Synthesis, Characterization, and Reactivities of Manganese(V)-Oxo Porphyrin Complexes

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• 作者：Woon Ju Song ; Mi Sook Seo ; Serena DeBeer George ; Takehiro Ohta ; Rita Song ; Min-Jung Kang ; Takehiko Tosha ; Teizo Kitagawa ; Edward I. Solomon ; Wonwoo Nam
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：February 7, 2007
• 年：2007
• 卷：129
• 期：5
• 页码：1268 - 1277
• 全文大小：239K
• 年卷期：v.129,no.5(February 7, 2007)
• ISSN：1520-5126

文摘

The reactions of manganese(III) porphyrin complexes with terminal oxidants, such as m-chloroperbenzoic acid, iodosylarenes, and H₂O₂, produced high-valent manganese(V)-oxo porphyrins inthe presence of base in organic solvents at room temperature. The manganese(V)-oxo porphyrins havebeen characterized with various spectroscopic techniques, including UV-vis, EPR, ¹H and ¹⁹F NMR,resonance Raman, and X-ray absorption spectroscopy. The combined spectroscopic results indicate thatthe manganese(V)-oxo porphyrins are diamagnetic low-spin (S = 0) species with a longer, weaker Mn-Obond than in previously reported Mn(V)-oxo complexes of non-porphyrin ligands. This is indicative of double-bond character between the manganese(V) ion and the oxygen atom and may be attributed to the presenceof a trans axial ligand. The [(Porp)Mn^V=O]⁺ species are stable in the presence of base at room temperature.The stability of the intermediates is dependent on base concentration. In the absence of base, (Porp)Mn^IV=O is generated instead of the [(Porp)Mn^V=O]⁺ species. The stability of the [(Porp)Mn^V=O]⁺ speciesalso depends on the electronic nature of the porphyrin ligands: [(Porp)Mn^V=O]⁺ complexes bearing electron-deficient porphyrin ligands are more stable than those bearing electron-rich porphyrins. Reactivity studiesof manganese(V)-oxo porphyrins revealed that the intermediates are capable of oxygenating PPh₃ andthioanisoles, but not olefins and alkanes at room temperature. These results indicate that the oxidizingpower of [(Porp)Mn^V=O]⁺ is low in the presence of base. However, when the [(Porp)Mn^V=O]⁺ complexeswere associated with iodosylbenzene in the presence of olefins and alkanes, high yields of oxygenatedproducts were obtained in the catalytic olefin epoxidation and alkane hydroxylation reactions. Mechanisticaspects, such as oxygen exchange between [(Porp)Mn^V=¹⁶O]⁺ and H₂¹⁸O, are also discussed.