Solid support catalysts

Heterogeneous reactions involving a solid supported catalyst form an important class of reactors and require special consideration. As discussed in the previous section, such reactors can be configured in different ways ... 

Of these, fixed-bed adiabatic reactors are the cheapest in terms of capital cost. Tubular reactors are more expensive than fixed-bed adiabatic reactors, with the highest capital costs associated with moving and fluidized beds. The choice of reactor configuration for reactions involving a solid supported catalyst is often dominated by the deactivation characteristics of the catalyst. 

Solid-supported technologies are already well established methods in medicinal chemistry and automated synthesis. Over the last couple of years new trends have evolved in this field which are of utmost importance as they have the potential to revolutionize the way chemical synthesis especially for library production is performed. Microchip-based synthesis technologies and multistep sequences with solid-supported catalysts or reagents in flow-through systems are only two spectacular examples. A new approach is the use of solid-supported systems for the scale-up of chemical reactions thereby enabling the rapid and smooth transition from discovery to development units. 

Keywords Catalysis, polymer-supported oxidovanadium (IV) complex, Solid supported catalysts, heterogenized homogeneous catalysts... 

S. M. Bachilo, L. Balzano, J. E. Herrera, F. Pompeo, D. E. Resasco, and R. B. Weisman, Narrow (ra,/n)-distribution of single-walled carbon nanotubes grown using a solid supported catalyst, J. Am. Chem. Soc. 125, 11186 (2003). 

In many supported catalytic systems, it is nearly impossible to determine either the specific species, responsible for the observed catalytic activity, or the mechanistic pathway of the reaction. Using a defined SAM system in which careful molecular design is followed by controlled deposition into a solid-supported catalyst of known morphology, surface coverage, mode of binding and molecular orientation, allows direct correlation of an observed catalytic activity with the structure on the molecular scale. SAM and LB-systems allow detailed and meaningful studies of established surface bound catalysts to understand their behavior in heterogeneous... 

WUes and Watts [48,53] have reported the use of a rather successful heterogenic catalytic system to carry out these reactions. They have tested a borosilicate glass microreactor (dimensions 3.0 x 3.0 x 0.6 cm) consisting of two etched layers with two inlets, mixing channels, a larger etched region and the outlet. A solid-supported catalyst was dry-packed in this structure (Fig. 4). 

Another review concerning the synthesis of cyclic peroxides has been published and a solid-supported catalyst 231 for both cycloaddition reactions and singlet oxygen ene reactions was synthesized and demonstrated to be an efficient, mild, and recyclable alternative to solution-phase photooxygenation catalysts <2006JOC724>. 

Highly enantioselective allylic alkylations by using solid-supported catalysts have been developed by several... 

Due to the heterogeneity of the recently advanced solid-support catalyst for the hydroformylation, direct structural information on catalyst surface has been collected by extended X-ray absorption fine structure (EXAFS). Iwasawa is the first to directly characterize the structure of dimeric rhodium complexes supported on... 

The ansa-sandwich complexes, sometimes called constrained-geometry catalysts, exhibit a good ability to incorporate co-monomers. The catalysts (a) to (g) are soluble in solvents such as toluene. In the catalyst (h) the metallocene is supported on silica. Such solid-supported catalysts can be suspended in hydrocarbons for metering into the polymerization reactor [4],... 

Fig. 49 Releasing of cyclic oligolactides from solid supported catalyst...

In 2007, Wiles et al. (2007c) demonstrated the ability to employ solid-supported catalysts in series within an EOF-based microreactor. As summarized in Scheme 39, the model reaction sequence involved combining a previously investigated acid-catalyzed deprotection with a base-catalyzed condensation reaction to enable the synthesis of a,(3-unsaturated carbonyl compounds from dimethyl acetals. 

Table 22 Summary of the results obtained for the synthesis of 2-(benzyloxy)tetrahy-dropyran 151, employing an array of solid-supported catalysts...

From the examples above it can be seen that the incorporation of solid-supported catalysts into flow reactors can afford extremely efficient processes however, recently numerous authors have reported the use of... 

An alternative to solid-supported catalysts are catalysts that are insoluble themselves [136]. A pyridine-aldoxime ligand was presented and evaluated in the Suzuki-Miyaura reaction using water as a solvent. Using an Irori kan to contain the polymeric catalyst, the reaction could be repeated 14 times without any noticeable reduction in efficiency. The optimized reaction conditions were then used to create a small library of approximately 30 biaryl compounds using aryl iodides, bromides, triflates as well as an activated chloride (Scheme 56) [136]. 

The use of solid supported, recyclable catalysts, is a well-assessed technique in classic organic chemistry, and many exhaustive reviews dealing with this subject are available [105, 115]. The use of solid supported catalysts for library synthesis in solution has also been reported. Among others, Kobayashi et al. presented the use of a new supported scandium catalyst for 3CC reactions leading to solution libraries of amino ketones, esters, and nitriles (24-member model discrete library) [116], or to quinolines (15-member model discrete library) [117], and Jang [118] presented a polymer bound Pd-catalyzed Suzuki coupling of organoboron compounds with halides and triflates. This area was also briefly reviewed recently [119]. 

Jacob et al. [22] presented an improved green solvent free methodology for the selective synthesis of 1,2-disubstituted benzimidazoles (xiii) by the condensation of o-phenylenediamine and aldehydes using solid-supported catalyst (Si02/ZnCl2). 

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