"Microencapsulated" and Related Catalysts for Organic Chemistry and Organic Synthesis

New types of polymer-supported catalysts, microencapsulated and related catalysts, which were developed based on the microencapsulation technique for binding catalysts to polymers utilizing physical envelopment by polymer backbones and interaction between π electrons of benzene rings of the polystyrenes used as polymer backbones and vacant orbitals, are discussed. In most cases, the catalysts are recovered quantitatively by simple filtration and reused without loss of activity. The catalysts have comparable activities to homogeneous catalysts in many cases, and sometimes even higher activities. Many catalysts have been immobilized by using these new techniques, mechanistic aspects, including immobilization and catalytic activity, have not been clarified yet. It is expected that many other catalysts can be immobilized using these techniques and that these catalysts can contribute to environmentally benign and powerful high- throughput organic synthesis.