Carbon-palladium compounds

Pd(II) compounds coordinate to alkenes to form rr-complexes. Roughly, a decrease in the electron density of alkenes by coordination to electrophilic Pd(II) permits attack by various nucleophiles on the coordinated alkenes. In contrast, electrophilic attack is commonly observed with uncomplexed alkenes. The attack of nucleophiles with concomitant formation of a carbon-palladium r-bond 1 is called the palladation of alkenes. This reaction is similar to the mercuration reaction. However, unlike the mercuration products, which are stable and isolable, the product 1 of the palladation is usually unstable and undergoes rapid decomposition. The palladation reaction is followed by two reactions. The elimination of H—Pd—Cl from 1 to form vinyl compounds 2 is one reaction path, resulting in nucleophilic substitution of the olefinic proton. When the displacement of the Pd in 1 with another nucleophile takes place, the nucleophilic addition of alkenes occurs to give 3. Depending on the reactants and conditions, either nucleophilic substitution of alkenes or nucleophilic addition to alkenes takes place. 

Water hydroly2es pure diketene only slowly to give acetoacetic acid [541-50-4] which quickly decomposes to acetone and carbon dioxide, but increasing the pH or adding catalysts (amines, palladium compounds) increases the rate of hydrolysis. The solvolysis of diketene in ammonia results in aceto acetamide [5977-14-0] if used in stoichiometric amounts (99), and P-arninocrotonarnide [15846-25-0] if used in excess (100). 

The diimine palladium compounds are less active than their nickel analogs, producing highly branched (e.g., 100 branches per 1,000 carbons) PE. However, they may be used for the copolymerization of Q-olefins with polar co-monomers such as methyl acrylate.318,319 Cationic derivatives, such as (121), have been reported to initiate the living polymerization of ethylene at 5°C and 100-400 psi.320 The catalyst is long-lived under these conditions and monodisperse PE (Mw/Mn= 1.05-1.08) may be prepared with a linear increase in Mn vs. time. 

The copolymerization of carbon monoxide and a-olefins is one of the most challenging problems in polymer synthesis. Sen and his coworkers discovered that some cationic palladium compounds catalyze this alternative copolymerization, giving polyketones (Eq. 13). 

Reaction of organic halides with alkenes catalyzed by palladium compounds (Heck-type reaction) is known to be a useful method for carbon-carbon bond formation at unsubstituted vinyl positions. The first report on the application of microwave methodology to this type of reaction was published by Hallberg et al. in 1996 [86], Recently, the palladium catalyzed Heck coupling reaction induced by microwave irradiation was reported under solventless liquid-liquid phase-transfer catalytic conditions in the presence of potassium carbonate and a small amount of [Pd(PPh3)2Cl2]-TBAB as a catalyst [87]. The arylation of alkenes with aryl iodides proceeded smoothly to afford exclusively trans product in high yields (86-93%) (Eq. 61). 

Intramolecular arylation of G-H bonds gives cyclic aromatic compounds. In this intramolecular arylation, the carbon-palladium cr-bond is first formed by the oxidative addition of Pd(0) species and then the resulting electrophilic Pd(n) species undergoes the intramolecular G-H bond activation leading to the formation of the palladacycle, which finally affords the cyclic aromatic compounds via reductive elimination.87 For example, the fluoroanthene derivative is formed by the palladium-catalyzed reaction of the binaphthyl triflate, as shown in Scheme 8.88 This type of intramolecular arylation is applied to the construction of five- and six-membered carbocyclic and heterocyclic systems.89 89 89 ... 

HCHO and PH3 proceeds in the presence of K2PtCl4 at room temperature and affords the crystalline product in an essentially quantitative yield in 2.5 h [4]. Palladium compounds are also active in the catalysis [5]. In these reactions the active species is believed to be zero valent. Two mechanistic possibilities have been proposed as illustrated in Scheme 2. The first elemental process involved in the catalytic cycle is oxidative addition of a P-H bond, which is well precedented [6]. In one of the mechanistic possibilities the processes that follow the oxidative addition are the insertion of the C=0 bond into H-M species and P-C reductive elimination, the latter of which is also precedented [7]. In the other, the coordinating phosphide ligand makes a nucleophilic attack [8] at the formaldehyde carbon forming zwitterionic species. 

