Arene dendrimer

A first generation poly(amido amine) dendrimer has been functionalized with three calyx[4]arenes, each carrying a pyrene fluorophore (4) [30]. In acetonitrile solution the emission spectrum shows both the monomer and the excimer emission band, typical of the pyrene chromophore. Upon addition of Al3+ as perchlorate salt, a decrease in the excimer emission and a consequent revival of the monomer emission is observed. This can be interpreted as a change in the dendrimer structure and flexibility upon metal ion complexation that inhibits close proximity of pyrenyl units, thus decreasing the excimer formation probability. 1H NMR studies of dendrimer 4 revealed marked differences upon Al3+ addition only in the chemical shifts of the CH2 protons linked to the central amine group, demonstrating that the metal ion is coordinated by the dendrimer core. MALDI-TOF experiments gave evidence of a 1 1 complex. Similar results have been obtained for In3+, while other cations such as Ag+, Cd2+, and Zn2+ do not affect the luminescence properties of... 

In a second example, Astruc et al. showed that the redox potential of FeCp(rjb-arene) core dendrimers (molecule 2 is the largest example studied) was similar to smaller molecules.86 The degree of hyperbranching is minimal in this molecule. Moreover, the authors also pointed out that the redox orbital is quite well buried at... 

Such units, together with methyl derivatives of ferrocene and cyclopentadienyl (r 6-arene)-iron(II), [FeCp(r 6-arene)]+, have been extensively used as dendrimer peripheral units, but examples of dendrimers containing metallocene residues both as a core and as terminal units and as a core are also reported.5a,b 17... 

Miller and Neenan succeeded in the very same year in producing the first hydrocarbon dendrimers based exclusively on arene units, also using a convergent synthetic strategy [16] (Fig. 1.7). 

Hardly any purely aliphatic hydrocarbon dendrimers have hitherto been prepared (see also Section 6.2.3.3), probably owing to fundamental synthetic problems in the formation of unsymmetrical C-C bonds. The dendritic hydrocarbons described so far are nearly all made up of condensed or coupled arene or/ and multiply bonded components, which is easier to achieve synthetically. As a rule, such molecules are generally much more conformationally rigid than their aliphatic analogues made up of [CH2]n units. 

Dendrimers from arene and multiply bonded building blocks... 

Fig. 5.18 Photoexcited states of the cyclam dendrimer shown in Fig. 5.17 which are responsible for the observed emission a) before, b) after protonation (schematic). Ar stands for an arene, such as a naphthalene unit, N for the N atom of an amine Ar-Ar-N...

Scanning probe microscopy AFM, STM (arene-rich dendrimers)... 

A range of amphiphilic dendrimers have been reported based on fullerene C60 or a calix[4]arene core with dendritic branches on one side and long aliphatic tails on the other, Figure 14.8. The amphiphiles self-assemble into micelles with the aliphatic chains buried in the micelle core and the more hydrophilic dendritic portion facing out.14... 

For the larger dendrimers incorporating an arene 9 and adamantyl core 10, preliminary membrane filtration experiments showed quantitative retention of the dendrimer-rhodium complexes using a Millipore Centricon-3 membrane and methanol as the solvent [53]. Results on hydrogenation reactions using these dendrimer catalysts in a CFMR have not yet been reported. 

The octasubstituted cored dendrimer 24-FeAr containing 24 cationic aminoarene iron moieties [dendr-( 6-NHC6H4MeFeCp )24] (Cp = rj5-CsMes), i.e. eight tripods, was compared to the analogous mono- and trimetallic amino-arene cationic complexes (resp. 1-FeAr and 3-FeAr, Scheme 9 and Fig. 12) with the same amino-arene iron-sandwich structure for the... 

While investigating the potential to improve on the original method of cascade prepa-rationf59, Moors and Vdgtle 60a constructed a hexaimine dendrimer, which was readily converted to the tris-Co complex (66) in quantitative yield. Lhotak and Shankai[60b have addressed the potential for creation of calix[4]arene-based dendrimers and examined some metal-binding properties for the corresponding oligomers. 

The olefin metathesis between alkenyl groups has been frequently used in recent years to stabilize molecules (e.g., dendrimers [46]) or molecular assemblies [47] by additional covalent connectivities [48] and to synthesize macrocydes or more demanding structures like multiple catenanes [24]. Therefore, this reaction was chosen for the connection of alkenyl residues attached to a calix[4]arene via the urea residues. To avoid complications by ds/trans isomerism around the newly formed double bond, the crude reaction mixture was always hydrogenated before working up (Scheme 5.10). 

Such a self-sorting process can also lead to the formation of structurally well-defined assemblies of the dendrimer type [66], We have demonstrated this in a first example, using the dimerization of tri-ureas 26 derived from triphenylmethanes [67]. It has been shown that this dimerization is independent of the dimerization of tetra-urea calix[4]arenes. It is neither disturbed by tetra-ureas nor does it disturb their dimerization. In addition, Figure 5.20 even shows that the dimerization of rigidified tetra-ureas 25 also occurs independently [68]. 

Pitto-Barry A, Barry NPE, Zava O, Deschenaux R, Dyson PJ, Therrien B (2011) Double targeting of tumours with pyrenyl-modified dendrimers encapsulated in an arene-ruthenium metallaprism. Chem Eur J 17 1966-1971... 

Besides these classical aromatics and polyaromatic hydrocarbons, other very important classes or arene molecules are porphyrins [60, 61], phthalocyanins [61, 62], porphycens [63], calixarenes [64], resorcarenes [64], cydophanes [47], dendrimers [65], elementa-arenes [66], organometallic arene (hexahapto) [67], benzyne (dihapto), and aryl- and benzyl (monohapto) complexes [68], inorganic pyridine and polypyridine complexes [69], fullerenes [70, 71], and... 

I have reviewed, in Chapter No. 12, the activation of arenes by the strongly electron-withdrawing 12-electron fragment CpFe+, isolobal to Cr(CO)3 and Mn(CO)3+, and its application to the synthesis of dendritic cores, dendrons, dendrimers, and metallodendrimers, including molecular batteries. 

Although other deprotonated complexes are sometimes not as stable as [CpFe( 5-QMesCF )], they can be generated and used at low temperature to form the desired bonds [27e]. Using the base and electrophile in excess, the reactions can be carried out at room temperature because the deprotonated species immediately reacts with the electrophile in situ. This kind of deprotonation/alkylation sequence underpins the star and dendrimer construction described herein (vide infra). In this way, the complexes [FeCp( s-arene)][PF6] also act as proton reservoirs [33]. 

A new type of core is used in dendrimer 19 functionalized with 24 [FeCp( -arene)]+ units, thus obtaining a 24+ polycationic species. Cyclic voltammetry in DMF features a single reversible 24-electron reduction wave [61 j. FI NMR spectroscopy indicates that 19 recognizes CC and Br ions, whereas electrochemistry was in this case an ineffective technique. 

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