Six new N-heterocyclic carbene (NHC) ligands bearing long-chain alkyl groups on N-atom of 5,6-dimethylbenzimidazole skeleton and their Pd(II) complexes (PEPPSI type) with a close formula of trans-[PdX₂(NHC)Py] (X = Cl or Br; Py = pyridine) were successfully synthesized. The yielded NHC ligands and their Pd(II) complexes were characterized by elemental analysis, ¹H- and ¹³C NMR, FT-IR spectroscopy, and mass spectroscopy and the molecular structure of 3f was determined by X-ray crystallography. All synthesized NHC-Pd(II) complexes were air-stable both as powder and in solution under ambient conditions, which allow us to test them as catalysts in Suzuki-Miyaura cross-coupling (SMC) reactions and to use them as precursors for the in situ synthesis of NHC-stabilized Pd(0) nanoparticles (NPs) during the dehydrogenation of ammonia borane (AB) in dry tetrahydrofuran solution at room temperature. In this protocol, AB served both as a reducing agent for the reduction of NHC-Pd(II) complexes to yield NHC-stabilized Pd(0) NPs and a chemical hydrogen storage material for the concomitant hydrogen generation. The in situ synthesized NHC-stabilized Pd(0) NPs were characterized by UV–Vis spectroscopy, TEM, and XRD techniques. The catalytic activity of the in situ generated NHC-stabilized Pd(0) NPs in the dehydrogenation of AB was followed by measuring the volume of hydrogen generated versus time at room temperature. Among the five different NHC-Pd(II) complexes, 3c (dichloro[1-octadesyl-3-(2,4,6-trimethylbenzyl)-(5,6-dimethylbenzimidazol-2-ylidene)](pyridine)palladium(II)) yielded the most stable Pd(0) NPs along with the highest catalytic activity in the dehydrogenation of AB (TOF= 37.7 min⁻¹ at 1 eqv. H₂ release). The ¹¹B-NMR analysis of the THF solution after the catalytic dehydrogenation of AB revealed the formation of cyclopolyborazane, which is one of the important dehydrocoupling products of AB. Additionally, all NHC-Pd(II) complexes provided high yields in the SMC reactions of phenylboronic acid with various aryl bromides bearing electron-withdrawing or electron-donating groups and even for aryl chlorides bearing electron-withdrawing group at room temperature with the low catalyst loadings. This study revealed that the length of the alkyl chain of NHC ligands has a significant effect on the catalytic activity of the NHC-Pd(II) complexes in the SMC reactions, the longer the alkyl chain on the N atom of NHC ligand, the higher activity of NHC-Pd(II) complex in SMC reactions. It also influences the particle size, morphology and catalytic activity of in situ generated Pd(0) NPs in the dehydrogenation of AB.

六个新的N-杂环卡宾（NHC）配体，它们在5,6-二甲基苯并咪唑骨架的N原子上带有长链烷基，并具有近似于反式-[PdX ₂（NHC ）的Pd（II）配合物[Py]（X  = Cl或Br； Py =吡啶）已成功合成。通过元素分析，¹ H和¹³ C NMR，FT-IR光谱，质谱和3f的分子结构表征了生成的NHC配体及其Pd（II）配合物通过X射线晶体学测定。所有合成的NHC-Pd（II）配合物在环境条件下均呈粉末和溶液形式均在空气中稳定，这使我们能够将其作为Suzuki-Miyaura交叉偶联（SMC）反应的催化剂进行测试，并用作前体在室温下在干燥的四氢呋喃溶液中氨硼烷（AB）脱氢过程中原位合成NHC稳定的Pd（0）纳米颗粒（NPs）。在该协议中，AB既用作还原NHC-Pd（II）络合物以产生NHC稳定的Pd（0）NP的还原剂，又用作化学氢存储材料，用于同时产生氢。原位合成的NHC稳定的Pd（0）NPs通过UV-Vis光谱，TEM和XRD技术进行了表征。在AB的脱氢中原位生成的NHC稳定的Pd（0）NPs的催化活性随后是在室温下测量氢气随时间变化的量。在五种不同的NHC-Pd（II）配合物中，3c（二氯[1-十八烷基-3-（2,4,6-三甲基苄基）-（5,6-二甲基苯并咪唑-2-亚基）]（吡啶）钯（II））产生最稳定的Pd（0）NPs在AB脱氢中具有最高的催化活性（在1 eqv。H ₂释放下，TOF = 37.7 min ^-1）。在¹¹AB催化脱氢后的THF溶液的B-NMR分析表明形成了环聚硼氮烷，这是AB的重要脱氢偶联产物之一。另外，所有NHC-Pd（II）配合物在苯基硼酸与各种带有吸电子或给电子基团的芳基溴化物的SMC反应中，甚至对于室温下带有低吸催化剂的带有吸电子基团的芳基氯化物，都能在SMC反应中提供高收率。加载。这项研究表明，NHC配体的烷基链长度对SMC反应中NHC-Pd（II）配合物的催化活性有显着影响，NHC配体的N原子上的烷基链越长， NHC-Pd（II）配合物在SMC反应中的活性 它也会影响粒径