Geng Caiyun, Li Jilai, Weiske Thomas, Schwarz Helmut
Institut für Chemie , Technische Universität Berlin , Straße des 17 Juni 115 , Berlin 10623 , Germany.
Institute of Theoretical Chemistry , Jilin University , Changchun 130023 , People's Republic of China.
J Am Chem Soc. 2018 Jul 25;140(29):9275-9281. doi: 10.1021/jacs.8b05618. Epub 2018 Jul 2.
Mechanistic insight into the thermal O-H bond activation of water by the cubane-like, prototypical heteronuclear oxide cluster [AlMgO] has been derived from a combined experimental/computational study. Experiments in the highly diluted gas phase using Fourier transform ion-cyclotron resonance mass spectrometry show that hydrogen-atom abstraction from water by the cluster cation [AlMgO] occurs at ambient conditions accompanied by the liberation of an OH radical. Because of a complete randomization of all oxygen atoms prior to fragmentation, about 83% of the oxygen atoms of the hydroxyl radical released originate from the oxide cluster itself. The experimental findings are supported by detailed high-level quantum chemical calculations. The theoretical analysis reveals that the transfer of a formal hydrogen atom from water to the metal-oxide cation can proceed mechanistically via proton- or hydrogen-atom transfer exploiting different active sites of the cluster oxide. In addition to the unprecedented oxygen-atom scrambling, one of the more general and quite unexpected findings concerns the role of spin density at the hydrogen-acceptor oxide atom. While this feature is crucial for [M-O]/CH couples, it is much less important in the O-H bond activation of water.
通过一项结合实验与计算的研究，已获得了关于类立方烷型典型异核氧化物簇[AlMgO]对水的热O-H键活化的机理见解。在高度稀释的气相中使用傅里叶变换离子回旋共振质谱进行的实验表明，簇阳离子[AlMgO]在环境条件下从水中夺取氢原子，同时释放出一个OH自由基。由于在碎片化之前所有氧原子完全随机化，释放出的羟基自由基中约83%的氧原子源自氧化物簇本身。详细的高水平量子化学计算支持了实验结果。理论分析表明，一个形式上的氢原子从水转移到金属氧化物阳离子的过程可以通过利用簇氧化物的不同活性位点进行质子或氢原子转移的机理来进行。除了前所未有的氧原子重排外，一个更普遍且相当意外的发现涉及氢受体氧化物原子处的自旋密度的作用。虽然这一特征对于[M-O]/CH对至关重要，但在水的O-H键活化中其重要性要小得多。
