化学学报 ›› 2013, Vol. 71 ›› Issue (05): 749-754.DOI: 10.6023/A13020177 上一篇    下一篇

研究论文

Fe+与CH3X (X=Cl, Br, I)反应的理论研究

孙小丽, 李吉来, 黄旭日, 孙家锺   

  1. 吉林大学理论化学研究所 理论化学国家重点实验室 长春 130023
  • 收稿日期:2013-02-05 出版日期:2013-05-14 发布日期:2013-03-26
  • 通讯作者: 李吉来,Jilai@jlu.edu.cn;黄旭日,huangxr@jlu.edu.cn E-mail:huangxr@jlu.edu.cn
  • 基金资助:

    项目受国家重点基础研究发展计划(973)(No. 2012CB932800)、国家自然科学基金(Nos. 21103064, 21073075和21173097)、教育部博士点基金(No. 20100061110046)、吉林大学理论化学国家重点实验室专项基金和吉林大学基本科研业务费(Nos. 421010061439, 450060445067)资助.

A Theoretical Study of the Reaction of Fe+ with CH3X (X=Cl, Br, I)

Sun Xiaoli, Li Jilai, Huang Xuri, Sun Chiachung   

  1. State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, China
  • Received:2013-02-05 Online:2013-05-14 Published:2013-03-26
  • Supported by:

    Project supported by the National Basic Research Program of China (973 Program) (No. 2012CB932800), the National Natural Science Foundation of China (Nos. 21103064, 21073075, 21173097), the Research Fund for the Doctoral Program of Higher Education of China (No. 20100061110046), the Special Funding of State Key Laboratory of Theoretical and Computational Chemistry, Jilin University and Basic Research Fund of Jilin University (Nos. 421010061439, 450060445067).

铁及其复合物催化的C—X键功能化日益引起人们的重视. 采用密度泛函理论(DFT), 在B3LYP/def2-SVP水平下详细研究了Fe+与CH3X (X=Cl, Br, I)的反应活性和机理. 计算结果表明标题反应存在两种反应机制, 即插入机制和SN2机制. 从机理上来看, 在插入机理中, 反应都始于Fe+离子从侧面进攻CH3X, 生成产物FeX+和 CH3·; 而在SN2机制中, 反应则始于Fe+离子从背后进攻CH3X, 生成产物FeCH3X和X·. 从我们的计算可以看出, 四重态或六重态下的 Fe+离子在C—X键活化中展现了截然不同的催化活性; 在所有通道中, 都以四重态为主导; SN2机制中相对较高的决速能垒使其丧失了竞争性. 再者, 计算表明在所有的插入机制中, 所有通道都是放热的, 而在SN2机制中, 仅有X=I时, 反应是放热的. 此外, 计算表明这些反应属于两态反应活性, 两种机制中, 在反应的入口和出口存在最小能量交叉点.此外, 反应途径电子结构追踪分析表明自旋极化对能量影响较大, 调控着反应采取的反应通道和主副产物比例. 通过本文的理论研究, 尤其是详细的电子结构分析, 为铁催化剂活化C—X键和C—C耦联反应提供了线索和以铁为基的催化剂设计提供理论依据.

关键词: Fe+, 插入, SN2, 反应机制, 能垒, 电子结构

The C—X bond functionalization catalyzed by iron and their complexes has attracted much attention. Using density functional theory (DFT), we herein studied the reactivity and mechanism of iron cation (Fe+) towards C—X bond cleavage of CH3X (X=Cl, Br, I) at B3LYP/def2-SVP level of theory. The results show that there are two possible pathways available for the title reactions, i.e. the insertion mechanism and the SN2 mechanism, respectively. Mechanistically, in the insertion mechanism, the reactions stem from Fe+ attacking on the side of CH3X and results in the generation the products FeX+ and CH3·; whereas in the SN2 mechanism, the Fe+ initially attacks the substrate from the back of C—X yielding FeCH3+ and X·. The results show that the sextet and the quartet states of Fe+ demonstrate quite distinct reactivity towards the cleavage of C—X bonds in the most potential pathways, and the quartet pathways are dominant in all the pathways. The relative higher barriers in the SN2 pathways results in their lower competitiveness in the title reactions. In addition, our results show that, for all the three reaction systems, the insertion mechanism is exothermic; whereas for the SN2 mechanism, only X=I is exothermic, however. Furthermore, the calculations also show that these reactions demonstrate two-state reactivity (TSR) scenario. There are minimum energy crossing points (MECPs) between the sextet and quartet state on potential energy surfaces (PESs) both at the entrance and export sides for the two reaction mechanisms. On the other hand, the electron transfer evolution analysis indicates that the spin polarization plays important role in the stabilization of the potential energy surfaces and as a result, it controls the pathways by which it takes place and the branch ratio of the major products and byproducts. This thorough theoretical study, especially the detailed electronic structure analysis, may provide important clues for understanding the C—X bond activation and theoretical fundamental evidences for iron-based catalysts design.

Key words: Fe+, insertion, SN2, reaction mechanism, activation barrier, electronic structure