Oxidation of N III and N –I by an {Mn 4 O 6 } 4+ Core in Aqueous Media: Proton‐Coupled Electron Transfer

[Mn 4 (μ‐O) 6 (bipy) 6 ] 4+ ( 1 4+ ; bipy = 2,2′‐bipyridine) and its conjugate acid [Mn 4 (μ‐O) 5 (μ‐OH)(bipy) 6 ] 5+ ( 1 H 5+ ) quantitatively oxidise N III (HNO 2 and NO 2 – ) and N –I (NH 3 OH + and NH 2 OH) to N V (nitrate) and N I (nitrous oxide), respectively, in aqueous solution (pH 2.0–6.0), with 1 H 5+ reacting much faster than 1 4+ . An uncommon feature of these reactions is the kinetic superiority of HNO 2 over its conjugate base NO 2 – . NH 2 OH, however, behaves normally ― the conjugate acid NH 3 OH + is less reactive than NH 2 OH. These reactions show remarkable kinetic isotope effects: the observed rate of N III oxidation increases in D 2 O media whereas the N –I oxidation rate slows down in media enriched with D 2 O. A search of the available data on the redox kinetics of multinuclear oxidants suggests that the title {Mn 4 O 6 } 4+ reduction by N III , the rate of which is accelerated in D 2 O, is the only one established so far. A hydrogen atom transfer (HAT) mechanism (1e, 1H + ; electroprotic) is proposed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)