Rhodium(II) acetate


Rhodium acetate is the chemical compound with the formula Rh24, where AcO− is the acetate ion. This dark green powder is slightly soluble in polar solvents, including water. It is used as a catalyst for cyclopropanation of alkenes.

Preparation

Rhodium acetate is usually prepared by the heating of hydrated rhodium chloride in acetic acid : Rhodium acetate dimer undergoes ligand exchange, the replacement of the acetate group by other carboxylates and related groups.

Structure and properties

The structure of rhodium 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. Copper acetate and chromium acetate adopt similar structures.

Chemical properties

The application of dirhodium tetraacetate to organic synthesis was pioneered by Teyssie and co-workers. An extensive range of reactions including insertion into bonds and the cyclopropanation of alkenes and aromatic systems. It selectively binds ribonucleosides by binding selectively to ribonucleosides at their 2′ and 3′ –OH groups. Rhodium acetate dimer, compared to copper acetate, is more reactive and useful in differentiating ribonucleosides and deoxynucleosides because it is soluble in aqueous solution like water whereas copper 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.
  1. Cyclopropanation
  2. :
through the decomposition of diazocarbonyl compounds, the intra- and intermolecular cyclopropanation reactions occurs.
  1. Aromatic cycloaddition
  2. :
Rhodium acetate catalyzes both two-component cycloaddition as well as three-component 1,3-dipolar cycloadditions.
  1. C–H insertion
  2. :
Rh-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.
  1. Oxidation of alcohols
  2. :
Allylic and benzylic alcohols were oxidized to the corresponding carbonyl compounds using tert-butyl hydroperoxide in stoichiometric amounts and Rh24 as catalyst in dichloromethane at ambient temperature.
  1. X–H insertion
  2. :
Rh carbenoid reacts with amines, alcohols or thiols to yield the product of a formal intra- or intermolecular X–H bond insertion via the formation of an ylide intermediate.