Amide Functionalized Pyridine/Pyrimidine Chelating N-Heterocyclic Carbene Palladium Complexes: Synthesis, Structure, and Catalysis for C-5 Arylation of Imidazoles

A series of N-alkylamide-N'-pyridine/pyrimidine di-functionalized imidazolium salts were synthesized using amino acids as starting material. The following direction metallation with Pd(OAc) 2 in CH2Cl2 at room temperature produced chelating N-heterocyclic carbene (NHC) palladium complexes with pyridine/pyrimidine coordinated. The structures have been characterized by nuclear magnetic resonance (NMR), mass spectrum (MS) or elemental analysis (EA). The molecular strucuture of pyridine chelating NHC palladium complex 5c has been further characterized unambiguously by X-ray single crystal analysis. Catalytic activity exploration of the complexes demonstrated their high efficiency towards the C-5 arylation of imidazole derivatives in dimethylacetamide (DMAc) with KOAc as base.