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

The complex [Mn-4(mu-O)(6)(bipy)(6)](4+) 1 (bipy=2,2'-bipyridine) quantitatively oxidised N2H5+ to N-2. 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 [Mn-4(mu-O)(6)(bipy)(5)(H2O)(N2H4)](4+) appears to be the reactive species. The overall first-order rate constant k(0) decreases linearly with increased mole % of D2O and k(0) 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.