Redox disproportionation cleavage of an α-pyrrolidonate-bridged mixed-valent tetranuclear platinum complex

Abstract

The solution properties of α-pyrrolidonate-bridged dinuclear and tetranuclear platinum complexes are described. The general formula of the compounds is [Pt 2(NH 3) 4(C 4H 6NO) 2] n m+ , where C 4H 6NO=deprotonated α-pyrrolidone, n=1 or 2, m=2–4 per dimer unit. The charge m depends on the average Pt oxidation state in the range 2.0–3.0 (the complex takes the four oxidation states Pt II 2, Pt II 3Pt III, Pt II 2Pt III 2, and Pt III 2). The behavior of the mixed- valent tetranuclear platinum complex[Pt IIPt III(NH 3) 4(C 4H 6NO) 2] 2 6+ ( n=2, m=6) in aqueous media was investigated by means of UV-Vis and 1H NMR spectroscopy. It was shown that [Pt IIPt III(NH 3) 4(C 4H 6NO) 2] 2 6+ undergoes a rapid disproportionation cleavage into the dinuclear complexes [Pt II 2(NH 3) 4(C 4H 6NO) 2] 2+ ( n=1, m=2) and [Pt III 2(NH 3) 4(C 4H 6NO) 2LL′] 4+ ( n=1, m=4; L, L′ are axial ligands). It was also found that the reaction is a reversible process and the equilibrium is largely shifted to the side of the dimers. A 1H NMR study on the solution of [Pt IIPt III(NH 3) 4(C 4H 6NO) 2] 2 6+ confirms the formation of the two dimers in the molar ratio of c. 1:1. An equilibrium study on the axial ligand substitution of [Pt III 2(NH 3) 4(C 4H 6NO) 2(H 2O) 2] 4+ shows the existence of three different chemical species, diaqua-, aqua-sulfato- and disulfato-coordinated Pt III 2 dimers, in aqueous sulfuric acid solution. The study also confirms that the disproportionation cleavage of [Pt IIPt III(NH 3) 4(C 4H 6NO) 2] 2 6+ in aqueous sulfuric acid solution produces these Pt III 2 dimers.