Divergent synthetic approach, dendrimers

The divergent synthetic approach is schematically summarized in Figure 7. Reaction of the mononuclear complex-ligand tRu(2,3-dpp)j] with the complex-metal [Ru(2,3-Medpp)2Cl2] in a 1 3 molecular ratio leads to a tetranuclear complex (first dendrimer generation) which in its peiipheiy contains six protected chelating sites. Demethylation of this species restores its ligand ability and yields... 

Figure 5.1 Schematization of the divergent synthetic approach to buildup dendrimers.

FIGURE 15.3 Two most common synthetic strategies for dendrimers. (a) Divergent synthetic approach, (b) Convergent synthetic approach. 

Dendrimers are structurally defined branched polymeric molecules and can form good X-ray quality crystals. This is particularly useful in the correlation of structure and properties. Two main synthetic approaches have been used divergent, which is appropriate for smaller dendrimers, and convergent, which is better for larger dendrimers. Branched polysilanes with a structurally defined branched core were described in 1994, but the growth from the core was not controlled and non-uniform structures were obtained.357... 

In order to obtain both series of dendrimers a divergent stepwise synthetic approach was designed. Each generation growth step of this synthetic approach implies four consecutive reactions (a-b) two successive alkylation reactions that... 

Figure 7. Divergent synthetic strategy to obtain polynuclear metal complexes of dendrimer shape. - ° Each deprotected compound of the dive ent synthetic approach can be used as a core in convergent synthetic processes. Some of these routes starting from a tetranuclear core are illustrated in Figure 8.

Kim and Kwon reported the divergent synthesis of a dendritic carbosiloxane from a cyclic siloxane tetramer core130 using the standard carbosilane dendrimer synthetic approach. Allyl alcohol was employed as the nucleophilic reagent and trichlorosilane... 

Fig. 3.7-6 Synthetic approaches for dendrimers (a) divergent method (b) convergent method (c) self-assembly.

The first example of a dendrimer-like polymer (in fact, a dendrimer-like PEO of the third generation) was described in 1995 by Gnanou et al. [10]. Iterative synthetic approaches, using either a divergent or a convergent strategy, can be followed... 

The first example of an iterative synthetic approach toward dendrimers has been reported in 1978 by Vbgtle [3], who called it cascade synthesis . In the mid-1980s, Tomalia [4] and Newkome [5] independently reported the divergent synthesis of two new families of dendrimers poly(amidoamine) and the so-called arborols , respectively. A growing interest on these macromolecules lead in 1990 to the convergent synthesis of aromatic polyether dendrimers by Frechet [6]. The two different synthetic approaches can be explained as follows ... 

Different synthetic routes to dendrimers have been reported in literature however, the most widely known methods include the classical divergent and convergent synthetic approaches. The development of other synthetic methods for preparation of dendrimer is aimed at decreasing the disadvantages of the classical methods. Most of the newly developed methods have their own merits and drawbacks. Therefore, the S3mthesis method chosen for a particular dendrimer depends on the properties required of the dendrimer. 

Dendrimers produced by divergent or convergent methods are nearly perfectly branched with great structural precision. However, the multistep synthesis of dendrimers can be expensive and time consuming. The treelike structure of dendrimers can be approached through a one-step synthetic methodology.31 The step-growth polymerization of ABx-type monomers, particularly AB2, results in a randomly branched macromolecule referred to as hyperbranch polymers. 

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