Dendrimers multiple coordination sites

Dendrimers containing coordination sites (e.g., amine, amide groups) in their structure can act as ligands of metal ions. We can distinguish dendrimers containing a single coordination site, for example, in the core (Fig. 2c), or multiple coordination sites in the branches (Fig. 2d). 

A. Dendrimers with Multiple Coordination Sites A.I. Amide coordinating units... 

In most cases, metal ion coordination by a dendrimer takes place by units that are present along the dendrimer branches (e.g., amine, imine, or amide groups) or appended at the dendrimer periphery (e.g., terpyridine, cathecolamide ligands). When multiple identical coordinating units are present, dendrimers give rise to metal complexes of variable stoichiometry and unknown structures. Luminescent dendrimers with a well defined metal-coordinating site have been reported so far [16, 17], and the most used coordination site is 1,4,8,11-tetraazacyclotetradecane (cyclam). 

For historical reasons, examples of case 2d, containing multiple amine or amide groups in their branches, will be discussed first. These types of dendrimers give rise to metal complexes of variable stoichiometry and unknown structures since they contain several more or less equivalent ligand units and not well-defined coordination sites. 

Transmetallation reactions are useful for the synthesis of NCN pincer derivatives, since the free ligand is readily metallated with LiBu (Scheme 25). This method is best suited for the synthesis of dendrimeric molecules capped with NCN-Ni units, as multiple oxidative addition processes compete with the one-electron oxidation of the Ni(ii) centers. Dendrimers containing from 4 to 36 NCN coordination sites have been prepared and metallation levels of up... 

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