Dithiolate and Catecholate Binding of Copper by the OO∼SS Bifunctional Ligand: Regioselectivity and Regioisomeric Transformations

o‐Quinone bearing annulated dithiete ring (DitQ) provides a unique opportunity for comparison of properties of benzodithiolene and benzodioxolene coordination sites. The majority of Pd, Pt or alkali metal containing metallofragments are regioselectively bound either by dithiolene or dioxolene site of the DitQ, whereas Cu(II) adducts with phenanthroline or bipyridine display equilibrium between catecholate and dithiolate forms. To the best of our knowledge this is a rare example of equilibrium between regioisomeric coordination compounds. We determined the energetic parameters of this equilibrium from temperature‐dependent electron paramagnetic resonance measurements. Unambiguous dithiolate binding mode for DitQ was found in case of trinuclear Cu(I)−Cu(II)−Cu(I) species where a formal oxidation state of copper is +11/3 . o‐Quinone fused with 1,2‐dithiete ring is a model system that provides an opportunity for study of competition for binding of metal ion by dithiolene and dioxolene coordination sites. Copper (II) complexes with phenanthroline or bipyridine ligands and this o‐quinone displaying a temperature dependent equilibrium between dithiolate and catecholate regioisomeric forms in solution was reported.