Dendrimer ferrocene-type units

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... 

Dendrimers Containing Ferrocene-Type Units at Their Periphery By exploiting efficient synthetic approaches (dendrimer growth strategy pioneered by Newkome18 and click chemistry), several dendrimers containing 27 (compound 1, Fig. 6.1), 54, 81, and 243 ferrocene units in their periphery have been... 

Because of the peculiar electrochemical behavior (a single cyclic voltammetric wave characterized by remarkable electrochemical and chemical reversibility), dendrimers terminated with ferrocene-type units can be profitable used as exoreceptors, provided that they contain a group able of interacting through noncovalent bonds with the species to be recognized. Furthermore, such a group has to be located near the ferrocene units to sufficiently perturb their electrochemical response as a consequence of the interaction with the guest species. 

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. 

Decafunctionalization of ferrocene with allyl units has been used to construct a dendrimer (7) having a ferrocene-type core and ten ferrocene-type... 

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... 

Poly(propylene amine) dendrimers containing 4, 8, and 64 amidoferrocene peripheral units have also been incorporated in the highly ordered channels of mesoporous silica obtaining a novel type of redox-active materials. One significant feature of these new composite materials is that the ferrocene units of the guest dendrimers are easily accessible to electrochemical oxidation, as revealed by studies carried out in MeCN solutions by using Pt electrodes derivatized with films of such dendrimer-matrix complexes.33... 

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. 

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