Synthetic, Structural And Catalytic Study On [FeFe]-hydrogenase Active Site Models Containing Porphyrin And Porphyrinozinc Moieties

Because of the extremely high activity of [FeFe]-hydrogenase for catalytic production of molecular hydrogen, the synthetic, structural and functional studies on [FeFe]-hydrogenase models have received great attention in bioorganometallic chemistry. The artificial models of [FeFe]-hydrogenase with the ability of hydrogen production provide not only insight into structure and catalytic mechanism of its active center, but also a route for solving the increasing problems of energy crisis and environmental pollutions. In order to develop biomimetic chemistry of [FeFe]-hydrogenase, we carried out our studies on the synthesis, structure and catalytic function of a series of new light-driven model compounds containing porphyrin or porphyrinozinc moieties. Also, a series of new precursor compounds of these light-driven models were synthesized and structurally characterized. The main results described in this thesis are as follows:1. A total of 13 new compounds were successfully synthesized, including 7 [FeFe]-hydrogenase active center model compunds containing porphyrin or porphyrinozinc moieties, 3 precursors containing [2Fe2S] moieties and 3 precursors without metal. The structures for all these new compounds were fully characterized by elemental analysis, IR , ¹H NMR, ³¹P NMR and ¹³C NMR spectroscopies, as well as for 6 of them by single-crystal X-ray diffraction methods. Part of these compounds were investigated by electrochemistry, Uv-vis and fluorescence spectra, and 6 model compounds containing porphyrin or porphyrinozinc moieties were studied by photoinduced hydrogen production experiments.2.A new [FeFe]-hydrogenase model compound 5-{p-C₆H₄N(CH₂S-μ)₂] Fe₂(CO)₅PPh₃},10,15,20-Ph₃PorphH₂ (1) containing PPh₃ ligand and porphyrin moiety was synthesized. Two new model compounds 5-{[(C₆H₄-p)NC(O)(μ-SCH₂)₂] Fe₂(CO)₆},10,15,20-Ph₃PorphH₂ (3) and 5-{[(C₆H₄-p)NC(O)(μ-SCH₂)₂]Fe₂(CO)₆}, 10,15,20-Ph₃PorphZn (4) in which porphyrin or porphyrinozinc moiety was covalently bonded to the N atom of a diiron-ADT moiety also synthesized. A new compound [(CHOC₆H₄-p)NC(O)(μ-SCH₂)₂]Fe₂(CO)₆ (2) as the precursor of 3 and 4 was synthesized . The molecular structures of 2 and 4 were confirmed by X-ray diffraction techniques. The possibilities of intramolecular electron transfer of 1,3 and 4 from porphyrin to diiron moiety were studied by fluorescence spectra and Rehm-weller equation. In water soluble micelle system the influences of the hydrogen-producing ability of representative model 3 upon irradiation time, surfactant, pH value and concentration of 3 were systematically studied. In addition, the structural factors of 1, 3 and 4 were discussed by comparing their hydrogen-producing abilities in micelle system. Furthermore, a homogeneous system of photoinduced hydrogen production catalyzed by known model 5-[p-{Fe₂(CO)₆(μ-SCH₂)₂NC₆H₄]-10,15,20- Ph₃PorphH₂ was first carried out. It proved that this system is better than the micelle system for the porphyrin-containing model compounds. A possible mechanism of photoinduced catalytic cycle of hydrogen production for this kind of models was proposed.3.Two new [FeFe]-hydrogenase model compounds 5-{[μ-S₂(CH₂)₃] Fe₂(CO)₅PPh₂(C₆H₄-p)},10,15,20-Ph₃PorphH₂ (3) and 5-{[(μ-SCH₂)₂NC₆H₄CO₂ CH₃-p]Fe₂(CO)₅PPh₂(C₆H₄-p)},10,15,20-Ph₃PorphH₂ (4) in which the porphyrin macrocycle is attached to diiron-PDT or -ADT moiety through a Fe-P coordination bond were synthesized.Two new compounds [μ-S₂(CH₂)₃]Fe₂(CO)₅PPh₂(C₆H₄CHO-p) (1) and [(μ-SCH₂)₂NC₆H₄CO₂CH₃-p]Fe₂(CO)₅PPh₂(C₆H₄CHO-p) (2) as the precursors of 3 and 4 were also synthesized. The molecular structures of 1, 3 and 4 were confirmed by X-ray diffraction techniques. The intramolecular electron transfer through the Fe-P bond in 3 and 4 were studied by fluorescence spectra and Rehm-weller equation. Studies of photoinduced catalytic hydrogen production of the homogeneous system containing representative model 4 were carried out successfully in CH₂Cl₂ and THF. It proved that the electron transfer via the Fe-P coordination bond is more efficient than via the dithiolate bridge. A possible mechanism for the abnormally hydrogen production in the absence of electron donor was proposed.4. A new [FeFe]-hydrogenase model compound 5-{[(μ-SCH₂)₂NC₂H₄C₆H₄-p-SFe₂(CO)₅},10,15,20-Ph₃PorphH₂ (5) in which the porphyrin moiety is attached to diiron-ADT moiety through a Fe-S coordination bond was synthesized. The synthetic route involves six steps and started from a simple material HSC₂H₄NH₂·HCl Four new compounds as precursors of 5, namely BOC-N(H)C₂H₄SC₆H₄CHO-p (1), 5-[BOC-N(H)C₂H₄SC₆H₄-p],10,15,20-Ph3PorphH2(2),5-[H₂NC₂H₄SC₆H₄-p],10,15,20 -Ph₃PorphH₂(3) and 5-{[(μ-SCH₂)₂NC₂H₄C₆H₄S-p)]Fe₂(CO)₆},10,15,20-Ph₃PorphH₂ (4) were synthesized. The molecular structure of precursor compound 4 was confirmed by X-ray diffraction techniques. The influences of the linking mode between porphyrin and diiron moieties, as well as the substituents attached to diiron moiety on electron transfer and photoinduced H₂ evolution were investigated by using electrochemistry, Uv-vis spectra, fluorescence spectra and homogeneous photoinduced hydrogen production experiment of 4 and 5. The properties and H₂ evolution abilitily of 4 and 5 were compared with those of the other model compounds previously reported by our group. All of the aforementioned studies would be helpful for designing and modifying the light-driven [FeFe]-hydrogenase models in the future.