Tetrasilyl-Substituted Cyclobutadiene Dianion Dilithium Salt: Synthesis and Structure.

The reaction of tetrakis(trimethylsilyl)cyclobutadienylcyclopentadienyl cobalt complex (Me3Si)4C4CoCp with lithium metal in THF yielded the dilithium salt of cyclobutadiene dianion CBD2– stabilized by four trimethylsilyl groups, Li+ 2[(Me3Si)4C4]2–. The bridged CBD2– dianion was also synthesized by a similar procedure starting from the bridged cobalt complex, which was prepared from the reaction of 2,2,5,5,8,8,11,11-octamethyl-2,5,8,11-tetrasilacyclododeca-1,6-diyne with CpCo(CO)2 in refluxing octane. The aromaticity of the CBD2– is discussed on the basis of the structural characteristics and magnetic properties.