Synthetic procedures to monomethyl-platinum(II) complexes containing nitrogen ligands of biological relevance

Abstract

The complex trans-bis(dimethylsulfoxide)chloromethylplatinum(II) (1) is fairly soluble in water, where it undergoes multiple equilibria involving the formation of geometrically distinct [Pt(H2O)(DMSO)Cl(CH3)] aqua-species. On reacting an aqueous solution of 1 with monodentate nitrogen donor ligands L, such as pyridines or amines, two well distinct patterns of behavior can be recognized: (i) a single stage fast substitution of one DMSO by the entering ligand, yielding a complex of the type trans(C,N)-[Pt(DMSO)(L)Cl(CH3)] which contains four different groups coordinated to the metal and which undergoes a slow conversion into its cis-isomer, (ii) a double substitution affording cationic complex ions of the type cis-[Pt(L)2(DMSO)(CH3)]+. When this latter reaction is carried out using sterically hindered ligands, slow rotation of the bulk ligand around the Pt–N bond allows for the identification of head-to-head and head-to-tail rotamers in solution, through 1H NMR spectrometry. The addition of chloride anion to 1 leads to the anionic species cis-[Pt(DMSO)Cl2(CH3)]−, where a molecule of DMSO still remains coordinated to the metal center, despite its quite fast rate of ligand exchange (kexch with free DMSO=12±1 s−1). The reaction of complex 1 with bidentate ligands, such as ethylenediamine (en) or simple amino acids, leads to the cationic species [Pt(en)(DMSO)(CH3)]+ or to the neutral [Pt(DMSO)(N–O)(CH3)], (where N–O=GlyO−, AlaO−).