Tetramethyl disilane

Spirocompound 43 was prepared in low yields (20%) by salt metathesis reaction of tetrakis(lithiomethyl)silane with l,2-dichloro-l,l,2,2-tetramethyl disilane <20000M4223>. 

Photodegradable aramids based on l,2-bis(p-aminophenyl)tetramethyl-disilane and various aromatic diacid chlorides (4.97) have been investigated [1682]. 

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. 

The reaction of 1-boraadamantane with l,l,2,2-tetramethyl-di(l-propyl)disilane 101 proceeds analogously leading first to a disiladibora derivative 102 which is further transformed into compound 103 - a silahomoloque of 88a (Scheme 40) <2001CEJ775>. 

Contrasting results are obtained for the peralkylated disilanes RMe2SiSi-Me2R (R = Me, "Bu, Bu), which yield only trace amounts of the 1,4-addition products under the same reaction conditions. Attempts to increase double silylation yields by use of other platinum or palladium catalyst precursors under carbon monoxide pressure or inert atmosphere were also unsuccessful for these peralkylated disilanes. Additionally, the reaction of tetramethyl-l,2-divinyldisilane results in conversion to an intractable product mixture, with no incorporation of the 1,3-diene. Phenyl-substituted disilanes are also effective reagents in the Pt(dba)2-catalyzed double silylation of phenylacetylene, but again, the alkylated disilanes and the vinyl-substituted disilane do not give double silylation products. 

The reaction mechanism can be explained by the formation of a dimethylsilylene intermediate which is able to undergo an insertion reaction into a Si—H bond (for more about this type of reaction, see Chapter 7 Silylenes). The formation of the silylene can be explained by an a elimination from the n metal-complexed disilane. The presence of the silylene has been proved by a capture reaction with diphenylacetylene, when the expected 1,1,4,4-tetramethyl-1,4-disilacyclohexa-diene could be isolated. 

A different approach that even obviates the use of a preformed silyllithium reagent takes advantage of the cleavage of the Si-Si bond of a disilane by a copper salt. Hosomi and co-workers185 have reported on the reaction of various enones or enals 250 with hexamethyldisilane or l,l,2,2-tetramethyl-l,2-diphenyldisilane, catalyzed by copper(i) triflate-benzene complex (Scheme 61). The transformation requires heating to 80-100 °C in DMF or DMI and the presence of tri-/z-butylphosphine in order to stabilize the copper catalyst under these harsh conditions. The addition products 251 were obtained with high yield after acidic work-up. The application of the method to alkylidene malonates as the Michael acceptor was recently disclosed.1... 

Similar products were produced from copolymers such as poly-(cyclohexylmethylsilane-co-dimethylsilane), and materials characteristic of the copolymer composition were obtained. Three disilanes (i.e., 1,2-dicy-clohexyl-1,2-dimethyl- 1,1,2,2-tetramethyl- and 1-cyclohexyl-1,2,2-tri-methyldisilane), as well as the two substituted silylene adducts, were produced from the predominantly random copolymer. The disilanes, which are taken to be diagnostic of silyl radical abstraction, were assumed to accumulate in the mixture, because they no longer absorbed light significantly at 254 nm. The photoinstability of a model trisilane, 2-n-butyl-l, 1,1,2,3,3,3-hepta-methyltrisilane, was demonstrated under the reaction conditions even though its absorption maximum occurred at 215 nm. 

The enthalpies, KH, of the homolytic cleavage of the central Si-Si bond in disilane dimers a can be calculated from temperature-dependent ESR experiments, using Eq. 3, in which C is the concentration of the radical, T is the absolute temperature and A is a. constant. The change in the concentration of the radicals as a function of temperature could be followed by EPR as shown in Fig. 6a for radical 3b. The concentrations of the thermally generated radicals (2b and 3b) were determined by calibration of the height of the EPR signal of the silyl radicals in comparison with a 3 X 10 M toluene solution of TEMPO (2,2,6,6-tetramethyl-piperidinooxy). 

Thermolysis of hexamethylsilacyclopropane at 60-80°C generates dimethylsilylene and tetra-methylethylene. The half-life of this reaction is greater than nine days at room temperature (75JA2273). Dimethylsilylene can be trapped by various substrates when the thermolysis is conducted in their presence. For example, interception of dimethylsilylene with diethyl silane gave disilane (42) in 48% yield, whereas trapping with 2,3-dimethyl-1,3-butadiene gave 1,1,3,4-tetramethyl-l-silacyclopent-3-ene (43) in 34% yield (Equations (6) and (7)) <75JA7162>. 

Previously, it had been shown that pyrolysis of (86) at 620°C in a vertical nitrogen-flow system gave a complex mixture of products, including (88) (3.5%), (64 R, R = H) (0.8%), 1,1,3,3-tetramethyl-1,3-disila-2-methylidenecyclopentane (2.1 %) and 3,3,4,5,5-pentamethyl-3,5-disilacyclo-pentene (2%) <79JOM(168)23>. Formation of disilacyclopentanes by platinum-catalyzed rearrangement of vinyl disilanes also has been reported <86JAP61207389). 

Isocyanides undergo palladium catalyzed insertion into the Si—Si bond of disilanes, and, in the case of l,l,2,2-tetramethyl-l,2-disilacyclopentane, ring expansion occurs and the 1,3-disilacyclo-hexane (15) results <87TL1293>. A 1,3-disilacyclohexane may also result from the photolysis of a... 

Fig. 9.2. Newman projections of major calculated conformations (X-ray data for 5). a 1,1,2,2-tetramethyl ethane and disilane relation sc to p = 2 1 b 1,1,2,2-tetra-rert-butyl ethane and disilane c 1,1,2,2-tetra-cyclohexyl ethane, disilane and diphosphine...

Disilane, hexamethyl-. See Hexamethyidisilane Disilicane. See Disilane Disiloxane, 1,3-diethenyl-1,1,3,3-tetramethyl-. See Divinyltetramethyidisiloxane Disiloxane, hexamethyl-. See Hexamethyidisiloxane Disiloxane, 1,1,2,2,2-pentamethyl-1-(2-phenylethyl)-. See Phenethyl disiloxane Disiloxane, 1,1,3,3-tetramethyl-. Seel,1,3,3-Tetramethyldisiloxane... 

Summary Disilacyclopentanes containing a heteroelement have been prepared by specific routes starting from bis(lithiomethyl)silanes or bis(lithiomethyI)disilanes. The key reaction in the sequence of synthesis is the reductive cleavage of C-S bonds of bis(phenylthiomethyl)silanes and -disilanes to obtain the corresponding difunctional lithioalkyl compounds. The crystal structures of two novel l,2-disila-4-element-cyclo-pentanes and a spirocyclic disilane were obtained and show strained ring systems. Three reaction sites of l,l,2,2-tetramethyl-4,4-diphenyl-l,2,4-trisilacyclopentane could be activated selectively. 

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