Dicarbonylacetylacetonato rhodium(I)
[CAS# 14874-82-9]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic rhodium
• Name: Dicarbonylacetylacetonato rhodium(I)
• Synonyms: (Acetylacetonato)dicarbonylrhodium(I)
• Molecular Formula: C₇H₇O₄Rh
• Molecular Weight: 258.03
• CAS Registry Number: 14874-82-9
• EC Number: 238-947-9
• SMILES: [C-]#[O+].[C-]#[O+].CC(=O)\C=C(\C)O[Rh]

Properties

• Melting point: 154-156 ºC
• Water solubility: insoluble

Safety Data

• Hazard Symbols: GHS02;GHS06;GHS07;GHS09 DangerGHS02
• Hazard Statements: H228-H301-H315-H317-H319-H335-H411-H412
• Precautionary Statements: P210-P240-P241-P261-P264-P264+P265-P270-P271-P272-P273-P280-P301+P316-P302+P352-P304+P340-P305+P351+P338-P319-P321-P330-P332+P317-P333+P317-P337+P317-P362+P364-P370+P378-P391-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	3	H301
Eye irritation	Eye Irrit.	2	H319
Flammable solids	Flam. Sol.	1	H228
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Skin sensitization	Skin Sens.	1	H317
Skin sensitization	Skin Sens.	1A	H317
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin irritation	Skin Irrit.	2	H315
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Flammable solids	Flam. Sol.	2	H228

Discovory and Applicatios

Dicarbonylacetylacetonato rhodium(I), commonly written as Rh(acac)(CO)₂, is a well-characterized organometallic complex of rhodium in the +1 oxidation state. It consists of one acetylacetonate ligand (acac) and two carbonyl (CO) ligands coordinated to a central rhodium atom. The complex is neutral, monomeric, and adopts a square planar geometry, which is typical for d⁸ metal centers like Rh(I).

This compound is generally prepared by reacting rhodium(I) chloride carbonyl dimer, \[RhCl(CO)₂]₂, with sodium or potassium acetylacetonate under an inert atmosphere. During this process, the chloride ligands are replaced by a single bidentate acetylacetonate ligand, and the monomeric Rh(acac)(CO)₂ complex is formed. The product is typically a yellow to pale orange crystalline solid that is soluble in a variety of organic solvents such as dichloromethane and benzene.

In the structure of Rh(acac)(CO)₂, the acetylacetonate ligand coordinates in a bidentate fashion through its two oxygen atoms, forming a five-membered chelate ring with rhodium. The two carbonyl ligands are coordinated via the carbon atom, forming Rh–C≡O bonds. These carbonyl ligands are strong field ligands and are stabilized by back-donation of electron density from the filled d-orbitals of rhodium into the empty π\* orbitals of CO. The resulting metal–ligand bonding is characterized by strong σ-donation and π-backbonding, which is evident in the characteristic infrared absorptions of the CO ligands around 2000–2100 cm⁻¹.

Rh(acac)(CO)₂ is used primarily as a catalyst precursor in homogeneous catalysis. Its solubility and thermal stability make it suitable for use in reactions such as hydroformylation, hydrogenation, and carbonylation. In particular, it has been employed in hydroformylation of alkenes, where an aldehyde group is added to a carbon–carbon double bond under syngas (CO/H₂) in the presence of rhodium catalysts. This reaction is widely used in the industrial synthesis of aldehydes, alcohols, and related compounds.

The compound also serves as a convenient starting material for the synthesis of other rhodium(I) complexes. The acetylacetonate and carbonyl ligands can be substituted under appropriate conditions to produce mixed-ligand rhodium complexes for use in organometallic research or tailored catalytic systems. Ligand substitution typically involves displacement of one or both CO ligands by phosphines, isocyanides, or nitrogen-containing heterocycles, generating complexes with varied steric and electronic properties.

Due to the presence of volatile and potentially toxic CO ligands, Rh(acac)(CO)₂ should be handled with care. Although the complex is relatively stable under normal conditions, it can release CO upon heating or photolysis. Proper ventilation, use of a fume hood, and personal protective equipment are recommended during its handling. It should also be stored in a sealed container under inert atmosphere to prevent degradation or oxidation.

In summary, dicarbonylacetylacetonato rhodium(I), Rh(acac)(CO)₂, is a square planar organometallic complex used extensively in catalysis and organometallic synthesis. It is prepared from rhodium(I) carbonyl precursors and is characterized by its stability, solubility, and ability to undergo ligand substitution. Its role as a catalyst precursor in hydroformylation and other transformations makes it a valuable reagent in both academic and industrial chemistry.

References

2023. Promising Applications of Polyethyleneimine as a Ligand in Rhodium-Catalyzed Tandem Hydroformylation/Hydrogenation of Olefins. Petroleum Chemistry, 63(3).
DOI: 10.1134/s0965544123030222

2024. Autonomous reaction Pareto-front mapping with a self-driving catalysis laboratory. Nature Chemical Engineering, 1(2).
DOI: 10.1038/s44286-024-00033-5

2020. Continuous Catalytic Processes with Supported Ionic Liquid Phase (SILP) Materials. Green Chemistry and Sustainable Technology.
DOI: 10.1007/978-3-030-35245-5_3