Electrocatalytic Interconversions of CO and Formate on a Versatile Iron-Thiolate Platform.

Exploring bidirectional CO/HCO catalysis holds significant potential in constructing integrated (photo)electrochemical formate fuel cells for energy storage and applications. Herein, we report selective CO/HCO electrochemical interconversion by exploiting the flexible coordination modes and rich redox properties of a versatile iron-thiolate platform, Cp*Fe(II)L (L = 1,2-PhPCHS). Upon oxidation, this iron complex undergoes formate binding to generate a diferric formate complex, [(L)Fe(III)(μ-HCO)Fe(III)], which exhibits remarkable electrocatalytic performance for the HCO-to-CO transformation with a maximum turnover frequency (TOF) ∼10 s and a Faraday efficiency (FE) ∼92(±4)%. Conversely, this iron system also allows for reduction at -1.85 V (vs Fc) and exhibits an impressive FE ∼93 (±3)% for the CO-to-HCO conversion. Mechanism studies revealed that the HCO-to-CO electrocatalysis passes through dicationic [(L)Fe(III)(μ-HCO)Fe(III)] generated by unconventional oxidation of the diferric formate species taking place at ligand L, while the CO-to-HCO reduction involves a critical intermediate of [Fe(II)-H] that was independently synthesized and structurally characterized.