RADICAL CATIONS FROM ARYL-SILANES, ARYL-GERMANES AND ARYL-DIGERMANES

During irradiation of trimethyl(p-tolyl)silane 1b with (CF3CO2)(2)Hg i n CF3CO2H, an EPR spectrum due to 1b(.+) is observed. The spin density in the transient radical cation resembles that of 1b(.-). In contrast to this, the analogous germane 3b gives the radical cation of p-bitol yl. After irradiation of tetrakis-(p-methoxyphenyl)silane 2d, the radi cal cation 2d(.+) is identified by ENDOR. However, the radical cation of p-bi(methoxyphenyl) is formed with p-methoxyphenyl(trimethyl)silane 1d and tetrakis(p-methoxyphenyl)germane 4d. The reaction of phenyl-si lanes and -germanes 1a, 4a, 5a with AlCl3 in CH2Cl2 or CHCl2CH3 yields the radical cations of anthracene, I, or 9,10-dimethylanthracene, II. Treatment of para-substituted phenyl-silanes, -germanes and -digerman es 1-5 with AlCl3 in CH2Cl2 leads to 2,6-disubstituted, and with AlCl3 in CHCl2CH3 to 2,6,9,10-tetrasubstituted, anthracene radical cations III-VII. The first step of the reaction is an electrophilic ipso-subst itution of the silyl or germyl residue followed by a condensation and an oxidation. With hexamesityldigermane 5e, intermolecular methyl tran sfer takes place to give the radical cations of 1,2,3,4,5,6,7,8-octame thyl- and 1,2,4,5,6,8-hexamethyl-anthracene VIII and IX.