Selenium-bridged diiron hexacarbonyl complexes as biomimetic models for the active site of Fe–Fe hydrogenases

Abstract

Three N-substituted selenium-bridged diiron complexes [{(μ-SeCH₂)₂NC₆H₄R}Fe₂(CO)₆] (R = 4-NO₂, 7; R = H, 8; R = 4-CH₃, 9) were firstly prepared as biomimetic models for the Fe–Fe hydrogenases active site. Models 7–9 could be generated by the convergent reaction of [(μ-HSe)₂Fe₂(CO)₆] (6) with N,N-bis(hydroxymethyl)-4-nitroaniline (1), N,N-bis(hydroxymethyl)aniline (2), and N,N-bis(hydroxymethyl)-4-methylaniline (3) in 46–52% yields. All the new complexes 7–9 were characterized by IR, ¹H and ¹³C NMR and HRMS spectra and their molecular structures were determined by single-crystal X-ray analysis. The redox properties of 7–9 and their dithiolate analogues [{(μ-SCH₂)₂NC₆H₄R}Fe₂(CO)₆] (R = 4-NO₂, 7s; R = H, 8s; R = 4-CH₃, 9s) were evaluated by cyclic voltammograms. The electrochemical proton reduction by 9 and 9s were investigated in the presence of p-toluenesulfonic acid (HOTs) to evaluate the influence of changing the coordinating S atoms of the bridging ligands to Se atoms on the electrocatalytic activity for proton reduction.