Dendrimer catalysis

The first example of asymmetric rhodium-catalyzed hydrogenation of prochi-ral olefins in dendrimer catalysis was reported by Togni et al., who immobilized the chiral ferrocenyl diphosphine Josiphos at the end groups of dendrimers, thus obtaining systems of up to 24 chiral metal centres in the periphery (Fig. 2) [12-14]. The fact that the catalytic properties of the dendrimer catalysts were almost identical to those of the mononuclear catalysts was interpreted as a manifestation of the independence of the individual catalytic sites in the macromolecular systems. 

An interesting example of this kind of stereoselective dendrimer catalysis has been reported by Rico-Lattes et al., who prepared glycoden-... 

However, the results obtained in recent years have also established that the structural characteristics of the established dendrimer systems, such as the absence of a well-defined secondary structure, have limited the development of efficient abiotic enzyme mimics based on dendrimers. To achieve this ambitious goal, more efforts in dendrimer synthesis will be necessary. The use of dendritic catalysts in biphasic solvent systems has only just begun and appears to be a particularly fruitful field for further developments. These utilitarian aspects aside, it is the aesthetic attraction of these topologically highly regular macromolecules that continues to fascinate those working in the field of dendrimer catalysis. 

The aim of catalyst recycling and the exploitation of possible constructive interactions between catalytic sites underlie the rapidly growing field of stereoselective dendrimer catalysis. Since enantioselection is governed by small increments in the free enthalpy of activation, such transformations are particularly suited to assessing dendrimer effects , which result from the immobilization of catalysts. 

A decade after the initial pioneering studies, dendrimer catalysis has developed into a highly varied and complex field of research. While much of the fascination is derived from the aesthetic appeal of dendrimers (as with other applications of this class of macromolecule), dendrimer catalysts have vindicated many of the utilitarian aspects of this research. This volume provides a comprehensive overview of the current state of the art. 

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