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  • PhenTAA: A Redox-Active N4‑...
    Epping, Roel F. J.; de Zwart, Felix J.; van Leest, Nicolaas P.; van der Vlugt, Jarl Ivar; Siegler, Maxime A.; Mathew, Simon; Reek, Joost N. H.; de Bruin, Bas

    Inorganic chemistry, 01/2024, Letnik: 63, Številka: 4
    Journal Article

    Here, we present the development and characterization of the novel PhenTAA macrocycle as well as a series of Ni­(R2PhenTAA)n complexes featuring two sites for ligand-centered redox-activity. These differ in the substituent R (R = H, Me, or Ph) and overall charge of the complex n (n = −2, −1, 0, +1, or +2). Electrochemical and spectroscopic techniques (CV, UV/vis–SEC, X-band EPR) reveal that all redox events of the Ni­(R2PhenTAA) complexes are ligand-based, with accessible ligand charges of −2, −1, 0, +1, and +2. The o-phenylenediamide (OPD) group functions as the electron donor, while the imine moieties act as electron acceptors. The flanking o-aminobenzaldimine groups delocalize spin density in both the oxidized and reduced ligand states. The reduced complexes have different stabilities depending on the substituent R. For R = H, dimerization occurs upon reduction, whereas for R = Me/Ph, the reduced imine groups are stabilized. This also gives electrochemical access to a Ni­(R2PhenTAA)2– species. DFT and TD–DFT calculations corroborate these findings and further illustrate the unique donor–acceptor properties of the respective OPD and imine moieties. The novel Ni­(R2PhenTAA) complexes exhibit up to five different ligand-based oxidation states and are electrochemically stable in a range from −2.4 to +1.8 V for the Me/Ph complexes (vs Fc/Fc+).