Thioether–NHC‐Ligated PdII Complex for Crafting a Filtration‐Free Magnetically Retrievable Catalyst for Suzuki–Miyaura Coupling in Water
Thioether–NHC‐Ligated PdII Complex for Crafting a Filtration‐Free Magnetically Retrievable Catalyst for Suzuki–Miyaura Coupling in Water
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DOI：
10.1002/ejic.201800209
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发表时间：
2018-04
影响因子：
2.3
通讯作者：
K. Sharma;N. Satrawala;R. Joshi
中科院分区：
文献类型：
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作者：
K. Sharma;N. Satrawala;R. Joshi
以1 H-苯并咪唑为原料，依次与1，2-二氯乙烷、硫酚钠和N-苄基-2-氯乙酰胺反应，合成了一种新型的苯并咪唑盐1-[苄氨基羰基甲基]-3-（2-苯硫基乙基）-1H-苯并咪唑氯化物（L），它是一种新型硫醚官能化NHC的前体。通过L与PdCl 2反应制备了对水分/空气不敏感的配合物[Pd（L-HCl）Cl 2]（1）。通过X射线晶体学建立的1的分子结构显示了Pd周围的正方形平面几何形状。对配合物1进行了筛选，并用于室温下不同芳基/杂芳基溴化物在水中的Suzuki-Miyaura偶联反应（2 h内产率高达94%）。此外，通过逐步修饰策略将络合物1固定到氨丙基官能化的二氧化硅包覆的磁铁矿纳米颗粒[NPs，Fe3O4@SiO2-（CH 2）3-NH 2]的表面上，以开发非均相磁回收催化剂Fe3O4@SiO2 - 1′，其中NHC-PdII络合物中NHC侧臂中存在的酰胺官能团作为连接体。这种磁性纳米载体带有钯络合物，该钯络合物结合了新型硫醚基NHC配体，该配体在水性需氧介质中起作用并且可以容易地分离，使得Fe3O4@SiO2 - 1′成为Suzuki-Miyaura偶联反应最理想的催化剂。还观察到，催化剂在多达七个循环中是有效的，并且通过使用外部磁体容易地从反应介质中分离，进一步增加了其吸引力。
A new benzimidazolium salt, 1‐[benzylaminocarbonylmethyl]‐3‐(2‐phenylsulfanylethyl)‐1H‐benzimidazolium chloride (L), which is a precursor of a novel thioether‐functionalized NHC, has been synthesized by subjecting 1H‐benzimidazole to a sequence of reactions with 1,2‐dichloroethane, sodium thiophenolate, andN‐benzyl‐2‐chloroacetamide, successively. The moisture/air‐insensitive complex [Pd(L–HCl)Cl2] (1) was prepared by the reaction ofLwith PdCl2. The molecular structure of1, established by X‐ray crystallography, revealed a square‐planar geometry around Pd. Complex1was screened for Suzuki–Miyaura coupling reactions of various aryl/heteroaryl bromides (yields of up to 94 % in 2 h) in water at room temperature. Furthermore, complex1was immobilized onto the surface of aminopropyl‐functionalized silica‐coated magnetite nanoparticles [NPs, Fe3O4@SiO2‐(CH2)3‐NH2] by a stepwise modification strategy to develop the heterogeneous magnetically retrievable catalyst Fe3O4@SiO2‐1′, in which the amide functionality present in the side‐arm of the NHC within the NHC–PdIIcomplex serves as linker. This magnetic nanosupport, bearing palladium complexes incorporating a novel thioether‐based NHC ligand that functions in aqueous aerobic medium and can be easily separated, renders Fe3O4@SiO2‐1′a most desirable catalyst for the Suzuki–Miyaura coupling reaction. It was also observed that the catalyst was effective for up to seven cycles and was easily separated from the reaction medium by the use of an external magnet, further increasing its appeal.