Pentamethylcyclopentadienyl iridium dichloride dimer is an organometallic compound with the formula [(C<sub>5</sub>(CH<sub>3</sub>)<sub>5</sub>IrCl<sub>2</sub>)]2, commonly abbreviated [Cp*IrCl<sub>2</sub>]2 This bright orange air-stable diamagnetic solid is a reagent in organometallic chemistry.
The compound has C2h symmetry. Each metal is pseudo-octahedral. The terminal and bridging Ir-Cl bonds have the lengths 2.39 and 2.45 Å, respectively.
Pentamethylcyclopentadienyl iridium dichloride dimer was first prepared by the reaction of hydrated iridium trichloride with hexamethyl Dewar benzene.[1] More conveniently, the compound is prepared by the reaction of hydrated iridium trichloride and pentamethylcyclopentadiene in hot methanol, from which the product precipitates[2]
2 Cp*H + 2 IrCl3(H2O)3 → [Cp*IrCl<sub>2</sub>]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*IrL<sub>3</sub>]2+. The chloride ligands can also be replaced by other anions such as carboxylates, nitrite, and azide.
Reduction of [Cp*IrCl<sub>2</sub>]2 in the presence of CO affords [Cp*Ir(CO)<sub>2</sub>], which can be decarbonylated to give the unsaturated derivative [Cp*Ir(CO)]2.[3] Treatment of [Cp*IrCl<sub>2</sub>]2 with borohydride under an atmosphere of H2 gives the iridium(V) derivative Cp*IrH4.
[Cp*IrCl<sub>2</sub>]2 is a precursor to catalysts for the asymmetric transfer hydrogenation of ketones.[4]