Rhodium(II) acetate

Rhodium(II) acetate is the coordination compound with the formula Rh2(AcO)4, where AcO− is the acetate ion (CH
3CO−
2). This dark green powder is slightly soluble in polar solvents, including water. It is used as a catalyst for cyclopropanation of alkenes. It is a widely studied example of a transition metal carboxylate complex.

Rhodium(II) acetate
Names
IUPAC name
Rhodium(II) acetate
Other names
Dirhodium tetraacetate,
Tetrakis(acetato)dirhodium(II),
Rhodium diacetate dimer,
Tetrakis(μ-acetato)dirhodium
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.036.425
EC Number
  • 240-084-8
RTECS number
  • VI9361000
UNII
Properties
C8H12O8Rh2
Molar mass 441.99 g/mol
Appearance Emerald green powder
Density 1.126 g/cm3
Melting point >100 °C
Boiling point decomposes
soluble
Solubility in other solvents polar organic solvents
Structure
monoclinic
octahedral
0 D
Hazards
Safety data sheet Coleparmer MSDS
R-phrases (outdated) 36/38
S-phrases (outdated) 15, 26, 28A, 37/39
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
3
0
Flash point low flammability
Related compounds
Related compounds
 Copper(II) acetate
Chromium(II) acetate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Preparation

Rhodium(II) acetate is usually prepared by the heating of 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 HO2CR → Rh2(O2CR)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, water, and a Rh–Rh bond of length 2.39 Å. The water adduct is exchangeable, and a variety of other Lewis bases bind to the axial positions.[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] An extensive range of reactions including insertion into bonds and the cyclopropanation of alkenes[5] and aromatic systems.[6] It selectively binds ribonucleosides (vs. 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

Dirhodium tetraacetate is also used as catalyst for insertion into C–H and X–H bonds (X = N, S, O).

  1. Cyclopropanation

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

    Rhodium acetate catalyzes both two-component cycloaddition as well as three-component 1,3-dipolar cycloadditions.
  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, S, O) insertion via the formation of an ylide intermediate.

References
  1. Rempel, G. A.; Legzdins, P.; Smith, H.; Wilkinson, G. (1972). Tetrakis(acetato)dirhodium(II) and Similar Carboxylato Compounds. Inorg. Synth. Inorganic Syntheses. 13. pp. 90–91. doi:10.1002/9780470132449.ch16. ISBN 9780470132449.
  2. Doyle, M. P. (2000). "Asymmetric Addition and Insertion Reactions of Catalytically-Generated Metal Carbenes". In Ojima, Iwao (ed.). Catalytic Asymmetric Synthesis (2nd ed.). New York: Wiley. ISBN 978-0-471-29805-2.
  3. 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 Crystallogr B. 27 (8): 1664. doi:10.1107/S0567740871004527.
  4. 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 Lett. 14 (24): 2233. doi:10.1016/S0040-4039(01)87603-6.
  5. 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 Lett. 17 (16): 1317. doi:10.1016/S0040-4039(00)78050-6.
  6. Anciaux, A. J.; Demonceau, A.; Hubert, A. J.; Noels, A. F.; Petiniot, N.; Teyssié, 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". J. Chem. Soc., Chem. Commun. (16): 765–766. doi:10.1039/C39800000765.
  7. 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): 237–40. doi:10.1038/newbio239237a0. PMID 4538853.
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