Dendritic bromides

Wooley et al.234 reported the first dendrimer— fullerene hybrid, 165 (Scheme 21), via the alkylation of a prederivatized fullerene diphenol, 166, with the dendritic bromide 6. Because of purification problems related to impure fullerene starting material, Hawker et al. later investigated the direct cycloaddition235 of a fourth generation azide-functionalized Frechet-type dendron, 167, with Ceo- This dendritic fullerene, 168, could be easily isolated by flash chromatography and showed a significant increase in solubility over the parent fullerene. Avent et al. reported a similar cycloaddition of poly(phenylacetylene) dendrons bearing a focal tosylhydrazone functionality.236... 

An alternative approach developed by Schluter and co-workers involves the attachment of convergently prepared dendrons onto a preformed, functional linear polymer. This was first attempted by the Williamson ether couplings between dendritic bromides and pendant hydroxyl groups on poly([ 1.1.1]-propellane)412 and polyp-phenylene).413 Nearly quan-... 

Figure 2. Overlay of SEC traces for the dendritic bromides from [G-0] to [G-6] with nominal molecular weights shown.

J.M.J. Frechet (C. J. Hawker, 1990) replaced the divergent synthesis by a convergent growth of a dendritic polymer. The repeatedly employed monomer, 5-hydroxymethyl-l, 3-benzenediol, was 1,3-O-dibenzylatcd with 3,5-bis(benzyloxy)benzyl bromide. The resulting benzyl alcohol containing 7 benzene rings was converted to the benzyl bromide which was... 

Fig. 22. The influence of different configurations in the dendritic branch bromides 61 and 62 on coupling with the same chiral core 54 [88,90]...

A mixture of the selected dendritic benzyl bromide (for example 9, 31 mmoles),... 

Kenawy 64) immobilized ammonium and phosphonium peripheral functionalized dendritic branches on a montmorillonite supported chloromethylstyrene/methyl methacrylate copolymer (74-75). These polymer/montmorillonite-supported dendrimers were used as phase transfer catalysts (PTC) for the nucleophilic substitution reaction between -butyl bromide and thiocyanate, cyanide, and nitrite anions in a toluene or a benzene/water system. These PT catalysts could be recycled by filtration of the functionalized montmorillonite from the reaction mixture. Generally,... 

Wang etal. [213] investigated the effect of bismuth ion and tetrabutylammonium bromide (TBAB) on the dendritic growth of zinc in alkaline zincate solution on Zn electrode. It was found that this growth is inhibited by the synergistic effect of Bi(III) and TBAB at higher overpotentials. The zinc electrodeposits... 

However, these bifunctionalisation methods are comparatively laborious and applicable only in special cases, since the monofunctionalisation step is limited to substrates possessing an additional coupling site in protected form for the second functional unit. A more versatile method of local bifunctionalisation, which has no need of a deprotection step and also utilises commercially available dendrimer scaffolds, consists in the functionalisation of POPAM dendrimers bearing amine terminal groups with sulphonyl chlorides and subsequent substitution of the sulphonamide proton with other sulphonyl chlorides [63] or with alkyl- or (dendritic) benzyl bromides [64] (see Fig. 3.13). 

Subsequent substitution of the sulphonamide proton with other sulphonyl chlorides or with alkyl- or (dendritic) benzyl bromides. 

Information about transmission of chirality in dendrimer molecules also came from various generations of dendrimers derived from optically active alkaloids. Starting from atropine or quinine, corresponding ammonium salts 1 or 2, respectively, of up to the third generation were synthesised by quatemisation at the aliphatic nitrogen with Frechet-type dendritic benzyl bromides (Fig. 4.67) [22]. 

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). 

---