The electrochemical behavior of metal carbonyls in a mixture of a room temperature molten salt and benzene

The electrochemical oxidation of six metal carbonyls was studied in a mixture of the high Lewis acid, room temperature molten salt, composed of aluminum chloride and ethylpyridinium bromide (2:1 molar ratio) and benzene (50% v/v). Chromiuim hexacarbonyl was found to be reversibly oxidized to the seventeen electron cationo Cr(CO)⁺₆, isoelectronic with vanadium hexacarbonyl. Some stability was also found for the corresponding 17 electron cation of iron pentacarbonyl. The other carbonyl compounds studied Mo(CO)₆, W(CO)₆, Re₂(CO)₁₀, and Mn₂(CO)₁₀ exhibit electrochemical behavior characteristic of chemical and electrochemical reactions following the electron transfer reaction. Based on the large dependence of the oxidation potentials on the nature of the central metal atom in this solvent, it is proposed that the metal carbonyls interact with electron deficient species in the melt, decreasing the σ donor ability of the ligand, but increasing its π acceptor capabilities.