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

The synthesis of new tetradentate dianionic N 2 O 2 ligand juglophen (H 2 jp, 1 ) and its nickel( ii ) complex [Ni(jp)] ( 2 ) is reported. The unprecedented ligand synthesis is accomplished via oxidative coupling of 1,5-dihydroxynapthalene and o -phenylenediamine by hypervalent phenyliodine( iii )-diacetate. Ligand 1 and complex 2 were characterized via 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 6 to form [Ni(jp)] + [PF 6 ] − ( 3 ) whereas one-electron reduction with [Cp 2 Co] generated [Cp 2 Co] + [Ni(jp)] − ( 4 ). The paramagnetic nature of the oxidized and reduced species 3 and 4 was validated via 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 ). The synthesis of new tetradentate dianionic N 2 O 2 ligand juglophen (H 2 jp, 1 ), its nickel( ii ) complex [Ni(jp)] ( 2 ) as well as oxidized [Ni(jp)] + (3) and reduced [Ni(jp)] − (4) ionic species are reported.