Mechanism of Electrocatalytic N₂O Reduction to N₂ 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 Re^1-) 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 ${\mathrm{Re}}^I\text{-}\stackrel{\stackrel{NO}{\parallel }}{N}\text{-}{\mathrm{Re}}^0$). The catalytic cycle proceeds through a key three-membered ring transition state, forming [Int4^•]^- (formally Re^I-N₂O-Re⁰) that decomposes to release N₂ and yield oxide species [5]^- (formally Re^I-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-OH^₂•] (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.