In recent years, the trend in synthetic organic chemistry has been to put special emphasis on harmonization with the environment and reaction efficiency. Currently, much R&D is taking place to address these issues. Polymer-supported synthetic reagents and catalysts are drawing much attention due to the ease of recovery of the reagent after reaction. For this reason, many polymer-supported reagents with excellent properties have been reported.
Amos et al. have developed a triphenylphosphine supported on polystyrene for use in the Mitsunobu reaction. In the Mitsunobu reaction, the riphenylphosphine oxide by-product is unavoidable, but this often prevents the purification of desired reaction product. By using polymer-supported triphenylphosphine, it is possible to eliminate the triphenylphosphine oxide by-product by filtration, thus enabling easy purification of the reaction product.¹⁾
One of the most common hypervalent iodine compounds, diacetoxyiodobenzene, has been supported on polystyrene by Togo and co-workers, and they have reported the oxidation of various functional groups. For example, they have reported the oxidation of alcohols in the presence of this polymer-supported reagent and TEMPO.²⁾ Ishikawa and co-workers have developed 1,3-dimethylimidazolidinone supported on polystyrene. The derived 2-chloro-1,3-dimethylimidazolidium, using oxalyl chloride, is used for the esterification as a polymer-supported dehydrating and condensation reagent.³⁾
On the other hand, active research for development of the polymer-supported catalysts has also been carried out. Ishihara and his group have developed a polystyrene-bound 4-bis(triflyl)methyl-2,3,5,6-tetrafluorobenzene and demonstrated its applications as a solid super Brønsted acid catalyst.⁴⁾ This solid catalyst swells effectively in organic solvents, and shows excellent activity with various acid catalyzed reactions. This catalyst has been used in esterification, Friedel-Crafts reaction, Michael addition, acetalization, Sakurai-Hosomi allylation, and Mukaiyama aldol reaction. The catalytic activity of this solid catalyst was superior even to that of Nafion, which is well known as a solid strong acid. After reaction, the solid catalyst was quantitatively recovered by simple filtration and reused repeatedly. This solid catalyst was also packed in a syringe as reaction column, and various acid-promoted reactions were performed to afford the desired products by passing a solution of reactants through the syringe.
Ikegami and co-workers have developed the Pd complex catalyst, one of the most utilized catalyst in the organic synthesis, to support the polymer, and reported its usefulness.⁵⁾ This catalyst is a solid-phase catalyst which consists of an amphiphilic copolymer ligands, chloride, and palladium. It takes up substrates and reagents of both hydrophilic and hydrophobic nature in the vicinity of palladium to smoothly promote the reaction. The palladium complex catalyst forms a networked supermolecular complex, which is insoluble in water and organic solvents, and is easily recovered from reaction system. Since the palladium is firmly held in place by the phosphine group of copolymer ligand, it is not lost during the reaction or upon work up; therefore, the catalyst can be recovered and reused multiple times. Ikegami and co-workers have demonstrated the uses of this catalyst for Suzuki-Miyaura coupling reaction in water, and Heck reaction in organic solvent. This amphiphilic polymer-supported Pd complex catalyst possesses high catalytic efficiency, and can be used in either water or organic solvents. This catalyst is now attracting attention as is has fulfilled harmonization with the environment and reaction efficiency.

D3525	H1208	M1452
B2368	D2765	D2766
B2292	I0680	M1857
A2006	B2370	B2371
B2372	C2141	P1415
P1425	P1697	S0545
T2419