Effects of geometric configuration and steric hindrance on rates and mechanisms of oxidation of diaminedichloroplatinum(II) complexes by tetrachloroaurate(III) ions

Abstract

The oxidation reactions of trans- and/or cis-[PtCl₂(NH₂R)₂] by [AuCI₄]^– in the presence of [NEt₄]CI have been kinetically investigated in acetonitrile (R = H, Me, Et, Prⁿ, Prⁱ, Buⁿ, Buⁱ, Bu^s, Bu^t, CH₂Bu^t, CH₂Ph, or cyclo-C₆H₁₁). The rate law for the oxidation of the trans complexes consists mainly of a third-order rate term, k_c[PtCl₂(NH₂R)₂][AuCl₄^–][Cl^–], whereas an additional rate term, k_a[ PtCI₂(NH₂ R)₂][AuCl₄^–][CI^–]/(1 +k_b[CI^–]), operates in the case of the cis complexes. A reaction scheme is proposed. The oxidation rates of both cis and trans complexes appear to be reduced by increasing the steric hindrance of the amine, cis complexes being more sensitive towards changes of steric hindrance than traps analogues. Approximate linear relationships correlate the reactivities (log k) of both cis and trans complexes with an amine steric hindrance parameter.