Dendritic phase transfer catalysts

Phase transfer catalysts enable the reaction of insoluble materials and reagents to occur in solvents that would otherwise prove inaccessible. The ability to combine a hydrophobic core unit with hydrophilic peripheral moieties, or vice versa, render dendrimers highly suited 

Poly(alkyl aryl ether) dendrimers functionalised at the periphery with carboxylic acid groups [69] or phenol groups [70] have been employed in this capacity by Ramamurthy and co-workers. After the presence of a hydrophobic microenvironment within the den-drimer core had been established via pyrene solubilisation studies, photochemical reactions were carried out to assess the viability of the dendrimers as reaction cages or phase transfer catalysts. All of the photochemical reactions studied were carried out successfully in aqueous media, on compounds normally water insoluble, with increasing cage effect observed for higher generation dendrimers. The viability of these dendrimer systems as photochemical reaction media was thus established. 

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Fig. 7.9 Dendritic phase-transfer catalyst according to Vogtle et at. (left) transmission electron micrograph of the dendritically stabilised gold nanoparticle (black) after reduction of the gold salt solution in the organic phase...

Kenawy 64) immobilized ammonium and phosphonium peripheral functionalized dendritic branches on a montmorillonite supported chloromethylstyrene/methyl methacrylate copolymer (74-75). These polymer/montmorillonite-supported dendrimers were used as phase transfer catalysts (PTC) for the nucleophilic substitution reaction between -butyl bromide and thiocyanate, cyanide, and nitrite anions in a toluene or a benzene/water system. These PT catalysts could be recycled by filtration of the functionalized montmorillonite from the reaction mixture. Generally,... 

Fig. 4 A dendritic box has been shown to trap molecular guests (i.e., 22), while fluorinated constructs (23) show promise as phase-transfer catalysts.

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