茂金属催化剂的负载化

负载化是茂金属催化剂发展的一个新方向。本文系统地描述了茂金属负载化催化剂的主要制备方法;分析了活性中心的本质、结构以及生成机理;并且讨论了负载化对茂金属催化剂烯烃聚合性能的影响。     

负载型茂金属烯烃聚合催化剂有机载体研究进展

综述了近年来各种有机载体负载茂金属催化剂的负载方法,介绍了有机载体型茂金属催化剂的特点、负载方式、负载化对催化烯烃聚合性能和聚合物性能的影响。目前还不能完全解释清楚有机载体对聚烯烃形态以及聚合活性的影响效果。在有机载体合成方面,可以通过高分子工程,进行有机载体的设计,将茂金属催化剂负载到有机载体上,进一步提高有机载体型茂金属催化剂的活性、改善有机载体的形态和结构,将会推进有机载体负载型茂金属催化剂的工业化开发。     

新型聚合物载体茂金属催化剂

均相茂金属催化剂虽然有许多优点和特点,但也存在着某些不足之处,例如,不适于现在通用的气相和淤浆聚合工艺;要想达到足够的聚合活性需大量价格昂贵的MAO;相当多的均相茂金属催化剂不适于高温聚合（活性降低,分子极低）,不能很好地控制聚合物的形态,为了在工业上得到实际应用,必须将它们载体（非均相）化。通常采用的载体都是无机物,如SiO2、MgCl2、Al2O3等。由于无机载体表面具有酸性,负载茂金属催化剂活性有所降低,用聚合和作茂金属催化剂的载体很少有报道,我们研制了一种新型的聚合物载体茂金属催化剂,即可保持均相茂金属催化特点和优点,又能克服其缺点。其合成路线如下。     

负载型烯烃聚合催化剂合成的新方法

介绍了负载型烯烃聚合催化剂合成的新方法,探讨了不同载体负载的Ziegler- Natta催化剂各组分之间的相互作用机理及活性中心的形成途径。对负载茂金属催 化剂的新型载体及新的负载方法进行了评述。     

烷基铝对球形MgCl_2负载的茂金属催化剂催化乙烯聚合的影响

以甲基铝氧烷(MAO)为助催化剂的茂金属催化剂虽然具有催化活性高、分子量分布窄、聚合物化学组成均匀等优点,但其极高的Al/Zr比和聚合物颗粒形态差等缺点限制了其工业化应用,因此对茂金属催化剂的负载化成为近年来的研究热点.在众多的载体中,球形MgCl2是研究得很少的一类载体,文献中曾采用先负载主催化剂茂金属配合物,聚合时再加入助催化剂MAO的方法[1],由于加入的MAO与主催化剂的络合能力很强,会使部分载上的主催化剂溶解下来,成为均相聚合[2,3],导致聚合物颗粒形态差,且粘釜现象严重.我们则采用相反的思路,即先将助催化剂MAO负载在球形MgCl2上,制得MgCl2/MAO,在聚合前再将MgCl2/MAO与Et[Ind]2ZrCl2混合陈化,并立即在少量烷基铝活化下引发乙烯聚合[4],实验结果表明,该催化剂聚合活性高、聚合物的颗粒形态好、且不粘釜,是一种新型的载体催化剂.由于烷基铝的加入可使催化剂的活性大幅度提高,所以本文将烷基铝也称作助催化剂,来研究其对该载体催化剂催化乙烯聚合的影响.     

苯乙烯-4-乙烯基吡啶无规共聚物/SiO2纳米杂化材料负载茂钛催化剂的制备及苯乙烯聚合

均相茂金属催化剂的非均相化已成为高分子化学领域一个新的研究热点. 该催化剂负载于不溶性的载体上, 形成的负载型催化剂既有均相催化剂单一活性特点（如金属原子利用率及催化活性高、反应快、条件温和及分子量分布窄）, 又兼有非均相催化剂的优点（产物易于分离, 可用于淤浆聚合、气相聚合或本体聚合来制备几何形状均一的聚合物）[1]. 由于无机和有机载体都有某些特殊优点和一些弊端, 故将无机和有机载体复配, 以得到性能优越的复合载体已成为催化剂载体研究的一个重要方向.     

