Reduction of tetrakis(trimethylsilyl)butatriene by lithium: Monomeric and dimeric structures of the dilithium butatriene dianion

Treatment of tetrakis(trimethylsilyl)butatriene (2) with lithium in tetrahydrofuran (THF) led to quantitative formation of the corresponding dianion species. Yellow crystals of the dilithium salts of 2 were isolated as an unexpected dimeric structure (4) as well as a monomeric structure (3). Both of the crystal structures, which havebeen confirmed by X-ray diffraction, reveal a doubly bridged lithium bisallylic structure. The unique dynamic behaviour of the lithium ions of the dimer 4 in toluene-d₈ is demonstrated.