Dendritic substitution

In a second variant, growth of metallodendrimers can proceed via complexa-tion of a metal cation with dendritic ligands. In this way, Balzani, Vogtle, De Cola et al. [34] obtained photoactive ruthenium complexes by spontaneous self-assembly of the components starting from various dendritically substituted bi-pyridines. Fig. 2.9 shows a representative example (see Sections 5.1.2.3 and... 

E.g. dendritically substituted photoactive metal complexes Review V. Balzani, P. Ceroni, A. Juris, M. Venturi, S. Campagna, F. Puntoriero, S. Serroni, Coord. Chem. Rev. 2001, 219-221, 545-572. 

Fig. 4.68 Circular dichrograms of dendritically substituted atropines (1) and quinines (2) each of zeroth to second generation (according to Vogtle et al.)...

Fig. 6.26 Molecular tweezers 1 as host compound and dicationic, dendritically substituted viologen guest compounds (3 and 4) of different generation numbers (according to Balzani, Klarner, Vogtle et al.)...

In addition, chiral dendrimers (see Section 4.2) can be resolved with the aid of HPLC into their enantiomers, if the silica gel material used as stationary phase has optically active substances bound to its surface [9]. Since the chiral stationary phase (CSP) [10] undergoes different intensities of interaction with the enantiomeric dendrimers, they are retained to different degrees, and in the ideal case two completely separated (baseline separated) peaks are obtained. This separation technique was successfully applied inter alia to racemic mixtures of planar-chiral dendro[2.2]paracyclophanes, cycloenantiomeric dendro[2] rotaxanes, topologically chiral dendro[2]catenanes [11] as well as topologically chiral, dendritically substituted molecular knots (knotanes) [12] (Section 4.2.3). 

There are several remarkable features of these immobilized salens, notably the fact that the dendritic branches do not appear to decrease the catalytic activity with respect to the complexes in solution. Moreover, the reactions with dendritic catalysts incorporated in polystyrene gave products of essentially the same enantiopurity as those observed in homogeneous solution, with the dendritically substituted or with the original Jacobsen-Katsuki complexes. Some of the Mn-loaded beads were stored for a year without loss of activity. Especially, the biphenyl- and acetylene-linked salen polymers gave Mn complexes of excellent performance, which after ten catalytic rims showed no loss of enantioselectivity or degree of conversion. 

Very recently, Seebach and coworkers reported a different approach for the immobilisation of TADEXDL derivatives. Dendritically substituted TADDOLs (90) were co-polymerised with styrene in a suspension polymerisation procedure and subsequently transformed into their titanium complexes. 

A polymer-bound catalyst of type 86 gave also quantitative conversion and 96% e.e. whereas the reaction rate was much smaller. The dendritically substituted TADDOLate seems more accessible for the substrates than the traditionally linked derivatives. 

Also, while the dendritic TADDOL polymer gave a somewhat slower tita-nate catalyst for the above mentioned reaction than the simple copolymerized TADDOL, a unique feature emerged with the former Scheme 14) the monomeric, dendritically substituted Ti-TADDOLate was found to be slower than the polymeric one (under diffusion-controlled conditions) Thus, our investigations on chiral dendrimers (review [84]) have fertilized the TADDOL work, and they may lead to a new type of high-performance polymer-bound reagents, beyond the TADDOLs. 

B.E.T Time-to-Failure Model for Dendrites. Substituting Eqs. 6 and 9 into Eq. 8, we have,... 

All the fullerene-containing dendrimers reported to date have been prepared with a Cgo core but never with fullerene units at their surface or with Cgg spheres in the dendritic branches. We have recently started a research program on the synthesis of dendrons substituted with fullerene moieties. These fulleroden-drons are interesting building blocks for the preparation of monodisperse fullerene-rich macromolecules. In addition, they are also amphiphilic compounds capable of forming stable Langmuir films at the air-water interface. 

To increase efficiency and ease of product separation from reaction mixtures, we also prepared styryl-substituted TADDOL-dendrimers that can act as crosslinkers in styrene suspension polymerizations, and thus lead to beads with intimately incorporated TADDOL sites [106,107]. Due to the presence of the con-formationally flexible dendritic spacers between the chiral ligand and the poly-... 

Following a procedure previously employed for simple styryl TADDOLs [105], dendritic styryl-substituted TADDOLs were copolymerized with styrene... 

K. Aoi, K. Tsutsumiuchi, A. Yamamoto, and M. Okada, Globular carbohydrate macromolecule sugar balls 3. Radial-growth polymerization of sugar-substituted x-amino acid N-carboxyanhydrides (glyco-NCAs) with a dendritic initiator, Tetrahedron, 53 (1997) 15415-15427. 

In a separate study, we have reported the use of aliphatic ether dendrimers as a solubilizing platform for the preparation of soluble oligothiophenes with minimal main-chain substitution (Figure 7.16B) [67], Aliphatic ether dendritic blocks... 

The approach outlined in Scheme 7 was directly applied to the synthesis of dendritic poly(isoprenes), by simple substitution of isoprene for the styrene monomer [29]. Two coupling agents were examined in this case, namely CDMSS and 2-chlorodimethylsilyl-l,3-butadiene. Other interesting architec-... 

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