The First Isolation and Full Characterization of Fulvene Dianion. Synthesis and X-ray Structure of Dilithium Hexasilylfulvene Dianion

Treatment of hexasilylfulvene ( 4 ) with lithium metal in tetrahydrofuran yields yellow crystals of the dilithium hexasilylfulvene dianion ( 5 ). The dilithium hexasilylfulvene dianion ( 5 ) has a monomeric structure and forms a contact ion pair (bis-CIP) in the crystals. One of the lithium atoms is located above the center of the five-membered ring, whereas the other one is bonded to the exocyclic carbon atom. The bis-CIP structure determined by X-ray crystallography is maintained in solution.