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−

Abstract

The reactions of [Pt_3n(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 Pt₃ triangular unit up to the formation of [Pt_3n(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.