【作者】 孙慧；

【导师】 张冬菊；

【作者基本信息】 山东大学 ， 理论与计算化学， 2010， 博士

【摘要】 离子液体是一类完全由阴、阳离子组成的新型液态化合物。它们具有一些优良的物理化学性质,如低熔点、宽液程、高的热稳定性、良好的溶解性、不易燃、不易挥发、可循环使用等。其中,离子液体不易挥发、可循环使用的独特性能,符合绿色化学、绿色合成的理念,被认为是一类理想的环境友好介质和绿色功能材料,近二十年来一直受到国际学术界和工业领域的广泛关注。此外,离子液体还拥有“可设计”特征,可以通过改变阴、阳离子的种类和大小来调节其物理化学性质,使人们可以根据特定的用途和需要设计具有特殊功能的离子液体。到目前为止,离子液体的实验应用研究已经取得了很大进展,在化学合成与催化、萃取与分离、电化学、生物化学等领域被广泛用作溶剂、反应介质、催化剂和功能材料。与离子液体的实验研究相比,其理论研究发展明显滞后。纵观离子液体理论研究现状,众多研究工作主要致力于应用量子化学和分子动力学模拟方法研究咪唑类离子液体的微观结构,以及构-效关系,而对其他类型离子液体(如吡啶类离子液体,季铵盐类离子液体等)结构及性质的理论研究则相对较少。这一研究现状既不利于人们全面了解离子液体的微观结构,又不利于离子液体构-效关系的建立,也影响了新型功能化离子液体的开发和应用。另外,人们对离子液体催化反应机理的认识仍不清晰,由此在一定程度上限制了新型高效离子液体催化剂的发展和应用。开展相关的理论研究是当今理论化学工作者面临的一项重要任务。本论文围绕几种性能优良的离子液体开展了一系列研究工作。一方面借助了量子化学和分子动力学模拟方法分别研究了典型二价离子液体和吡啶类离子液体的微观结构,探讨了结构对其本身物理化学性质的影响,为离子液体构-效关系的建立提供了有价值的信息。另一方面应用密度泛函方法研究了咪唑类离子液体和手性离子液体催化的几类重要有机合成反应,揭示其微观反应机制,弄清了离子液体催化行为和催化活性的本质,掌握了控制反应的关键因素,为定向设计、合成具有独特性能的功能化离子液体催化剂提供了一定的理论指导。本论文主要创新成果如下：1.研究了毗啶类离子液体[BPy]+[BF4]-和新型二价离子液体[(MIm)C3(MIm)](2+)[Br]-的离子对结构,给出了其稳定的几何结构和电子性质,探讨了阴阳离子间相互作用的本质,分析了离子液体结构与性质之间的内在联系,丰富了人们对离子液体微观结构的认知。用密度泛函方法详细地研究了典型吡啶类离子液体[BPy]+[BF4]-的几何构型,讨论了离子对各种可能构型间的相对稳定性,获得了阴离子在阳离子周围的优势取向,同时还对阴阳离子间的氢键相互作用进行了探讨,给出了氢键的分布及强度信息。研究发现[BPy]+[BF4]-离子液体离子对结构的相对稳定性由阴阳离子间的静电相互作用和氢键相互作用共同决定。对二价离子液体[(MIm)C3(MIm)]2+[Br]2-阳离子和离子对的几何和电子结构进行了详细地密度泛函理论研究。分析了阳离子及离子对的各种可能构型,发现在最稳定离子对结构中两个咪唑环之间存在π…π兀相互作用,这是影响[(MIm)C3(MIm)]2+[Br]-2离子对结构稳定性的重要因素。此外,本文还采用自然键轨道分析方法深入研究了阳离子及离子对结构中的电子离域情况,给出了咪唑环上氢原子酸性的相对强弱。同时应用前线分子轨道分析探讨了阴阳离子间的电子转移和相互作用的本质。结果表明：阴阳离子间相互作用表现为二价阳离子的69C-H和π‘轨道与Br-离子的pAO轨道间的相互作用,阴阳离子间的电荷转移主要借助二价阳离子的σ*C-H轨道与Br-离子的一个pAO轨道间的v相互作用。阴阳离子间较大的电子转移和较高的离子对稳定化能为二价离子液体的高熔点和高热稳定性提供了合理的解释。有关结果发表在J. Phys. Chem. A (2010,114,3990-3996)和J. Mol. Struct. (THEOCHEM) (2009,900,37-43)杂志上。2.采用分子动力学模拟方法深入分析[BPy]+[BF4]-离子液体的微观结构,以及H20对[BPy]+[BF4]-离子液体微观结构和动力学性质的影响,加深了人们对吡啶类离子液体微观结构的认识,探讨了H20与吡啶类离子液体二元混合物的构-效关系。在量子化学计算的基础上,选择了适合的力场与计算模型,对[BPy]+[BF4]-离子液体进行了分子动力学模拟。通过径向分布函数和空间分布函数分析发现,[BPy]+[BF4]-离子液体呈阴阳离子交替排列的长程有序结构,阴离子主要位于阳离子周围的第一配位层,其在阳离子周围的空间分布情况与量子化学计算所得结论一致,而阳离子主要位于给定阳离子周围第二配位层中阴离子在第一配位层中没有占据的区域。两吡啶阳离子间的排布方式以T型排列为主。阴阳离子间的氢键分布及强度信息通过分析[BPy]+阳离子上的H原子与[BF4]-阴离子中的F原子间的位-位径向分布函数获得。所得氢键强度趋势与密度泛函理论计算所得结论一致,但分子动力学模拟所得氢键强度均弱于密度泛函理论计算所得结果。[BPy]+[BF4]--H20混合体系的分子动力学模拟考察了不同含量的H20对[BPy]+[BF4]-离子液体微观结构及动力学性质的影响。由径向分布函数和空间分布函数分析可知,H2O的存在并没有改变[BPy]+[BF4]-离子液体的基本结构特征,以及阴阳离子间的氢键强度趋势。体积较小的H20分子位于给定阳离子周围的第一配位层,其在阳离子周围的分布区域与上述阴离子的分布区域基本一致,然而不如阴离子的分布区域广。阴离子占据阳离子周围的第二配位层。H20分子与离子液体中的阴离子距离更近,相互作用更强。随着H20含量的增加,阴、阳离子周围的H20分子数目增多,而阳离子或阴离子数目减少,阴阳离子间相互作用减弱,由此阳离子的旋转速度和阴阳离子的扩散程度也都随之增加,表明H20的存在能有效降低[BPy]+[BF4]-离子液体的粘度。有关结果发表在J.Phys.Chem.A(2010,114,3990-3996)杂志上。3.研究了咪唑类离子液体催化的Deils-Alder (D-A)反应、Markovnikov加成反应和CO2与环氧丙烷的环加成反应,揭示了其微观反应机制,弄清了离子液体中阴、阳离子催化行为和催化活性的本质,掌握了控制反应的关键因素。(1)系统地研究了[EEIm]+催化的环戊二烯与异丁烯醛的D-A反应,探索了催化剂缺乏和存在时D-A反应的四条可能路径,揭示了非催化反应与催化反应的机理细节,获得了有关反应的势能面轮廓。对比非催化与催化反应过程发现,[EEIm]+的存在不仅降低了反应的能垒,而且增加反应的异步性,但没有改变反应的势能面轮廓,非催化与催化反应都以协同机理进行,并且exo-cis为能量最低路径。结果表明,[EEIm]+在反应中作为弱Lewis酸来催化反应。有关结果发表在Inter. J. Quant. Chem.(2007,107(9),1875-1885)杂志上。(2)详细地研究了[BMIm]+[OH]-催化的咪唑与乙烯乙酸酯的Markovnikov加成反应,探讨了其反应机理,获得了势能面上各驻点的能量信息。结果表明：由于反应物乙烯乙酸酯构型的不同,反应可分别以分步和协同机理进行；这两个过程均系高放热反应；[BMIm]+[OH]-中的阴、阳离子在Markovnikov加成反应中都扮演了重要角色,其中[BMIm]+稳定了反应过程中生成的C负离子,而OH-夺取了咪唑上的N1-H氢原子,增强了咪唑的亲核能力。有关结果发表在J. Phys. Chem. A(2007,111,4535-4541)杂志上(3)以CO2和环氧丙烷为例,研究了在[R1MIm]+[C1]-(R1=Ethyl,Butyl,和Hexyl)存在下CO2与环氧化合物的环加成反应,探索了在离子液体缺乏和存在时环加成反应的可能路径,并获得了相应势能面轮廓,得出了一些有意义的结论。结果出示：在离子液体缺乏时,环加成反应可经由两条反应通道,均以协同机理进行,但其反应能垒高达59.71和55.10 kcal mol-1：而在离子液体存在时,环加成反应是一个多通道反应,可以通过至少五条反应路径进行,每一条路径包含两到三个基元步,并且决速步(均包含环氧丙烷的开环过程)的能垒比非催化反应的能垒降低了20-30 kcal mol-1。[EMIm]+[Cl]-的催化活性来源于阴、阳离子的协同作用,其中阳离子利用氢键稳定了中间体和过渡态,而阴离子亲核进攻环氧丙烷,使其开环过程更容易发生。有关结果发表在J. Phys. Chem. A(2007,111,8036-8043)杂志上。4.通过密度泛函理论计算,详细地研究了吡咯咪唑溴催化的环已酮和硝基苯乙烯间的Michael加成反应,揭示了其详细的微观反应机理,分析了酸性加成物对Michael加成反应活性的影响,明确了吡咯型手性离子液体在反应过程中所扮演的角色,并探讨了不对称Michael加成产物高立体选择性的原因。结果表明：此反应分两阶段进行,即烯胺形成阶段和Michael加成阶段；酸性加成物的存在改变了烯胺形成机理,降低了反应势垒,并使烯胺形成过程高度放热；吡咯型手性离子液体中的阴、阳离子联合推动反应的进行,其中Br-负离子作为质子接受体协助亚胺-烯胺互变过程中的质子转移,而阳离子通过静电和氢键相互作用稳定了C-C键形成过程中C原子上增长的负电荷；咪唑阳离子与硝基苯乙烯间氢键的形成,以及咪唑阳离子在烯胺Si-面的空间位阻导致了Michael加成产物高的立体选择性。有关结果发表在Chirality (Early View)杂志上。更多还原

