Synthesis, structures and electrochemical characterization of ferrocene-substituted porphyrin and porphodimethene

Condensation of ferrocenecarboxaldehyde and dipyrrolylmethane gave 5,15-diferrocenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethyl-5,15-dihydroporphyrin (H21), and 5,15-diferrocenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin (H22) in 31 and 49% yield, respectively. Structures of H21·CHCl3 and H22·0.5C6H5Me have been determined by X-ray diffraction. Compound H21 has syn-axial configuration and H22 has syn configuration of two ferrocenyl groups. Compound H21 was only proven to be an intermediate species of H22 in the photooxidation pathway. The large steric bulkiness of the ferrocenyl group permitted the isolation of compounds H21 and H22 directly from the oxidation reaction of 5,15-diferrocenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrinogen. Porphodimethene H21 has exceptional stability toward air and light in the absence of acid. Electrochemically, ferrocene subunits of H21 are oxidized with a reversible two-electron transfer process (0.33 V), while those of H22 are oxidized with two reversible one-electron transfer processes (0.06 and 0.27 V).