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设计并合成了系列具有不同代数以及不同结构的手性树状分子BINAP配体.以Ru-催化的2-芳基丙烯酸的不对称氢化和Rh-催化的乙酰氨基肉桂酸的不对称氢化为模型反应,结合圆二色谱分析方法,系统研究了树状分子催化剂的结构与催化性能的关系.在2-芳基丙烯酸的不对称氢化中,发现双边取代的树状分子催化剂表现出明显高于小分子催化剂的催化活性,反应速度随着树状分子代数的增加而加快,当反应溶剂由甲苯/甲醇(1∶1,V/V)变为纯甲苯时,这种树状分子加速效应更加明显;而单边取代的树状分子催化剂,由于催化活性中心远离树状分子载体,因此其催化活性与小分子催化剂几乎相同.此外,圆二色(CD)谱研究表明,双边取代的树状分子配体有不同于单边取代树状分子配体和小分子BINAP配体的Cotton效应,说明树状分子的引入可能影响到位于其核心的手性配体的微环境.这些结果显示树状分子载体在催化活性中心周围所构筑的微环境在促进催化剂活性中发挥了关键作用.这种“微环境效应”还在脱氢氨基酸的不对称氢化中得到了进一步证明.最后,通过溶剂沉淀法,实现了树状分子催化剂与产物的方便分离,催化剂至少可以回收使用三次,其催化活性和对映选择性没有任何降低.
A series of BINAP ligands of chiral dendrimers with different algebraic structures and different structures were designed and synthesized.The asymmetric hydrogenation of 2-arylacrylic acid and asymmetric hydrogenation of acetylaminocinnamic acid catalyzed by Rh-catalyzed Ru- Reaction, combined with circular dichroism analysis, the relationship between the structure and catalytic performance of dendrimer was studied systematically.In the asymmetric hydrogenation of 2-arylacrylic acid, it was found that the dendrimer-substituted dendrimer showed significantly higher The catalytic activity of the molecular catalyst accelerates with the increase of the dendrimer algebra. When the reaction solvent changes from toluene / methanol (1: 1, V / V) to pure toluene, the accelerating effect of this dendrimer becomes more obvious However, the unmodified dendrimer has almost the same catalytic activity as the small molecule catalyst due to its catalytic activity center away from the dendrimer support.Furthermore, circular dichroism (CD) spectra show that the dendrimer Ligands have a Cotton effect that is different from unilateral substitution of dendrimer ligands and small molecule BINAP ligands, suggesting that the introduction of dendrimers may affect the microenvironment of chiral ligands located in their core. The results show that the microenvironment formed by the dendrimer around the catalytic active center plays a key role in promoting the activity of the catalyst, which is further evidenced by the asymmetric hydrogenation of dehydro amino acids. Finally, the solvent-precipitation method is used to facilitate the separation of the dendrimer catalyst from the product. The catalyst can be recycled at least three times without any decrease in the catalytic activity and enantioselectivity.