Electrosynthesis, electrochemistry, and crystal structure of the tetracationic Zn-meso-tetrapyridiniumyl-beta-octaethylporphyrin

Exhaustive electro-oxidation of ZnOEP in the presence of pyridine and Et4NP F6 affords in high yield the new tetracationic porphyrin in which the four meso protons of ZnOEP are replaced by four pyridinium groups linked via the ir nitrogens: [Zn-5,10,15,20-tetrakis(N-pyridiniumyl)-2,3,7,8,12,13,17,18-o ctaethylporphytin](4+) (PF6-)(4), I. The compound has been characterized by elemental analysis, H-1 NMR, and crystallography. The latter confirms the preparative electrosynthetic methodology and molecular structure of 1, and shows the porphyrin skeleton to adopt a severely nonplanar saddle conformat ion which minimizes steric crowding between the 12 peripheral substituents. As a consequence of the nonplanarity (and the high charge) of the complex, I exhibits significant redshifts of the visible and Soret bands as well as a considerable broadening and loss of intensity of the latter. I first und ergoes four one-electron reduction steps at the four pyridinium sites befor e the normal one-electron reduction of the porphyrin pi -system. Copyright (C) 2001 John Wiley & Sons, Ltd.