Pentamethylcyclopentadienyl rhodium dichloride dimer is an organometallic compound with the formula [(C5(CH3)5RhCl2)]2, commonly abbreviated [Cp*RhCl2]2 This dark red air-stable diamagnetic solid is a reagent in organometallic chemistry.

The compound is prepared by the reaction of rhodium trichloride trihydrate and pentamethylcyclopentadiene in hot methanol, from which the product precipitates:[1] It was first prepared by the reaction of hydrated rhodium trichloride with hexamethyl Dewar benzene[2] This complex was first prepared from hexamethyl Dewar benzene and RhCl3(H2O)3.

[3][4][5] The hydrohalic acid necessary for the ring-contraction rearrangement is generated in situ in methanolic solutions of the rhodium salt, and the second step has been carried out separately, confirming this mechanistic description.

[8] The Rh-μ-Cl bonds are labile and cleave en route to a variety of adducts of the general formula Cp*RhCl2L.

The chemistry is similar to that of the analog pentamethylcyclopentadienyl iridium dichloride dimer.