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Biomimetics Learning from nature Part 6

Tham khảo tài liệu 'biomimetics learning from nature part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 148 Biomimetics Learning from Nature Fig. 3. Plausible mechanism of olefin epoxidation catalyzed by Mn III porphyrins in the presence of molecular oxygen and isobutyraldehyde Compared with mono-metallporphyrins as catalyst remarkable enhancement of reactivity was obtained for p-oxo-bisiron III porphyrin-catalyzed olefin epoxidation system Scheme 8 in which the turnover number TON of the catalyst has doubled from about 700 million to 1 400 million.74 Scheme 8. Structure of p-oxo-bisiron III porphyrin It is usually considered that p-oxo dimeric metalloporphyrins could easily form monometalloporphyrins during the catalytic process. In fact whether the dinuclear intermediate or the mononuclear intermediate is the active species remains controversial for the oxygenation of hydrocarbons by using p-oxo dimeric metalloporphyrins as catalyst. The results of in situ UV-vis spectra indicate that both the dinuclear and the mononuclear high-valent intermediate exist in the catalytic system. Probably two kinds of oxo-iron intermediates that is O VFe-O-FeV O and FeV O were formed by series of free radical processes. Few examples on the metalloporphyrins-catalyzed epoxidation by dioxygen in the absence of a co-reductant could be found. It is worthy mentioning that RuVI TMP O 2 catalyzes olefin epoxidation with O2 without the requirement a sacrificial reductant reported by Biomimetic homogeneous oxidation catalyzed by metalloporphyrins with green oxidants 149 Groves group.75 76 The proposed mechanism is shown in Scheme 9. The active oxidant RuVI TMP O 2 reacts with an olefin to afford the epoxide and RuIV TMP O and the disproportionation of the latter generates RuII TMP and the active oxidant RuVI TMP O 2. The RuII TMP re-enters the catalytic cycle after being oxidized by dioxygen to RuIV TMP O . Run TMP O2 Scheme 9. Ru TMP -catalyzed olefins epoxidation with dioxygen 4. Oxidation of alcohols Oxidation of alcohols to the corresponding carbonyl compounds is a very important step for