Rhodium(II) acetate

Rhodium (II) Acetate
IUPAC name Rhodium (II) acetate
Other names Dirhodium tetraacetate, Tetrakis(acetato)dirhodium(II), Rhodium diacetate dimer, Tetrakis-(mu-acetato)dirhodium
Identifiers
CAS number	15956-28-2 Y
PubChem	152122
ChemSpider	20370 Y
EC number	240-084-8
RTECS number	VI9361000
InChI InChI=1S/2C2H4O2.Rh/c2*1-2(3)4;/h2*1H3,(H,3,4);/q;;+2/p-2 Y Key: ITDJKCJYYAQMRO-UHFFFAOYSA-L Y InChI=1S/4C2H4O2.2Rh/c4*1-2(3)4;;/h4*1H3,(H,3,4);;/q;;;;2*+2/p-4 Key: : SYBXSZMNKDOUCA-UHFFFAOYSA-J
Properties
Molecular formula	C8H12O8Rh2
Molar mass	441.99 g/mol
Appearance	Emerald green powder
Density	1.126 g/cm3
Melting point	>100 °C
Boiling point	decomposes
Solubility in water	soluble
Solubility in other solvents	polar organic solvents
Structure
Crystal structure	monoclinic
Coordination geometry	octahedral
Dipole moment	0 D
Hazards
MSDS	Coleparmer MSDS
R-phrases	36/38
S-phrases	15, 26, 28A, 37/39
NFPA 704	0 3 0
Flash point	low flammability
Related compounds
Related compounds	Copper(II) acetate Chromium(II) acetate
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Rhodium(II) acetate is the chemical compound with the formula Rh₂(AcO)₄, where AcO⁻ is the acetate ion (CH₃CO₂⁻). This emerald green powder is a catalyst for cyclopropanation of alkenes. It is also used as catalyst for insertion into C-H and X-H bonds (X = N/S/O) and for ylide formation for organic syntheses.

Preparation

Rhodium(II) acetate is usually prepared by the heating hydrated rhodium(III) chloride in acetic acid (CH₃COOH):^[1] Rhodium(II) acetate dimer undergoes ligand exchange, the replacement of the acetate group by other carboxylates and related groups.^[2]

Rh₂(OAc)₄ + 4 HO₂Y → Rh₂(O₂Y)₄ + 4 HOAc

Structure and Properties

The dinuclear structure of hydrated rhodium(II) acetate

The structure of rhodium(II) acetate features a pair of rhodium atoms, each with octahedral molecular geometry, defined by four acetate oxygen atoms, a water ligand, and a Rh-Rh bond (2.39 Å.^[3]. Copper(II) acetate and chromium(II) acetate adopt similar structures.

Chemical Properties

The application of dirhodium tetraacetate to organic synthesis was pioneered by Teyssie and co-workers.^[4] A extensive library of successful transformations rapidly evolved, ranging from Rh(II)-catalyzed OH and NH insertions to cyclopropanation of olefins^[5] and aromatic systems.^[6] Nowadays, it is used mainly as a catalyst. It can help distinguish between ribonucleosides and deoxynucleosides by binding selectively to ribonucleosides at their 2' and 3' OH groups^[7]. Rhodium(II) acetate dimer, compared to copper(II) acetate, is more reactive and useful in differentiating ribonucleosides and deoxynucleosides because it is soluble in aqueous solution like water whereas copper(II) acetate only dissolves in non-aqueous solution.

Selected catalytic reactions

1. Cyclopropanation

through the decomposition of diazocarbonyl compounds, the intra- and intermolecular cyclopropanation reactions occurs.

2. Aromatic cycloaddition

Rhodium acetate is a very efficient catalyst for two-component cycloaddition as well as three-component 1,3-dipolar cycloaddition reactions.

3. C-H insertion

Rh(II)-catalyzed regioselective intramolecular and regiospecific intermolecular C-H insertion into aliphatic and aromatic C-H bonds is a useful method for the synthesis of a diverse range of organic compounds.

4. Oxidation of alcohols

Allylic and benzylic alcohols were oxidized to the corresponding carbonyl compounds using tert-butyl hydroperoxide in stoichiometric amounts and Rh₂(OAc)₄ as catalyst in dichloromethane at ambient temperature.

5. X-H insertion (X = N/S/O)

Rh(II) carbenoid reacts with amines, alcohols or thiols to yield the product of a formal intra- or intermolecular X-H bond (X = N/O/S) insertion via the formation of an ylide intermediate.

References