Carsch Kurtis M, de Ruiter Graham, Agapie Theodor
Division of Chemistry and Chemical Engineering, California Institute of Technology , 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States.
Inorg Chem. 2017 Aug 7;56(15):9044-9054. doi: 10.1021/acs.inorgchem.7b01022. Epub 2017 Jul 21.
The dangler manganese center in the oxygen-evolving complex (OEC) of photosystem II plays an important role in the oxidation of water to dioxygen. Inspired by the structure of the OEC, we synthesized a series of site-differentiated tetra-manganese clusters [LMn(PhPz)OMn][OTf] (2: x = 2; 3: x = 1) that features an apical manganese ion-distinct from the others-that is appended to a trinuclear manganese core through an μ-oxygen atom bridge. This cluster design was targeted to facilitate studies of high-valent Mn-oxo formation, which is a proposed step in the mechanism for water oxidation by the OEC. Terminal Mn-oxo species-supported by a multinuclear motif-were targeted by treating 2 and 3 with iodosobenzene. Akin to our previously reported iron complexes, intramolecular arene hydroxylation was observed to yield the C-H bond oxygenated complexes [LMn(PhPz)(OArPz)OMn][OTf] (5: x = 2; 6: x = 1). The fluorinated series [LMn(FArPz)OMn][OTf] (8: x = 2; 9: x = 1) was also synthesized to mitigate the observed intramolecular hydroxylation. Treatment of 8 and 9 with iodosobenzene results in intramolecular arene C-F bond oxygenation as judged by electrospray ionization mass spectrometry. The observed aromatic C-H and C-F hydroxylation is suggestive of a putative high-valent terminal metal-oxo species, and it is one of the very few examples capable of oxygenating C-F bonds.
光系统II析氧复合物（OEC）中悬空的锰中心在水氧化为氧气的过程中起着重要作用。受OEC结构的启发，我们合成了一系列位点分化的四锰簇[LMn(PhPz)OMn][OTf]（2：x = 2；3：x = 1），其特征是有一个顶端锰离子——与其他锰离子不同——通过一个μ-氧原子桥连接到一个三核锰核上。这种簇设计旨在促进对高价锰氧形成的研究，这是OEC水氧化机制中一个假定的步骤。通过用亚碘酰苯处理2和3，以多核基序为支撑的末端锰氧物种成为目标。与我们之前报道的铁配合物类似，观察到分子内芳烃羟基化生成了C-H键氧化的配合物[LMn(PhPz)(OArPz)OMn][OTf]（5：x = 2；6：x = 1）。还合成了氟化系列[LMn(FArPz)OMn][OTf]（8：x = 2；9：x = 1）以减轻观察到的分子内羟基化。通过电喷雾电离质谱判断，用亚碘酰苯处理8和9会导致分子内芳烃C-F键氧化。观察到的芳香族C-H和C-F羟基化暗示了一种假定的高价末端金属氧物种，并且它是能够氧化C-F键的极少数例子之一。
