REDOX DISPROPORTIONATION CLEAVAGE OF AN ALPHA-PYRROLIDONATE-BRIDGED MIXED-VALENT TETRANUCLEAR PLATINUM COMPLEX

The solution properties of alpha-pyrrolidonate-bridged dinuclear and tetranuclear platinum complexes are described. The general formula of the compounds is [Pt-2(NH3)(4)(C4H6NO)2](m+)(n), where C4H6NO=deprotonated alpha-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-2(II), (Pt3PtIII)-Pt-II, (Pt2Pt2III)-Pt-II, and Pt-2(III)). The behavior of the mixed-valent tetranuclear platinum complex [(PtPtIII)-Pt-II(NH3)(4)(C4H6NO)(2)](6+)(2) (n=2, m=6) in aqueous media was investigated by means of UV-Vis and H-1 NMR spectroscopy. It was shown that [(PtPtIII)-Pt-II(NH3)(4)(C4H6NO)(2)](6+)(2) undergoes a rapid disproportionation cleavage into the dinuclear complexes [Pt-2(II)(NH3)(4)(C4H6NO)(2)](2+) (n=1, m=2) and [Pt-2(III)(NH3)(4)(C4H6NO)(2)LL'](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 H-1 NMR study on the solution of [(PtPtIII)-Pt-II(NH3)(4)(C4H6NO)(2)](6+)(2) 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-2(III)(NH3)(4)(C4H6NO)(2)(H2O)(2)](4+) shows the existence of three different chemical species, diaqua-, aqua-sulfato- and disulfato-coordinated Pt-2(III), dimers, in aqueous sulfuric acid solution. The study also confirms that the disproportionation cleavage of [(PtPtIII)-Pt-II(NH3)(4)(C4H6NO)(2)](6+)(2) in aqueous sulfuric acid solution produces these Pt-2(III), dimers.