【Abstract】 In the past two decade, Ionic liquids (ILs), a new class of liquids that are entirely composed of ions, have been one of the most heated research topics in the academic and industrial fields. This is mainly attributed to their fascinating "green" characteristic, such as high thermal and chemical stability, nonflammability, nonvolatility and good reusability, which make ILs be widely recognized as environmentally friendly medium. Moreover, the designable characteristic is another important factor that is responsible for the unprecedented prosperity of ILs. Cations and anions constituting ILs can be optionally varied so that ILs can be designed technically to possess unique properties for special applications. So far, the applications of ILs have traversed many fields, including organic synthesis and catalysis, chemical separation, electrochemistry, and biochemistry, where they were widely used as solvents, reaction mediums, catalysts, and functional materials.Compared with the experimental researches on ILs, their theoretical studies are relatively laggard. Researchers paid much attention to investigating the structures, properties and structure-property relationships of ILs through the quantum chemistry calculations and molecular dynamics (MD) simulations. However, most of the theoretical studies in this area focused on imidazolium-based ILs, and the corresponding concern for other type of ILs, such as pyridinium- and aminophenol-based ILs, is relatively less. This situation is unfavorable to thoroughly knowing the microstructures of ILs, building up the perfect structure-property relationships of ILs, and developing new kind of task-specific ILs. Furthermore, theoretical studies of how ILs control desired reactions are very limited in contrast with their increasing applications as catalysts. This lack will prevent the understanding for the catalytic mechanism of ILs and the wide use of new IL catalysts with high performance. These indicate uniformly the further need for the theoretical researches on ILs.In this dissertation, a series of theoretical studies have been carried out for several kinds of ILs with excellent performance. On the one hand, by performing density functional theory (DFT) calculations and MD simulations, we have shown the microstructure details of typical pyridinium-based ILs and new dicationic ILs, and investigated the corresponding structure-property relationships. On the other hand, Our specific attention is focused on addressing the microscopic details on how ILs influence chemical reactivity and selectivity based on DFT calculations. The important and valuable results in this dissertation can be summarized as follows:1. DFT calculations have been carried out to investigate the ion pair structures of ILs [BPy]+[BF4]- and [(MIm)C3(MIm)]2+[Br]-2, the representatives of pyridinium-based ILs and geminal dicationic ILs. The stable geometries and electronic properties for the ion pairs are shown, and the intrinsic interactions