Chinese Journal of Organic Chemistry ›› 2023, Vol. 43 ›› Issue (2): 660-667.DOI: 10.6023/cjoc202203012 Previous Articles     Next Articles

Pd(0)催化1-R-3-苯基亚丙基环丙烷(R=Me/H)与呋喃甲醛[3+2]环加成反应机理的密度泛函理论研究

刘悦灵, 钟欣欣, 张干兵*()   

  1. 湖北大学化学化工学院 有机化工新材料省部共建协同创新中心有机合成与应用教育部重点实验室 武汉 430062
  • 收稿日期:2022-07-07 修回日期:2022-08-30 发布日期:2022-10-31
  • 基金资助:
    国家自然科学基金(22076059)

Density Functional Theory Study for Exploring the Mechanisms of the [3+2] Cycloaddition Reactions between 1-R-3-Phenylpropylidenecyclopropane (R=Me/H) and Furfural Catalyzed by Pd(0)

Yueling Liu, Xinxin Zhong, Ganbing Zhang()   

  1. Collaborative Innovation Center for Advanced Organic Chemical Materials Co-constructed by the Province and Ministry, Ministry-of-Education Key Laboratory for the Synthesis and Applications of Organic Functional Molecules, College of Chemistry and Chemical Engineering, Hubei University, Wuhan 430062
  • Received:2022-07-07 Revised:2022-08-30 Published:2022-10-31
  • Contact: *E-mail: gbzhang@hubu.edu.cn
  • Supported by:
    National Natural Science Foundation of China(22076059)

The optimal geometric structures and thermodynamic properties for all stationary points (reactants, intermediates, transition states, and products) on each pathway of the [3+2] cycloaddition reactions between 1-R-3-phenylpropylidenecyclo- propane (R=Me/H) and furfural with model catalyst Pd(PH3)2 have been computed by using density functional theory (DFT) method with M06 functional combined with Stuttgart/Dresden relativistic effective core potential for exploring the mechanisms of the reactions catalyzed by Pd(PPh3)4. Based on the obtained free energy curves, energetic span analyses were carried out. The calculated results show that both reactions go through three steps: (1) Pd(PH3)2 catalyst oxidatively added to methylenecyclopropanes, in which Pd inserted into the distal carbon-carbon bond of methylenecyclopropanes ternary ring to form palladium cyclobutane intermediate; (2) six-membered oxa-metal ring compounds were formed by stepwise additions of palladium cyclobutane intermediate with the carbonyl of furan formaldehyde; (3) Pd(PH3)2 catalyst dissociates from the six-membered oxy-hetero-metal ring compound through reductive elimination, and the five-membered-ring final products, methylene tetrahydrofurans were obtained. In addition, with the energetic span model proposed by Kozuch and Shaik, the calculated turnover frequency (TOF)-determining transition states (TDTS) for both catalytic cycles with R=Me/H are the same as the transition state (TS) of the reductive elimination step, however the TOF-determining intermediate (TDI) in each catalytic cycle is different from each other. As a result, the apparent free energy barrier (energetic span, δE) for the catalytic cycle with R=Me is 9.5 kJ/mol lower than that for the catalytic cycle with R=H, and the estimated TOF at 120 ℃ for the catalytic cycle with R=Me is ca 18 times larger than that for the catalytic cycle with R=H. These indicate that Pd(PPh3)4 is more effective for catalytic cycle with R=Me, which accounts well for the previous experimental observation that the yield for the reaction with R=Me is much higher than that for the reaction with R=H under the catalysis of Pd(PPh3)4 at 120 ℃.

Key words: methylenecyclopropanes, [3+2] cycloaddition, reaction mechanism, density functional theory (DFT), tetrahydrofuran, turnover frequency (TOF), rate-determining state, energetic span