Juglophen: a tetradentate non-innocent electron sponge naphthoquinone-imine ligand and its reduced and oxidized nickel complexes [Ni(jp)] -,0

The synthesis of new tetradentate dianionic N O ligand juglophen (H jp, 1) and its nickel(II) complex [Ni(jp)] (2) is reported. The unprecedented ligand synthesis is accomplished oxidative coupling of 1,5-dihydroxynapthalene and -phenylenediamine by hypervalent phenyliodine(III)-diacetate. Ligand 1 and complex 2 were characterized NMR, IR, UV-Vis spectroscopy, mass spectrometry, cyclic voltammetry and by XRD analysis. In order to investigate the non-innocent character of ligand 1, [Ni(jp)] (2) was oxidized using AgPF to form [Ni(jp)] [PF ] (3) whereas one-electron reduction with [Cp Co] generated [Cp Co] [Ni(jp)] (4). The paramagnetic nature of the oxidized and reduced species 3 and 4 was validated EPR spectroscopy and further investigated pursuing DFT calculations at the PBE-D3(BJ)/def2-TZVPP level of theory. Predominantly ligand-centered SOMOs of 3 and 4 are allowing insight towards a deeper understanding of the redox behavior of [Ni(jp)] (2).