Ferrocene-containing dendrimer

Fig. 63 Structure of the ferrocene-containing dendrimer with six mesogenic arms...

Fig. 65 Structure of the mixed [60]fullerene-ferrocene-containing dendrimer and of its precursory malonate...

Recently, the Kaifer group, whose work combines supramolecular electrochemistry with solid spectroscopic characterization of their systems, studied the interaction of cucurbit[7]uril (CB7, 37) with ferrocene-containing dendrimers up to three generations (FGl (38), FG2 (39), and FG3 (40) see Fig. 6.18). They found, inter alia, that, at pH 7, the diffusion coefficients of the functionalized dendrimers are smaller than the corresponding diffusion coefficients measured at pH 2 which, according to the authors, should be attributed to the fact that, under acidic condi-... 

A water-soluble ferrocene-containing dendrimer, 305, has been prepared via the incorporation of carbohydrate groups.356 This dendrimer was found to mimic redox active proteins and formed different conformers in aqueous solution. 

There are, of course, metal-containing dendrimers that belong to more than one of the above-mentioned categories. Examples are the heptametallic dendrimer made of a central Fe(Cp)(C6Me6)+ core and coated with 6 ferrocene moieties [ 12], and the heterometallic dendrimers made of an organic core, containing up to 6 Pt(IV)-based organometallic species in the branches, and coated with up to 12 ferrocene units [13]. 

Figure 28 A schematic representation of the possible composition of ferrocene-based dendrimers. (a) Dendrimers containing a single ferrocene unit (b) dendrimers containing multiple ferrocene units...

CREATIVE EXPLORATIONS OF TOPOLOGY FROM METAL BIPYRIDINE- AND TERPYRIDINE-CONTAINING DENDRIMERS TO OFF-CENTER FERROCENES... 

Ferrocene-containing co-polyesters, preparation, 12, 350 Ferrocene-containing liquid crystals dendrimers, 12, 235 disubstituted ferrocenes, 12, 227 hydrogen-bonded ferrocene derivatives, 12, 234 monosubstituted ferrocenes, 12, 222 polycatenar ferrocenes, 12, 234 properties, 12, 221... 

Ashton PR, Balzani V, Clemente-Leon M, Colonna B, Credi A, Jayaraman N, Raymo FM, Stoddart JF, Venturi M (2002) Ferrocene-containing carbohydrate dendrimers. Chem Eur J 8 673-684... 

The synthesis of a ferrocene-capped dendrimer with a stealth cyclotriphazene core was reported by Sengupta.320 Electrochemical studies showed that this dendrimer contained equivalent iron centers. A liquid crystalline ferrocene-containing six-arm star, 304, has been reported.344 This orange star showed an enantiotropic smectic A phase.349... 

A potentially attractive generation of dendritic architectures, mostly bearing carbohydrate entities, has appeared and will provide a useful pool of hydrophilic ligands [73, 74]. In such a way ferrocene-containing carbohydrate dendrimers open future prospects [75]. 

The section commences with monosubstituted ferrocene derivatives, after which the influence of the substitution pattern on the formation and stability of liquid-crystalline phases for disub-stituted ferrocene derivatives will be discussed. Next, the influence of the three-dimensional structure of ferrocene on the mesomorphic properties will be highlighted, optically active ferrocene materials will be described and, finally, ferrocene-containing liquid-crystalline dendrimers will be introduced ferrocene-containing liquid-crystalline polymers will not be reported. Note that a review devoted to ferrocene-containing thermotropic liquid crystals has already been published. ... 

Another interesting application of water-soluble dendrimers has been described by Stoddart and co-workers and utilises ferrocene containing carbohydrate dendrimers [102]. A ferrocene core substituted with glucopyranosyl residues was found to form complexes with 3-cyclodextrin and has formed the basis for a supramolecular switch. 

Chiral phosphorus-containing dendrimers which have ferrocene molecules at the periphery have been the subject of work by Majoral and co-workers. These materials will have obvious applications in catalysis. Layer-by-layer dendrimers, which are built up containing chiral ferrocenylphosphine molecules, have also been prepared, and their chiroptical and electrochemical properties have been investigated. A recent article covers the basic chemistry of ferrocene-containing liquid-crystalline polymers which stems from the extensive work of Deschenaux, who essentially pioneered the area. A ferrocene end-capped dendrimer has also been used in carbon monoxide sensing. The actual dendrimer, shown as 19, has 48 ferrocene molecules on the periphery. 

The morphology of ferrocene-containing polymers has been examined in some detail. In the block copolymer of poly(ferrocenyldimethylsilane-b-dimethyl-siloxane) (PFDMS-b-PDMS) with a 1 6 block ratio long rodlike micelles are observed rather than spherical structures in a variety of PDMS-selective n-alkane solvents when the solutions are prepared at or near ambient temperature. The reasons for these observations are subsequently discussed in detail. A further series of mixed ferrocene cobaltocenium dendrimers have been obtained these have been prepared in the reaction of the acyl chlorides of ferrocene and the cobaltocenium PF " with polypropylene dendrimers. ... 

Turrin C-O, Chiffre J, de Montauzon D, Daran J-C, Caminade A-M, Manoury E, Balavoine GGA, Majoral J-P (2001) New chiral phosphorus-containing dendrimers with ferrocenes on the periphery. Tetrahedron 57 2521-2536... 

Turrin C-O, Chifffe J, de Montauzon D, Balavoine G, Manoury E, Caminade A-C, Majoral J-P (2002) Behavior of an optically active ferrocene chiral shell located within phosphorus-containing dendrimers. Organometallics 21 1891-1897... 

Togni and co-workers have used the convergent methodology to link phosphine-containing chiral ferrocene ligands on the cyclophosphazene core to obtain dendrimeric structures of the type 37 (Fig. 21) (201). The reaction with the cyclophosphazene end occurs by the replacement of the P-Cl bond and by the formation of the P-0 bond. The dendrimers contain twelve and sixteen ferrocene moieties respectively. The phosphine units present can coordinate to Rh(I) to afford metallic dendrimers, which have been shown to be excellent catalysts for the enantioselective hydrogenation of dimethyl itaconate. The product... 

Mesomorphic dendrimers containing electroactive units have potential for construction of dendrimer based molecular switches. Deschenaux et al. reported [154] the synthesis and liquid-crystalline properties of a novel dendrimer containing six mesomorphic ferrocene units. Apart from exhibiting a broad enantiotropic smectic A phase as determined by polarized optical microscopy, DSC, and XRD studies, thermogravimetry revealed the excellent thermal stability of the macromolecule. 

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. 

The electrochemical behavior of ferrocene-based polymers [15] and of complexes containing a large, well defined number of ferrocene-type units [16] had already been reported when several groups became interested in dendrimer research. In the past few years several dendrimers of different chemical nature and structure carrying ferrocene-type units in the periphery have been synthesized... 

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