Rh2OAc4

Rh2(OAc)4, commonly written Rh2(OAc)4, is a dirhodium tetraacetate complex consisting of two rhodium(II) centers linked by a Rh–Rh bond and bridged by four acetate ligands in a paddlewheel arrangement. It is widely used as a catalyst precursor in organic synthesis, particularly for carbene transfer reactions.

The core structure features a dinuclear Rh(II) unit with four bridging acetate ligands. The Rh–Rh bond and the four μ2-acetate bridges create a robust, relatively air-stable complex that can act as a reservoir for catalytic rhodium carbenoids. The acetates can be displaced by substrates during catalytic cycles, allowing conversion to active rhodium species in situ.

Rh2(OAc)4 is typically prepared by treating rhodium precursors, such as RhCl3·3H2O, with acetate sources in acetic acid under heat, which promotes condensation to the tetracarboxylate complex. The resulting material is commonly isolated as a crystalline solid and is soluble in a range of organic solvents while being largely insoluble in water.

In use, Rh2(OAc)4 serves as a versatile precatalyst for carbene transfer reactions, including cyclopropanation of alkenes, intramolecular C–H insertion, and related transformations that proceed via rhodium carbenoid intermediates. Its success stems from the ability to generate reactive carbenoid species under mild conditions and to be modified with various carboxylate ligands to tune selectivity, including well-known chiral derivatives.

Safety and handling follow standard laboratory practices for organometallic rhodium compounds. Rh2(OAc)4 is generally handled with gloves and in a fume hood, with attention to avoiding inhalation or ingestion and proper disposal of metal-containing waste.