175) as a major product[96]. The reaction of octaethyltetrasilylane (176) with DMAD proceeds by ring insertion to give the six-membered ring compounds 177 and 178[97], The l-sila-4-stannacyclohexa-2,5-diene 181 was obtained by a two-step reaction of two alkynes with the disilanylstannane 179 via the l-sila-2-stannacyclobutane 180[98],... 

The thermal decomposition of silanes in the presence of hydrogen into siUcon for production of ultrapure, semiconductor-grade siUcon has become an important art, known as the Siemens process (13). A variety of process parameters, which usually include the introduction of hydrogen, have been studied. Silane can be used to deposit siUcon at temperatures below 1000°C (14). Dichlorosilane deposits siUcon at 1000—1150°C (15,16). Ttichlorosilane has been reported as a source for siUcon deposition at >1150° C (17). Tribromosilane is ordinarily a source for siUcon deposition at 600—800°C (18). Thin-film deposition of siUcon metal from silane and disilane takes place at temperatures as low as 640°C, but results in amorphous hydrogenated siUcon (19). 

Oxidation. AH inorganic siUcon hydrides are readily oxidized. Silane and disilane are pyrophoric in air and form siUcon dioxide and water as combustion products thus, the soot from these materials is white. The activation energies of the reaction of silane with molecular and atomic oxygen have been reported (20,21). The oxidation reaction of dichlorosilane under low pressure has been used for the vapor deposition of siUcon dioxide (22). 

Using hexamethylphosphoramide as the solvent, only the second reaction occurs. Disilane also reacts with potassium in 1,2-dimethoxyethane to form KS1H3, although S1H4 and nonvolatile polysHanes are also produced (28,31). Pure crystalline KSiH prepared from SiH and potassium in 1,2-dimethoxyethane has been obtained by slow evaporation of the solvent. WhenHquid ammonia is used as the solvent, only a small fraction of SiH is converted into metal salt most of the SiH undergoes ammonolysis (32). 

Other specialty silanes used in microelectronic apphcations include dichlorosilane and disilane. Trihromosilane [7789-57-3] iodosilanes, and trisilylamine [13862-16-3] are of interest for microelectronics in low temperature deposition technologies. 

Sodium and magnesium do not react with tetrachlorosilane at room temperature, but do so at elevated temperatures and ia the presence of polar aprotic solvents at moderately elevated temperatures. The Wurtz-Fittig coupling of organosilanes to form disilanes (168) and polysdanes (169) is usually accomphshed usiag molten sodium ia toluene or xylene. 

Methylchlorodisilanes are by-products of the dkect-process residue, commonly called high boiling point residue or simply residue, and are formed in about 4% of the total (CH2)2SiCl2 produced, which in 1994 was about 30,000 tons per year. Disilanes are key constituents of the residue, and novel reactions forming Si—Cl bonds have been described (44,45). Some chemical reactions of dkect-process disilanes are shown in Figure 2. Cleavage chemistry of Si—Si compounds with HCl practiced industrially has also been described (47). 

Difluorocarbene generated by the thermolysis of trimethyltnfluoromethylsilane reacts with disilanes by insertion into the silicon-silicon bond [S] (equation 9) Thermolysis of pentafluoroethyltnfluorosilane at 200 °C gives tetrafluoro ethylidene carbene, which reacts with phosphorus trifluonde to give trifluoro vinyltetrafluorophosphorane [9] (equation 10) and with perfluorotnmethylphos-phine to give perfluorodimethyhsopropylphosphine and perfluoro-2-butene [9] (equation 10)... 

Siheium-athan, n. silicoethane (methylsilane, CHsSiHs, or disilane, SiQsSiHs). -bromid,... 

With the stable donor adducts of silylene complexes, valuable model compounds are now available for reactive intermediates which otherwise cannot be observed directly. For example, a side reaction occurring in the hydrosilation process [61 -63], is the dehydrogenative coupling of silanes to disilanes. This reaction could be explained in terms of a silylene transfer reaction with a coordinated silylene as the key intermediate. 

Recent investigations have been concerned with the reactivities observed with secondary silanes R2SiH2. In these cases, a dehydrogenative coupling of silanes to disilanes is observed as a side reaction of the hydrosilation. However, the hydrosilation can be totally suppressed if the olefins are omitted. The key intermediate in the coupling reaction has been identified as a silylene complex (sect. 2.5.4). 

The dehydrogenative coupling of silanes does not stop at the stage of disilanes in the coordination sphere of early transition metals like Zr and Hf, but chain polymers of low molecular weight are formed. As reactive intermediates in this reaction, silylene complexes are also assumed. However, alternative mechanisms have been discussed (sect. 2.5.4). 

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]. 

Table 5b. Relative rates of disilane formation and hydrosilation process in the presence of various catalysts...

Evidence for a 7t-coordination was obtained through the reaction of various disilenes with Hg(OCOCF3)2, a reaction which leads regioselectively to bis(tri-fluoracetyl)disilanes. A disilene n-complex (79), which is stable up to — 50 °C, could be identified as an intermediate by spectroscopic methods. 

For an earlier report, without details, on the selective dcsilylation of an acetylenic/ propargylic disilane, see B. Bennetau, J.-P. Pillot, J. Dunogues and R. Calas, /. Chem. Soc. Chem. Commun. 1094 (1981). 

Early work on the chemistry of organosilyl anions/anionoids has been thoroughly reviewed (/). The most frequently employed preparative routes involve either cleavage of a disilane, when HMPA (CAUTION—CANCER SUSPECT AGENT) is normally required as solvent, or reaction of bulky silyl chlorides with lithium metal. 

Deposition from disilane (Si2H6) in anRF induction heated reactor at 850°C.[ 1... 

Another deposition reaction uses disilane as the silicon source at atmospheric pressure and at a deposition temperature of290-300°C, with nitrogen and hydrogen dilution as follows ... 

Delahoy, A., Doele, B., Ellis, F., Ramaprasad, K., Tonon, T., and Van Dine, J., Amorphous Silicon Films and Solar Cells Prepared by Mercury-Sensitized Photo-CVD of Silane and Disilane, Materials Issues in Applications of Amorphous Silicon Technology, (D. Adler, et al., eds), MRS Proc., (49) 33-39 (1985)... 

In another nonelectrolytic process, arylacetic acids are converted to vi c-diaryl compounds 2A1CR2COOH —> ArCR2CR2Ar by treatment with sodium persulfate (Na2S20g) and a catalytic amount of AgNOs." Both of these reactions involve dimerization of free radicals. In still another process, electron-deficient aromatic acyl chlorides are dimerized to biaryls (2 ArCOCl —> ArAr) by treatment with a disilane RsSiSiRs and a palladium catalyst." " ... 

Whereas ethylene oxide gives with 17 at ambient temperature a quantitative yield of l-trimethylsilyloxy-2-iodoethane [5, 31], substituted epoxides such as 846b react with 17 to give 848 as the main product [32]. Excess 17, however, leads to the bis-iodo compounds 849 and HMDSO 7 [4, 5]. In the presence of DBU the epoxides 850 are converted by 17, which is generated in situ from hexamethyl-disilane 857 and I2, into the allyl alcohols 851 [4, 32] (Scheme 6.14). Cycloctene epoxide 852 is opened by SiCl4 at -78 °C in the presence of catalytic amounts of the asymmetric catalyst 853 to give 61% of the chlorohydrin 854 in 98% ee [33]. 

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