Rhodium(II) acetate is the chemical compound with the formula Rh2(AcO)4, where AcO- is the acetate group (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.
Rhodium(II) acetate is usually prepared by the heating hydrated rhodium(III) chloride
in acetic acid
COOH): Rhodium(II) acetate dimer undergoes ligand exchange, the replacement of the acetate group by other carboxylates
and related groups.
- Rh2(OAc)4 + 4 HO2Y → Rh2(O2Y)4 + 4 HOAc
Structure and Properties
The structure of rhodium(II) acetate freatures 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.. Copper(II) acetate and chromium(II) acetate adopt similar structures.
The application of dirhodium tetraacetate to organic synthesis was pioneered by Teyssie and co-workers. A extensive library of successful transformations rapidly evolved, ranging from Rh(II)-catalyzed OH and NH insertions to cyclopropanation
systems. Nowadays, it is used mainly as a catalyst
. It can help distinguish between ribonucleosides
by binding selectively to ribonucleosides at their 2' and 3' OH groups. 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
- 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.