Palladium(II) Complexes of N-Heterocyclic Carbene Amidates Derived from Chalcogenated Acetamide-Functionalized 1H-Benzimidazolium Salts: Recyclable Catalyst for Regioselective Arylation of Imidazoles under Aerobic Conditions
Palladium(II) Complexes of N-Heterocyclic Carbene Amidates Derived from Chalcogenated Acetamide-Functionalized 1H-Benzimidazolium Salts: Recyclable Catalyst for Regioselective Arylation of Imidazoles under Aerobic Conditions
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DOI：
10.1021/acs.organomet.8b00246
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发表时间：
2018-08-27
期刊：
影响因子：
2.8
通讯作者：
Singh, Ajai K.
中科院分区：
文献类型：
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作者：
Bhaskar, Renu;Sharma, Alpesh K.;Singh, Ajai K.
硫族化的乙酰胺官能化的1H-苯并咪唑鎓盐前体[1-（CH 2C（O）NH（CH 2）（2）S/ SePh）-3-R-C7 H5 N2]（+）（X）在bar上（L1-L4; R = Me，CH 2Ph;以2-溴代-N-苯并咪唑为原料，通过反应合成了一系列含C、N、S/Se的配体。（2-苯硫基/硒基）乙基）乙酰胺（Al/A2），然后用甲基/苄基溴/碘处理。L1-L4与Ag 2 O反应，然后用[Pd（CH 3CN）（2）Cl-2]处理，得到络合物[Pd（C，N，E）Cl]（C1-C4），其中C，N-，E钳形配体衍生自L1-IA。L1-L4和C1-C4通过元素分析、HR-MS和H-1、C-13{H-1}和Se-77{H-1} NMR光谱表征。用X射线衍射建立的L2和C1-C3的单晶结构揭示钯的几何形状为近似正方形平面，并且NHC环的排列为近似垂直于Pd的配位平面。在C1-C3中，Pd-C键距在1.974（5）-1.982（2）埃的范围内。C1和C3的Pd-S键长分别为2.369（10）和2.357（7）埃。在C2中，Pd-Se键距为2.464（7）埃。C1-C4可以在环境条件下储存数月而不分解，表明它们对空气和水分不敏感。配合物C1-C4在有氧条件下均能有效地进行咪唑类化合物的区域选择性C-5芳基化反应。对于良好的转化率，发现最佳催化剂负载量为0.5-1摩尔%。宽范围的ArCl/Br可以与本发明的催化剂一起使用。复合物C3和C4似乎比C1和C2更有效。类似地，含硒配体的络合物与其硫对应物相比作为催化剂更有效。C1-C4被发现可回收多达6次，用于咪唑的区域选择性芳基化，效率几乎没有降低。用X-射线单晶衍射法对咪唑与少量ArX的区域选择性芳基化反应产物进行了鉴定。
The chalcogenated acetamide-functionalized 1H-benzimidazolium salt precursors [1-(CH2C(O)NH(CH2)(2)S/ SePh)-3-R-C7H5N2](+) (X) over bar (LI-L4; R = Me, CH2Ph; X = Br, I) to C,N,S/Se ligands were synthesized by reaction of 1Hbenzimidazole with 2-bromo-N-(2-phenylthio/seleno)ethyl)acetamide (Al/A2), followed by treatment with methyl/benzyl bromide/iodide. The reaction of Ll-L4 with Ag20 followed by treatment with [Pd(CH3CN)(2)Cl-2] resulted in complexes [Pd(C,N,E)Cl] (C1-C4), where the C,N-,E pincer ligand was derived from L1-IA. Ll-L4 and C1-C4 were characterized by elemental analyses, HR-MS, and H-1, C-13{H-1}, and Se-77{H-1} NMR spectroscopy. Single-crystal structures of L2 and CI-C3 established with X-ray diffraction reveal the geometry of palladium as being nearly square planar and alignment of NHC rings as being nearly perpendicular to the coordination plane of Pd. In C1-C3 the Pd-C bond distances are in the range 1.974(5)1.982(2) angstrom. The Pd-S bond lengths for Cl and C3 are 2.369(10) and 2.357(7) angstrom, respectively. In C2, the Pd-Se bond distance is 2.464(7) angstrom. C1-C4 can be stored under ambient conditions for several months without decomposition, indicating their air and moisture insensitivity. Complexes C1-C4 were all found to be efficient for regioselective C-5 arylation of imidazoles under aerobic conditions. The optimum catalyst loading for good conversion was found to be 0.5-1 mol %. A wide range of ArCl/Br can be used with the present catalysts. Complexes C3 and C4 appear to be more efficient than C1 and C2. Similarly the complexes of selenium-containing ligands are more efficient as catalysts in comparison to their sulfur counterparts. C1-C4 were found to be recyclable up to six times for regioselective arylation of imidazole with very little decrease in efficiency. The products of regioselective arylation of imidazole with few ArX were identified by X-ray diffraction on their single crystals.