Energetics of Proton‐Coupled Electron Transfer in Hydroxy‐Bridged Dicopper Complexes with N ‐Heterocyclic Carbene (NHC) Ligands

A series of dinuclear μ ‐hydroxo bridged copper(II) complexes bearing N‐heterocyclic carbene (NHC) ligands were designed to probe the ligand effect governing the activity patterns of particulate methane monooxygenase (pMMO). By systematically correlating experimental parameters (redox potentials E 1/2 and acid dissociation constants p K a ), we constructed stepwise thermodynamic frameworks that reveal a continuous O─H bond dissociation free energy (BDFE O‐H ) range spanning 68.5 to 106.7 kcal/mol in these copper–oxygen cores. Notably, while ligand substitution elicited only marginal variations in BDFE O‐H when maintaining a fixed overall charge of Cu─O─Cu structure, modulation of the Cu─O─Cu core charge demonstrated superior efficacy over conventional steric/electronic ligand modifications for activating inert C─H bonds. Mechanistic studies revealed an efficient concerted electron–proton transfer (CEPT) pathway between the Cu II ─O─Cu II and TEMPOH, achieving a remarkable second‐order rate constant of 1745.4 M −1 s −1 . This quantitative correlation between thermodynamic parameters and reaction kinetics provides fundamental principles for rational catalyst engineering.