修饰Al2O3负载的烯基取代茂金属催化体系催化乙烯聚合的研究

经过十几年的研究和开发,茂金属催化剂已经有了很大的发展,部分已经工业化,同时新的茂金催化体系仍然在不断地开发出来［１～４］．均相烯烃聚合催化剂经负载后能有效地改善所得聚合物的颗粒形态,并可用于气相聚合,同时也出现了许多新的聚合特征,这方面的研究一直是烯烃聚合催化剂研究领域的一个热点［５～８］．在负载型催化剂的制备时,通常用ＭＡＯ先对载体进行处理,然后再负载茂金属,这样ＭＡＯ的用量就很大．茂环上的取代基对聚合有较大的影响,许多聚合规律仍在探索之中．尽管硼化合物作为助催化剂的茂金属催化体系已经被应用…     

负载双核茂金属催化剂催化乙烯聚合反应动力学研究

以SiO2为载体,制备了负载的双核茂金属[（η5-C5H5）Zr Cl2]2[μ,μ-（SiMe2）2（η5-allyl C5H2）2]/MAO/SiO2催化剂,以己烷为溶剂进行了淤浆条件下乙烯聚合反应,研究了扩散因素、乙烯聚合压力和聚合温度对乙烯淤浆聚合动力学参数的影响,测定了聚合反应级数和表观活化能,采用动力学和相对分子质量法计算了负载催化剂的活性中心浓度,并对链增长速率常数等动力学参数进行了计算.结果表明,以负载双核茂金属催化剂催化乙烯淤浆聚合反应速率对单体浓度呈1.11级依赖,反应活化能Ea为72.47 kJ/mol,活性中心浓度C＊为0.33 mol/mol,链增长速率常数Kp为1.06×106L.（mol.h）-1.     

一段反应法制备宽/双峰聚乙烯催化剂的研究进展

阐述了采用一段反应法制备宽/双峰聚乙烯催化剂的研究开发进展,并根据催化剂的组成和结构,将催化体系归纳为复合催化剂和单组分催化剂.复合催化剂包括茂金属/Ziegler-Natta复合催化剂、不同茂金属复合催化剂、铬系/Ziegler-Natta复合催化剂、茂金属/后过渡金属复合催化剂、非茂单活性中心/茂金属复合催化剂、非茂单活性中心/Ziegler-Natta复合催化剂和不同后过渡金属复合催化剂.复合催化剂中多活性组分具有不同的链增长、链转移、链终止速率常数,从而在聚合反应中得到不同相对分子质量的聚合物,导致其相对分子质量分布加宽,因而复合催化剂可用于一段反应法制备宽/双峰聚乙烯.单组分催化剂包括单核茂金属催化剂、多核茂金属催化剂、后过渡金属催化剂及其它单组分催化剂.单组分催化剂可用于一段反应法制备宽/双峰聚乙烯,其催化机理是中心金属原子与主配体、辅配体、助催化剂、其它添加剂及载体形成了多种活性中心.     

MgCl_2/AlEt_n(OEt)_(3-n)负载单茂钛催化剂催化乙烯聚合研究

以MgCl2/AlEtn(OEt)3-n为载体,分别负载五甲基茂基三氯化钛(Cp*TiCl3)和五甲基茂基三苄氧基钛(Cp*Ti(OBz)3),得到两种负载催化剂,在较廉价的AlEt2Cl为助催化剂常压下可以高效地催化乙烯聚合.报道了载体的制备、聚合条件(不同的烷基铝助催化剂、聚合温度、铝钛摩尔比)对催化剂的聚合行为以及聚合物结构的影响.研究结果表明,两种负载催化体系对乙烯聚合具有较高的催化活性,可达105g PE/(molTi·h)数量级,所得聚乙烯的黏均分子量在105以上.经过13C-NMR和DSC分析,两种负载催化剂得到的均为线型聚乙烯.与均相催化剂相比,负载后的单茂钛催化体系的聚合反应动力学表现高效而平稳.这表明载体的微孔结构使活性中心得到了有效的分散,有效地提高了催化剂的活性,同时载体的受限空间有效抑制了聚乙烯增长链的β-H消除反应.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.