Spectroscopic and thermal study of monoalkyl [α-(4-benzeneazoanilino)-N-benzyl]phosphonates and their palladium(II) complexes

Spectroscopic (IR, UV/VIS) and thermal (TG, DTA) studies of the monoethyl (HL1) and monobutyl (HL2) esters of [α-(4-benzeneazoanilino)-N-benzyl]phosphonic acid and their cyclopalladated binuclear complexes, [PdL(μ-Cl)]2, as well as mononuclear chelate complexes, PdL2, have been carried out to determine structural and decomposition properties of these biologically interesting compounds. Thermal decomposition of the complexes takes place through a multistep process. In the chloro-bridged cyclopalladated complexes ligand deesterification coupled with dehalogenation is followed by a complex pyrolysis, while decomposition of the mononuclear complexes includes deesterification and other ligand degradation processes that leads to metallic palladium and P2O5. The X-ray and infrared spectroscopic study confirmed this mixture as the final residue in both types of complexes. No stable intermediate products were found during the thermal decomposition due to its complexity and to the overlap of the degradation processes. The spectral and thermal properties of the complexes were compared with those obtained for the complexes of dialkyl [α-(4-benzeneazoanilino)-N-benzyl]phosphonates and discussed with respect to their structure-stability relationship.