Kinetics and mechanism of cleavage of the oxygen–oxygen bond in hydrogen peroxide and dibenzoyl peroxide by arylplatinum(ii) complexes

Abstract

Reaction of [PtAr₂(NN)] (Ar = Ph, p-MeC₆H₄, m-MeC₆H₄ or p-MeOC₆H₄; NN = 2,2′-bipyridyl or 1,10-phenanthroline) with R₂O₂, in which R = H or C(O)Ph, gives the platinum(IV) complexes cis,trans-[PtAr₂(OH)₂(NN)] or [PtAr₂(OCOPh)₂(NN)] (as a 5 ∶ 1 mixture of cis,trans and cis,cis isomers), respectively. The kinetics of these oxidative addition reactions in acetone was followed by visible spectrophotometry between 10 and 40 °C. The reactions followed simple second-order kinetics, rate = k₂[PtAr₂(NN)][peroxide], and the rates were insensitive to change of solvent. Activation parameters have been determined and large negative values for ΔS^≠ were obtained. A mechanism is suggested which involves a concerted three-center transition state, followed by homolytic cleavage of the O–O bond and formation of the final products.