Dendrimeric structures

Togni and co-workers have used the convergent methodology to link phosphine-containing chiral ferrocene ligands on the cyclophosphazene core to obtain dendrimeric structures of the type 37 (Fig. 21) (201). The reaction with the cyclophosphazene end occurs by the replacement of the P-Cl bond and by the formation of the P-0 bond. The dendrimers contain twelve and sixteen ferrocene moieties respectively. The phosphine units present can coordinate to Rh(I) to afford metallic dendrimers, which have been shown to be excellent catalysts for the enantioselective hydrogenation of dimethyl itaconate. The product... 

As part of a program directed toward the synthesis of dendrimeric structures containing the 1,2,4-triazole moiety, 3,5-dichloro-4(4-methoxyphenyl)-4/7-l,2,4-triazole 69 was reacted with phenol 77 under basic conditions to give the dendron 78 in a yield of 80% (Equation 28) <2006T2677>. 

Fig. 11 In-situ synthesized dendrimeric structure prepared from an aminosilanized surface and multifunctional linkers [38]...

Radial dendrimeric structures can be achieved by choosing a core, e.g., benzylic bromides, because (g) will attach to the core at the bromine location, as schematized in Fig. 2.16. 

Fig. 1 The dendrimer Pheo complex Pi6 (with 16 chromophores) in a solvent box of ethanol molecules (the Pheo molecules are shown in red, the dendrimeric structure is displayed in green). Respective MD runs comprise 272613 atoms with 78 per Pheo, 310 of the dendrimeric structure and with 2895 ethanol molecules.

Fig. 3 Flat dendrimeric structure of Ps (left) and of Pi6 (right, the red (light grey) R symbolize the covalently bound Pheo, Fig. 2).

It has been observed that tbe conductivity was actually higher than the conductivity reported for pure diimide anion radical salts, because dendrimeric structures may produce 7t-s lac king formation in three dimensions, a structural feature differing from the usual one-dimensional structures of small molecular stacks. 

Both, esters and tertiary amino groups are tolerated, giving rise to products 6f and 6h which are useful as centers for dendrimeric structures. The pentakisalde-hyde 6g was obtained from 4-bromobenzaldehyde protected as the ethylene glycol acetal. Attempts to use heterocyclic bromides for arylation were hitherto unsuccessful. 

Many octupolar chromophores have threefold symmetry based around 1,3,5-substituted benzene or triazine cores an example [66] is shown in Fig. 11.8 and this type of chromphore has more recently also been used in extended dendrimeric structures [67]. However, other non-centrosymmetric cores have been used, for example, four-coordinate tetrahedral tin centers [68],... 

Functionalized polymers with comb-like, rotaxanic-, and dendrimeric structures [H. Ritter, GITFachz. Lab. 1994, 38(6), 615-619]. 

This group was successful in proliferating the dendrimeric structures out to generation = 3 to give molecular weights of greater than 14000. All dendrimer... 

The high degree of completion and selectivity and the high yields make the hydrosilation reaction an ideal candidate for the bnildup of dendrimeric structures. The combination with allylation, vinylation, and alkynylation reactions provides very efficient syntheses of carbosUane dendrimers (Scheme 8). ... 

Most carbohydrates contain ethane-1,2-diol fragments, therefore they were also successfully included into crown ether macrocycles [313]. Polyvalency of carbohydrates was studied based on dendrimeric structures which were generated on successful glycosylations of highly branched polyethylene glycol units [314]. 

Chiral auxiliaries have also been included in dendrimeric structures (cf. Section 3.2.2). Two general strategies are possible for that purpose. Thus, multiple auxi-... 

The construction of a dendrimeric structure, rather than a linear one, requires a point of branching on the connecting ligand. This is provided with the connecting ligand l,3,5-tris(2,2 6,2"-terpyridin-4 -yl)benzene... 

Two-Photon Absorption Properties of Fluorene V-Shapes and Dendrimeric Structures... 

Particular examples of V-shape and dendrimeric structures are represented in Fig. 38. A V-shape molecule is noted Yn and consists of two identical 9,9-dihexylfluorene oligomers of size n, substituted in meta position on a benzene core. A dendrimer is noted DnGg and consists of identical 9,9-dihexylfluorene oligomers of size n organized around benzene cores, on which they are substituted in meta position. Each benzene core bears three oligomers and g represents the dendritic generation. 

Fig. 41 Correlation between experimental and calculated one- and two-photon absorption properties of oligomeric, V-shape and dendrimeric structures. (A) One-photon absorption energy (cm ). (B) Oscillator strength per monomer. (C) Two-photon absorption energy (cm ). (D) Two-photon absorption strength per monomer...

Enhancement of two-photon cross-sections by two-dimensional and three-dimensional arrangements of monomers has been demonstrated with fluorene V-shapes and dendrimeric structures. Such multidimensional structures lead to lower two-photon absorptions than Hnear oUgomers, but they have better one-photon transparencies. An accurate calculation of large exitonic systems is obtained by diagonalizing the Hamiltonian operator on a reduced basis set. 

Step-by-step growth of phosphazene chains can be achieved and the five-phosphorus chain can be converted into a dendrimeric structure. The fascinating chemistry of dendrimeric phosphors-nitrogen molecular architecture has been reviewed. ... 

Non-covalent drug encapsulation In this method, the drug is physically encapsulated in a dendrimeric structure by virtue of a micellar structure. Although it is relatively easy to produce a drug delivery systan with this approach, the drug release is often uncontrolled. ... 

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