Monocopper model of CuB site of pMMO in N4‐environment oxidizes C−H bonds

Discrepancies regarding the coordination environment, donor atoms, nuclearity, and oxidation state of the active site of particulate methane monooxygenase (pMMO), a copper‐dependent enzyme capable of activating the strong C−H bond of methane, persist despite numerous structural and spectroscopic studies. To address the proposed mono‐ (Cu II ) or bimetallic (2Cu I ) nature of the so‐called Cu B site, we report the bis(benzimidazole)‐based NMe−N,N’‐(1‐Me‐2‐CH 2 C 7 H 4 N 2 ) 2 C 6 H 4 ligand ( N4 ) and its copper complexes. In the solid state [Cu( N4 )(ClO 4 )]ClO 4 features tetragonal geometry defined by the chelating ligand and an axial perchlorate; geometric and EPR parameters are very close to those reported for the Cu B site. Attempts to obtain a dicopper(I) analog resulted in [Cu( N4 )][CuCl 2 ], based on spectroscopic, electrochemical, and ESI‐MS data. Although these results support the assignment of Cu B as a monometallic site, air exposure of [Cu( N4 )][CuCl 2 ] leads to ligand oxidation in the structurally characterized [Cu( N4=O )Cl], raising the possibility of distorted tetragonal Cu(I) centers activating O 2 and oxidizing substrates, in C−H activation chemistry that may take place at Cu B .