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submitted on 24.03.2020 and posted on 25.03.2020by Andrew McNeece, Kate Jesse, Jiaze Xie, Alexander S. Filatov, John Anderson
Metal ligand cooperativity is a powerful
strategy in transition metal chemistry. This type of mechanism for the
activation of O2 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 tBu,TolDHP
activate O2 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 withfunctionally redox-inactive Ni centers enables oxidative transformations
more commonly mediated by metals such as Fe and Cu.