Synthesis of silver(I) and palladium(II) N-heterocyclic carbene complexes and their use as catalysts for the direct C5 arylation of heteroaromatic compounds

Silver(I) N-heterocyclic carbene complexes were synthesized in good yields by the reactions of 1,3-dialkylperhydrobenzimidazolium salts with silver(I) oxide in dichloromethane. The silver complexes were used as carbene-transfer agents to synthesize palladium(II) N-heterocyclic carbene complexes. All of the complexes were characterized by physicochemical and spectroscopic methods. The new palladium complexes were tested as catalysts in the direct C5 arylation of 2-n-butylfuran, 2-n-butylthiophene and 2-n-propylthiazole with aryl bromides at 130 °C in N,N-dimethylacetamide. The arylation reactions proceeded selectively at the C5 position of the heteroaromatic compounds, and the corresponding coupling products were obtained in moderate to good yields by using 0.5 mol% of the palladium complex.