A new form of aromaticity by shuffling of substituents

Chemists from Imperial College report an isomer of hexasilabenzene in Science, which displays a new form of aromaticity arising from a hitherto unrecognized type of cyclic electronic resonance.

Cyclic electron delocalisation in dismutational isomer of hexasilabenzene

The phenomenon of aromaticity and its archetypical representative, benzene C6H6, are ubiquitous in chemistry. The extraordinary stability of benzene is derived from the cyclic delocalisation of its three double bonds. Despite the well-known reluctance of silicon to engage in multiple bonding, a team of Imperial College Chemists led by Dr David Scheschkewitz and Professor Henry Rzepa now reports on the isolation of an isomer of hexasilabenzene. The dark-green compound exhibits aromaticity even though its substituents - unlike in benzene - are unequally distributed. The formal shifting of two of the six substituents of a hypothetical benzene-type structure leads to the isomer featuring silicon atoms bearing two, one and no substituents. The authors have coined the term ‘dismutational aromaticity' to describe this new form of the well-known stabilising effect (‘dismutation' or ‘disproportionation' is defined as the change from a uniform oxidation state to one higher and one lower value).

The original article is available online here. In addition the article has been highlighted in Chemistry World online  and C &E News here 

View circling camera views of single crystal and 3D structure of hexasilabenzene isomer on You Tube