In this report, we present the dinuclear copper(II) dimethylglyoxime (H2dmg) complex [Cu2(H2dmg)(Hdmg)(dmg)]+ (1), which, in contrast to its mononuclear analogue [Cu(Hdmg)2] (2), is subject to a cooperativity‐driven hydrolysis. The combined Lewis acidity of both copper centers increases the electrophilicity of the carbon atom in the bridging μ2‐O−N=C‐group of H2dmg and thus, facilitates the nucleophilic attack of H2O. This hydrolysis yields butane‐2,3‐dione monoxime (3) and NH2OH that, depending on the solvent, is then either oxidized or reduced. In ethanol, NH2OH is reduced to NH4+, yielding acetaldehyde as the oxidation product. In contrast, in CH3CN, NH2OH is oxidized by CuII to form N2O and [Cu(CH3CN)4]+. Herein are presented the combined synthetic, theoretical, spectroscopic and spectrometric methods that indicate and establish the reaction pathway of this solvent‐dependent reaction.

The cover picture shows a closer look at the decomposition of the tetrafluoroborate anion (BF4‐) during the reaction of Cu(BF4)2⋅6H2O and dimethylglyoxime (H2dmg) to formally “BF2+” and 2F‐. Whereas the high affinity of fluoride anions towards silicon lead to the formation of SiF62‐, BF2 is inserted into the ligand framework to yield diverse O,O‐bidentate difluoroboron copper(II) complexes. These resulting complexes have been isolated and structurally characterized. Their molecular structures frame the magnifying glass that highlights the decomposition of BF4‐. (DOI: 10.1002/zaac.202200150).

Cooperativity at the crossroad: The two copper centers in the dinuclear copper(II) dimethylglyoxime complex work in concert to facilitate ligand hydrolysis that yields butane‐2,3‐dione monoxime and NH2OH. The fate of NH2OH depends on the solvent used, in CH3CN, for example, NH2OH is oxidized to N2O yielding [Cu(CH3CN)4]+ as reduced species. In ethanol, however, NH2OH is reduced to NH4+, which in turn yields acetaldehyde as oxidized species. More information can be found in the Research Article by S. Becker and co‐workers (DOI: 10.1002/chem.202203438).

The reaction of copper(II) tetrafluoroborate with dimethylglyoxime (H2dmg) leads to the formation of the dinuclear complexes [Cu2(dmg)(Hdmg)(EtOH)(H2dmg)]BF4 (1) and [Cu2(dmg ⋅ BF2)(Hdmg)(H2dmg)]BF4 (2). In 2, BF2 deriving from BF4− has been inserted into the oxime groups to form an O,O‐bidentate difluoroboron complex. Co‐crystallization of 1 and 2 impeded a thorough characterization of 2. In further attempts to prepare pure 2, the difluoroboron complexes [Cu(dmg ⋅ BF2)2(MeCN)] (3) and [Cu(dmg ⋅ BF2)(Hdmg)] (4) have been obtained. Attempts to isolate the BF2‐bridged ligand failed. Even though BF4− readily is decomposed to formally form BF2+ that is inserted into the resulting complexes and F−, the nascent F− ions are not a suitable F− source for organic fluorination reactions. Nevertheless, the described, facile route to prepare O,O‐bidentate difluoroboron complexes without the usage of the highly toxic BF3 ⋅ OEt2 but BF4− instead is of interest for synthetically working chemists.