Palladium activations

Surfaces. Essentially any electrically conductive surface can be electroplated, although special techniques may be required to make the surface electrically conductive. Many techniques ate used to metalline nonconductive surfaces. These are weU-covered ia the Hterature (3) and can range from coating with metallic-loaded paints or reduced-silver spray, to autocatalytic processes on tin—palladium activated surfaces or vapor-deposited metals. Preparation steps must be optimized and closely controlled for each substrate being electroplated. 

The use of heterogeneous catalysts in this reaction has also been achieved palladium-montmorillonite clays [93] or palladium/activated carbon [94] in the presence of dppb transformed 2-allylphenols into lactones, the regiose-lectivity of the reaction being largely dependant on the nature of the support. Very recently, palladium complexes immobilized onto silica-supported (polyaminoamido)dendrimers were used as catalysts in the presence of dppb for the cyclocarbonylation of 2-allylphenols, 2-allylanilines, 2-vinylphenols, and 2-vinylanilines affording five-, six-, or seven-membered lactones and lactams. Good conversions are realized and the catalyst can be recycled 3-5 times [95]. 

An alternative deprotection method, which proceeds without prior isomerisation, involves heating under reflux the allyl ether in aqueous methanol with palladium/activated charcoal in the presence of toluene-p-sulphonic acid.79... 

Palladium activates halogen at the 5-position of 2-substituted 1,2,3-triazole 1-oxides and brings 361 and 370 to react as acceptors in crosscoupling reactions as described in Section 4.1.6.7. 

Kohler K, Heidenreich RG, Krauter JGE, Pietsch J (2002) Highly active palladium/activated carbon catalysts for Heck reactions correlation of activity, catalyst properties, and Pd leaching. Chem Eur J 8 622-631... 

It is not always clear which one (or more) of these forms operates, although the cationic species might appear to be most prone to nucleophilic attack. We have already seen that coordination of alkenes to divalent palladium activates them towards nucleophilic attack. In a similar manner, a wide range of nucleophiles may be introduced in a step which, in generating a new alkene, also reduces the palladium (II - 0) for introduction into the next cycle (Figure 7.11). 

The most active nickel and palladium catalysts are either ionic or contain a Lewis acid as a co-catalyst. In the case of palladium, activation has been reported in the presence of BF3 OEt2 [17, 18] while ionic species have been prepared by reacting [( -2-MeC3H4)Pd(cod)] BF4 with a donor ligand [20] or by treating the appropriate halide with a silver salt (e. g., eq. (2)) [16, 19, 20]. 

The aim of the present article is to report the use of carbon nanotubes as eatalyst support for a palladium active phase in the selective C=C hydrogenation of cinnamaldehyde in liquid-phase. Such reaction is of interest especially in the fine chemieal domain where speeific hydrogenation is actively sought. The catalytic performance was evaluated by comparing the observed activity and selectivity with those of a commercial catalyst supported on a high surfece area activated chareoal. The influenee of the support morphology and microstructure on the hydrogenation activity and selectivity will also be discussed. 

Other palladium-catalyzed 1,5-C-H activation processes reported are extensions of known work. In these examples, palladium activates the C-H bond, but whether the migration occurs or not is still debatable. An aryl to imidoyl C-H activation takes place in substrate 28 (7) under the same reaction conditions that promote the 1,4-palladium migration. However, this reaction affords a much lower yield (compare with Scheme 10), which implies a relatively low efficiency for this 1,5-C-H activation. Mechanistically, the reaction can either go through a direct C-H activation to form a six-membered palladacycle, followed by reductive elimination, or a proton channeling-based palladium migration, followed by an arylation with the original aromatic ring. The exact path has not been established experimentally or computationally. 

Scheme 16.14 A safety-catch palladium activated linker by Lyttle et al.

Somewhat different behaviour has been found when Group 11 metals are added to platinum and palladium. Activities fall continuously, and activation energy initially, but the former is determined subsequently by the decrease in the pre-exponential factor (Figure 10.7). Activities were also increased by adding molybdenum, rhenium - or iridium to platinum. There are conflicting... 

One of the uses of o-chloronitrobenzene is in the production of o-chloroaniline, which is obtained by catalytic reduction with sulfided palladium/active carbon catalysts. These catalysts enable dechlorination to be suppressed. 

