Synthesis, characterization and catalytic activity of PEPPSI-type palladium–NHC complexes

Abstract

Eight benzimidazolium salts (2a–h) with two nitrogen atoms substituted by various alkyl groups have been synthesized in high yields. The benzimidazolium salts were readily converted into the corresponding PEPPSI-type palladium–NHC complexes (PEPPSI = pyridine-enhanced precatalyst preparation, stabilization, and initiation) (3a–h). The structures of all compounds were characterized by 1H NMR, 13C NMR, and IR spectroscopy as well as by elemental analysis techniques, which support the proposed structures. The catalytic activity of the PEPPSI-type palladium–NHC complexes was evaluated with respect to the direct C5-arylation of 2-substituted heteroaryl derivatives (thiophene, furan and thiazole) with various aryl bromides. This arylation occurs efficiently and selectively at the C5-position of the 2-substituted thiophene, furan and thiazole derivatives.