Phosphine-substituted Fe–Te clusters related to the active site of [FeFe]-H2ases†
In order to enrich the chemistry of the Fe/Te cluster compounds related to the active site of the [FeFe]-hydrogenase, the reactions of compound Fe2(μ-TeAr)2(CO)6 with tertiary phosphines were described. Three types of novel phosphine substituted Fe/Te model compounds were successfully prepared. That is, the treatment of Fe2(μ-TeAr)2(CO)6 (Ar = C6H5 A, C6H4-F-4 B) with 2 equivalents of PPh3 under UV conditions produced dinuclear compounds Fe2(μ-TeC6H5)2(CO)4(PPh3)2 (1) and Fe2(μ-TeC6H4-F-4)2(CO)4(PPh3)2 (2) in moderate yields together with unusual tetranuclear compounds Fe4(μ-TeC6H5)6(CO)6(PPh3)2 (3) and Fe4(μ-TeC6H4-4-F)6(CO)6(PPh3)2 (4). The syn- and anti-isomers of 1 and 2 were isolated in the solid state using the TLC method. Furthermore, the reaction of Fe2(μ-TeAr)2(CO)6 and 4 equivalents of PMe3 gave new types of mononuclear PMe3-disubstituted compounds Fe(TeC6H5)2(CO)2(PMe3)2 (5) and Fe(TeC6H4-4-F)2(CO)2(PMe3)2 (6) which could mimic Fed of the [FeFe]-hydrogenase. All the new compounds were fully characterized by elemental analysis, IR, NMR spectroscopy, UV-Visible absorption and particularly some of them by X-ray crystallography. The electrochemical properties of 1, 2, 5 and 6 were also investigated, demonstrating that these compounds can be considered as electrochemical catalysts for the hydrogen evolution reaction. According to the electrochemical behavior of 5 and 6, a CEECC mechanism was proposed for the catalytic process.