温度敏感型纳米贵金属材料的制备及在不对称氢化中的应用

The asymmetric hydrogenation of prochiral ketones to corresponding optically pure secondary alcohols is one of the most important reactions in the field of chiral pharmaceuticals and fine chemicals. The investigation on heterogeneous hydrogenation catalyst combining the advantages of ready preparation, high catalytic performance, as well as easy separation and reuse, has attracted more and more attention in the recent years. .The present subject therefore aims to develop a novel metal nanocatalyst grafted with PNIPAAm, a thermosensitive polymer. The polymer-modified metal nanoparticles would combine the merits of both metal colloidal catalyst and thermosensitive polymer. So it is expected that the modified metal nanocatalyst could exhibit high catalytic activity and enantioselectivity for the asymmetric hydrogenation of α-ketoesters in the presence of cinchona as chiral modifier. And this metal nanocatalyst is also expected to be easily separated from the catalytic reaction system due to the sensitive temperature-induced phase separation contributed by PNIPAAm. Moreover, the strong interaction between polymer molecules and metal surface could protect the small metal particles from migration, aggregation and leaching. This research would develop a novel heterogeneous asymmetric hydrogenation catalyst system with high catalytic performance and recyclability, as well as provide an effective approach for the preparation of heterogeneous chiral catalyst.

潜手性酮不对称氢化生成的手性仲醇是合成手性药物和精细化学品的重要有机中间体，设计研制易制备、催化性能良好、又易于与体系分离和循环使用的多相不对称氢化催化剂是该领域研究的重要课题。本项目拟通过温敏聚合物与金属纳米粒子之间的强相互作用，制备温敏聚合物PNIPAAm修饰的金属催化剂。这些催化剂不仅具备金属胶体粒子的优点，有望手性修饰后在α-潜手性酮的不对称催化氢化反应中表现出较高的活性和对映选择性，并且可以利用聚合物对环境温度变化的敏感相变转换，实现与反应体系的简单分离，此外聚合物与金属表面的强相互作用，可以有效防止体系中金属的迁移、聚集和流失。通过项目的研究，以期发展一类新型、高效、稳定耐用的多相不对称氢化催化剂体系，进一步拓宽多相不对称氢化反应的研究领域，同时也开发一种有效的多相手性催化剂的制备方法。

潜手性酮不对称氢化生成的手性仲醇是合成手性药物和精细化学品的重要有机中间体，设计研制易制备、催化性能良好、又易于与体系分离和循环使用的多相不对称氢化催化剂是该领域研究的重要课题。本项目通过RAFT法合成并还原了温敏聚合物PNIPAAm，之后通过四种不同的方法制备了催化剂Pt@PNIPAAm，并将其经金鸡纳生物碱修饰后用于催化丙酮酸乙酯不对称氢化反应。系统地考察了催化剂的制备方法、氢气压力、聚合物的链长及修饰密度、手性修饰剂的用量等对反应活性和对映选择性的影响，获得了很好的反应结果，反应转化率高达99.9%以上，产物最高ee值超过80%；同时着重研究了催化剂的回收再利用性能，结果表明利用聚合物的温敏特性可以简单实现纳米Pt催化剂的回收再利用，催化剂循环使用11次而转化率和ee值无明显降低，且循环过程中金属Pt的总流失量不超过1%。在此基础上又研究了PNIPAAm修饰的Rh催化体系在丙酮酸乙酯不对称氢化反应中的催化性能，同样获得了较高的催化活性和对映选择性以及良好的重复利用性能。