| Abstract
| - The voltammetry of the 1-methylimidazole complex of cobalt “picket fence” porphyrin in benzonitrile is modified only slightly in the presence of O2 despite the coordination of O2 by the cobalt porphyrin. In acidified benzonitrile, neither cobalt “picket fence” nor cobalt tetraphenylporphyrin shows appreciable affinity for O2, but the latter porphyrin exhibits superior properties as a catalyst for the electroreduction of O2.
- The electrochemical behavior of cobalt 5,10,15,20-tetrakis(α,α,α,α-2-pivalamidophenyl)porphyrin (CoIITpivPP)was examined in benzonitrile solutions. The electrochemical responses were changed significantly by the additionof 1-methylimidazole which coordinates once to the Co(II) and twice to the Co(III) porphyrin. The correspondingequilibrium binding constants were estimated as 2.9 × 103 M-1 and 1.7 × 1020 M-2. The cyclic voltammetricresponses were affected by the rates of the ligand association/dissociation reactions. Formation of the O2 adductof the Co(II) porphyrin resulted in only small changes in the cyclic voltammetric pattern. Comparison betweenCoIITpivPP and cobalt tetraphenylporphyrin (CoIITPP) as catalysts for the electroreduction of O2 showed thelatter to be the superior catalyst both when adsorbed on graphite electrodes and when dissolved in thin layers ofacidified benzonitrile where CoIITpivPP exhibited unimpressive catalytic activity compared with CoIITPP, whichappeared to catalyze the reduction of O2 by significantly more than 2 electrons per molecule.
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