Palladium catalytic activity with functional

Numerous quantum mechanic calculations have been carried out to better understand the bonding of nitrogen oxide on transition metal surfaces. For instance, the group of Sautet et al have reported a comparative density-functional theory (DFT) study of the chemisorption and dissociation of NO molecules on the close-packed (111), the more open (100), and the stepped (511) surfaces of palladium and rhodium to estimate both energetics and kinetics of the reaction pathways [75], The structure sensitivity of the adsorption was found to correlate well with catalytic activity, as estimated from the calculated dissociation rate constants at 300 K. The latter were found to agree with numerous experimental observations, with (111) facets rather inactive towards NO dissociation and stepped surfaces far more active, and to follow the sequence Rh(100) > terraces in Rh(511) > steps in Rh(511) > steps in Pd(511) > Rh(lll) > Pd(100) > terraces in Pd (511) > Pd (111). The effect of the steps on activity was found to be clearly favorable on the Pd(511) surface but unfavorable on the Rh(511) surface, perhaps explaining the difference in activity between the two metals. The influence of... 

The area of catalytic activation of most unreactive C-Cl bonds has flourished tremendously over the last decade. Because of its considerable practical importance the field keeps growing at an impressive pace. Numerous novel techniques have been developed for the synthesis of various functionalized aromatic compounds from the corresponding chloroarenes. A series of new palladium, nickel, and rhodium catalysts have been synthesized for C-Cl activation and much information has been accrued on the mechanism of catalysis with these complexes. 

Given the published studies that indicate that the insertion of nonfunction-alized norbomenes into metal-carbon bonds occurs with exo, exo- stereochemistry (e.g., Fig. 9.1) we sought to determine whether the presence of an endo functionality would change the insertion stereochemistry. Because of the relative instability of the catalytically active palladium species, detailed studies encompassing the coordination and insertion of norbornene derivatives were carried using the model... 

In this context, a functionalized ionic liquid, 1-(2-hydroxyethyl)-3-methyl imidazolium tetrafluoroborate [hemim][BF4], is reported as an efficient and recyclable reaction medium for the palladium catalyzed Heck reaction. The olefination of iodoarenes and bromoarenes with olefins generates the corresponding products in good to excellent yields under phosphine-ffee reaction conditions. After separation of the product, fresh starting materials are charged into the recovered ionic liquid which entraps the palladium catalyst. The reactions still proceed quantitatively for six cycles, without significant loss of catalytic activity. " The effect of both the cation and the anion on the chemical yield is shown in Figure 28. 

To test the hypothesis that the catalytic activity of a Group VIII metal is associated with an unfilled (/-band, various workers determined reaction rates on alloys such as nickel-copper and palladium-gold as a function of composition. It was reasoned that the extent of filling of the (/-band would be determined by the composition of the alloy hence it should be possible to relate catalytic activity to (/-band vacancies. 

Palladium Catalysts Palladium catalysts are effective and powerful for C—H bond functionalization. Carbene precursors and directing groups are commonly used strategies. Generally, sp3 C—H bond activation is more difficult than sp2 C—H bond activation due to instability of potential alkylpalladium intermediates. By choosing specific substrates, such as these with allylic C—H bonds, palladium catalytic systems have been successful. Both intramolecular and intermolecular allylic alkylation have been developed (Scheme 11.3) [18]. This methodology has presented another alternative way to achieve the traditional Tsuji-Trost reactions. 

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