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‐)

Abstract The reaction of Cu(OAc) 2 with dimethylglyoxime (H 2 dmg) yields the mononuclear complex [Cu(Hdmg) 2 ] ( 1 ), whereas the reaction of Cu(ClO 4 ) 2 ⋅ 6H 2 O with H 2 dmg yields a dinuclear complex [Cu 2 (H 2 dmg)(Hdmg)(dmg)]ClO 4 ( 2 a ). 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 H 2 dmg. A conversion of one species into the other can only be achieved by simultaneous change of pH and addition of H 2 dmg. Accordingly, among sole addition of a base, 2 a isomerizes but does not change its nuclearity. In contrast, if NaO t Bu and H 2 dmg are added, 2 a converts into 1 . The same happens if the slightly basic salt Na 2 dmg is added to a solution of 2 a . Furthermore, the formation of 2 a can be exploited for the preparation of [Cu(CH 3 CN) 4 ]X (X=ClO 4 − , BF 4 − , OTf − ) due to a recently reported cooperativity‐driven decomposition of 2 a .