Kinetic data for outer-sphere V2+ and [Ru(NH3)6]2+ reductions of platinum(IV) complexes and a correlation of rate constants
Abstract
The kinetics of 2 : 1 V2+ and [Ru(NH3)6]2+ reductions of six PtIV complexes: trans-[Pt(NH3)4Cl2]2+, trans-[Pt(NH2CH3)4Cl2]2+, [Pt(NH3)5Cl]3+, [Pt(NH3)5Br]3+, mer-[Pt(NH3)3Cl3]+, and [PtCl6]2– have been studied. Reactions involve one-equivalent changes, PtIV→ PtIII→ PtII where the first step is rate determining and PtIII is a transient intermediate. A linear correlation of second-order rate constants (15 °C)kV and kRu, log kV= 0.89 log kRu– 1.68, is obtained at I= 0.10M(LiClO4),consistent with outer-sphere reactions, and non-utilization (by V2+) of inner-sphere pathways involving Cl– and Br– bridges. The occurrence of outer-sphere reactions appears to preclude two-equivalent changes. Rate constants for the V2+ reductions of trans-[Pt(NH3)4Cl2]2+ > [Pt(NH3)5Cl]3+ differ by a factor of 60, whereas those for corresponding [Pt(NH3)4]2+ reductions, which involve two-equivalent changes, have previously been shown to differ by a factor 104. Activation parameters have been determined for five of the V2+ reductions. Those for the reduction of trans-[Pt(NH3)4Cl2]2+ and trans-[Pt(NH2CH3)4Cl2]2+ differ significantly indicating an influence of the methyl groups.