Department of Chemical and Biological Engineering , University of Colorado , Boulder , Colorado 80309 , United States.
Department of Chemistry , University of Colorado , Boulder , Colorado 80309 , United States.
J Am Chem Soc. 2019 Jan 9;141(1):272-280. doi: 10.1021/jacs.8b09653. Epub 2018 Dec 10.
We report a novel metal-free chemical reduction of CO by a recyclable benzimidazole-based organo-hydride, whose choice was guided by quantum chemical calculations. Notably, benzimidazole-based hydride donors rival the hydride-donating abilities of noble-metal-based hydrides such as [Ru(tpy)(bpy)H] and [Pt(depe)H]. Chemical CO reduction to the formate anion (HCOO) was carried out in the absence of biological enzymes, a sacrificial Lewis acid, or a base to activate the substrate or reductant. CO experiments confirmed the formation of HCOO by CO reduction with the formate product characterized by H NMR and C NMR spectroscopy and ESI-MS. The highest formate yield of 66% was obtained in the presence of potassium tetrafluoroborate under mild conditions. The likely role of exogenous salt additives in this reaction is to stabilize and shift the equilibrium toward the ionic products. After CO reduction, the benzimidazole-based hydride donor was quantitatively oxidized to its aromatic benzimidazolium cation, establishing its recyclability. In addition, we electrochemically reduced the benzimidazolium cation to its organo-hydride form in quantitative yield, demonstrating its potential for electrocatalytic CO reduction. These results serve as a proof of concept for the electrocatalytic reduction of CO by sustainable, recyclable, and metal-free organo-hydrides.
我们报告了一种新型的无金属 CO 化学还原方法，使用可回收的苯并咪唑基有机氢化物，其选择是通过量子化学计算指导的。值得注意的是，苯并咪唑基氢化物供体与贵金属基氢化物（如[Ru(tpy)(bpy)H]和[Pt(depe)H]）的供氢能力相当。在没有生物酶、牺牲路易斯酸或碱来激活底物或还原剂的情况下，进行了 CO 的化学还原，生成了甲酸盐阴离子（HCOO）。通过 CO 还原实验证实了 HCOO 的形成，HCOO 的产物通过 H NMR 和 C NMR 光谱和 ESI-MS 进行了表征。在温和条件下，存在四氟硼酸钾时，甲酸盐的产率最高可达 66%。外源性盐添加剂在该反应中的可能作用是稳定并将平衡向离子产物转移。CO 还原后，苯并咪唑基氢化物供体被定量氧化为其芳香苯并咪唑翁阳离子，从而证明了其可回收性。此外，我们在定量产率下通过电化学还原将苯并咪唑翁阳离子还原为其有机氢化物形式，证明了其在电催化 CO 还原中的潜力。这些结果为可持续、可回收和无金属的有机氢化物电催化还原 CO 提供了概念验证。
