[FeFe] Hydrogenase: 2-Propanethiolato-Bridged {FeFe} Systems as Electrocatalysts for Hydrogen Production in Acetonitrile-Water

Diiron bis(monothiolato)-bridged hydrogenase mimics Fe₂(μ-SⁱPr)₂(CO)₆] A (ⁱPr=isopropyl) and their phosphine derivatives Fe₂(μ-SⁱPr)₂(CO)₅( L_1/2 )] and Fe₂(μ-SⁱPr)₂(CO)₄( L₃ )] {tricyclohexylphosphine ( L₁ , PCy₃) 1 , triphenylphosphine ( L₂ , PPh₃) 2 and cis-1,2-bis(diphenylphosphino)ethylene ( L₃ , dppv) 3 } have been synthesized and investigated for electrocatalytic proton reduction activity in CH₃CN−H₂O. Based on the FTIR data (red-shift), the electron-donating ability of the phosphines followed the order: dppv>PCy₃>PPh₃ (average shift value with respect to complex A was 61 ( 1 ), 51 ( 2 ) and 80 ( 3 ) cm⁻¹). From CV measurements, it was seen that the catalytic reduction potential (acetic acid as proton source) shifted considerably towards positive potentials (anodic shift) on changing the solvent from pure CH₃CN to CH₃CN−H₂O (4 : 1 v/v). An increase in the percentage of water in CH₃CN led to the decomposition of complexes 1 and 3 . Though complexes A and 2 were stable in CH₃CN−H₂O (3 : 2 v/v), no improvement in electrocatalytic currents was observed.