A Dicationic fac-Re(bpy)(CO)₃Cl for CO₂ Electroreduction at a Reduced Overpotential

Abstract

A dicationic Re bipyridine-type complex, fac-Re-(6,6′-(2-((trimethylammonio)-methyl)phenyl)-2,2′-bipyridine )-(CO) 3 Cl hexafluorophosphate (1 2+ ), has been synthesized, and its electrochemical behavior under Ar and CO 2 has been investigated. The presence of pendent tetra-alkylammonium cations induces an anodic shift in the electrocatalytic potential for CO 2 reduction relative to structurally similar model complexes. The electrochemical mechanisms in anhydrous CH 3 CN and in the presence of weak acids (water or trifluoroethanol) have been analyzed using cyclic voltammetry assisted by infrared spectroelectrochemistry and theoretical calculations. The dication enables catalysis at a diminished potential through Coulombic stabilization of the doubly reduced pentacoordinate species, its CO 2 adduct, the hydroxide anion, and the conjugate base formed during acid-assisted C−OH bond cleavage of the metallocarboxylic acid to the metallocarbonyl and H 2 O. The major reduction product is CO, but in the presence of trifluoroethanol, formate is also produced with 14% Faradaic efficiency.

Electronic and Electrochemical Control of Isostructural Ruthenium Hydricities and the Implications for Catalytic Overpotentials

“…For the complexes (H)­Ru-CH 3 CN 2+ , (CH 3 )­Ru-CH 3 CN 2+ , and (CH 3 O)­Ru-CH 3 CN 2+ , the reversibility of the second reduction depends on the scan rate. At high scan rates, the second reduction is reversible; however, reversibility decreases at slow scan rates due to competitive reactions, such as formation of the hydride via the protonation of the strongly basic reduced complex with the tetrabutylammonium cation of the electrolyte via the Hofmann degradation (see below). , In contrast, both reduction processes for complexes (Cl)­Ru-CH 3 CN 2+ and (CF 3 )­Ru-CH 3 CN 2+ were reversible, indicating that CH 3 CN dissociation and competitive reactions are slower for the electron-poor molecules.…”

Modular preparation of cationic bipyridines and azaarenes via C–H activation

“… 18 Ertem, Manbeck, and coworkers have shown that even when the trimethylaminium is further separated from the metal center, the impact of the charge has beneficial properties on catalysis. 19 …”

“…18 Ertem, Manbeck, and coworkers have shown that even when the trimethylaminium is further separated from the metal center, the impact of the charge has benecial properties on catalysis. 19 To expand the series of accessible non-N methylated cationic bipyridines and azaarenes, we sought a modular and facile preparation for the direct attachment of trimethylaminium functionalities to azaarenes. Using 6-trimethylaminium-2,2 ′bipyridyl 1 as the target molecule, we initially envisioned synthetic access through either methylation of 6-dimethylamino-2,2 ′ -bipyridyl (Scheme 1), 20 or nucleophilic aromatic substitution of 6-halo-2,2 ′ -bipyridyl with trimethylamine (NMe 3 ) (Scheme 1).…”