Department of Chemistry and Nano Science , Ewha Womans University , Seoul 03760 , Korea.
Picobiology Institute, Graduate School of Life Science , University of Hyogo , RSC-UH LP Center, Hyogo 679-5148 , Japan.
Inorg Chem. 2018 Aug 20;57(16):10232-10240. doi: 10.1021/acs.inorgchem.8b01426. Epub 2018 Aug 6.
Mn(III)-iodosylarene porphyrin adducts, [Mn(III)(ArIO)(Porp)], were synthesized by reacting electron-deficient Mn(III) porphyrin complexes with iodosylarene (ArIO) at -60 °C and characterized using various spectroscopic methods. The [Mn(III)(ArIO)(Porp)] species were then investigated in the epoxidation of olefins under stoichiometric conditions. In the epoxidation of olefins by the Mn(III)-iodosylarene porphyrin species, epoxide was formed as the sole product with high chemoselectivities and stereoselectivities. For example, cyclohexene oxide was formed exclusively with trace amounts of allylic oxidation products; cis- and trans-stilbenes were oxidized to the corresponding cis- and trans-stilbene oxides, respectively. In the catalytic epoxidation of cyclohexene by an electron-deficient Mn(III) porphyrin complex and PhIO at low temperature (e.g., -60 °C), the Mn(III)-iodosylarene porphyrin species was evidenced as the active oxidant that effects the olefin epoxidation to give epoxide as the product. However, at high temperature (e.g., 0 °C) or in the case of using an electron-rich manganese(III) porphyrin catalyst, allylic oxidation products, along with cyclohexene oxide, were yielded, indicating that the active oxidant(s) was not the Mn(III)-iodosylarene adduct but probably high-valent Mn-oxo species in the catalytic reactions. We also report the conversion of the Mn(III)-iodosylarene porphyrins to high-valent Mn-oxo porphyrins under various conditions, such as at high temperature, with electron-rich porphyrin ligand, and in the presence of base (OH). The present study reports the first example of spectroscopically well-characterized Mn(III)-iodosylarene porphyrin species being an active oxidant in the stoichiometric and catalytic oxidation reactions. Other aspects, such as one oxidant versus multiple oxidants debate, also were discussed.
Mn(III)-碘代芳烃卟啉加合物 [Mn(III)(ArIO)(Porp)] 通过在-60°C 下将缺电子 Mn(III)卟啉配合物与碘代芳烃 (ArIO) 反应合成，并通过各种光谱方法进行表征。然后，在化学计量条件下研究了 [Mn(III)(ArIO)(Porp)] 物种在烯烃环氧化中的作用。在 Mn(III)-碘代芳烃卟啉物种的烯烃环氧化中，仅形成环氧化物作为唯一产物，具有高化学选择性和立体选择性。例如，环己烯氧化物的形成是唯一的，副产物是微量的烯丙基氧化产物；顺式和反式二苯乙烯分别被氧化为相应的顺式和反式二苯乙烯氧化物。在低温（例如-60°C）下，用缺电子 Mn(III)卟啉配合物和 PhIO 催化环己烯环氧化时，证明 Mn(III)-碘代芳烃卟啉物种是有效的氧化剂，可使烯烃环氧化生成环氧化物作为产物。然而，在高温（例如 0°C）或使用富电子锰(III)卟啉催化剂的情况下，除了环己烯氧化物外，还生成了烯丙基氧化产物，表明活性氧化剂不是 Mn(III)-碘代芳烃加合物，而是催化反应中的高价 Mn-氧物种。我们还报告了在各种条件下将 Mn(III)-碘代芳烃卟啉转化为高价 Mn-氧卟啉，例如在高温下、富电子卟啉配体存在下和在碱性条件下（OH）。本研究报告了第一个光谱上特征良好的 Mn(III)-碘代芳烃卟啉物种作为化学计量和催化氧化反应中有效氧化剂的实例。还讨论了其他方面，例如一个氧化剂与多个氧化剂的争论。