Palladium metal clusters confined in zeolites have been prepared from Pd (CO)y species accommodated in zeolite cages. These species can be obtained by carbon-ylation of impregnated or exchanged palladium compounds such as PdCh or [Pd(NH3)4] [47, 48]. 

Palladium dichloride is a starting material for preparing several palladium compounds. It also is used for detection of carbon monoxide. For such detection, a paper is soaked in very dilute solution of PdCb which is decolorized by CO, methane and other reducing substances. It also is used in toning and electroplating solutions and in photography for porcelain pictures. 

When the Pd bears chiral ligands, these reactions can be enantioselective.1448 ir-Allylmo-lybdenum compounds behave similarly.1449 Because palladium compounds are expensive, a catalytic synthesis, which uses much smaller amounts of the complex, was developed. That is, a substrate such as an allylic acetate, alcohol, amine, or nitro compound1450 is treated with the nucleophile, and a catalytic amount of a palladium salt is added. The rr-allylpal-ladium complex is generated in situ. Alkene-palladium complexes (introducing the nucleophile at a vinylic rather than an allylic carbon) can also be used.1451... 

Sodium or potassium phenoxide can be carboxylated regioselectively in the para position in high yield by treatment with sodium or potassium carbonate and carbon monoxide.316 14C labeling showed that it is the carbonate carbon that appears in the p-hydroxybenzoic acid product.317 The CO is converted to sodium or potassium formate. Carbon monoxide has also been used to carboxylate aromatic rings with palladium compounds as catalysts.318 In addition, a palladium-catalyzed reaction has been used directly to prepare acyl fluorides ArH — ArCOF.31 ... 

Carboxylic acids can be prepared in moderate-to-high yields by treatment of diazonium fluoroborates with carbon monoxide and palladium acetate383 or copper(II) chloride.384 The mixed anhydride ArCOOCOMe is an intermediate that can be isolated. Other mixed anhydrides can be prepared by the use of other salts instead of sodium acetate.385 An aryl-palladium compound is probably an intermediate.385 OS V, 139. 

Miscellaneous. Reduction of a palladium salt by CO is the basis of a visual test for ambient carbon monoxide (227). Palladium compounds are used as photographic sensitizers (228). The low dimensional mixed valence compound Csq 3[Pd(S2C2(CN)2)] 0.5H2O behaves as a semimetal at room temperature (229). Palladium compounds isostructural with potent platinum antitumor compounds have poor antitumor activity (230). 

Xlld does not involve the chiral center, so if the reaction takes place by this pathway, the migration of the alkyl group from sulfur to palladium (with the concomitant or subsequent loss of sulfur dioxide) must take place with inversion of configuration at carbon. Inversion of configuration at carbon has been observed in the reverse-type reaction, the sulfur dioxide insertion into a carbon-iron sigma bond (49). Nucleophilic displacement at carbon in compounds of type Xld is unusually difficult, so the reaction via the sulfite intermediate Xlld would appear to be more likely. Conversion of the tosylate of l-phenyl-2,2,2-trifluoroethanol to the corresponding chloride, a reaction which takes place in the presence of tetra- (n-butyl) ajnmonium chloride with inversion of configuration at carbon, requires 100°C for 24 hrs in dimethylsulfoxide. 

Carbonylation of organometallic reagents.1 The review covers the carbon-ylation of organolithium, -magnesium, -boron, -mercury, and -palladium compounds (86 references). 

M. J. H. Russell, The advantageous use of palladium compounds in organic syntheses formation of carbon-carbon bonds , Plat. Met. Rev., 1989, 33,186-192. 

