Oxidative Decarboxylation of Carboxylic Acids with Tetrabutylammonium Periodate Catalyzed by Manganese (III) Meso-Tetraarylporphyrins: Effect of Metals, Meso-Substituents, and Anionic Axial Ligands

In association with tetrabutylammonium periodate (n-Bu4NIO4) and imidazole (ImH), manganese meso-tetraarylporphyrins have provided an effective catalytic system for the oxidative decarboxylation of carboxylic acids. Meso-tetraarylporphyrins bearing electron-withdrawing and/or bulky aryl groups at meso-positions lowered the catalytic activity of the metalloporphyrins. Although the presence of ImH and the choice of the metal center are crucial for the catalytic properties of the metalloporphyrins, the counter ion plays an important role in this catalytic system. However, the best catalytic activity has been observed for the Mn(TPP)CN/n-Bu4NIO4/ImH system. A catalytic cycle is postulated, in which the oxidative decarboxylation of diphenylacetic acid involves the interaction of a high-valent Mn–oxo species with the substrate. Attempts have been made to visualize the possible interactions and electronic changes responsible for the formation of the corresponding carbonyl products.