【作者】 李平；

【导师】 孙立成； 王梅；

【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，蛋白质晶体研究结果表明其活性中心具有双八面体的蝶状几何构型，与金属有机配合物[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。本论文主要研究了配体取代对[2Fe2S]模型配合物结构和性能的影响。以丙烷桥连接的六羰基二铁二硫配合物[（μ-pdt）Fe₂（CO）₆]（pdt=propane-1，3-dithiolato）为母体，通过分步的膦配体取代反应，合成了一系列非对称双膦配体取代[2Fe2S]模型配合物，[（μ-pdt）{Fe（CO）₂L¹}{Fe（CO）₂L²}][L¹=PMe₃，L²=PMe₂Ph，4；L¹=PMe₃，L²=PPh₃，5；L¹=PMe₃，L²=PCy₃，6；L¹=PMe₃，L²=P（OEt）₃，7；L¹=PMe₂Ph，L²=PPh₃，8；L¹=PMe₂Ph，L²=P（OEt）₃，9；L¹=P（OEt）₃，L²=PPh₃，10；L¹=P（OEt）₃，L²=PCy₃，11]，并以同样的方法合成了与配合物5类似的乙烷桥连接的配合物[（μ-edt）{Fe（CO）₂（PMe₃）}{Fe（CO）₂（PPh₃）}]（edt=ethane-1,2-dithiolato，12）。X光单晶衍射表明在此类非对称双膦取代[2Fe2S]模型配合物中体积较大的膦配体倾向于占据顶位的位置，而体积相对较小的配体处于基位；当两个配体体积均较大时，如配合物10中的PPh₃和P（OEt）₃，此时两个配体均在顶位。电化学测试结果表明，在非对称双膦配体取代的[2Fe2S]模型配合物中，不同膦配体对氧化还原电位的调变能力相差约200 mV。通过配体取代将水溶性三羟甲基膦（THP）引入到[2Fe2S]模型配合物中，合成了单取代配合物[（μ-pdt）Fe₂（CO）₅（THP）]（13）和双取代配合物[（μ-pdt）{Fe（CO）₂（THP）}₂]（14）。配合物14虽水溶性较好，但在空气中不稳定。配合物13在纯水中溶解度很小，却能够较好地溶于乙腈／水混合溶剂。醋酸存在条件下，配合物13在乙腈／水（1：1，v／v）中电催化质子还原活性远高于在纯乙腈溶液中的催化活性。配合物13的晶体结构表明其在空间上呈无限延伸的FeS／OH／FeS的夹心结构，并且通过分子内和分子间O-H…O氢键构成波浪状无限延伸的二维网络结构，其中的左旋和右旋O-H…O-H螺旋链交替分布。通过膦配体取代将吡啶环作为分子内碱性基团引入到[2Fe2S]模型配合物中，设计合成了配合物[（μ-pdt）Fe₂（CO）₅L]（L=Ph₂PCH₂Py，15；Ph₂PPy，16）。在三氟甲磺酸作用下，循环伏安法测定其第一还原电位分别向正方向移动360和490 mV，推测是由于吡啶氮原子发生质子化。分离得到配合物15和16的质子化产物19和20，并通过X光单晶衍射确定了配合物19和20空间结构。为了增加此类含吡啶基团二铁二硫配合物中Fe-Fe键的碱性，以利于俘获质子，论文设计合成了双取代配合物[（μ-pdt）{Fe（CO）₂（PMe₃）}{Fe（CO）₂L}]（L=Ph₂CH₂Py，17；Ph₂PPy，18），通过低温核磁（-55℃）滴定和原位红外光谱（-10℃）跟踪了配合物18在三氟甲磺酸存在下的质子化过程。研究表明，配合物18在三氟甲磺酸的作用下首先发生在Fe-Fe键之间，最终生成双质子化物种[18HyH]²⁺，该双质子化物种只能在低温下检测到；在室温下不稳定，容易分解。通过Fe₂（CO）₉与过硫酯（?）或（?）在四氢呋喃中室温反应将含吸电性基团（C=O）的刚性共轭桥连结构引入到[2Fe2S]模型配合物中，设计合成了配合物[μ-SC₆H₄-2-（CO）S-μ]Fe₂（CO）₆（21）和[μ-2-SC₅H₃N-3-（CO）S-μ]Fe₂（CO）₆（22）。电化学研究表明含吸电性基团（C=O）刚性共轭桥连结构能够降低[2Fe2S]模型配合物的还原电位，其中配合物22的第一还原电位为-1．18 V（vs.Fc／Fc⁺），比配合物21低100 mV。所有合成的[2Fe2S]模型配合物均通过红外光谱、核磁、质谱和元素分析的表征。其中配合物4-6、8-10、12和15-22通过X光单晶衍射测定了空间结构。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 attract the great interest of synthesis researchers. 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 ligand exchange on the structure and property of the diiron dithiolate complexes were studied.A series of unsymetrically diphosphine substituted [2Fe2S] model complexes, [（μ-pdt）{Fe（CO）₂L¹}{Fe（CO）₂L²}] [pdt = propane-1,3-dithiolato; L¹ = PMe₃, L² = PMe₂Ph, 4; L¹ = PMe₃, L² = PPh₃, 5; L¹ = PMe₃, L² = PCy₃,6; L¹ = PMe₃, L² = P（OEt）₃, 7; L¹ = PMe₂Ph, L² = PPh₃, 8; L¹ = PMe₂Ph, L² = P（OEt）₃, 9; L¹ = P（OEt）₃, L² = PPh₃,10; L¹= P（OEt）₃, L² = PCy₃, 11] and [（μ-edt）{Fe（CO）₂（PMe₃）}{Fe（CO）₂（PPh₃）}] （edt = ethane-1,2-dithiolato, 12） were successfully synthesized by stepwise phosphine ligand replacement. X-ray single crystal diffraction reveals that bulky phosphine ligand prefers the apical site, while the smaller one coordinates at the basal site. When two phosphine ligands, i.e., PPh₃ and P（OEt）₃ in complex 10, are both bulky ligands, an apical/apical coordination conformation is preferred. Electrochemistry results indicated that different phosphine ligands led to ca. 200 mV difference for the redox potentials of the unsymetrically diphosphine