Synthesis, characterization, DFT studies and biological assessment of palladium(II) complexes with imidazole derivatives

Six palladium(II) complexes (1–6) with 2-phenylimidazole (L₁) and 1,2-dimethylimidazole (L₂), were synthesized and characterized by elemental analyses, IR and NMR spectroscopy. The crystal structure of one of them ([Pd(2-phenylimidazole)₂Br₂], 1) was determined by X-ray crystallography. The palladium(II) ion in complex 1 is coordinated by two nitrogen atoms of 2-phenylimidazole and two bromide ions at trans positions, adopting a nearly regular square planar geometry. The structures of PdBr₂ complexes {[Pd(2-phenylimidazole)₂Br₂] (1) and [Pd(1,2-dimethylimidazole)₂Br₂] (4)} as well as their chloride analogues, {[Pd(2-phenylimidazole)₂Cl₂] (1a) and [Pd(1,2-dimethylimidazole)₂Cl₂] (4a)} were predicted by DFT calculations. Complexes 1 and 1a appeared to be stabilized by a weak agostic interaction between palladium and hydrogen atoms. The energy of Pd⋯H bond was estimated to be 1.6 kcal/mol for both complexes that was comparable to the strength of Cl⋯H hydrogen bond in 1a (1.7 kcal/mol). The complexes were examined for various biological activities including; antimicrobial, antioxidant and anti-diabetic assays. The complexes exhibited moderate antimicrobial activities but they were not good as antioxidants. However, the alpha amylase inhibition assay showed the excellent anti-diabetic effect of the complexes.