Effect of peripheral substitution and extended conjugation on the redox potentials of nickel porphycenes

FRANCIS D'SOUZA; PIERRE L. BOULAS; MICHAEL KISTERS; SAMBROTTA LUIS; ALLY M. AUKAULOO; ROGER GUILARD; KARL M. KADISH

INORGANIC CHEMISTRY COMMUNICATIONS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1996 vol. 35 p. 5743 - 5746

1387-7003

Several reports have appeared in the literature describing the spectral and electrochemical behavior of porphycenes, the most widely investigated of the porphyrin structural isomers.The redox properties of metalloporphycenes are similar to those of metalloporphyrins upon oxidation but not upon reduction where reduction at the metal is more difficult to achieve and ring-centered reactions predominate in the case of the porphycenes.The ring-centered reductions of metalloporphycenes such as octaethylporphycene (OEPc) and tetrapropylporphycene (TPrPc) occur at potentials which are shifted positively by upto 300 mV with respect to E1/2 of the corresponding metalloporphyrins containing octaethylporphyrin (OEP) or tetraphenylporphyrin (TPP) macrocycles.1a,b The more facile reduction of the metalloporphycenes leads to a smaller HOMO-LUMO energy gap as compared to the metalloporphyrins with the same central metal ion and this value, given by ¢E1/2 ) E1/2(ox) -E1/2(red), has been proposed to average 1.85 ( 0.15 V for a variety of porphycenes as compared to the well-quoted value of 2.25 ( 0.15 V for porphyrins containing OEP or TPP type macrocycles.