Dendrimers thermomorphic

Mizugaki et al. 74) have recently utilized thermomorphic properties of Pd(0)-complexed phosphinated dendrimers for dendritic catalyst recycling. Using the method developed by Reetz 16), they prepared dendritic ligands containing, respectively, 2, 8, 16, and 32 chelating diphosphines. Palladium dichloride was com-plexed to the dendrimers, and a reduction in the presence of triphenylphosphine gave the Pd(0)-complexed dendrimers (80—83). The dendritic complexes were active... 

Dendrimers too can be used in thermomorphic systems. In a report describing dendrimer-bound Pd(0) catalysis [163], Kaneda compared the liq-uid/liquid thermomorphic separation scheme with more established membrane and solvent precipitation procedures. Starting with commercially available third-, fourth-, and fifth-generation poly(propylene imine) dendrimers, the primary amine groups at the periphery were converted into chelating phosphines. The resulting phosphines were in turn allowed to react with Cl2Pd(PhCN)2 to form Pd(II) complexes that were reduced by hydrazine in the presence of triphenylphosphine to form the Pd(0) catalyst 126 (Eq. 63). This catalyst was successfully used in the allylic amination shown in Eq. 64. In this example, solvent precipitation, membrane filtration, and thermomorphic liq-uid/liquid separation were all used to recycle 126. The latter procedure proved to be simplest with the best recovery of active catalyst. 

The first application of dendrimers in a thermomorphic system was described by Kaneda and co-workers. Poly(propylene imine) dendrimer-bound Pd(0) complexes were synthesized by reduction of dendritic Pd(II) systems with hydrazine and used for the allylic substitution of trans-cinnamyl acetate with dibutylamine [Eq. (5)] [14]. 

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