1 , 2 - Di ( silyl ) benzene and l , 4 - Dibromo - 2 , 5 - di ( silyl ) benzene

Silanes, Silylbenzenes, Di(silyl)benzenes. Bromo(silyl)benzenes 1,2-Di(silyl)benzene (3). has been prepared in a three-step process starting with the reac­ tion of 1 ,2-dibromobenzene and /?-tolyl(chloro)silane with magnesium in tetrahydrofuran, which affords l,2-bis(p-tolylsilyl)benzene (1) as a stable high-yield intermediate. Compound 1 has been converted into 1 .2-bis(trifluoromethanesulfonatosilyl)benzene (2) with trifluoromethanesulfonic acid, and finally into 3 by reduction with lithiumaluminiumhydride, both again in high yields. In an attempt to prepare l,2,4.5-tetra(silyl)benzene in an analogous way. only the bis-silylated species could be obtained (from l,2,4,5-C6H2Br4, p-M eC6H4SiClH2 and Mg powder: l,4-dibromo-2,5-bis(p-tolylsilyl)benzene, 4, and l,4-dibromo-2,5-di(silyl)benzene, 6, via 1.4-dibromo-2,5-bis(trifluoromethanesulfonatosilyl)benzene, 5). The crystal structures of compounds 4 and 6 have been determined by X-ray diffraction. The results indicate no steric hindrance in these molecules and it is thus not obvious from the molecular structures why the silylation reaction does not proceed any further to give the tetrasilylated benzene derivatives. Electronic effects have to be invoked to rationalize the experimental findings.