Dihalide complexes of iron(II) have found use as a starting platform to more eleborate Fe(II) complexes, and as a catalyst in cross-coupling reactions.[1] A source of soluble iron(II) dihalide, FeBr2(dme) can be easily synthesized from its anhydrous FeBr2 precursor by stirring in dimethoxyethane.[2][3] It can also be purchased from chemical vendors (Strem), although it gets quite expensive if bough in multigram quantities.
Procedure:[3] In the glovebox, a 150mL one-neck round-bottom flask was charged with anhydrous iron(II) bromide (7.05g, 32.7mmol) and approximately 80mL of anhydrous 1,2-dimethoxyethane. The flask was sealed, transferred onto a swivel-frit apparatus attached to a dual-manifold vacuum line (or Schlenk line), and stirred overnight at room temperature under argon, and then at 75degC for 10h (to ensure complete FeBr2 reaction). After cooling to room temperature, the mixture was subsequently filtered, washed with anhydrous pentane, and dried under vacuum to yield the product complex as a pale tan powder (reported yield: 8.66g, 87%). The product was then transferred back into the glovebox for storage.
Notes:
- FeBr2(dme) is a paramagnetic, moisture sensitive solid and should be stored under argon/nitrogen to prevent decomposition. Soluble in THF.
- Anhydrous DME can be dried with molecular sieves for 48h prior to synthesis. Anhydrous cobalt(II) bromide can be purchased from chemical vendors (Millipore-Sigma, TCI, VWR).
- A considerable number of publications use FeBr2(dme) as a starting material towards the synthesis of more elaborate complexes. This is likely because of its far higher solubility compared to FeBr2, which leads to smoother reactions with higher yields.
[1] Weber, K.; Schnöckelborg, E.-M.; Wolf, R. ChemCatChem. 2011, 3, 1572-1577.
[2] Fowles, G. W. A.; Rice, D. A.; Walton, R. A. Donor properties of simple ethers. II. Complexes of manganese(II), iron(II), cobalt(II), and nickel(II) halides with tetrahydrofuran and 1,2-dimethoxyethane. J. Inorg. Nucl. Chem. 1969, 31, 3119-3131.
[3] Davis, L. M. Syntheses, Properties, and Reactions of Transition Metal Complexes of Di(tert-butyl)amide and 2,2,6,6-tetramethylpiperidide. Ph.D. Dissertation, University of Illinois: Urbana-Champaign, Urbana, IL, 2014.