Kinetics and mechanism of hydrazineoxidation by an oxo-bridged tetramanganese(IV) complex in weakly acidic media

Abstract

The complex [Mn₄(μ-O)₆(bipy)₆]⁴⁺1 (bipy = 2,2′-bipyridine) quantitatively oxidised N₂H₅⁺ to N₂. With an excess of N₂H₅⁺ the reaction proceeds through two parallel first-order paths. In one, 1 reacts with N₂H₅⁺ and the rate is independent of [H⁺] and the concentration of bipy. In the other path, the rate decreases with increasing concentration of ligand and [H⁺]. In this second path [Mn₄(μ-O)₆(bipy)₅(H₂O)(N₂H₄)]⁴⁺ appears to be the reactive species. The overall first-order rate constant k₀ decreases linearly with increased mole % of D₂O and k₀ in 98% D₂O is substantially (3.89 times) less than that in 0% D₂O. Transfer of one electron and one proton in the rate determining step is proposed for both the paths.