Switching from metal- to ligand-based oxidation in cobalt complexes with redox-active bisguanidine ligands

• Verfasst von: Lohmeyer, Lukas [VerfasserIn]
• Verfasst von: Kaifer, Elisabeth [VerfasserIn]
• Verfasst von: Enders, Markus [VerfasserIn]
• Verfasst von: Himmel, Hans-Jörg [VerfasserIn]
• Titel: Switching from metal- to ligand-based oxidation in cobalt complexes with redox-active bisguanidine ligands
• Verf.angabe: Lukas Lohmeyer, Elisabeth Kaifer, Markus Enders, and Hans-Jörg Himmel
• Jahr: 2021
• Umfang: 16 S.
• Fussnoten: First published: 08 June 2021 ; Gesehen am 25.11.2022
• Titel Quelle: Enthalten in: Chemistry - a European journal
• Ort Quelle: Weinheim : Wiley-VCH, 1995
• Jahr Quelle: 2021
• Band/Heft Quelle: 27(2021), 46, Seite 11852-11867
• ISSN Quelle: 1521-3765
• DOI: doi:10.1002/chem.202101364
• Datenträger: Online-Ressource
• Sprache: eng
• Sach-SW: cobalt
• Sach-SW: guanidine
• Sach-SW: oxidation
• Sach-SW: radical ligands
• Sach-SW: redox-active ligand
• K10plus-PPN: 1823668585
• K10plus-PPN:
  Universitätsbibliothek
• Lokale URL UB: Zum Volltext

Abstract

The control of the redox reactivity, magnetic and optical properties of the different redox states of complexes with redox-active ligands permits their rational use in catalysis and materials science. The redox-chemistry of octahedrally coordinated high-spin CoII complexes (three unpaired electrons) with one redox-active bisguanidine ligand and two acetylacetonato (acac) co-ligands is completely changed by replacing the acac by hexafluoro-acetylacetonato (hfacac) co-ligands. The first one-electron oxidation is metal-centered in the case of the complexes with acac co-ligands, giving diamagnetic CoIII complexes. By contrast, in the case of the less Lewis-basic hfacac co-ligands, the first one-electron oxidation becomes ligand-centered, leading to high-spin CoII complexes with a radical monocationic guanidine ligand unit (four unpaired electrons). Ferromagnetic coupling between the spins on the metal and the organic radical in solution is evidenced by temperature-dependent paramagnetic NMR studies, allowing to estimate the isotropic exchange coupling constant in solution. Second one-electron oxidation leads to high-spin CoII complexes with dicationic guanidine ligand units (three unpaired electrons) in the presence of hfacac co-ligands, but to low-spin CoIII complexes with radical monocationic, peralkylated guanidine ligand (one unpaired electron) in the presence of acac co-ligands. The analysis of the electronic structures is complemented by quantum-chemical calculations on the spin density distributions and relative energies of the possible redox isomers.