Heterogeneous Aqueous CO₂ Reduction Using a Pyrene-Modified Rhenium(I) Diimine Complex

The development of molecular catalysts and materials that can convert carbon dioxide (CO₂) into a value-added product is a great chemical challenge. Molecular catalysts set benchmarks in catalyst investigation and design, but their incorporation into solid-state materials, and optimization of the electrochemical operating conditions, is still needed. For example, rhenium(I) diimine catalysts show almost quantitative selectivity for the conversion of CO₂ to carbon monoxide (CO) in acetonitrile (MeCN), but the modification of diimine backbones can be challenging if the goal is to incorporate such molecules into materials. Presented here is a rhenium(I) complex with a 2-(2'-quinolyl)benzimidazole (QuBIm-H) ligand, where N-alkylation with a pyrene derivative allows access to a catalyst that can be adsorbed onto electrodes for aqueous CO₂ reduction chemistry. The rhenium(I) catalysts are inactive for homogeneous CO₂ reduction in MeCN. However, when adsorbed on edge-plane graphite, the same complexes show good activity for heterogeneous aqueous CO₂ reduction, with 90% selectivity for CO. Comparative electrochemical studies between covalent and noncovalent modification of the graphite surfaces were also carried out for related rhenium(I) tricarbonyl complexes.