From non-innocent to guilty: on the role of redox-active ligands in the electro-assisted reduction of CO₂ mediated by a cobalt(ii)-polypyridyl complex

Abstract

The ability of a polypyridyl cobalt(ii) complex containing a redox-active tetradentate ligand to assist the electroreduction of CO2 has been investigated in DMF.

Systematic Variation of 3d Metal Centers in a Redox-Innocent Ligand Environment: Structures, Electrochemical Properties, and Carbon Dioxide Activation

“…In the cyclic voltammogram of Co Cl (Figure ), a partially reversible reduction wave at E 0 = −1.21 V Fc (Δ E p = 94 mV) and an irreversible wave at E p,c = −1.98 V Fc can be observed, to which we assign the Co II/I and Co I/0 couples, respectively. Although the molecular structure obtained for Co Cl from an MeCN solution confirmed the inner-sphere coordination of both chlorido ligands in the solid state, we hypothesize that a dynamic ligand exchange between Cl – and MeCN takes place in solution . Likely, a cationic [Co II L (MeCN) n Cl] + ( n = 1 or 2) complex forms upon the dissolution of Co Cl into MeCN.…”

“…Although the molecular structure obtained for Co Cl from an MeCN solution confirmed the inner-sphere coordination of both chlorido ligands in the solid state, we hypothesize that a dynamic ligand exchange between Cl – and MeCN takes place in solution. 50 Likely, a cationic [Co II L (MeCN) n Cl] + ( n = 1 or 2) complex forms upon the dissolution of Co Cl into MeCN. We postulate that the complex reversibly reduces into a neutral [Co I L (MeCN) n Cl] species ( Figure 6 C).…”

“…Here we note that Fe, Co, and Ni complexes are among the most prominent eCO 2 R catalysts. 17 While ligand-centered reductions at mildly negative potentials are commonly proposed for Fe, Co, or Ni complexes 17 , 25 , 30 , 31 , 50 , 62 , 63 (e.g., with polypyridinic ligands having delocalized, low-energy π* orbitals), in our series, a comparison with the other complexes (of Mn, Cu, and Zn) allows assignment of the first two reductions ( Figure 8 C) solely to metal-centered orbitals in Fe MeCN , Co Cl , and Ni Cl .…”

Redox-Active Ligands in Electroassisted Catalytic H+ and CO2 Reductions: Benefits and Risks

“…Beyond the apparent benefits, a number of studies have also highlighted the occurrence of deactivation processes and decomposition mechanisms specific to redox-active ligands. Dearomatization, radical-driven reactivities (carboxylation, carbonation), and electron trapping within ligand-centered orbitals or weakly activated catalytic intermediates are among the most commonly met deleterious side reactions. ,− …”

Repurposing a Bio-Inspired NiFe Hydrogenase Model for CO2 Reduction with Selective Production of Methane as the Unique C-Based Product

“…Homogeneous CO 2 reduction electrocatalysts have so far demonstrated selectivity for the production of either CO or formate in aprotic solvents. Based on structure–function and mechanistic investigations carried out on series of first-row transition metal catalysts, including polypyridinyl Mn and N-based macrocyclic Fe and Co complexes, rational design of selective and efficient catalytic systems has become possible. − Their implementation in future devices now requires improving their stability and transitioning to aqueous solution. A promising strategy, developed by several groups, relies on surface immobilization to take full advantage of the benefits of heterogeneous catalysis.…”