Mn(Ⅲ)-四芳基卟啉与高碘酸四丁基铵催化羧酸的氧化脱羧:金属、取代基和轴向阴离子配体的影响

锰四芳基卟啉与高碘酸四丁基铵(n-Bu4NIO4)和咪唑(ImH)组合,为羧酸氧化脱羧提供了一个有效的催化剂体系.中位含有吸电子基团和/或大体积芳基的中位-四芳基卟啉使金属卟啉的活性降低.咪唑的存在和金属中心的选择对金属卟啉的催化性能起关键性作用,催化体系中的反离子也有重要影响.Mn(TPP)CN/n-Bu4NIO4/ImH体系的催化活性最好.二苯基乙酸的氧化脱羧可能涉及高价的含氧锰物种与反应物间的相互作用,提出了可能的反应机理.

Oxidative Decarboxylation of Carboxylic Acids with Tetrabutyl-ammonium 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.