Luo Chenguang, Li Longfei, Yue Xin, Li Pengjie, Zhang Lin, Yang Zuoyin, Pu Min, Cao Zexing, Lei Ming
State Key Laboratory of Chemical Resource Engineering, Institute of Computational Chemistry, College of Chemistry, Beijing University of Chemical Technology Beijing 100029 China
College of Pharmaceutical Science, Hebei University Baoding 071002 China.
RSC Adv. 2020 Mar 11;10(18):10411-10419. doi: 10.1039/c9ra10651k.
The reaction mechanism of the pH-dependent transfer hydrogenation of a ketone or the dehydrogenation of formic acid catalyzed by a [(η-arene)RuCl(κ-,-dmobpy)] complex in aqueous media has been investigated using the density functional theory (DFT) method. The TM-catalyzed TH of ketones with formic acid as the hydrogen source proceeds two steps: the formation of a metal hydride and the transfer of the hydride to the substrate ketone. The calculated results show that ruthenium hydride formation is the rate-determining step. This proceeds an ion-pair mechanism with an energy barrier of 14.1 kcal mol. Interestingly, the dihydrogen release process of formic acid and the hydride transfer process that produces alcohols are competitive under different pH environments. The investigation explores the feasibility of the two pathways under different pH environments. Under acidic conditions (pH = 4), the free energy barrier of the dihydrogen release pathway is 4.5 kcal mol that is higher than that of the hydride transfer pathway, suggesting that the hydride transfer pathway is more favorable than the dihydrogen release pathway. However, under strongly acidic conditions, the dihydrogen release pathway is more favorable compared to the hydride transfer pathway. In addition, the ruthenium hydride formation pathway is less favorable than the ruthenium hydroxo complex formation pathway under basic conditions.
采用密度泛函理论（DFT）方法研究了[(η-芳烃)RuCl(κ-，-dmobpy)]配合物在水介质中催化酮的pH依赖性转移氢化反应或甲酸脱氢反应的机理。以甲酸为氢源，TM催化的酮的转移氢化反应分两步进行：金属氢化物的形成以及氢化物向底物酮的转移。计算结果表明，氢化钌的形成是速率决定步骤。这一过程通过离子对机理进行，能垒为14.1 kcal/mol。有趣的是，在不同的pH环境下，甲酸的二氢释放过程和生成醇的氢化物转移过程是相互竞争的。该研究探讨了在不同pH环境下这两条途径的可行性。在酸性条件（pH = 4）下，二氢释放途径的自由能垒为4.5 kcal/mol，高于氢化物转移途径，这表明氢化物转移途径比二氢释放途径更有利。然而，在强酸性条件下，与氢化物转移途径相比，二氢释放途径更有利。此外，在碱性条件下，氢化钌的形成途径不如氢氧化钌配合物的形成途径有利。
