【作者】 唐思扬；

【导师】 刘柏平；

【作者基本信息】 华东理工大学 ， 化学工艺， 2014， 博士

【摘要】 1-已烯和1-辛烯是重要的化工中间体,主要用作共聚单体制备高性能聚烯烃产品。自上个世纪七十年代,乙烯三聚/四聚生产1-已烯/1-辛烯逐渐成为学术界和工业界的研究热点,多种乙烯选择性三聚催化体系被成功开发,其中Chevron-Phillips乙烯三聚催化体系已成功工业化。自2004年以来,几种基于含氮或磷类配体铬系催化体系成功用于乙烯选择性四聚,但目前尚没有乙烯选择性四聚生产1-辛烯的工业化报道。乙烯选择性三聚和四聚反应机理尚存在争议,虽然普遍认为乙烯选择性齐聚遵循金属环状机理,但活性中心结构和价态上存在争议,制约了催化体系的开发。本文选取了两个典型的乙烯选择性四聚体系,分别通过二维定量构效关系方法和密度泛函理论进行了系统研究。通过不同氮上取代的PNP型铬系催化体系的二维定量构效关系研究,考察了催化体系对1-已烯和1-辛烯选择性的影响,建立了相关的线性模型并设计和预测了新型PNP型铬系催化体系。采用密度泛函理论方法研究双吡啶铬系催化体系中乙烯选择性三聚/四聚的转化现象,证明乙烯选择性四聚的反应主要发生在二价铬单核金属活性中心模型上,并遵循金属环状机理。主要研究内容如下：首先,采用二维定量构效关系方法结合密度泛函理论考察了氮上烷基取代PNP型铬系催化体系,建立了该催化体系1-已烯、1-辛烯选择性的线性回归模型。同时采用了启发式方法和最佳多元线性回归方法,考察了自定义描述符和铬金属活性中心价态(包括Cr(Ⅰ)和Cr(Ⅱ))对线性回归模型的影响。研究发现：(1)基于密度泛函理论计算结果的自定义描述符的引入能够明显提高模型的相关性和稳定性；(2)基于一价Cr的活性中心模型更适合关联乙烯三聚选择性,二价Cr的活性中心模型更适合关联乙烯四聚选择性；(3)PNP-Cr骨架几何结构尤其是较小的PNP角度是获得较高1-已烯和1-辛烯选择性的关键。最后,根据最佳线性回归模型对新型PNP配体进行了预测,发现了9种新的PNP配体结构可能具有更高的1-辛烯或1-已烯／1-辛烯共选择性。其次,同样采用二维定量构效关系方法结合密度泛函理论对芳基取代的PNP型铬系催化体系进行了研究,考察了样本集、描述符集、回归方法和活性中心氧化态对线性回归的影响,基于一价Cr的活性中心模型建立了1-已烯选择性模型,基于二价Cr的活性中心模型建立了1-辛烯选择性的模型。研究发现PNP-Cr骨架结构具有好的对称性和平面性可以增加反应中1-辛烯的选择性,而增大氮上和磷上的取代基可以增加1-已烯的选择性。本文同样设计了6种PNP型配体,并根据最佳的线性回归模型对其铬系催化体系乙烯三聚／四聚性能进行了预测。对比两个不同取代的PNP型铬系催化体系研究结果,确认了基于密度泛函理论的二维定量构效关系方法可以有效的应用于铬系乙烯选择性齐聚催化体系,并进行新型配体分子设计研究。最后,采用密度泛函理论结合能量延展模型研究(2-C5H4N)2NR铬系催化体系的乙烯选择性四聚反应机理,该催化体系是目前报道的唯一的液态产物中1-辛烯选择性大于99%的催化体系,本文设计了单核和双核活性中心模型,考察了一价铬和二价铬两种活性中心价态,并对实验报道中的配体上取代基位置转换引起的乙烯选择性三聚／四聚转化现象进行了研究。结果表明,双核金属活性中心在反应条件下并不能够稳定存在,同时发现,乙烯选择性四聚可能发生在二价铬单核活性中心上,并遵循金属环状反应机理,同时,反应中发生了一次电子自旋跃迁现象。更多还原