between cations and anions are discussed. The present results may establish a basis for understanding the structures and properties of the two kinds of ILs.We studied the geometries of [BPy]+[BF4]- ion pair by mean of DFT method. The calculations show the relative stabilities between the different geometries of the isolated ion pair, from which the preferential localizations of [BF4]- anion around [BPy]+ cation are obtained. Moreover, the H-bond interactions between cation and anion are investigated, and the distribution and strength of H-bonds are shown. It is found that the relative stability for ion pair configurations is synergically determined by the electrostatic attractions and the H-bond interactions between the ions of opposite charge.Subsequently, DFT calculations were performed to investigate the geometrical and electronic structures of the dication and the ion pair in IL [(MIm)C3(MIm)]2+[Br]-2. The geometrical structures and relative stabilities for the dication and the ion pair are shown. It is found that there exist theπ…πstacking effect between two imidazole rings in the most stable ion pair structure, which play an important role for stabilizing the ion pair. Moreover, based on the natural bond orbital (NBO) analyses, the electronic delocalization in the dication and ion pair is discussed in detail, and the relative acidity of the H atoms on the imidazole ring is measured. The intrinsic interaction between the dication and Br- anions in the most stable conformer was studied by using frontier molecular orbital (FMO) analyses. The calculations show the interactions between the dication and Br- anions mainly occur between theσ* C-H andπ* orbitals of the dication moiety and one pAO of Br-anions, and the excessive electrons on Br- anions are transferred to the dication moiety mainly through the a-type interactions between one of the Br- pAOs and theσ* C-H orbitals. The great charge transfer and interaction energy between Br- anions and the dications offer support for the higher melting point and thermal stability of the dicationic ILs.The corresponding results have been published in J. Phys. Chem. A (2010,114, 3990-3996) and J. Mol. Struct. (THEOCHEM) (2009,900,37-43).2. MD simulations have been performed to deeply study the microstructure of IL [BPy]+[BF4]- and the influence of H2O on the microstructure and dynamic properties of IL [BPy]+[BF4]-. The calculated results bring about a better understanding of the microstructure of pyridinium-based ILs, and reveal the structure-property relationship for the binary system of pyridinium-based ILs with H2O to some extent.Based on the above DFT calculations, we choose reliable force field and computational modes to investigate the microstructure details of [BPy]+[BF4]- IL by performing MD simulation. The results show that [BPy]+[BF4]- IL represents strong long-range ordered structure with cations and anions alternately arranging. In the first coordination shell surrounding the cation, the favorable sites occupied by the anions from MD simulations are in good agreement with the findings from the DFT calculations. While the cations mainly lie in the next space that does not be occupied by anions in the first coordinate shell. Unlike the imidazolium-based ILs, T-shaped orientation plays a key role for the interaction between two pyridine rings. The H-bond details between the cations and anions is further shown by analyzing the site-site radial distribution functions (RDF) between the H atoms of [BPy]- cations