Palladium heterogenization

The SM reactions catalysed by Miyaura s diphenylphosphine-bounded palladium heterogeneous catalyst (342) Preparation of the catalyst and the cross-coupling reaction of 4-tolylboronic acid (271) with 2-chloro pyridine (149) /139I... 

Birch also illustrated tire difference in selectivity between Wilkinson s catalyst and typical heterogeneous catalysts. Hydrogenation of 1,4-dihydrobenzenes (derived from the "Birch reductions" of arenes) in the presence of Wilkinson s catalyst forms the tetra-substituted alkene product, whereas hydrogenation with classic platinum and palladium heterogeneous catalysts causes disproportionation to form arene byproducts (Equation 15.6). Like the (3-keto alcohol in Equation 15.5, the ester in Equation 15.6 is not reduced. 

Gao H., Angelici R.J. Combination catalysts consisting ofa homogeneous catalyst tethered to a silica-supported palladium heterogeneous catalyst Arene hydrogenation. J. Am. Chem. Soc. 1997 119 6937-6938... 

This section discusses the processes for nitrile rubber hydrogenation developed during past years using a heterogeneous catalyst. The published reports suggest that mostly the palladium catalyst has been used for nitrile... 

It can be summarized from the available data in Table 3 that supported palladium catalysts selectively hydrogenated carbon-carbon double bonds in the presence of the nitrile group in NBR. However, there is no detailed fundamental study on heterogeneous catalytic hydrogenation of nitrile rubber in the literature that can provide an insight into the reaction. The available information is limited since most of the literature is patented. 

In the preceding section, it has been shown that considerable attention has been devoted to palladium as a heterogeneous catalyst. The present section describes the homogeneous palladium catalysts developed for hydrogenation of NBR. The main drive behind the development of various catalyst systems is to find suitable substituents of the Rh catalyst. Palladium complexes are much cheaper as compared with Rh and exhibit comparable activity and selectivity to Rh and Ru complexes. 

The situation has now changed and currently an area of considerable research interest is in heterogenizing homogeneous catalysts. One such instance is to be found in the ethylene based manufacture of vinyl acetate (11). A homogeneous catalytic process based on palladium and copper salts was first devised, but corrosion problems were made much less serious in a heterogeneous system based on the same chemical principles. 

Hardy and Linnett (59) studied the heterogeneous recombination of atomic hydrogen at room temperature on nickel and nickel alloy foils. They did not find any similarity to the behavior of palladium and its alloys with gold studied earlier (35). There was no evidence that, as a result of exposure to atomic hydrogen, hydride was formed in any metal catalyst investigated with a resulting change in the activity of the initial parent metal catalysts. 

We have investigated the arylation of different primary or secondary amines with different aryl chlorides or bromides in heterogeneous or homogeneous catalysis conditions using palladium(O) or palladium(II) derivatives (Fig. 5). 

Volume 2, Catalytic Reactions. An account of palladium-catalyzed reactions involving formation of C—C, C—O, C—H, C-halogen, C—N, C—S, or C—Si bonds, and heterogeneous reactions. 

The coordination of ligands at the surface of metal nanoparticles has to influence the reactivity of these particles. However, only a few examples of asymmetric heterogeneous catalysis have been reported, the most popular ones using a platinum cinchonidine system [65,66]. In order to demonstrate the directing effect of asymmetric ligands, we have studied their coordination on ruthenium, palladium, and platinum nanoparticles and the influence of their presence on selected catalytic transformations. 

WiESSMEiER, G., Honigke, D., Heterogeneously catalyzed gas-phase hydrogenation of cis,trans,trans-1,5,9-cyclododecatriene on palladium catalysts having regular pore systems,... 

The catalytic applications of Moiseev s giant cationic palladium clusters have extensively been reviewed by Finke et al. [167], In a recent review chapter we have outlined the potential of surfactant-stabilized nanocolloids in the different fields of catalysis [53]. Our three-step precursor concept for the manufacture of heterogeneous egg-shell - nanocatalysts catalysts based on surfactant-stabilized organosols or hydrosols was developed in the 1990s [173-177] and has been fully elaborated in recent time as a standard procedure for the manufacture of egg-shell - nanometal catalysts, namely for the preparation of high-performance fuel cell catalysts. For details consult the following Refs. [53,181,387]. 

Pol5uireas were among the first polycondensation pol-5mers to be employed as catal dic supports for heterogeneous metal catalysts. The first report about palladium on polyurea, by Zhang and Neckers [99] dates back to 1979. They obtained their catalyst in a two step preparation, where the co-monomers (2,4- toluendiisocyanate, TDI, and the complex between palladium acetate and 4,4 -di-amino-2,2 -bip5Tiridine) were condensed together and... 

This argument is confirmed by the study of CO pulse chemisorption by Biffis at al., mentioned above. In this piece of investigation, the authors prepared a 2% (w/w) palladium catalyst supported by Lewatit UCP 118, a macroreticular resin (nominal cld = 18 %) from Bayer. Its TEM characterization showed a remarkably heterogeneous distribution of the metal nanoclusters, which are apparently located close to the surface of the polymer nodules [62] (Figure 9). 

In the present chapter, we focus on the catalyst nature in solution using well-defined metal NPs as catal 4 ic precursors it means, soluble (or dispersible) heterogeneous pre-catalysts, as stated by Finke [6]. Some experiments described in the literature concerning the distinction between homogeneous and heterogeneous catalysts are discussed (see Section 3), followed by a particular case studied by us with regard to the catalyst nature in the allylic alkylation reaction, using preformed palladium NPs as catalytic precursors (see Section 4). 

---