IR Spectrum of Tris(acetylacetonato)iron(III)

Tris(acetylacetonato) iron(III), often abbreviated Fe(acac)₃, is a

ferric In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to sp ...

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

featuring

acetylacetonate Acetylacetone is an organic compound with the chemical formula . It is a colorless liquid, classified as a 1,3-diketone. It exists in equilibrium with a tautomer . These tautomers interconvert so rapidly under most conditions that they are tr ...

(acac)

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

s, making it one of a family of

metal acetylacetonates Metal acetylacetonates are coordination complexes derived from the acetylacetonate anion () and metal ions, usually transition metals. The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal t ...

. It is a red air-stable solid that dissolves in nonpolar organic solvents.

Preparation

Fe(acac)₃ is prepared by treating freshly precipitated Fe(OH)₃ with acetylacetone. :Fe(OH)₃ + 3 HC₅H₇O₂ → Fe(C₅H₇O₂)₃ + 3 H₂O

Structure and properties

Fe(acac)₃ 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. As the metal orbitals are all evenly occupied the complex is not subject to Jahn-Teller distortions and thus adopts a D₃

molecular symmetry Molecular symmetry in chemistry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explain m ...

. In contrast, the related metal acetylacetonate Mn(acac)₃ adopts a more distorted octahedral structure. The 5 unpaired ''d''-electrons also result in the complex being

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, d ...

, with a

magnetic moment In electromagnetism, the magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. Examples of objects that have magnetic moments include loops of electric current (such as electromagnets ...

of 5.90 μ_B. Fe(acac)₃ possesses

helical chirality Helical may refer to: * Helix, the mathematical concept for the shape * Helical engine, a proposed spacecraft propulsion drive * Helical spring, a coilspring * Helical plc, a British property company, once a maker of steel bar stock * Helicoil A t ...

. The Δ- and Λ-

enantiomer In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...

s slowly inter-convert via Bailar and

Ray–Dutt twist The Ray–Dutt twist is a mechanism proposed for the racemization of octahedral complexes containing three bidentate chelate rings. Such complexes typically adopt an octahedral molecular geometry in their ground states, in which case they posses ...

s. The rate of interconversion is sufficiently slow to allow its enantiomers to be partially resolved.

Reactions

Fe(acac)₃ 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, Fe(acac)₃ was shown to promote cross-coupling a

diene In organic chemistry a diene ( ) (diolefin ( ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nomenclature. ...

to an olefin. Fe(acac)₃ catalyzes the dimerization of

isoprene Isoprene, or 2-methyl-1,3-butadiene, is a common volatile organic compound with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. Isoprene is an unsaturated hydrocarbon. It is produced by many plants and animals ...

to a mixture of 1,5-dimethyl-1,5-cyclooctadiene and 2,5-dimethyl-1,5-cyclooctadiene. : Fe(acac)₃ also catalyzes the ring-opening polymerization of 1,3-benzoxazine. Beyond the area of polymerization, Fe(acac)₃ has been found to catalyze the reaction of N-sulfonyl oxaziridines with olefins to form 1,3-oxazolidine products. :

References

{{Acetylacetonate complexes Iron(III) compounds Acetylacetonate complexes Iron complexes