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

• Published in: ChemElectroChem Vol. 8; no. 23; pp. 4456 - 4465
• Main Authors: Fernández, Sergio, Cañellas, Santiago, Franco, Federico, Luis, Josep M., Pericàs, Miquel À., Lloret‐Fillol, Julio
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.12.2021
• Subjects: Binding sites; Carbon dioxide; Carbon monoxide; Chemical reduction; CO2 reduction; Cobalt compounds; cyclic voltammetry; electrocatalysis; Electrode potentials; Hydrogen bonding; Light irradiation; reaction mechanisms; spectroelectrochemistry
• ISSN: 2196-0216; 2196-0216
• DOI: 10.1002/celc.202100859

CO2 electroreduction could be improved by applying conceptualized strategies to overcome catalytic bottlenecks. In this regard, we report two new cobalt(II) complexes [Co(Py2RN3)(OTf)](OTf) (CoR, R=H, Me) based on a new C2‐symmetric pentacoordinate chiral ligand that are active on the electrochemical CO2 reduction to CO. One of the complexes has a N−H group oriented towards the CO2 binding site (CoH), while the other has a N−Me group with the same orientation (CoMe), as showed by X‐ray diffraction. We have studied the effect of introducing hydrogen bonding sites, i. e. N−H in CoH, as a strategy to stabilize reaction intermediates. The complex bearing coordinating unprotected N−H group (CoH) displays catalytic CO2 reduction at the CoII/I redox potential (−1.9 V vs. Fc, ca. 40 % FYCO) whereas CoMe shows CO2 reduction at the CoI/0 redox pair. FTIR‐SEC and DFT calculations identified a [CoI−CO]+ cation as catalytic intermediate. The beneficial effect of the N−H group has been attributed to the stabilization of reaction intermediates or transition states and by the larger electron‐donating capacity, thus enhancing the nucleophilic character of the CoI intermediate. The study also points to the CO dissociation from the Co(I)−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 (−1.9 V, 81 % FYCO, 11.2 TONCO) at the CoII/I redox potential. Effect of coordinating N−H groups and light irradiation in the electrocatalytic CO2 reduction to CO with two new Co complexes, CoH and CoMe, is reported. CoH displays catalytic CO2 reduction at the CoII/I redox potential (−1.9 V vs. Fc, ca. 40 % FYCO), which improves upon light irradiation (−1.9 V, 81 % FYCO). FTIR‐SEC and DFT calculations identify [CoI−CO]+ as one of the key intermediates in the reaction pathway.