Salts palladium

Palladium catalysts are useful alternatives to Adams platinum oxide catalyst described in Section 111,150. The nearest equivalent to the latter is palladium chloride upon carbon and it can be stored indefinitely the palladium salt is reduced to the metal as required ... 

Under high pressures and temperatures, iodine reacts with oxygen to form iodine pentoxide [12029-98-0] (44). The reaction of iodine with carbon monoxide under acidic conditions is catalyzed by palladium salts (45). Phosphorous vapor and iodine react to form phosphoms trHodide [13455-01 -17, PI (46). 

Other processes described in the Hterature for the production of malonates but which have not gained industrial importance are the reaction of ketene [463-51-4] with carbon monoxide in the presence of alkyl nitrite and a palladium salt as a catalyst (35) and the reaction of dichioromethane [75-09-2] with carbon monoxide in the presence of an alcohol, dicobalt octacarbonyl, and an imida2ole (36). 

Electronic Applications. The PGMs have a number of important and diverse appHcations in the electronics industry (30). The most widely used are palladium and mthenium. Palladium or palladium—silver thick-film pastes are used in multilayer ceramic capacitors and conductor inks for hybrid integrated circuits (qv). In multilayer ceramic capacitors, the termination electrodes are silver or a silver-rich Pd—Ag alloy. The internal electrodes use a palladium-rich Pd—Ag alloy. Palladium salts are increasingly used to plate edge connectors and lead frames of semiconductors (qv), as a cost-effective alternative to gold. In 1994, 45% of total mthenium demand was for use in mthenium oxide resistor pastes (see Electrical connectors). 

Miscellaneous. Reductioa of a palladium salt by CO is the basis of a visual test for ambieat carboa moaoxide (227). Palladium compouads are used as photographic seasitizers (228). The low dimensional mixed valeace compouad Csq g3[Pd(S2C2(CN)2)] 0.5H2O behaves as a semimetal at room temperature (229). Palladium compouads isostmctural with poteat platiaum antitumor compounds have poor antitumor activity (230). 

The alkali metal xanthates react with the lower alkylamines ia the presence of catalytic amounts of nickel or palladium salts to give dialkjdthionocarbamates (62) ... 

The oxidative carbonylation of styrene with carbon monoxide, oxygen, and an aUphatic alcohol in the presence of a palladium salt, a copper salt, and sodium propionate also provides the requisite cinnamate. 

Palladium catalysts have been prepared by fusion of palladium chloride in sodium nitrate to give palladium oxide by reduction of palladium salts by alkaline formaldehyde or sodium formate, by hydrazine and by the reduction of palladium salts with hydrogen.The metal has been prepared in the form of palladium black, and in colloidal form in water containing a protective material, as well as upon supports. The supports commonly used are asbestos, barium carbonate, ... 

The colloidal palladium solution is prepared as follows A solution of a palladium salt is added to a solution of an alkali salt of an acid of high molecular weight, the sodium salt of protalbinic acid being suitable. An excess of alkali dissolves the precipitate formed, and the solution contains tine palladium in the form of a hydrosol of its hydroxide. The solution is purified by dialysis, and the hydroxide reduced with hydrazine hydrate. On further dialysis and evaporation to dryness a water-soluble product is obtained, consisting of colloidal palladium and sodium protalbinate, the latter acting as a protective colloid. 

Palladium-reihe, /. palladium series, -salz, n. palladium salt, -schwamm, m. palladium sponge. -Schwarz, n. palladium black, -was-serstoff, m. palladium hydride. 

Palladium salts are able to catalyse diyne carbonylation, so the reaction can be performed at room temperature under 1 atm of carbon monoxide. Thiourea (H2NCSNH2), which is added to stabilise the Pd catalyst (Scheme 34), is described as the best ligand for the efficiency of this reaction [124]. 

In this review, CPOs constructed by covalent bonds are mainly focused on however, stable coordination bonds comparable to the stability of the covalent bonds have potential for future enhanced molecular design of novel CPOs. One representative is the bond between pyridine-type nitrogen and metal, which is widely used in supramolecular chemistry, that is, the cyclic supramolecular formation reaction between pyridine-substituted porphyrin and metal salts (Fig. 6d) [27,28]. Palladium salts are frequently used as the metal salts. From the viewpoint of the hard and soft acid and base theory (HSAB), this N-Pd coordination bond is a well-balanced combination, because the bonds between nitrogen and other group X metals, N-Ni and Ni-Pt coordination bonds, are too weak and too strong to obtain the desired CPOs, respectively. For the former, the supramolecular architectures tend to dissociate into pieces in the solution state, and for the latter. 

The palladium salt/dppe combination catalyzes the hydroamination of 1,3-butadi-ene with NH3 to give a mixture of 1 1, bis-(l l) and tris-(l l) hydroamination products (Eq. 4.48) [182]. 

Trifluoromethyl imidates show similar reactivity.262 Imidate rearrangements are catalyzed by palladium salts.263 The mechanism is presumably similar to that for the Cope rearrangement (see p. 555). 

I am indebted to the many hardworking students who have contributed so much both experimentally and intellectually to the chemistry described in this article. Many of their names appear in the references that follow. I also wish to acknowledge the Petroleum Research Fund, the National Institutes of Health, and the National Science Foundation for their financial support Kawaken Fine Chemicals Co. and Johnson Matthey Inc. for donating the palladium salts and Frontier Scientific for providing the arylboronic acids used in this work. 

