The anions and dianions of group 14 metalloles

The synthesis, structures, and physical and chemical properties of mono- and dianions of group 14 metalloles (1-metallacyclopentadiene), heavier congeners of the cyclopentadienyl anion, are described. Dianions of metalloles have a substantial aromatic character owing to strong participation of divalent resonance forms and the silole anion shows different degrees of aromaticity depending on the substituent, but there is no evidence for aromaticity in the germole anion. Dianions of benzannulated metalloles have more aromatic character in the metallole ring than in the benzene ring. The synthesis and characterization of η5-silolyl and η5-germolyl metal complexes, analogs of ferrocene, and their unique reactivity are also described.