Imidazole containing palladium(II) complexes as efficient pre-catalyst systems for Heck and Suzuki coupling reaction: Synthesis, structural characterization and catalytic properties

A series of new palladium(II) complexes of the general formula trans-[PdX2L2] [X = Cl, Br; L = 1-phenylimidazole (PI), 1-(4-methoxyphenyl)-1H-imidazole (MPI), 4(5)-(hydroxymethyl)-imidazole (HMI), 1-(4-cyanophenyl)-imidazole) (CPI)] [X = Cl; L = PI(1), X = Cl; L = MPI(2), X = Cl; L = HMI(3), X = Cl; L = CPI(4), X = Br; L = PI(5), X = Br; L = MPI(6), X = Br; L = HMI(7), X = Br; L = CPI(8)] have been synthesized. Resulting complexes have been characterized by elemental analyses, IR, 1H and 13C NMR, FAB-MS and electronic spectral studies. The molecular structures of 1, and 6 have been determined by single crystal X-ray analyses. The catalytic activities of all the Pd complexes (1–8) in coupling reactions such as the Mizoroki–Heck and Suzuki–Miyaura coupling reaction have also been studied. Among the 1–8 complexes in our investigations, 1, 2, 5, and 6 exhibited highest catalytic activity as compared to 3, 4, 7, and 8 complexes which is due to formation of Pd nanoparticles that might be actually the true active species.

Eight new palladium(II) complexes of the general formula trans-[PdX2L2] [X = Cl; L = PI(1), X = Cl; L = MPI(2), X = Cl; L = HMI(3), X = Cl; L = CPI(4), X = Br; L = PI(5), X = Br; L = MPI(6), X = Br; L = HMI(7), X = Br; L = CPI(8)] have been synthesized. The catalytic activities of all new Pd complexes (1–8) in coupling reactions such as the Mizoroki–Heck reaction and Suzuki–Miyaura coupling have also been studied.Figure optionsDownload as PowerPoint slideHighlights
► Neutral palladium(II) complexes were synthesized containing imidazole ligands.
► X-ray crystal structure of trans-[PdCl2(PI)2] and trans-[PdBr2(MPI)2].
► The palladium complexes have been used in Mizoroki–Heck and Suzuki–Miyaura coupling reactions.
► The palladium complexes work as pre-catalyst for the generation of Pd(0) nanoparticles.