Metallodendrimers with metals

Representative examples of other metallodendrimers with metal atoms at the surface are the ruthenium materials 24 549-551 organometallic dendrimers 244, which possess peripheral cobalt clusters that were prepared by... 

Different types of metallodendrimers with metal compounds at each repeating unit throughout the dendrimer have been reviewed [195,197]. Because of their high concentration of metal centers, they can be considered as nanoparticle equivalents. One example is the platinum acetylide dendrimer 72 obtained by a stoichiometric transmetallation to form acetylides [204]. This metallodendrimer has a precedent in earlier syntheses of linear Pt-acetylide coordination polymers. Several papers describe the synthesis of various Ru pyridyl complexes as repeating units for photochemical investigations and non-... 

Balzani et al. prepared dendrimers with metal complexes serving both as core [36] and as branching unit The metallodendrimer in Fig. 2.10 is constructed solely from polypyridine ligands and transition metal ions. Such dendritic transition metal complexes can be synthesised both convergently and divergently and different transition metal ions (ruthenium/osmium) can be incorporated. This provides a means of influencing the luminescence properties of the den-drimer. Thus the energy transfer process proceeds from the inside outwards in... 

Newkome et al. prepared metallodendrimers with a ligand/metal/ligand architecture allowing separate construction of the dendrons. Two polyamide den-drons were preconstructed and linked to a ruthenium complex [38] (see Section 4.1.11). 

Dendrimers with metal complex moieties in their branches require the prior incorporation of specific coordination sites into the dendrimer scaffold. Newkome et al. used such a dendrimer with twelve alkyne units for spot-on introduction of l,2-dicarba-c oso-dodecaborane groups (Fig. 4.59, above right) [127]. Moreover, on-target coordination with dicobalt-octacarbonyl to form a metallodendrimer with twelve dicobalt-hexacarbonyl units was also accomplished. These units can serve as protective groups on the one hand [128], and as catalysts on the other [129]. 

Some metallodendrimers with one or more stereogenic centers have been prepared without control of the chirality. Vogtle and Balzani [74] have tried several strategies to prepare dendrimers in which a ruthenium cation is the core of the final compound. In these compounds, the only centre of chirality is that of the metal, but as it was not controlled racemic mixtures were obtained. Controlling the stereochemistry of the starting complex would have allowed the authors to prepare a optically pure metallodendrimer. Denti, Campagna, Balzani, and their co-workers have studied polymetallic dendrimers based on bipyridine and 2,3- 7s -(2-pyridyl)pyrazine (2,3-... 

For the formation of metallodendrimers of precise nature, a second favorable position in the overall structure for complexation can obviously be at the periphery. Excellent examples of such systems have been reported that include a silicon dendrimer decorated with 243 ferrocenyl units at the periphery with stable redox activity [58]. Catalytic activity of dendrimers with metals located at the periphery has also proven to be of great interest as it has been recently reviewed by several authors [59,60]. Placing photoactive centers at this specific location can nonetheless be more intricate in this case, as demonstrated by the limited number of reported examples. 

The preparation of metallodendrimers, incorporating metallic species within their structure, is a relatively facile process given the ease and versatility of dendrimer functionalization which can be tailored for metal coordination. For example, the PAMAM dendrimers discussed earlier can coordinate different transition metals through their nitrogen atoms. Metals able to coordinate with the PAMAM structure include among others Cu [20, 21], Au [22], Pd [23], Pt... 

Dendrimers can be constructed from chemical species other than purely organic monomers. For example, they can be built up from metal branching centres such as ruthenium or osmium with multidentate ligands. The resulting molecules are known as metallodendrimers. Such molecules can retain their structure by a variety of mechanisms, including complexation, hydrogen bonding and ionic interactions. 

Metallodendrimers can be constructed via binding of groups with suitable donor atoms (e.g., polydentate ligands) on either the periphery or the core of the dendrimer and the subsequent complexation/coordination of these ligands to an appropriate metal salt. Ultimately, this binding can involve the formation of a direct a bond linkage (i.e., a M-C bond). This chapter describes various... 

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