Macromolecular Ligands or Supports

U sing polymers was one of the very first methods in order to heterogenize the catalyst in a homogeneous catalytic reaction. Thus, thanks to these supports, the catalyst acquires the property of insolubility while maintaining its catalytic performance [39-42]. Some authors synthesized phosphonated resins, such as polystyrene, and used them as a ligand in several rhodium and platinum complexes. Thus, hydrogenation [43, 44], hydrosilylation [45], and hydroformylation of olefins were catalyzed. 

Other authors have described the use of the previously seen framework [39]. The grafting of the DIOP ligand (Eqs. 5-7) onto a Merrifield resin was performed by treatment of the insoluble aldehyde 21 with the (+)-diol 22 of the DIOP, leading to the ditosylate 23. This product was then treated with lithium diphenylphos-phide, affording the desired phosphinated resin 24, which contains 0.5 meq/g of phosphorus functions. The reaction with [RhCl(C2H4)2]2 gave an insoluble complex that may be used further in catalysis. 

The second procedure is related to a copolymerization reaction [40]. Reacting (—)-l,4-ditosylthreitol with 4-vinylbenzaldehyde afforded a styryl monomer (Eq. 8). When this monomer (8% w/w) copolymerized at 70 °C with hydroxyethyl metha- 

Although these authors used the supported catalyst only in benzene for the grafted polymer, and in polar solvents for the copolymer, it is obvious that these catalysts can be used in water the copolymer is indeed insoluble but the active part is water-soluble. 

Some years ago, Malmstrom etal. synthesized water-soluble metal phosphine complexes based on water-soluble polymers [41], In order to have solubility in both an acidic and a basic medium, they prepared two different water-soluble polymers. For the first, they made methyl [4-(diphenylphosphino)benzyl]amine (PNH) react with poly(acrylic acid) (PAA) using dicydocarbodiimide (DCC) as the coupling agent, under strict exclusion of oxygen (25). For the second, they reacted (4-carboxy-phenyl)diphenylphosphine with polyethylene imine (PEI) at room temperature (26). The reduction by sodium borohydride was made in situ, followed by the addition of methanesulfonic add and diethyl ether. Then, the methanesulfonic salt of phosphinated polyethylenimine was predpitated. 

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