Paramagnetic Organometallic Molecules. 4. Electrochemical Investigation of the Iron Group Carbonyls and Their Phosphine-Substituted Derivatives

The redox behavior of the iron carbonyl species Fe₃(CO)_12-nL_n (n = 0-3) and Fe(CO)_5-nL_n (n = 0-2) (L = PPh₃, P(OMe)₃, P(OPh)₃) has been studied in acetone and dichloromethane using the techniques of dc polarography at mercury electrodes and dc cyclic voltammetry at platinum electrodes. A chemically reversible one-electron reduction step was observed for the triiron species within the temperature range 203-293 K. The E^T 1/2 values for the reduction became increasingly negative with increasing phosphine substitution which correlates well with the charge density on the iron atoms in the parent complexes. The carbonyls Ru₃(CO)₁₂ and Os₃(CO)₁₂ undergo an irreversible reduction within the temperature range of this investigation leading to rapid decomposition of the carbonyl moieties. Further reduction to the dianions Fe₃(CO)_12-nL_n^2- occurred for the iron species and caused irreversible disintegration of the cluster unit. A one-electron oxidation step was observed for Fe₃(CO)₉[P(OMe)₃]₃. The mononuclear iron derivatives gave well-defined one-electron oxidation and two-electron reduction waves at mercury electrodes. The oxidation step was found to be chemically reversible. No evidence was found for the formation of the radical anion Fe(CO)₅^- under the experimental conditions employed.