The main product from 2-nitrotoluene is 2-toluidine, which can be manufactured by batchwise or continuous reduction. In the batch process moderate hydrogen pressures of 20-50 bar are employed, while higher pressures, in excess of 100 bar are used in continuous hydrogenation. The catalysts are commonly nickel or noble metals such as palladium/active carbon. 

Palladium is more abundant in nature and sells at half the current market price of platinum. Unlike Pt, the Pd-based electrocatalysts are more active towards the oxidation of a plethora of substrates in alkaline media. The high activity of Pd in alkaline media is advantageous considering that non-noble metals are sufficiently stable in alkaline for electrochemical applications. Importantly, it is believed that the integration of Pd with non-noble metals (as bimetallic or ternary catalysts) can remarkably reduce the cost of the membrane electrode assemblies (MEAs) and boost the widespread application or commercialization of DAFCs [1]. Palladium has proved to be a better catalyst for alcohol electrooxidation in alkaline electrolytes than Pt [2]. Palladium activity towards the electrooxidation of low-molecular weight alcohols can be enhanced by the presence of a second or third metal, either alloyed or in the oxide form [3]. 

The intramolecular addition of nudeophiles to palladium-activated triple bonds generates the palladated intermediate 9 (Scheme 6.13). While the latter can be protonated to liberate product, the reactivity of palladium can also be employed to intercept this intermediate with other bond forming reactions. These have provided methods to derivatize the heterocycle at the same time as it is generated. A range of substrates have been coupled with cydization via this approach, including aryl or vinyl halides, allylic and related R-X substrates, amines, halides, as well as carbon monoxide and olefins. 

Thio>gIycal derivatives act as useful donors in a palladium-activated coupling with acceptor alcohols (Scheme 5). 2,3-Unsaturated thioglycosides are also donors. ... 

Neopact, from Atotech, uses a tin-free palladium activator in colloidal form. The subsequent postdip removes the protective organic polymer from the palladium, leaving it exposed and with increased conductivity. It has been adapted to conveyorized horizontal equipment, works well in vertical, and can be followed by pattern or panel electroplating. (See Fig. 30.4.)... 

Carbon Suspensions. Black Hole, the second direct metallization techniqne, was patented by Dr. Carl Minten in 1988 and pioneered by Olin Hnnt, who sold their technology to MacDermid in 1991. MacDermid improved the process considerably and called it Black Hole II. Instead of palladium activator. Black Hole II uses carbon suspensions as its conductive medium. Polyelectrolyte conditioned nonconductive surfaces absorb carbon sites, and they line up after heating. To ensure sufficient conductivity, the carbon treatment is performed twice. Residues of carbon sites must be removed from the copper foil surface by a... 

It has been reported recently that the addition of platinum to a Pd/y-Al203 catalyst resulted in an increase of catalytic activity. Moreover, it was effective in preventing the deactivation of the catalysts for benzene combustion. On the contrary, the addition of platinum beyond a certain amount decreases activity, because the palladium active sites block the platinum active sites. It was reported that the activity of the catalysts was related to the oxidation state of the metal, Pd/Al ratio and particle size. Complete benzene oxidation over Pt-Pd bimetal catalyst supported on y-Al203 was also affected by the Pt-Pd ratio and the formation of small particles with a uniform size distribution was suggested to increase the activity. The full benzene conversion was obtained at 250°C. 

In a Schlenk reaction tube (5)-MLMI was dissolved in ethyl acetate, and 10 % palladium-activated carbon was added to the solution. For evacuation of reaction mixture, the aspirator was used and the same was replaced by hydrogen gas 5 times. After stirred under hydrogen atmosphere for 15 h, the reaction tube was again evacuated by an aspirator and replaced by nitrogen gas. Thereafter the reaction mixture was filtered to remove palladium-activated carbon. Finally, the filtrate was concentrated under pressure to afford (5)-iV-succionyl-L-leucine methyl ester ((S)-MLSI) as a white solid with 99.7 % yield [88]. 

Functionalization of Alkenes with Palladium-activated Carbon Nucleophiles. 

Alkenes can be functionalized with palladium-activated arenes, 3nelding styrene derivatives in a process applicable to a wide range of substrate combinations. An early demonstration of the possibilities of the Heck arylation was the coupling of 3-bromopyridine... 

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