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.