论文部分内容阅读
不对称氢甲酰化是合成具有单一光学活性物质(如光学活性的醛、α-氨基酸和醇等)最为重要的反应之一.尽管不对称氢甲酰化反应的研究超过40年,但仍然是催化体系中具有挑战性的课题.该反应涉及到产物的化学选择性、立体选择性和对映体选择性的优化.目前,在Rh催化体系中,使用磷-亚磷酸酯手性配体或双亚磷酸酯配体可以在不对称氢甲酰化反应中取得优异的催化性能.然而在Rh/手性双膦配体催化体系中,不对称氢甲酰化反应性能通常很低.以BINAP配体为例,负载Rh金属后,在催化苯乙烯不对称氢甲酰化反应中,产物的ee值只有25%.同时,由于均相催化体系存在催化剂回收和产物提纯等问题,因此有必要研究多相不对称氢甲酰化反应催化剂.本文使用乙烯基修饰的BINAP配体5,5’-divinyl-BINAP与具有不同结构的共聚单体二乙烯基苯或1,3,5-三乙烯基苯基苯共聚,得到具有不同孔结构的聚合物Poly-1和Poly-2.为了比较,利用线性共聚单体乙二醇二甲基丙烯酸甲酯与乙烯基BINAP共聚得到聚合物Poly-3.上述三种聚合物材料负载金属Rh后,用作苯乙烯不对称氢甲酰化反应的催化剂.固体~(13)C核磁分析表明,三种聚合物材料负载金属后仍然保持较为稳定的C骨架结构.通过~(31)P核磁可以看到,嵌入在材料骨架中的BIANP仍然保持未被氧化的状态.N_2物理吸附结果发现Poly-1和Poly-2具有较大的比表面积和孔体积,而Poly-3的比表面积最小.热重分析显示,这些材料具有较高的热稳定性.在不同反应溶剂中催化剂活性差异较大.通过优化反应温度和合成气压力后,催化剂Rh/Poly-1在80℃和0.2MPa下产物的对映体选择性可高达58.9%,支链醛与直链醛的比值为8.5;而在相同反应条件下,均相催化剂Rh-BINAP的ee值仅为35.3%,但高于Rh/Poly-3.这是由于三个多相催化剂骨架中BINAP周围环境不同所致.前两个催化剂中,BINAP与空间位阻较大的单体相连接,使得反应底物按照特定方向与催化活性位点接触,形成了类似于手性口袋的结构.而Rh/Poly-3中,BIANP周围是线性的共聚单体,不能形成有效的手性口袋结构.Rh/Poly-1重复使用7次后,催化活性没有显著下降.拓展X射线吸收精细结构表征结果表明,Rh/Poly-1催化剂使用前没有Rh-Rh键存在,但经重复使用后,Rh金属部分聚集,生成了Rh-Rh键.球差电镜照片也证实了这一点.
Asymmetric hydroformylation is one of the most important reactions in the synthesis of a single optically active substance such as optically active aldehydes, a-amino acids and alcohols, etc. Although asymmetric hydroformylation has been studied for more than 40 years, Is a challenging topic in the catalysis system, which involves the chemical selectivity, stereoselectivity and enantioselectivity optimization of the products.At present, in the Rh catalyst system, phospho-phosphite chiral ligands Or bisphosphite ligands can obtain excellent catalytic performance in the asymmetric hydroformylation.However, asymmetric hydroformylation reaction performance is usually low in the Rh / chiral bisphosphine ligand catalytic system BINAP ligand as an example, after loading Rh metal, the ee value of the product is only 25% in the asymmetric hydroformylation of styrene, meanwhile, because of the problems of catalyst recovery and product purification in the homogeneous catalyst system, there are It is necessary to study the heterogeneous asymmetric hydroformylation catalyst.In this paper, vinyl-modified BINAP ligand 5,5’-divinyl-BINAP and different structural comonomers divinylbenzene or 1,3,5-tris Vinyl phenyl benzene, resulting in different pores Poly-1 and Poly-2 polymers were synthesized by the copolymerization of ethylene glycol dimethacrylate (LLDPE) and vinyl BINAP to obtain polymer Poly-3.The above three polymer materials supported metal Rh , Which was used as a catalyst for the asymmetric hydroformylation of styrene.The NMR analysis of solid ~ (13) C showed that the three polymer materials retained a relatively stable C framework structure after metal loading.According to ~ (31) P NMR It can be seen that the BIANP embedded in the material framework remains unoxidized.N_2 physical adsorption results show that Poly-1 and Poly-2 have a larger specific surface area and pore volume, while Poly-3 has the smallest specific surface area. Thermogravimetric analysis showed that these materials have higher thermal stability and different catalyst activity in different reaction solvents.After optimizing the reaction temperature and pressure of the synthesis gas, the catalyst Rh / Poly-1 at 80 ℃ and 0.2MPa product Enantioselectivity of up to 58.9%, branched chain aldehyde to linear aldehyde ratio of 8.5; under the same reaction conditions, the average ee value of the homogeneous catalyst Rh-BINAP was only 35.3%, but higher than that of Rh / Poly -3 This is due to the different surroundings of BINAP in the three heterogeneous catalyst frameworks In the first two catalysts, BINAP interacts with the steric hindrance monomer, making the reaction substrate contact with the catalytically active sites in a specific direction, forming a structure similar to the chiral pocket, whereas Rh / Poly-3 , The linear comonomer around BIANP could not form an effective chiral pocket structure.The catalytic activity was not significantly decreased after repeated use of Rh / Poly-1 for 7 times.Expansion of the X-ray absorption fine structure characterization results showed that Rh / Poly -1 catalyst did not exist before the use of Rh-Rh bond, but after repeated use, Rh metal part of the aggregation, generated Rh-Rh bond. Spherical electron microscopy photo also confirmed this point.