New pentamethylene-bridged bis-imidazolium dication ligands and its palladium(II) complexes: Synthesis, characterization, and catalysis

Two new pentamethylene-bridged bis-imidazolium dication ligands (L 1 = 1,5-bis(1-(4-cyanophenyl)-imidazolium-1-yl)pentane dibromide) and L 2 = 1,5-bis(1-(4-methoxyphenyl)-imidazolium-1-yl)pentane dibromide) bearing CPI (1-(4-cyanophenyl)-imidazole) and MPI (1-(4-methoxyphenyl)-1H-imidazole)-functionality have been prepared via the reaction of 1,5-dibromopentane with a substituted imidazole derivative. The imidazolium ligand L 1 and L 2 on reaction with [PdBr 2(C 6H 5CN) 2] led to the formation of neutral bis-imidazolium dication palladium(II) complexes [L 1] [PdBr 4] [1] (L 1 = 1,5-bis(1-(4-cyanophenylimidazolium-1-yl)pentane) and [L 2] [PdBr 4] [2] (L 2 = 1,5-bis(1-(4-methoxyphenyl) imidazolium-1-yl)pentane), respectively. The new ligands as well as their palladium(II) complexes, has been characterized by elemental analysis, electronic, IR, 1H and 13C NMR, FAB-MS and ESI-MS spectroscopy. The molecular structure of the representative complex [L 2] [PdBr 4] [2] have been determined by single crystal X-ray analysis. Complex 2 exhibits the strong intra- and inter-molecular C-H···X (X = Br, O, π) weak interactions, which plays an important role in stabilizing the crystal packing. Furthermore, the C-H···O interactions in 2 lead to a single-helical motif. The complexes 1 and 2 exhibited good activity in a model Suzuki-Miyaura coupling reaction.