Dendrimers metal complex

Fig. 8. Site-specific metal complexing dendrimers reported by Newkome et al.

Figure 6, 28 platinum centers are clustered in this metal-complex dendrimer (Fhiddephatt et al.) [36]... 

Metal-acetylide complexes have been used as a unit of organometallic polymers that have metallic species in the main chain [20]. Representative examples are metal-poly(yne) polymers (19) of group 10 metals depicted in Scheme 5. These polymers are easily prepared from M(PR3)2Cl2 (M=Pt, Pd) and dialkynyl compounds catalyzed by Cu(I) salts in amine. Recently, this synthetic method was successfully applied to the construction of metal-acetylide dendrimers. 

Metal-acetylide complexes including metal-poly(yne) polymers often show unique properties [21-23]. Thus, metal-acetylide dendrimers are of interest because amplification of the functionality due to metal-acetylide units based on three-dimensional assembly with a regular dendritic structure is expected. 

Fig. 12. Convergent routes to pseudorotaxane-terminated dendrimers with a metal complex at the cores and p CD at the periphery...

Dendrimer 1 + is a classical example of a dendrimer containing a luminescent metal complex core. In this dendrimer the 2,2 -bipyridine (bpy) ligands of the [Ru(bpy)3] +-type core carry branches containing 1,2-dimethoxybenzene- and 2-naphthyl-type chromophoric units [15]. 

Self-assembly of aromatic dendron subunits has been tried by the design of coordination to multivalent metal cations (i.e., metal-cored dendrimer complexes). Several metal-cored dendrimer complexes have successfully exhibited luminescence by antenna effects. 

PBE dendrimers with a cyclic polyamine core at the focal point have been synthesized to form transition-metal complexes [27]. Tb + complexes exhibited luminescence by the excitation of the dendrons. 

Precise placement of metal complexing sites within the infrastructure of a cascade molecule is of importance from a variety of perspectives. In the construction of the above noted Micellane family (cf. Sect. 3.1), we reported the construction of dendrimers with four alkyne moieties at sites equidistant from each other in the interior (17, Fig. 8) [60]. These were treated with decaborane (B10H14) to afford 1,2-dicarba-closo-dodecaboranes (o-carboranes) [71]. Rendering boron clusters soluble in water is of interest because of their use in cancer treatment by Boron Neutron Cancer Therapy. First and second generation water-soluble dendrimers containing four and twelve precisely located boron cluster sites, respectively, were synthesized (e.g., 18). These water soluble dendrimers and their precursors were characterized by 13C-, and nB-NMR spectroscopy (Fig. 8). 

In a recent report [171] Newkome and He extended this concept and described the use of two ruthenium centers per appendage [—(Ru)—(x)—(Ru)—] towards construction of a four-directional dendrimer (e.g., 81, Fig. 36). A combination of convergent and divergent approaches, hence, allowed the stepwise construction of metallodendrimers via controlled metal complexation. 

Complexation of gold ions, [Au(I)], with peripheral phosphine groups of a P-based dendrimer was reported by Majoral et al. [185]. Transmission electron microscopy (TEM) was used to analyze the large aggregates formed by the dendritic gold complexes and a direct correlation was observed between the size of the particles and the dendrimer generation number. In a recent report [186], Majoral et al. further demonstrated that up to 48 diphosphino groups could be anchored to the surface of dendrimers and various dendritic metal-complexes... 

Dendrimers Containing Polypyridine-Type Metal Complexes. 203... 

Dendrimers with a Porphyrin Metal Complex as a Core.212... 

Dendrimers Built Around a Metal Complex as a Core.216... 

Dendrimers built around a metal complex as a core. These compounds can be considered metal complexes of ligands carrying dendritic substituents (Fig. 1 a). The most commonly used metal complex cores are porphyrin complexes, polypyridine complexes, and ferrocene-type compounds. 

Dendrimers containing metal complexes as peripheral units. These dendrimers (Fig. lb) belong to the class of dendrimers functionalized on the surface. Dendrimers coated with up to 48 Ru(Cp)(CO)2R [3], 64 Fe(Cp)2 [4], and 3072 AuCl [5] units have been reported. 

Fig. la-d. Different kinds of metal-containing dendrimers a a metal complex as a core b metal complexes only as peripheral units c metal complexes only in the branches d metals as branching centers... 

Dendrimers containing metal complexes in the branches. In these compounds (Fig. lc), metal complexes may play the role of connectors along the branches of a dendritic structure as in the case of (tpy)Ru(tpy)2+ (tpy=2,2 6, 2"-ter-pyridine) [6], or may be attached to specific sites as in the case of cobalt carbonyls [7]. 

The electroactive units in the dendrimers that we are going to discuss are the metal-based moieties. An important requirement for any kind of application is the chemical redox reversibility of such moieties. The most common metal complexes able to exhibit a chemically reversible redox behavior are ferrocene and its derivatives and the iron, ruthenium and osmium complexes of polypyridine ligands. Therefore it is not surprising that most of the investigated dendrimers contain such metal-based moieties. In the electrochemical window accessible in the usual solvents (around +2/-2V) ferrocene-type complexes undergo only one redox process, whereas iron, ruthenium and osmium polypyridine complexes undergo a metal-based oxidation process and at least three ligand-based reduction processes. 

When the only metal complex of a dendrimer is that constituting the core of the structure (Fig. la), the most interesting problem is whether and, if so, how much the electrochemical properties (potential value, kinetic reversibility) of the metal-based core are modified by the surrounding branches. 

When the metal complexes constitute the peripheral units (Fig. lb) and/or belong to the branches (Fig. 1 c) of a dendrimer, a number of equivalent metal-based centers are present since dendrimers are usually highly symmetric species by their own nature. The metal-based centers may or may not interact, depending on distance and nature of the connector units. Multielectron redox processes can therefore be observed, whose specific patterns are related to the degree of interaction among the various units. 

For space reasons, we will deal mainly with the electrochemical behavior of large dendritic compounds. Therefore, the electrochemical properties of a number of borderline compounds [14] between metal complexes and dendrimers have not been included in this review. 

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