Homoleptic Fe(III) and Fe(IV) Complexes of a Dianionic C3-Symmetric Scorpionate

Serhii Tretiakov; Martin Lutz; Charles James Titus; Frank de Groot; Joscha Nehrkorn; Thomas Lohmiller; Karsten Holldack; Alexander Schnegg; Maxime François Xavier Tarrago; Peng Zhang; Shengfa Ye; Dmitry Aleshin; Alexander Pavlov; Valentin Novikov; Marc-Etienne Moret

doi:10.1021/acs.inorgchem.3c00871

Homoleptic Fe(III) and Fe(IV) Complexes of a Dianionic C₃-Symmetric Scorpionate

Inorg Chem. 2023 Jul 10;62(27):10613-10625. doi: 10.1021/acs.inorgchem.3c00871. Epub 2023 Jun 27.

Authors

Serhii Tretiakov¹, Martin Lutz², Charles James Titus³, Frank de Groot⁴, Joscha Nehrkorn⁵, Thomas Lohmiller⁶, Karsten Holldack⁷, Alexander Schnegg⁵, Maxime François Xavier Tarrago⁸, Peng Zhang^{9

10}, Shengfa Ye⁹, Dmitry Aleshin¹¹, Alexander Pavlov^{11

12}, Valentin Novikov¹², Marc-Etienne Moret¹

Affiliations

¹ Organic Chemistry & Catalysis, Institute for Sustainable and Circular Chemistry, Utrecht University, 3584 CG Utrecht, The Netherlands.
² Structural Biochemistry, Bijvoet Centre for Biomolecular Research, Faculty of Science, Utrecht University, 3584 CG Utrecht, The Netherlands.
³ Department of Physics, Stanford University, Stanford, California 94305, United States.
⁴ Materials Chemistry & Catalysis, Debye Institute for Materials Science, Utrecht University, 3584 CG Utrecht, The Netherlands.
⁵ Max-Planck-Institute for Chemical Energy Conversion, EPR Research Group, 45470 Mülheim/Ruhr, Germany.
⁶ Department Spins in Energy Conversion and Quantum Information Science, Helmholtz Zentrum Berlin für Materialien und Energie GmbH, EPR4 Energy Joint Lab, 12489 Berlin, Germany.
⁷ Department of Optics and Beamlines, Helmholtz Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany.
⁸ Department of Molecular Theory and Spectroscopy, Max Planck Institut für Kohlenforschung, 45470 Mülheim/Ruhr, Germany.
⁹ State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P. R. China.
¹⁰ University of Chinese Academy of Sciences, Beijing 10049, China.
¹¹ A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova Street 28, Moscow 119991, Russia.
¹² Moscow Institute of Physics and Technology, Institutskiy per., 9, Dolgoprudny, Moscow 119991, Russia.

Abstract

High-valent iron species have been implicated as key intermediates in catalytic oxidation reactions, both in biological and synthetic systems. Many heteroleptic Fe(IV) complexes have now been prepared and characterized, especially using strongly π-donating oxo, imido, or nitrido ligands. On the other hand, homoleptic examples are scarce. Herein, we investigate the redox chemistry of iron complexes of the dianonic tris-skatylmethylphosphonium (TSMP^2-) scorpionate ligand. One-electron oxidation of the tetrahedral, bis-ligated [(TSMP)₂Fe^II]^2- leads to the octahedral [(TSMP)₂Fe^III]^-. The latter undergoes thermal spin-cross-over both in the solid state and solution, which we characterize using superconducting quantum inference device (SQUID), Evans method, and paramagnetic nuclear magnetic resonance spectroscopy. Furthermore, [(TSMP)₂Fe^III]^- can be reversibly oxidized to the stable high-valent [(TSMP)₂Fe^IV]⁰ complex. We use a variety of electrochemical, spectroscopic, and computational techniques as well as SQUID magnetometry to establish a triplet (S = 1) ground state with a metal-centered oxidation and little spin delocalization on the ligand. The complex also has a fairly isotropic g-tensor (g_iso = 1.97) combined with a positive zero-field splitting (ZFS) parameter D (+19.1 cm^-1) and very low rhombicity, in agreement with quantum chemical calculations. This thorough spectroscopic characterization contributes to a general understanding of octahedral Fe(IV) complexes.