Desenvolvimento de complexos de Pd(II) e Pt(II) a partir da diacetilmonoxima tiossemicarbazona: síntese e elucidação estrutural

Abstract

Thiosemicarbazones constitute an important class of ligands due to their high structural versatility and the diverse biological properties associated with their metal complexes. In particular, PdII and PtII complexes containing these ligands have attracted considerable interest as potential metallodrugs, since modifications in the coordination sphere can directly influence their structural, electronic, and chemical properties. In this context, the present study aimed to synthesize and characterize new PdII and PtII complexes containing a diacetyl monoxime-derived thiosemicarbazone, as well as to investigate the influence of replacing the fourth coordination site with different phosphine ligands and the effect of the solvent employed during the syntheses. Initially, the ligand H₂DMTSC was synthesized, followed by the preparation of complexes of the type [M(HL)X] (M = PdII and PtII; X = Cl- and I-). Subsequently, complexes containing the phosphines 1,3,5-triaza-7-phosphaadamantane (PTA) and tris(diethylamino)phosphine (TDA) were synthesized to afford complexes of the type [M(HL)(PR₃)]. The compounds were characterized by infrared and UV–Vis spectroscopy, 1H and 31P nuclear magnetic resonance spectroscopy, high-resolution electrospray ionization mass spectrometry, and single-crystal X-ray diffraction. The results confirmed the tridentate coordination mode of the thiosemicarbazone ligand and demonstrated that substitution at the fourth coordination site promotes significant changes in the spectroscopic properties of the complexes. Furthermore, it was demonstrated that the use of methanol as the reaction solvent promotes the replacement of the diethylamino groups of TDA by methoxy groups, leading to the formation of complexes containing P(OMe)₃ instead of P(NEt₂)₃. This transformation occurs only after complexation, highlighting the influence of both the metal center and the solvent on the final composition of the products. The results demonstrated that the [MCl(HL)] complexes can be employed as versatile precursors for the synthesis of new complexes through modification of the fourth coordination site and that, depending on the phosphine employed, the reaction solvent may influence the final composition of the species formed. Overall, these findings contribute to a better understanding of the reactivity of these systems, providing valuable insights for the development of new synthetic strategies and the preparation of compounds with potential antitumor activity.