The Dual Effect of Coordinating −NH Groups and Light in the Electrochemical CO₂ Reduction with Pyridylamino Co Complexes

Abstract

Dedicated to JM Savéant for his pioneering work on molecular electrochemistry. CO 2 electroreduction could be improved by applying conceptualized strategies to overcome catalytic bottlenecks. In this regard, we report two new cobalt(II) complexes [Co-(Py 2 R N 3 )(OTf)](OTf) (Co R , R=H, Me) based on a new C 2 -symmetric pentacoordinate chiral ligand that are active on the electrochemical CO 2 reduction to CO. One of the complexes has a NÀ H group oriented towards the CO 2 binding site (Co H ), while the other has a NÀ Me group with the same orientation (Co Me ), as showed by X-ray diffraction. We have studied the effect of introducing hydrogen bonding sites, i. e. NÀ H in Co H , as a strategy to stabilize reaction intermediates. The complex bearing coordinating unprotected NÀ H group (Co H ) displays catalytic CO 2 reduction at the Co II/I redox potential (À 1.9 V vs. Fc, ca. 40 % FY CO ) whereas Co Me shows CO 2 reduction at the Co I/0 redox pair. FTIR-SEC and DFT calculations identified a [Co I À CO] + cation as catalytic intermediate. The beneficial effect of the NÀ H group has been attributed to the stabilization of reaction intermediates or transition states and by the larger electrondonating capacity, thus enhancing the nucleophilic character of the Co I intermediate. The study also points to the CO dissociation from the Co(I)À CO resting state intermediate as one of the bottlenecks of the catalytic cycle, which can be overcome with light irradiation, resulting in an increase of the total CO production (À 1.9 V, 81 % FY CO , 11.2 TON CO ) at the Co II/I redox potential.

Exploring the Parameters Controlling Product Selectivity in Electrochemical CO2 Reduction in Competition with Hydrogen Evolution Employing Manganese Bipyridine Complexes

“…Additionally, the presence of the amine functionalities is also known to stabilize the carboxylate intermediate, 7 , by forming an intramolecular hydrogen bond, which then favors CO formation (blue pathway, Scheme ). − Since amines accelerate all three pathways, the selectivity originates from other contributing factors, such as the nature of the metal, geometrical structure, hydricity, and p K a . In the case of Mn complexes, CO has been the dominant product for the nonamine-containing complexes ( 1b* and 1c* ).…”

Molecularly dispersed nickel complexes on N-doped graphene for electrochemical CO2reduction

“…Consequently, the strategy to incorporate hydrogen-bond donors (e.g., N-H and O-H) or proton relay groups on the periphery of ligands has been receiving considerable attention for enhancing ECR activity. 25,[45][46][47][48][49][50][51] For example, [Ni(cyclam)] 2+ and [CoL] 2+ (L = azacalix [4](2,6)pyridine) possess N-H moieties from the ligands and were postulated to interact with [M − CO 2 − ] intermediates through the hydrogen-bonding interaction, resulting in high ECR performance. 17,49 In contrast, their respective methylated analogues showed little to no ECR activity.…”

A Binuclear Cobalt Complex for Molecular CO2 Electrocatalysis

“…Thus, considering that electrocatalytic inhibition could arise from CO binding to cobalt centers, we performed electrochemistry experiments under irradiation with 60 blue LED lamps (470 nm), [55] keeping the temperature of the cell controlled at 20 ºC. These attempts did not improve the faradaic efficiency of the catalysis (Table S12), neither experiments performed at higher temperature (Table S9).…”