Introduction of NHC Moiety to Primary Amines Through Phthalimide Linkage

N-heterocyclic carbenes (NHCs) have been widely studied recent years. However, the synthesis of NHC could sometimes be complicated, especially when non-chelating symmetrical poly-functional carbene ligands are anticipated. Therefore, we decided to develop a simple method to introduce NHC unit to various molecular backbones using a sole NHC precursor. In this research, a LEGO brick bifunctional ligand, which bears an imidazole moiety on one side of the molecule and phthalic anhydride functionality on the other side, was synthesized. While the imidazole part represents the NHC precursor, the phthalic anhydride group reacts with primary amine containing molecule to introduce the NHC moiety via phthalimide linkage. With this synthetic protocol, poly NHCs and the corresponding poly-nuclear nickel complexes with 1-D, 2-D, and 3-D molecular structure were synthesized. Catalytic performances of these poly-Ni complexes illustrated the negligible interactions between the nickel centers. Furthermore, the synthetic protocol was found to be applicable to various amino acids to give the amino acid tethered benzimidazolium salts and the corresponding metal complexes. The combination of amino acid and NHC ligand is anticipated to improve the bio-compatibility of NHC-metal complexes for selective drug delivery.