Iron(II) chloride

Technical Specifications

Product Description & Scientific Applications

Iron(II) chloride (ferrous chloride), the anhydrous salt FeCl₂, is an inexpensive, high-spin iron(II) reagent and a general precursor to iron complexes and catalysts. Iron is redox-versatile: the iron(II) and iron(III) states interconvert readily, and the labile iron(II) coordination sphere binds nitrogen, phosphorus and carbon donors.

Solid-state structure and magnetism. Anhydrous iron(II) chloride adopts the rhombohedral CdCl₂ structure: edge-sharing FeCl₆ octahedra form triangular nets, stacked as layers separated by van der Waals gaps between the chloride anions. It is an antiferromagnet with stronger ferromagnetic coupling within each layer, so an applied magnetic field drives a metamagnetic transition near 11 kOe, and the ordered moment is 4.5 μB. Under pressure the lattice converts to the CdI₂ structure near 0.6 GPa; further compression quenches the orbital moment and drives an insulator–metal transition. The layers can be exfoliated toward monolayers, of interest for two-dimensional magnetism and van der Waals heterostructures.

Iron-catalysed carbon–carbon bond formation. With a supporting bisphosphine such as SciOPP, iron(II) chloride is a precatalyst for Kumada-type cross-coupling of alkyl halides with Grignard reagents. Iron salts are inexpensive, low-toxicity alternatives to precious-metal catalysts for carbon–carbon bond formation. The active species depends on the nucleophile: methyl Grignards generate iron-ate complexes, and a "super-ate" forms on reaction of iron(II) chloride with excess methyllithium; Grignard reagents bearing two or more carbons instead give highly reduced iron clusters of formal composition [Fe(MgX)₂]ₙ in situ.

Iron-catalysed C–H amination. As a commercially available iron(II) salt, iron(II) chloride is a first-choice amination catalyst; paired with terpyridine it aminates the formyl C–H bond of aldehydes. Iron nitrene intermediates generated from organic azides build nitrogen heterocycles.

Fenton oxidation. Iron(II) reduces hydrogen peroxide to hydroxyl radicals, the Fenton reaction, and is oxidised to iron(III). Hydroxyl radical production from inorganic iron(II) is well established at acidic pH; at circumneutral pH the iron must be complexed. The reaction is exploited in water treatment.

Precursor to organoiron compounds. Reaction of iron(II) chloride with sodium cyclopentadienide in tetrahydrofuran gives the metallocene ferrocene in 67–73% yield, and up to 90% under optimised conditions, the classic Wilkinson preparation. Ferric chloride may substitute directly, at lower yield, because sodium cyclopentadienide reduces iron(III) to iron(II). With phosphine, terpyridine or cyclopentadienyl ligands, iron(II) chloride is the general entry to defined iron(II) precatalysts and organoiron complexes.

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