Electrochemical Conversion of CO₂ to CO by a Competent Fe^I Intermediate Bearing a Schiff Base Ligand

Abstract

Iron complexes with a N2O2‐type N,N′‐bis(salicylaldehyde)‐1,2‐phenylenediamine salophen ligand catalyze the electrochemical reduction of CO2 to CO in acetonitrile with phenol as the proton donor, giving rise to 90–99 % selectivity, faradaic efficiency up to 58 %, and turnover frequency up to 103 s−1 at an overpotential of 0.65 V. This novel class of molecular catalyst for CO2 reduction operate through a mononuclear FeI intermediate, with phenol being involved in the process with first‐order kinetics. The molecular nature of the catalyst and the low cost, easy synthesis and functionalization of the salophen ligand paves the way for catalyst engineering and optimization. Competitive electrodeposition of the coordination complex at the electrode surface results in the formation of iron‐based nanoparticles, which are active towards heterogeneous electrocatalytic processes mainly leading to proton reduction to hydrogen (faradaic efficiency up to 80 %) but also to the direct reduction of CO2 to methane with a faradaic efficiency of 1–2 %.

Carbon Dioxide Reduction Mediated by Iron Catalysts: Mechanism and Intermediates That Guide Selectivity

“…Non-heme mononuclear iron complexes have been developed as another class of catalysts for CO 2 reduction, with mechanistic details and principles being common to both categories (Figure ). − However, differently from the previously discussed iron porphyrins, these systems share the common feature of operating through a formal Fe­(I) intermediate.…”

Mechanism and selectivity of photocatalyzed CO2reduction by a function-integrated Ru catalyst

“…5 CO 2 reduction involving multiple electron transfers coupled with proton transfers is less expensive but more complex. In recent years, significant progress has been achieved, 6,7 and many elegant transition metal-based electrocatalysts have been reported, such as Re, 8–10 Ru, 11–13 Fe, 14–16 Co, 17–20 Ni, 21,22 Cu, 23,24 Mn, 25 and Mo 26 complexes.…”

FeI Intermediates in N2O2 Schiff Base Complexes: Effect of Electronic Character of the Ligand and of the Proton Donor on the Reactivity with Carbon Dioxide

“…Iron porphyrins, where iron is coordinated by a N 4 tetradentate heme motif, are the most investigated class of coordination compounds for the reduction of CO 2 , and operate through the generation of a formal Fe 0 state that binds CO 2 and further promotes its conversion [9]. Conversely, iron complexes with tetradentate N 2 O 2 Schiff base ligands have been less explored; examples have reported the use of 2-hydroxybenzene pendants on 1,10-phenanthroline (2,9-bis(2-hydroxyphenyl)-1,10-phenanthroline, dophen) [10], 2,2bipyridine scaffolds (6,6 -di(3,5-di-tert-butyl-2-hydroxybenzene)-2,2 -bipyridine, tBu dhbpy) [11], and a recent report by some of us taking advantage of the N,N -bis(salicylaldehyde)-1,2phenylenediamine (salophen) ligand [12]. In Fe(salophen), the reactivity with CO 2 involves an electrogenerated Fe I intermediate, that in the presence of phenol as the proton donor, leads to the selective production of CO with appealing catalytic properties including an overpotential of 0.65 V and a turnover frequency up to 10 3 s −1 [12]; the nature and the concentration of the proton donor were found to play a key role in the catalytic process, in terms of product selectivity and of Fe(salophen) stability [12].…”