Isomeric Palladium Complexes Bearing Imidazopyridine-Based Abnormal Carbene Ligands: Synthesis, Characterization, and Catalytic Activity in Direct C-H Arylation Reaction

Yan Yi Lee, Han Wei Zseng, Zong Han Tsai, Yong Siang Su, Ching-Han Hu, Hon Man Lee

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A series of "abnormal" NHC ligand precursors based on imidazopyridines and their corresponding NHC-palladium diiodide complexes were prepared. Our study included the first report on a palladium complex with an abnormal NHC ligand derived from imidazo[1,5-a]pyridine. DFT calculation on the free ligands confirmed the higher electron-donating properties of the abnormal NHC ligands than their normal NHC isomers. The structural properties of all the complexes were studied in detail by single-crystal X-ray diffraction studies, revealing that, in general, Pd-carbene bond distances in palladium complexes with abnormal NHCs were longer than those in their isomers with normal NHCs. A significant trans influence is observed in the palladium complexes with abnormal NHC ligands. But in the complexes with normal NHC ligands, both Pd-carbene and Pd-N bond distances are short. Catalytic studies revealed that the palladium complexes were very efficient in catalyzing direct C-H arylation between 1,2-dimethylimidazole and aryl halides using a low Pd loading of 0.5 mol %. The difference in catalytic activity between the normal and abnormal isomers is, however, small.

Original languageEnglish
Pages (from-to)805-815
Number of pages11
Issue number4
Publication statusPublished - 2019 Feb 25


All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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