Carbonyltris(triphenylphosphine)rhodium(I) hydride
[CAS# 17185-29-4]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic rhodium
• Name: Carbonyltris(triphenylphosphine)rhodium(I) hydride
• Synonyms: Hydridocarbonyltris(triphenylphosphine)rhodium(I)
• Molecular Formula: C₅₅H₄₆OP₃Rh
• Molecular Weight: 918.79
• CAS Registry Number: 17185-29-4
• EC Number: 241-230-3
• SMILES: [H-].[C-]#[O+].C1=CC=C(C=C1)P(C2=CC=CC=C2)C3=CC=CC=C3.C1=CC=C(C=C1)P(C2=CC=CC=C2)C3=CC=CC=C3.C1=CC=C(C=C1)P(C2=CC=CC=C2)C3=CC=CC=C3.[Rh]

Properties

• Melting point: 150 °C (dec.)

Safety Data

• Hazard Symbols: GHS06 Danger
• Risk Statements: H301-H311-H331-H413
• Safety Statements: P261-P262-P264-P270-P271-P273-P280-P301+P316-P302+P352-P304+P340-P316-P321-P330-P361+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	3	H301
Acute toxicity	Acute Tox.	3	H331
Acute toxicity	Acute Tox.	3	H311
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413

• Transport Information: UN 2811

Discovery and Applications

Carbonyltris(triphenylphosphine)rhodium(I) hydride is a well-known organometallic complex with the formula HRh(CO)(PPh₃)₃. This compound features a rhodium(I) center coordinated by one carbonyl ligand (CO), three triphenylphosphine (PPh₃) ligands, and one hydride (H⁻) ligand. The rhodium atom is in the +1 oxidation state, and the complex adopts a square planar geometry typical for d⁸ transition metal complexes.

The synthesis of carbonyltris(triphenylphosphine)rhodium(I) hydride usually involves the reduction of rhodium(I) precursors, such as Wilkinson’s catalyst (RhCl(PPh₃)₃), under a hydrogen atmosphere in the presence of carbon monoxide. The reaction proceeds by substituting the chloride ligand with a hydride and incorporating CO to yield the hydride carbonyl complex. Alternatively, it can be prepared by treatment of Rh(CO)(PPh₃)₃ with hydride donors like sodium borohydride.

Structurally, the complex exhibits a square planar coordination geometry around rhodium, with the hydride ligand positioned cis to the carbonyl ligand and trans to one of the triphenylphosphines. The bonding involves σ-donation from the phosphine and hydride ligands to the metal center, and π-backbonding from rhodium to the CO ligand, stabilizing the complex. The hydride ligand is detectable by characteristic signals in proton NMR spectroscopy, often appearing as a high-field resonance due to its direct bonding to the metal.

Carbonyltris(triphenylphosphine)rhodium(I) hydride is of great significance in homogeneous catalysis. It serves as an active intermediate in many catalytic cycles, particularly in hydrogenation and hydroformylation reactions. Its ability to transfer hydride ions makes it effective for catalytic hydrogenation of alkenes, alkynes, and other unsaturated substrates under mild conditions, with high selectivity and efficiency.

In hydroformylation, the complex or related species catalyze the addition of syngas (CO and H₂) to alkenes, producing aldehydes valuable in fine chemical and polymer industries. The hydride ligand plays a crucial role in these catalytic cycles by facilitating migratory insertion and reductive elimination steps necessary for substrate transformation.

Beyond catalysis, carbonyltris(triphenylphosphine)rhodium(I) hydride has been extensively studied as a model compound in organometallic chemistry. Its well-defined structure and reactivity provide insights into metal-hydride bonding, ligand effects, and reaction mechanisms involving rhodium complexes. It also serves as a precursor for synthesizing other rhodium hydride complexes with modified ligands, enabling exploration of structure–activity relationships.

Handling of this complex requires typical precautions for air-sensitive organometallic compounds. It is generally stable under inert atmosphere but sensitive to moisture and oxygen, which can lead to decomposition. Proper storage and manipulation under inert gas are necessary to maintain its purity and catalytic activity.

In summary, carbonyltris(triphenylphosphine)rhodium(I) hydride is a square planar rhodium(I) complex containing hydride, carbonyl, and triphenylphosphine ligands. It plays a pivotal role as an intermediate and catalyst in homogeneous hydrogenation and hydroformylation processes, with well-characterized structural and electronic properties that have made it a cornerstone of rhodium organometallic chemistry.

References

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