Mechanism of Electrocatalytic N ₂ O Reduction to N ₂ by a Rhenium Bipyridyl Carbonyl Complex

The rhenium(I) complex, [Re(bpy)(CO)₃Cl] serves as an effective electrocatalyst for N₂O reduction to N₂ in acetonitrile. Density functional theory (DFT) calculations reveal a dinuclear mechanism initiated by two successive one-electron reductions of the precatalyst, yielding active species [3]⁻ (formally Re¹⁻) with concomitant Cl⁻ dissociation. Species [3]⁻ attacks N₂O via energetically favored η¹-N terminal coordination to form [3-N2O(end-N)]⁻, which subsequently couples with monoreduced species [2•] (formally Re⁰) to generate dinuclear intermediate[Int3•]⁻(formally Re⁡I-N∥NO-Re⁡0). The catalytic cycle proceeds through a key three-membered ring transition state, forming [Int4•]⁻ (formally ReI-N₂O-Re⁰) that decomposes to release N₂ and yield oxide species [5]⁻ (formally ReI-O) while regenerating [2•]. Species [5]⁻ undergoes a proton-coupled electron transfer (PCET) reduction to form the hydroxyl intermediate [2-OH•]- (formally Re⁰-OH), which is further protonated to generate [2-OH₂•] (formally Re⁰-OH₂). The dissociation of water (H₂O) subsequently regenerates [2•], allowing the cycle to continue. COPASI simulations demonstrated that the dinuclear mechanism is kinetically more favorable than the mononuclear mechanism. This study provides novel insight into the role of N₂O coordination modes in modulating the reaction barrier, showing that the Re-catalyst preferentially binds N₂O at an electron-transfer active center to initiate the reaction. These findings offer guidance for the future design of catalysts for N₂O conversion.