Catalysis resin-supported

Although our main research interest has been in the field of heterogeneous catalysis, we have performed several proof of concept studies showing that FTIR imaging is flexible enough to be applied to the study of resin-supported combinatorial libraries, of the type commonly employed in split-and-pool syntheses. It was shown that the... 

Although the first aim of the use of a water-soluble palladium catalyst in allylic alkylation in a two-phase system was the recycling of the catalyst, this methodology finds quite interesting applications in the deprotection of peptides as well as in the selective alkylation of uracils and thiouracils. More recently, the effective use of supported aqueous-phase catalysis as well as asymmetric alkylation in water in the presence of surfactants or amphiphilic resin-supported phosphines open new applications and developments for the future. 

In triphase catalysis, solvated resin supports are important carriers for solid-phase organic synthesis in combinatorial chemistry. The physical properties of resin, resin swelling, dynamic solvation, and solvated supports are important factors in affecting the synthesis. However, these factors are also affected by solvent. Selective solvation of resin alters the local reactivity and accessibility of the bound substrate and the mobility of the entrapped re-... 

Uozumi, Y. and Watanabe, T. (1999) Green catalysis Hydroxycarbonylation of aryl halides in water catalyzed by an amphiphilic resin-supported phosphine-paUadium complex. J. Org. Chem., 64, 6921-3. 

Gazi, S., Ananthakrishnan, R. (2011). Metal-free-photocatalytic reduction of 4-nitrophenol by resin-supported dye under the visible irradiation. Applied Catalysis B Environmental, 105, 317—325. http //dx.doi.Org/10.1016/j.apcath.2011.04.025. 

Tandem Friedel-Crafts-type allgrlation-a-oxyamination reaction catalysed by chiral resin-supported peptide catalysis and enz5rme catatysis. 

Polymers can find use in heterogeneous catalysis as support for metallic catalysts (as we have seen in the example of Pd dispersed on silk or resins [78, 80, 82]). A third class should be added, that of insoluble polymers containing catalytic pendant groups (e.g. a polyvinylimidazole in a system in which only substrate and products are soluble, and not the polymer). However, this kind of catalysis has not yet been investigated in detail. 

The same group also reported an amphiphiHc PS-PEG resin-supported mthe-nium complex, which could catalyze the Kharasch reaction in water under heterogeneous conditions without any radical initiators (Scheme 8.29) [65]. Owing to the self-concentration of hydrophobic organic substrates inside the polymer matrix in water, it was claimed that the catalytic efficiency of the PS-PEG Ru in water was comparable to the most efficient homogeneous Ru catalysis reported thus far. 

Base catalysis is most effective with alkali metals dispersed on solid supports or, in the homogeneous form, as aldoxides, amides, and so on. Small amounts of promoters form organoalkali comnpounds that really contribute the catalytic power. Basic ion exchange resins also are usebil. Base-catalyzed processes include isomerization and oligomerization of olefins, reactions of olefins with aromatics, and hydrogenation of polynuclear aromatics. 

The most well-developed recent examples of catalysis concern catalysts for oxidation reactions these are essentially achiral or chiral metal-salen complexes. Taking into account a number of results suggesting the importance of a degree of mobility of the bound complex, Sherrington et al. synthesized a series of polymer-supported complexes in which [Mn(salen)Cl] units are immobilized in a pendant fashion by only one of the aromatic rings, to polystyrene or poly(methacrylate) resin beads of various morphology (Figure 6).78,79... 

However, styrene and cyclohexene gave complex product mixtures, and 1-octene did not react under the same reaction conditions. Thus, the activity of this catalyst is intrinsically low. Jacobs and co-workers [159,160] applied Veturello s catalyst [PO WCKOj ]3- (tethered on a commercial nitrate-form resin with alkylammonium cations) to the epoxidation of allylic alcohols and terpenes. The regio- and diastereoselectivity of the parent homogeneous catalysts were preserved in the supported catalyst. For bulky alkenes, the reactivity of the POM catalyst was superior to that of Ti-based catalysts with large pore sizes such as Ti-p and Ti-MCM-48. The catalytic activity of the recycled catalyst was completely maintained after several cycles and the filtrate was catalytically inactive, indicating that the observed catalysis is truly heterogeneous in nature. 

Dendritic polymeric supports or hybrids of these with solid-phase resins are among the most promising candidates for new high-loading supports in organic synthesis and catalysis. However, every new polymeric support has to compete with the current bench mark, the so-called Merrifield resin and its derivatives. 

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