Influence of Intermolecular Hydrogen Bonding Interactions on the Electrocatalytic Reduction of CO₂ to CO by 6,6′‐Amine Substituted Rhenium Bipyridine Complexes

Abstract

The introduction of biologically inspired motifs into electrocatalysts is an attractive strategy for efficiently transforming harmful fossil fuel combustion products such as carbon dioxide into useful chemical fuels. Herein, we present a series of Re(bpy)(CO) 3 Cl electrocatalysts with pendant primary, secondary, and tertiary amines with the aim of determining the effect of available pendant protons on the reduction of CO 2 to CO. Cyclic voltammetry studies indicate that the availability of pendant protons leads to intermolecular hydrogen bonding interactions, altering the electrochemical behavior of the complexes. Further, controlled potential electrolysis studies show a clear trend in the catalytic activity of these complexes based on the availability of pendant protons. For the NMe 2substituted complex with no pendant protons, the Faradaic efficiency (FE) remains quite stable with changing potential (41-65 % FE CO ), but for the NH 2 -substituted complex with maximum available pendant protons, the FE CO increases with more negative potentials, peaking at 83 % FE CO . Together with the formation of H 2 by the NH 2 -substituted Re(bpy)(CO) 3 Cl complex, this suggests a change in electrocatalytic behavior due to the intermolecular hydrogen bonding interactions that occur with additional pendant protons.

Electrocatalytic reduction of CO2 to CO by a series of organometallic Re(i)-tpy complexes

“…39 Recent work on Mn and Re catalysts with bipyridine ligand scaffolds decorated with primary amines, hydroxyls, pendant imidazole and a thiourea tether shows a significant influence of the donor groups on CO 2 -to-CO activity. 33,[41][42][43][44][45][46][47] We envisioned that using substituted terpyridines (tpy) as the ligand offers a handle to tune the primary and secondary coordination structures in tandem. Terpyridine can coordinate to a [Re(CO) 3 X] unit in a robust bidentate fashion, leaving a pendant pyridine group near the active site.…”

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

“…Electrocatalysis of CO 2 reduction using transition metal complexes is one desirable approach to this problem due to the tunable properties of these catalysts, their potential for rapid turnover, and their suitability for detailed mechanistic analyses that guide improvements. − Developmental research is still needed to improve control over product selectivity and catalyst durability. In the past decade, researchers have increasingly investigated sophisticated ligands that place functional groups within the secondary coordination sphere of the metal center with the broad goals of tuning overpotentials and accelerating catalysis by stabilizing rate-limiting transition states. − This enzymatic strategy is partially motivated by the hydrogen-bonding network of CO dehydrogenase, and a variety of pendent functionalities, including acids, bases, , ionic groups, , and hydrogen bond donors/acceptors, , have been examined.…”

“…In the past decade, researchers have increasingly investigated sophisticated ligands that place functional groups within the secondary coordination sphere of the metal center with the broad goals of tuning overpotentials and accelerating catalysis by stabilizing ratelimiting transition states. 7−11 This enzymatic strategy is partially motivated by the hydrogen-bonding network of CO dehydrogenase, 12 and a variety of pendent functionalities, including acids, 13 bases, 14,15 ionic groups, 16,17 and hydrogen bond donors/acceptors, 18,19 have been examined.…”

Spontaneous Reactivity of La2CuO4 toward CO2 Diagnosed Using Variable Temperature Raman Spectroscopy

“…Additional variables complicate the analysis of reaction mechanisms and subsequent catalyst optimization. Recent studies have shown that such reactions are affected not only by the thermodynamics and kinetics of reactions on the catalyst surface, but also by mass transfer considerations, , variations in the electrochemical double layer structure, − secondary effects such as hydrogen bonding or the presence of cocatalysts, − and reversible or irreversible structural changes in the catalyst. − Despite such complications, correlations between gas phase and condensed phase energetics exist that enable density functional theory calculations to provide theoretical insights into reaction mechanisms in the absence of solvent models. Extrapolating this notion, the analysis of chemical reactivity between a solid-state surface and a gaseous species may permit the analysis of chemical reactivity without the complicating variables of a condensed phase medium.…”