Metal complex dendrimers characterization

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). 

Dendrimer 1 (Fig. 5) is a classical example of a dendrimer built around a metal complex core. In this compound, the 2,2 -bipyridine ligands, that constitute the first coordination sphere of the Ru ion, carry branches containing 1,3-dimethoxybenzene and 2-naphthyl chromophoric imits separated by aliphatic connectors (10). Since the interchromophoric interactions are weak, the absorption spectrum of 1 is substantially equal to the summation of the spectra of [Ru(bpy)s], which is characterized by a broad spin-allowed Ru bpy metal-to-ligand (MLCT) band around 450 nm (11), and of the chromophoric groups contained in the branches, which show very intense bands in the near UV region. 

Electrochemical characterization has been performed in acetonitrile solution on a great variety of dendrimers built with metal complexes as branching centers in the whole structure [16]. An interesting example is that represented by the decametallic dendrimers 30-32, where the metal centers are linked by bridging ligands made of two, closely connected bis-chelating units such as 2,3-dpp (2,3-dpp = 2,3-bis(2-pyridyl)pyrazine) [76, 78]. In the dendritic species, each mononuclear component brings its own redox properties, more or less affected by intercomponent inter-... 

Polypyridyl transition metal complexes, especially those of ruthenium(II), have been extensively apphed in light harvesting and information storage, because they exhibit a wide range of photophysical and electrochemical properties. Storrier et al. have reported the synthesis and characterization of PAMAM dendrimers functionalized with tris(bipyridyl) ruthenium(II) (dend- -[Ru(bpy)3] +) or bis (terpyridyl) ruthe-nium(II) (dend-n-[Ru(tpy)2] ) complexes (GO, 1, 2, 3, and 4 with 4, 8, 16, 32,... 

Storrier GD, Takada K, Abruna HD (1999) Synthesis, characterization, electrochemistry, and EQCM studies of polyamidoamine dendrimers surface-functionalized with polypyridyl metal complexes. Langmuir 15 872-884... 

Ishizu et al.194 synthesized hyperbranched macromolecules that resemble dendrimers. The synthetic approach involved the preparation of poly(4-methyl-styrene-b-PS-b-poly(4-methylstyrene) triblock copolymer by using naphthalene lithium as difunctional initiator. The 4-methyl groups of the terminal blocks were metalated with s-BuLi/tetramethylethylenedi-amine (TMEDA) complex in a molar ratio of 1 2. After removal of the excess s-BuLi by repeated precipitation of the living polymer and transfer of supernatant solution to another flask under high vacuum conditions, the polymer was dissolved in THF and was used as the initiator of a-methylstyrene at —78 °C. After the polymerization of a-methylstyrene, a small amount of 4-methylstyrene was added. The procedure of metalation of the a-methyl groups and polymerization of a-methylstyrene can be repeated many times to form a dendritic type hyperbranched polymer (Scheme 99). The characterization of the inter-... 

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