Metal ligand cooperativity is a powerful
strategy in transition metal chemistry. This type of mechanism for the
activation of O<sub>2</sub> is best exemplified by heme centers in biological
systems. While aerobic oxidations with Fe and Cu are well precedented, Ni-based
oxidations are frequently less common due to less-accessible metal-based redox couples.
Some Ni enzymes utilize special ligand environments for tuning the Ni(II)/(III)
redox couple such as strongly donating thiolates in Ni superoxide dismutase. A
recently characterized example of a Ni-containing protein, however, suggests an
alternative strategy for mediating redox chemistry with Ni by utilizing
ligand-based reducing equivalents to enable oxygen binding. While this
mechanism has little synthetic precedent, we show here that Ni complexes of the
redox-active ligand<i><sup> t</sup></i><sup>Bu,Tol</sup>DHP
(<i><sup>t</sup></i><sup>Bu,Tol</sup>DHP =
2,5-bis((2-<i>t</i>-butylhydrazono)(<i>p</i>-tolyl)methyl)-pyrrole)
activate O<sub>2</sub> to generate a Ni(II) superoxo complex via ligand-based
electron transfer. This superoxo complex is competent for stoichiometric
oxidation chemistry with alcohols and hydrocarbons. This work demonstrates that
coupling ligand-based redox chemistry with<b>
</b>functionally redox-inactive Ni centers enables oxidative transformations
more commonly mediated by metals such as Fe and Cu.