and the negatively charged F atoms of [BF4]- anions. It is found that the H-bonds between the F atoms and the H atoms on the pyridine rings are stronger than those between the F atoms and the butyl chain H atoms, which is consistent to those observed in the DFT calculations. However, the strengths of the C-H…F H-bonds obtained from MD simulations are weaker than those found from the DFT calculations.MD simulation on the mixtures of [BPy]+[BF4]- IL with H2O was also performed to investigate how H2O influences the microstructure and dynamics properties of [BPy]+ [BF4]- IL. RDFs and spatial distribution functions analyses show that the presence of H2O does not change the basic structural characteristics of [BPy]+[BF4]-IL, as well as the trend of the H-bond strength between cations and anions. H2O molecules with small size are mainly located in the first coordination shell around the given cation, and their distribution areas surrounding the cation are similar to, but not as wide as, these high probability areas of anions around cations obtained above. Anions are distributed in the second coordination shell around the given cation. The interactions of H2O molecules with the anions are much stronger. With increasing the H2O content, the number of H2O molecules around the cations and anions increases, and the number for the ions of opposite charge decreases, which results in the reduction of the interaction between cations and anions. Moreover, the rotation of the cation and the diffusive motion of cations and anions accelerate with the increase of the H2O content, indicating the presence of H2O can efficiently reduce the viscosity of [BPy]+[BF4]-IL.The corresponding results have been published in J. Phys. Chem. A (2010,114, 3990-3996).3. We have launched a theoretical project of primary researches on the important organic synthesis reactions catalyzed by imidazolium-based ILs, such as Diels-Alder (D-A) reaction, Markovnikov addition and the cycloaddtion of CO2 with propylene oxide, by performing DFT calculations. These theoretical researches revealed the catalytic mechanism of imidazolium-based ILs, make clear the roles of cations and anions in imidazolium-based ILs played in the reactions, and mastered the key factor controlling the reactions.(1) We consider the D-A reaction of cyclopentadiene with methacrolein in the presence of diethylimidazolium salts as the first prototype of our systemic studies about important organic synthesis reactions catalyzed by imidazolium-based ILs. The calculations show the mechanism details of the D-A reaction with and without the dialkylimidazolium cation and the corresponding potential energy surface (PES) profiles. It was found that the diethylimidazolium cation acts as a Lewis acid centre to catalyze the D-A reaction, which decreases the barrier and increases the asynchronicity of the D-A reaction, but does not change the PES profile of the reaction compared to the non catalyzed processes. The effect of diethylimidazolium cation on the D-A reaction has been rationalized via performing the FMO analysis and NBO analysis.The corresponding results have been published in Inter. J. Quant. Chem. (2007, 107(9),1875-1885).