Synthesis, characterization, and reactivities of manganese(V)-oxo porphyrin complexes
Synthesis, characterization, and reactivities of manganese(V)-oxo porphyrin complexes
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DOI：
10.1021/ja066460v
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发表时间：
2007-02-07
影响因子：
15
通讯作者：
Nam, Wonwoo
中科院分区：
文献类型：
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作者：
Song, Woon Ju;Seo, Mi Sook;Nam, Wonwoo
在碱存在下，卟啉锰配合物与间氯过苯甲酸、碘代芳烃和H2 O2等末端氧化剂反应，在室温下生成高价锰卟啉氧代化合物。锰（V）-氧代卟啉已经用各种光谱技术表征，包括UV-vis，EPR，H-1和F-19 NMR，共振拉曼和X-射线吸收光谱。结合光谱结果表明，锰（V）-氧代卟啉是抗磁性的低自旋（S = 0）物种，其Mn-O键比以前报道的非卟啉配体的Mn（V）-氧代配合物更长、更弱。这表明锰（V）离子和氧原子之间的双键特征，并且可能归因于存在跨轴配体。[（Porp）（MnO）-O-V]（+）物种在室温碱存在下是稳定的。中间体的稳定性取决于碱浓度。在不存在碱的情况下，生成（Porp）（MnO）-O-IV而不是[（Porp）（MnO）-O-V]（+）物种。[（Porp）（MnO）-O-V]（+）物种的稳定性还取决于卟啉配体的电子性质：带有缺电子卟啉配体的[（Porp）（MnO）-O-V]（+）络合物比带有富电子卟啉的那些更稳定。锰（V）-氧代卟啉的反应性研究表明，中间体能够氧化PPh 3和苯硫醚，但不是烯烃和烷烃在室温下。这些结果表明，[（Porp）（MnO）-O-V]（+）在碱存在下的氧化能力较低。而当[（Porp）（MnO）-O-V]（+）配合物与碘酰苯在烯烃和烷烃存在下缔合时，在催化烯烃环氧化和烷烃羟基化反应中获得了高产率的含氧产物。讨论了[（Porp）（MnO）-O-V_（16）]（+）与（H_2 O）-O_（18）之间的氧交换机理。
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 in the presence of base in organic solvents at room temperature. The manganese(V)-oxo porphyrins have been characterized with various spectroscopic techniques, including UV-vis, EPR, H-1 and F-19 NMR, resonance Raman, and X-ray absorption spectroscopy. The combined spectroscopic results indicate that the manganese(V)-oxo porphyrins are diamagnetic low-spin (S = 0) species with a longer, weaker Mn-O bond 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 presence of a trans axial ligand. The [(Porp)(MnO)-O-V](+) 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)(MnO)-O-IV is generated instead of the [(Porp)(MnO)-O-V](+) species. The stability of the [(Porp)(MnO)-O-V](+) species also depends on the electronic nature of the porphyrin ligands: [(Porp)(MnO)-O-V](+) complexes bearing electron-deficient porphyrin ligands are more stable than those bearing electron-rich porphyrins. Reactivity studies of manganese(V)-oxo porphyrins revealed that the intermediates are capable of oxygenating PPh3 and thioanisoles, but not olefins and alkanes at room temperature. These results indicate that the oxidizing power of [(Porp)(MnO)-O-V](+) is low in the presence of base. However, when the [(Porp)(MnO)-O-V](+) complexes were associated with iodosylbenzene in the presence of olefins and alkanes, high yields of oxygenated products were obtained in the catalytic olefin epoxidation and alkane hydroxylation reactions. Mechanistic aspects, such as oxygen exchange between [(Porp)(MnO)-O-V16](+) and (H2O)-O-18, are also discussed.