【作者】 高尚；

【导师】 彭孝军；

【作者基本信息】 大连理工大学 ， 应用化学， 2008， 博士

【摘要】 自然界中微生物体内的铁铁氢化酶能够可逆催化质子还原产氢,晶体和红外光谱研究表明其活性中心具有双八面体的蝶状几何构型,与早有研究的金属有机配合物[Fe₂（μ-SR）₂（CO）_6-nL_n]非常相似。因其简单的结构组成和高催化性能,铁铁氢化酶活性中心的结构和功能模拟引起了生物无机化学家们极大的兴趣。人们力求进一步揭示铁铁氢化酶催化产氢的机理,并最终制得廉价高效的制氢催化剂。本论文主要合成了一系列二铁配合物作为铁铁氢化酶活性中心的结构和功能模型。为考察桥连配体中硫原子的替换对模型配合物性质的影响,合成了3个氮杂桥连[2Fe2Se]模型配合物[{（μ-SeCH₂）₂NC₆H₄R}Fe₂（CO）₆]（R=4-NO₂,7;R=H,8;R=4-CH₃,9）。X射线单晶衍射表明配合物7-9的分子构型与其对应的[2Fe2S]类似物[{（μ-SCH₂）₂NC₆H₄R}Fe₂（CO）₆]（R=4-NO₂,7s;R=H,8s;R=4-CH₃,9s）非常相似。红外光谱和电化学循环伏安曲线表明将桥连配体中硫原子替换成硒原子增大了中心铁原子上的平均电子云密度。选择配合物9考察催化活性时发现,在对甲苯磺酸（HOTs）的存在下,配合物9有着比其[2Fe2S]类似物9s略高的电催化质子还原活性。基于光驱动电子转移还原质子产氢的构想,合成了3个连接苯并噻唑类有机光敏体[2Fe2S]模型配合物16-18。为进一步考察光敏体和[2Fe2S]单元的电子相互作用,合成了3个参比化合物16r-18r。利用吸收和发射光谱及闪光光解研究了配合物16-18及参比化合物16r-18r的光物理性质。与16r及16r和等摩尔[（μ-S）₂Fe₂（CO）₆]的混合物相比较,配合物16的荧光光谱产生淬灭,并且配合物16的常温激发态寿命要短于16r。这些结果表明配合物16中光敏体和[2Fe2S]单元之间发生了分子内能量转移。通过配体取代将水溶性三吗啉膦（TMP）引入到[2Fe2S]模型配合物中,合成了单取代配合物[（μ-pdt）Fe₂（CO）₅（TMP）]（20）和双取代配合物[（μ-pdt）Fe₂（CO）₄（TMP）₂]（21）。红外光谱表明TMP配体比其它膦配体（如PMe₃,PTA,PPh₃）具有更强的供电子能力。电化学循环伏安曲线表明:乙酸存在条件下,配合物20和21在乙腈/水混合溶液体系中的催化质子还原活性要高于在纯乙腈中催化活性,并且在乙腈/水（10:1,v/v）中达到最高。通过Fe₃（CO）₁₂与2,3-二巯基吡嗪在四氢呋喃中回流反应将刚性共轭桥连结构引入到[2Fe2S]模型配合物中,合成了配合物[μ-SC₄N₂H₂S-μ]Fe₂（CO）₆（24）。在对配合物24进行PMe₃配体取代时,得到了其单取代配合物[μ-SC₄N₂H₂S-μ]Fe₂（CO）₅（PMe₃）（26）和一种意外的单核铁配合物[μ-SC₄N₂H₂S-μ]Fe（CO）₂（PMe₃）₂（25）。分离得到了配合物24和25的质子化产物24H⁺、25H⁺和25H₂²⁺,并通过X射线单晶衍射表征了3种质子化产物的结构,质子化过程则通过UV/Vis、IR和NMR光谱跟踪。电化学研究表明刚性共轭桥连结构能够降低[2Fe2S]模型配合物的还原电位,配合物24的第一还原电位为-1.19 V（vs.Fc/Fc⁺）。所有合成的化合物均通过红外光谱、核磁和高分辨质谱的表征。其中配合物7-9、16-18、20、21、24-26、24H⁺、25H⁺和25H₂²⁺通过X射线单晶衍射测定了分子结构。更多还原

