Cross-coupling reactions polymer support catalysts

Steel PG, Teasdale CWT. Polymer supported palladium A-heterocyclic carbene complexes long lived recyclable catalysts for cross coupling reactions. Tetrahedron Lett 2004 45 8977-8980. 

Pd is also a potential contaminant and Nobile and coworkers recently employed a polymer-supported palladium complex (Pd-pol, Figure 5.3.1), obtained by copolymerization of Pd(AAEMA)2 with ethyl methacrylate and ethylenene glycol dimethacrylate (AAEMA is the deprotonated form of 2-(acetoacetoxy)ethyl methacrylate), as a catalyst in Stille cross-coupling reactions [Equation (5.3.14)]. The reaction can be performed in air without any activating ligand and with non-dried solvents. The catalyst can be recycled several times. 

The commercially available palladium catalyst FibreCat has also been applied to the Suzuki reaction [53]. The polymer-supported catalyst with microwave heating gave rise to cross-coupled product in good yield as exemplified in the transformation of 152 and 153 into arylpyridine 154. 

Palladium species immobilized on various supports have also been applied as catalysts for Suzuki cross-coupling reactions of aryl bromides and chlorides with phenylboronic acids. Polymers, dendrimers, micro- and meso-porous materials, carbon and metal oxides have been used as carriers for Pd particles or complexes for these reactions. Polymers as supports were applied by Lee and Valiyaveettil et al. (using a particular capillary microreactor) [173] and by Bedford et al. (very efficient activation of aryl chlorides by polymer bound palladacycles) [174]. Buch-meiser et al. reported on the use of bispyrimidine-based Pd catalysts which were anchored onto a polymer support for Suzuki couplings of several aryl bromides [171]. Investigations of Corma et al. [130] and Plenio and coworkers [175] focused on the separation and reusability of Pd catalysts supported on soluble polymers. Astruc and Heuze et al. efficiently converted aryl chlorides using diphosphino Pd(II)-complexes on dendrimers [176]. 

The polymeric imide could then be reacted with primary amines or ammonia to form ammonium salts for a subsequent reactions with a carboxylic acid in the presence of a coupling reagent. It could then be converted to amides or functionalized as a uranium salt for use as polymer-supported peptide coupling. In addition, the anhydride was also reacted with di(2-pyrldyl)methylamine and formed a recoverable palladium catalyst for cross-coupling reactions that could take place in water. 

The Ni Bt2(bpy) complex was found to be an efficient catalyst precursor, not only in the synthesis of ArSAr derivatives, but also in the catalytic formation of ArSeAr compounds (via the cross-coupling reaction of aryl selenols). Polymer-supported borohydride was used as a reducing agent and polymer-supported aryl iodide as a reagent. The reaction was carried out with high yield and resulted in high purity of the products leading to the construction of a library of supported species (Scheme 3.21) [48]. 

Phan, N.T.S., Brown, D.H., and Styring, P. (2004) A polymer-supported salen-type palladium complex as a catalyst for the Suzuki-Miyaura cross-coupling reaction. Tetrahedron Lett., 45 (42), 7915-7919. 

The corresponding catalytic version of this reaction was performed using either naphthalene- or biphenyl-supported polymers 594 or 595, respectively, which were prepared by cross-coupling copolymerization of 2-vinylnaphthalene or 4-vinylbiphenyl with vinyl-benzene and divinylbenzene promoted by AIBN in THF and polyvinyl alcohoP . These polymers have been used as catalysts (10%) in lithiation reactions involving either chlorinated functionalized compounds or dichlorinated materials in THF at —78°C and were re-used up to ten times without loss of activity, which is comparable to the use of the corresponding soluble arenes. 

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