Enantioselective Catalysis Using Dendrimer Supports

Since the pioneering studies reported by van Koten and coworkers in 1994 [20], dendrimers as catalyst supports have been attracting increasing attention. The metaUodendrimers and their catalytic applications have been frequently reported and reviewed [7-15]. As a novel type of soluble macromolecular support, dendrimers feature homogeneous reaction conditions (faster kinetics, accessibility of the metal site, and so on) and enable the application of common analytical techniques such as thin-layer chromatography (TLC) and nuclear magnetic resonance 

Handbook of Asymmetric Heterogeneous Catalysis. Edited by K. Ding and Y. Uozumi Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31913-8 

Figu re 4.1 Commonly encountered chiral catalyst immobilization on dendritic polymer supports (a) core-functionalized chiral dendrimers (b) peripherally modified chiral dendrimers (c) solid-supported dendritic chiral catalysts. 

In this chapter, we attempt to summarize the recently developed chiral dendrimer catalysts with their chiral catalytically active species located either at the core or at the periphery of the dendritic macromolecular supports. The discussion will also be focused on dendrimer effects and the development of new methodologies for the recovery and reuse of chiral dendrimer catalysts, with special emphasis on their applications in enantioselective synthesis. The published data have been classified according to the type of reachon in each of the following three sections. 

In the case of the core-functionalized dendrimers, it is expected that a steric shielding or blocking effect of the specific microenvironment created by the dendritic structure might modulate the catalytic behavior of the core [11, 26]. This site-isolahon effects in dendrimer catalysts may be beneficial for some reactions, whereby the catalysts often suffer from deactivahon caused by coordination saturation of the metal centers, or by the irreversible formation of an inactive metallic dimer under conventional homogenous reaction conditions. The encapsulation of such an organometallic catalyst into a dendrimer framework can specifically prevent the deachvahon pathways and consequently enhance the stability and 

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Fan, Q.H., Deng, G.J., Feng, Y., and He, Y.M. (2008) Enantioselective catalysis using dendrimer supports, in Handbook of Asymmetric Heterogeneous Catalysis (eds K. Ding and Y. Uozumi), Wiley-VCH Verlag GmbH, Weinheim. (c)... 

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