Effect of ligand structure, solvent, and temperature on the electrochemical behavior of polyarene–iron complexes

The electrochemical investigation of a number of polyarene–iron complexes ([3]2+–[9]5+) containing etheric, sulphide, and sulphone bridges indicated that there were various degrees of interaction based on the nature of the bridging heteroatoms. While the electrochemical investigation of all etheric complexes showed that the metallic moieties behaved as isolated redox centers, it was found that there was electronic communication (ca. 70–80 mV) for the isomeric sulphide complexes [4]2+ and [6]2+. The rate constant of the following chemical reaction (kf) was calculated for some of these complexes and it was found that these rates were affected by the nature of the solvent, the bridging ligand, and the temperature. At various temperatures, kf indicated a higher degree of stability for complexes containing sulphide bridges than for those containing etheric bridges, especially at room temperature. The effect of a strong coordinating solvent, such as acetonitrile, on the kf of complex [3]2+ indicated that the substitution of the arene ligand with acetonitrile molecules proceeded as a dissociative mechanism. Controlled potential coulometry was also used to verify the transfer of two electrons in the first reduction process of the di-iron complexes. Key words: cyclopentadienyliron, cyclic voltammetry, arene complexes, isolated and interacting redox centers.