Stepwise oxidation of anilines by cis-[RuIV(bpy)2(py)(O)]2+

The net six-electron oxidation of aniline to nitrobenzene or azoxybenzene by cis-[RuIV(bpy)2(py)(O)]2+ (bpy is 2,2‘-bipyridine; py is pyridine) occurs in a series of discrete stages. In the first, initial two-electron oxidation is followed by competition between oxidative coupling with aniline to give 1,2-diphenylhydrazine and capture by H2O to give N-phenylhydroxylamine. The kinetics are first order in aniline and first order in Ru(IV) with k(25.1 °C, CH3CN) = (2.05 ± 0.18) × 102 M-1 s-1 (ΔH⧧ = 5.0 ± 0.7 kcal/mol; ΔS⧧ = −31 ± 2 eu). On the basis of competition experiments, kH2O/kD2O kinetic isotope effects, and the results of an 18O labeling study, it is concluded that the initial redox step probably involves proton-coupled two-electron transfer from aniline to cis-[RuIV(bpy)2(py)(O)]2+ (RuIVO2+). The product is an intermediate nitrene (PhN) or a protonated nitrene (PhNH+) which is captured by water to give PhNHOH or aniline to give PhNHNHPh. In the following stages, PhNHOH, once formed, is rapidly oxidi...