Modelling Study On [FeFe]-Hydrogenase Butterfly Active Site

In view 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 studies have significant value not only in theory but also in practice for solving the increasingly environmental pollution and energy crisis. In order to develop the biomimetic chemistry of [FeFe]-hydrogenase, we have carried out a study on the synthesis, structure and properties of a series of new model complexes for the [FeFe]-hydrogenase active site, which contain the butterfly [2Fe2Se] and [2Fe2S] clusters. And, we also carried out a study on a series of the "open" butterfly [2Fe2Se] cluster complexes. The main results obtained from this study are as follows:1. 22 new models for the [FeFe]-hydrogenase active site and 5 new "open" butterfly [2Fe2Se] cluster complexes were successfully synthesized. The structures for all these models and complexes were fully characterized by elemental analysis, IR, ’H-NMR. Some of them were further characterized by 31P-NMR, 77Se-NMR and 13C-NMR, as well as for 15 representatives by single-crystal X-ray diffraction methods.2. The parent model complex [(μ-SeCH2)2CH(OH)]Fe2(CO)6 containing a single-butterfly [2Fe2Se] cluster was first prepared. 3 phosphine-functionalized complexes and 1 double-butterfly model containing one or two butterfly [2Fe2S] clusters were first prepared through the functional transformations of [(μ-SeCH2)2CH(OH)]Fe2(CO)6. The structures of parent model and its three derivatives were determined by X-ray diffraction analysis. In addition, the electrochemical properties of the parent model were described.3. During the synthesis of [(μ-SeCH2)2CH(OH)]Fe2(CO)6, we isolated an "open" butterfly cluster complex (μ-SeEt)[(μ-SeCH2CH(OH)(CH2Br)]Fe2(CO)6, unexpectedly. Treatment of this cluster complex with Ph2PCl or 4-pyridinecarboxylic chloride in the presence of Et3N resulted in formation of (μ-SeEt)[μ-SeCH2CH(CH2Br)(OPPh2-η1)]Fe2(CO)5 determined by X-ray diffraction analysis and (μ-SeEt)[μ-SeCH2CH(CH2Br)(O2CC5H4N-4)]Fe2(CO)6. The electrochemical properties of (μ-SeEt)[(μ-SeCH2CH(OH)(CH2Br)]Fe2(CO)6 were described. For further comparison, we prepared complex (μ-SenBu)[μ-SeCH2CH(OH)CH2Br]Fe2(CO)6.4. Five new acyl-functionalized ADT complexes [(μ-SeCH2)2NR]Fe2(CO)6 (R= MeC(O), PhC(O), PhCH2OC(O), EtC(O), PhCH2C(O)) were first prepared. Complex [(μ-SeCH2)2NH]Fe2(CO)6 was produced by deprotection of the amino group of [(μ-SeCH2)2NR]Fe2(CO)6 (R=PhCH2OC(O)). Complexes [(μ-SeCH2)2NR]Fe2(CO)6 (R=EtC(O), PhCH2C(O)) were the acylated products of the bridgehead N atom of [(μ-SeCH2)2NH]Fe2(CO)6. The five bridgehead N atom-functionalized complexes were determined by X-ray diffraction analysis. In addition, the electrochemical properties of [(μ-SeCH2)2NR]Fe2(CO)6 (R=MeC(O), PhC(O)) were described.5. The new hydroxyethyl-functionalized ADT complex [(μ-SeCH2)2NCH2CH2OH]Fe2(CO)6 was first prepared. Further reactions of this complex with the acylating agents CH2(C(O)Cl)2 and 1,3,5-benzenetricarboxylic acid chloride in the presence of Et3N produced the double and triple models, respectively. The electrochemical properties of [(μ-SeCH2)2NCH2CH2OH]Fe2(CO)6 were described.6. The new ether-functionalized PDT complex [(μ-SCH2)2CH(OCH2Ph)]Fe2(CO)6 containing a butterfly [2Fe2S] cluster was first prepared. A new NHC ligand-monosubstituted product and 6 phosphine-mono and-disubstituted products were prepared by CO substitution reactions of the above-mentioned parent complex. The Pb3P-disubstituted product was prepared at room temperature, while the other disubstituted products were obtained in toluene at reflux. Five substituted derivatives were determined by X-ray diffraction analysis. In addition, the electrochemical properties of the parent model and three phosphine-substituted products were described.