Aromatic Silicon Analog For Benzene

Chemists have long debated whether hexasilabenzene, the aromatic silicon analog of benzene, might ever be coaxed into existence. Until 1981, chemists didn’t even realize that stable π bonding between two silicon atoms could occur at room temperature. Then in 1993, the first isomer of hexasilabenzene was made, but it wasn’t aromatic. Now, a research team led by David Scheschkewitz of Imperial College London has built the first aromatic ring compound based on a scaffold of six silicon atoms 
(Science 2010, 327, 564). In particular, 
Scheschkewitz and coworkers used a systematic synthesis to couple two cyclotrisilanes containing zero, one, or two bulky triisopropylphenyl substituents on the silicon atoms. X-ray crystallography reveals that molecules in hexasilabenzene’s bright green crystals form a tricyclic, chairlike conformation. In theoretical studies, Scheschkewitz’ team found that the six delocalized electrons in the hexasilabenzene isomer are not uniformly distributed over the entire molecule as they are in benzene, leading them to coin the term “dismutational aromaticity” to describe the phenomenon. The hexasilabenzenes or similar compounds may one day be useful in optical electronics, the researchers note.