Scandium Microencapsulated

However, a catalyst made by microencapsulating scandium triflate in polystyrene was easy to recover and reuse with no loss in activity by filtration. In the imino aldol reaction (6.11), its activity was greater than that of the unencapsulated counterpart, maintaining activity (90% yields) after seven cycles 55 (Many Lewis acids do not work well in this reaction.)... 

Polymer-microencapsulated scandium and osmium catalysts have recently been developed by Kobayashi and coworkers [ 119-121]. This protocol has been... 

MCSc(OTf)3] = Microencapsulated scandium trifluoro methane sulfonate... 

The microencapsulation technique has been developed by Kobayashi for the immobilization of metal Lewis acid catalyst in polymer [57]. The catalysts were immobilized on to polymers using physical environment by polymer backbones and interaction between 71 electrons of benzene rings of the polystyrenes and vacant orbitals of the catalysts. Microencapsulated scandium trifiuoromethanesul-fonate was easily prepared from polystyrene and Sc(OTf)3 in cyclohexane, which was successfully used in several important Lewis acid catalyzed carbon-carbon bond-forming reactions [57]. 

Kobayashi and coworkers further developed a new immobilizing technique for metal catalysts, a PI method [58-61]. They originally used the technique for palladium catalysts, and then applied it to Lewis acids. The PI method was successfully used for the preparation of immobilized Sc(OTf)3. When copolymer (122) was used for the microencapsulation of Sc(OTf)3, remarkable solvent effects were observed. Random aggregation of copolymer (122)-Sc(OTf)3 was obtained in toluene, which was named as polymer incarcerated (PI) Sc(OTf)3. On the other hand, spherical micelles were formed in THF-cyclohexane, which was named polymer-micelle incarcerated (PMI) Sc(OTf)3.. PMI Sc(OTf)3 worked well in the Mukaiyama-aldol reaction of benzaldehyde with (123) and showed higher catalytic activity compared to that of PI Sc(OTf)3 mainly due to its larger surface area of PMI Sc(OTf)3. This catalyst was also used in other reactions such as Mannich-type (123) and (125) and Michael (127) and (128) reactions. For Michael reactions, inorganic support such as montmorilonite-enwrapped Scandium is also an efficient catalyst [62]. 

Scandium(III) trifluoromethanesulfonate (Sc(OTf)3) is extensively used in organic synthesis to catalyze a wide variety of carbon-carbon bond-forming reactions in aqueous media. The polymer microencapsulated triflate ME catalysts are recoverable and reusable, often reduce metal leaching, and have activity similar to that of their homogeneous counterparts [128]. 

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