Synthesis and Characterization of Supported Chiral Catalysts-猫眼课题宝

DOI：

10.1002/9781118087992.ch3

发表时间：

2011-07

期刊：

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

C. Aprile;H. García;P. Pescarmona

对映体纯化合物的合成通常使用手性催化剂，利用其自身的手性来诱导产物的手性。手性催化剂的一大类别是手性配合物或作为均相催化剂的手性化合物。均相催化剂的工业应用有限，主要是由于从反应介质中分离昂贵的催化剂很困难。为了解决这一问题，人们进行了许多尝试，将手性催化剂固定在合适的载体上，以将均相体系转化为多相催化剂。多相催化剂是有利的，因为它们可以很容易地从反应混合物中分离出来，并且可以回收，这也意味着产物的纯化更直接。第1章和第2章报道了许多可回收手性催化剂的例子。本章将讨论负载性手性催化剂的一般合成策略和表征方法。第四章报道了有机聚合物负载手性催化剂的合成。多相催化的世界无疑是迷人的，并且永远相关。值得注意的是，超过90%的化学制造业在其工艺的至少一个步骤中使用催化。多相催化的科学和技术显然具有核心和实用的重要性，也因为所选固体的固有特性，如孔隙率和表面积对催化性能起着至关重要的作用。传统上，均相催化和多相催化这两个领域被认为是独立的领域，但均相催化剂转化为多相催化剂的方式不同，这有助于弥合这两个领域之间的差距，并在各自的优势和劣势之间取得最佳平衡。手性均相催化剂“异质化”过程的缺点主要与催化活性有关，因为使用固体载体时，对映体选择性和产率都可能降低。较低的对映体选择性可能是由于固定化有机部分的结构扭曲或位阻使催化剂无法达到均相中达到的过渡态几何形状。由于位于支架内的活性位点的可达性降低，活性会降低。还应特别注意有机部分可能从固体支撑物中浸出。尽管存在这些问题，但最近在多相不对称催化方面的所有进展都表明，在保持固体载体易于回收和再循环特性的同时，可以获得与均相体系相当的具有良好活性和选择性的材料。本章的主要重点是回顾了用于固定化手性催化剂的各种载体。由于已经使用的固体或构成用于此目的的合适候选物的数量庞大且不断增加，因此对其进行了广泛的描述

The synthesis of enantiomerically pure compounds is generally achieved using chiral catalysts, which exploit their own chirality to induce that of the products. A vast class of chiral catalysts is represented by chiral complexes or chiral compounds that act as homogeneous catalysts. Homogenous catalysts find limited industrial applications, mainly due to the difficulty in separating the often expensive catalysts from the reaction medium. To solve this issue, many attempts have been made to immobilize the chiral catalysts on suitable supports in order to transform the homogeneous system into a heterogeneous catalyst. Heterogeneous catalysts are advantageous because they can be easily separated from the reaction mixture and can be recycled, which also implies a more straightforward purification of the products. Many examples of recyclable chiral catalysts are reported in Chapters 1 and 2. In this chapter, the general synthetic strategies and characterization procedures of supported chiral catalysts will be discussed. In Chapter 4, the synthesis of chiral catalysts supported on organic polymers is reported. The world of heterogeneous catalysis is decidedly fascinating and perennially relevant. It is worth noting that more than 90% of the chemical manufacturing industries use catalysis in at least one step of their processes. The science and technology of heterogeneous catalysis are clearly of central and practical importance, also because the intrinsic characteristics of the selected solid such as porosity and surface area play a crucial role in the catalytic performances. Traditionally, the two fields of homogeneous and heterogeneous catalysis are considered as separate domains, but there are different ways in which a homogeneous catalyst can be converted into a heterogeneous one, which helps to bridge the gap between these two fields and create an optimum balance between the respective advantages and disadvantages. The drawbacks of the process of “heterogenization” of a chiral homogeneous catalyst are predominantly related to the catalytic activity, since both enantioselectivity and yield may suffer a decrease when a solid support is used. The lower enantioselectivity can be due to the distortion of the structure of the immobilized organic moiety or to the steric hindrance that precludes the catalyst from reaching the transition state geometry achieved in homogeneous phase. The activity can diminish due to the decreased accessibility of the active sites located within the support. Particular attention should also be given to the possible leaching of the organic moiety from the solid supports. In spite of these problems, all the recent advances in heterogeneous asymmetric catalysis demonstrate that is possible to obtain materials with good activity and selectivity, comparable with those of homogeneous systems, while maintaining the easy recovery and recycling properties of the solid support. The main focus of this chapter is on reviewing the various supports that have been used for the immobilization of chiral catalysts. Due to the large and constantly increasing number of solids that have been already used or that constitute suitable candidates for this purpose, an extensive description with

Synthesis and Characterization of Supported Chiral Catalysts

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