An Isolable Bisma­benzene: Synthesis, Structure, and Reactivity

A stable bisma­benzene
was synthesized, isolated, and structurally
characterized. The prospective aromaticity of this heavy benzene,
bearing a sixth-row element, was examined by X-ray crystallography
and NMR and UV–vis spectroscopy, as well as theoretical DFT
calculations. Structural analysis of this bisma­benzene revealed
a planar ring containing unsaturated Bi–C and C–C bonds.
As bond alternations could not be observed, these results are consistent
with the formal criteria of aromaticity. Theoretical calculations
also support the aromatic nature of this bisma­benzene, which
reacted with an alkyne to form the corresponding [4+2] cycloadduct,
thus demonstrating a small yet tangible aromatic stabilization energy.