Ti^＋离子和C2H4分子自旋禁阻反应中C—H键活化机理的理论研究

用密度泛函B3LYP方法，研究了二重态和四重态势能面自旋禁阻反应Ti^＋（^4F，3d^24s^1）＋C2H4→TiC2H2^＋（^2A2）＋H2的微观机理．通过自旋．轨道耦合的计算讨论了势能面交叉点和可能的自旋翻转过程．中间体IM1-^4B2处，四重态和二重态间的旋-轨耦合值为59．3cm^-1．自旋多重度必将发生变化，从四重态系间穿越到二重态势能面形成共价型复合物IM1-^2A1，同时导致四重态势能面的势垒明显降低．到插入中间体IM2后，二重态势能面上有两条不同的反应路径，即分步和协同路径，后者在二重态势能面上得到放热产物TiC2H2^＋（^2A2）＋H2具有较低的活化势垒，4．52kcal／mol，其主反应路径为：Ti^＋＋C2H4→^4IC→IM1—^4B2→4.2ISC→IM1—^2A1→^2TSins]→IM2-^2A”→^2TSMCTS]→IM5→TiC2H2^＋（^2A2）＋H2．

Theoretical study of the mechanism for C-H bond activation in spin-forbidden reaction between Ti~+ and C_2H_4

Abstract： The mechanism of the spin-forbidden reaction Ti^＋（^4F,3d^24s^1）＋C2H4→TiC2H2^＋（^2A2）＋H2 on both doublet and quartet potential energy surfaces has been investigated at the B3LYP level of theory. Crossing points between the potential energy surfaces and the possible spin inversion process are discussed by means of spin-orbit coupling （SOC） calculations. The strength of the SOC between the low-lying quartet state and the doublet state is 59.3 cm^-1 in the intermediate complex IM1-^4B2. Thus, the changes of its spin multiplicity may occur from the quartet to the doublet surface to form IM1- ^2A1, leading to a significant decrease in the barrier height on the quartet PES. After the insertion intermediate IM2, two distinct reaction paths on the doublet PES have been found, i.e., a stepwise path and a concerted path. The latter is found to be the lowest energy path on the doublet PES to exothermic TiC2H2^＋ （^2A2） ＋ HE products, with the active barrier of 4.52 kcal/mol. In other words, this reaction proceeds in the following way： Ti^＋＋C2H4→^4IC→IM1-^4B2→4.2ISC→IM1-^2A1→^2TSins]→IM2-^2A＂→^2TSMCTS]→IM5→TiC2H2^＋（^2A2）＋H2.