【Abstract】 1-Hexene and1-octene are important comonomers for the synthesis of high performance polyolefins. Ethylene selective oligomerization with advantages of high atomic efficiency and a simple reaction procedure has attracted comprehensive interests to match the increasing demand of highly valuable linear a-olefins (LAOs) including1-hexene and1-octene in the last decades. Many catalytic systems were carried out for ethylene selective trimerization, and ethylene trimerization was first commercialized over Cr-pyrrole catalyst system by Chevron-Phillips Company in2003at Qatar. Since the first ethylene tetramerization report in2004, several chromium based catalytic system were reported to be effective to catalyze ethylene tetramerizaiton. However, no commercialization of ethylene tetramerization is reported yet. Although the metallacyclic mechanism is well accepted for ethylene selective oligomerization, the active site structures and the redox valence are still controversial. In this work, two ethylene selective tetramerization systems were studied using the quantitative structure activity/property relationship (QSAR/QSPR) and the density functional theory (DFT) methods, respectively. The alkyl and aryl substituted Cr-bis(diphenylphosphino)amine (PNP-Cr) catalysts which show the potential as excellent candidates for highly selective ethylene trimerization/tetramerization were studied with QSPR method based on DFT calculations. The linear regression models of1-hexene selectivity and1-octene selectivity were established over the alkyl and aryl substituted PNP-Cr systems, respectively. Several new kinds PNP ligand proposed by molecular design were predicted to be with a better ethylene trimerization/tetramerization performance. A switching mechanism between ethylene tetramerization and trimerization on the Cr-2,2-dipyridylamine catalyst was studied using DFT calculation. And a Cr(II)/Cr(IV) metallacycle reaction pathway on the mononuclear active site was found to be most plausibly responsible for ethylene tetramerization.A series of alkyl-substituting PNP-Cr catalysts were studied by QSPR method based on DFT calculations in Chapter2. The heuristic method (HM) and best multi-linear regression (BMLR) were used for establishing the best linear regression models to describe the relationship between catalyst selectivity and its structure. Both Cr(I) and Cr(II) active site models for ethylene trimerization/tetramerization were considered. It was found that:(1) Using self-defined descriptors from DFT calculations could increase the relativity and stability of the models.(2) Monovalent Cr(I) center was the most plausible active site for ethylene trimerization, while ethylene tetramerization was most possibly proceeded over divalent Cr(II) active site.(3) The skeleton structures of the PNP-Cr system especially a small PNP angle were crucial for achieving excellent catalytic selectivity. Nine new PNP ligands with high selectivity towards ethylene trimerization/tetramerization were predicted based on the best linear regression models providing a good basis for further development of novel catalyst systems with better performance. A series of aryl-substituted PNP-Cr catalysts were studied by QSPR method based on DFT calculations in Chapter3. The effects of the sample set, data set, linear regression method and the active site oxidation state on the linear regression models were investigated separately. The best1-hexene selectivity linear model was built with the Cr(Ⅰ) active site, while the best1-octene selectivity linear model was built with the Cr(Ⅱ) sites. It was also found that the skeleton structures of the PNP-Cr system with good complanation and symmetry were crucial for achieving excellent catalytic selectivity of1-octene, while the PNP-Cr backbone with a large steric effect on N atom would benefit ethylene trimerization. Six new PNP ligands with high selectivity towards ethylene trimerization/tetramerization were predicted based on descriptor analysis and the best linear regression models. By comparing the QSPR results of Chapter2and Chapter3, it is found that QSPR method is effective to study the relationship between the chromium based catalyst systems and its ethylene selective oligomerizaion properties. The QSPR study can also provide a good basis for further development of novel catalyst systems with better performance.The switching mechanism between ethylene tetramerization and trimerization using a different substituting Cr-2,2-dipyridylamine catalysts were disclosed with DFT calculation and turnover of frequency (TOF) calculation in Chapter4. This catalyst system was reported to be able to catalyze ethylene tetramerization with a very high1-octene selectivity (>99%). Both the binuclear site and the mononuclear site were proposed to be possible active site model for the ethylene tetramerization. And different oxidation states were considered for the calculations. The binuclear models were predicted to be unstable in the experimental conditions. The metalacyclic mechanism over Cr(Ⅱ) mononuclear active site was confirmed to be responsible for ethylene tetramerization, while one spin flipping from the quintet potential energy surfaces to triplet potential energy surfaces was found in the calculations. Consequently, the divalent mononuclear active site which involves a mixing of quintet and triplet potential energy surfaces was found to be responsible for the switching between ethylene tetramerization and trimerization.更多还原