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 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.