Acidic Properties of (Dimethyl sulfoxide)(l,5-diamino-3-azapentane)platinum(II) Perchlorate and Kinetics of the Displacement of Dimethyl Sulfoxide from the Conjugate Base

[Pt(dien)(Me2SO)](ClO4)2(dien = 1,5-diamino-3-azapentane) is a weak acid; pKa-11.94 • 0.02 at 25.0 °C and / = 0.10. 1H and 13C NMR evidence is presented to show that the proton is removed from the 3-nitrogen. The kinetics of the displacement of Me2SO from the conjugate base by the nucleophiles X = Cl-, Br-, I-, N3-, SCN-, and S2O32- have been studied by working in the presence of 0.50 mol dm-3 NaOH, The displacement of Me2SO by X is followed by the displacement of X by OH“, and in the case of the more weakly bound nucleophiles Cl- and Br-, the second stage is much faster than the first and the reaction appears to be a halide-catalyzed replacement of Me2SO by OH-. The reactions, studied under first-order conditions, follow the simple rate law kobsd= k2[X], and values of k2for the corresponding reactions of the amine complex in the absence of OH- but at / = 1.0 have also been obtained. Deprotonation leads to a relatively small decrease in reactivity (a factor of ~2 at I = 1.0, extrapolating to a factor of ~8 at I = 0). [Pt(en)(Me2SO)2]2+(en = 1,2-diaminoethane) undergoes a similar deprotonation in basic solution but, because of its solvolytic lability, the pKacould not be determined. Its amido conjugate base, however, is some 10 times more labile than the amine species. © 1986, American Chemical Society. All rights reserved.