Cu(I)/O2 chemistry using a ß-diketiminate supporting ligand derived from N,N-dimethylhydrazine: a [Cu3O2]3+ complex with novel reactivity.

ABSTRACT

A Cu(I) complex, LCu(CH(3)CN), was prepared and characterized, where L(-) is a sterically unencumbered ß-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(CH(3)CN) 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(CH(3)CN) generated a bis(µ-oxo)tricopper complex with a S = 1 [Cu(3)O(2)](3+) core that was identified on the basis of UV-vis (λ(max) (ε, M(-1) cm(-1) per Cu) = 328 (10700), 420 (1500), 590 (835) nm) and X-band electron paramagnetic resonance (EPR) spectroscopy (Δm(s) = 2 transition at 1500 G), electrospray ionization (ESI) mass spectrometry, and spectrophotometric titration (0.35(2) equiv of O(2) per copper atom), magnetic susceptibility (µ(eff) = 2.8(1) BM), and H(2)O(2) detection experiments (no H(2)O(2) evolved upon acidification). Unlike other reported variants supported by neutral N-donor ligands, L(3)Cu(3)O(2) is not reduced by ferrocene, does not abstract H-atoms from phenols or 1,2-dihydroanthracene, oxidizes PPh(3) to Ph(3)P═O, and generates carbonate species upon exposure to CO(2). This unique reactivity for a [Cu(3)O(2)](3+) complex may be traced to the anionic charge and strong electron donating characteristics of L(-).