Pentamethylcyclopentadienyl iridium dichloride dimer was first prepared by the reaction of hydrated
iridium trichloride with
hexamethyl Dewar benzene. More conveniently, the compound is prepared by the reaction of hydrated iridium trichloride and
pentamethylcyclopentadiene in hot methanol, from which the product precipitates :2 Cp*H + 2 IrCl3(H2O)3 → [Cp*IrCl2]2 + 2 HCl + 6 H2O The Ir-
μ-Cl bonds are labile and can be cleaved to give a variety of adducts of the general formula Cp*IrCl2L. Such adducts undergo further substitution to afford cations and [Cp*IrL3]2+. The chloride ligands can also be replaced by other anions such as
carboxylates,
nitrite, and
azide. Reduction of [Cp*IrCl2]2 in the presence of CO affords [Cp*Ir(CO)2], which can be decarbonylated to give the unsaturated derivative [Cp*Ir(CO)]2. Treatment of [Cp*IrCl2]2 with
borohydride under an atmosphere of H2 gives the iridium(V) derivative Cp*IrH4. [Cp*IrCl2]2 is a precursor to catalysts for the asymmetric
transfer hydrogenation of ketones. ==Related compounds==