Radical cations from aryl-silanes, -germanes and -digermanes

Abstract

During irradiation of trimethyl(p-tolyl)silane 1b with (CF₃CO₂)₂Hg in 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-bitolyl. After irradiation of tetrakis-(pmethoxyphenyl)silane 2d, the radical 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-silanes 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 -digermanes 1–5 with AICl₃ in CH₂Cl₂ leads to 2,6-disubstituted, and with AICl₃ in CHCl₂CH₃ to 2,6,9,10-tetrasubstituted, anthracene radical cations III–VII. The first step of the reaction is an electrophilic ipso-substitution of the silyl or germyl residue followed by a condensation and an oxidation. With hexamesityldigermane 5e, intermolecular methyl transfer takes place to give the radical cations of 1,2,3,4,5,6,1,8-octamethyl- and 1,2,4,5,6,8-hexamethyl-anthracene VIII and IX.