Synthesis and Characterization of Heterometallic Complex of Lanthanide and Pt with DTPA Derivates as Ligands

In this work a preliminary investigation was carried out aiming to the preparation of heterobimetallic complexes incorporating both a lanthanide core and a platinum-based residue. In particular, f-metalloligands were designed for the coordination of platinum compounds. Diethylenetriaminepentaacetic acid (DTPA) was chosen as the preferential, chelating lanthanide ligand, due to the presence of many coordination sites, assuring a certain inertia to the usually labile lanthanide centre. This cheap, commercially available poliaminocarboxylic acid can be usefully desymmetrized, reacting suitable ditopic nucleophiles (a, p-toluidine; b, 2-aminomethylpyridine; c, 2,2-pyridylethylamine; d, 4-aminepyridine; e, 4-methilpyridinemethanol) with the DTPA bis-anydride. The DTPA derivatives obtained (1a-1e) maintain several binding sites for the lanthanide center, (three of the original five carboxylic groups and the nitrogen atoms of the diethylenetriamine scaffold), besides two pending pyridine residues to bind the Pt moiety, except for 1a. A useful protocol was found to prepare the f-metalloligand, reacting ligands (1a-1e) with the lanthanide (Y, Eu) hydroxide in water. The reaction always afforded a pure single product (2a-2e) where the DTPA nitrogen atoms and carboxylate groups, together with a water molecule, are coordinated to the lanthanide centre. A group of platinum precursors were tested in the last complexation step, to obtain the final heterobimetallic compound. Both ligands and complexes were characterized through elemental analysis, IR spectroscopy and NMR spectroscopy