Formation and Isolation of a Four-Electron-Reduced Porphyrin Derivative by Reduction of a Stable 20π Isophlorin.

The two-electron reduction of a diprotonated dodecaphenylporphyrin derivative by Na2 S2 O4 gave a corresponding isophlorin (Iph) selectively. Formation of Iph was confirmed by spectroscopic measurements and the isolation of tetramethylated Iph. Further reduction of Iph proceeded to form an unprecedented four-electron-reduced porphyrin (IphH2 ), which was fully characterized by spectroscopic and X-ray crystallographic analysis. IphH2 , with a unique conformation, could be oxidized to reproduce the starting porphyrin, resulting in a proton-coupled four-electron reversible redox system.