Solutions of the nickel(IV) complex of the dianion of 2,6-diacetylpyridine dioxime (chelate II in text) are stable enough at low pH values to allow redox studies involving aquametal cations as reductants. This Ni(IV) derivative is reduced cleanly to Ni(II) by aqueous solutions of Fe(II), Sn(II), I-, and U(IV) but reacts unobservably slowly with the 2e reductants H3PO2 and H3AsO3. There is no evidence for accumulation of the intermediate state Ni(III), even with the oxidant in large excess. Rate laws for reductions by Fe(II), Sn(II), and I- feature prominent [H+]-dependent terms, reflecting partial protonation of the oxidant. The Sn(II) reduction is strongly catalyzed by Cl-, suggesting involvement of an unusually reactive chloro-substituted reductant. Reductions by U(IV) at [H+] below 0.02 M are catalyzed by UO22+; under these conditions, rates are proportional to ([U-VI][U-IV])(1/2). The overall kinetic picture of the Ni(IV)-U(IV) system supports a sequence in which the reactive intermediate, a U(V) species, may undergo one of two competing processes-reduction of Ni(IV) or reversible disproportionation to U-VI and U-IV. Each of the proposed steps is a single electron transfer. These results, taken together, bolster the view that conversions of Ni(IV) to Ni(II), a net 2e process, must entail pairs of le steps. Such is the case even for the (relatively slow) reduction by Sn(II), which appears to be initiated by formation of a Sn(III) species significantly stabilized via ligation by chloride.