【Abstract】 Fe-Fe hydrogenases are enzymes which can reversibly catalyze the proton reduction to hydrogen in microorganisms.Crystallographic and IR spectroscopy studies reveal that the active site of Fe-Fe hydrogenases adopts a square-pyramidal butterfly coordination geometry,which highly resemble the well-known organometallic complexes formulated as [Fe₂（μ-SR）₂（CO）_6-nL_n].Owing to the simple structure and the high efficiency,biomimetic models related to the active site of the Fe-Fe hydrogenases are of particular interest to bioinorganic chemists.They try to further understand the catalytic mechanism for proton reduction and eventually find the synthetic competitive catalysts that function with hydrogenase-like capability.In this thesis,a series of diiron complexes were synthesized as the structural and functional models for the Fe-Fe hydrogenases active site.Three N-substituted aza diselenide diiron complexes[{（μ-SeCH₂）₂NC₆H₄R}Fe₂（CO）₆] （R=4-NO₂,7;R=H,8;R=4-CH₃,9） were firstly synthesized to investigate the effects of changing the S atoms of the bridging dithiolate ligands on the biomimetic models.X-ray single crystal diffraction reveals the overall molecular structures of 7-9 are analogous to those of their dithiolate analogues[{（μ-SCH₂）₂NC₆H₄R}Fe₂（CO）₆]（R=4-NO₂,7s;R=H, 8s;R=4-CH₃,9s）.IR spectra and electrochemical studies indicate that changing the S atoms of the bridging ligands to Se atoms enhance the average electron density of the iron cores.As a typical object we chose,complex 9 shows a slightly higher electrocatalytic activity for proton reduction from HOTs than its dithiolate analogue 9s.On the basis of the concept of light-induced electron transfer（ET） to drive proton reduction to hydrogen,three novel benzothiazole photosensitizer-[2Fe2S]complexes 16-18 were successfully synthesized and well characterized.In addition,three reference compounds 16r-18r were prepared to further investigate the electronic interaction between the photosensitizer and the[2Fe2S]subunit.The photophysical properties of 16-18 and 16r-18r have been investigated by absorption & emission spectra and flash photolysis.As compared to 16r and the equimolar mixture of 16r and[（μ-S）₂Fe₂（CO）₆],the fluorescent spectra of 16 is quenched.Meanwhile,the emission lifetime is shorter than that of 16r. These results show that the intramolecular energy transfer from the photosensitizer to the [2Fe2S]subunit occurs in complex 16. Mono-and disubstituted complexes,[（μ-pdt）Fe₂（CO）₅（TMP）]（20） and[（μ-pdt） Fe₂（CO）₄（TMP）₂]（21）,were synthesized to introduce a water soluble phosphine ligand, tris（morpholino）phosphine（TMP）,to the[2Fe2S]model complex.IR spectra indicate that the TMP ligand has better electron-donating ability than that of other phosphine ligands, such as PMe₃,PTA（1,3,5-triaza-7-phosphaadamantane）,PPh₃.Electrochemical CVs reveal that both complexes 20 and 21 could electrocatalyze the protons reduction from HOAc in higher activity in CH₃CN/H₂O mixed solutions than in pure CH₃CN solution.And in CH₃CN/H₂O（10:1,v/v）,the catalytic activity is highest.In order to tune the reduction potential of the[2Fe2S]model,complex [μ-SC₄N₂H₂S-μ]Fe₂（CO）₆（24） with the rigid and conjugated bridge was prepared by the reaction of Fe₃（CO）₁₂ and pyrazine-2,3-dithiol in THF at refluxing temperature.The monotrimethylphosphine substituted complex[μ-SC₄N₂H₂S-μ]Fe₂（CO）₅（PMe₃）（26） and an unexpected monometallic complex[μ-SC₄N₂H₂S-μ]Fe（CO）₂（PMe₃）₂（25） were obtained in the PMe₃ ligand replacements.Protonated species of complexes 24 and 25,those 24H⁺,25H⁺ and 25H₂²⁺ were isolated and characterized by X-ray crystal diffraction.The protonation processes are traced by UV/Vis,IR and NMR spectra in the presence of HOTf. The results of electrochemistry indicate that the rigid and conjugated bridge indeed results in the positive shift of the reduction potential.The first reduction peak of complex 24 appears at -1.19V（vs.Fc/Fc⁺）.All synthesized complexes were characterized by IR,NMR and HR-MS.Structures of complexes 7-9,16-18,20,21,24-26,24H⁺,25H⁺ and 25H₂²⁺ were determined by X-ray single crystal diffraction.更多还原