Amphiphilic resin-supported ligand

The reaction which is accelerated by the presence of water can be carried out in water when a 2/3-cyclodextrin-[Rh(OH)(cod)]2,943,944 [Rh(cod)Cl]2/TPPTS,945 or amphiphilic resin-supported rhodium(i) complex was used.946 It was also reported that potassium alkenyl and aryltrifluoroborates [RBF3]K undergo similar addition to enones in the presence of an Rh(i) catalyst.935,947,948 The cationic rhodium(i) complexes such as [Rh(cod)]BF4, [Rh(cod)(CH3CN)2]BF4, or its combination with a diphosphine ligand (dppp or dppb) efficiently catalyzed the reaction. The neutral complexes, generated in situ from Rh(acac)(GH2=GH2)2, or Rh(acac)(coe)2, and dppp or dppb, were also effective. The effects of catalysts, solvents, and bases,949 and the mechanism of catalytic cycle950 have been studied in detail. 

Some preliminary results were obtained concerning the asymmetric Pd-cata-lyzed alkylation of l,3-diphenyl-2-propenyl acetate in water or in an aqueous/or-ganic biphasic medium, using as the chemical ligands phosphines derived from carbohydrates (ee up to 85%) [32], amphiphilic resin-supported MOP and P,N-che-lating ligands (ee up to 98%) [33, 34], or BINAP in the presence of surfactants (ee up to 92%) [35],... 

Water-soluble polymer-bound Pd(0)-phosphine catalyst has also been efficiently used in aqueous or mixed aqueous/organic media, the catalyst being recycled by solvent or thermal preparation methods [17]. Amphiphilic resin-supported palladium-phosphine complexes show high catalytic activity in allylic substitution reactions of various allylic acetates with different nucleophiles in aqueous media [18, 19]. Enantiomeric excess up to 98% is obtained using amphiphilic resin-supported MOP ligand or resin-supported P,N-chelating palladium complexes, the catalyst being recyclable [20,21]. The catalyst could be recovered by simple filtration and re-used without any loss of activity and enantioselectivity. 

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... 

Uozumi, Y., Danjo, H. and Hayashi, T., Palladium-catalyzed asymmetric allylic substitution in aqueous media using amphiphilic resin-supported MOP ligands. Tetrahedron Lett., 1998, 39, 8303-8306. 

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]. 

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... 

Suzuki couplings of aryl halides (eight varieties) and aryl- or vinylboronic adds (12 varieties) have been reported in water in the presence of a palladitmi complex of an amphiphilic polystyrene-poly(ethylene glycol) copolymer resin-supported N-an-chored 2-aza-l,3-bis(diphenylphosphino)propane ligand and potassium carbonate to give uniform and quantitative yields of the corresponding biaryls products (96 combinations) (Equation 75) [104]. 

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