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Secondary Coordination Effect on Monobipyridyl Ru(II) Catalysts in Photochemical CO2 Reduction: Effective Proton Shuttle of Pendant Brønsted Acid/Base Sites (OH and N(CH3)2) and Its Mechanistic Investigation
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2021-09-02 , DOI: 10.1021/acs.inorgchem.1c01559
Changhyun Back 1 , Yunjeong Seo 1 , Sunghan Choi 1 , Min Su Choe 1 , Daehan Lee 1 , Jin-Ook Baeg 2 , Ho-Jin Son 1 , Sang Ook Kang 1
Affiliation  

While the incorporation of pendant Brønsted acid/base sites in the secondary coordination sphere is a promising and effective strategy to increase the catalytic performance and product selectivity in organometallic catalysis for CO2 reduction, the control of product selectivity still faces a great challenge. Herein, we report two new trans(Cl)-[Ru(6-X-bpy)(CO)2Cl2] complexes functionalized with a saturated ethylene-linked functional group (bpy = 2,2′-bipyridine; X = −(CH2)2–OH or −(CH2)2–N(CH3)2) at the ortho(6)-position of bpy ligand, which are named Ru-bpyOH and Ru-bpydiMeN, respectively. In the series of photolysis experiments, compared to nontethered case, the asymmetric attachment of tethering ligand to the bpy ligand led to less efficient but more selective formate production with inactivation of CO2-to-CO conversion route during photoreaction. From a series of in situ FTIR analyses, it was found that the Ru–formate intermediates are stabilized by a highly probable hydrogen bonding between pendent proton donors (−diMeN+H or −OH) and the oxygen atom of metal-bound formate (RuI–OCHO···H–E–(CH2)2–, E = O or diMeN+). Under such conformation, the liberation of formate from the stabilized RuI–formate becomes less efficient compared to the nontethered case, consequently lowering the CO2-to-formate conversion activities during photoreaction. At the same time, such stabilization of Ru–formate species prevents the dehydration reaction route (η1-OCHO → η1-COOH on Ru metal) which leads toward the generation of Ru–CO species (key intermediate for CO production), eventually leading to the reduction of CO2-to-CO conversion activity.

中文翻译:

光化学 CO2 还原中单联吡啶 Ru(II) 催化剂的二次配位效应:悬垂的 Brønsted 酸/碱位点(OH 和 N(CH3)2)的有效质子穿梭及其机理研究

虽然在二级配位球中加入布朗斯台德酸碱悬垂位点是提高有机金属催化 CO 2还原的催化性能和产物选择性的一种有前景且有效的策略,但产物选择性的控制仍面临巨大挑战。在此,我们报告了两种新的反式(Cl)-[Ru(6-X-bpy)(CO) 2 Cl 2 ] 复合物,它们被饱和的乙烯连接官能团(bpy = 2,2'-联吡啶;X = - (CH 2 ) 2 –OH 或 -(CH 2 ) 2 –N(CH 3 ) 2 ) 在bpy 配体的(6)-位,它们被命名为分别为 Ru-bpy OHRu-bpy diMeN。在一系列光解实验中,与非束缚的情况相比,束缚配体与 bpy 配体的不对称连接导致效率较低但更具选择性的甲酸盐生产,在光反应过程中 CO 2到 CO 的转化路线失活。从一系列原位FTIR 分析中发现,Ru-甲酸盐中间体通过悬垂质子供体(-diMeN + H 或 -OH)与金属结合甲酸盐(Ru I –OCHO……H– E –(CH 2 ) 2 –, E= O 或 diMeN + )。在这种构象下,与非束缚情况相比,从稳定的 Ru I -甲酸盐中释放甲酸盐的效率较低,因此降低了光反应过程中CO 2到甲酸盐的转化活性。同时,Ru-甲酸盐物种的这种稳定化阻止了脱水反应路线(η 1 -OCHO → η 1 -COOH 在 Ru 金属上),导致产生 Ru-CO 物种(CO 生产的关键中间体),最终导致 CO 2到 CO 的转化活性降低。
更新日期:2021-09-20
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