Dendrimer peripherally complexed metal

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... 

First generation dendrimers (tetranuclear complexes) of the same family with branches containing different metals have also been synthesized and energy migration patterns leading to one or two peripheral units have been obtained [58]. 

Figure 46. Subunits of porphyrin-containing dendrimers (see 87 and 88 of Figures 47 and 48) built on Pd-pincer complex metal fragments. 85 is the core, and 86 is a peripheral unit.

PBE dendrons bearing a focal bipyridine moiety have been demonstrated to coordinate to Ru + cations, exhibiting luminescence from the metal cation core by the excitation of the dendron subunits [28-30]. The terminal peripheral unit was examined (e.g., phenyl, naphthyl, 4-f-butylphenyl) to control the luminescence. The Ru +-cored dendrimer complexes are thought to be photo/redox-active, and photophysical properties, electrochemical behavior, and excited-state electron-transfer reactions are reported. 

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 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. 

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. 

ECL investigations of dinuclear or polynuclear Ru(II) complexes have been recently performed with hope for developing more efficient electrochemiluminescent materials. Centrally or peripherally functionalized dendrimers with active RuL32 + chelate units can produce higher (up to four to five times) ECL intensities as compared to their monomeric RuL32 + precursors alone. It was also found that the ECL intensities of metallodendrimers become larger as the multiplicity of the involved Ru(II) units increases. Similar observations have been reported for binuclear Ru(II) complexes with weak interaction between both metallic centers.84-88 These results indicate that further studies in such direction may result in design of still more efficient ECL systems based on Ru(II) luminophores. 

The group of Van Leeuwen has reported the synthesis of a series of functionalized diphenylphosphines using carbosilane dendrimers as supports. These were applied as ligands for palladium-catalyzed allylic substitution and amination, as well as for rhodium-catalyzed hydroformylation reactions [20,21,44,45]. Carbosilane dendrimers containing two and three carbon atoms between the silicon branching points were used as models in order to investigate the effect of compactness and flexibility of the dendritic ligands on the catalytic performance of their metal complexes. Peripherally phosphine-functionalized carbosilane dendrimers (with both monodentate... 

The electroactive units are the peripheral groups (Figure 2b). These dendrimers are functionalized on their surface, and all the units are equivalent. The most common units of this type are ferrocene and metal-polypyridine complexes. 

Dendrimers based on octahedral metal complexes may be structurally not well defined because of the presence of several stereogenic centers [116]. Recently, the first examples of stereochemically pure tetrametallic Ru dendrimers have been described compound 34 depicts the A A3 isomer [106]. On oxidation in acetonitrile, a three-electron wave due to the peripheral Ru units is followed by the mono-... 

Metallodendrimers are an interesting class of molecules in the area of dendrimer chemistry. They combine dendritic structures with the specific activity of metal complex centers. Metal coordination has facilitated the synthesis of a number of dendritic, supramolecular structures. Metals have been incorporated in all of the topologically different parts of dendrimers in the repeat or branching unit, in the molecular core and in the peripheral units. Because this field of metallodendrimers has been reviewed recently [195-197], only a few examples are given below. Other supramolecular organizations such as catenanes and rotaxanes have been mentioned previously in this chapter. 

One example of a dendrimer substituted at the peripheral units with a metal complex is shown in Eq. 7-16. 71 is obtained by treating the fourth generation of the poly(propylene imine) dendrimer (DAB-dendr-(NH2) c) (x = 32) with chlorocarbonylferrocene and the PFg salt of chlorocarbonylcobaltocenium [202], Statistical substitution by the two different metallocenes is observed. 

There are numerous examples of dendrimers and star polymers that contain metal coordination complexes based on pyridine ligands. There is also interest in the incorporation of more than one type of metal complex into these materials. Constable and coworkers have reported the synthesis of heptametallic complexes containing six peripheral ruthenium coordination complexes and a central iron or cobalt complex. Scheme 21 illustrates the reaction of 89 with either iron or cobalt complexes to produce the heptametallic dendrimer 90. A heptametallic star-shaped complex with a CpFe -coordinated arene as the core and ruthenium Aexa-pyridine complexes at the periphery has also been reported by Astruc. ... 

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