Synthesis and cytotoxicity of some cyclometallated palladium complexes

Several monomeric cyclometallated palladium complexes have been prepared by bridge opening reactions of their corresponding dimeric precursors with various amines. The complexes were characterized by elemental analyses and proton NMR spectroscopy. The general formula for the complexes can be given as Pd(N-C)LX where (N-C) is an aromatic or aliphatic amine coordinated as a chelating ligand through the amine and a formal cyclometallated Pd-C bond; L = amine, X = chloride or acetate. A unique complex based on the cyclopalladation of 2-phenyl phenanthroline was also prepared directly. The series of complexes was screened for cytotoxicity against a panel of seven human tumor cell lines. All complexes were found to be cytotoxic (IC50) at micrograms/ml concentrations, while two complexes also displayed some differential cytotoxicity.