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Catalytic Mechanisms of Transfer Hydrogenation of Azobenzene with Ammonia Borane by Pincer Bismuth Complex: Crucial Role of C=N Functional Group on the Pincer Ligand |
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| Authors: | Qin Zhu Shuoqi Zhang Prof. Dr. Jing Ma Prof. Dr. Jun Zhu Prof. Dr. Shuhua Li Prof. Dr. Guixiang Zeng |
| Affiliation: | 1. 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 State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChem), Fujian Provincial Key Laboratory of Theoretical Computational Chemistry and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005 P. R. China;2. Kuang Yaming Honors School, Nanjing University, Nanjing, 210093 P. R. China;3. 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;4. State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChem), Fujian Provincial Key Laboratory of Theoretical Computational Chemistry and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005 P. R. China |
| Abstract: | 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 3CN , 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. 3CN 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. |
| Keywords: | Ammonia borane Bismuth Density functional theory Metal-ligand cooperation Transfer hydrogenation |