Synthesis of palladium complexes containing benzimidazole core and their catalytic activities in direct C[sbnd]H functionalization of five-membered heterocyclic bioactive motifs

Abstract

Herein, we reported the synthesis of nine new PEPPSI-Pd(II)–N-heterocyclic carbene (NHC) complexes 3a-h containing benzimidazole core and examined their catalytic activities in the direct arylation of heteroaromatic species with aryl bromides and arylchlorides. Nine new Pd benzimidazole complexes were synthesized and their structures were elucidated by 1H and 13C NMR spectroscopy, FT-IR spectroscopy, and elemental analysis methods. In the 13C NMR spectra, NCHN peaks of Pd(II) complexes were observed between 159.7–161.5 ppm. Further, direct arylation reaction, using KOAc as base and DMAc as solvent under inert conditions, were carried out with the synthesized complexes in the presence of various aryl bromides and chlorides, and 2-acetyl furan, and furfuryl acetate 2-acetylthiophene and N-methylpyrrole-2- carboxaldehyde. Moreover, moderate to hig yields were obtained in the direct arylation of heteroarenes and aryl bromides under 1 mol% catalyst loading at 150 °C for 2 h loading conditions. The results showed that electron-donating and electron-withdrawing substituents on the aryl halides might produce coupling products in good yields in the presence of complexes 2a-d. Taken together, our findings are expected to contribute to the synthesis and design of palladium complexes containing benzimidazole core structures.