Synthesis and Structure of <i>cis</i>-1,4-Di(1-pyrenyl)decamethylcyclohexasilane

The synthesis and structure of <i>cis</i>-1,4-di(1-pyrenyl)decamethylcyclohexasilane (<b>2</b>), one of the first <i>cis</i>-1,4-substituted cyclohexasilanes, are reported. This isomer is unexpectedly formed as the major product in the reaction of a mixture of <i>trans</i>- and <i>cis</i>-1,4-dichlorodecamethylcyclohexasilane (<b>4a</b> and <b>4b</b>, respectively) with 1-pyrenyllithium. Reaction of <b>4a</b>,<b>b</b> with phenyllithium showed that preferential formation of the <i>cis</i>-product is a general feature of this kind of reaction. According to the X-ray crystal structures of two different solvates, the cyclohexasilane ring in <b>2</b> adopts a unique boatlike geometry, with the pyrenyl substituents occupying an equatorial or bisectional position. ¹H NMR data indicate that a boatlike geometry also occurs in solution. Furthermore, the X-ray crystal structure of <i>trans</i>-1,4-dihydrodecamethylcyclohexasilane, which is an intermediate in the synthetic pathway to <b>2</b>, is reported.