The anions formed from methylalumoxane (MAO) and suitable donors (e.g. octamethyltrisiloxane) are amenable to mass spectrometric (MS) analysis. Their composition as deduced from this data allows direct insight into the chemical transformations of their neutral precursors. One such process is oxidation, which is well‐known to be facile for MAO without any clear idea of what actually occurs at a molecular level. Addition of O₂ to MAO results in immediate gelation, but MS analysis reveals no corresponding change to the composition of the principal oligomeric anions. A slow (hours) reaction does occur that involves net incorporation of Me₂AlOMe into the oligomeric anions, and the identities of the OMe‐containing anions were confirmed by ¹H NMR spectroscopy, MS/MS analysis, and addition of an authentic sample of Me₂AlOMe to MAO. The result tallies with the fact that addition of O₂ to MAO produces Me₂AlOMe from free Me₃Al which eventually leads to formation of oxidized MAO oligomers and changes in ion abundance. Aging of the oxygenated MAO results in further growth of the oligomers similar to that of the non‐oxidized species. Mass spectrometric analysis therefore reveals useful insights into the environmental history of a given MAO batch.

中文翻译：

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甲基铝氧烷低聚物的氧化

由甲基铝氧烷（MAO）和合适的供体（例如八甲基三硅氧烷）形成的阴离子适用于质谱（MS）分析。从这些数据推导出它们的组成，可以直接洞察其中性前体的化学转化。一种这样的过程是氧化，众所周知，氧化对于MAO很容易，而对分子水平上实际发生的事情没有任何清楚的了解。O ₂加入MAO会立即凝胶化，但MS分析表明主要的低聚阴离子的组成没有相应的变化。确实发生了缓慢的（几小时）反应，其中涉及将Me ₂ AlOMe净掺入低聚阴离子中，并且含OMe的阴离子的身份由¹确认。1 H NMR光谱，MS / MS分析，以及将真实的Me ₂ AlOMe样品添加至MAO。结果符合以下事实：将O _2添加到MAO中会从游离的Me ₃ Al中产生Me ₂ AlOMe ，最终导致氧化的MAO低聚物的形成和离子丰度的变化。氧化的MAO的老化会导致寡聚体的进一步生长，类似于未氧化的物种。因此，质谱分析揭示了对给定MAO批次的环境历史的有用见解。