Ferrocenyl-functionalized dendrimers

Peripheral ferrocenyl-functionalized dendrimers are in fact one of the most common type of metallodendrimers synthesized today. Due to the chemical and thermal stabilities of this kind of metallocene, formation of the intended dendrimer-supported metallocene complex can be performed in a single reaction step the metallocene fragment is introduced onto the surface of a (commercially available) dendrimer as the final construction step [56,57]. 

Fig. 9. Pseudorotaxane-terminated dendrimers ferrocenyl-functionalized polypropylimine...

NIL patterns were also used for the assembly of nanoparticles via supramole-cular host-guest interactions.95 The NIL-patterned substrate was functionalized with CD SAMs via a three-step synthesis process. The fabrication of 3D nanostructures was achieved by the alternating assembly of multivalent guest-functionalized dendrimers and CD-fnnctionalized Au nanoparticles.88 This methodology can be applied to various nanoparticles, regardless of their size and core material. For instance, CD-functionalized silica and polystyrene nanoparticles were adsorbed onto NIL-patterned CD SAMs with preadsorbed guest-fnnctionalized dendrimers.60 92 Recently, Huskens et al. demonstrated the supramolecular LbL assembly of 3D multicomponent nanostructures of nanoparticles by alternating assembly steps of complementary ferrocenyl-functionalized silica nanoparticles and different kinds of host-fnnctionalized nanoparticles (see Fig. 13.8).66... 

A phthalocyanine core was functionalized with four, eight, and 16 ferrocenyl units (compounds 49-51) [67]. Cyclic voltammetry experiments in DMF or CH2CI2 showed the presence of many quasi-reversible waves. All the ferrocenyl units behave independently, giving rise in all three compounds to a single oxidation wave, which is accompanied by one or two oxidation and by two or three reduction processes due to the phthalocyanine rt-system. For 51, the presence of a stripping peak indicates precipitation of the oxidized product in CH2CI2, as often observed in ferrocene-functionalized dendrimers (see Section 9.4.1). 

Figure 5. Structures of some functional dendrimers A. Dendrimer with lanthanide ion as the central core with dendrons as ligands B. Dendrimer based on metal complex C. Silicon-based ferrocenyl dendrimer and D. Dendrimer with zinc-porphyrin core...

In 2007, using a similar type of phosphorus dendrimer support, the same group synthesized a series of functionalized dendrimers bearing chiral ferrocenyl... 

Summary Starting with octa(vinyldimethylsiloxy)octasilsesquioxane (QsMs ) as the central core molecule, allyl- and chloro-substituted dendritic macromolecules have been prepared by the divergent route. The sequence of hydrosilylation with dichloro-methylsilane followed by allylation of all Si-Cl groups with CH2=CHCH2MgBr, was used for building up each generation (G1-G4). We also functionalized the dendrimer periphery via hydrosilylation reaction of allyl-functionalized dendrimers with dimethylsilylferrocene. These novel molecules have been characterized by H/ C/ Si-NMR, IR spectroscopy and MALDl-TOF spectrometry. The ferrocenyl-substituted molecules have also been analyzed by cyclovoltammetry. 

The research group of Van Leeuwen has focused on catalysis at the core of a carbosilane dendrimer in an effort to be able to control stereoselectivity [10]. To this end, a ferrocenyl diphosphine backbone was functionalized with different generations of carbosilane dendrons producing a series of dendrimer phosphine ligands with an increasing steric demand (see 7 for an example, Scheme 6). In situ... 

When the catalyst is located in the core of a dendrimer, its stability can also be increased by site-isolation effects. Core-functionalized dendritic catalysts supported on a carbosilane backbone were reported by Oosterom et al. 19). A novel route was developed to synthesize dendritic wedges with arylbromide as the focal point. These wedges were divergently coupled to a ferrocenyl diphosphine core to form dppf-like ligands (5). Other core-functionalized phosphine dendritic ligands have also been prepared by the same strategy 20). 

Reversible attachment of nanostructures at molecular printboards was exemplified by the adsorption and desorption of CD-functionalized nanoparticles onto and from stimuli-responsive pre-adsorbed ferrocenyl-dendrimers at a CD SAM (Fig. 13.7).65 Electrochemical oxidation of the ferrocenyl endgroups was employed to induce desorption of the nanostructure from the CD SAM. An in situ adsorption and desorption of ferrocenyl dendrimers and CD-functionalized Au nanoparticles (d 3 nm) onto and from the molecular printboard was observed by a combination of surface plasmon resonance spectroscopy (SPR) and electrochemistry. Similar behavior was observed when larger CD-functionalized silica nanoparticles (d 60 nm) were desorbed from the surface with the aid of ultrasonication. 

Figure 13.7 The adsorption and desorption of CD-functionalized nanoparticles onto and from a CD SAM with ferrocenyl dendrimers as a reversible supramolecular glue.

Ferrocenyl diphosphine core-functionalized carbosilane dendrimers have been prepared as ligands for homogeneous catalytic reactions applied in a CFMR by Van Leeuwen et al. [20,21,67,68]. The syntheses of these dppf-like ligands (Go-G2)-17 were performed using carbosilane dendritic wedges with an aryl bromide as focal point. These wedges were coupled to the core via quenching of the lithiated species with ferrocenyl phosphonites (Scheme 11). 

Figure 11.3 Cyclic voltammogram of the 243-ferrocenyl dendrimer ( 243-Fc ) in CH2CI2 solution containing 0.1 M [u-Bu4N][PF6] (a) in solution (10-4M) at lOOmV s-1 on the Pt anode (b) Pt anode modified with 243-Fc at various scan rates, dendrimer-free clear CH2CI2 solution. (Inset intensity as a function of scan rate the linearity shows the expected behavior of a modified electrode with a fully adsorbed dendrimer.)...

PAM AM-based dendrimers partially functionalized with various degrees of ferrocenyl moieties have also been used... 

A PAMAM dendrimer (G4) monolayer partially functionalized with both ferrocenyl and biotinamidocaproate residues was constructed on a Au electrode and utilized as a biosensor for avidin on the basis of its binding to biotin [110]. The electrochemical response was generated by the oxidation of free glucose catalyzed by GOx present in the electrolyte. The magnitude... 

Figure 36 Scheme for attachment of a ferrocenyl dendrimer, 137, to a gold surface functionalized with j8-CD, 138, and subsequent release upon oxidation of the ferrocenyl groups to ferrocinium groups, 139, which do not complex significantly in jS-CD. 

The synthesis and properties of star polymers and dendrimers functionalized with ferrocene units has attracted a great deal of attention. The synthesis of high-generation dendrimers functionalized with chiral ferrocenyl units in their structures has been reported. The chiroptical properties of this class of dendrimer was dependent on the number of ferrocenyl groups and their chemical environment, but not on their position within the dendrimer. Deschenaux has reported the synthesis of hquid crystalline ferrocene-based polymers prossessing an enantiotropic smectic A phase. Ferrocene-functionahzed cyclic siloxane (29) and silsesquioxane branched polymers have also been reported. A hyperbranched polymer with a cubic silsesquioxane core was used to mediate the electrocatalytic oxidation of ascorbic acid. 

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