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 O activation play a key role for controlling the reactivity of Cu/O 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 O-derived ligands is scarce. Here we present a detailed study of the reversible interconversion of a μ-peroxodicopper(II) complex ([1]) and its μ-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-peroxo/μ-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 (μ-O) species are revealed. DFT calculations allowed to fully map and correlate the trajectories of H-transfer and μ-peroxo→μ-peroxo rearrangement. These findings enhance our understanding of two key intermediates in bioinspired Cu/O chemistry.