CO2 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 CO2 reduction to CO. One of the complexes has a N-H group oriented towards the CO2 binding site (Co-H), while the other has a N-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. N-H in Co-H, as a strategy to stabilize reaction intermediates. The complex bearing coordinating unprotected N-H group (Co-H) displays catalytic CO2 reduction at the Co-II/I redox potential (-1.9 V vs. Fc, ca. 40 % FYCO) whereas Co-Me shows CO2 reduction at the Co-I/0 redox pair. FTIR-SEC and DFT calculations identified a [Co-I-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 Co-I 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 Co-II/I redox potential.
