Five-membered [C,N] and [N,O] metallocyclic complexes of palladium(II) with monoalkyl [α-(4-benzeneazoanilino)-N-benzyl]phosphonates: synthesis, characterization and antitumour activity

Abstract The synthesis, spectroscopic and biological properties of the novel palladium(II) complexes with monoethyl (HL1) and monobutyl (HL2) esters of [α-(4-benzeneazoanilino)- N -benzyl]phosphonic acid, have been prepared and studied. These potential polydentate ligands form two types of metallocyclic compounds, those with [C,N] and [N,O] five-membered chelate rings. The former are cyclopalladated chloro-bridged binuclear complexes, [PdL(μ-Cl)] 2 , in which the deprotonated ligand undergoes palladation at the azo nitrogen and the ortho -carbon, while the latter mononuclear complexes, PdL 2 , contain the organophosphorus ligand bonded through the aniline nitrogen and the deprotonated phosphonic acid oxygen. The complexes were identified and characterized by elemental analysis, magnetic and conductance measurements as well as by IR, 1 H, 13 C and 31 P nuclear magnetic resonance and ESI-mass spectroscopic studies. The in vitro antitumour activity of all the complexes was evaluated against the human KB cell line as a preliminary screening for their biological activity. The coordination behaviour of monoalkyl benzeneazophosphonates as well as the spectral and biological properties of their complexes were compared with the results reported for the corresponding dialkyl phosphonates and their palladium(II) complexes.