Miss Lin Cheng
High-valent transition metal oxo complexes, with high oxidizing power, are widely used in chemical and biological systems. Permanganate, which is relatively stable at room temperature, has been studied in the cleavage of C-H bond for decades but still has limitation because of the high energy barrier for hydrocarbon bond breaking. Therefore, high-efficient and low-cost catalysts are extremely needed. Brønsted acids have long been applied in the activation of metal oxo species. The activating effect of Lewis acids on the metal oxo species had drawn more attention after the discovery of the active site in Mn4CaO5 cluster. To investigate the activating effect of Ca(OTf)+ (OTf is CF3SO3−) and/or acetic acids on MnO4– for the cyclohexane oxidation in the solvent of acetonitrile, the theoretical study by density functional theory (DFT) is carried out in this work. The first transition states (TS1s) of the mechanisms being studied here are all characterized as normal HAT transition states and the rate-determined steps. The results show that the activating effect by one acetic acid (AcOH) cannot allow the reaction to occur at room temperature readily. As the consumption of acetic acids increase to three portions, the reaction barrier (ΔG298‡) is obviously reduced on account of the hydrogen bonding effect. When the Ca(OTf)+ is used, the ΔG298‡ can be decreased markedly. The ΔG298‡ for one portion or three AcOH with Ca(OTf)+ of the cyclohexane oxidation by MnO4– in CH3CN has been reduced remarkably. So, the Ca(OTf)+ and acetic acids are predicted to have a significant cooperative effect to lower down the ΔG298‡ in the cyclohexane oxidation by MnO4– that allow the C-H bond to be conveniently oxidized at room temperature.