Amphiphilic PS-PEG

Heterogeneous aquacatalytic palladium-catalyzed allylic substitution with nitromethane as the Cl nucleophile has been developed by Uozumi (Scheme 3.71). By using an amphiphilic PS-PEG polymer-supported chiral palladium complex, the asymmetric allyhc nitromethylation of cycloalkenyl esters proceeded smoothly in water. For example, when polymer-supported palladium complex 214 was employed in the asymmetric nitromethylation of cycloheptenyl carbonate 215... 

Figure 6.1 Amphiphilic PS-PEG resin-supported palladium-phosphine complexes.

Cross-coupling reactions have also been examined in water using amphiphilic PS-PEG resin-supported palladium complexes. Palladium-catalyzed coupling of aryl halides with aryl(or alkenyl)boronic acids (the so-called Suzuki-Miyaura coupling) took place in aqueous alkaline solution in the presence of polymeric catalyst 59 at 25 °C to give the biaryls in excellent yields [90,... 

The oxidation of alcohols to the corresponding aldehydes or ketones is an important reaaion in organic synthesis. " This reaction can be catalyzed under aerobic conditions and the alcohol conversion can be monitored by gas chromatography (GC). It is important to note that water is almost the only solvent currently deemed suitable for the industrial application of this catalytic process, because it avoids the hazards associated with the use of oxidizable organic solvents under oxygen pressure. Recently, Uozumi et have reported the aerobic oxidation in water of various alcohols by using amphiphilic PS-PEG resin-supported Pt NPs as catalyst. Biffs et have studied the catalytic activity of microgel-stabilized Au nanoclusters in the aerobic oxidation of benzylic and aliphatic alcohols in water under mild conditions (50-70 °C, 1-3 atm O2). 

The catalyst supported on amphiphilic PS-PEG resin (same as in Scheme 49) has been used for carbonylation of water-insoluble iodoarenes in water at room temperature to give near to quantitative conversions. The catalyst survived as many as 30 reuses without loss of activity, which makes it one of the most durable supported catalysts described so... 

Amphiphilic resin supported ruthenium(II) complexes similar to those displayed in structure 1 were employed as recyclable catalysts for dimethylformamide production from supercritical C02 itself [96]. Tertiary phosphines were attached to crosslinked polystyrene-poly(ethyleneglycol) graft copolymers (PS-PEG resin) with amino groups to form an immobilized chelating phosphine. In this case recycling was not particularly effective as catalytic activity declined with each subsequent cycle, probably due to oxidation of the phosphines and metal leaching. 

An amphiphilic polystyrene-poly(ethylene glycol) (PS-PEG) resin-support has been used successfully as a suitable support for asymmetric catalysts in aqueous media. A polymeric (R]-2-(diphenylphosphino) binaphthyl (MOP) ligand 205 anchored onto the PS-PEG resin was shown to be an effective chiral ligand for the enantioselective p-allyhc substitution under aqueous condihons (Scheme 3.67) [130]. 

An alternative approach to a PS-PEG amphiphilic BINAP has been reported involving reaction of BINAP-carboxylic acid 116 with an amine-functionalized PEG-PS support to give 117 (Scheme 54). ... 

The Uozumi group developed unique recyclable amphiphilic resin-supported tri-arylphosphines (PEP) attached to polyethylene glycol-polystyrene graft copolymer (PEG-PS), and found that Pd(PEP) is an active catalyst for allylation in water [40a]. They immobilized a chiral amine on PS-PEG-NH2 resin to give PS-PEG resin-supported chiral P,N-ligand R,S) 106. Asymmetric allylation of diethyl malonate... 

Palladium bound to polymeric support has been employed for allylic substitution. Amphiphilic resins based on block PS-PEG-bearing phosphine residues (cf. Scheme 49) were used for allyhc substitution in aqueous media both in achiral and in enantios-elective reactions, hi the latter, MOP-type ligand has been tethered by a chiral link containing a residue of natural amino acid to the amphiphilic block-copolymer... 

Jankova, K., et al. (1998). S5mthesis of amphiphilic PS-b-PEG-b-PS by atom transfer radical polymerization. Macromolecules, 31(2) 538-541. 

Carbonylation of reactive iodides proceeds using PdCl2(PPh3)2 as a standard catalyst under mild conditions in the presence of a base. Several modified catalyst systems have been reported. For example, ligandless Pd charcoal is an active catalyst at 140 °C [1]. Uozumi reported that the amphiphilic phosphine-Pd complex (Pd-PEP) bound to PEG-PS resin is a very active and useful catalyst. Carbonylation... 

---