Soluble Polymer Supported Catalysis

This chapter will only deal with catalytic systems covalently attached to the support. Dendrimer [96-101], hyperbranched polymer [102, 103], or other polymer [100] encapsulated catalysts, micellar catalysis [104] and non-cova-lently bound catalysts (via ionic [105,106], fluorous, etc. intercations) are not being treated. Also catalysis with colloidal polymers [ 107,108] and biocatalysts, such as enzymes and RNA, will not be reviewed here. 

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Datta, A., Ebert, K. and Plenio, H. (2003) Nanofiltration for homogeneous catalysis separation soluble polymer-supported... 

Bergbreiter DE, Tian J, Hongfa C (2009) Using soluble polymer supports to facilitate homogeneous catalysis. Chem Rev 109(2) 530-582... 

While developing new catalysts is an appropriate and desirable way to new greener chemical processes, our work has focused on new ways to carry out homogeneous catalysis. This has involved two approaches. The first approach explores the use of polymer-supported catalysts in non-traditional media like water or fluorocarbon phases. The second approach expands on the use of polymers to recover reusable homogeneous catalysts after a reaction is complete. Essentially all of our work has been with soluble polymer supports. 

Figure 6. Thermomorphic system where the catalysis is carried out homogeneously at 70 °C in a monophasic system but where the separation is carried out at room temperature in a biphasic system with the soluble polymer-supported catalyst (e,g, 5 or 6) exclusively dissolved in the aqueous ethanol phase at 20...

A. Datta, K. Ebert, H. Plenio, Nanofiltration for homogeneous catalysis separation Soluble polymer-supported palladium catalysts for Heck, Sonogashira, and Suzuki coupling of aryl halides, OrganometaUics 22 (2003) 4685-4691. 

The aim of this review is to discuss the contribution of soluble polymer-supported ligands and insoluble polymer-supported ligands to asymmetric catalysis in the field of reduction of C=0 bonds, cyclopropanation, Diels-Alder, alkylation, allylation, dihydroxylations,... 

The catalytic activity of polymer-supported chiral salen has been also studied in the enantioselective diethylzinc addition to aldehydes since the importance of this type of hgand in asymmetric catalysis. Soluble polymer-supported salens have been synthesized by Venkataraman... 

In conclusion, the selected examples in this chapter have demonstrated that the soluble polymer-supported chiral catalysts may offer a potential combination of the advantages of homogeneous and heterogeneous asymmetric catalysis, and... 

Polymer-supported catalysts incorporating organometaUic complexes also behave in much the same way as their soluble analogues (28). Extensive research has been done in attempts to develop supported rhodium complex catalysts for olefin hydroformylation and methanol carbonylation, but the effort has not been commercially successful. The difficulty is that the polymer-supported catalysts are not sufftciendy stable the valuable metal is continuously leached into the product stream (28). Consequendy, the soHd catalysts fail to eliminate the problems of corrosion and catalyst recovery and recycle that are characteristic of solution catalysis. 

These siUca-supported catalysts demonstrate the close connections between catalysis in solutions and catalysis on surfaces, but they are not industrial catalysts. However, siUca is used as a support for chromium complexes, formed either from chromocene or chromium salts, that are industrial catalysts for polymerization of a-olefins (64,65). Supported chromium complex catalysts are used on an enormous scale in the manufacture of linear polyethylene in the Unipol and Phillips processes (see Olefin polymers). The exact stmctures of the surface species are still not known, but it is evident that there is a close analogy linking soluble and supported metal complex catalysts for olefin polymerization. 

Dendrimers and soluble polymers provide alternative supports to solids, which have the advantage that access to the catalytically active sites is not restricted. The main problem in these cases is not in the catalysis - reactions with high rates and selectivities have been reported - but rather in the separation which relies on nano- or... 

Many different soluble polymers have been used as supports for catalyst immobilization. Since solvation of otherwise insoluble catalysts can frequently be accom-pHshed by attachment to a soluble polymer, these supports have found significant use in the immobihzation of classical solution phase catalysts. Here, we will only survey polyethylene glycol (PEG) as a soluble polymeric support for catalysis. The use of other types of soluble polymers (e.g., polyethylene, non-cross-linked polystyrene) has been reviewed elsewhere [49]. 

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