Fluorinated dendrimer

Pitois, C., Hult, A., and Lindgren, M. (2005) Lanthanide-cored fluorinated dendrimer complexes synthesis and luminescence characterization. Journal of Luminescence, 111, 265. 

It is noteworthy that the fluorine content differences can be generated by attaching either similar reaction domains to different fluorous tags [13] or the same fluorous tag to reaction domains of different sizes (Figure 7.1). For example, a class of fluorinated dendrimers with the same fluorinated domain (fluorous tag), G0-G3, can be separated from each other by fluorous HPLC because of the over 10% differences in their fluorine content (Figure 7.3). Comparing the HPLC profile of dendrimers on the fluorous phase with that on normal phase and reverse phase, it is clear that fluorous HPLC gives the best separation. 

Figure 7.3 Fluorous HPLC separation of fluorinated dendrimers. (a) Structure of fluori-nated dendrimers C0-C3 and (b) HPLC profile of fluorinated dendrimers on fluorous, normal phase, and reverse phase.

Stability, and complex formulation procedures, a class of dendritic fluorinated MRl agents, G0-G3, were developed (Figure 7.3). These fluorinated dendrimers, G0-G3, of different sizes are perfect MRl agents for screening, and G2 was identified as a stable and rapidly excreted MRl agent. Here, a fluorous-assisted synthesis of the fluorinated dendrimer G2 and a FMS of four fluorinated dendrimers are selected as examples to illustrate how fluorous synthesis works. 

The synthesis of the fluorinated dendrimer G2 was first carried out (Scheme 7.4) in a sequential manner which involved repetitive deprotection/condensation cycles. 

To carry the synthesis one step further, a FMS of four fluorinated dendrimers was then carried out. As mentioned above, it is feasible to rapidly synthesize four fluorinated dendrimers with dramatically reduced synthetic steps and convenient purification of the intermediates and final products through fluorous methods (Scheme 7.5). 

Scheme 7.5 Fluorous mixture synthesis of fluorinated dendrimers.

Another possibility to find out more about the structure of these dendrimers was chosen by incorporating fluorine atoms. The use of 19F-NMR spectroscopy offered an additional tool to study the conformation of the dendrimer, especially with the fluorines attached close to the stereogenic centers [91 ]. Following our previously developed methods [92], fluorine-containing 1st- and 2nd-genera-tion chiral dendrimers such as 76 were synthesized (Fig. 24). 

Fig. 24. Fluorine-containing 2nd-generation dendrimer 76 and 19F-NMR spectrum showing the different chemical environment in the two dendrimer-layers [91]... 

Ribaudo F, van Leeuwen PWNM, Reek JNH (2006) Supramolecular Dendritic Catalysis Noncovalent Catalyst Anchoring to Fimctionalized Dendrimers. 20 39-59 Richmond TG (1999) Metal Reagents for Activation and Functionalization of Carbon-Fluorine Bonds. 3 243-269... 

Scheme 11. Palladium catalyzed synthesis of fluorinated polyphenylene dendrimers...

The bulky methylaluminoxane anion stabilizes the coordinatively unsaturated metal cation. Stabilization by noncoordinating anions such as carbosilane dendrimers is also viable.571 Aluminoxanes, however, are required to be used in large excess to be effective. Alternatively, the active catalyst can also be prepared by reacting a metal dialkyl with fluorinated boranes, borate salts or aluminate salts. 

Recently fluorinated chains were also attached to amine based dendrimers, like PPI and poly(amido amine) (PAMAM), by means of ionic self assembly with semiperfluorinated alkanoic acids (Fig. 71, 216, 217). All dendrimer complexes 216 with perfluorinated alkanoic acids show SmA phases except the fifth generation dendrimer which shows a Colrec phase [378]. Also semiperfluorinated 4-alkoxybenzoic acids 217 [379] and mixed systems combining fluorinated and nonfluorinated alkanoic or benzoic acids (216, 217) have been reported [379-381]. In most cases layer structures (SmA) and for higher generation dendrimers also modulated SmA phases (Colrec phases) were observed. The layer thickness of the SmA phases of the mixed complexes 216 depends on the ratio of fluorinated and non-fluorinated acids, where smaller d values were observed for dendrimers with low Rp-content for Rp-rich dendrimers the more rigid Rp-chains provide... 

Fig. 71 Examples of PPI based molecular (215) and supramolecular third generation dendrimers (216-217) with fluorinated chains and mixed RF/RH-chains [377-381]...

Fig. 80. Fluorinated dendrons and corresponding lanthanide dendrimer of first generation.

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