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

Two new pentamethylene-bridged bis-imidazolium dication ligands (L1 = 1,5-bis(1-(4-cyanophenyl)-imidazolium-1-yl)pentane dibromide) and L2 = 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 L1 and L2 on reaction with [PdBr2(C6H5CN)2] led to the formation of neutral bis-imidazolium dication palladium(II) complexes [L1] [PdBr4] [1] (L1 = 1,5-bis(1-(4-cyanophenylimidazolium-1-yl)pentane) and [L2] [PdBr4] [2] (L2 = 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 [L2] [PdBr4] [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.

Graphical abstractTwo new pentamethylene-bridged bis-imidazolium dication ligands (L1 = 1,5-bis(1-(4-cyanophenyl)-imidazolium-1-yl)pentane dibromide) and L2 = 1,5-bis(1-(4-methoxyphenyl)-imidazolium-1-yl)pentane dibromide) bearing CPI and MPI-functionality and their Pd(II) complexes (1 and 2) are reported. The molecular structure of 2 has been determined by single crystal X-ray analysis and exhibited good catalytic activity in Suzuki-Miyaura coupling reaction.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of new pentamethylene-bridged bis-imidazolium dication ligands bearing CPI and MPI-functionality. ► Synthesis of bis-imidazolium dication Pd(II) complexes with single crystal X-ray analysis. ► Application of the Pd(II) complexes as good catalysts for the Suzuki–Miyaura reaction.