Kuang Yaming Honors School, Nanjing University, Nanjing, 210093, P. R. China.
School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing, 210093, P. R. China.
Chem Asian J. 2023 Jan 3;18(1):e202201069. doi: 10.1002/asia.202201069. Epub 2022 Dec 3.
Transfer hydrogenation of azobenzene with ammonia borane mediated by pincer bismuth complex 1 was systematically investigated through density functional theory calculations. An unusual metal-ligand cooperation mechanism was disclosed, in which the saturation/regeneration of the C=N functional group on the pincer ligand plays an essential role. The reaction is initiated by the hydrogenation of the C=N bond (saturation) with ammonia borane to afford 3 , which is the rate-determining step with Gibbs energy barrier (ΔG ) and Gibbs reaction energy (ΔG) of 25.6 and -7.3 kcal/mol, respectively. 3 is then converted to a Bi-H intermediate through a water-bridged pathway, which is followed up with the transfer hydrogenation of azobenzene to produce the final product N,N'-diphenylhydrazine and regenerate the catalyst. Finally, the catalyst could be improved by substituting the phenyl group for the tert-butyl group on the pincer ligand, where the ΔG value (rate-determining step) decreases to 24.0 kcal/mol.
通过密度泛函理论计算，系统研究了钳形铋配合物 1 介导的偶氮苯与氨硼烷的转移氢化反应。揭示了一种不寻常的金属-配体协同作用机制，其中钳形配体上的 C=N 官能团的饱和/再生起着至关重要的作用。反应由氨硼烷对 C=N 键的加氢（饱和）引发，生成 3 ，这是速率决定步骤，吉布斯能量势垒（ΔG）和吉布斯反应能（ΔG）分别为 25.6 和-7.3 kcal/mol。3 然后通过水桥途径转化为 Bi-H 中间体，随后进行偶氮苯的转移氢化，生成最终产物 N,N'-二苯基肼并再生催化剂。最后，通过将钳形配体上的苯基基团替换为叔丁基基团，可以改进催化剂，其中 ΔG 值（速率决定步骤）降低至 24.0 kcal/mol。
