Quantum Chemical Studies of Methane Oxidation to Methanol on a Biomimetic Tricopper Complex: Mechanistic Insights

Particulate methane monooxygenase (pMMO) is known to be the most efficient oxidizer for the conversion of methane (CH 4 ) into methanol (CH 3 OH) at room temperature. Recently, the tricopper cluster complex [Cu 3 (7‐ N ‐Etppz)] 1+ has been shown to mediate facile CH 4 oxidation upon activation by dioxygen (O 2 ) just like the pMMO enzyme. In this work, we investigate by unrestricted density functional theory (DFT) calculations the oxidation of CH 4 on the biomimetic tricopper complex. We find that CH 4 can interact with the activated tricopper complex to form a C−H⋅⋅⋅O hydrogen bond between one of the C−H bonds of CH 4 and the O 2 molecule activating the tricopper cluster complex. We consider both the direct “oxene insertion” mechanism as well as the “hydrogen‐atom abstraction geminal radical rebound” mechanism for the process. Our calculations indicate low kinetic barriers for both reaction pathways, accounting for why the tricopper cluster of the biomimetic complex [Cu 3 (7‐ N ‐Etppz)] 1+ is a good functional model of the active site in pMMO.