Acid/base triggered interconversion of μ-η2:η2-peroxido and bis(μ-oxido) dicopper intermediates capped by proton-responsive ligands

Abstract

Cu^II₂(μ-η²:η²-peroxido) and Cu^III₂(μ-oxido)₂ cores represent key intermediates in copper/dioxygen chemistry, and they are mechanistically important for biological hydroxylation and oxidation reactions mediated by dinuclear (type III) copper metalloenzymes. While the exact nature of the active species in different enzymes is still under debate, shifting equilibria between Cu_x/O₂ species is increasingly recognized as a means of switching between distinct reactivity patterns of these intermediates. Herein we report comprehensive spectroscopic, crystallographic and computational analysis of a family of synthetic Cu^II₂(μ-η²:η²-peroxido) and Cu^III₂(μ-oxido)₂ dicopper complexes with a bis(oxazoline) (BOX) capping ligand. In particular, we demonstrate that a reversible peroxido/bis(μ-oxido) interconversion of the [Cu₂O₂] core can be triggered by peripheral (de)protonation events on the ligand backbone. As the copper ions in the enzymes are typically supported by histidine imidazoles that offer a backside N atom amenable to potential (de)protonation, it is well conceivable that the shifting of equilibria between the [Cu₂O₂] species in response to changes in local pH is biologically relevant.