Metallodendrimers potential applications

Metallocenes have frequently been used as terminal moieties in dendrimer chemistry - as already demonstrated in previous sections. They are of interest primarily because of their potential application in catalysis [123]. An unusual metallodendrimer with peripheral ferrocene entities and optically active ferro-cenyldiphosphine ligands (josiphos ligands) was prepared by Togni et al. (Fig. 4.58) [124]. Adamantanetetracarboxlic acid was one of the core units employed. 

The initial focus in dendrimer research was largely on their synthesis, but recently more importance has been given towards their functional aspects [23]. The successful blending of dendrimer chemistry with several contemporary themes such as host-guest chemistry [24], metallo-organic chemistry [25], luminescent materials [26], catalysis [20a], medicinal chemistry [18d] and polymers [27] has contributed enormously over the years to a rich chemistry with potential applications. As a detailed survey of this area is beyond the scope of this chapter, we will restrict ourselves to two topics involving these molecules (a) dendritic self-assembly [28] and (b) metallodendrimers [25,26]. 

The properties of metallodendrimers with a view to their potential applications have been reviewed in [195-197] sensors, binding of small molecules, catalysis, reactive centers, molecular antennas by visible light irradiation. 

Metallodendrimers are a mature area of nanoscience with versatile potential applications. These compounds have been subjected to numerous studies. Several review articles summarized the recent advances and applications of metallo-dendrimers[ll,12]. Metallodendrimers can be classified as monometallic and bimetallic dendrimers. 

Dendrimers have attracted considerable attention since their discovery three decades ago [1 3], Potential applications involve supramolecular properties [11] in the fields of nanomedicine [29], materials science [4-13] and catalysis [16, 30, 38 3], Since the late 1980s, we have focused our attention on metallodendrimers [14, 44] with the aim to develop knowledge concerning redox properties that are useful for redox sensing and catalysis as well as for the design of molecular batteries. In this microreview article, we will illustrate the design of our recent smes of metallodendrimers and some of their properties and applications. 

In conclusion, the potential of soluble, nanosized metallodendrimers as catalysts in homogeneous reactions is well-consolidated. Future applications of these species are foreseen in high-tech nanotechnology applications in the fields of nano- and microreactors, cascade catalysis, and catalytic biomonitoring and biosensing. In this respect, the recent use of noncovalent strategies for the construction of multicomponent catalytic assemblies, and the use of biomacromolecules within dendritic structures is intriguing [60-62,92,93]. 

The unique features of dendritic architecture and the rich chemistry of organo-transition metal complexes have been combined in metallodendrimers to create the potential for a wide range of utilitarian applications. Because dendrimers allow scientists to probe the twilight zone between homogeneous and heterogeneous catalysis as well as to apply the techniques associated with combinatorial-type chemistry, diverse new areas of the nanoworld have became accessible. Since many new avenues in supramolecular chemistry have been opened by organometalhc complexes, metallodendrimers will continue to play an important role in not only organometalhc chemistry and polymer science, but also in material science. These new interfaces will be rich areas for future science to pursue. 

S.-H. Hwang and G.R. Newkome, Metallodendrimers and their potential utilitarian applications in A.S. Abd-El-Aziz and I. Manners (Eds.), Frontiers in Transition Metal-Containing Polymers, Wiley, Chichester, 2007. 

Ferrocene dendrimers are also of interest for reasons other than their redox activity. For example, metallodendrimer 8.26 possesses planar chiral ferrocene units that make the bidentate phosphine ligation sites of potential interest for applications in asymmetric catalysis. Indeed, asymmetric hydrogenations of dimethyl ita-conate catalyzed by Rh complexes of 8.26 showed impressive enantiomeric excess values of 98% [47]. 

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