Benzimidazole bearing Pd–PEPPSI complexes catalyzed direct C2-arylation/heteroarylation of N-substituted benzimidazoles

A convenient and highly efficient palladium-catalyzed direct C2-arylation/heteroarylation of N-substituted benzimidazole derivatives such as N-benzyl/3-chlorobenzyl/2,4,6-trimethylbenzyl/2,4,6-triisopropylbenzyl/aryl benzimidazoles with various aryl/heteroaryl bromides in the presence of Pd–PEPPSI (palladium-pyridine enhanced pre-catalyst preparation stabilization and initiation) complexes is reported. In order to that we have prepared a series of different symmetrical and unsymmetrical N,N′-diaralkyl benzimidazole-bearing Pd–PEPPSI complexes. Among all of the the prepared complexes, Pd–PEPPSI- 3 effectively tuned the reaction at a relatively higher rate under mild reaction conditions in an ethanol–water system. In addition, the catalytic process avoids the use of external ligand and additives. Further the reactivity was compared with commercially available copper-N-heterocyclic carbene catalyst, but the reaction was less successful. With the optimized reaction conditions, a wide range of 2-aryl/heteroaryl-N-substituted benzimidazoles were synthesized in good to excellent yields via Csp²-H/Csp²-X biaryl cross-coupling.