Pd-PEPPSI-type expanded ring N-heterocyclic carbene complexes: synthesis, characterization, and catalytic activity in Suzuki-Miyaura cross coupling

In this work, we synthesized a series of six unsymmetrical benzimidazolium salts 2 and their pyridine-enhanced precatalyst preparation stabilization and initiation (PEPPSI)-themed palladium N-heterocyclic carbene complexes [PdCl2(NHC)(Py)]. All the products were isolated in satisfactory yields (75-85%). The synthesis of these novel palladium PEPPSI complexes involved in reacting NHC precursors with PdCl2 in pyridine at 60 degrees C in the presence of excess K2CO3. The structures of all compounds have been characterized by H-1 NMR, C-13 NMR, HRMS and IR spectroscopy, as well as elemental analysis techniques, which support the proposed structures. The catalytic activity of the six complexes was assessed in the Suzuki-Miyaura cross-coupling of phenylboronic acid and aryl halides. The reactions required only a low catalyst loading (0.1 mol%) and were carried out under mild aerobic conditions in a green, water-based solvent mixture.