Topchiy Maxim A, Zotova Maria A, Masoud Salekh M, Mailyan Artur K, Ananyev Ivan V, Nefedov Sergey E, Asachenko Andrey F, Osipov Sergey N
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov str. 28, 119991, Moscow, Russia.
Department of Chemistry and Biochemistry, University of California, Santa Barbara, California, 93106-9510, USA.
Chemistry. 2017 May 11;23(27):6663-6674. doi: 10.1002/chem.201700624. Epub 2017 Apr 21.
An efficient and scaled-up synthesis of the imidazol-2-ylidene-based unsymmetrical NHC precursors bearing the sterically demanding hexafluoroisopropylalkoxy group [(CF ) (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 pre-catalyst preparation stabilization and initiation) Pd complexes have demonstrated promising activity in alkane solvents.
开发了一种高效且可扩大规模的合成方法，用于制备在N - 芳基取代基的邻位带有空间位阻较大的六氟异丙基烷氧基[(CF ) (OR)C-]的基于咪唑 - 2 - 亚基的不对称NHC前体。该方法的关键步骤涉及通过与相应的双亲核氟烷基取代苯胺反应，将Mes取代的四氟硼酸恶唑啉盐进行转化。通过简单的一步O - 烷基化协议对所得含羟基盐进行后续后修饰，可得到一系列新的不对称氟化NHC前体。这些化合物已成功用于制备几种新型金属配合物。一些NHC前体及其金属配合物的分子结构已通过单晶X射线衍射分析明确表征。对钯配合物的催化活性进行了初步评估，以布赫瓦尔德 - 哈特维希胺化反应为模型。结果表明，两种PEPPSI型（PEPPSI = 吡啶增强的预催化剂制备稳定化和引发）钯配合物在烷烃溶剂中表现出良好的活性。
