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 copper(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), electron paramagnetic resonance spectroscopy (silent), and density functional theory 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 that highlight the potential for the formazan ligand to exhibit “noninnocent” behavior.