text: When bound in the η manner, arenes often function as unreactive spectator ligands, as illustrated by several homogeneous catalysts used for transfer hydrogenation, such as (η-CR)Ru(TsDPEN). In cationic arene complexes or those supported by several CO ligands, the arene is susceptible to attack by nucleophiles to give cyclohexadienyl derivatives.
  Particularly from the perspective of organic synthesis, the decomplexation of arenes is of interest. Decomplexation can often be induced by treatment with excess of ligand (MeCN, CO, etc).