The First Iridabenzenes: Syntheses, Properties and Reactions

Metallabenzenes differ from conventional aromatic compounds in that the π-bonding requires the involvement of metal dπ-orbitals rather than the pπ-orbitals used by main group elements. In 1982, the first example of a stable metallabenzene was reported by Roper. Following Roper's initial communication, there was a hiatus in the field until the late 1980s, when authors succeeded in synthesizing the first stable iridabenzene, using a pentadienyl reagent as the source of ring carbon atoms and C-H bond activation as the key ring-forming step. The initially formed six-membered ring was an iridacyclohexadiene, which was “dehydrogenated” to the iridabenzene in two steps. This straightforward high-yield synthesis allowed us the unique opportunity to study in detail the physical and chemical properties of a stable metallabenzene. This chapter summarizes the results of that fascinating scientific journey. The inscribed circle notation for iridabenzene 3 is used in the chapter as a shorthand for the two equivalent resonance structures.