METHANE ACTIVATION BY GROUP-IVB IMIDO COMPLEXES
METHANE ACTIVATION BY GROUP-IVB IMIDO COMPLEXES
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DOI：
10.1021/ja00052a060
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发表时间：
1992-12-16
影响因子：
15
通讯作者：
CUNDARI, TR
中科院分区：
文献类型：
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作者：
CUNDARI, TR
一项由IVB族亚胺络合物激活甲烷的从头算研究，结合现有的实验数据，揭示了这一重要反应的有趣图景。甲烷与(H)2M=NH的初始相互作用形成了几乎等于9 kcal mol-1的烷烃配合物。实验表明，C-H被激活的金属-配体键的极性对促进随后的断裂起着重要作用。计算支持这一假设，并表明烷烃络合物的形成增加了C（δ - h (δ +)）极化，为C- h裂解奠定了基础。计算出的(H)2M(CH3)(NH2) （M = Ti, Zr, Hf）的甲烷消除势垒在绝对数量和随金属的变化趋势方面与实验模型很好地吻合。计算得到的甲烷激活势垒顺序为Ti > Zr > Hf，与计算得到的放热强度一致。计算的几何形状表明甲烷消除的过渡状态较晚，与实验确定的激活参数一致。TSs具有风筝形状的几何形状，在C-H键的H被激活时呈钝角（H(t)），并且MH(t)距离较短，比正常情况大1-2%。较短的MH(t)距离表明相互作用稳定，由正键重叠居群支持。本征反应坐标的计算表明了N-H和M沿反应坐标相互作用的重要性。
An ab initio study of methane activation by group IVB imido complexes, when coupled with available experimental data, reveals an interesting picture of this important reaction. Initial interaction of methane and (H)2M=NH leads to the formation of alkane complexes bound by almost-equal-to 9 kcal mol-1. Experiment indicates that the polarity of the metal-ligand bond upon which the C-H is activated plays an important role in facilitating subsequent scission. Calculations support this hypothesis and suggest that formation of the alkane complex acts to increase C(delta-H(delta+) polarization, setting the stage for C-H cleavage. Calculated methane elimination barriers for (H)2M(CH3)(NH2) (M = Ti, Zr, Hf) are in good agreement with experimental models in terms of absolute numbers and trends as a function of metal. Calculated methane activation barriers follow the order Ti > Zr > Hf, in line with calculated exothermicities. Calculated geometries indicate a late transition state for methane elimination, in agreement with experimentally determined activation parameters. The TSs have a kite-shaped geometry with an obtuse angle about the H of the C-H bond being activated (H(t)) and a short MH(t) distance, 1-2% greater than normal. The short MH(t) distance suggests a stabilizing interaction, supported by a positive bond overlap population. Calculation of the intrinsic reaction coordinate demonstrates the importance of agostic interactions between N-H and M along the reaction coordinate.