Chin. J. Org. Chem. ›› 2017, Vol. 37 ›› Issue (5): 1231-1236.DOI: 10.6023/cjoc201701033 Previous Articles     Next Articles

Reviews

碱土金属催化碳二亚胺硼氢化反应机理的理论研究

徐冬冬, 单春晖, 白若鹏, 蓝宇   

  1. 重庆大学化学化工学院 重庆 400044
  • 收稿日期:2017-01-16 修回日期:2017-02-24 出版日期:2017-05-25 发布日期:2017-03-03
  • 通讯作者: 白若鹏,蓝宇 E-mail:ruopeng@cqu.edu.cn;lanyu@cqu.edu.cn
  • 基金资助:

    国家自然科学基金(No.21372266)资助项目.

Mechanism of Alkaline Earth Metal Catalyzed Hydroboration of Carbodiimides: A Theoretical Study

Xu Dongdong, Shan Chunhui, Bai Ruopeng, Lan Yu   

  1. School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030
  • Received:2017-01-16 Revised:2017-02-24 Online:2017-05-25 Published:2017-03-03
  • Contact: 10.6023/cjoc201701033 E-mail:ruopeng@cqu.edu.cn;lanyu@cqu.edu.cn
  • Supported by:

    Project supported by the National Natural Science Foundation of China (No. 21372266).

Density functional theory (DFT) calculations are employed to study the mechanism of alkaline earth metal catalyzed hydroboration of carbodiimides. Our theoretical study revealed that the active catalytic species is a hydridemagnesium complex when magnesium is used as catalyst. The catalytic cycle starts with a C=N bond insertion into Mg-H bond followed by a B-N bond formation. A hydride transfer from boron to magnesium regenerates the active catalytic species and yields the hydroboration product. This process is considered to be the rate-determining step. Moreover, the mechanism of calcium or strontium catalyzed corresponding reactions was also studied theoretically. Alternatively, DFT calculations showed that the active catalytic species is amide-metal complex, which could be generated by the carbodiimide insertion into metal-hydride bond. In this catalytic cycle, amide-metal complex reacts with borane to form a B-N bond. After the coordination of another molecular carbodiimide, a concerted hydride transfer takes place from boron to carbon, which yields the final product and regenerates the active species amide-metal. The different reaction pathway with calcium or strontium catalyzed corresponding reactions could be attributed to that the radius of calcium or strontium is larger than that of magnesium significantly. Thus, those two metals would be coordinated with an extra carbodiimide molecule, which is the precursor for the concerted hydride transfer. The DFT calculations showed that the activation free energy for the rate-determining step with calcium or strontium catalyst is much lower than that with magnesium catalyst. Therefore, a mild reaction condition might be found with calcium or strontium as catalyst for corresponding reactions.

Key words: alkaline earth metal catalysis, density functional theory, mechanistic study, hydroboration