A New Mode of Operation of Pd-NHC Systems Studied in a Catalytic Mizoroki–Heck Reaction
摘要:
Metal complexes bearing N-heterocyclic carbene (NHC) ligands are typically considered the system of choice for homogeneous catalysis with well-defined molecular active species due to their stable metal ligand framework. A detailed study involving 19 different Pd-NHC complexes with imidazolium, benzimidazolium, and triazolium ligands has been carried out in the present work and revealed a new mode of operation of metal-NHC systems. The catalytic activity of the studied Pd-NHC systems is predominantly determined by the cleavage of the metal NHC bond, while the catalyst performance is strongly affected by the stabilization of in situ formed metal clusters. In the present study, the formation of Pd nanopartides was observed from a broad range of metal complexes with NHC ligands under standard Mizoroki-Heck reaction conditions. A mechanistic analysis revealed two different pathways to connect Pd-NHC complexes to "cocktail"-type catalysis: (i) reductive elimination from a Pd(II) intermediate and the release of NHC-containing byproducts and (ii) dissociation of NHC ligands from Pd intermediates. Metal-NHC systems are ubiquitously applied in modern organic synthesis and catalysis, while the new mode of operation revealed in the present study guides catalyst design and opens a variety of novel opportunities. As shown by experimental studies and theoretical calculations, metal dusters and nanopartides can be readily formed from M-NHC complexes after formation of new M-C or M-H bonds followed by C-NHC or H-NHC coupling. Thus, a combination of a classical molecular mode of operation and a novel cocktail-type mode of operation, described in the present study, may be anticipated as an intrinsic feature of M-NHC catalytic systems.
摘要 新型有机非金属电催化剂代表1,3-二甲基-2-苯基-1H-苯并[ d ]咪唑鎓-3碘化物( I )在生成反应中的电化学性能和电催化活性研究了在不同强度的酸(甲磺酸(CH 3 SO 3 H)、高氯酸(HClO 4)和三氟乙酸(CF 3 COOH))存在下分子氢的形成。结果表明,电催化过程的效率很大程度上取决于 p Ka所用的酸。使用气相色谱法和半波电位下的制备电解,结果表明在所有情况下形成的分子氢均具有高法拉第产率。在所有酸存在的情况下,在各种酸和催化剂浓度比例下,循环伏安图(CV)上催化波的行为对于根据均相机理进行的过程来说是典型的。采用密度泛函方法(DFT)研究了该过程的机理,并鉴定了其主要中间体。化合物I的C-2碳原子处电化学产生的自由基的质子化,以及C-质子化自由基阳离子的形成,被证明是电催化析氢反应(HER)的关键阶段。
biologically active benzimidazole ring. Some benzimidazolium salts and their metal complexes, containing different groups, showed remarkable antibacterial, antifungal and antitumor effects. Most of these studies are generally related with the 2-unsubstituted derivatives of benzimidazolium salts which named as N-heterocyclic carbenes (NHCs). To enhance the efficacy of the benzimidazoles in the biological
Visible light-mediated metal-free double bond deuteration of substituted phenylalkenes
作者:Roman Iakovenko、Jan Hlaváč
DOI:10.1039/d0gc03081c
日期:——
Photoactivated metal free deuteration of a double bond was developed in an environmentally friendly manner.
双键的光活化金属无氘化反应以环境友好的方式进行了开发。
Cu-catalyzed controllable C–H mono-/di-/triarylations of imidazolium salts for ionic functional materials
作者:Shiqing Li、Junbin Tang、Yinsong Zhao、Ruyong Jiang、Tianbao Wang、Ge Gao、Jingsong You
DOI:10.1039/c7cc01076a
日期:——
The first Cu-catalyzed direct C-H mono-, di- and triarylations of imidazolium salts with aryl iodides/bromides are reported.
据报道,咪唑鎓盐与芳基碘化物/溴化物的第一个Cu催化的直接CH直接单,二和三芳基化反应。
Ionic Pd/NHC Catalytic System Enables Recoverable Homogeneous Catalysis: Mechanistic Study and Application in the Mizoroki–Heck Reaction
作者:Dmitry B. Eremin、Ekaterina A. Denisova、Alexander Yu. Kostyukovich、Jonathan Martens、Giel Berden、Jos Oomens、Victor N. Khrustalev、Victor M. Chernyshev、Valentine P. Ananikov
DOI:10.1002/chem.201903221
日期:2019.12.20
concentrations. The present study reveals a dynamic stabilization mechanism with labile metal-NHC binding and [PdX3 ]- [NHC-R]+ ion pair formation. Access to reactive anionic palladium intermediates formed by dissociation of the NHC ligands and plausible stabilization of the molecular catalyst in solution by interaction with the [NHC-R]+ azolium ion is of particular importance for an efficient and recyclable catalyst
Poly(phenylene) and <i>m</i>
-Terphenyl as Powerful Protecting Groups for the Preparation of Stable Organic Hydroxides
作者:Andrew G. Wright、Thomas Weissbach、Steven Holdcroft
DOI:10.1002/anie.201511184
日期:2016.4.4
benzimidazolium hydroxide compounds, in which the C2‐position is attached to a phenyl group possessing hydrogen, bromine, methyl groups, or phenyl groups at the ortho positions, are prepared and investigated for stability in a quantitative alkaline stability test. The differences between the stability of the various protectinggroups in caustic solutions are rationalized on the basis of their crystal structures
制备了四种苯并咪唑鎓氢氧化物,其中C2-位连接在邻位具有氢,溴,甲基或苯基的苯基上,并通过定量碱性稳定性试验研究了其稳定性。苛性溶液中各种保护基的稳定性之间的差异根据其晶体结构和DFT计算得以合理化。观察到的最高稳定性米-三联苯保护苯并咪唑,示出了3半衰期 米NaOD / CD 3 OD / d 2O在80°C下3240小时。制备了该模型化合物的高分子量聚合物类似物,该化合物具有出色的机械性能,高离子电导率和离子交换能力,并在碱性溶液中具有显着的氢氧化物稳定性:在2 m KOH中168 h后仅降解5% 在80°C下。这是迄今为止最稳定的传导氢氧化物的苯并咪唑聚合物。