Rhodium diacetate dimer,
|Molar mass||441.99 g/mol|
|Appearance||Emerald green powder|
|Melting point||>100 °C|
|Solubility in other solvents||polar organic solvents|
|Dipole moment||0 D|
|S-phrases||15, 26, 28A, 37/39|
|Flash point||low flammability|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
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.
Rhodium(II) acetate is usually prepared by the heating of hydrated rhodium(III) chloride in acetic acid (CH3COOH): 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 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). 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. An extensive library of successful transformations rapidly evolved, ranging from Rh(II)-catalyzed OH and NH insertions to cyclopropanation of olefins and aromatic systems. 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. 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.
- Rempel, G. A.; Legzdins, P.; Smith, H.; Wilkinson, G.; Ucko, D. A. (1972). "Tetrakis (Acetato) Dirhodium (II) and Similar Carboxylato Compounds". Inorganic Syntheses. Inorganic Syntheses 13. p. 90. doi:10.1002/9780470132449.ch16. ISBN 9780470132449.
- Doyle, M.P. (2000). "Asymmetric Addition and Insertion Reactions of Catalytically-Generated Metal Carbenes". In Ojima, Iwao. Catalytic Asymmetric Synthesis (2nd ed.). New York: Wiley. ISBN 0-471-29805-0.
- Cotton, F. A.; Deboer, B. G.; Laprade, M. D.; Pipal, J. R.; Ucko, D. A. (1971). "The crystal and molecular structures of dichromium tetraacetate dihydrate and dirhodium tetraacetate dihydrate". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry 27 (8): 1664. doi:10.1107/S0567740871004527.
- Paulissen, R.; Reimlinger, H.; Hayez, E.; Hubert, A. J.; Teyssié, P. (1973). "Transition metal catalysed reactions of diazocompounds - II insertion in the hydroxylic bond". Tetrahedron Letters 14 (24): 2233. doi:10.1016/S0040-4039(01)87603-6.
- Hubert, A. J.; Feron, A.; Warin, R.; Teyssie, P. (1976). "Synthesis of iminoaziridines from carbodiimides and diazoesters : A new example of transition metal salt catalysed reactions of carbenes". Tetrahedron Letters 17 (16): 1317. doi:10.1016/S0040-4039(00)78050-6.
- Anciaux, A. J.; Demonceau, A.; Hubert, A. J.; Noels, A. F.; Petiniot, N.; Teyssi�, P. (1980). "Catalytic control of reactions of dipoles and carbenes; an easy and efficient synthesis of cycloheptatrienes from aromatic compounds by an extension of Buchner's reaction". Journal of the Chemical Society, Chemical Communications (16): 765. doi:10.1039/C39800000765.
- Berger, N. A.; Tarien, E.; Eichhorn, G. L. (1972). "Stereoselective Differentiation between Ribonucleosides and Deoxynucleosides by Reaction with the Copper(II) Acetate Dimer". Nature New Biology 239 (95): 237. doi:10.1038/newbio239237a0. PMID 4538853.