Arene complexes

This chapter assesses arene complexes. Following the recognition in the early 1950s of the sandwich bonding principle for metallocenes, the existence of related sandwich complexes of neutral arenes such as benzene was demonstrated through the synthesis of bis-(benzene)chromium. The complex is isoelectronic to ferrocene and follows the 18-electron rule. Bonding in bis-(arene)metal complexes resembles that in metallocenes, and the MO diagram is qualitatively very similar. Since the aromatic ligands in bis-(arene) complexes are not negatively charged, there is no electrostatic contribution to bonding, and bis-(arene) complexes are in general less stable than metallocenes and more easily oxidized. The chapter then considers arene half-sandwich complexes; seven and eight membered ring ligands; heteroarene complexes; and multidecker complexes.