Poly -supported catalysts catalyst recovery

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... 

An amphoteric, water-soluble polymer support functionalized with a bidentate phosphine has been reported (Scheme 46). Starting from poly(maleic anhydride)-f-poly(methylvinylether), 91 was prepared by reaction with a bis(diphenylphosphino)ethylamine. Polymers with different phosphine loadings were made and soluble Rh complexes formed by reaction with [Rh(COD)] - - OTf. These supported metal complexes were then screened for activity in hydrogenation reactions. Recovery of the catalyst was effected by changing the pH of the reaction mixture to <7.5. 

Poly(4-ferf-butylstyrene) is an alternative to polystyrene that can be prepared by radical polymerization of a commercial monomer. While poly(4-ferf-butylstyrene) (PtBS) has received limited attention as a component in block copolymers [64], PtBS homopolymers have not generally been used as supports, presumably because they offer no advantages in separation if separation involves solvent precipitation chemistry. PtBS heptane solubility does make it useful in liquid/liquid biphasic separations. PtBS and other alkylated polystyrenes are otherwise similar to polystyrene and such heptane solubility under biphasic separation conditions is a general strategy for separation and recovery of species bound to these polystyrene-like polymers. A version of this polymer support suitable for catalyst immobilization (120) can be prepared by radical copolymerization with chloromethylstyrene as a comonomer (Eq. 58). This alkylated polystyrene is highly phase-selectively soluble in heptane when another polar phase like DMF or 90% aqueous ethanol is present, but is soluble in miscible mixtures of heptane with these polar solvents at 70 °C. 

A second nucleophilic catalyst supported by PtBS is the polymer-bound di-methylaminopyridine analog that was also used in latent biphasic catalysis with the poly(JV-alkylacrylamide) support 129 [131]. This example of a nucleophilic catalyst (133) was used to catalyze formation of a t-Boc derivative of 2,6-di-methylphenol (Eq. 70). In this case, the extent of recovery of the catalyst and the yields of product were directly comparable to those seen with thermomorphic systems. The isolated yield for the first five cycles of this reaction were 34.3, 60.9,82.2,94.6, and 99%. In this case we reused catalyst 133 through 20 cycles. Yields after the first few cycles were essentially quantitative (ca. 93% average for each of 20 cycles). Separation of the polymer from the aqueous ethanol phase was quantitative as judged by either visual observation or UV-visible spectroscopic analysis. 

With supported Mn(III)-salen complexes [27], the use of polymer-bound catalysts for the asymmetric epoxidation of olefins is possible, allowing once more the easy recovery of the catalyst by precipitation with a suitable solvent [28]. Poly(ethylene... 

MAJOR APPLICATIONS Poly (4-vinylpyridine) (P4VP) with its nucleophilic and weakly basic ring nitrogen has found uses in the areas of metal recovery (complex), and pollution control for removal of acidic and neutral materials. It is also used as an acid scavenger and catalyst and catalyst support. Commercial resin beads are mostly prepared by suspension polymerization with cross-linker such as divinylbenzene.t ... 

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