Substituents and Cocatalyst Effect on the Catalytic Response and Overpotential of Re(I) Catalysts for CO₂ Reduction

Abstract

To design an efficient electrocatalyst for CO 2 reduction, a comprehensive understanding of the catalytic architecture and the reaction mechanism is required. Herein, we synthesized and analyzed a series of fac-[Re(bpy-X) (CO) 3 Cl] (abbreviated as Re I (bpy-X); bpy-X = 4,4′-disubstituted-2,2′bipyridine; X = t Bu, CH 3 , mesityl, H, phenyl, and methyl ester) catalysts for electrocatalytic CO 2 reduction with and without adding the cocatalyst [Zn(cyclam)] 2+ (cyclam = 1,4,6,11tetraazacyclotetradecane). Both computational and experimental results show that in the experiments bearing the [Zn(cyclam)] 2+ cocatalyst, the Re(I) catalysts require less energy input to reduce the CO 2 , indicating that the CO 2 -to-CO conversion occurs at a lower overpotential. Interestingly, in the Re(I) electrocatalyst bearing a strong electron-withdrawing group (methyl ester), [Zn(cyclam)] 2+ does not improve the CO 2 reduction activity. These results emphasize the importance of how the electronic distribution throughout the molecular architecture can enhance or suppress the nucleophilicity of Re I (bpy-X) electrocatalysts, even in the presence of a cocatalyst.

Rhenium Carbonyl Molecular Catalysts for CO2 Electroreduction: Effects on Catalysis of Bipyridine Substituents Mimicking Anchorage Functions to Modify Electrodes

“…The effect of various substituents on the bpy ligand has been reported. 13 , 14 However, to the best of our knowledge, among the studied Re complexes, with bpy substituted by alkyl ester groups (e.g., [Re(2,2′-bpy-4,4′-(C(O)OR) 2 )(CO) 3 Cl] with R = Me or Et), 15,16 the electrochemical properties in reduction have not been investigated in detail, even if dicarboxy-2,2′-bipyridine derivatives have been used to immobilize Re complexes on surfaces or in organic−inorganic materials. 17 Only few studies, related to the photophysical properties of polypyridyl Re carbonyl complexes, report the redox raw data of [Re(L)-(CO) 3 Cl] (L = bpy(C(O)OEt) 2 ).…”

“…Since the first report by Lehn and co-workers, rhenium triscarbonyl bpy complexes are among the most studied molecular catalysts for homogeneous CO 2 electroreduction to CO. The effect of various substituents on the bpy ligand has been reported ,. However, to the best of our knowledge, among the studied Re complexes, with bpy substituted by alkyl ester groups (e.g., [Re­(2,2′-bpy-4,4′-(C­(O)­OR) 2 )­(CO) 3 Cl] with R = Me or Et), , the electrochemical properties in reduction have not been investigated in detail, even if dicarboxy-2,2′-bipyridine derivatives have been used to immobilize Re complexes on surfaces or in organic–inorganic materials .…”

A Comprehensive Review on Graphitic Carbon Nitride for Carbon Dioxide Photoreduction

“…[290] Besides, the use of co-catalyst entities is critical not only to increase efficiency but also to increase selectivity in various applications. [291] As co-catalyst materials for photocatalytic CO 2 RR, [292] in addition to metallic materials, [293,294] chalcogenides, [240,295,296] metal oxides, [297][298][299] and pnictide compounds [300][301][302] have been found to have important applications as co-catalyst materials. Alongside this, the high selectivity of the bimetallic co-catalysts to a wide range of substrates and products has recently attracted much attention from researchers.…”

A Blueprint for Secondary Coordination Sphere Editing: Approaches Toward Lewis‐Acid Assisted Carbon Dioxide Co‐Activation

“…The enzymatic features outlined above have been imitated using bimetallic complexes, main-group co-catalysts, and secondary coordination sphere effects, including pendant proton donor/ acceptor groups, to name a few. [26][27][28][29][30][31][32][33][34][35][36][37][38] Bimetallic catalysts, for example, show promising activity for CO 2 reduction as compared to their monometallic counterparts due to cooperativity between metal centers. [4,39] Additionally, pre-installed Lewis acids (in the secondary coordination sphere) have been shown to promote the stabilization of transition metal bound-CO 2 , leading to activation.…”