Ni原子催化乙炔三聚环化反应机理的理论研究

Theoretical study on the reaction mechanism of acetylene cyclotrimetization catalyzed by Ni atom

本文在B3LYP/6-311+G(3df),aug-cc-pvtz//6-311++G(2d,2p)水平下研究了Ni原子催化乙炔三聚环化生成苯在单重态和三重态势能面上的详细反应机理。结果表明,反应路径主要包含四个步骤:Ni原子先与两分子C2H2形成复合物C2H2NiC2H2,氧化加成环化为含Ni的五元环cyc-NiC4H4化合物,与第三分子C2H2环化为含Ni的七元环cyc-NiC6H6化合物,最后还原为Ni原子而生成苯环。并对此催化反应的转化频率(TOF)进行了分析,其值为2.34×10-22s-1。同时表明,关键中间体为复合物C2H2NiC2H2,关键步骤为复合物C2H2NiC2H2氧化加成环化为含Ni的五元环cyc-NiC4H4化合物,其能垒为192.4 kJ.mol-1。

The reaction mechanism of acetylene cyclotrimetization catalyzed by Ni atom has been detailedly investigated on the sin- glet and triplet potential energy surfaces at B3LYP/6-311 ＋G（ 3df）, aug-cc-pvtz//6-311 ＋＋G（ 2d, 2p）level. The reaction pathways mainly includes four reaction steps, （1）a C2 H2 NiC2 H2 complex formed from a nickel center and two C2 H2 monomers, （2）the met- allacyclopentadiene eye-NiC4 H4 compound formed through oxidative addition from C2 H2 NiC2 H2, （ 3 ） a seven-member cyc-NiC6 H6 formed through insertion of the third C2 H2, and （4） the final benzene formation with the reduction of nickel center. The turnover fre- quency （TOF） is calculated to be 2. 34 × 10^-22 s^-1. Besides, the TOF determining intermediate is C2 H2 NiC2 H2, while the TOF deter- mining transition state is the metallacyclopentadiene cye-NiC4H4 compound formed through oxidative addition from C2H2NiC2H2 with the energy barrier of 192.4 kJ·mol^-1.