Anthraphen: A Salphen‐Like Non‐Innocent Tetradentate Anthraquinone Imine Dye – Coordination and Electrochemistry

Abstract

AbstractA new, highly redox‐active chromophore ligand, H2(anthraphen) (1), containing two o‐phenylenediamine‐linked anthraquinone imine units has been synthesized in a three‐step synthesis and fully characterized by X‐ray crystallography, UV/Vis spectroscopy, and cyclic voltammetry. The dark‐red dye 1 shows molar extinction coefficients of up to 47000 L mol–1 cm–1 and four reversible reduction processes. This dianionic N2O2 ligand, with a significantly extended π system, offers a salphen‐like binding cavity for metal coordination, as has been demonstrated by the synthesis of [K2(anthraphen)] (2) and the transition‐metal complexes of TiIV (3), VIV (4), FeII (5), FeIII (6), CoII (7), NiII (8), CuII (9), PdII (10), PtII (11), and ZnII (12). These metal chromophores have colors ranging from dark‐red, violet, green to black. Their optical and electrochemical properties were investigated and compared with those of the diprotic ligand. Coordination led to an increase in the molar extinction coefficients up to 66400 L mol–1 cm–1 in the case of [V(anthraphen)O] (4), broadening of the absorption bands in the visible‐light region as well as a redshift of the lowest‐energy absorption band. The lowest‐energy absorption observed for these complexes to date is for [Ni(anthraphen)] (8) at 784 nm. The metal chromophores exhibit up to five fully reversible oxidation and reduction processes.