Isolable Silyl and Germyl Radicals Lacking Conjugation with π-Bonds: Synthesis, Characterization, and Reactivity

The one-electron oxidation reaction of tris[di-tert-butyl(methyl)silyl]silyl and -germyl anions with
dichlorogermylene−dioxane complex results in the formation of stable tris[di-tert-butyl(methyl)silyl]silyl and
-germyl radicals 1 and 2, representing the first isolable radical species of heavier Group 14 elements lacking
stabilization by conjugation with π-bonds. The crystal structures of both silyl and germyl radicals 1 and 2
showed a completely planar geometry around the radical centers. The ESR spectra of 1 and 2 showed
strong signals with characteristic satellites due to the coupling with the 29Si and 73Ge nuclei. The small
values of the hyperfine coupling constants a(29Si) and a(73Ge) clearly indicate the π-character of both radicals,
corresponding to a planar geometry and sp2 hybridization of the radical centers. Both 1 and 2 easily undergo
halogenation reactions with carbon tetrachloride, 1,2-dibromoethane, and benzyl bromide to form the
corresponding halosilanes and halogermanes.