Tetrasilaadamantane

Aluminum chloride induces polymerization of 1,1-dimethylsilacyclobutane but causes (66) to ring expand to th trisilacyclohexane and, remarkably, the tetrasilaadamantane (Scheme 115) (75IZV953). The polymerization of 1,3-disilacyclobutanes, variously substituted, both thermally and catalyzed has been widely studied by Russian workers. Di-/jl -chlorobis(cyclohexene)diplatinum(II) is most effective at catalyzing the polymerization of (66). The reaction is vigorous at 20-60 °C with small amounts of triethylsilane or carbon tetrabromide (Scheme 116) <66JCS(C)1137>. 

The 1,3,5,7-tetrasilaadamantane cage is formed in very low yield on pyrolysis of TMS. It is but one example of the carborundanes —fused six-membered rings exclusively in the chair conformation—formed in this pyrolysis. However, better yields result from the closed... 

Tetraselenafulvalenes, tetramethyl-Raman spectra, 6, 954, 955 structure, 6, 950 UV spectra, 6, 952 Tetraselenafulvalenes, tetraphenyl-synthesis, 6, 963 1,3,5,7-Tetrasilaadamantane formation, I, 622 Tetrasilabicyclo[3.3. l]octane synthesis, 1, 622 Tetratellurafulvalenes IR spectra, 6, 954... 

Reaction (26) produces l,3,3,5-tetrachloro-7,7-dimethyl-l,3,5,7-tetrasila-bicyclo-[3.3.1]nonane with four SiCl groups. A complete methylation would lead to compound 8. On carrying out that reaction it is observed that methylation does not go to completion, even if a 50% excess of Li is applied and the mixture is stirred for two days in boiling ether, though, 1,3,5,7-tetrasila-bicyclo-[3.3.1]nonane containing two SiCl groups is obtained, presumably compound 20. As with 1,3,5,7-tetrasilaadamantane, methylation with meMgCl does not occur because of steric hindrance. 

Of special interest is the behavior of l,l,3,3-tetramethyl-l,3-disilapentene as shown in Table 15. The formation of l,l,3,3-tetramethyl-l,3-disilacyclopentane is attributed to a simple hydrogenation. Apart from unidentified compounds of higher molecular weight, formation of 1,3,5,7-tetrasilaadamantane as well as 2,2,4,4,6,6,8,8-octa-methyl-2,4,6,8-tetrasilabicyclo[3.3.0]oct-l(5)ene should be emphasized. 

The Si C ratio in the methylsilanes used will obviously influence the structural types produced. This applies in the case of 1,3,5,7-tetrasilaadamantanes which are formed preferentially from pyrolysis of SiMe4 and Me3SiCl. The Si C ratio in this skeleton is 4 6, whereas in diadamantanes it is 7 10. 

The 1,3,5,7-tetrasilaadamantane structural unit itself has proved to be relatively stable against the effects of AIX3 (X = Br, Cl). Reaction between Si-methylated 1,3,5,7-tetrasilaadamantane 39 and AlBr3 occurs very slowly in benzene (30% converted in 8 days at 80 °C), but without solvent, the rate was much faster (30 % converted after 4 hrs at 90 °C). Apart from unconverted compound mono-brominated 1,3,5,7-... 

Through H-NMR spectroscopy and mass spectrometry, the methylene-linked tetrasilaadamantane chains in compounds 218 and 2, as well as their brominated analogues in 219, 22J and 222 were characterized. 

An extension of time for the reaction between 1,3,5,7-tetrasilaadamantane and AlBr3 showed at first the formation of pentane-insoluble oligomers which were soluble in THF or benzene (reaction time 4 to 7 hrs at 90 °C). Reaction times exceeding 7 hrs result in the synthesis of polymers insoluble in commonly used solvents, polymers which are constructed in the same way as those previously encountered. An IR spectroscopic investigation revealed the presence of absorption bands which are comparable to those of 1,3,5,7-tetrasilaadamantane or which are characteristic for oligo-tetrasilaadamantanes containing two to four tetrasilaadamantane structural units. 

As a result of this investigation, the insoluble polymers were shown to contain three-dimensional methylene-bridged tetrasilaadamantane units. Their skeletal structure was almost entirely resistant to attack by AlBr3, and on preservation of their skeletal structure a partial CH3/Br exchange on silicon resulted, producing brominated derivatives [59]. 

The formation of the CH2-bridged oligo-tetrasilaadamantanes can be clarified by consideration of mechanism 2 formulated for cyclization reactions. Here, methane is released by action of AlBr3 through an intermolecular and not through an intramolecular process. The presence of methane was proved experimentally [59]. 

The use of the weaker Lewis acid AICI3 meant a reduction in reaction rate without a change in the mechanism of reaction. Although the reaction of Si-methylated 1,3,5,7-tetrasilaadamantane with AICI3 in the absence of solvent at 90 °C yielded... 

An H-NMR investigation of the mass spectrometrically-identified compounds showed that an isomeric mixture of straight and branched-chain tetramers as well as n-, iso- and neo-pentane analogues of pentamers existed. The isomers of tetrameric tetrasilaadamantane could be separated and eventually isolated by HPLC. 

These correspond formally to an extension of the tetrasilaadamantane oligomers containing 1, 2 or 3 SiC3Hg structural units, as proved by a mass-spectrometric investigation of fractions Si and Si 3. 

One- to three-fold addition of SiC3Hg units to the 1,3,5,7-tetrasilaadamantane chain can be explained by consideration of two structural alternatives ... 

These compounds, amounting to 10-15% of the product mixture, require for their formation the dismantling of the 1,3,5,7-tetrasilaadamantane skeleton. Similar degradation reactions produce the SiMe found in the reactions involving AlBrg. However, because insurmountable difficulties arose in assigning peaks in the IH-NMR spectra of fractions Si and Si g, still no real distinction could be drawn between the two possible mechanisms. 

Synthesis of Si-Substituted 1,3,5,7-Tetrasilaadamantane Me3(Me3Si-CH2--SiMe2-CH2-SiMe2-CH2) Ad... 

The abbreviation Ad designates the 1,3,5,7-tetrasilaadamantane molecular skeleton. Substituents written in front of Ad are linked to the Si atoms, those written behind Ad are hnked to the C atoms of the adamantane skeleton. 

The underlying principle in this method is the metallation of a skeletal C atom in carbosilanes by organolithium compounds. As examples, (Me2Si— 112)3 and the Si-methylated 1,3,5,7-tetrasilaadamantane were investigated (Chapt. I1I.4). 

In the photochlorination of l,3,5,7-tetramethyl-l,3,5,7-tetrasilaadamantane both the methyl and methylene groups are chlorinated. However, selective halogenation is possible by means of photobromination [80]. The possibility to form partially brominated Si-adamantanes arises from the results presented in Table 27. Here 0.25 molar solutions of Me Ad in CCl were treated with varying amounts of bromine in mole ratios of Me AdrBr = 1 1, 1 2, 1 4 and 1 8 and irradiated with a high pressure Hg UV source. 

The reaction of perchloro-l,3,5,7-tetrasilaadamantane with ZnF2 does not proceed to its fluorinated derivative. At 110 °C in a sealed tube, cleavage occurs along with the formation of SiF and an SiF-containing residue. No reaction occurs at lower temperatures. 

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