P,N]-phosphinobenzimidazole ligands in palladium-catalyzed C-N cross-coupling reactions: The effect of the N-substituent of the benzimidazole scaffold on catalyst performance

Abstract

A series of [P,N]-phosphinobenzimidazole ligands is reported in which the charge (anionic vs. neutral) and size of the N-substituent of the benzimidazole scaffold has been varied. In order to evaluate the impact of the substituent's properties on the performance of the metal in catalytic reactions, each ligand was screened for its ability to promote the cross-coupling of aryl bromides with various primary aryl amines using palladium as the metal source. In general, the ligands formed active cross-coupling catalysts with palladium. Moreover, the ligand variants containing larger N-substituents boosted the efficiency of the cross-coupling reaction considerably, while their charge (either anionic or neutral) appeared to have no significant impact.