NOVEL PALLADIUM(II) COMPLEXES OF PYRAZOLE-CONTAINING SCHIFF BASE LIGANDS: SYNTHESIS, STRUCTURAL CHARACTERIZATION, AND CYTOTOXICITY OF THE PALLADIUM(II) COMPLEXES OF 2-{1-[2-(1,3-DIMETHYL-4-NITRO-1H-PYRAZOL-5-YL) HYDRAZONO]ETHYL} PYRIDINE (APHP) AND ITS ANALOGUE 2-{1-[2-(1,3-DIMETHYL-4-NITRO-1H-PYRAZOL-5-YL)HYDRAZONO]METHYL} PYRIDINE (PCHP)

Treatment of [Pd(PhCN)(2)Cl-2] with one equivalent of 2-{1-[2-(1,3-dimethyl-4-nitro-1H-pyrazol-5-yl)hydrazono]methyl} pyridine (PCHP) (3a) or its analogue 2-{1-[2-(1,3-dimethyl-4-nitro-1H-pyrazol-5-yl)hydrazono]ethyl} pyridine (APHP) (3b) produce corresponding pyridine-hydrazone Schiff base coordination complexes [Pd(PCHP)Cl-2] (4a) and [Pd(APHP)Cl-2] (4b), respectively. Compounds 4a,b are characterized by elemental analysis, IR spectroscopy, and H-1 NMR. Attempts to crystalize 4b lead to N-C(sp(3))-E pincer palladacycle [Pd(APHP-H)Cl(DMSO)] (5). The molecular structures of 5 in the solid state are determined by single crystal X-ray structure analysis. The X-ray crystal structure of 5 shows the existence of the five-membered metallacycle through the coordination of N-CH2- and pyridine N to the palladium center and the cis arrangement between the metalated nitrogen atom and DMSO. The cytotoxicity of the two ligands and palladium(II) complexes 4a and 5 evaluated against K562 human cancer cell line. The corresponding GI50 (50% growth inhibition) values are compared to the cytotoxicity of cisplatin, under the same experimental conditions, and the results indicate inactive ligands and a superior activity to cisplatin for the complexes.