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

Three N-substituted selenium-bridged diiron complexes [{(mu-SeCH2)(2)NC6H4R}Fe-2(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 [(mu-HSe)(2)Fe-2(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, H-1 and C-13 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 [{(mu-SCH2)(2)NC6H4R}Fe-2(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.