acetylacetonate

Acetylacetonate, commonly written acac-, is the anion produced by deprotonation of acetylacetone (2,4-pentanedione). It is a bidentate ligand that coordinates to metal centers through the two enolate oxygen atoms, typically forming five- or six-membered chelate rings and stabilizing a wide range of metal complexes.

In solution, 2,4-pentanedione exists predominantly in the enol form. Deprotonation to acac- yields a resonance-stabilized enolate that distributes negative charge over the two oxygens, which strengthens chelation to metal centers.

Acetylacetonate is prepared by treating acetylacetone with a base such as sodium hydroxide or sodium hydride to form the sodium salt, Na(acac). By metathesis, other metal salts can be converted to various metal acetylacetonates, M(acac)x, including common transition-metal variants.

In coordination chemistry, acac- is a widely used supporting ligand for many metals. Well-known examples include Fe(acac)3, Ni(acac)2, and Cu(acac)2, as well as lanthanide acetylacetonates Ln(acac)3. These complexes find use as catalysts, precursors for oxide materials, and stable intermediates in organometallic syntheses. The chelating nature of acac- often imparts thermal stability and well-defined reactivity to the metal center.

Overall, acetylacetonate serves as a versatile, well-characterized beta-diketonate ligand that enables a broad range of inorganic and organometallic applications through simple preparation and reliable binding to metals.