CIS AND CHARGE EFFECTS IN PLATINUM(II)-CATALYZED SUBSTITUTION REACTIONS OF PLATINUM(IV) COMPLEXES

Reactions of the type trans-Pt(NH3)4Cl22+ + Pt(dien)An+ + 2Br- → trans-Pt(dien)ABr2n+ + Pt(NH3)42+ + 2Cl- and Pt(dien)Br+ + trans-Pt(dien)ACl2n+ + 2Br- → trans-Pt(dien)Br3+ + Pt(dien)An+ + 2Cl- (where A = NO2-, Br-, or NH3; n = 1 or 2; dien = diethylenetriamine) were found to have third-order rate laws, with first-order rate dependences on the reactant Pt(IV) complex, the reactant Pt(II) complex, and bromide ion concentrations. The fastest reaction was less than ten times faster than the slowest, which indicates that cis and charge effects are relatively minor. The relative rates parallel the ease of oxidation of Pt(dien)An+ and of reduction of trans-Pt(dien)ACl2n+. The rate data are interpreted in terms of a bridged inner-sphere redox mechanism involving an activated complex of the type Pt-Cl-Pt. Rate constants and activation parameters are reported. Equilibrium constants related to these reactions were studied spectrophotometrically and correlated with the rate data. © 1969, American Chemical Society. All rights reserved.