The Research Of The Oxidative Reactivity Of Three Reactive Intermediates:Mn^Ⅳ=O、Mn^Ⅳ-OH And Mn^Ⅳ-OOH

Transition metal ions play significant roles in versatile biological and chemical oxidations. In addition to the generally believed metal oxo functional groups (Mn+=O), the metal hydroxo (Mn+-OH) and hydroperoxide functional groups (Mn+-OOH) have also been proposed to serve as the key active intermediates in versatile oxidation process. However, the reasons why natural redox metalloenzymes make ues of a metal oxo or hydroxo group to serve as their active intermediates in specific cases are not fully understood. Apparently, clarifying the oxidative relationships of these active intermediates would help to understand the enzymes’ selections on them, thus promote understanding of their mechsnisms and help the rational design of medicines, also it would benefit the design of selective oxidation catalysts. In this paper, we used model compound [MnⅣ(Me2EBC)(OH)2(PF6)2] as the research platform, disclosed the differences in reactivity of the MnⅣ=O, MnⅣ-OH and MnⅣ-OOH species, disscused the correlation of net charge, redox potential, and manganese(IV)-oxygen bond order with its oxidative reactivity.In chapter II, we used [MnⅣ(Me2EBC)(OH)2(PF6)2] as the research platform, had demonstrated that, in hydrogen abstraction by MnⅣ=O, the generated MnⅢ-OH moiety can rebond the OH group back to the substrate radical to form the hydroxylated product, whereas, in the case of the MnⅣ-OH moiety, the generated MnⅢ-OH2moiety is incapable of rebound. Whereas MnⅣ=O does not facilitate electron transfer, the MnⅣ-OH moiety demonstrates efficient electrontransfer capability, which can be further enhanced by increasing the net charge.In chapter Ⅲ, the influence of the net charge on the hydrogen abstraction and electron-transfer activity of the manganese(IV) species have MnⅣ-OH group had been investigated using the identical manganese(IV) model, and revealed that increasing the net charge of an active metal intermediate would substantially accelerate its electron-transfer rate, demonstrating charge-promoted electron transfer, whereas its influence on the hydrogen abstraction is ignorable because of the compensation effect between the redox potential and pKa.In chapter Ⅳ, the oxidative properties of MnⅣ-OOH moiety in hydrogen abstraction and oxygenation were investigated with the Mn(Me2EBC)Cl2complex. In oxidation reactions, the MnⅣ-OOH moiety was capable of both hydrogen abstraction and oxygenation, and its oxygenation efficiency was much higher than its hydrogen abstraction. Although its efficiency in hydrogen abstraction is substantially low, it had demonstrated much more powerful oxidizing ability than the corresponding MnⅣ-OH and MnⅣ=O moieties having an identical coordination environment and oxidation state. The isotopically labeling experiments using H218O and H218O2disclosed a dual mechanism for these MnⅣ-OOH moiety mediated oxidations. In hydrogen abstraction, the reaction proceeds by direct oxygen insertion with plausible electron transfer, while, in oxygenation, the reaction proceeds by concerted oxygen transfer and again, electron transfer.In summary, this paper had demonstrated the intermediates reactivity differences and similarities of redox metal oxo, hydroxo and hydroperoxide of the manganese(IV) complex. It will provide new insights into the roles they may play in biological and chemical oxidations.