Dendrimeric phosphines

Scheme 2.36 Synthesis of periphery-functionalized dendrimeric phosphines.

Caminade AM, Servin P, Laurent R, Majoral JP (2008) Dendrimeric phosphines in asymmetric catalysis. Chem Soc Rev 37 56-67... 

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... 

Repeating the sequence shown in Figure 18.8 another five or six times (when congestion at the periphery occurs) is not an easy task without the introduction of Si-O-Si links and very few silane dendrimers of such a high generation have been prepared. The reaction is much more facile when HSi(CH3)Cl2 is used. Equipped with phosphine complexes either in the core or at the periphery the dendrimeric systems are used as catalysts [12], Controlling the state of platinum seems to be a key problem. 

Dendrimeric supports are high molecular weight phosphine supports allowing precise distribution of catalytic sites and easily separated from the reaction products by precipitation and microporous membrane filtration. 

---