Electro‐ and Photochemical Reduction of CO<sub>2</sub> by Molecular Manganese Catalysts: Exploring the Positional Effect of Second‐Sphere Hydrogen‐Bond Donors
Sayontani Sinha Roy, Kallol Talukdar, Jonah W. Jurss
Abstract
Abstract A series of molecular Mn catalysts featuring aniline groups in the second‐coordination sphere has been developed for electrochemical and photochemical CO 2 reduction. The arylamine moieties were installed at the 6 position of 2,2’‐bipyridine (bpy) to generate a family of isomers in which the primary amine is located at the ortho‐ ( 1‐Mn ), meta‐ ( 2‐Mn ), or para‐ site ( 3‐Mn ) of the aniline ring. The proximity of the second‐sphere functionality to the active site is a critical factor in determining catalytic performance. Catalyst 1‐Mn , possessing the shortest distance between the amine and the active site, significantly outperformed the rest of the series and exhibited a 9‐fold improvement in turnover frequency relative to parent catalyst Mn(bpy)(CO) 3 Br (901 vs. 102 s −1 , respectively) at 150 mV lower overpotential. The electrocatalysts operated with high faradaic efficiencies (≥70 %) for CO evolution using trifluoroethanol as a proton source. Notably, under photocatalytic conditions, a concentration‐dependent shift in product selectivity from CO (at high [catalyst]) to HCO 2 H (at low [catalyst]) was observed with turnover numbers up to 4760 for formic acid and high selectivities for reduced carbon products.