Diiron models for active site of FeFe-hydrogenase armed with one or two chlorine butynyl groups: Synthesis, structures and electrochemistry

Abstract

Two new model complexes related to the [FeFe]-hydrogenase active site (μ-SCH2CCCH2Cl)2Fe2(CO)6 (1) and (μ-SC2H5)(μ-SCH2CCCH2Cl)Fe2(CO)6 (2) were obtained by treating (μ-LiS)2Fe2(CO)6 with 1, 4-dichloro-2-butyne. By controllable CO displacement of 1 or 2 with PPh3, mono- and di-substituted complexes, namely [(μ-SCH2CCCH2Cl)2Fe2(CO)6−X (PPh3)X] (3, X = 1; 5, X = 2), and [(μ-SC2H5)(μ-SCH2CCCH2Cl)Fe2(CO)6−X(PPh3)X] (4, X = 1; 6, X = 2) could be prepared in moderate yields. Treatment of 1 or 2 with bis(diphenylphosphino)ethane (dppe) afforded a double butterfly complex [(μ-SCH2CCCH2Cl)2Fe2(CO)5]2(μ-dppe) (7) and [(μ-SC2H5)(μ-SCH2CCCH2Cl)Fe2(CO)5]2(μ-dppe) (8), respectively. These molecular structures were characterized by FT-IR, 1H, 31P NMR spectra and the molecular structures of complexes 1, 3, 6 and 8 were determined by single crystal X-ray analyses. The electrochemistry of 1–8 was studied and the electrocatalytic property of 1 was investigated for proton reduction in the presence of acetic acid.