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

Abstract

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 1H NMR, 13C 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.

Applications of quinoxaline‐bridged bis(benzimidazolium) salts as ligand sources for the palladium‐catalyzed Suzuki and Heck cross‐coupling reactions in an aqueous medium

“…These data are in agreement with those of the benzimidazolium salts previously reported in the literature. [ 55,66–71 ]…”

“…These data are in agreement with those of the benzimidazolium salts previously reported in the literature. [55,[66][67][68][69][70][71] Photophysical properties of quinoxaline derivative 2a-2d molecules were investigated by UV-Vis absorption and fluorescence emission spectroscopy. UV-Vis absorption spectra of each molecule were scanned between 200-700 nm and four noticeable bands were recorded as shown in Figure 2.…”

Aminomethylpyridinequinones as new ligands for PEPPSI-type complexes

“…Similar activity was achieved when PEPPSI-themed palladium-NHC complexes based on benzimidazolium unsymmetrical N-heterocyclic carbenes were used. 18 Replacement of NHC with 1,2,3-triazolin-5-yliden-type ligand was another successful structural modification, developed by Pietraszuk et al 19 The pyridine ligand has been less frequently modified. In the original PEPPSI catalyst, the electron-withdrawing chlorine substituent at the 3-position facilitated the dissociation of this ligand and consequently activation of the catalyst.…”