Selective aromatic functionalization has been a permanent object of research since the ninenteenth century. Catalysis has offered a powerful tool to achieve this goal. Over the years we have worked out a complex catalytic system consisting of an inorganic compound such as a palladium salt and an organic molecule containing a strained double bond such as norbomene (1,2). We have seen that these two catalysts cooperatively react with an aromatic iodide, an alkyl iodide and a terminal olefin. The following equation reports an example (L = solvent and/or olefin) (3). 

Palladium-catalyzed carbon-carbon cross-coupling reactions are among the best studied reactions in recent decades since their discovery [102, 127-130], These processes involve molecular Pd complexes, and also palladium salts and ligand-free approaches, where palladium(O) species act as catalytically active species [131-135]. For example, the Heck reaction with aryl iodides or bromides is promoted by a plethora of Pd(II) and Pd(0) sources [128, 130], At least in the case of ligand-free palladium sources, the involvement of soluble Pd NPs as a reservoir for catalytically active species seems very plausible [136-138], Noteworthy, it is generally accepted that the true catalyst in the reactions catalyzed by Pd(0) NPs is probably molecular zerovalent species detached from the NP surface that enter the main catalytic cycle and subsequently agglomerate as N Ps or even as bulk metal. 

Until recently, the hydroformylation using palladium had been scarcely explored as the activity of palladium stayed behind that of more active platinum complexes. The initiating reagents are often very similar to those of platinum, i.e., divalent palladium salts, which under the reaction conditions presumably form monohydrido complexes of palladium(II). A common precursor is (39). The mechanism for palladium catalysts is, therefore, thought to be the same as that for platinum. New cationic complexes of palladium that are highly active as hydroformylation catalysts were discovered by Drent and co-workers at Shell and commercial applications may be expected, involving replacement of cobalt catalysts. 

Hydroxycarbonylation and alkoxycarbonylation of alkenes catalyzed by metal catalyst have been studied for the synthesis of acids, esters, and related derivatives. Palladium systems in particular have been popular and their use in hydroxycarbonylation and alkoxycarbonylation reactions has been reviewed.625,626 The catalysts were mainly designed for the carbonylation of alkenes in the presence of alcohols in order to prepare carboxylic esters, but they also work well for synthesizing carboxylic acids or anhydrides.137 627 They have also been used as catalysts in many other carbonyl-based processes that are of interest to industry. The hydroxycarbonylation of butadiene, the dicarboxylation of alkenes, the carbonylation of alkenes, the carbonylation of benzyl- and aryl-halide compounds, and oxidative carbonylations have been reviewed.6 8 The Pd-catalyzed hydroxycarbonylation of alkenes has attracted considerable interest in recent years as a way of obtaining carboxylic acids. In general, in acidic media, palladium salts in the presence of mono- or bidentate phosphines afford a mixture of linear and branched acids (see Scheme 9). 

Zhuang et al. [664] used palladium salts as a coprecipitation carrier for the concentration of cadmium, cobalt, and lead in seawater prior to analysis by atomic absorption spectrometry. 

Unlike nickel catalysts, palladium catalysts undergo neither cyclodimerization nor cyclotrimerization to form COD or CDT. Only one paper by Chepaikin and Khidekel reported that a mixture of divinylcyclobu-tanes was obtained from butadiene using palladium salts with noncom-plexing anions such as perchlorate and boron tetrafluoride (15). This is a big difference between the catalyses of palladium and nickel. 

CATALYTIC OXIDATION OF OLEFINS TO ALDEHYDES 10.6.1 Catalysis by Palladium Salts... 

Dienes are oxidized by palladium(II) salts if copper(II) chloride is added, the reactions become catalytic with respect to the palladium salt. Thus c/s-divinylcyclohexane reacts... 

The use of 1,6-diene systems usually does not result in cyclization reactions with palladium ) salts. For example, with 1,6-heptadiene a /i-elimination takes place from the cqjr-intermediate to give diene 22 as the major product (equation 10)27. However, more recently Trost and Burgess21 have shown that with a 4,4-bis(phenylsulfonyl) derivative of 1,6-heptadiene (23) an insertion takes place to give a 5-membered ring product (24, equation 11). The final step of the latter reaction is oxidative cleavage of the palladium-carbon bond by CuCl2 to produce a carbon-chlorine bond. 

Trost s group examined the possibility of carrying out cross-coupling reactions of alkynes and transformed this into a very powerful synthetic method. Either homocoupling or perhaps, more interesting, heterocoupling procedures were performed using catalytic amounts of a palladium salt (Equation (191)). 

It is worth noting, however, that chiral phosphine-palladium complexes generated from palladium salts and BINAP or MOP cannot be used for this oxidation because phosphines will be readily oxidized to phosphine oxides under the reaction conditions, leading to the deactivation of the catalyst. As reaction without the chiral catalyst will give a racemic product, this deactivation of the catalyst will cause a drop in the enantioselectivity of the whole process. 

Aromatic acid chlorides are converted into the corresponding anhydrides in high yields (>95%), when reacted with carbon monoxide under solid liquid basic catalysed conditions in the presence of a complexed cobalt or palladium salt [6]. In the absence of the quaternary ammonium salt, only hydrolysis to the carboxylic acid occurs. 

Palladium salts will attack C-H bonds in functionalised aromatics such as acetoaniline to form palladium-carbon bonds that subsequently undergo insertion of alkenes [31], (3-Hydride elimination gave styryl derivatives and palladium hydride, which requires re-oxidation of palladium by benzoquinone. The reaction can be regarded as a combined Murai reaction (C-H activation, if electrophilic) and a Heck reaction (arylalkene formation), notably without the production of salts as the cross-coupling reactions do. An example is shown in Figure 19.15. 

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