On the equilibrium of mono‐ and dinuclear Cu(II) dimethylglyoxime complexes and its exploitation for the simple preparation of Cu(I) salts [Cu(CH3CN)4]X (X = ClO4‐, BF4‐, OTf‐)

The reaction of Cu(OAc)2 with dimethylglyoxime (H2dmg) yields the mononuclear complex [Cu(Hdmg)2] (1), whereas the reaction of Cu(ClO4)2∙6H2O with H2dmg yields a dinuclear complex [Cu2(H2dmg)(Hdmg)(dmg)]ClO4 (2a). Systematic studies of the stoichiometric ratios of the reactants, the nature of the anion as well as pH value show that the pH value of the reaction solution/anion governs the nuclearity. I.e., basic anions and/or addition of a base yield 1. Once the product has formed in solution, it remains stable despite further changes of the pH value or addition of excess H2dmg. A conversion of one species into the other can only be achieved by simultaneous change of pH and addition of H2dmg. Accordingly, among sole addition of a base, 2a isomerizes but does not change its nuclearity. In contrast, if NaOtBu and H2dmg are added, 2a converts into 1. The same happens if the slightly basic salt Na2dmg is added to a solution of 2a. Furthermore, the formation of 2a can be exploited for the preparation of [Cu(CH3CN)4]X (X = ClO4‐, BF4‐, OTf‐) due to a recently reported cooperativity‐driven decomposition of 2a.