Rhodium (triphenylphosphine)carbonylacetylacetonate
[CAS# 25470-96-6]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic rhodium
• Name: Rhodium (triphenylphosphine)carbonylacetylacetonate
• Synonyms: Carbonyl(pentane-2,4-dionato-O,O')(triphenylphosphine)rhodium
• Molecular Formula: C₂₄H₂₂O₃PRh
• Molecular Weight: 492.31
• CAS Registry Number: 25470-96-6
• EC Number: 247-015-0
• SMILES: C/C(=C/C(=O)C)/[O-].[C-]#[O+].C1=CC=C(C=C1)P(C2=CC=CC=C2)C3=CC=CC=C3.[Rh]

Properties

• Melting point: 200-204 °C (Expl.)

Safety Data

• Hazard Symbols: GHS06;GHS07 Danger
• Risk Statements: H301-H319-H413
• Safety Statements: P301+P310-P305+P351+P338

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413

• Transport Information: UN 2811

Discovery and Applications

Rhodium (triphenylphosphine)carbonylacetylacetonate is a coordination complex consisting of a central rhodium(I) ion bonded to three different ligands: triphenylphosphine (PPh₃), carbon monoxide (CO), and acetylacetonate (acac). The compound is typically represented by the molecular formula Rh(acac)(CO)(PPh₃), where acac stands for the bidentate anion of acetylacetone (2,4-pentanedione).

This complex is a member of the broader class of organorhodium(I) compounds, known for their applications in homogeneous catalysis. The coordination sphere around the rhodium(I) center in this complex is square planar, a common geometry for d⁸ metal centers. The rhodium is coordinated to the bidentate acetylacetonate ligand via its two oxygen atoms, a carbonyl ligand through the carbon atom, and a phosphorus atom of the triphenylphosphine ligand. Each ligand plays a specific role in modulating the electronic and steric environment of the metal center.

The compound can be synthesized by substitution reactions starting from precursor complexes such as Rh(acac)(CO)₂ or RhCl(CO)(PPh₃)₂. For instance, treatment of Rh(acac)(CO)₂ with triphenylphosphine in an inert atmosphere (such as under nitrogen or argon) results in displacement of one carbonyl ligand and coordination of the PPh₃ ligand to give Rh(acac)(CO)(PPh₃).

Physically, Rh(acac)(CO)(PPh₃) is a yellow to orange crystalline solid. It is generally soluble in organic solvents such as dichloromethane, chloroform, benzene, and toluene. The compound is stable under dry conditions and at room temperature but is sensitive to air and moisture, requiring storage under inert conditions to prevent degradation or oxidation.

One of the main applications of rhodium (triphenylphosphine)carbonylacetylacetonate is in homogeneous catalysis, particularly in hydroformylation, hydrogenation, and carbonylation reactions. In hydroformylation, also known as the oxo process, the compound catalyzes the addition of carbon monoxide and hydrogen to alkenes to form aldehydes. The presence of triphenylphosphine stabilizes the rhodium center and tunes the electronic properties of the metal, affecting both the activity and selectivity of the catalytic process.

The acetylacetonate ligand confers increased stability to the complex, enabling its use in various solvent systems and allowing for catalyst recycling in some cases. The carbonyl ligand is a strong π-acceptor, which withdraws electron density from the rhodium center, further tuning the reactivity of the complex in electron-demanding catalytic cycles.

Analytical characterization of Rh(acac)(CO)(PPh₃) involves techniques such as infrared (IR) spectroscopy, which shows a strong C≡O stretching band typically in the region of 1,980–2,000 cm⁻¹, indicating the presence of a terminal carbonyl ligand. Nuclear magnetic resonance (NMR) spectroscopy, particularly ³¹P NMR, provides information on the phosphine coordination, while ¹H and ¹³C NMR confirm the identity of the acac and PPh₃ moieties. Mass spectrometry and elemental analysis are also used to confirm the molecular weight and composition.

In conclusion, rhodium (triphenylphosphine)carbonylacetylacetonate is a well-characterized organometallic complex with significant utility in catalysis. Its stable, tunable coordination environment and the presence of both σ-donating and π-accepting ligands make it an effective precursor or active species in several industrially relevant chemical transformations.

References

none