Abstract
Visible absorption spectra of 5, 10, 15, 20-tetra (p-methoxyphenyl) porphyrinatocobalt (II) [Co (II) (p-OCH3) TPP] and 5, 10, 15, 20-tetra (p-methoxyphenyl) porphyrinatocobalt (III) chloride [ClCo (III) (p-OCH3) TPP] were measured in toluene at room temperature in the absence or presence of O2. Changes of the spectra due to the presence of skatole and/or pyridine were investigated. The spectra of four-coordinate cobalt complexes of 5, 10, 15, 20-tetra (p-methoxyphenyl)-porphyrin were found to be practically indistinguishable from those of five-coordinate complexes, but clearly different from those of six-coordinate complexes, irrespective of the oxidation state of the central cobalt ion of complexes. The reaction medium for the oxygenation of skatole catalyzed by Co (II) (p-OCH3) TPP showed only the spectrum of a six-coordinate complex, (skatole) Co (II) (p-OCH3) TPP (O2). This result showed clearly that the oxygenation of skatole must proceed through a ternary complex of the type (skatole)-[Co (II) complex]-(O2). The addition of pyridine to the same reaction medium was found to produce a six-coordinate complex, (skatole) Co (II) (p-OCH3) TPP (pyridine), irreversibly. This explains why the oxygenation of skatole is remarkably repressed upon addition of a Lewis base such as pyridine to the reaction medium. The spectrum of the reaction medium for the oxygenation of skatole catalyzed by ClCo (III) (p-OCH3) TPP was found to consist of the superposed spectra of two six-coordinate complexes, ClCo (III) (p-OCH3) TPP (O2) and ClCo (III) (p-OCH3) TPP (skatole). Therefore, the oxygenation of skatole apparently proceeds through the interaction between these two six-coordinate complexes.
