Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo námestí 2, 16610 Prague 6, Czech Republic.
Chemistry. 2010 Apr 6;16(13):4110-9. doi: 10.1002/chem.200902373.
The C-H bond activation of small alkanes by the gaseous MgO(+) cation is probed by mass spectrometric means. In addition to H-atom abstraction from methane, the MgO(+) cation reacts with ethane, propane, n- and iso-butane through several pathways, which can all be assigned to the occurrence of initial C-H bond activations. Specifically, the formal C-C bond cleavages observed are assigned to C-H bond activation as the first step, followed by cleavage of a beta-C-C bond concomitant with release of the corresponding alkyl radical. Kinetic modeling of the observed product distributions reveals a high preference of MgO(+) for the attack of primary C-H bonds. This feature represents a notable distinction of the main-group metal oxide MgO(+) from various transition-metal oxide cations, which show a clear preference for the attack of secondary C-H bonds. The results of complementary theoretical calculations indicate that the C-H bond activation of larger alkanes by the MgO(+*) cation is subject to pronounced kinetic control.
气态 MgO(+)阳离子对小分子烷烃的 C-H 键活化作用通过质谱手段进行了探测。除了从甲烷中提取 H 原子外，MgO(+)阳离子还通过多种途径与乙烷、丙烷、正丁烷和异丁烷反应，这些途径都可以归因于初始 C-H 键的活化。具体来说，观察到的 C-C 键的形式断裂被分配给 C-H 键的活化，作为第一步，然后β-C-C 键断裂伴随着相应的烷基自由基的释放。对观察到的产物分布的动力学建模揭示了 MgO(+)对伯 C-H 键攻击的高度偏好。这一特征代表了主族金属氧化物 MgO(+)与各种过渡金属氧化物阳离子的显著区别，后者明显倾向于攻击仲 C-H 键。补充的理论计算结果表明，MgO(+*)阳离子对较大烷烃的 C-H 键活化受到明显的动力学控制。
