Arylation, using supported palladium

In 2003, the microwave-assisted coupUng of aryl hahdes with acetylenes using a palladium catalyst were carried out employing a modified Smith Process vial [49]. These vessels, equipped with a polypropylene frit and screw cap at the bottom, and sealed with an aluminum crimp cap fitted with a silicon septum at the top (Fig. 8), faciUtated the processing of approximately 1 g of solid support. Notably, they are compatible with stirring of the reaction mixture and monitoring of the temperature and pressure. 

The group of Ley has reported on the use of palladium-doped perovskites as recyclable and reusable catalysts for Suzuki couplings [151]. Microwave-mediated cross-couplings of phenylboronic acid with aryl halides were achieved within 1 h by utilizing the supported catalyst (0.25 mol% palladium) in aqueous 2-propanol (Scheme 7.127). The addition of water was crucial as attempted transformations in non-aqueous mixtures did not proceed. 

In experiments with a supported palladium catalyst, Pd/C, satisfactory yields were obtained without the use of phosphine ligands for the Heck reactions of aryl iodide with acrylonitrile, styrene, and methyl methacrylate in the ionic liquid [BMIM]PF6 (259). The addition of triethylamine improved the yields. The Pd/C remained in the ionic liquid only. The ionic liquid containing Pd/C can be reused as... 

In particular, cleavage of substrates from a solid support by use of palladium-promoted or -catalyzed reactions has some advantages over other cleavage methods. Because most protecting groups and functionalities are resistant toward palladium complexes, selective surgical removal is frequently possible. In addition, intermediate 7z>allyl- and er-aryl-palladium complexes can be used in principle for further derivatization with the use of appropriate linker types. 

Aryl sulfones have been prepared from sulfinic acid salts, aryl iodides and Formation of thiocyanates from unactivated aryl halides has been accomplished with charcoal supported copper(l) thiocyanate. " The copper catalyzed reaction of Na02SMe and aryl iodides give the aryl methyl sulfone. " A similar synthesis of diaryl sulfones has been reported using a palladium catalyst. " ... 

Figure 4.30 Amidation of aryl halides using a supported palladium catalyst...

A dendritic spacer of poly(aryl benzyl ether) was used for incorporation of phosphine ligands onto a PS resin support [116,117]. Thus, the condensation of 4-(diphenylphosphino)benzoic acid with Wang resin bearing poly(aryl benzyl ether) (generation 1-3) gave the PS-supported dendritic phosphine 86. Treatment of the dendritic phosphine 86 with Pd(dba)2 in THF afforded the bisphosphine-palladium complex 87 (Scheme 29) [ 118]. The PS-supported palladium complex exhibited a positive dendritic influence on the Heck reaction of bromobenzene with methyl acrylate. 

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,... 

Interestingly, Cai recently reported the use of fluorous silica gel (FSG)-supported palladium nanoparticles as an efficient and recyclable catalyst for the C2-arylation of indoles in conditions similar to the ones used by Sames (Scheme 6, 11CC806). The Pd-nanoparticles were prepared by... 

Cacchi s group reported an elegant synthesis of 2,5-diaryloxazoles 1616 using a palladium-catalyzed reaction of A -propargyl benzamides 1615 and aryl iodides (Scheme 1.412). The authors had evidence to support two different mechanistic pathways, depending on the substitution pattern of 1615 and the aryl iodide. The optimal reaction conditions were found to be Pd2(dba)3, P(2-furyl)3 as the ligand, NaOtBu as the base, and acetonitrile as the solvent. These conditions significantly reduce the reaction time and favor oxazole formation. 

Finally there are a number of very practical reasons which make supported palladium metal systems an attractive catalyst for organic synthesis in the laboratory and industrial fine chemical synthesis The most interesting catalysts do not need additional ligands like phosphines. It is not necessary to work under an inert atmosphere. The high thermal stability of supported palladium metal catalysts allows the use of higher temperatures for Heck reactions. The resulting higher reaction rate makes it possible to achvate less reachve aryl bromides and aryl chlorides in some cases. 

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