【作者】 杜娟；

【导师】 贾明君；

【作者基本信息】 吉林大学 ， 物理化学， 2012， 博士

【摘要】 多金属氧酸盐（POMs）由于其确定的结构、可控的尺寸以及独特的电荷传递等性能一直倍受关注，在许多领域中都具有重要的理论研究和实际应用价值。作为一类重要的烯烃环氧化催化剂体系，多金属氧酸盐对多种类型烯烃环氧化表现出了非常优异的催化性能。然而，这类催化剂在反应过程中往往会溶解在反应体系中，从而以均相催化剂的形式参与反应，因此人们一直期待能够制备出性能优异且易于分离和循环使用的多相多金属氧酸盐基催化剂体系。近期，伴随着配位化学及结构化学等学科的快速发展，一类以多金属氧酸盐和有机组分（配体）为分子建筑块构筑的无机-有机杂化材料得到了迅速发展。研究发现，通过利用有机分子优良的可裁剪性和修饰性，可以实现对多金属氧酸盐的结构和性质进行有效调控，进而构造出具有独特空间结构和性质的多金属氧酸盐基功能材料。这类材料往往能够显示出无机金属氧酸盐与有机组分两者结合的优点，在分子识别、生物传导材料、磁性材料、气体吸附材料及催化等领域中具有广泛的研究和发展空间。近期，文献中已有一些关于多金属氧酸盐基无机-有机杂化材料作为多相烯烃环氧化反应催化剂的研究报道，但从整体上来看，这类催化剂的性能（包括活性、选择性及结构稳定性）仍有待于进一步提高，并且一些相关基础问题也需深入研究和探讨，例如有机配体的种类以及与多金属氧酸盐的键合方式是如何影响催化剂的活性中心性质的，材料的空间结构特征与催化性能（活性和稳定性）之间的关系等。基于上述情况，本论文主要以氮杂环配体与多金属氧酸盐为结构基元，在水热条件下合成了一系列有机-无机杂化多金属氧酸盐催化材料，系统的研究了这类材料对不同类型烯烃（特别是难氧化的缺电子端基烯烃）环氧化反应的催化性能。另外，采用各种表征手段对材料的组成、结构、键合（配位）方式进行了表征，并结合理论化学计算等方法对材料的结构与催化性能之间关系进行了研究，探讨了催化剂活性中心性质和催化作用机制等问题。论文的主要研究内容和结果概述如下：1、由咪唑和β-构型八钼酸铵构筑的杂化超分子自组装体的结构和催化环氧化性能采用水热合成法将咪唑配体与β-构型八钼酸铵通过共价键、氢键和π-π堆积等相互作用构筑成两种具有多维空间构型的杂化超分子自组装体：（Himi）4[(Mo₈O₂₆)（imi）2]·H₂O （催化剂1）和[imi=咪唑]和（Himi）4[(Mo₈O₂₆)]（催化剂2）；另外，还将催化剂2通过340℃焙烧处理去除其中的咪唑配体而制得催化剂3。通过以叔丁基过氧化氢为氧化剂的环辛烯和1-辛烯的环氧化反应对这几种催化剂进行了反应性能评价。结果表明：催化剂1和2均对环辛烯环氧化反应表现出良好的催化活性和稳定性，性能明显优于催化剂3。进一步的实验结果表明催化剂1对较难氧化的端基烯烃（如1-辛烯）也表现出了很高的反应活性和稳定性，且催化剂可多次循环使用。通过对比三种催化剂在结构上和催化性能上存在的差异，我们推测催化剂1和2本身所具有的多维超分子结构特征，即由多种弱相互作用（如氢键和π-π堆积等）形成的超分子链接，是其表现出高活性和高稳定性的关键因素之一。此外，还根据文献报道的方法合成了（Himi）4[（nic-O）2(Mo₈O₂₆)]（nic=烟酸）（催化剂4），在结构和催化性能上与催化剂1进行了对比研究。结果表明：两种材料在配体与多金属氧酸盐的连接位置和键合方式，以及形成的超分子空间结构都非常相似，主要区别就在于与多金属氧酸盐共价连接的配体种类不同。催化反应结果表明催化剂1的反应活性明显高于催化剂4，这说明在催化剂所具有的空间结构（超分子结构）相似的情况下，与多金属氧酸盐以共价键方式结合的有机配体的种类的不同会显著影响催化剂的性能。结合理论化学计算结果，可以认为不同种类的配体会对与其配位的多金属氧酸盐产生不同的电子效应，继而对催化剂的性能产生影响。在催化剂1和4中的具体情况是：催化剂1中的咪唑配体分子形成的5中心6电子的π键所产生的共轭吸电子效应要强于催化剂4中羧基的吸电子效应，从而使催化剂1表现出更高的反应活性。2、由1，4-双（咪唑-1-基）丁烷和β-构型八钼酸铵构筑的杂化超分子自组装体的结构和催化环氧化性能采用水热法将1，4-双（咪唑-1-基）丁烷配体与β-构型八钼酸铵通过共价键和氢键等相互作用构筑成两种具有多维空间构型的杂化超分子自组装体：（H₂bbi）2[Mo₈O₂₆]（催化剂5）[bbi=1，4-双（咪唑-1-基）丁烷]和（H₂bbi）[（Hbbi）2(Mo₈O₂₆)] H₂O（催化剂6）。在催化剂6的结构中，1，4-双（咪唑-1-基）丁烷配体直接通过咪唑环上的一个氮原子与β-构型八钼酸铵中的一个钼原子通过共价键连接在一起，这是1，4-双（咪唑-1-基）丁烷与多酸的连接模式中较为新颖的。在一个完整的对称结构单元中，两个1，4-双（咪唑-1-基）丁烷配体分子分别共价连接在八钼酸铵两端的中心对称的位置上，并且多个单元之间通过配体上N-H键上的H原子与多金属氧酸盐上的二桥O原子间形成的氢键连接成超分子结构。通过以叔丁基过氧化氢为氧化剂的环辛烯环氧化催化反应对这两种催化剂进行了反应性能评价，结果表明：催化剂5和6具有较好的活性和选择性，但是在反应中均有活性物种流失的现象。相比较来说，催化剂5在反应中的稳定性略好于催化剂6，但是活性却略低。这可能是由于催化剂6在反应过程中活性物种的流失相对较多，所产生的均相催化作用使得其表现出较高的催化活性。结合XPS等表征结果以及与催化剂1的结构特点相比较，可以认为：催化剂5和6的结构中，与β-构型八钼酸铵共价结合的有机配体基团所产生的推电子效应会导致与配体共价连接的钼原子上的正电性降低，从而不利于与亲核基团的结合，这可能是影响催化剂5和6的催化性能的主要原因。3、以有机银与饱和十二磷钼酸构筑的杂化超分子自组装体的结构和催化环氧化性能采用水热法将银的1，2，4-三唑有机衍生物与饱和十二磷钼酸通过静电相互作用构筑成具有多维空间构型的超分子自组装体：[Ag₁₂（C₂N₃）₉](PMo₁₂O₄₀)·4H₂O（催化剂7）。催化剂7具有新颖的拓扑空间构型：金属银离子与小分子氮杂环配体1，2，4-三唑以共价键结合成具有互锁型多维空间结构的大分子伪轮烷构型，这个多维有机银骨架实际上是由多个由银离子与1，2，4-三唑配体构成的八面体笼状单元通过角与角的互锁连接而成的，其中银离子均处于配位不饱和的状态（配位数为2）。而多金属氧酸盐阴离子单元通过静电力的作用存在于这些八面体笼状结构的空隙中，并在一定程度上起到了稳定结构的作用。这种结构在此类型的材料中是十分新颖和罕见的。分别以叔丁基过氧化氢和分子氧作为氧化剂，考察了催化剂7对环辛烯环氧化反应的性能。结果表明：催化剂7在两种反应体系中均表现出较高的催化活性和稳定性。催化剂7所具有的直接活化氧气分子的能力非常有意义，值得深入研究和探讨。结合催化剂7结构上的特点可以认为饱和十二磷钼酸阴离子应该是反应的主要活性中心。而对于银离子来说，由于处于配位不饱和状态，导致其显示出一定的正电性，从而使其能够与饱和十二磷钼酸的端氧原子（带有孤对电子）间产生静电力，起到了稳定活性中心的作用。此外，在反应过程中，有机银骨架单元很可能与无机多金属氧酸盐之间产生协同效应，从而使催化剂表现出较高的烯烃环氧化性能。更多还原

