Cyclohexasilanes reactions

To obtain di- or trihalogenated methylated cyclohexasilanes reaction of dodecamethylcyclohexasilane with SbClg has become an established route [132, 133]. Depending on the conditions this reaction gives mixtures of 1,3-dichloro-and 1,4-dichlorodecamethylcyclohexasilane isomers or a mixture of these in addition to isomers of 1,3,5-trichlorononamethylcyclohexasilane (Scheme 16). 

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... 

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. 

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). 

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. 

The reaction of 1,1,1,4,4,4-hexakis(trimethylsilyl)tetramethyltetrasilane with two equivalents of potassium fert-butoxide and 18-crown-6 affords the 1,4-dianion 1 in almost quantitative yield [3]. When 1 is reacted with 1,2-dibromotetramethyldisilane, l,l,4,4-tetrakis(trimethylsilyl)octamethyl-cyclohexasilane (2) is obtained (Scheme 1). Reaction of 2 with one or two equivalents of potassium... 

With SbClj, either one, two, or three of the methyl groups present in SieMeja can be replaced by chlorine depending on the stoichiomettic ratio of the reactants [4]. The reaction of the partially chlorinated cyclohexasilanes 1-4 thus obtained with lithium silanolates easily affords the corresponding siloxy derivatives 5-8. 

Reactions of the partially chlorinated cyclohexasilanes 5-8 with various nucleophiles such as H, [(CO)2CpFe], RS or R , afford the corresponding substitution products. The siloxy-substituted cyclohexasilanes 10-13 can be prepared in a similar way by reacting 5-8 with lithium silanolates according to Scheme 15.4 ... 

The skeleton rearrangement of methylpolysilanes was found by Kumada in 1969, in which the rearrangement is carried out at room temperatures by the reaction of cyclohexasilane with trimethylchlorosilane in the presence of aluminum chloride catalyst and the monochloro derivative is obtained and the arylation with Grignard reagents proceeds as shown in eq. (8.34) [25]. 

The cyclohexasilane derivatives [(CO)2CpFe]—SisMen, [(CO)3PPh3Co]—SieMen, 1,3- or l,4-[(CO)2CpFe]2—SisMeio and l,4-[(CO)3PPh3Co]2-SieMem can be made quite similarly Manganese derivatives of cyclosilanes have also been prepared . An inverse salt elimination procedure, however, has to be applied in order to prevent extensive transmetallation reactions (equation 30). 

Much of the cyclohexasilane chemistry carried out recently is based on dodecamethylcyclohexasilane. One approach in this direction employs the reaction of dodecamethylcyclohexasilane with t-BuOK which leads to undecamethylcyclo-hexasilanyl potassium [126]. Reactions of the latter provided access to several... 

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