Syntheses and structures of an "alumole" and its dianion.

Base free: An alumole was synthesized and treatment with lithium afforded the lithium salt of the alumole dianion. The structures of these two molecules were then investigated. The C-C bond lengths of the AlC4 ring in the dianion are nearly equal. DFT calculations revealed that the 3p(Al)-π* conjugation lowers the LUMO level of the alumole and that coordination of two lithium cations to the alumole dianion results in a planar AlC4 ring.