Influence of the macrocycle structure on the ability of Co(II)-porphyrins to oxidize in the presence of organic bases

Abstract

By spectrophotometric titration, 1H NMR and cyclic voltammetry the processes of Co(II)-5,10,15,20-tetraphenylporphyrin, Co(II)-5,10,15,20-tetraphenyl-2,3,7,8,12,13,17,18-tetrabenzoporphyrin, Co(II)-2,3,7,8,12,13,17,18-octaphenyl-5,10,15,20-tetraazaporphyrin, Co(II)-2,3,7,8,12,13,17,18-octa(4-bromphenyl)-5,10,15,20-tetraazaporphyrin and Co(II)-2,3,7,8,12,13,17,18-octa(4-nitrophenyl)-5,10,15,20-tetraazaporphyrin interaction with imidazole (Im) in benzene in the presence and absence of atmospheric oxygen has been investigated. If the Co(II)-porphyrins with high Epc upon complexation with the imidazole form stable mono-axial complexes Co(II)P(Im), then the Co(II)-porphyrins with low Epc are oxidized into low-spin six-coordinate Co(III)-porphyrins with formation of bis-axial complexes Co(III)P(Im)2. The thermodynamic and kinetic parameters of the coordination and oxidation processes have been calculated and corresponding structural correlations have been carried out.