Pentamethylcyclopentadienyl-rhodium and -iridium complexes. Part VI. π-Arene, π-cyclohexadienyl, and π-pyrrolyl complexes

A new method for the preparation of π-arene and π-pyrrolyl complexes is described. The trifluoroacetates [M(C5Me5)(OCOCF3)2, H2O](M = Rh, Ir) in trifluoracetic acid react with a variety of methylated benzenes to give [M(C5Me5)(arene)]2+. The π-arene complexes of IrIII are more stable than those of RhIII and their stability increases with increasing methylation. The complex [Rh(C5Me5)(p-xylene)]2+ undergoes rapid displacement of p-xylene by dimethyl sulphoxide to give [Rh(C5Me5)(Me2SO)3]2+. The π-arene complexes react with nucleophiles (NaBH4, MeLi) to give π-cyclohexadienyl complexes where the attacking group becomes the exo-substituent. The π-pyrrolyl complexes [M(C5Me5)(C4H4N)]+ are obtained in high yield from the trifluoroacetates and do not react with nucleophiles under these conditions.