Immobilization systems solid-bound catalysts

Further simplification was attained by immobilization of the catalyst on a solid polymer (49), so that its separation from the product was reduced to mere mechanical filtration the resin bound catalyst could then be used for another run. Ofthe number of polymeric supports investigated, Merrifield (49) and Wang resins were identified as most suitable, exhibiting the same behavior and efficiency [18]. However, owing to the heterogeneous nature of the system, the enantioselectivity of the reaction decreased by 10 15% ee (Table 4.11, entries 6 12). In view ofthe swelling properties, toluene was found to be less suitable than chloroform (compare entries 6 and 7), which makes the method less environment friendly. Furthermore, a conditioning effect was observed for these systems the second run was always found to be more enantioselective than the first one by 10% ee and this level was maintained in the subsequent runs (compare entries 7 with 8 12). The latter effect stems from the... 

This review will consist of three parts (i) rationale and need for immobilizing palladium on a solid support, (ii) comparison of various palladium immobilization systems and (iii) applications of these solid-bound palladium catalysts in organic chemistry. Some personal speculations about the future of this burgeoning field will also be included for the sole purpose of eliciting further interest and discussion. The term solid support will be... 

With a view to producing catalysts that can easily be removed from reaction products, typical phase-transfer catalysts such as onium salts, crown ethers, and cryptands have been immobilized on polymer supports. The use of such catalysts in liquid-liquid and liquid-solid two-phase systems has been described as triphase catalysis (Regen, 1975, 1977). Cinquini et al. (1976) have compared the activities of catalysts consisting of ligands bound to chloromethylated polystyrene cross-linked with 2 or 4% divinylbenzene and having different densities of catalytic sites ([126], [127], [ 132]—[ 135]) in the... 

Unfortunately, most enzymes do not obey simple Michaelis-Menten kinetics. Substrate and product inhibition, presence of more than one substrate and product, or coupled enzyme reactions in multi-enzyme systems require much more complicated rate equations. Gaseous or solid substrates or enzymes bound in immobilized cells need additional transport barriers to be taken into consideration. Instead of porous spherical particles, other geometries of catalyst particles can be apphed in stirred tanks, plug-flow reactors and others which need some modified treatment of diffusional restrictions and reaction technology. 

A review article by Blumel describes classical and modern solid-state NMR methods that allow to gain insight into catalyst systems where one or two metal complexes are bound to oxide supports via bifunctional phosphine linkers, such as (EtO)3Si(CH2)3PPh2. It has been shown that many aspects of the immobilized molecular catalysts can be elucidated with the corresponding NMR technique. For example, the bulk of the support can be studied, as well as the interface of the support with the ethoxysilane. In addition, electrostatic bonding to the support via phosphonium groups can be proven by solid-state NMR. For the immobilized catalysts, leaching, and even horizontal translational mobility effects, as probed by HR MAS NMR under realistic conditions in the presence of solvents, are described. 

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