Cyclohexasilane

Normally, no small cyclopolysilanes are observed in these reactions. Two exceptions we have noted are the very slow reaction of phenylsilane under the influence of Cp2TiMe2 and the reaction of benzylsilane under the influence of dimethyltitanocene at very long reaction times. From both of these reactions we isolate a single isomer of the cyclohexasilane, in ca. 10 per cent yield in the case of the phenylsilane and ca. 60 per cent yield in the case of the benzylsilane. These isomers are believed to be the all-trans isomers. The phenyl derivative is identical to that... 

The formation of cyclohexasilanes and the zirconium catalyzed hydrosilation of poly(phenylsilylene), referred to above, both suggest that slow cleavage of polymer chains may occur in the presence of the catalysts. Such cleavage may also play an... 

The cyclohexasilane ring of trans-lfl has a chair form and both chlorine atoms occupy axial positions. The cyclotetrasilane ring has a folded structure with the fold angles of 33.0 and 33.6°. The structure of the silicon framework of trans-lfl resembles that of bicyclo[4.2.0]octane, in which the cyclohexane ring has a chair form and the cyclobutane ring has a folded structure.67... 

The broad emission and low-fluorescence quantum yield of PPS suggested a distribution of trapping sites in the Si skeleton, which were also considered responsible for the lower-than-expected conductivity. The far-IR spectrum of PPS suggested the existence of cyclohexasilane rings connected by linear chains.361,362 Subsequent investigations by Irie et al. on the electronic absorption spectra of radical ions of poly(alkylsilyne)s were taken to indicate the presence of various cyclic silicon species, in corroboration of this conclusion.363 The large Stokes shift and broadness of the fluorescence emission indicate a range of fluorophore structures, different from the chromophore structures. This is... 

Whereas photolysis of cyclohexasilanes usually results in silylene elimination and the successive formation of cyclopentasilanes and cyclotetrasilanes79, attachment of the Fp group to the ring as in 162 results in rearrangement to a silyl-substituted cyclopentasilane, 163, revealing that the presence of the transition metal alters the chemistry of these systems... 

Undecamethylcyclohexasilanylpotassium is a useful starting material for the synthesis of various cyclohexasilane derivatives, as shown in Scheme 14. Reactions affording bicyclic and polycyclic silanes are reviewed in Section V.A. 

Another route to cyclohexasilane rings with silanyl side chains begins with cyclosilanylpotassium and chlorosilanes Ph Me3 SiCl (Scheme 15). Dephenylation of the resulting silyl-substituted cyclohexasilanes with triflic acid and subsequent reduction... 

As shown in Scheme 26, cyclohexasilane derivatives bearing two different transition metal fragments are accessible from l,4-Br2Si6Meio by temporarily protecting one of the Si—Br valences with hydrogen101. 

The reaction with excess R2(C6H5)SiLi reagents in tetrahydrofuran for a prolonged period of time leads to considerable formation of dodecamethyl-cyclohexasilane, [(CH3)2Si]6, and R2(C6H5)SiSi(C6H5)R2 (see Section III, C, 7). 

If all-iraws-(PhMeSi)6 is reacted with HCI and AICI3, an isomeric mixture of all possible (SiClMe)6 isomers results, which means that the chlorination is accompanied by racemization56. In the course of the chlorination of the permethylated six-membered ring (SiMe2)6, the second substitution occurs only in the 3 and 4 position57 (equation 32). The formed 1,3- and 1,4-dichlorodecamethylcyclohexasilanes can be separated via their hydrolysis products, 1,3-dihydroxydecamethylcyclohexasilane and decamethyl-7-oxa-hexasilanorbornane58. 1,2-Dichlorodecamethylcyclohexasilane is accessible via a stepwise synthesis of the cyclohexasilane skeleton59. 

Summary l,4-Di(undecamethylcyclohexasilanyl)benzene has been synthesized and its X-ray structure determined. The new cyclohexasilanes Ph-(c> c/o-Si5Meio)-X (X = CF3SO3, H, Cl, Br) have been prepared. The coupling reaction between Ph-(cyc/o-Si Meio)-H and (tBu)2Hg resulted in the bicyclic Si-system (Ph-cyc/o-Si6Meio)2Hg, which is easily converted to (Ph-c>/c/o-SijMeio)2 by UV-irradiation. 

Potassium undecamethylcyclohexasilane is formed in the reaction of the permethylated cyclohexasilane with potassium rbutanolate in glyme solvents at room temperature over a period of two weeks. This provides a simple access to 1. 

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