A reaction mechanism for oxidative addition of halogen to platinum(II), reductive elimination of halide from platinum(IV) and halide assisted anations of platinum(IV) complexes

Article abstract of DOI:10.1016/S0020-1693(00)91090-9

The oxidative addition of iodine to Pt(CN)₄^2- is first-order with respect to iodide, iodine and complex. The reverse reductive elimination of iodide from trans-Pt(CN)₄I_22- is first-order with respect to iodide and Pt(CN)₄I_22-. The kinetics for the reaction between bromide and trans-Pt(CN)₄ClH₂O^2- involves a rate-determining reductive elimination of chloride, followed by a rapid oxidative addition of bromine to the formed Pt(CN)₄^2-. The reactions between trans-Pt(CN)₄BrH₂O^- and bromide or chloride can be described as halide assisted anations. The rate constant for the bromide anation is k_exp = k′[Br^-]² and for the chloride anation (in the presence of bromide) k′[Br^-][Cl^-] + k′' [Cl^-]². All reactions were followed using a stopped-flow technique at 25°C in 0.50M perchloric acid medium. The equilibrium constant for the redox equilibrium between Pt(CN)₄^2-, iodine and Pt(CN)₄I₂^2- was determined separately to be (1.29 ± 0.03) × 10⁴M^-1. Exploratory stopped-flow experiments indicate that the oxidative addition of chlorine to PtCl₂^2- is first-order with respect to both chlorine and tetrachloroplatinate. The experimental rate laws can be described by a reaction mechanism which resembles that introduced previously for Pt(II)-catalyzed anations and substitutions, in that both mechanisms can be considered as oxidative additions/reductive eliminations.