Resin-bound palladium catalyst

Zhang and Allen [97] have recently reported an easily prepared, air- and moisture-stable resin-bound palladium catalyst for the Suzuki coupling reaction. Commercially available resin-bound thiourea, Deloxan THP II [98], was used as the starting material. The resin-bound catalyst was prepared simply by treating the wet Deloxan resin with a solution of Pd(OAc)2 in methanol. Suzuki coupling reactions were then carried out using the resin at a... 

A unique class of polymer, polyquinone-bearing sulfonic acid functional groups, when combined with Pd(II), displayed activities for the oxidation of aUcenes to aldehyde, without the need for a cocatalyst such as CuCl2. ° Here the polymer matrix serves both as a catalyst carrier and a redox mediator. A remarkable solvent effect on the selectivities of a polymer-bound palladium catalyst was observed with the oxidation of 2-octene, affording 97% 2-octayne in Et0H-H20 and 89% 2-octanone when EtOH was replaced with dixoane. Oxidation of 2-methylnaphthalene to 2-methyl-1,4-naphthoquinone (vitamin K3) can be effected by palladium absorbed on ion exchanged resin with aqueous H2O2. 

Acid derivatives that can be converted to amides include thiol acids (RCOSH), thiol esters (RCOSR), ° acyloxyboranes [RCOB(OR )2]. silicic esters [(RCOO)4Si], 1,1,1-trihalo ketones (RCOCXa), a-keto nitriles, acyl azides, and non-enolizable ketones (see the Haller-Bauer reaction 12-31). A polymer-bound acyl derivative was converted to an amide using tributylvinyl tin, trifluoroacetic acid, AsPh3, and a palladium catalyst. The source of amine in this reaction was the polymer itself, which was an amide resin. 

Several palladium catalysts for formation of aryl sulfides from aryl halides have been investigated more recently. A combination of Pd2(dba)3 and DPEphos catalyzed the formation of a broad range of diaryl sulfides in the presence of 1 mol.% palladium and NaO-t-Bu base in toluene solvent.12,rThe highest yields of alkyl aryl sulfides were obtained from aryl triflates and n-butyl thiol catalyzed by a combination of palladium acetate and BINAP. However, these reactions contained 10 mol.% catalyst, were long, and required deactivated aryl triflates. A combination of Pd2(dba)3 and DPPF catalyzed the coupling of thiols with resin-bound aryl halides.121... 

Several combinatorial approaches to the discovery of transition metal based catalysts for olefin polymerization have been described. In one study Brookhart-type polymer-bound Ni- and Pd-(l,2-diimine) complexes were prepared and used in ethylene polymerization (Scheme 3).60,61 A resin-bound diketone was condensed with 48 commercially available aminoarenes having different steric properties. The library was then split into 48 nickel and 48 palladium complexes by reaction with [NiBr2(dme)] and [PdClMe(COD)], respectively, all 96 pre-catalysts being spatially addressable. 

Buchwald has shown that, in combination with palladium(II) acetate or Pd2(dba)3 [tris(dibenzylideneacetone)dipalladium], the Merrifield resin-bound electron-rich dialkylphosphinobiphenyl ligand (45) (Scheme 4.29) forms the active polymer-supported catalysts for amination and Suzuki reactions [121]. Inactivated aryl iodides, bromides, or even chlorides can be employed as substrates in these reactions. The catalyst derived from ligand (45) and a palladium source can be recycled for both amination and Suzuki reactions without addition of palladium. 

Numerous groups have used the BINAP/Pd- and DPPF/Pd-based reaction protocols for the arylation of cyclic secondary amines. Independently, Ward and Farina [31] as well as Willoughby and Chapman [32] disclosed that the palladium-catalyzed arylation reaction could be effected on resin-bound amines, Eq. (7). Both groups reported that while the (o-tol)3P-based catalysts were often inferior to the BINAP-based system, using DPPF as ligand often resulted in comparable yields and reaction rates. They also observed that BINAP-derived catalysts usually yielded smaller amounts of reduced arene by-products. 

Deprotection of the Resin-Bound Glycopeptide Allyl Ester 12 with a Palladium Catalyst and A,iV-Dunethylbarbituric Acid ... 

Rapid and efficient Suzuki coupling of protoxygencol has been developed using polymer-supported palladium catalysts under microwave conditions at 110 °C within 10 min. in the synthesis of various benzolidines [15]. Radical cyclization of resin-bound N-(2-bromophenyl)acrylamides using Bu3SnH proceeded smoothly in DMF or toluene as solvent under the action of microwave irradiation for preparation of 2-oxindoles as illustrated in Scheme 10.9. This method is superior to conventional solution synthesis [16]. 

In a related study, polymer-supported triphenyl phosphine was used in palladium-catalyzed cyanations [136]. Commercially available resin-bound triphe-nylphosphine was mixed with palladium(II) acetate in N,N-dimethylformamide to generate the heterogeneous catalytic system under a nitrogen atmosphere. The reagents were then added to the activated catalyst and the mixture was irradiated at 140 °C for 30-50 min (Scheme 16.89). Finally, the resin was removed by filtration and evaporation of the solvent furnished the desired benzonitriles in high yields and excellent purity. 

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. 

One of the earliest examples of polystyrene-bound palladium was reported by Tera-sawa and co-workers in 1975, when such a system was used for hydrogenation of olefins and acetylenes and isomerization of double bonds. However, it is not clear if the high activity exhibited by resin-bound catalysts toward hydrogenation was due to the reduced heterogeneous paUadium deposited on the resin. Pittman et al. in 1976 prepared a series of diphenylphosphinated PS-based palladium catalysts and studied their behavior... 

Esters of general structure B can be cleaved with the same reagents described for the esters of general structure A. The multifunctionality of the resulting compounds is Umited because the carbonyl part of the functionality remains on the resin. Most type-B esters are released as alcohols from the resin (path a) but there are a few examples which obtain other derivatives of the resin-bound structures (Schemes 16,18 and 19). Path b in Scheme 16 illustrates the cleavage of methylarenes 108 on polymeric support pubhshed by Sucholeiki in 1997 [140]. Release from the resin affords addition of a palladium catalyst (Pd(OAc)2) and formate reduction. 

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