Computational insights into the photocatalytic conversion of CO2 to C2H4 on synergistic dual sites in tandem rhenium-bipyridine/copper-porphyrinic system

The rhenium(I)-bipyridine complex (Re-bpy) has been reported to be a very active photocatalyst to stabilize the *CO species in CO₂ reduction, and the copper-porphyrinic triazine framework Cu-PTF was found to be a very good relay partner and cooperator in facilitating the C−C coupling process to generate C₂H₄. To unravel the mechanism of reduction of CO₂ to C₁ and C₂ products and how such two catalysts synergistically promote C−C coupling, we conducted density functional theory (DFT) calculations. The most favorable mechanism comprises the following key steps: CO₂ activation by Re-bpy, formation of Re−CO species, proton-coupled electron transfer (PCET) to form Re−CHO species, synergistic coupling between Re−CHO and Cu−CO to form Cu−CO−CHO−Re intermediate, the PCET to form resting state Cu−CHO−CH₂−Re intermediate, another PCET to generate Cu−CHOH−CH₂−Re, PCET and elimination of H₂O and dissociation to yield C₂H₄. Our DFT calculations provides insights into the catalytic pathways and the cooperative interactions between the two catalysts, paving the way for the development of more efficient catalytic systems for CO₂ reduction reactions.