Encapsulated Catalysts

Acknowledgements—This work was supported by the Office of Naval Research, the National Science Foundation, the Robert A. Welch Foundation, and used equipment designed for study of fullerene-encapsulated catalysts supported by the Department of Energy, Division of Chemical Sciences. 

Table 6. Cyclohexene hydrogenation-dehydrogenation rates on Pt/SBA-15 nanoparticle encapsulation catalyst series [18].

CoSalen Y carries oxygen as a cargo.72 The catalytic properties of the zeolite-encapsulated metal complexes depend mainly on the complexed metal atoms, which are used usually as oxidation catalysts but other applications are also beginning to emerge. The zeolite-encapsulated catalysts can be regarded as biomimetic oxidation catalysts.73 In liquid-phase oxidation reactions catalyzed... 

Acid (PSTA)-catalyzed acetal hydrolysis followed by base-catalyzed [4-(dialkylamino) pyridine] Baylis-Hillman addition of MVK Catalysts are part of the monomers used to make the resulting star polymer-encapsulated catalysts... 

S. Kobayashi and R. Akiyama, Renaissance of immobilized catalysts. New types of polymer-supported catalysts, micro-encapsulated catalysts, which enable environmentally benign and powerful high-throughput organic synthesis, Chem. Commun., 2003, 449. 

Some conclusions can be drawn from comparison of the TOF values obtained using biphasic catalysis with literature data for the same reactions catalyzed by a polymer-supported Pd(0) catalyst (Table 2) [161]. First, although the TOFs for the dendrimer-encapsulated catalysts are consistently lower than for the polymer-supported catalysts, the values are in some cases comparable. Second, the selectivity pattern exhibited by the two types of catalysts is somewhat different. Specifically, the range of TOF numbers for biphasic catalysis is far greater than for conventional polymer catalysis, which suggests the possibility of the type of... 

To demonstrate further the powerful utiHty of the fluorous/organic biphasic approach to catalyst recycling, a dendrimer-encapsulated catalyst (DEC) with covalently attached perfluorinated polyether chains was synthesized [17] and metallic nanoparticles were introduced into the interior. 

Microcapsule properties make them attractive materials for a wide variety of practical applications. In the area of catalysts, microcapsules provide semipermeable membranes that are readily produced and dispersed. These properties, along with others, have inspired systems that include synthetic or man-made encapsulated catalysts, such as organocatalysts, metal particles, enzymes, and organometallic... 

To prevent false positives, the homogeneous reaction should be carried out in the same reaction vessel. This also serves as an internal control experiment to show if the reaction with encapsulated catalyst works at all. 

Organocatalysts. Sometimes it is desired that an encapsulated catalyst never leave the confines of the capsule because other reagents or catalysts in the reaction mixture would then interfere with it, or vice versa. In this case, the organocatalyst must be attached to a much larger molecule that cannot diffuse out of the shell or to the inside of the shell itself. 

The oxidation of various other alkenes using the optimal heterogeneous system (10% PEO-10% PPO) was compared to a typical homogeneous reaction using MeOH as solvent (data reported in Table 13). Compared to the homogeneous standard, the polyether tethered-silica-encapsulated catalysts show somewhat lower activity but much better selectivity. 

FigureS.I Useoffunctional groups to form encapsulated catalysts by assembly (A), to form bidentate ligands by assembly (B), and to support the catalyst by supramolecular interactions (C).

More recently, the encapsulated catalyst HRh(CO)3(3 TPP)3) (Figure 8.4) was also used as a catalyst for the hydroformylation of 2-octene and 3-octene [11], Hydroformylation of trflns-2-octene at room temperature using a (non-encapsulated)... 

The hydroformylation of trflns-3-octene at room temperature using the (non-encapsulated) rhodium catalyst based on tris(weta-pyridyl)phosphine afforded 2-ethylheptana] and 2-propylhexanal in exactly a 1 1 ratio. The encapsulated catalyst provided an unprecedented selectivity for 2-propylhexanal of 75% (Scheme 8.3). Again the selectivity is largely retained at 40 °C whereas at 80 °C the isomerization side reaction prohibits the selective formation of aldehydes. Similar regioselectivities were obtained in the hydroformylation of frflns-2-hexene, trans-2-nonene and trans-3-nonene at 25 °C. 

---