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Fluorinated Unsymmetrical N,N’-Diaryl Imidazolium Salts—New Functionalized NHC-Ligand Precursors

机译:氟化非对称N,N'-二芳基咪唑鎓盐 - 新官能化NHC-配体前体

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摘要

An efficient and scaled-up synthesis of the imidazol- 2-ylidene-based unsymmetrical NHC precursors bearing the sterically demanding hexafluoroisopropylalkoxy group [(CF_3)_2(OR)C-] at the ortho position of the N-aryl substituent was developed. The key step of the method involved the transformation of a Mes-substituted oxazolinium tetrafluoroborate salt through the reaction with the corresponding binucleophilic fluoroalkyl-substituted aniline. The subsequent post-modification of the resulting hydroxyl-containing salt through a simple one-step O-alkylation protocol provided access to a new family of unsymmetrical fluorinated NHC precursors. These compounds were successfully utilized for the preparation of several novel metal complexes. The molecular structures of some NHC precursors and their metal complexes have been unambiguously characterized by single-crystal X-ray diffraction analysis. A preliminary evaluation of the catalytic activity of the palladium complexes was performed on a Buchwald–Hartwig amination reaction. As a result, two PEPPSI-type (PEPPSI=pyridine-enhanced precatalyst preparation stabilization and initiation) Pd complexes have demonstrated promising activity in alkane solvents.
机译:产生高效和缩小的基于甲基氟异丙烯烷氧基[(CF_3)_2(或)在N-芳基取代基的邻位的基于基于咪唑-2- ylidene的非对称NHC前体的合成。该方法的关键步骤涉及MES-取代的恶唑啉鎓四氟硼酸盐通过与相应的二核氟烷基烷基取代的苯胺的反应转化。随后通过简单的单步O-烷基化方案进行所得含羟基盐的后改性,提供了对新的非对称氟化NHC前体的新系列。这些化合物已成功用于制备几种新型金属配合物。一些NHC前体和它们的金属配合物的分子结构通过单晶X射线衍射分析明确地表征。对钯配合物的催化活性进行初步评价,对Buchwald-Hartwig胺化反应进行。结果,两种胃蛋白酶型(Peppsi =吡啶增强的预催化剂制备稳定化和引发)Pd络合物在烷烃溶剂中表现出有希望的活性。

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