The Discovery and Future Prospects of Artificial Porphyrins: Molecular Batteries Functioning with the Reversible Formation and Cleavage of Cyclopropane Units

The absence of the meso-hydrogen atoms in meso-octaalkylporphyrinogens enable the generation of novel forms of the oxidized porphyrinogen, 'artificial porphyrins'. A stepwise four-electron oxidation of meso-octaalkylporphyrinogen transitionmetal complexes led to an unusual aromatization of the porphyrinogen with the loss of four hydrogen atoms and the introduction of one, followed by two cyclopropane units into the porphyrinogen frame. Such oxidized forms of porphyrinogen function as two-electron shuttles via the formation and cleavage of the cyclopropane unit. Furthermore, the appropriate site opening of the cyclopropane may lead to important modifications of the porphyrinogen frame.