Synthesis of Bulky 4-Amino-1,3-diarylimidazolium Salts as NHC-Ligand Precursors and Derived M/NHC Complexes (M = Cu, Pd)

An approach was developed for the synthesis of novel 1,3-bis(4-R-2,6-dibenzhydrylphenyl)-4aminoimidazolium chlorides, precursors of amino-functionalized sterically bulky NHC ligands, starting from N-aryl formamides via reaction with POCl₃ with subsequent amination of the in situ formed imidoyl chloride with arylamine and condensation of the thus formed formamidine with chloroacetonitrile. The applicability of the aminoimidazolium salts obtained for further functionalization of the NH₂ group and selective metalation of the imidazole C²–H bond to give Cu/NHC and Pd/NHC complexes was demonstrated.