【作者】 王宁；

【导师】 王梅； 孙立成；

【作者基本信息】 大连理工大学 ， 应用化学， 2009， 博士

【摘要】 自然界中的铁铁氢化酶能够可逆催化质子还原产氢反应,蛋白质晶体研究结果表明其活性中心是一个具有双八面体蝶状几何构型的[2Fe2S]簇,与已知的金属有机配合物[Fe₂（μ-SR）₂（CO）_6-nL_n]非常相似。简单的结构组成和高效的催化性能引起了合成化学家的极大兴趣,人们期望对铁铁氢化酶活性中心结构进行化学模拟,揭示其催化产氢机理,并最终制得廉价高效的制氢催化剂。本论文主要研究了分子内碱基对[2Fe2S]模型配合物结构和性能的影响。通过改变Fe₂（CO）₉与配体（EtO）₂PN（Me）P（OEt）₂ （PMP）、1,3-丙二硫醇的反应顺序可以分别得到螫合双取代配合物[（μ-pdt）{Fe（CO）₃}{Fe（CO）（κ²-PMP）}] （3）和分子内桥连双取代配合物[（μ-pdt）（μ-PMP）Fe₂（CO）₄] （4）。深入研究了配合物3的膦配体取代反应的历程。配合物3与膦配体PR₃（R=Me,OEt）反应,生成PR₃配位而PMP配体中一个P原子配位解离的双取代配合物[（μ-pdt）{Fe（CO）₂PR₃}{Fe（CO）₂（PMP）}] （R = Me, 5; OEt, 7）。分别在CO和N₂的气氛下进行配合物3的膦配体取代反应,反应速度没有任何变化;同时在¹³CO气氛下进行反应,也没有观察到含¹³CO产物的生成,表明配合物3的膦配体取代反应为双分子反应。配合物5和7可以在甲苯回流的条件下进一步发生分子内膦配体取代反应,生成三取代配合物（μ-pdt）（μ-PMP）[Fe（CO）PR₃][Fe（CO）₂] （R = Me, 6; OEt, 8）。通过变温³¹P NMR证明模型配合物6和8在溶液中PMP配体存在摆动,形成两种构象互变现象。以丙烷桥连接的六羰基[2Fe2S]配合物[（μ-pdt）Fe₂（CO）₆]（pdt=propane-1,3-dithiolato）为母体,通过含氮双齿膦配体Ph₂PCH₂N（n-Pr）CH₂PPh₂ （PNP）和Ph₂PCH₂N（Ph）CH₂PPh₂ （PAP）,将氮原子作为分子内碱性基团引入到[2Fe2S]模型配合物中。合成了分子内螯合双取代配合物[（μ-pdt）{Fe（CO）₃}{Fe（CO）（κ²-PNP）}] （9）、分子内对称双取代配合物[（μ-pdt）{μ-PNP}Fe₂（CO）₄] （10）和分子间双取代配合物[{（μ-pdt）Fe₂（CO）₅}₂（μ,κ¹,κ¹-PNP）] （11）与[{（μ-pdt）Fe₂（CO）₅}₂（μ,κ¹,κ¹-PAP）] （12）。通过¹H NMR和³¹P NMR观察了配合物9的质子化历程,并首次得到双质子化产物[（μ-H）（μ-pdt）{Fe（CO）₃){Fe（CO）（κ²-PNHP）}]（OTf）₂ [9（H_NH_μ）]（OTf）₂的晶体结构。通过晶体结构可以发现配合物[9（H_NH_μ）]（OTf）₂中H⁺…H^-距离为3.934 （?）。脱质子实验表明,模型配合物[9（H_NH_μ）]²⁺中μ-H具有类似t-H的化学活性。配合物[9（H_NH_μ）]²⁺和[9（H_μ）]⁺中μ-H与溶液中的D⁺能够发生H/D交换反应,表明N原子在[2Fe2S]模型配合物中可以起到质子转移的重要作用。通过Fe₂（CO）₉与硫代草酰胺反应将含氮原子的刚性C₂桥连结构引入到[2Fe2S]模型配合物中。通过膦配体取代合成了配合物[μ-SC（NBn）CH（NHBn）S-μ]Fe₂（CO）₅PR₃（R=Me,15;Ph,16;Pyr,17）,并得到了氮原子质子化产物[16（H_N）]OTf的晶体。研究了配合物17的电化学性质,并与氮杂丙烷桥配合物18进行了比较。电化学研究表明含碱基的C₂刚性桥连结构能够降低[2Fe2S]模型配合物的还原电位,并且配合物17中的氮原子比18中的桥基氮原子更易发生质子化,其氮质子化产物的第一还原电位比配合物18的氮质子化产物低270 mV。更多还原

