Effects of Electron-Deficient β-Diketiminate and Formazan Supporting Ligands on Copper(I)-Mediated Dioxygen Activation

Copper(I) complexes of a diketiminate featuring CF3 groups on the backbone and dimethylphenyl substituents (4) and a nitroformazan (5) were synthesized and shown by spectroscopy, X-ray crystallography, cyclic voltammetry, and theory to contain Cu(I) sites electron deficient relative to those supported by previously studied diketiminate complexes comprising alkyl or aryl backbone substituents. Despite their electron poor nature, oxygenation of LCu(CH3CN) (L = 4 or 5) at room temperature yielded bis(hydroxo)dicopper(II) compounds and at − 80 °C yielded bis(μ-oxo)dicopper complexes that were identified on the basis of UV-vis and resonance Raman spectroscopy, spectrophotometric titration results (2:1 Cu/O2 ratio), EPR silence, and DFT calculations. The bis(μ-oxo)dicopper complex supported by 5 exhibited unusual spectroscopic properties and decayed via a novel intermediate proposed to be a metallaverdazyl radical complex, findings which highlight the potential for the formazan ligand to exhibit ‘non-innocent’ behavior.