A kinetic investigation on the oxidation of platinum(II) complexes by hexachloroiridate(IV). Role of steric hindrance

Abstract

The oxidation reactions of platinum(II) complexes of the type [Pt(en)L₂]²⁺[en = H₂NCH₂CH₂NH₂, L = NH₃, NH₂R (R = Me, Et, Prⁿ, CH₂Bu^t, CH₂Ph, Buⁿ, C₄H₇, C₅H₉, or C₆H₁₁), 4-cyanopyridine, ½ MeHNCH₂CH₂NH₂, ½ Me₂NCH₂CH₂NH₂, or ½ Me₂NCH₂CH₂NMe₂] and [PtL₄]²⁺[L = NH₃ or NH₂R (R = Me, Et, or Prⁿ)] by IrCl₆^2– in the presence of chloride ions have been kinetically investigated in aqueous perchlorate media (pH 2.0–3.0, I= 1.0 mol dm^–3). In the absence of IrCl₆^3– the reactions obey the rate law –d[IrCl₆^2–]/dt= 2 (k_a+k_b[Cl^–])[complex][IrCl₆^2–]. The iridium(III) reaction product, IrCl₆^3–, lowers the rates. The results obtained are consistent with a redox mechanism involving a five-co-ordinate platinum(II) intermediate and two successive one-electron-transfer steps. The reactivity of the complexes is strongly dependent on the ligands co-ordinated to platinum(II), steric hindrance being the most important factor in the observed trend.