Iron(III) and copper(II) complexes of trans -bis(ferrocenyl)porphyrin: Effect of metal ions on long-range electronic communication

A series of complex with a general formula of M(Fc2Ph2P) [Fc2Ph2P = 5,10-bisferrocenyl-15,20-bisphenylporphyrin (2 −); M = Fe(III)Cl Fe(III)(ClO4) and Cu(II)] have been synthesized and characterized. The single crystal X-ray structure of Cu II(Fc2Ph2P) has been reported in which two ferrocene moieties are in anti form with respect to each other. The ferrocenyl groups of Cu II(Fc2Ph2P) are more easily oxidized via a single two-electron quasi-reversible process compared to the free base ligand in which two 1e-oxidative response separated by 0.23 V are observed. Electrochemical study of FeIII(Fc2Ph2P)Cl revealed ferrocene-based two-electron quasi-reversible oxidation at 0.72 V indicating no observable coupling of the ferrocene moieties. The higher oxidation state of Fe(III) reduces the electron releasing tendency of the porphyrin ring and thus make the ferrocene oxidation difficult. The porphyrin, however, lack substituents at the β-pyrrolic positions, and the ferrocenyl moieties are therefore free to rotate. The observed electrochemical analyses thus demonstrate that the oxidation of the ferrocene subunit is strongly affected by porphyrin ring as well as the central metal through extended π-conjugation.