Triaryl-silyl, -germyl, and -stannyl radicals .MAr 3 (M = Si, Ge, or Sn and Ar = 2,4,6-Me 3C 6H 2) and .Ge(2,6-Me 2C 6H 3) 3: Synthesis and ESR studies

Abstract

The triarylmetal-centred radicals .MAr 3 (M = Si, Ge, or Sn; Ar = 2,6-Me 2C 6H 3 or 2,4,6-Me 3C 6H 2) have been prepared from the appropriate triarylmetal chloride, MAr 3Cl, and an electron-rich olefin [R NCH 2CH 2NRC ] 2 (R = Me or Et) under UV irradiation in toluene at low temperature. The triarylgermyl radicals are persistent ( t 1 2 > 24 h, 20°C) whilst the analogous tin and silicon radicals are only stable under constant irradiation at temperatures below −20°C; the ESR spectra of the germanium radicals and of .Si(2,4,6-Me 3C 6H 2) 3 (which is the first triarylsilyl radical to be spectroscopically identified) show coincidental equivalence of all the proton couplings due to twisting of thearomatic rings into a “propeller” arrangement about the metal. The synthesis and characterisation of precursors to these radicals are also reported.