Synthesis, Structure, and Reactivity of Heavier Group 14 Element-centered Free Radicals : From Phantom Species to Grams-Order-Scale Materials

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The chemistry of the stable free radicals of heavier group 14 elements has been studied, including both neutral and charged radical species. The electronic and crystal structural features of these radicals, both in the solid state and in solution, are compared with each other. The most important parameters affecting the stability, geometry and electronic configuration of the radicals are investigated, based upon the experimental and computational data.1. Upon one-electron reduction with ^tBuLi, tetrakis(di-tert-butylmethylsilyl)disilene produced a disilene anion radical, which was isolated in the form of its lithium salt. The molecular structure was established by X-ray crystallography, which showed a nearly orthogonal structure with the central Si-Si bond length of 2.341(5) Å. One of the central Si atoms has radical character, whereas the other Si atom has silyl anion character. The EPR study indicates that rapid spin exchange occurs between these central Si atoms on the EPR time scale.2. The one-electron oxidation reaction of tris[di-tert-butyl(methyl)silyl]silyl and germyl anions with dichlorogermylene dioxane complex resulted in the formation of stable tris[di-tert-butyl(methyl)silyl]silyl and germyl radicals. The crystal structures of both silyl and germyl radicals showed a completely planar geometry around the radical centers. The EPR spectra indicate the p-character of both radicals, corresponding to a planar geometry and sp^2 hybridization of the radical centers.3. The one-electron reduction of tris[di-tert-butyl(methyl)silyl]aluminum and-gallium with alkali metals (Li, Na, K) resulted in the formation of the corresponding radical anions [(tBu_2MeSi)_3Al]^-・and [(^tBu_2MeSi)_3Ga]・^-. Their molecular structures were established by X-ray crystallography, which showed a nearly planar geometry around the radical centers.