The molecular mechanism of the Oxygen Evolving Center of photosystem II has been under debate for decades. One frequently cited proposal is the nucleophilic attack by water hydroxide on a pendant Mn═O moiety, though no chemical example of this reactivity at a manganese cubane cluster has been reported. We describe here the preparation, characterization, and a reactivity study of a synthetic manganese cubane cluster with a pendant manganese-oxo moiety. Reaction of this cluster with alkenes results in oxygen and hydrogen atom transfer reactions to form alcohol- and ketone-based oxygen-containing products. Nitrene transfer from core imides is negligible. The inorganic product is a cluster identical to the precursor, but with the pendant Mn═O moiety replaced by a hydrogen abstracted from the organic substrate, and is isolated in quantitative yield. 18O and 2H isotopic labeling studies confirm the transfer of atoms between the cluster and the organic substrate. The results suggest that the core cubane structure of this model compound remains intact, and that the pendant Mn═O moiety is preferentially reactive.

中文翻译：

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光合氧释放复合物中拟定 S4 态合成结构模型中的反应性侧链 Mn=O

数十年来，关于光系统 II 氧演化中心的分子机制一直存在争议。一个经常被引用的提议是氢氧化水对悬垂的 Mn=O 部分的亲核攻击，尽管没有报道在锰立方烷簇上的这种反应性的化学例子。我们在这里描述了具有悬垂锰氧部分的合成锰立方簇的制备、表征和反应性研究。该簇与烯烃的反应导致氧和氢原子转移反应，形成基于醇和酮的含氧产物。从核心酰亚胺转移的氮烯可以忽略不计。无机产物是与前体相同的簇，但侧链 Mn=O 部分被从有机基质中提取的氢取代，并以定量产率分离。18O 和 2H 同位素标记研究证实了原子团和有机底物之间的原子转移。结果表明，该模型化合物的核心立方烷结构保持完整，并且悬垂的 Mn=O 部分具有优先反应性。