Polymers for Green C–C Couplings

Abstract

Cleaner and environmentally more friendly cross-coupling reactions can be carried out by the use of polymers as supports. A lot of work has been devoted to attach palladium catalysts on polymers, so they can be easily separated from the reaction mixture and reused. An overview of the methods used for this purpose is given; they include the encapsulation of palladium complexes or palladium nanoparticles by polymers and the synthesis of polymeric ligands that coordinate to palladium. Polymer-supported reagents are also important

Hydroxylated surface of GaAs as a scaffold for a heterogeneous Pd catalyst

“…3 It is well-known that the Pd(0) species catalyzes the crosscoupling reaction. [1][2][3][4][5] Hence, a reducing agent is necessary to 25 convert Pd(II) to Pd(0). We hypothesized that hydroxy groups both attract Pd(II) to the surface as well as reduce it.…”

Synthesis and Transformation of Halochromones

“…Subsequently, the proximity of the carbon atoms bound to the metal assists in their coupling with the formation of a new carbon-carbon single bond. This powerful synthetic methodology [147][148][149][150][151] is considered a golden strategic tool to build novel complex molecules, which have promising bioactive properties [152]. The awarding of the 2010 Nobel Prize in Chemistry to R. F. Heck, E. Negishi, and A. Suzuki, gave even more the attention to the development of these reactions [153,154].…”

Suzuki–Miyaura coupling under air in water promoted by polymer supported palladium nanoparticles

“…In fact, despite of the large number of reports concerning the use of polymer supported catalysts for promoting the Suzuki reaction in water, there are still margins of improvement. First of all the supported catalysts are generally less active (Pd mol% ≥ 0.1) than their homogeneous counterparts [12,14,16,43] (with homogeneous catalysts sometimes homeopathic concentration of palladium are sufficient [9,44]). In some cases supported catalysts suffer of considerable metal leaching and very often they are not able to promote the coupling of the aryl chlorides (more evaluable from an industrial point of view) [12,14,16].…”

“…First of all the supported catalysts are generally less active (Pd mol% ≥ 0.1) than their homogeneous counterparts [12,14,16,43] (with homogeneous catalysts sometimes homeopathic concentration of palladium are sufficient [9,44]). In some cases supported catalysts suffer of considerable metal leaching and very often they are not able to promote the coupling of the aryl chlorides (more evaluable from an industrial point of view) [12,14,16]. Moreover, most of the polymer supported catalysts are not active in neat water (maybe for the swelling proprieties of the polymeric matrix), needing for promoting the reaction, even with aryl bromides and iodides, the presence of a conventional organic co-solvent [21,23,29,45,46] and/or the addition of a phase transfer agent [29], both disadvantageous from the environmental point of view.…”

“…Usually, this crosscoupling reaction is catalyzed by soluble phosphane palladium complexes in organic solvents but such a protocol suffers from the difficulty in recovering and reusing the expensive homogeneous catalysts. To overcome this drawback, much work has been devoted to the development of reusable Pd heterogeneous catalysts [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In this regard, recyclable nanocatalysts [20][21][22][23][24][25][26][27][28] experienced great prosperity in the past decade, because they combine high surface area with excellent accessibility of the reactants to the active sites.…”