Frechet-type dendritic wedges

Scheme 5.13. The rate of reaction of Frechet-type dendritic wedges with poly(ethylene oxide) [PEO] and poly(ethylene glycol) [PEG] was determined to increase dendron generation and block length increased.

A carbosilane dendrimer decorated with Ru(bpy)3 units has been prepared and electrochemical studies reported. " " Newkome has reported first-generation stars with surface polyoxometallate decoration. " A silsesquioxane core has been functionalized and a series of dendritic systems bearing Frechet-type dendritic wedges and pendant Ru(tpy)(bpy)2 decoration has been described. Up to 32 of these units containing didentate tpy ligands have been attached to the surface. ... 

Dendrimer based-BINAP polymers have been prepared from 124. A series of soluble dendritic mono-BINAP ligands with Frechet-type polyether wedges like 127 and dendritic poly-BlNAP ligands like 128 have been reported Ruthenium complexes of both classes of dendrimer were prepared and found to be comparable both in catalytic activity and enatioselectivity as homogeneous BINAP analogs in asymmetric hydrogenation reactions. 

In one of several important studies on dendronized polymers [4c, 4d]. Schluter and coworkers explored the stiffening of polystyrene chains through the incorporation of Frechet-type dendrons as side chains [28, 29]. While the G-l and G-2 dendrons were not sufficiently bulky to effectively stiffen the polystyrene chain, the G-3 dendron provides enough steric bulk to force the hybrid polymer into adopting a cylindrical shape in solution [28b], In a complementary study, Neubert and Schluter demonstrated that adding charges to the dendritic wedges leads to an expansion of the chains of the hybrid copolymer in aqueous solution [29],... 

Stoddart and co-workers have made use of Frechet-type dendrons as dendritic stoppers for self-assembled [n]rotaxanes [65]. The solubility enhancement that results from incorporating dendritic wedges at the termini facilitated the purification of these materials by column chromatography despite the polycationic nature of their bipyridinium backbone. Again, the dendritic wedges did not alter the electrochemical characteristics of the viologen subunits. Flowever, the enhanced solubility resulting from the presence of the dendritic components en-... 

Liu et al. 43) prepared chiral BINOL ligands bearing dendritic Frechet-type polybenzyl ether wedges ((J )-41-(J )-44), which were assessed in enantioselective Lewis acid-catalyzed addition of Et2Zn to benzaldehyde. 

This type of Au NCDs can also be obtained using similar Frechet-type polyaryl ether dendritic disulfide wedges from generations 1 to 5 by the reduction of HAuCfi phase-transferred into toluene in the presence of the dendrons. analysis shows that the NCDs are small (2.01-3.93 nm) and not very monodisperse [130]. 

Schliiter et alJ65,66 have recently used rod-shaped polymers1673 such as poly(p-phe-nylene)s and poly([l.l.l]propellane)s as cores for the attachment of convergently generated dendrons. These new branched macromolecules possess a rigid backbone wrapped with structural wedges, which become increasingly more dense toward the outer cylindrical surface. The Pd-catalyzed copolymerization of dibromobiphenyl derivatives with the Frechet-type ethereal dendrons with a substituted aryl diboronic acid afforded the dendritic coated poly(p-phenylene) rod. 

Scheme 1. a) Frechet-type [18] dendritic wedges used as conical or fan-like building units b) schematic image of a polymer chain that bears dendritic side groups [27J. 

Recently, Fan et al. reported a series of chiral BINOL-cored dendrimers via substitution at the 3,3 -positions of the binaphthyl backbone by different generations of Frechet-type dendrons (Figure 4.18) [73]. The proximity of the dendritic wedges to the catalytic center is expected to induce catalytic properties different from BINOL. In the absence of Ti(Oi Pr)4, the chiral dendrimer ligands showed much... 

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