Stimulation of Redox‐Induced Electron Transfer by Interligand Hydrogen Bonding in a Cobalt Complex with Redox‐Active Guanidine Ligand. Issue 18 (18th March 2021)

• Record Type: Journal Article
• Authors: Lohmeyer, Lukas; Schön, Florian; Kaifer, Elisabeth; Himmel, Hans‐Jörg
• Is Part Of: Angewandte Chemie international edition. Volume 60:Issue 18(2021)
• Page Start: 10415
• Page End: 10422
• Publication Date: 2021-03-18
• Subjects: cobalt -- electron transfer -- guanidine -- hydrogen bonding -- redox active ligand; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202101423
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Octahedrally coordinated cobalt(II) complexes with a redox‐active bisguanidine ligand and acac co‐ligands were synthesized and their redox chemistry analysed in detail. The N−H functions in a bisguanidine ligand with partially alkylated guanidino groups form N−H⋅⋅⋅O hydrogen bonds with the acac co‐ligands, thereby massively influencing the redox chemistry. For all complexes, the first one‐electron oxidation is metal‐centred, leading to Co III complexes with neutral bisguanidine ligand units. Further one‐electron oxidation is ligand‐centred in the case of Co–bisguanidine complexes with fully alkylated guanidino groups, giving Co III complexes with radical monocationic bisguanidine ligands. On the other hand, the hydrogen‐bond strengthening upon oxidation of the Co–bisguanidine complex with partially alkylated guanidino groups initiates metal reduction (Co III →Co II ) and two‐electron oxidation of the guanidine ligand, providing the first example for the stimulation of redox‐induced electron transfer by interligand hydrogen bonding. Abstract : The strengthening of interligand hydrogen bonding triggers a redox‐induced intramolecular electron transfer (RIET) upon oxidation of a Co III complex with a neutral redox‐active bisguanidine ligand, leading to metal reduction (Co III →Co II ) and two‐electron oxidation of the bisguanidine ligand. In the absence of interligand hydrogen bonding, oxidation leads to a Co III complex with a radical monocationic guanidine ligand.