text: The first reported stable metallabenzene was the osmabenzene Os(CHS)CO(PPh). Characteristic of other metallaarenes, the Os-C bonds are about 0.6 Å longer than the C-C bonds (in benzene these are 1.39 Å), resulting in a distortion of the hexagonal ring. H NMR signals for the ring protons are downfield, consistent with aromatic "ring current." Osmabenzene and its derivatives can be regarded as an Os(II), d octahedral complex.
  Metallabenzenes have also been characterized with metals ruthenium, iridium, platinum, and rhenium.