Multi-dendron dendrimers

Abstract Enantioselection in a stoichiometric or catalytic reaction is governed by small increments of free enthalpy of activation, and such transformations are thus in principle suited to assessing dendrimer effects which result from the immobilization of molecular catalysts. Chiral dendrimer catalysts, which possess a high level of structural regularity, molecular monodispersity and well-defined catalytic sites, have been generated either by attachment of achiral complexes to chiral dendrimer structures or by immobilization of chiral catalysts to non-chiral dendrimers. As monodispersed macromolecular supports they provide ideal model systems for less regularly structured but commercially more viable supports such as hyperbranched polymers, and have been successfully employed in continuous-flow membrane reactors. The combination of an efficient control over the environment of the active sites of multi-functional catalysts and their immobilization on an insoluble macromolecular support has resulted in the synthesis of catalytic dendronized polymers. In these, the catalysts are attached in a well-defined way to the dendritic sections, thus ensuring a well-defined microenvironment which is similar to that of the soluble molecular species or at least closely related to the dendrimer catalysts themselves. 

Alternatively, dendrimers may be synthesized directly by our original II Divergent Core Proliferation method. This method may involve the exponential covalent assembly of monomer units around a multi-valent core to produce branch cells in situ or it may involve the direct use of pre-formed branch cell reagents. In either case the resulting covalent structure consists of precise numbers of dendrons organized around the initiator core. 

Finally, a two stage dendrimer synthesis [117] was demonstrated by preconstructing a lower generation dendrimer using the convergent dendron/diver-gent anchor method as shown in Scheme 13. Secondly, coupling pre-formed dendrons to this multi-valent hyperbranched/dendrimer core produced a... 

Star-shaped multi-porphyrin arrays have been constructed to mimic energy funneUng in photosynthesis. These dendrimers contain free-base porphyrin cores (Pfb) connected to four dendrons consisting of 1,3, or 7 zinc-metallated porphyrins (Pzn) embedded in an organic matrix coimected by ether linkages (Scheme 21) [70,71]. The periphery consists of methoxy-terminated poly(aryl ether) dendrons. For comparison, cone-shaped arrays consisting of Pfb cores monosubstituted with Pz dendrons were also synthesized. 

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