Making C–H bonds with CO₂: production of formate by molecular electrocatalysts

Abstract

Molecular approaches to the electrocatalytic reduction of CO2 to formate are varied and versatile in their methods. We discuss recent efforts to catalyse this reaction including significant progress made in the last 5 years. This Feature Article begins with a survey of molecular electrocatalysts that produce CO or H2, but have been observed under certain conditions to afford some formate. These examples are included because they provide valuable mechanistic insight for design of catalysts that produce hydrogenated products selectively from CO2. The subsequent discussion describes catalyst properties that favour C-H bond formation with CO2 and this is followed by recent advances that have been made in developing these catalysts. The focus on specific catalyst systems includes recently reported Ir PCP-type pincer complexes and Fe carbonyl clusters, such as [Fe4N(CO)12](-), that selectively produce formate from CO2 in aqueous solution. A discussion of the relevant thermochemical properties of the catalysts in the context of formate production is included.

Recent Trends, Benchmarking, and Challenges of Electrochemical Reduction of CO2 by Molecular Catalysts

“…Berben et al [59][60][61] pioneered the synthesis of various iron carbonyl clusters (Figure 24) that facilitated the formation of CH bond, resulting in the production of formates from CO 2 . Berben et al [59][60][61] pioneered the synthesis of various iron carbonyl clusters (Figure 24) that facilitated the formation of CH bond, resulting in the production of formates from CO 2 .…”

Visible‐Light Photocatalytic Reduction of CO2 to Formic Acid with a Ru Catalyst Supported by N,N′‐Bis(diphenylphosphino)‐2,6‐diaminopyridine Ligands

“…In light of previous reports, [10,14,36,37] experimental observations and standard electron counting rules lead us to propose a photocatalytic mechanismf or HCO 2 Hp roduction from CO 2 by using complexes 1 + + Cl À and 2 + + Cl À (Scheme 2a nd FigureS8). [36,37] In addition, the fact that we did not observe formation of CO as ap roduct also mitigated against formation of aC O 2 adduct with Ru 0 .T hus, protonation of this lone electron pair of Ru 0 yields the hydridec omplex, RuH.T he insertiono fC O 2 into the RuÀHc omplex yields the metallacarboxylic acid species RuCOOH,w hich through reduction releases formate and generatest he Ru I complex Ru + + .T he catalytic cycle closes with return to Ru 0 by reduction from PS À . Entry into the catalytic cycle comes from the reduction of A ( Figure S10), which during optimization, spontaneously dissociated aC l À anion to yield ad istorted square pyramidal complex labeled Ru 0 .V isualization of the HOMO of this complex shows that the electron density is localized in ad z 2 -type orbital with some contributions from the CO ligands ( Figures S11a nd S12).…”

Effect of PDI ligand binding pattern on the electrocatalytic activity of two Ru(II) complexes for CO2 reduction

“…Carbon dioxide holds immense promise as a sustainable feedstock for the synthesis of high energy density fuels . Research has revealed that electrocatalytic reduction of carbon dioxide to carbon oxide, formic acid, or other high added‐value products can provide a promising strategy for reducing greenhouse gas and solving energy issues . Development of catalysts with high selectivity, efficiency, and stability for converting CO 2 is still very challenging.…”