Yang Yong, Zhang Zhenyu, Chang Xiaoyong, Zhang Ya-Qiong, Liao Rong-Zhen, Duan Lele
Department of Chemistry, Southern University of Science and Technology (SUSTech), Shenzhen 518055, P. R. China.
Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, P. R. China.
Inorg Chem. 2020 Jul 20;59(14):10234-10242. doi: 10.1021/acs.inorgchem.0c01364. Epub 2020 Jun 25.
Because of the strong σ-donor and weak π-acceptor of the N-heterocyclic carbene (NHC), Mn-NHC complexes were found to be active for the reduction of CO to CO with high activity. However, some NHC-based manganese complexes showed low catalytic activity and required very negative potentials. We report herein that complex -[Mn(bis-NHC)(CO)Br] [; bis-NHC = 3,3-bis(2,4,6-trimethylphenyl)-(1,1'-diimidazolin-2,2'-diylidene)methane] could catalyze the electrochemical reduction of CO to CO with high activity (TOF = 3180 ± 6 s) at a less negative potential. Due to the introduction of the bulky Mes groups, a one-electron-reduced intermediate {[Mn(bis-NHC)(CO)] ()} was isolated as a packed "dimer" and crystallographically characterized. Stopped-flow Fourier-transform infrared spectroscopy was used to prove the direct reaction between doubly reduced intermediate -[Mn(bis-NHC)(CO)] and CO; the tetracarbonyl Mn complex [Mn(bis-NHC)(CO)] ([-CO]) was captured, and its further reduction proposed as the rate-limiting step.
由于氮杂环卡宾（NHC）具有强σ供体和弱π受体特性，发现锰-氮杂环卡宾配合物对将CO还原为CO具有高活性。然而，一些基于NHC的锰配合物显示出低催化活性且需要非常负的电位。我们在此报告，配合物-[Mn（双-NHC）（CO）Br] [；双-NHC = 3,3-双（2,4,6-三甲基苯基）-（1,1'-二咪唑啉-2,2'-二亚基）甲烷]能够在较低的负电位下以高活性（TOF = 3180 ± 6 s）催化CO的电化学还原为CO。由于引入了庞大的Mes基团，一种单电子还原中间体{[Mn（双-NHC）（CO）]（）}被分离为堆积的“二聚体”并通过晶体学进行了表征。采用停流傅里叶变换红外光谱法证明了双还原中间体-[Mn（双-NHC）（CO）]与CO之间的直接反应；捕获了四羰基锰配合物[Mn（双-NHC）（CO）]（[-CO]），并提出其进一步还原为限速步骤。
