The synthesis and characterization of Re(CO)₃ pyca-anthraquinone conjugates

Three rhenium carbonyl anthraquinone species have been synthesized (compounds 1–3) using a one-pot methodology. The synthesis involves use of pyridine-2-carboxyaldehyde, which reacts with primary amines and Re(CO)₅X to form a metal bound diamine. Reactions with Re(CO)₅Cl and Re(CO)₅Br afford compounds 1 and 2 respectively, where the anthraquinone unit is pendant to the pyridine aldimine unit. Compound 3 can be produced upon replacement of the halide in 1 and 3 with pyridine. These three complexes have been fully characterized, including by single crystal X-ray diffraction. Compounds 1–3 exhibit metal-to-ligand charge transfer bands in their UV–visible spectra. Additionally, the electrochemical behaviour of 1–3 has been investigated, and all three compounds show positive shifts in their reduction potentials relative to aminoanthraquinone.