substituted complexes.Mono- and disubstituted complexes, [（μ-pdt）Fe₂（CO）₅（THP）] （13） and [（μ-pdt）{Fe（CO）₂（THP）}₂] （14）, were synthesized for the purpose of introduction of a water soluble phosphine ligand, tris（hydroxymethyl）phosphine （THP）, to the [2Fe2S] model complex. Disubstituted complex 14 possesses good water solubility in water and bad stability in air atmosphere. Complex 13 has poor solubility in pure water while it can be dissolved in CH₃CN/H₂O mixed solution. The catalytic activity for proton reduction of complex 13 in CH₃CN/H₂O （1:1, v/v） is higher than that in pure CH₃CN in the presence of HOAc. Indefinitely extended sandwich FeS/OH/FeS packing mode is found in the packing diagram of complex 13. Wavily assembled two dimensional networks are constructed by intra- and intermolecular O-H…O hydrogen bonds. Right- and left-handed O-H…O-H helical chains are alternately arranged in the extended network.Phosphine ligands featuring an internal base of pyridine ring were introduced to the [2Fe2S] model by synthesis of complexes [（μ-pdt）Fe₂（CO）₅L] （L = Ph₂PCH₂Py, 15; Ph₂PPy, 16）. Potential shifts of 360 and 490 mV to positive direction were found for the first reductions of complexes 15 and 16, respectively, in the presence of HOTf. It is proposed that the anodic shifts are caused by the protonation of the pyridyl-N atoms in Ph₂PCH₂Py and Ph₂PPy. Protonated species [（μ-pdt）Fe₂（CO）₅L][OTf] （L = [Ph₂PCH₂PyH]⁺, 19; [Ph₂PPyH]⁺, 20） were isolated and characterized by X-ray crystal diffraction. Complexes [（μ-pdt）{Fe（CO）₂（PMe₃）}{Fe（CO）₂L}] （L = Ph₂CH₂Py, 17; Ph₂PPy, 18） were synthesized for the enhancement on the protophilicity of the Fe-Fe bonds while remaining the pyridine ring as an internal base in the same molecular. Low temperature NMR （-55℃） techniques and in situ IR （-10℃） spectroscopy were used to trace the protonation process of complex 18 in the presence of strong acid （HOTf）. The results showed that complex 18 was protonated first on the Fe-Fe bond. The doubly protonated species [18HyH]²⁺ was formed and detected at low temperature while it would decomposed at room temperature.In order to tune the reduction potential of the [2Fe2S] complex, the rigid and conjugated bridge containing the electron withdrawing group （C=O） was introduced to the [2Fe2S] model. Complexes [μ-SC₆H₄-2-（CO）S-μ]Fe₂（CO）₆ （21） and [μ-2-SC₅H₃N-3-（CO）S-μ]Fe₂（CO）₆ （22）were prepared by the reactions of Fe₂（CO）₉ and （?） or （?） in THF at room temperature, respectively. X-ray crystal diffraction confirms the plane structure of the bridge in complexes 21 and 22. The results of electrochemistry indicate that the rigid and conjugated bridge indeed results in the positive shift of the reduction potentials. The first reduction event of complex 22 appears at -1.18 V （vs. Fc/Fc⁺）, which is 100 mV positive than that of complex 21.All synthesized diiron dithiolate complexes were characterized by IR, NMR, MS and elemental analysis. Structures of complexes 4-6, 8-10, 12, and 15-22 were determined by X-ray single crystal diffraction.更多还原