【Abstract】 Polyoxometalates （POMs） have always attracted many attentions due to theirdefinite structures, controllable sizes and unique charge transfer properties, and haveimportant theoretical research and practical application values in many fields. As animportant epoxidation catalyst system of olefin, polyoxometalates showed excellentcatalytic performance for many types of olefin epoxidation. However, these catalystsoften dissolved during the process of reactions, and then were involved in reaction ashomogeneous catalysts. So people always are looking forward to prepare apolyoxometalate-based heterogeneous catalyst system which has the advantages ofexcellent performance, easy separation and recycling.Recently, with the rapid developments of the coordination chemistry and structuralchemistry and other related disciplines, a class of inorganic-organic hybrid materialswhich were builded by polyoxometalates and organic components （ligands） has beendeveloping rapidly. It was found that the structures and properties ofpolyoxometalates could be of effective regulation and control by using the advantagesof organic molecules. Thus these polyoxometalate-based functional materials wereoften showed the advantages both of inorganic POMs and organic components, andhave extensive research and development space in the fields of molecular recognition,bio-conductive materials, magnetic materials, materials of gas adsorption andcatalysis. Recently, there have been some reports about polyoxometalate-basedinorganic-organic hybrid materials as heterogeneous olefin epoxidation catalyst.Based on the above, in this paper the polyoxometalates and N-heterocyclic ligandswere used to be as the main structural units to synthesize a series of organic-inorganichybrid-polyoxometalate catalytic materials under hydrothermal conditions, and thento study the catalytic properties of such materials on the different types of olefinepoxidation reaction, especially the dysoxidizable election-deficient terminal olefin. Inaddition, the compositions, structures and bonding （coordination） modes of these materials were characterized through related characterization techniques, and combined thestudy of theoretical calculation of chemiatry on the relationship between structure andcatalytic properties of these materials to explore the catalytic properties of active sitesand catalytic mechanism. The main research contents and results were summarized asfollows:1. Structures and catalytic epoxidation properties of hybrid supramolecularself-assemblies based on imidazole and β-octamolybdate.Two hybrid supramolecular self-assemblies with muti-dimensional spatialconformations were synthesized under the hydrothermal conditions, which include（Himi）₄[(Mo₈O₂₆)（imi）2]·H₂O （catalyst1）[imi=imidazole] and （Himi）4[(Mo₈O₂₆)]（catalyst2）. Their structures were directed by the interactions, such as covalent bondsand hydrogen bonds and π-π stacking, between imidazole and β-octamolybdate. Inaddition, the catalyst3was prepared through calcining catalyst2at340°C to removethe imidazole ligands. The catalytic performance evaluations were given to thesecatalysts by the epoxidation reactions of cyclooctene