Solvent-Dependent Reactivity of Fe(CO)₅ under Superacidic and Oxidative Conditions

Herein, we report the solvent-dependent reactivity of Fe(CO)₅ toward AsF₅ in either anhydrous HF or liquid SO₂. The reaction of Fe(CO)₅ with the superacid HF/AsF₅ leads to the protonation of the iron center and allows for the first-time structural characterization of [FeH(CO)₅]⁺ in the solid state, representing one of the most acidic transition metal hydride complexes to ever be isolated and structurally characterized. In the aprotic but oxidation-stable solvent SO₂, Fe(CO)₅ is oxidized and dimerized to [Fe₂(CO)₁₀]²⁺, which is isoelectronic with well-known Mn₂(CO)₁₀. [Fe₂(CO)₁₀]²⁺ is the first structurally characterized example of a homoleptic dinuclear transition metal carbonyl cation. Together with Fe(CO)₅ and [Fe(CO)₅]^+•, it is a rare example of an iron-centered triad from which the neutral, the radical cationic, and the dimerized dicationic species have been structurally and spectroscopically characterized. All characterizations are well supported by quantum chemical calculations. We also make the argument that the dimerization of [Fe(CO)₅]^+• is largely dependent on the employed solvent.