Synthesis, Protonation And Electrochemical Properties Of The Fe/S Complexes With The Internal Basic Site

Hydrogenase enzymes can efficiently catalyze the reduction of proton or the oxidation of hydrogen. Since the crystal structure of hydrogenases was published, more and more efforts have been put on the bio-inspired structural/functional models of hydrogenases. It is thought that the active sites in both iron-only and nickel-iron hydrogenases possess an internal base near the metallic catalytic centers which can assist the heterolytic cleavage of hydrogen and the H-H bond formation between a proton and a hydride. In this thesis, a series of Fe/S complexes with the internal basic site as a proton relay were synthesized aiming at preparing structural/functional models for hydrogenases.An asymmetrically disubstituted diiron complex (μ-pdt)[Fe(CO)₃][Fe(CO){κ²-(Ph₂P -CH₂)₂NⁿPr}] (2) was prepared as biomimetic model of the Fe-Fe hydrogenases active site. It was characterized by MS, IR, ¹H NMR, ³¹P NMR, EA and X-ray crystal diffraction. Upon addition of a small amount of HOTf to the solution of 2, two species appeared, theμ-hydride complex [2(FeHFe)]⁺ and the [2(NH)]⁺ complex. As 3 equiv HOTf was added, both of the complexes transfered to the complex [2(FeHFe)(NH)]²⁺. The complex [2(FeHFe)(NH)](OTf)₂was successfully isolated, and characterized by IR, ¹H NMR, ³¹P NMR, and X-ray crystal diffraction. The distance between the two H atoms is 3.934(?) in the crystalline state of the complex [2(FeHFe)(NH)](OTf)₂. The proton/hydride diiron model for the Fe-Fe hydrogenases active site has not been reported so far.Two dimeric diiron dithiolate complexes with the internal basic site [(μ-pdt)Fe₂(CO)₅(Ph₂PCH₂)₂NR(μ-pdt)Fe₂(CO)₅] (4: R =ⁿPr; 5: R=Ph) were prepared and characterized by MS, IR, ¹H NMR, ³¹P NMR, EA and X-ray crystal diffraction. Cyclic voltammograms of 4 were studied to evaluate its redox properties. It was found that complex 4 could catalyze electrochemical proton reduction at -2. 29 V in the presence of acetic acid.5-Methoxy-1H-benzoimidazole-2-thiol reacted with Fe₃(CO)₁₂ to produce a [3Fe2S] complex [Fe₃(μ₃-S)₂(C₈H₈N₂O)(CO)₈] (7), which was characterized by IR, ¹H NMR, EA and X-ray crystal diffraction. The structure of 7 is similar with the complex [Fe₃(μ₃-S)₂(CO)₉]. The chemical bond between carbene and the Fe atom has double bond characteristics and the bonds between carbene and N atoms are also partial double bonds.