(2) The Markovnikov addition of imidazole to vinyl acetate in the presence of the basic ionic liquid [BMIm]+[OH]-has been chosen as the second prototype of our systemic studies. Our DFT calculations have showed clearly the catalytic mechanism details of [BMIm]+[OH]-controlling the Markovnikov addition as a catalyst. It is found that the different vinyl acetate conformations result in two different reaction pathways (stepwise and concerted). The Markovnikov addition in the presence of [BMIm]+[OH]-is highly exothermic and exergonic. Both the cation and anion of [BMIm]+[OH]-play important roles in the Markovnikov addition, which decrease the barrier and increase the selectivity of Markovnikov addition. [BMIm]+stabilizes transition state via its coulombic attraction to C7 atom, while OH- deprives N1-proton of imidazole to strengthen its nucleophilic ability.The corresponding results have been published in J. Phys. Chem. A (2007,111, 4535-4541).(3) We studied the cycloaddition of CO2 with propylene oxide to synthesize five-membered cyclic carbonates in the absence and presence of [R1MIm]+[Cl]-(Ri=Ethyl, Butyl, and Hexyl) by performing DFT calculations. In the absence of [RiMIm]+[Cl]- the reaction proceeds via two possible channels (each of them involves one elementary step) and the corresponding barriers are found to be as high as 59.71 and 55.10 kcal mol-1. In the presence of [R1MIm]+[Cl]-there exist five possible reaction channels (each of them involves two or three elementary steps) and the barriers of the rate-determining steps are reduced to 27.93-38.05 kcal mol-1, clearly indicating that [R1MIm]+[Cl]- promotes the reaction via modifying the reaction mechanism and thereby remarkably decreases the barrier. The notable catalytic activity of [RiMIm]+[Cl]- may originate from the cooperative actions of the cation and anion, which stabilize the intermediates and transition states through the H-bond interaction and make the ring opening easier via the nucleophilic attack to propylene oxide, respectively.The corresponding results have been published in J. Phys. Chem. A (2007,111, 8036-8043).4. The Michael addition of cyclohexanone with trans-β-nitrostyrene catalyzed by pyrrolidine-imidazolium bromide, which represents a prototype of Chiral IL-promoted asymmetric syntheses, has been investigated by performing DFT calculations. We show the details of the mechanism and energetics, the influence of the acid additive on the reactivity, the functional role of the Chiral IL in the asymmetric addition, and the origin of good diastereoselectivity and high enantioselectivity of the Michael adduct. From the theoretical results, we provide a reasonable explanation for the experimental observations and reveal a valuable clue for the further Chiral IL design with high catalytic efficiency.It is found that the reaction proceeds via two stages, i.e. the initial enamine formation and the subsequent Michael addition. The calculations show that the presence of the acid additive changes the imine formation mechanism and lowers the reaction barrier, as well as, more importantly, makes the reaction become highly thermodynamically favored. It is also suggested that both the anion and cation of the Chiral IL synergically facilitate the reaction, which act as the proton acceptor in the imine-enamine tautomerism and the stabilizer of the negative charge in the C-C bond formation process, respectively. By comparison of the C-C bond forming processes in the absence and presence of Br- anion, we found that the intermolecular H-bonds between the imidazolium cation and the nitro group of trans-β-nitrostyrene and the steric hindrance of the imidazolium cation moiety on the Si-face of enamine dominate the stereoselectivity of the Michael addition. The corresponding results have been published in Chirality (Early View).更多还原