Bis[(pentamethylcyclopentadienyl)dichloro-rhodium]
[CAS# 12354-85-7]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic rhodium
• Name: Bis[(pentamethylcyclopentadienyl)dichloro-rhodium]
• Synonyms: Dichloro(pentamethylcyclopentadienyl)rhodium(III) dimer; Pentamethylcyclopentadienylrhodium(III) chloride dimer
• Molecular Formula: C₂₀H₃₀Cl₄Rh₂
• Molecular Weight: 618.08
• CAS Registry Number: 12354-85-7
• EC Number: 625-704-0
• SMILES: Cl[Rh]Cl.Cl[Rh]Cl.C[C]1[C](C)[C](C)[C](C)[C]1C.C[C]2[C](C)[C](C)[C](C)[C]2C

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302+H312+H332-H315-H319
• Safety Statements: P501-P261-P270-P271-P264-P280-P337+P313-P305+P351+P338-P362+P364-P332+P313-P301+P312+P330-P302+P352+P312-P304+P340+P312

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H312
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	4	H302
Specific target organ toxicity - single exposure	STOT SE	3	H335
Respiratory sensitization	Resp. Sens.	1	H334
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413
Eye irritation	Eye Irrit.	2A	H319

Discovery and Applications

Bis[(pentamethylcyclopentadienyl)dichloro-rhodium] is an organorhodium complex with the formula [(C₅Me₅)RhCl₂]₂, where C₅Me₅ represents the pentamethylcyclopentadienyl (Cp*) ligand. The complex consists of two rhodium(III) centers, each coordinated by one η⁵-pentamethylcyclopentadienyl ligand and two chloride ligands. These two rhodium units are bridged via chloride ligands, forming a dimeric structure. The compound commonly appears as a red-orange crystalline solid and is soluble in various organic solvents such as dichloromethane and chloroform.

This compound was characterized during studies of cyclopentadienyl transition metal complexes in the late 20th century, when the pentamethylcyclopentadienyl ligand was found to provide enhanced steric protection and electron donation compared to the unsubstituted cyclopentadienyl ring. Structural analyses, including X-ray crystallography, confirmed the dimeric arrangement and octahedral coordination geometry around each rhodium center, with the Cp* ligand occupying one face of the octahedron and chlorides completing the coordination sphere.

Bis[(pentamethylcyclopentadienyl)dichloro-rhodium] is typically synthesized by reacting rhodium trichloride hydrate with pentamethylcyclopentadiene under reflux conditions, sometimes with added base to facilitate complex formation. The product can be isolated by crystallization or filtration from the reaction mixture.

This complex serves as an important precursor in the preparation of rhodium-based catalysts and organometallic derivatives. The chloride ligands can be substituted by various ligands, including phosphines, nitrogen donors, or carbenes, leading to monomeric or polynuclear species with tailored catalytic properties. Such derivatives find applications in homogeneous catalysis, including hydrogenation, hydroformylation, and C–H activation reactions.

The compound’s stability and solubility also make it useful in mechanistic studies and as a building block for advanced organometallic architectures.

Handling of bis[(pentamethylcyclopentadienyl)dichloro-rhodium] requires care due to the toxicity of rhodium compounds and potential irritant effects. Appropriate protective equipment and good laboratory practices should be observed.

In summary, bis[(pentamethylcyclopentadienyl)dichloro-rhodium] is a stable dimeric rhodium(III) complex featuring Cp* and chloride ligands. It is widely used as a versatile precursor in organometallic synthesis and catalysis because of its ligand exchangeability and robust structural properties.

References

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