锰配合物催化CO2加氢生成甲酸的理论研究

Theoretical Study on Mechanism of CO2 Hydrogenation to Formic Acid Catalyzed by Manganese Complex

采用密度泛函理论(DFT)对锰配合物催化二氧化碳加氢生成甲酸的反应进行了理论研究.整个催化循环主要包括氢气活化和二氧化碳氢化2个阶段.计算结果表明,甲酸的参与明显降低了氢气活化的反应能垒;二氧化碳的氢化过程遵循外层机理并且氢转移是分步进行的,决速步骤为氢负离子的转移过程,自由能垒为21.0 kJ/mol.对配合物中硫原子上的取代基R进行了调变,研究结果表明,当R为吸电子基团时能降低氢气裂解和二氧化碳氢化过程中质子转移的能垒,而当R为推电子基团时有利于氢负离子的转移,当R=CF3时整个反应的能量跨度(80.4 kJ/mol)最小.

Density functional theory(DFT) was used to study the mechanism of carbon dioxide hydrogenation to formic acid catalyzed by manganese complex. The whole catalytic cycle mainly includes two stages of hydrogen activation and carbon dioxide hydrogenation. The calculation results show that the participation of formic acid significantly reduces the reaction energy barrier of hydrogen activation. The hydrogenation process of carbon dioxide follows the outer-sphere mechanism and hydrogen transfer is a stepwise process, in which the hydride transfer is the rate-determining step, with an energy barrier of 21.0 kJ/mol. In addition, the modulation effect of R group on S atom was explored. The results show that when R is an electron-withdrawing group, it can reduce the activation barriers of hydrogen cracking and proton transfer during carbon dioxide hydrogenation. The transfer of hydride is facilitated when the R group is an electron-donating group. When R=CF 3 , the energy span of the whole reaction is the smallest, which is 80.4 kJ/mol.