and1-octene with tert-butylhydrogen peroxide as oxidant. The results indicated that the catalytic activities andstabilities of catalyst1and2were much better than catalyst3. Further results ofexperiments showed that to the dysoxidizable terminal olefin, such as1-octene, catalyst1alsoshowed high reactivity and stability, and can be recycled many times. Compared thedifferences of three catalysts’ structures and catalytic performances, it can bespeculated that the key factor for the high activities and stabilities of catalyst1and2was the multi-dimensional supramolecular structure they owned, which were formedby a variety of weak interactions, including hydrogen bonding and π-π stacking, etc.Moreover, synthesized catalyst4,（Himi）4[（nic-O）2(Mo₈O₂₆)]（nic=nicotinic acid）,according to the literature, and compared the structures and catalytic performanceswith catalyst1. The results showed that these two materials were very similar eitheron the connection positions of the ligands and polyoxometalates or on the bondingmodes, as well as supramolecular spatial structure. The main difference between thesetwo catalysts was the types of ligands which linked with polyoxometalates covalently.Catalytic reaction results show that the reactivity of the catalyst1was evidentlyhigher than catalyst4. It indicated that when the spatial structures （supramolecularstructures） of catalysts were similar, the different types of organic ligands coordinatedwith polyoxometalates may noticeably influence the catalytic properties of catalysts. the results of theoretical chemistry calculation it can be thought that different kinds ofligands may take different electronic effects on the polyoxometalates, and then affectthe the performance of the catalysts. The specific situation to catalysts1and4is: theimidazole ring connected to a Mo atom of [Mo₈O₂₆]4-to form a conjugative π bondwith5centers of6electrons, and this electronic withdrawing effect of conjugationwas stronger than that of carboxyl group.Therefore, catalyst1exhibited higher activities.2. Structures and catalytic epoxidation properties of hybrid supramolecularself-assemblies based on1,1’-（1,4-butanediyl）bis（imidazolium） andβ-octamolybdate.Two hybrid supramolecular self-assemblies with muti-dimensional spatialconformations were synthesized under the hydrothermal conditions, which include（H₂bbi）₂[Mo₈O₂₆]（catalyst5）（H₂bbi=1,1’-（1,4-butanediyl）bis（imidazolium）） and（H₂bbi）[（Hbbi）2(Mo₈O₂₆)]· H₂O （catalyst6）. In the structure of catalyst6,1,1’-（1,4-butanediyl） bis（imidazolium） ligands through one nitrogen atom of aimidazole ring covalently connected with one molybdenum atom of β-octamolybdate. This is a novel connection mode between1,1’-（1,4-butanediyl）bis（imidazolium） ligands and polyoxometalates. In a symmetric structural unit, twoligand molecules covalently attached to octamolybdate at two positions of centersymmetry, and then many this kind of units connected into supramolecular structuresthrough hydrogen bonds between the bridge O atoms of polyoxometalates and N-Hbond of imidazole ring in the ligand.The catalytic performance evaluations were given to these