Structural Snapshots, Trajectory and Thermodynamics of the Reversible μ-1,2-Peroxo/μ-1,1-Hydroperoxo Dicopper(II) Interconversion

Hydrogen bonds involving the oxygen atoms of intermediates that result from copper-mediated O₂ activation play a key role for controlling the reactivity of Cu_x/O₂ active sites in metalloenzymes and synthetic model complexes. However, structural insight into H-bonding in such transient species as well as thermodynamic information about proton transfer to or from the O₂-derived ligands is scarce. Here we present a detailed study of the reversible interconversion of a μ_1,2-peroxodicopper(II) complex ([1]⁺) and its μ_1,1-hydroperoxo congener ([2]⁺) via (de)protonation, including the isolation and structural characterization of several H-bond donor (HBD) adducts of [1]⁺ and the determination of binding constants. For one of these adducts a temperature-dependent μ_1,2-peroxo/μ_1,1-hydroperoxo equilibrium associated with reversible H⁺-translocation is observed, its thermodynamics investigated experimentally and computationally, and effects of H-bonding on spectroscopic parameters of the Cu^II₂(μ_1,2-O₂) species are revealed. DFT calculations allowed to fully map and correlate the trajectories of H⁺-transfer and μ_1,2-peroxo→μ_1,1-peroxo rearrangement. These findings enhance our understanding of two key intermediates in bioinspired Cu₂/O₂ chemistry.