Reversible O−O Bond Cleavage in Copper−Dioxygen Isomers:  Impact of Anion Basicity

Low-temperature oxygenation of copper(I) complexes of N,N,N ‘,N ‘-tetraethylpropane-1,3-diamine yields solutions containing both μ-η2:η2-peroxodicopper(II) (P) and bis(μ-oxo)dicopper(III) (O) valence isomers. The P/O equilibrium position depends on the nature of the counteranion; P is favored with more basic anions. Titration and EXAFS experiments as well as DFT calculations suggest that axial donation from a sulfonate anion to the copper centers imparts an electronic/electrostatic bias toward the P isomer.