| The active site of Fe-only hydrogenase contains a binuclear iron center with two bridging thiolates and diatomic ligands CO and CN, (μ-pdt)[Fe(CO) 2(CN)][Fe(CO)(CN)Scys] (pdt = −SCH 2CH2CH2S−). Using PMe 3 as a mimic of the CN ligand in Fe-only hydrogenase, the binuclear FeIFeI compound (μ-pdt)[Fe(CO)2(PMe 3)]2 was synthesized from the reaction of PMe3 with (μ-pdt)[Fe(CO)3]2. The two Fe centers exist as edge-bridged bi-square pyramids with two bridging thiolates and an Fe-Fe bond distance of 2.55 Å. The Fe2S2 butterfly core is therefore a good structural analogue of the [Fe]H2ase active site. The Fe-Fe bond in (μ-pdt)[Fe(CO)2(PMe3)] 2 reacts with HCl to produce the binuclear FeIIFe II compound {lcub}(μ-H)(μ-pdt)[Fe(CO)2(PMe3)] 2{rcub}+[PF6]−, which was characterized as a face-bridged bioctahedron with (μ-H)(μ-SRS) bridges and an Fe-Fe distance of 2.58 Å. The 3-carbon S to S link enforces a syn′ orientation at the dithiolate bridge. The coordinated phosphines are directed into basal positions (ba/ba, transoid) on the edge-bridged square pyramids.; The {lcub}(μ-H)(μ-pdt)[Fe(CO)2(PMe3)]2{rcub} +[PF6]− compound undergoes H/D exchange at the μ-H in the presence of D2O or D2 gas. Studies of the gaseous reaction were performed in medium pressure NMR tubes, using 2H NMR as monitor. H2/D2 mixtures showed HD formation as catalyzed by the active-site mimics. Such H/D exchange reactions have been used as assays of hydrogenase activity, indicating that compound {lcub}(μ-H)(μ-pdt)[Fe(CO) 2(PMe3)]2{rcub}+[PF6]− and analogues (similar binuclear FeII(μ-H)Fe II complexes with different bridges, μ-SCH2CH2 S, μ-o-SCH2C6H4CH2S, μ-SCH 2CH2PPh2 and μ-SEt) serve as functional models for the heterolytic H2 activation in Fe-only hydrogenase. Under photolysis, the H/D exchange reaction between D2 and small alkenes (ethylene, propene and 1-butene), but not bulkier alkenes such as 2-butene or cyclohexene, can also be catalyzed by {lcub}(μ-H)(μ-pdt)[Fe(CO)2 (PMe3)]2{rcub}+[PF6] −. The two-iron organometallics, inspired from active sites of biological catalysts, appear to function as do expensive noble metals which perform 2-electron redox processes. |
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