Palladium leaching

The catalytic activity, however, is generally associated with leaching of the metal into solution, the reaction being most likely catalyzed by soluble active Pd species. Palladium leaching is generally caused by oxidative attack of the aryl halide on the metal nanoparticles, giving catalyt-ically active aryl halide Pd(II) species in solution [30]. 

The supported aqueous phase methodology was applied to the system Pd(OAc)2/5 TPPTS, a catalytic precursor for the Trost-Tsuji reaction. The characterization of the solid by 31P MAS NMR confirms the presence of Pd°(TPPTS)3 as the main surface species. The catalytic properties of the solid were tested for the allylic substitution of E-cinnamylethylcarbonate by different nucleophiles such as ethyl acetoacetate, dimethyl malonate, morpholine, phenol, and 2-mercapto-pyridine. The absence of palladium leaching was demonstrated, and having solved the problem of water leaching from the solid to the organic phase, the SAP-Pd catalyst was successfully recycled several times without loss in its activity. It was used in a continuous flow experiment which... 

Further investigations using model compounds showed that the formation of PdCl2 by a reaction with the solvent, as suggested by Brinkmann el al. [30], was also not responsible for the observed rapid deactivation. Palladium leaching after formation of Pd(0) was also excluded by experiments. The authors concluded therefore that the presence of allyl acetate facilitated the decomposition. 

Bidentate chiral water-soluble ligands such as (S,S)-2,4-bis(diphenyl-sulfonatophosphino)butane BDPPTS (Fig. 2) or (R,R) 1,2-bis(diphenylsul-fonatophosphinomethyl)cyclobutane have been prepared [25]. Their palladium complexes catalyze the synthesis of chiral acids from various viny-larenes and an ee of 43% has been reached for p-methoxystyrene with the BDPPTS ligand. Furthermore, recycling of the aqueous phase has shown that the regio- and enantioselectivity are maintained and that no palladium leaches. 

The palladium leaching to the product phase was investigated via ICP-OES measurements. In all cases about 5% of the metal catalyst is lost. This palladium loss is in the same range as in the biphasic reaction in water with subsequent extraction with cyclohexane. Therefore, one can conclude that the use of cyclodextrins has almost no influence on the palladiiun leaching. For the reaction described in this work, this makes the use of cyclodextrins as PCT catalysts more attractive than the TMS systems to overcome mass transfer limitations. 

Carbon supported powdered palladium catalysts have been widely used in the chemical industry. In addition to activity and selectivity of those catalysts, the recovery rate of the incorporated precious metal has a major impact on the economic performance of the catalyst. In this study, the effects of catalyst age, oxidation state of the incorporated metal and temperature treatment on the palladium leaching resistance as well as on activity and dispersion of carbon supported palladium catalysts were investigated. 

Similar trends were found for the palladium leaching values when leaching fresh catalysts. However, the overall amount of palladium leached is higher in this case. The results of the leaching tests performed one day after the catalyst preparation show values between 140 and 240 ppm for the reduced and of 30 to 60 ppm for the non-reduced catalysts. A comparison of the decrease of metal leaching over time shows different aging effects for the dry catalysts compared to the wet catalysts of... 

The biphasic system was further improved by running the EG telomerization in a three-step mixer settler set-up, to overcome issues with the diminished rate arising from mass transport limitations. The process was run for 30 h with a 75% yield of mono-telomer and palladium leaching limited to only 19 ppm [76]. 

C imHPFe] Silica-supported Pd nanoparticles Et3N 80 °C. Phosphine-free arylation of acrylates with aryliodide PdCl2(NH3)2 as catalyst precursor palladium leaches from the support into the ionic liquid phase product extracted with tert-butyl methyl ether. [85]... 

The solvent also affects palladium leaching. For more precise determination, conditions favoring palladium leaching (T = 80 °C, as mentioned above) were applied in the coupling of p-bromoacetophenone and styrene (Table 4, entries 1-... 

The guanidinium phosphine 1 (cf. Fig. 2) was also successfully tested for allylic substitutions. The reaction of allyl acetate 6 and malonate 7 afforded coupling product 8 in 56% yield. The palladium leaching was determined to be about 0.3% (Scheme 5). 

Fourth- and fifth-generation phosphine-functionalized DAB dendrimers were applied, for which 100% conversion was obtained at the beginning. A 20% decrease was observed after 100 h, as well as palladium leaching between 0.07 and 0.14% per residence time. The soluble support, on the other hand, was completely retained in the membrane reactor. 

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