Iron catalysis of the reduction of oxime-bound nickel(IV) by hydroxylamine

The nickel(IV) complex of the dianion of 2,6-diacetylpyridine dioxime was reduced very slowly by NH3OH+ at pH 1-3, hut this reduction is catalysed dramatically by dissolved iron, with Fe-II being the active reductant. With NH3OH+ in excess, the products of the catalysed reaction are N-2 and Ni-II. Non-exponential kinetic profiles for this reaction are consistent with a sequence in which Fe-II is generated by 1e(-) reduction of Fe-III by NH2OH, after which Fe-II reduces Ni-IV to Ni-III via competing protonated and non-protonated paths. Subsequent reduction of Ni-III is taken to be rapid. Rate constants and equilibrium quotients calculated from 15 runs are in accord with literature values.