Metal-Peroxo versus Metal-Oxo Oxidants in Non-Heme Iron-Catalyzed Olefin Oxidations: Computational and Experimental Studies on the Effect of Water

摘要

Our computational and experimental studies show that Fe(BPMEN)-catalyzed olefin oxidation has a complex reaction mechanism that allows both Fe~(Ⅲ)—OOH and Fe~Ⅴ=O species to act as oxidants with comparable activation barriers. The presence of water favors formation of an HO—Fe~Ⅴ=O oxidant via water-assisted O—OH bond cleavage and leads to, both epoxide and cis-diol products. In its absence, the oxidant is the Fe~(Ⅲ)—OOH (or (MeCN)-Fe~(Ⅲ)—OOH), and. oxidation mainly leads to epoxide. This conclusion differs from that derived from DFT investigations of iron— porphyrin-catalyzed olefin epoxidation, where the Fe~(Ⅲ)—OOH pathway is deemed too high in energy to be plausible. The difference between these two systems may lie in the more flexible coordination environment of the non-heme iron complex, which has an available adjacent coordination site that contributes to the activation of the peroxide in both wa and nwa pathways.