Electrocatalytic proton reduction by thiolate-capped triiron clusters [Fe₃(CO)₉(μ₃-SR)(μ-H)] (R = ⁱPr, ^tBu)

The redox behaviour and electrocatalytic proton reduction ability of the thiolate-capped triiron clusters [Fe₃(CO)₉(μ₃-SR)(μ-H)] (1, R = ⁱPr; 2, R = ^tBu) have been investigated. In CH₂Cl₂, both show a quasi-reversible reduction and an irreversible oxidation. The thiol substituent has a significant influence on their reduction potentials (E_1/2 = −1.24 V for 1 and E_1/2 = −1.40 V for 2 vs. Fc⁺/Fc) but less impact on oxidation potentials (E_1/2 = 0.99 V for 1 and E_1/2 = 0.93 V for 2 vs. Fc⁺/Fc). Reduction is quasi-reversible and DFT studies reveal that this is due to scission of an iron-iron bond. While the clusters are not protonated by CF₃CO₂H or HBF₄·Et₂O, they can catalyse proton reduction of these acids at their corresponding reduction potentials following an ECEC mechanism.