engleski

NMR spectroscopic study of Pd(II) halide complexes with diethyl quinolylmethylphosphonates

The coordination chemistry of organophosphorus compounds e.g. derivatives of various aminophosphonic acids, has currently attracted a considerable interest. This arises because of their complexation ability towards a number of metal ions and of their biological activity. As a part of our continuous study on palladium(II) halide complexes with phosphonate ligands derived from quinoline and aniline, which have been found effective in the treatment of various types of animal and human carcinomas, in the present work we describe a detailed ^1H and ^13C NMR spectroscopic study of diethyl esters of 2- and 8-quinolylmethylphosphonic acids (2-dqmp and 8-dqmp) and their dihalopalladium(II) complexes PdL_2X_2 (X=Cl, Br) containing quinoline N-bonded ligands in a trans square-planar fashion. Diethyl quinolylmethylphosphonates are ligands with two potential donor atoms, quinoline nitrogen and phosphoryl oxygen. While 2-dqmp can act as monodentate N-bonded or as bidentate N, O-bonded chelate ligand forming the square planar palladium dihalide complexes with 1:2, trans-[Pd(2-dqmp)_2X_2], or 1:1, cis-[Pd(2-dqmp)X_2], metal-to-ligand-ratios, 8-dqmp binds palladium ion only through the nitrogen atom forming 1:2 complexes, trans-[Pd(8-dqmp)_2X_2], X=Cl, Br. In HX acidic media both ligands form the ion-pair salt complexes, [HL]_2 [PdX_4], with the protonated quinoline ligand as cation and the tetrahalogenopalladium complex as anion. The multinuclear NMR spectroscopic studies provide important information on the bonding mode of the ligands which may coordinate to a metal center through several donor sites. The ^1H and ^13C NMR spectral data of free diethyl quinolylmethyl-phosphonates provided a basis for interpreting spectra of their palladium(II) complexes. The analysis was accomplished by one- and two-dimensional homo- and heteronuclear correlation experiments, including ^1H-^1H COSY, NOESY, TOCSY and HMBC. In the spectra of complexes considerable variations in chemical shifts were observed for nuclei in vicinity of the ligation site, which may be explained by combination of the electronic and steric effects. Thus, the significant differences between chemical shifts in the free ligands and their complexes are found for proton and carbon resonances close to the quinoline nitrogen. Corresponding resonance of the PO(OR)_2 group and quinoline atoms, which are far from the metal ligation place, show relative small changes upon complex formation. The increased complexity in the spectra of 2-dqmp complexes arises from the presence of more isomeric forms caused by restricted rotation around the metal-ligand bond.

palladium(II) complex; quinolylmethylphosphonate; NMR study

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