The Heavy Analogue of CpLi: Lithium 1,2-Disila-3-germacyclopentadienide, a 6π-Electron Aromatic System

Lithium 1,2-disila-3-germacyclopentadienide 2-·Li+ was synthesized by the reduction of 1,2-disila-3-germacyclopenta-2,4-diene 1 with potassium graphite followed by treatment with an excess amount of LiBr. The X-ray analysis of 2-·[Li+(THF)] revealed a delocalized aromatic cyclopentadienide-type structure with the diagnostic η5-coordination of the Li+ cation to the five-membered ring. Aromaticity of this compound was verified and confirmed by theoretical calculations. The solution behavior of the 2-·Li+ is different in nonpolar and polar solvents; in nonpolar toluene, 2-·Li+ maintained the properties of a delocalized aromatic compound with the characteristically shielded 7Li NMR resonance at −5.4 ppm, whereas in polar THF, 2-·Li+ exhibited the properties of a localized nonaromatic compound with the negative charge situated on the Ge atom.