Tris(acetylacetonato)iron(III)

Trisiron, often abbreviated Fe₃, is a ferric coordination complex featuring acetylacetonate ligands, making it one of a family of metal acetylacetonates. It is a red air-stable solid that dissolves in nonpolar organic solvents.

Preparation

Fe₃ is prepared by treating freshly precipitated Fe₃ with acetylacetone.

Fe₃ is an octahedral complex with six equivalent Fe-O bonds with bond distances of about 2.00 Å. The regular geometry is consistent with a high-spin Fe³⁺ core with sp3d2 hybridization. As the metal orbitals are all evenly occupied the complex is not subject to Jahn-Teller distortions and thus adopts a D₃ molecular symmetry. In contrast, the related metal acetylacetonate Mn₃ adopts a more distorted octahedral structure. The 5 unpaired d-electrons also result in the complex being paramagnetic, with a magnetic moment of 5.90 μ_B.
Fe₃ possesses helical chirality. The Δ- and Λ-enantiomers slowly inter-convert via Bailar and Ray–Dutt twists. The rate of interconversion is sufficiently slow to allow its enantiomers to be partially resolved.

Fe₃ has been examined as a precatalyst and reagent in organic chemistry, although the active iron-containing species is usually unidentified in these processes. In one instance, Fe₃ was shown to promote cross-coupling a diene to an olefin. Fe₃ catalyzes the dimerization of isoprene to a mixture of 1,5-dimethyl-1,5-cyclooctadiene and 2,5-dimethyl-1,5-cyclooctadiene.
Fe₃ also catalyzes the ring-opening polymerization of 1,3-benzoxazine. Beyond the area of polymerization, Fe₃ has been found to catalyze the reaction of N-sulfonyl oxaziridines with olefins to form 1,3-oxazolidine products.