Pd catalyst effect

Isomerization/cyclization of ct-dienyl-to-allyl acetates (carbonates). This Pd catalyst effects isomerization and cyclization of these substrates to vic-disubsti-... 

Buchwald s original BINAP/Pd-catalyst effectively couples aryl bromides with aniline derivatives, and either alkoxide bases [30] such as NaOt-Bu or mild bases such as CS2CO3 may be used, Eq. (79) [27, 37]. Similarly, Hayashi et al. have reported the use of DPBP (11) in the coupling of an aryl bromide and aniline. 

Simakova I, Simakova O, Maki-Arvela P, Simakov A, Estrada M, Murzin DY. Deoxygenation of stearic acid over supported Pd catalysts Effect of metal dispersion. Appl. Catal. A Gen. 2009 355 100. 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

In earlier studies (24), the reaction was carried out at temperatures above 200°C under autogenous pressure conditions usiag alkaU metal hydroxide or alkoxide catalysts significant amounts of carboxyUc acid, RCH2COOH, were formed as were other by-products. More recent reports describe catalysts which minimize by-products MgO—K CO —CUC2O2 (25), less basic but stiU requiring high temperatures Rh, Ir, Pt, or Ru complexes (26) and an alkaU metal alkoxide plus Ni or Pd (27), effective at much lower temperatures. 

Larock has developed a new catalyst system for the Pd-catalyzed cyclization of olefinic tosylamides. Whereas typical conditions require either stoichiometric amounts of Pd(II) salts or catalytic amounts of Pd(II) in the presence of benzoquinone as a reoxidant, the new catalyst system utilizes catalytic Pd(OAc)2 under an atmosphere of O2 in DMSO with no additional reoxidant <96JOC3584>. Although o-vinylic tosylamides 76 can be cyclized to Af-tosylindoles 77 using this catalyst system, PdCla/benzoquinone is more effective for such cyclizations. Interestingly, in the case of o-allylic tosylanilides, the cyclization can be modulated to afford either dihydroindole or dihydroquinoline products. In a related approach involving a common 7i-aUyl Pd-intermediate, 2-iodoanilines were coupled with vinylic cyclopropanes or cyclobutanes in the presence of a Pd catalyst to afford dihydroindoles <96T2743>. 

Notice the reagents that we use to accomplish a hydrogenation reaction (H2 and a metal catalyst). A variety of metal catalysts can be used, such as Pt, Pd, or Ni. The hydrogen molecules (H2) interact with the surface of the metal catalyst, effectively breaking the H—H bonds ... 

The use of well-defined complexes has been widespread in this reaction, despite intriguing studies by Beller and others that have shown that in situ catalytic systems often give better yields in comparison to isolated carbene-Pd(O) complexes [147-149]. Since the mechanism consists of an oxidative addition on a Pd(0)-monocarbene species, efforts in catalyst synthesis have been directed towards Pd(ll)-monocarbene complexes with other labile groups that can be easily released leading to the formation of Pd(0). This is the case for dimers of the type [Pd( j,-C1)C1(NHC)]2, a family of pre-catalysts effective under aerobic conditions [150], the [Pd(acac)Cl(NHC)] complexes [151] and related palladacycles [152-154],... 

Size Controlled Pd Nanoparticles Anchored to Carbon Fiber Fabrics Novel Structured Catalyst Effective for Selective Hydrogenation... 

The activity of both Pd and sulfided Pt catalysts for the synthesis of N-(l,3-dimethylbutyl)-N-phenylamine from aniline and MIBK was lower than that with acetone. This could be attributed to the steric hindrance effect (14). The selectivity over sulfided Pt catalysts was higher compared to unsulfided Pd catalysts due to formation of byproducts as with aniline-acetone reaction. 

The BS2 catalyst was more selective toward the formation of the dialkylated product than the Pd catalysts tested. The activity of BS2 for DAE-MIBK reaction was slower than that with acetone due to steric effects posed by the larger ketone. Here again, the imine tends to rapidly cychze to form imidazolidines or pyrimidines. Figure 17.2 shows the stepwise formation of various side products observed during the reductive alkylation of DAE with acetone. 

Alkyl substituents on boron in 9-BBN derivatives can be coupled with either vinyl or aryl halides through Pd catalysts.22413 This is an especially interesting reaction because of its ability to effect coupling of saturated alkyl groups. Palladium-catalyzed couplings of alkyl groups by most other methods often fail because of the tendency for (3-elimination... 

Iglesias-Juez, A., Martinez-Arias, A. and Fernandez-Garcia, M. (2004) Metal-promoter interface in Pd/(Ce,Zr)0 c/Al203 catalysts Effect of thermal aging, J. Catal., 221, 148. 

Lanthanides in combination with transition metals have been shown to have a positive effect in promoting heterogeneous catalytic reactions. The bimetallic Yb—Pd catalyst obtained from the precursor (pMF)i0Yb2 Pd(CN)4]3 K on a titania surface offers improved performance over a palladium-only catalyst for the reduction of NO by CH4 in the presence of 02.99 100 The structure, shown in Figure 6, consists of two inverted parallel zigzag chains that are connected through the lanthanide atoms by trans-bridging [Pd(CN)4]2- anions.101... 

S. Y Wang, and J. P. Chen et al., Selective Debenzylation in the Presence of Aromatic Chlorine on Pd/C Catalysts Effects of Catalyst Types and Reaction Kinetics , paper presented at 20th Organic Reactions Catalysis Society Meeting, March 21-25, 2004, Hilton Head Island, SC, USA. 

One drawback to this alkyne annulation chemistry is that it requires either symmetrical alkynes or unsymmetrical alkynes in which the two substitutents on the internal alkyne are sterically quite different or else one obtains mixtures of regioisomers. One way to overcome this problem is to prepare the corresponding arylalkyne through catalytic Pd/Cu chemistry and then effect electrophilic cyclization using organic halides and a Pd catalyst (Scheme 8).9... 

We have demonstrated that supported Pd and Cu catalysts are effective in catalyzing the oxidative carbonylation at low pressure reaction condition and the supported metal catalysts can be easily separated from the product mixture in both fixed bed and slurry phase reactors (12,17). The objective of this study is to investigate the feasibility of using Al203-supported Pd catalysts for catalyzing the reductive carbonylation of nitrobenzene with ethanol. 

Figure 3 demonstrates the influence of different modifiers on the reaction rate. Compared to the unmodified 5%Pd catalyst, the addition of 20 pi of pyridine or 20 pi of ethylenediamine increased the reaction rate from 1.5 to 2 mmol / (min gram) catalyst. Adding twice the amount of modifier (40 pi pyridine) does not increase the reaction rate any further. Obviously all the available surface palladium is already effectively modified. In contrast triethylamine does not exhibit any influence on the reaction rate. 

Selective Debenzylation in the Presence of Aromatic Chlorine on Pd/C Catalysts Effects of Catalyst Types and Reaction Kinetics... 

FIGURE 2.32 DMSO modification of Pt catalysts to stop hydrogenation at hydroxylamine. Note DMSO is not effective with Pd catalysts. 

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