过渡金属离子与烷烃反应机理的理论研究: 镍离子与丙烷反应 中甲烷的还原消 除机理

用量子化学方法在B3LYP/6-311++g(3df,3pd)水平上研究了Ni^+与C3H8的反应，获得了Ni,C3,H8]^+基态(双重态)势能面上CH4还原消除的详细机理。结果表明：该势能面上CH4消除反应经历两个基元步骤：Ni^+首先通过C—C活化过渡态形成插入型中间体，然后分别过不同的H-转移鞍点异构化为产物型中间体，并继而解离生成CH4，这些结果与以前从实验推测的反应机理明显不同。计算表明：对于该势面能上的甲烷消除反应，能量最有利的反应通道是Ni^+C3H8→Ni(C2H4)^++CH4,计算的反应热为127.85kJ/mol，与实验结果(106.13kJ/mol)符合较好。

Theoretical lstudies of the mechanism and energetics for the reaction of transition metal ions with alkanes: Methane elimination mechanism in the reaction of Ni^+ (2^D) with propane

The reaction of Ni^+ with propane has been studies extensively using density functional theory. The detailed information regarding the mechanism and energetics of CH4 elimination on the potential energy surface of Ni, C3, H8]^+ has been obtained at B3LYP/6-311++g(3df, 3pd) level of theory. The present study indicates that the CH4 elimination in the reaction of Ni^+ with propane undergoes two elementary steps, namely, the initial C—C bond activation in propane mediated by Ni^+ and the subsequent isomerization of the inserted intermediate. Ni^+ inserting into the initial primary C—H bond cannot results in the elimination of CH4, which is in contrast to the early postulated mechanism. After the C—C inserted species are formed on the potential energy surface, three reaction channels are open, which result in the elimination of CH4. The relative energy of the energetically most favored transition state is found to be 9. 18kJ/mol above the entrance channel. The heat of reaction for Ni^+C3H8 → Ni(C2H4)^++CH4 is calculated to be 127.85kJ/mol. This result is in good agreement with the experimental finding, a value of 106.13kJ/mol.