Reversible Dioxygen Binding to Co(II) Complexes with Noninnocent Ligands

Authors

Praveen Kumar, Marquette University
Laxmi Devkota, Marquette University
Maximilian C. Casey, Marquette University
Anne A. Fischer, Marquette University
Sergey V. Lindeman, Marquette UniversityFollow
Adam T. Fiedler, Marquette UniversityFollow

Document Type

Article

Publication Date

10-2022

Publisher

ACS Publications

Source Publication

Inorganic Chemistry

Source ISSN

1520-5126

Original Item ID

doi.10.1021/acs.inorgchem.2c02246

Abstract

A series of mononuclear Co(II) complexes with noninnocent (redox-active) ligands are prepared that exhibit metal–ligand cooperativity during the reversible binding of O₂. The complexes have the general formula, [Co^II(L^S,N)(Tp^R2)] (R = Me, Ph), where L^S,N is a bidentate o-aminothiophenolate and Tp^R2 is a hydrotris(pyrazol-1-yl)borate scorpionate with R-substituents at the 3- and 5-positions. Exposure to O₂ at room temperature results in one-electron oxidation and deprotonation of L^S,N. The oxidized derivatives possess substantial “singlet diradical” character arising from antiferromagnetic coupling between an iminothiosemiquinonate (ITSQ^•–) ligand radical and a low-spin Co(II) ion. The [Co^II(Tp^Me2)(^X2ITSQ)] complexes, where X = H or tBu, coordinate O₂ reversibly at reduced temperatures to provide Co/O₂ adducts. The O₂ binding reactions closely resemble those previously reported by our group (Kumar et al., J. Am. Chem. Soc. 2019,141, 10984–10987) for the related complexes [Co^II(Tp^Me2)(^tBu2SQ)] and [Co^II(Tp^Me2)(^tBu2ISQ)], where ^tBu2(I)SQ represents 4,6-di-tert-butyl-(2-imino)semiquinonate radicals. In each case, the oxygenation reaction proceeds via the addition of O₂ to both the cobalt ion and the ligand radical, generating metallocyclic cobalt(III)-alkylperoxo structures. Thermodynamic measurements elucidate the relationship between O₂ affinity and redox potentials of the (imino)(thio)semiquinonate radicals, as well as energetic differences between these reactions and conventional metal-based oxygenations. The results highlight the utility and versatility of noninnocent ligands in the design of O₂-absorbing compounds.

Comments

Accepted version. Inorganic Chemistry, Vol. 61, No. 42 (October 2022): 16664-16677. DOI. © American Chemical Society. Used with permission.

Recommended Citation

Kumar, Praveen; Devkota, Laxmi; Casey, Maximilian C.; Fischer, Anne A.; Lindeman, Sergey V.; and Fiedler, Adam T., "Reversible Dioxygen Binding to Co(II) Complexes with Noninnocent Ligands" (2022). Chemistry Faculty Research and Publications. 1064.
https://epublications.marquette.edu/chem_fac/1064