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.