Cyclophosphazenes dendrimers

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... 

This methodology has been repeated to give dendrimers up to the third generation. A variation of this strategy consists of utilizing the phosphine Ph2PCH2OH in a Mannich-type reaction with the terminal NH group on the cyclophosphazene in the second step of the dendrimer... 

The Saga of Spherical Dendrimers On the Scent of Cyclophosphazenic Dandelions [J.-F. Labarre, F. Sournies, F. Crasnier, M.-C. Labarre, C. Videl, J.-P. Faucher, M. Graf-feuil, Main Group Chem. News 1995, 3, 4-8]. 

Among inorganic heterocycles, perhalogenated cyclic phosphazenes occupy a very prominent place as the precursors for polyphosphazenes whose properties can he tuned by changing the substituents on the phosphorus sites (J). The heterocycles, as such, provide a robust framework for building a variety of novel molecules that have high thermal stability and flame retardancy, and have also been used recently to prepare a variety of dendrimers (2). The most widely studied among these are the perchlorinated cyclophosphazenes. Their syntheses reactions, properties, and application potential have been well documented a, 3-7). 

A second strategy is to place mnltiple chiral Josiphos-type (329) units along the exterior of dendrimers, and snccessful apphcations for rhodium-catalyzed asynunetric hydrogenation ntUize cores composed of benzene-l,3,5-tricarboxyhc acid esters (381), adamantane-l,3,5,7-tetracarboxylic acid esters (382), and cyclophosphazenes see Phosphazenes) (383)." Enantioselectivities are excellent and these dendrimeric materials can be recovered by filtration throngh a nanofiltration membrane. 

Togni et al.169 synthesized dendrimers using a cyclophosphazene core and 16 peripheral chiral ferrocenyl ligands (Figure 10.13). The periphery of these ferrocenyldiphosphine metallo-dendrimers was decorated with [Rh(COD)2][BF4] to instill the desired catalytic properties necessary to reduce dimethyl itaconate. These metalloconstructs showed 98% ee, which compared well with the 99% ee obtained with monomeric Rh-based josiphos catalyst. 

XU) or resorcinarenes, cyclophosphazenes (XLIII), gluddic precursors, aliphatic polyols (XXXI, XXXII), adamantane-based cores, dendrimers, and metallic cores... 

Cyclophosphazene-containing dendrimers bearing sulfonamide groups (73) and (74) were synthesized. These contain up to 96 mesogenic... 

Another dendrimer-like cyclophosphazene containing cyclic carbonate appendages (84a-84b) were utilized to probe the mechanism of lithium ion transport. The latter was measured by Li pulse-field gradient (PFB) NMR. These results indicate that the coordination between the acyclic carbonate functionality and Li is too tight to allow fast ion dynamics. ... 

Cyclophosphazene-based dendrimer-like compounds have also been used in polymer hybrids. Thus, cyclophosphazene (85) containing six epojg arms was used as a monomer along with 4,4 -diaminodiphenyl methane to obtain thermosetting resins which showed good flame retardant properties. ... 

Cyclophosphazenes containing stable TEMPO radicals (86) have been prepared and have been used as models to assemble dendrimer derivatives up to the fifth generation. SQUID and EPR studies reveal the presence of anti-ferromagnetic interactions between the radicals. ... 

Another interesting application of dendrimer-like cyclophosphazene derivatives, involved the formulation of docataxel by micelle-encapsulation using a tripodal cyclotriphosphazene amphiphile, [NP(MPEG750)(GlyPheLeu)2Et]3 (90). The latter apparently has better properties (significantly lower clearance rate) than the currently used derivatives. ... 

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