1,2-DI(SILYL)BENZENE AND 1,4-DIBROMO-2,5-DI(SILYL)BENZENE

1,2-Di(silyl)benzene (3), has been prepared in a three-step process st arting with the reaction of 1,2-dibromobenzene and p-tolyl(chloro)sila ne with magnesium in tetrahydrofuran, which affords 1,2-bis(p-tolylsil yl)benzene (1) as a stable high-yield intermediate. Compound 1 has bee n converted into 1,2-bis(trifluoromethanesulfonatosilyl)benzene (2) wi th trifluoromethanesulfonic acid, and finally into 3 by reduction with lithiumaluminiumhydride, bath again in high yields. - In an attempt t o prepare 1,2,4,5-tetra(silyl)benzene in an analogous way, only the bi s-silylated species could be obtained (from 1,2,4,5-C6H2Br4, p-MeC(6)H (4)SiClH(2) and Mg powder: 1,4-dibromo-2,5-bis(p-tolylsilyl)benzene 4, and 1,4-dibromo-2,5-di(silyl)benzene, 6, via omo-2,5-bis(trifluoromet hanesulfonatosilyl)benzene 5). The crystal structures of compounds 4 a nd 6 have been determined by X-ray diffraction. The results indicate n o 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.