Ammonium and Phosphonium Salts Containing Monoanionic Iron(II) Half-Sandwich Complexes [Fe(η5-Cp*)X2]− (X = Cl − I)

Abstract

Half-sandwich iron(II) dihalido complexes of the type [Fe(η5-Cp’)X2]− (Cp’ = C5H5 or substituted cyclopentadienyl) which are thermally stable at room temperature are extremely scarce, being limited to congeners containing the bulky C5H2-1,2,4-tBu3 ligand. We extended this to homologues [Fe(η5-Cp*)X2]− (X = Cl, Br, I) containing the particularly popular C5Me5 (Cp*) ligand. Corresponding ionic compounds ER4[Fe(η5-Cp*)X2] are easily accessible from FeX2, MCp* (M = Li, K) and a suitable halide source R4EX (E = N, P) in THF. Despite their high sensitivity towards air and moisture, the new compounds NnPr4[Fe(η5-Cp*)X2] (X = Cl, Br), NnPr4[Fe(η5-Cp*)BrCl], and PPh4[Fe(η5-Cp*)X2] (X = Cl, Br, I) were structurally characterised using single-crystal X-ray diffraction. NnPr4[Fe(η5-Cp*)Cl2] reacts readily with CO to afford [Fe(η5-Cp*)Cl(CO)2], indicating the synthetic potential of ER4[Fe(η5-Cp*)X2] in FeCp* half-sandwich chemistry.