Protonation and protolysis of [Fe4(CO)12(CCH3)]−

The reaction of [Fe₄(CO)₁₂(CCH₃)]^? with HSO₃CF₃ in CH₂Cl₂ solution yields the compound HFe₄(CO)₁₂(CCH₃), which was characterized chemically, spectroscopically and by single crystal X-ray diffraction. This compound retains the approximately tetrahedral 4-iron framework characteristic of the parent anion and protonation appears to have occurred on an FeFe bond. In neat HSO₃CF₃, infrared and NMR spectroscopic evidence indicates that another proton adds to the metal framework producing [H₂Fe₄(CO)₁₂(CCH₃]⁺. On long standing, this solution evolves CO, and H₂, and small amounts of CH₄ and C₂H₆. On the time scale of the experiments described here the latter two gases are obtained in an approximately $\text{1}\text{3}$ ratio. Deuterated acid leads to mixtures of the various isotopomers of CH₄ but the ethane is CD₃CH₃. Possible mechanisms for hydrocarbon production are discussed.