Porphyrins and Tetraazaporphyrins as Ligands in Metal Complexes

Porphyrins constitute an important class of electron-transfer ligands. In nature, the biological electron-transfer conversion of light into chemical energy, known as photosynthesis , which takes place either in green plants or photosynthetic bacteria, is primarily driven by photosynthetic 

The electrochemical behaviour of a high number of metalloporphyrins has been reviewed some years ago.90 We would like here to point out a few electrochemical-to-structural aspects of such derivatives. 

In confirmation that these redox changes are centred on the porphyrin ligand, the free porphyrin (i.e. [H2TPP]) exhibits the same electron transfer processes (2sjy+ = +0.90 N E+j2+ = +1.23 V Eqj = 

The subsequent exhaustive electrolysis at the potentials of the second anodic process to generate the [Zn(TPP)]2+ dication gives rise to important results. In fact, the electrogenerated dication is stable in the absence of nucleophilic agents, but, in the presence of nucleophilic agents (such as methanol), it transforms into zinc(II) 5 -methoxyl-5,l0,15,20-tetraphenyl isoporphyrin, [Zn(TPiPOCH3)]+, 98 

A water molecule trapped during the crystallization is axially coordinated (05) and induces the zinc ion to move out of the plane of the four nitrogen atoms by 0.31 A. It can be seen that the saturation of the carbon responsible for the break of the double bond conjugation is localized on the C5 carbon atom. 

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