Palladium(II) 9,10-phenanthrenequinone N-substituted thiosemicarbazone/semicarbazone complexes as efficient catalysts for N-arylation of imidazole

A series of palladium complexes, [PdCl(L_1–4)] (1–4) (L₁ = 9,10-phenanthrenequinone thiosemicarbazone, L₂ = 9,10-phenanthrenequinone methylthiosemicarbazone, L₃ = 9,10-phenanthrenequinone phenylthiosemicarbazone, and L₄ = 9,10-phenanthrenequinone semicarbazone), have been synthesized and characterized by elemental analyses, UV–vis, FT-IR, ¹H and ¹³C NMR, and ESI-Mass spectroscopic methods. The catalytic efficiency of the synthesized complexes was examined against N-arylation of imidazole. The system works well with the electron-rich, -neutral, and -deficient aryl halides to afford the products in good to excellent yields. Sterically congested aryl halides and heteroaryl halides have also been used as substrates to provide N-arylated heterocycles. In addition, this methodology can be applicable to other substrates with N-containing heterocycles.