Cu(I)/O2 Chemistry Using a β-Diketiminate Supporting Ligand Derived from N,N-Dimethylhydrazine: A [Cu3O2]3+ Complex with Novel Reactivity

A Cu­(I) complex, LCu­(CH3CN), was prepared and characterized, where L– is a sterically unencumbered β-diketiminate ligand, the deprotonated version of 4-(2,2-dimethylhydrazino)­dimethylhydrazone-3-penten-2-one (LH). Analysis of FTIR spectra of the products of the reaction of LCu­(CH3CN) with CO indicate that L– is strongly electron donating, and support an equilibrium in solution between monomeric and dimeric forms with terminal and bridging CO ligands, respectively. Low temperature oxygenation of LCu­(CH3CN) generated a bis­(μ-oxo)­tricopper complex with a S = 1 [Cu3O2]3+ core that was identified on the basis of UV–vis (λmax (ε, M–1 cm–1 per Cu) = 328 (10700), 420 (1500), 590 (835) nm) and X-band electron paramagnetic resonance (EPR) spectroscopy (Δms = 2 transition at 1500 G), electrospray ionization (ESI) mass spectrometry, and spectrophotometric titration (0.35(2) equiv of O2 per copper atom), magnetic susceptibility (μeff = 2.8(1) BM), and H2O2 detection experiments (no H2O2 evolved upon acidification). Unlike other reported variants supported by neutral N-donor ligands, L3Cu3O2 is not reduced by ferrocene, does not abstract H-atoms from phenols or 1,2-dihydroanthracene, oxidizes PPh3 to Ph3PO, and generates carbonate species upon exposure to CO2. This unique reactivity for a [Cu3O2]3+ complex may be traced to the anionic charge and strong electron donating characteristics of L–.