An anionic aluminabenzene bearing aromatic and ambiphilic contributions.

The synthesis and structure of an anionic aluminabenzene, which is the first example of an aluminum-containing heterobenzene, are reported. The molecular structure of this aluminabenzene exhibits a planar six-membered ring, and the absence of any bond alternation between its unsaturated bonds is consistent with the structural criteria of aromaticity. Theoretical calculations and the NMR spectroscopic analysis of this anionic aluminabenzene furthermore suggest that, in addition to the aromatic conjugation of six π-electrons, an ambiphilic contribution from a Lewis acidic aluminum center and an anionic pentadienyl moiety are present. Due to this contribution, the aluminabenzene is able to react with Lewis bases such as 4-dimethylaminopyridine and electrophiles such as methyl iodide.