Metallodendrimers

Although most of the dendrimers are synthesized by one of these two strategies, examples of metallodendrimer syntheses applying both methodologies have also been reported, which is done to improve their overall synthesis and/or purity (polydispersity) by minimizing the possible formation of defects in the dendritic framework. 

Core-functionalized metallodendrimers have the advantage of creating isolated sites due to the environment of the dendritic framework. In the case of core-functionalized dendrimers, the molecular weight per catalytic site (ligand/catalyst) is higher than for periphery-functionalized dendrimers, which therefore involves higher costs from a commercial point of view. The 

Different approaches have been developed for binding a metal or organo-metallic moiety to these dendrimer frameworks. In numerous coordination compounds, the dendrimer and the metal are linked through a dative metal-heteroatom bond [32], while in organometallic compounds the linkage between the metal and the dendritic framework is realized via a or n metal-carbon bonding [11]. 

In this opening chapter, we will focus our discussion on metallodendritic catalysts that localize their catalytic functions either at the periphery or at the core of a dendritic macromolecule. These types of dendritic catalyst have been by far the most widely applied of the metallodendrimers in combination with membrane separation technologies. 

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Metallodendrimers with heterocyclic fragments as supersupramolecules with novel properties 99CRV1689. 

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. 

Onitsuka K, Takahashi S (2003) Metallodendrimers Composed of Organometallic Building Blocks. 228 39-63... 

Keywords. Metallodendrimer, Organometallic complex. Metal acetylide... 

Given that the presence of three alkoxy chains in the phenyl group produces such a dramatic change in the properties of the material to the point that columnar mesophases are formed at room temperature, the structure of the aryl isocyanide ligand has been further modified to introduce more paraffinic chains, and examples of metallodendrimers containing monodendrons with an isocyanide group in the focal point, and its gold compound 9, have been reported [26]. 

The synthesis and structural characterization of luminescent di- and tri-nuclear organopalla-dium complexes with rigid conjugated alkynyl-aryl bridges and preliminary experiments on the formation of the first generation metallodendrimer using the trinuclear complex as the backbone were reported.102... 

Dendrimers are attractive nanosize model compounds because of their globular architecture and their highly functionalized surface. These hyperbranched compounds are synthesized in a repetitive reaction sequence of nearly quantitative reactions. The synthetic route can either be divergent, starting from the nucleus toward the surface, or convergent, where dendrons or wedges are covalently linked to a polyfunctional nucleus. The number of metallodendrimers is still limited.493-506... 

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. 

Constable has described [172] the construction of a variety of metallodendrimers using both convergent and divergent approaches wherein the metal... 

Organic functional groups can also be placed on the Cp ligands in CpMG2B3 complexes, e.g., 59,60 and this approach has been exploited to generate metallodendrimers such as 60 [DAB-32 = diaminobutane-dend(NH2)32].60... 

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... 

Beside these catalytically active metallophosphine dendrimers (see above), preliminary studies on the chemical properties of phoshorus-based dendrimers complexed to metals such as platinum, palladium and rhodium have been described by Majoral, Caminade and Chaudret [21], They showed that these macromolecules (see Scheme 13) could be useful for the (in situ) generation of metallodendrimer catalysts. 

The research group of Van Leeuwen reported the use of carbosilane de-ndrimers appended with peripherial diphenylphosphino end groups (i.e. 25, Scheme 26) [37]. After in situ complexation with allylpalladium chloride, the resultant metallodendrimer 25 was used as catalyst in the allylic alkylation of sodium diethyl malonate with allyl trifluoroacetate in a continuous flow reactor. Unlike in the batch reaction, in which a very high activity of the dendrimer catalyst and quantitative conversion of the substrate was observed, a rapid decrease in space time yield of the product was noted inside the membrane reactor. The authors concluded that this can most probably be ascribed to catalyst decomposition. The product flow (i.e. outside the membrane reactor)... 

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