Radicals and Anions of Siloles and Germoles.

The synthesis of persistent sila- and germa-cyclo-penta-dien-yl (silolyl- and germolyl-) radicals by careful stoichiometric reduction of the corresponding halides with potassium is reported. The radicals were characterized by EPR spectroscopy and trapping reactions. The reduction of tris (trimethylsilyl)silyl-substituted halides was successful while smaller substituents (i.e., t -Butyl, Ph) gave the corresponding dimers. The EPR spectroscopic parameter of the synthesized tetrolyl radicals indicate only small spin delocalization to the butadiene unit due to cross-hyperconjugation. Silolyl- and germolyl anions are unavoidable byproducts and are isolated in the form of their potassium salts and characterized by X-ray crystallography. The comparison of the molecular structures of two closely related potassium silolides provided an example for different coordination of the potassium cation to the silolyl anion (η 1 vs. η 5 coordination) that triggers the switch between delocalized and localized states.