Recyclable Polymer‐Supported Nanometal Catalysts in Water

Abstract

Two types of polymer-supported nanometal catalysts with high catalytic activity and recyclability in water have been developed. One catalyst was composed of linear polystyrene-stabilized metal nanoparticles (PS-MtNPs). A palladium catalyst (PS-PdONPs) was prepared in water by the thermal decomposition of Pd(OAc)2 in the presence of polystyrene. The degree of immobilization of Pd, but not the size of the Pd nanoparticles, was dependent on the molecular weight and cross-linking of the polystyrene. The PS-PdONPs exhibited high catalytic activity for Suzuki, Heck, and Sonogashira coupling reactions in water and they could be recycled without loss of activity. Linear polystyrene was also suitable as a stabilizer for in situ generated PdNPs and PtNPs. The second catalyst was a polyion complex that was composed of poly[4-chloromethylstyrene-co-(4-vinylbenzyl)tributylammonium chloride] and poly(acrylic acid)-stabilized PdNPs (PIC-PdNPs). Aggregation and redispersion of PIC-PdNPs were easily controlled by adjusting the pH value of the solution.

Recent Advances in Heterogeneous Catalytic Systems Containing Metal Ions for Phosphate Ester Hydrolysis

“…Silica is a very versatile material that can be prepared with good control of particle size and morphology. For example, silica nanospheres can be synthesised by means of microemulsions [31, 51, 52] or by modified synthesis of Stöber sol–gels [72] …”

“…Approaches that use photolytic degradation by sunlight [16] and biological pathways, [17] as well as their hydrolysis by biomimetic compounds, have been employed to solve the problem of the natural persistence of such compounds [18–30] . The use of biomimetic compounds offers a number of advantages, including the possibility to immobilise these compounds on the surface of insoluble solid matrices for easier handling and reuse [31] …”

A Recyclable Palladium-Catalyzed Synthesis of 2-Methylene-2,3-Dihydrobenzofuran-3-ols by Cycloisomerization of 2-(1-Hydroxyprop-2-ynyl)phenols in Ionic Liquids

“…We have also found that, in BmimBF 4 , methylenedihydrobenzofuranols 2 can be readily converted into 2-hydroxymethylbenzofurans 3 or 2-methoxymethylbenzofurans 4 by acid-catalyzed allylic isomerization or allylic nucleophilic substitution in a one-pot fashion. The recyclability of metal catalysts has acquired an increasing importance in the modern organic synthesis, as testified by recent publications in this field [32,33,34,35,36,37,38,39,40,41].…”

A mechanistic study of cross-coupling reactions catalyzed by palladium nanoparticles supported on polyaniline nanofibers

“…19,20 A shift toward palladium nanoparticles has been apparent in the past decade because they offer the benefits of heterogeneous catalysis. [21][22][23][24] Although their role in catalysis is not well understood, metal nanoparticles provide advantages specific to both heterogeneous and homogeneous catalysts and because of that are sometimes called "semi-heterogeneous" catalysts. 21 These advantages relate to the fact that small clusters of metals in low oxidation states are stabilized in solution, and include recoverability and reusability as well as high activity and selectivity.…”

“…21,22,30,31 In general, a reducing agent is required for palladium nanoparticle formation. [21][22] Polyaniline (PANI), [32][33][34][35] however, provides both stabilization and reducing properties. PANI has been used for various applications due to its electrical conductivity.…”