Kathuria Lakshay, Din Reshi Noor U, Samuelson Ashoka G
Inorganic and Physical Chemistry Department, Indian Institute of Science, Bangalore, Karnataka, 560012, India.
Chemistry. 2020 Jun 18;26(34):7622-7630. doi: 10.1002/chem.202000142. Epub 2020 May 20.
Tethered and untethered ruthenium half-sandwich complexes were synthesized and characterized spectroscopically. X-ray crystallographic analysis of three untethered and two tethered Ru N-heterocyclic carbene (NHC) complexes were also carried out. These RuNHC complexes catalyze transfer hydrogenation of aromatic ketones in 2-propanol under reflux, optimally in the presence of (25 mol %) KOH. Under these conditions, the formation of 2-3 nm-sized Ru nanoparticles was detected by TEM measurements. A solid-state NMR investigation of the nanoparticles suggested that the NHC ligands were bound to the surface of the Ru nanoparticles (NPs). This base-promoted route to NHC-stabilized ruthenium nanoparticles directly from arene-tethered ruthenium-NHC complexes and from untethered ruthenium-NHC complexes is more convenient than previously known routes to NHC-stabilized Ru nanocatalysts. Similar catalytically active RuNPs were also generated from the reaction of a mixture of [RuCl (p-cymene)] and the NHC precursor with KOH in isopropanol under reflux. The transfer hydrogenation catalyzed by these NHC-stabilized RuNPs possess a high turnover number. The catalytic efficiency was significantly reduced if nanoparticles were exposed to air or allowed to aggregate and precipitate by cooling the reaction mixtures during the reaction.
合成了键连和非键连的钌半三明治配合物，并通过光谱对其进行了表征。还对三种非键连和两种键连的钌N-杂环卡宾（NHC）配合物进行了X射线晶体学分析。这些RuNHC配合物在回流条件下于2-丙醇中催化芳香酮的转移氢化反应，最佳条件是存在（25 mol %）的KOH。在这些条件下，通过透射电子显微镜（TEM）测量检测到形成了尺寸为2 - 3 nm的钌纳米颗粒。对纳米颗粒的固态核磁共振研究表明，NHC配体与钌纳米颗粒（NPs）的表面结合。这种从芳烃键连的钌-NHC配合物和非键连的钌-NHC配合物直接制备NHC稳定的钌纳米颗粒的碱促进途径比先前已知的制备NHC稳定的钌纳米催化剂的途径更方便。在回流条件下，[RuCl (对异丙基苯)]和NHC前体的混合物与KOH在异丙醇中反应也生成了类似的具有催化活性的RuNPs。这些NHC稳定的RuNPs催化的转移氢化反应具有高周转数。如果在反应过程中纳米颗粒暴露于空气中或通过冷却反应混合物使其聚集和沉淀，则催化效率会显著降低。
