Polystyrene Supported Catalysts

TABLE 3.1. Asymmetric hydroformylation of styrene using polystyrene supported rhodium catalysts based 

Volatile substrates were again reacted in the gas-phase, and selectivities equal to those from the homogeneous phase reactions were obtained. For less volatile substrates supercritical CO2 was used as mobile phase and the substrates were added via a stepwise injection. For styrene a small drop in selectivity was observed compared to the 

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Scheme 54 Suzuki-Miyaura couplings with polystyrene-supported catalyst...

The multifaceted applications of phase-transfer catalysts (PTC) in organic synthesis contributed decisively to the establishment of organic catalysts as useful preparative tools. Polymer-supported PTC was examined extensively but it was noted that the catalytic activity of the insoluble polystyrene-supported catalysts was strongly reduced in com-... 

Soluble polystyrene supports differ from the terminally functionalized PEGs and polyethylene oligomers discussed above in that the catalyst moieties are attached to polystyrene via pendant groups, the loading of which can affect both the catalyst activity and separability. One example of a simple polystyrene-supported catalyst is the polystyrene copolymer-supported quaternary ammonium salts 66 and 67 [ 103]. These copolymers can be prepared with varying ratios of the styrene unit in the copolymer - the most active catalysts had 20-40 mol% of the vinylbenzylammonium groups in the copolymers. The utility of these catalysts was studied in a variety of solvents in the addition reaction of glycidyl methacrylate and carbon dioxide (Eq. 23). Polar solvents were most useful. The necessary polymer supports for preparation of catalysts 66 and 67 were prepared from chloromethylstyrene-styrene or chloromethyl-styrene-iV,JV-dimethylacrylamide copolymers that were in turn prepared by radical polymerization of the styrene or acrylamide monomers. The catalysts were recycled up to four times with small (ca. 6%) decreases in activity - de-... 

Figure 1. Recycling of insoluble, cross-linked polystyrene-supported catalyst The product is separatedfrom the catalyst by its solubility.

In 2009, Kudo and coworkers investigated the asymmetric Michael-type addition of N-methylated and unsubstituted indoles to a,(3-unsaturated aldehydes by resin-supported polypeptides. In an initial survey of several amphiphilic polyethyleneglycol-grafted crosslinked polystyrene-supported catalysts, organocatalyst 22, which adopts a p-turn conformation aided by the polyleucine moiety under aqueous conditions, was revealed as the ideal catalyst for the preparation of a series of Michael adducts that were, in a final... 

Metathesis catalysts including Gmbbs ruthenium catalyst (see Chap. 5) are hard to separate from the reaction products. Chemists therefore sought ways to overcome this problem by immobilizing the catalyst on various supports. Buchmeister recently reviewed various polymer-supported metathesis catalysts [54]. A few are reported here. Early, Grubbs described a phosphine-derivatized polystyrene-supported catalyst [55]... 

Scheme 14.10 Enantioselective addition of isobutyric aldehyde to nitrostyrene in flow with a packed-bed reactor containing a polystyrene-supported catalyst.

Silica-supported hydrogenation catalysts show less substrate selectivity than polystyrene-supported catalysts (Michalska and Webster, 1975 Ichikawa, 1976 Sinfelt, 1977). The rates of hydrogenation with silica-supported catalysts are high, although they are still lower than the equivalent homogeneous catalysts. It also appears that, unlike polystyrene, the reactive groups are confined only to the surface of silica. Ruthenium has also been immobilized in a zeolite matrix (Coughlan et al., 1977). 

In the case of polystyrene-supported catalysts, an additional study explored the influence of the isolation of the catalyst environment on the outcome of the hydroformylation reaction. For this purpose, first- and second-generation dendrons (very similar to those described above) were constructed and the biphosphine-Rh complex was assembled only on... 

The rate of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion (eq 6) 9 highly sensitive to solvent. Polystyrene-supported catalysts having 2-15% divinylbenzene cross-linking and 22-92%... 

Cyclopentadienylrhodium complexes were used for tandem Claisen re-arrangement-hydrocylation of the allylenolethers 62 to the pentenals 63, which were subsequently cyclized to the cyclopentanones 64 (Scheme 26). Activity of the monomeric (rj -C5H5)Rh(CO)2 65 and the polystyrene supported catalyst 66 was compared. The results clearly showed that the latter one gave the better results (Table 13) [33]. 

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