Soluble polymers, polymer-facilitated catalysis

Nearly everything my group has done in polymer-facilitated catalysis uses soluble polymers, a practice that has been followed by others as well.(5-7) Our group has emphasized chemistry using soluble polymers where the polymers are separable by some sort of precipitation or phase isolation technique. This paper presents examples of several catalysts and discusses several sorts of polymers. First, there is a discussion of some of our older work using functionalized polyolefins as the support. In this case, catalyst use, recovery and separation are possible because polyethylene is insoluble in all solvents at room temperature but soluble on heating. Next, the paper discusses catalysts that separate on heating. Two examples, poly(alkene oxide)-supported catalysts and poly(N-isopropylacrylamide)-supported catalysts that both... 

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

Apart from the aforementioned concepts for water-soluble catalysts, there are some new trends for ligands and catalysts that promise to facilitate their utilization in water. These concepts include nonionic donor ligands, water-soluble polymers (cf. Section 7.6) and inorganic polyoxometallates as redox-active ligands and/ or complex ions in homogeneous aqueous-phase catalysis. 

In the search to develop new materials for immobilization of homogeneous transition metal catalyst to facilitate catalyst-product separation and catalyst recychng, the study of dendrimers and hyperbranched polymers for application in catalysis has become a subject of intense research in the last five years [68], because they have excellent solubility and a high number of easily accessible active sites. Moreover, the pseudo-spherical structure with nanometer dimensions opens the possibility of separation and recycling by nanofiltration methods. Although dendrimers allow for controlled incorporation of transition metal catalysts in the core [69] as well as at the surface [70], a serious drawback of this approach is the tedious preparation of functionalized dendrimers by multi-step synthesis. 

Polymer-bound catalysts share some of the limitations intrinsic in both classical homogeneous and heterogeneous catalysis. Like soluble catalysts, the range of reactions they facilitate is rather limited. As with heterogeneous catalysts it is often difficult to learn the intimate details of ligand coordination, mechanism, and catalyst poisoning. Normally, such interpretations rely heavily upon the characteristics of soluble complexes, though it is clear the correspondence is imperfect. 

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