Water soluble derivatives of platinum carbonyl Chini clusters: Synthesis, molecular structures and cytotoxicity of [Pt12(CO)20(PTA)4]2-and [Pt15(CO)25(PTA)5]2-

The reactions of [Pt3n(CO)6n]2-(n = 2-5) homoleptic Chini-type clusters with increasing amounts of 1,3,5-triaza-7-phosphaadamantane (PTA) result in the stepwise substitution of one terminal CO ligand per Pt3triangular unit up to the formation of [Pt3n(CO)5n(PTA)n]2-(n = 2-5). Competition between the nonredox substitution with retention of the nuclearity and the redox fragmentation to afford lower nuclearity heteroleptic Chini-type clusters is observed as a function of the amount of PTA and the nuclearity of the starting cluster. Because of this, [Pt12(CO)20(PTA)4]2-and [Pt15(CO)25(PTA)5]2-are more conveniently obtained via the oxidation of [Pt9(CO)15(PTA)3]2-. All the new species were spectroscopically characterized, and the structures of [Pt12(CO)20(PTA)4]2-and [Pt15(CO)25(PTA)5]2-were determined by single-crystal X-ray diffraction. These clusters may be viewed as heteroleptic Chini-type clusters composed of stacks of four and five Pt3(μ-CO)3(CO)2(PTA) units, respectively. The solubility in water of [Pt12(CO)20(PTA)4]2-and [Pt15(CO)25(PTA)5]2-has been determined and their cytotoxicity towards human ovarian (A2780) cancer cells and their cisplatin-resistant strain (A2780cisR) has been evaluated.