【Abstract】 [FeFe] Hydrogenases in microorgamisms can reversibly catalyze the proton reduction for hydrogen evolution. Studies on the crystal structures of the enzymes show that the active site of [FeFe] hydrogenases features a square-pyramidal butterfly coordination geometry, which is quite similar to that of the reported organometallic complexes formulated as [Fe₂（μ-SR）₂（CO）_6-nL_n]. The simple structure and the high efficiency of the [FeFe] hydrogenase active site inspire a great interest for chemists. They try to explore the catalytic mechanism for proton reduction and eventually find cheap and efficient catalysts for hydrogen production by mimicking the structure of the active site. In this thesis, the effect of internal N-base on the structures and properties of the diiron dithiolate complexes were studied.Two isomeric diiron dithiolate complexes [（μ-pdt）{Fe（CO）₃}{Fe（CO）（κ²-PMP）}] （3） and [（μ-pdt）（μ-PMP）Fe₂（CO）₄] （4） containing the （EtO）₂PN（Me）P（OEt）₂ （PMP） ligand have been prepared. The PMP ligand is in an unsymmetrical chelating mode for 3 and in a symmetrically bridging mode for 4. Complex 3 was converted to 4 in 75% yield after reflux in toluene for a long time. The reactions of 3 with PMe₃ and P（OEt）₃ afforded bis-monodentate P-donor complexes [（μ-pdt）{Fe（CO）₂PR₃}{Fe（CO）₂（PMP）}] （R = Me, 5; OEt, 7）, respectively, which are formed via the coordination of PR₃ accompanied by an intramolecular CO-migration process from the Fe（CO）₃ to the Fe（CO）（PMP） unit and opening of the Fe-PMP chelate ring. The PMP-monodentate complexes 5 and 7 were converted to a trisubstituted diiron complex （μ-pdt）（μ-PMP）[Fe（CO）PR₃][Fe（CO）₂] （R = Me, 6; OEt, 8） with release of an equiv of CO when they are refluxing in toluene. Variable temperature ³¹P NMR spectra show that trisubstituted diiron complexes each exist as two conformation isomers in solution. All diiron dithiolate complexes obtained were characterized by MS, IR, NMR spectroscopy, elemental analysis, and X-ray diffraction studies.The CO-displacement of [（μ-pdt）Fe₂（CO）₆] with Ph₂PCH₂N（n-Pr）CH₂PPh₂ （PNP） in refluxing toluene gave an unsymmetrical chelating complex[（μ-pdt）{Fe（CO）₃}{Fe（CO）（κ²-PNP）}] （9） as a major product, together with a small amount of the symmetrical intramolecular bridging complex [（μ-pdt）{μ-PNP}Fe₂（CO）₄] （10） and the intermolecular bridging complex [{（μ-pdt）Fe₂（CO）₅}₂（μ,κ¹,κ¹-PNP）] （11）, while the reaction of [（μ-pdt）Fe₂（CO）₆] with Ph₂PCH₂N（Ph）CH₂PPh₂ （PAP） afforded only the intermolecular bridging complex [{（μ-pdt）Fe₂（CO）₅}₂（μ,κ¹,κ¹-PAP）] （12）. The molecular structures of 9,11, 12, as well as the doubly protonated complex [9（H_NH_μ）]（OTf）₂ were determined by X-ray analyses. The protonation processes of 9 with HBF₄·Et₂O and HOTf were studied. Theμ-hydride of [9（H_μ）]⁺ and [9（H_NH_μ）]²⁺ can take place facile deprotonation in the presence of an equivalent of aniline and rapid H/D exchange with deutons in solution.Three diiron dithiolate complexes [μ-SC（NBn）CH（NHBn）S-μ]Fe₂（CO）₅PR₃ （R = Me, 15; Ph, 16; Pyr, 17） containing a functionalized C₂ bridge with two vicinal basic sites were prepared and characterized. The molecular structures of 16 and its N-protonated form [（16H_N）]OTf were determined by X-ray analyses of single crystals. The complexes 16 and 17 are relatively protophilic. The cyclic voltammograms show that complex 17 can be protonated by the mild acid CF₃COOH. Electrochemical studies show that the first reduction peak of 17 at -1.51 V versus Fc⁺/Fc is 110 mV more positive than that （-1.62 V） found for the analogous diiron azadithiolate complex [{（μ-SCH₂）₂N（CH₂C₆H₅）}Fe₂（CO）₅P（Pyr）₃] （18）. Protonation of 17 leads to the anodic shifts of 610-650 mV for the Fe^ⅠFe^Ⅰ/Fe^ⅠFe⁰ reduction potentials. The shifts are apparently larger than that （450 mV） displayed by protonation of 18. The reaction of the all-carbonyl complex [{μ-SC（NBn）CH（NHBn）S-μ}Fe₂（CO）₆] （14） with two equivalents of bis（diphenylphosphino）methane （dppm） in refluxing toluene forms dppm mono-dentate intermediate [{μ-SC（NBn）CH（NHBn）S-μ}Fe₂（CO）₅（κ¹-dppm）] （19） and a dppmμ-bridging species [{μ-SC（NBn）CH（NHBn）S-μ}Fe₂（CO）₄（μ-dppm）] （20） depending on reaction time. A desulfurized complex [（μ-S）（μ-dppm）₂Fe₂（CO）₄] （21） was obtained after refluxing in toluene for a long time.更多还原