Direct CO 2 Reduction to CO with an Fe 4 S 4 -Based Coordination Polymer

Fe4S4 clusters play essential roles in nature, classically in electron transport but increasingly in newly discovered reactivity or catalysis. These roles have spurred interest in developing synthetic Fe4S4 systems and while several molecular and material systems built from Fe4S4 clusters have been developed, comparatively few examples of synthetic Fe4S4 cluster-based catalysts exist. Herein, we present the use of an Fe4S4-based coordination polymer as a catalyst for the direct and selective electroreduction of CO2 to CO. Computational studies suggest that the reaction proceeds through CO2 binding to a reduced Fe4S4 cluster, followed by a series of protonation, reduction, and H2O loss steps to yield a CO-bound cluster that can finally exchange with CO2 to restart the catalytic cycle. CO bound clusters are predicted to be thermodynamically stable, suggesting that carbonyl species might be off-cycle intermediates. Mechanistic CV studies as well as in situ studies by IR spectroscopy provide evidence for carbonyl-ligated clusters, supporting these compounds as unusual examples of small molecule binding to Fe4S4 clusters. This work establishes Fe4S4 cluster-based coordination polymers as direct electrocatalysts for CO2 reduction and provides mechanistic insights into how these species mediate catalytic conversions of small molecules.