Metal-superoxo and -peroxo species are commonly proposed intermediates in the O2 activation mechanisms of metalloenzymes, including nonheme enzymes that incorporate both atoms of O2 into their substrate (i.e., dioxygenases). We have prepared a series of bioinspired iron and cobalt complexes supported by hydrotris(pyrazolyl)borate scorpionates. In certain cases, these complexes react with O2 to yield iron- and cobalt-superoxo adducts that resemble those proposed in dioxygenase catalysis. In addition, we have observed that cobalt complexes with “noninnocent” imino(thio)semiquinonate ligands bind dioxygen reversibly to generate novel cobalt(III)-alkylperoxo structures. The identities and structures of these various intermediates have been probed using multiple spectroscopic techniques, including electronic absorption, electron paramagnetic resonance, and resonance Raman spectroscopies. Thermodynamic parameters have been measured to better understand the electronic factors that control the O2 binding affinities of cobalt ions in both biological and synthetic contexts. The implications of these biomimetic studies for our understanding of metalloenzyme catalysis will be discussed.

Probing the dioxygen reactivity of biologically-relevant iron and cobalt complexes with redox-active ligands

ACS Spring Meeting 2021

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