Well-defined PEPPSI-themed palladium-NHC complexes: synthesis, and catalytic application in the direct arylation of heteroarenes

In this study, a series of benzimidazolium salts were synthesized as unsymmetrical N-heterocyclic carbene (NHC) precursors. Benzimidazolium salts were used for synthesis of the PEPPSI (pyridine enhanced precatalyst preparation stabilization and initiation)-themed, six new Pd-complexes with the general formula [PdX2(NHC)(pyridine)]. The structures of all compounds were characterized by various spectroscopic techniques such as H-1 NMR, C-13 NMR and FT-IR. The more detailed structural characterization of four of the complexes was determined by single-crystal X-ray diffraction study. The catalytic activities of all Pd-complexes were evaluated in the direct arylation of the 2-acetylfuran and 2-acetylthiophene with aryl bromides in the presence of 1 mol% catalyst loading.