Pnictogen-silicon additions to the inorganic benzene family

The discovery of borazine (B₃N₃H₆) as the first inorganic analog of benzene 90 years ago opened the eyes of chemists to the possibility of creating noncarbon aromatic compounds. Although researchers have explored many possible combinations of group 13 to group 15 elements in pursuit of additional examples, only a handful have been found. Building on that work, a team led by Manfred Scheer of the University of Regensburg has now added two new molecules to the collection by synthesizing aromatic phosphorus-silicon and arsenic-silicon benzene analogs, along with their related antiaromatic cyclobutadiene analogs (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b07389). The researchers formed the triphospha- and triarsatrisilabenzenes by a metathesis reaction between phosphorus- or arsenic-containing zirconium cyclopentadienyl complexes and a bulky chlorosilylene. Structural studies show that the benzene analogs have slightly distorted ring shapes with P-Si and As-Si bond lengths intermediate between single and double bonds, as expected for conjugated aromatic rings. Computational studies verify the aromatic character of the compounds. These new benzene analogs “give an insight into the chemistry of inorganic aromatic systems and aromaticity in general—150 years after Kekulé’s first report on aromatic compounds,” Scheer and his colleagues write.