N-Methylphthalimide-substituted benzimidazolium salts and PEPPSI Pd-NHC complexes: synthesis, characterization and catalytic activity in carbon-carbon bond-forming reactions

A series of novel benzimidazolium salts (1-4) and their pyridine enhanced precatalyst preparation stabilization and initiation (PEPPSI) themed palladium N-heterocyclic carbene complexes [ PdCl2(NHC)(Py)] (5-8), where NHC = 1-(N-methylphthalimide)3- alkylbenzimidazolin-2-ylidene and Py = 3-chloropyridine, were synthesized and characterized by means of H-1 and C-13{H-1} NMR, UV-vis (for 5-8), ESI-FTICR-MS (for 2, 4, 6-8) and FTIR spectroscopic methods and elemental analysis. The synthesized compounds were tested in Suzuki-Miyaura cross-coupling (for 1-8) and arylation (for 5-8) reactions. As catalysts, they demonstrated a highly efficient route for the formation of asymmetric biaryl compounds even though they were used in very low loading. For example, all compounds displayed good catalytic activity for the C-C bond formation of 4-tert-butylphenylboronic acid with 4-chlorotoluene.