Abnormal olefin arylation reactions which are of interest mechanistically and preparatively occur with some allylically substituted compounds. The ailylic esters and ethers appear normal and produce cinnamyl derivatives exclusively while ailylic alcohols and chlorides are abnormal. Ailylic alcohols and "arylpalladium acetates form 3-arylaldehydes from primary ailylic alcohols and 3-arylketones from secondary alcohols 3°). The mechanism of reaction apparently involves anti-Markovnikov addition of the palladium compound to the double bond followed by elimination of the hydrogen atom on the hydroxyl-bearing carbon rather than the benzylic hydrogen. This again would be elimination of the more electronegative hydrogen atom. 

Previously Davidson and Triggs have reported that arylboronic acids react with sodium palladate to give the dimeric biaryls. The synthetic utility of this dimerization reaction is, however, limited owing to stoichiometric requirement of the palladium compound. On the other hand, the palladium-catalyzed crosscoupling reaction between arylboronic acids and haloarenes in the presence of bases provides a clean synthesis of biaryls (Eq. 106) In this case, sodium carbonate has been proven to be most effective base. 

Vinylic ethers (44) can be synthesized in high yields by the cross-coupling of aryl or benzyl halides with tris(2-ethoxyvinyl)borane (4S) in the presence of 1 molej% of a palladium compound such as tetrakis(triphenylphosphine)palladium and a base (Eq. 108) Since vinylic ethers (44) thus obtained can readily be hydrolyzed to aldehydes, this reaction provides a convenient procedure for converting aryl or benzylic halides into the corresponding aldehydes with two more carbon atoms. 

Organopalladium compounds—compounds that contain a carbon-palladium bond—are... 

Organopalladium compound (Section 26.2) An organometallic compound that contains a carbon-palladium bond. 

Corrosive reaction streams. In some application environments, the reactive or corrosive nature of one or more of the reaction components in a membrane reactor can pose a great technical challenge to the selection as well as the design of the membrane element Feed streams often contain some Impurities that may significantly affect the performance of the membrane. Therefore, attention should also be paid to the response of the selected membrane material to certain impurities in the reactant or product streams. Care should be taken to pretreat the feed streams to remove the key contaminants as far as the membrane is concerned in these cases. For example, palladium alloy membranes can not withstand sulfur- or carbon-containing compounds at a temperature higher than, say, 500 C [Kamcyama et al., 1981]. Even at lOO C, the rate of hydrogen absorption (and, therefore, permeation) in a pure palladium disk is... 

It has been noted that unlike the palladium and platinum complexes, the nickel derivatives afford nickel iodide instead of the free metal. The reaction is accompanied by carbon monoxide evolution, which is increased in the presence of iodine. Independently of the stoichiometric ratio of Pd to Fe employed, the reaction consumes approximately half the amount of allyl-palladium compound. Hence the present authors assume that iron enneacarbonyl produces two moieties under the conditions of reaction ... 

Addition of water to dienes is catalyzed by palladium complexes. The reaction has been used for synthesizing unsaturated alcohols and ethers from aliphatic conjugated C4 and Cg olefins 248). In particular, the hydration of butadiene with water in the presence of bis(2,4-pentane-dionato)palladium and triphenylphosphine gave 2,7-octadien-l-ol, l,7-octadien-3-ol, and 1,3,5,7-octatetraene 18). The reaction was accelerated by carbon dioxide. Compounds Pd(PPh3)4 and Pd(02C0)-(PPh3)2 were also effective. 

Compound 10b has been treated with a solution of the nitrating mixture made from acetic anhydride and nitric acid in dioxane affording nitro derivative 10c, with not very high yields. The catalytic reduction of nitro derivative 10c, carried out with hydrazine in ethanol in the presence of palladium on calcium carbonate, affords compound lOd. The guanidino group at C-5 has be i introduced by reaction of compound lOd with ( anamide in solution of hydrochloric acid affording the objective molecule 10. 

The nitro group attached to an carbon in compounds 205, 211, and 244 and to the phenyl ring of compounds such as 334 was reduced to an amino group with iron powder,tin - and tin(II) chloride di-hydrate 10.268.355 jj, hydrochloric acid and/or acetic acid medium, or by catalytic hydrogenation over palladium on carbon in ethanol. ... 

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