All-hydrocarbon dendrimer

Figure 11.3 Chemical structures of the (a) arborol dendrimer and (b) water-soluble, all-hydrocarbon dendrimer.

A unique class of structures referred to as iptycenes has recently been reported by Hart et al. [129-131]. These architectures represent the first examples of all-hydrocarbon dendrimer prototypes. Starting with either benzene or triptycene as the initiator core, branch junctures were constructed in situ by Diels-Alder adduct formation to give the heptaiptycene (A) and the nonaiptycene (tri-... 

The versatility in the construction of dendritic macromolecules, and the unique advantages offered by a controlled step-wise approach, are perhaps best illustrated by the all hydrocarbon family of arylacetylenic dendrimers devel-... 

Hardly any purely aliphatic hydrocarbon dendrimers have hitherto been prepared (see also Section 6.2.3.3), probably owing to fundamental synthetic problems in the formation of unsymmetrical C-C bonds. The dendritic hydrocarbons described so far are nearly all made up of condensed or coupled arene or/ and multiply bonded components, which is easier to achieve synthetically. As a rule, such molecules are generally much more conformationally rigid than their aliphatic analogues made up of [CH2]n units. 

Scheme 5.10. Employment of Suzuki coupling leads to the construction of all aromatic hydrocarbon dendrimers.

Micellane series registered trademark (University of South Florida) descriptor of the all-hydrocarbon based dendrimers MRI magnetic resonance imaging NBS N-bromosuccinimide... 

A unique dendrimer series possessing an all-hydrocarbon interior and up to 36 surface carboxylic acid groups has exhibited very interesting unimolecular micelle properties. These products have been shown to form host-guest complexes with various hydrophobic guest molecules. Newkome refers to these products as micellanes [137, 138]. 

More recent work has shown that this GDS strategy may be used to produce all hydrocarbon, poly (styrene) type dendrimers that the authors refer to as being derived from arborescent grafting [181]. Hybridization of Starburst/Cascade architecture with Comb-burst dendrimer structure, has been reported by our group very recently [182], thus clearly establishing the vast breadth and scope of GDS techniques for the construction and design of nanoscopically sized macromolecules (i.e., 1-100 nm in diameter). 

Fig. 2 Early t/is-terminated, branched architectures (i.e.. 3 and 4) were described as possessing micellar architecture and character and study of the properties of nuinerous encapsulated molecular guests proved the micellar character of the first, all-alkyl hydrocarbon dendrimer 7.

Using the dendrimer route, it is possible to prepare supported catalysts not available via traditional routes. Dendrimer derived Pt-Au catalysts having compositions within the bulk miscibility gap can be prepared on several oxide supports. For all the supports studied, the bimetallic catalysts exhibited synergism with respect to mono- and cometallic catalysts for the CO oxidation and hydrocarbon NOx SCR reactions. The bimetallic Pt-Au catalysts also showed evidence of exchanging surface and subsurface atoms in response to strongly binding ligands such as CO. 

Koch [82] and optimized further by us. The polyphenylene 28, which represents a first-generation dendrimer, forms 28 new bonds yielding the planar polycyclic aromatic hydrocarbon 56 (Scheme 23). Owing to its extreme insolubility in all common solvents, PAH 56 is characterized by laser desorption mass spectrometry based on its M+ peak at miz =1621. 

The molecular area per alkyl chain is approximately 0.25 nm which is a value often found in X-ray structures of hydrocarbon chains. These results indicate that the higher generation dendrimer have a more flat conformation because in that case all the attached chains can count for the observed molecular area. 

Finally, anionic surface dendrimers have been constructed as balloons attached along a Merrifield resin backbone.48 Using an elaboration method based on the diethyl malonate and triethyl methanetricarboxylate procedures previously described,61 dendrimers bearing double and triple branching hydrocarbon arms were prepared with carboxylate termini. These dendrimers are insoluble in all ordinary solvents and serve as high-capacity cation-exchange materials. 

---