Mononuclear Iron-(hydro/semi)quinonate Complexes Featuring Neutral and Charged Scorpionates: Synthetic Models of Intermediates in the Hydroquinone Dioxygenase Mechanism

Authors

Amanda E. Baum, Marquette UniversityFollow
Sergey V. Lindeman, Marquette UniversityFollow
Adam T. Fiedler, Marquette UniversityFollow

Document Type

Article

Language

eng

Format of Original

10 p.

Publication Date

6-2016

Publisher

Wiley-VCH Verlag

Source Publication

European Journal of Inorganic Chemistry

Source ISSN

1434-1948

Abstract

Neutral and anionic scorpionate ligands have been employed to generate active-site models of hydroquinone dioxygenases (HQDOs). While the nonheme Fe center in nearly all HQDOs is coordinated to one Asp (or Glu) and two His residues, 1,2-gentisate dioxygenase (GDO) is unique in featuring a three His triad instead. A synthetic GDO model was therefore prepared with the neutral tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (^Ph2TIP) ligand. The gentisate substrate was mimicked with the bidentate ligand 2-(1-methylbenzimidazol-2-yl)hydroquinonate (BIHQ). X-ray diffraction analysis of the resulting complex, [Fe(^Ph2TIP)(BIHQ)]OTf (1a), revealed a distorted square-pyramidal geometry. Structural and electrochemical data collected for 1a were compared to those previously reported for [Fe(^Ph2Tp)(BIHQ)] (1b), which features an anionic hydridotris(3,5-diphenylpyrazol-1-yl)borate (^Ph2Tp) ligand. Oxidation of 1a and 1b provides the corresponding Fe^III complexes (2a/2b) and the crystal structure of 2b is reported. Both complexes undergo reversible deprotonation to yield the brown chromophores, 3a and 3b. Detailed studies of 3a and 3b with spectroscopic (UV/Vis absorption, EPR, resonance Raman) and computational methods determined that each complex consists of a high-spin Fe^II center ferromagnetically coupled to a p-semiquinonate radical (BISQ). The (de)protonation-induced valence tautomerization described here resembles key steps in the putative HQDO mechanism.

Comments

Accepted version. European Journal of Inorganic Chemistry, Vol. 2016, No. 15-16 (June 2016): 2455-2464. DOI. © 2016 Wiley. Used with permission.

Recommended Citation

Baum, Amanda E.; Lindeman, Sergey V.; and Fiedler, Adam T., "Mononuclear Iron-(hydro/semi)quinonate Complexes Featuring Neutral and Charged Scorpionates: Synthetic Models of Intermediates in the Hydroquinone Dioxygenase Mechanism" (2016). Chemistry Faculty Research and Publications. 562.
https://epublications.marquette.edu/chem_fac/562