catalysts by theepoxidation reactions of cyclooctene with tert-butyl hydrogen peroxide as oxidant.The results indicated that both catalyst5and6have good activity and selectivity, buthave the phenomenons of active specie loss. In comparison the stability of catalyst5was a little better than catalyst6, but the activity was a little lower. This could be dueto the active species loss of catalyst6is relatively more, and the homogeneouscatalysis made the activity of catalyst6higher. Combined with the results of XPS andother characterization, as well as the structural characteristics of catalyst1, it can beconsidered that in the structures of catalysts5and6, the electron donating effect oforganic ligands covalently bonding with octamolybdates would reduced theelectropositivity of molybdenum atoms of octamolybdates, which can lead to make against the molybdenum atoms combined with nucleophilic group. It is may be themain reasons which affected the catalytic properties of catalysts5and6.3. Structures and catalytic epoxidation properties of hybrid supramolecularself-assemblies based on organosilver and phosphomolybdateA hybrid supramolecular self-assembly with muti-dimensional spatialconformations were synthesized under the hydrothermal conditions using1,2,4-triazole organic derivative of silver and phosphomolybdate as the building blocks,which is [Ag12（C2N3）9]（PMo12O40）·4H₂O （catalyst7）. Catalyst7has a verynovel topological space configuration: metal silver ions and small-moleculeN-heterocyclic-ligand1,2,4-triazole use covalent bond together to form themacromolecules pseudorotaxane configuration, which have interlockmulti-dimensional supramolecular structure. The structural units of thismulti-dimensional organicsilver framework is octahedral cages consisted of silverions and1,2,4-triazole ligands, and these units connected together trough angle andangle interlock. In these octahedral cages, silver ions are unsaturated coordinations（the coordination number is2）. Polyoxometalate anions present in the gap of thesecages by electrostatic force, and a certain extent play a role to stabilize structure. Thisstructure in this type of material is very new and rare.The catalytic performance evaluations were given to catalyst7by the epoxidationreactions of cyclooctene with tert-butyl hydrogen peroxide and molecular oxygen asoxidant. The results indicated that catalyst7have high activity and stability. Theability of catalyst7to direct activation of oxygen molecules is very meaningful, andworthy to further study and discussion. Combined with the structural characteristics ofcatalyst7, it can be considered the phosphomolybdate anion should be the main activecenter. The silver ions showed electropositivity because of their unsaturatedcoordinations, so there are electrostatic force between silver ions andphosphomolybdate anion, and then this interaction acted stabilization on activecenters of catalyst. In addition, during the reaction, there maybe exist synergisticeffect between inorganic polyoxometalates and organic organic metal framework, sothat the catalyst showed high catalytic performance.更多还原