Polyether dendrons

Bis(oxazoline)copper(II) complexes elaborated with polyether dendrons (e.g.,... 

Preparation of Frechet-type Polyether Dendrons and Aliphatic Polyester Dendrimers by Convergent Growth An Experimental Primer... 

FRECHET-TYPE POLYETHER DENDRONS BASED ON 3,5-DIHYDROXYBENZYL ALCOHOL... 

A variety of small convergent polyether dendrons are available commercially from Tokyo Kasei Co., Ltd, see http //www.tokyokasei.co.jp. Unfortunately, at the time of this writing, sales were limited to Japan. Figure 24.1 outlines the preparation of these dendrons to generation four. 

In aqueous media, they assemble into spherical capsules capable of encapsulating Nile Red with remarkably low CMC values (2 x 10 M for G1 and 3 x 10 M for G2). Similarly, the size of the aggregate derived from a related dendron-rod-dendron copolymer, composed of a phenylene vinylene rod capped on each end by amphiphilic polyether dendrons, could be tuned in the melt state by modifying the generation level of the dendron (Fig. 11.28 Lee et al. 2002). 

Figure 11.18 Dendron chain copolymers, (a) A polyether dendron displaying a focal PEG chain and (b) notional representation of the self-assembly of the dendron chain copolymers.

Frechet et al. were able to coordinate polyether dendrons having carboxylate functional groups at the focal point with lanthanide ions up to the fourth generation (Fig. 2.11) [41]. Preparation by straightforward ligand exchange starting from lanthanide triacetates with dendron carboxylates was made possible by the... 

Fig. 4.24 Convergent synthesis strategy for polyether dendrons (according to Fr chet et a. )...

Similar dendritic architectures were formed by fixing polyether dendrons to a terpyridine [132] core unit by means of iron(II) ions [133]. 

For this purpose, a series of Frechet-type polyether dendrons of zeroth-to third-generation containing an NCN-pincer metal complex (M = Pt, Ni) at the focal point of the wedge were prepared [69]. Their synthesis was either... 

Following up this work, the same group recently published the synthesis of hybrid dendritic ligands containing a combination of dendritic chiral DPEN and Frechet polyether dendrons (Scheme 7) [50]. The solubility of these hybrid dendrimers was found to be controlled by the polyether den-dron. Compared with the simple core-functionalized systems displayed in Fig. 21, the hybrid dendrimers showed similar catalytic activity but reduced recyclability. 

Fig. 12 The specific swelling of PS-b-PS/DAP diblock copolymer using complementary Thy-Gx polyether dendron resulted in a series of morphologies (through TEM analysis)...

In 2004, Fan and coworkers synthesized a series of chiral dendrimer hgands bearing a chiral diphosphine Pyrphos at the focal point of the Frechet-type polyether dendrons (Figure 4.6) [43]. The relationship between the primary structure of the dendrimer and its catalytic properties was established in the Rh-catalyzed hydrogenation of a-acetamidocinnamic acid (Scheme 4.5). High enantioselectivi-... 

In order to facilitate recycling of the multiple TsDPEN-functionalized dendrimer catalysts, the same group recently reported the synthesis of a novel form of hybrid dendrimer ligands by coupling polyether dendrons with peripherally TsDPEN-functionahzed Newkome-type poly(ether-amide) dendrimer (Figure 4.28) [90]. The solubility of these hybrid dendrimers was found to be affected by the generation of the polyether dendron. The ruthenium complexes produced were applied in the asymmetric transfer hydrogenation of ketones, enones, imines and activated... 

Later work by Frechet et al. attempted to prepare ABA diblock copolymers using the same methodology [255]. Two polyether dendrons were connected to a dihydroxy functional TEMPO moiety, which was then used to initiate, as well as control, the polymerization of St and formed dumbbell-shaped block copolymers (Scheme 29). The ABA block copolymers were formed however, there was some initial contamination from mono- and bis-dendritic species, which were removed by column chromatography. In addition, XH NMR analysis determined that the purified ABA triblock copolymers were also contaminated with AB diblock copolymers. This was attributed to the persistent radical effect, as well as inherent problems with the mobility of the bulky dendron counter radical, both of which will result in the AB diblock copolymers. Thermal polymerization may also contribute to diblock formation, as the radicals generated will be trapped by the counter radical dendron, but would not contain the initiating dendron moiety. Pure ABA triblock copolymer was obtained after two purification cycles using column chromatography [255]. 

Scheme 29. Functionalization of a polyether dendron using a dihydroxy-TEMPO moiety followed by the formation of ABA dumbbell-shaped block copolymers with St [255]...

Frechet-type polyether dendrons were complexed with Pt for use as SO2 sensor and with Ni for the Kharasch addition of CCI4 to methyl methacrylate [37]. The dendron wedges, when functionalized at their focal point, displayed adequate catalytic activity with easy recovery and good stability. 

Wendland and Zimmerman [31] had remarked in their 1999 paper that what they referred to as cored dendrimers represented a system closely analogous to polymer imprinting, but within the framework of adiscrete single molecule. In their approach, a dendrimer is prepared by the assembly of branched polyether dendrons , around a central core by esterification. The periphery of the dendrimer is fully substituted... 

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