Copper(II)-Oxyl Formation in a Biomimetic Complex Activated by Hydrogen Peroxide: The Key Role of Trans-Bis(Hydroxo) Species

Enzymes in nature, such as the copper-based lytic polysaccharide
monooxygenases (LPMOs), have gained significant attention for their
exceptional performance in C–H activation reactions. The use
of H2O2 by LPMOs enzymes has also increased
the interest in understanding the oxidation mechanism promoted by
this oxidant. While some literature proposes Fenton-like chemistry
involving the formation of Cu(II)–OH species and the hydroxyl
radical, others contend that Cu(I) activation by H2O2 yields a Cu(II)–oxyl intermediate. In this study,
we focused on a bioinspired Cu(I) complex to investigate the reaction
mechanism of its oxidation by H2O2 using density
functional theory and ab initio molecular dynamics simulations. The
latter approach was found to be critical for finding the key Cu intermediates.
Our results show that the highly flexible coordination environment
of copper strongly influences the nature of the oxidized Cu(II) species.
Furthermore, they suggest the favorable formation of trans-Cu(II)–(OH)2 moieties in low-coordinated Cu(II)
species. This trans configuration hinders the formation
of Cu(II)–oxyl species, facilitating intramolecular H–abstraction
reactions in line with experimentally observed ligand oxidation processes.