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.