Five-membered bismuth ring opens up ‘a new era for aromatic compounds’

A five-membered aromatic bismuth ring, prepared by researchers in Germany, addresses a long-standing challenge in synthetic chemistry. The isolation of a complex containing the motif means that analogues of the classic cyclopentadienide anion have now been produced using all of the naturally occurring pnictogen elements.

Cyclopentadiene is a widely used ligand in transition metal chemistry that features an aromatic five-membered carbon ring, with the formula C₅H₅. Perhaps the most famous example of its use is in ferrocene, where two cyclopentadiene ligands sandwich an iron atom.