Carbonylation palladium salt catalyst

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]. 

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). 

As the last example of C-C bond-formation reactions catalyzed by alkaline earth hydroxides, we mention the recently reported a-arylation of diethyl malonate in the presence of a palladium catalyst and a base in a separate phase 299). The arylation of carbonyl compounds is a carbon-carbon coupling reaction between an aryl halide and an enolate, which is usually catalyzed by palladium salts in the presence of an appropriate base (300,301). The arylation of diethyl malonate with bromobenzene (Scheme 48) was performed with tetrachloropalladate as the... 

An alternative scheme to simultaneous formation of acetaldehyde and acetic anhydride could entail the carbonylation of methyl acetate to acetic anhydride which is subsequently reduced to acetaldehyde and acetic acid. The reaction of acetaldehyde with excess anhydride would form EDA. In fact, Fenton has described production of EDA by the reduction of acetic anhydride using both rhodium and palladium salts as catalysts when modified with triphenylphosphine (26). Two possible mechanisms for the reduction are postulated in equation 16. 

Neither the palladium nor nickel catalyst described will promote the carbonylation of saturated aliphatic halides as noted above. However, this reaction can be catalyzed with cobalt (17) or iron (77) and probably with manganese (18) carbonyl anion salts. These carbonyl anions are strongly nucleophilic species and readily displace halide or other good leaving groups from primary or secondary positions giving alkyl metal carbonyl complexes. 

Palladium catalysts are best known for oxidizing alkenes to ketones or vinyl derivatives. However, formation of a,P-unsaturated carbonyl compounds by UV irradiation of oxygenated solutions of alkenes in the presence of catalytic amounts of palladium salts has been observed by Muzart. - This reaction is believed to proceed through a ir-allylpalladium trifluoroacetate complex, e.g. (77). 

The acid-catalyzed hydrocarboxylation of alkenes (the Koch reaction) can be performed in a number of ways. In one method, the alkene is treated with carbon monoxide and water at 100-350°C and 500-1000-atm pressure with a mineral acid catalyst. However, the reaction can also be performed under milder conditions. If the alkene is first treated with CO and catalyst and then water added, the reaction can be accomplished at 0-50°C and 1-100 atm. If formic acid is used as the source of both the CO and the water, the reaction can be carried out at room temperature and atmospheric pressure.The formic acid procedure is called the Koch-Haaf reaction (the Koch-Haaf reaction can also be applied to alcohols, see 10-77). Nearly all alkenes can be hydrocarboxylated by one or more of these procedures. However, conjugated dienes are polymerized instead. Hydrocarboxylation can also be accomplished under mild conditions (160°C and 50 atm) by the use of nickel carbonyl as catalyst. Acid catalysts are used along with the nickel carbonyl, but basic catalysts can also be employed. Other metallic salts and complexes can be used, sometimes with variations in the reaction procedure, including palladium, platinum, and rhodium catalysts. The Ni(CO)4-catalyzed oxidative carbonylation with CO and water as a nucleophile is often called Reppe carbonylationP The toxic nature of nickel... 

Surprisingly, palladium(II) salts supported on NaY zeolite produce DMC, even without halogens. The preferred support seems to be active carbon compared to zeolites because of higher DMC selectivities based on both MN and carbon monoxide, >95% in the case of active carbon and 80-90% in the case of zeolites. Palladium chloride/copper chloride on active carbon is likely used as a catalytic system in the industrial process. Because the carbonylation of MN to DMC occurs without water coproduction, the use of palladium salts as catalysts does not adversely affect selectivity. In the carbonylation reactor outlet some amount of methyl-chloroformate is present, as expected because it is known that palladium(II) chloride supported on alumina or silica catalyzes the reaction between MN, CO, and HCl to give methylchloroformate. " The presence of halide ions in the catalytic system and the methylchloroformate generation likely raise some corrosiveness issues. 

Beletskaya and co-workers have shown that the reaction is possible in neat water as solvent. Thus, aryl iodides have been carbonylated with various palladium salts lacking phosphine ligands as depicted in Eq. (4) [7]. Although this reaction is not a truely biphasic process the results are remarkable regarding catalyst efficiency. Thus, a maximum turnover number (TON) of 100000 was described (R = p-COOH, quantitative yield after 6 days). Quite different is the performance of a water-soluble palladium phosphine catalyst described by Kalck et al. [8]. The hy-drocarboxylation of the less activated bromobenzene with either Pd(TPPTS)3 or a mixture of Pd(OAc)2 and TPPTS proceeds only sluggishly (turnover frequency TOF < 10 h 1). In order to prevent decomposition of palladium an excess of phosphine has to be used. At least 15 equiv. of ligand is necessary to prevent formation of metallic palladium. Because of rapid oxidation of the ligand the re-use of the water phase is not possible. 

Hydrocarboxylation is the formal addition of hydrogen and a carboxylic group to double or triple bonds to form carboxylic acids or their derivatives. It is achieved by transition metal catalyzed conversion of unsaturated substrates with carbon monoxide in the presence of water, alcohols, or other acidic reagents. Ester formation is also called hydroesterification or hydrocarb(o)alkoxylation . The transition metal catalyst precursors are nickel, iron or cobalt carbonyls or salts of nickel, iron, cobalt, rhodium, palladium, platinum, or other metals4 5. 

Gladysz showed that a thermomorphic fluorous paUadacyde acts as a PdNP catalyst precursor for the Heck reaction at 80-140 C in DMF with very high turnover numbers [24a]. Molecular palladium complexes such as palladacycles and other palladium salts have also been used as PdNP precursors upon treatment with CO in DMF or toluene at room temperature, and these PdNPs catalyzed nudeophiUc substitution/carbonylation/amination affording iso-indolinones at room temperature [24bj. PdNPs capped with spedal ligands such as polyoxometal-... 

The production of another important chemical and polymer intermediate, acetic acid, was revolutionized by the Wacker process that was introduced in 1960. It was a simple, high yield process for converting ethylene to acetaldehyde, which replaced the older process based on ethanol and acetylene. In the Wacker reaction, the palladium catalyst is reduced and then reoxidized. Ethylene reacts with water and palladium chloride to produce acetaldehyde and palladium metal. The palladium metal is reoxidized by reaction with cupric chloride, which is regenerated by reaction with o gen and hydrochloric acid. In 1968, BASF commercialized an acetic acid process based on the reaction of carbon monoxide and methanol, using carbonyl cobalt promoted with an iodide ion (74). Two years later, however, Monsanto scored a major success with its rhodium salt catalyst with methyl iodide promoter. Developed by James F. Roth, this new catalyst allowed operation at much milder conditions (180°C, 30-40 atm) and demonstrated high selectivity for acetic acid (75). 

Anion Source for Palladium Catalysis. The reagent serves as a source of weakly coordinating anions in the palladium-catalyzed formation of mixed phenyl ureas, a known class of commercially available herbicides, using palladium(II) acetate, copper(II) toluenesulfonate, and 2,2 -dipyridyl as the catalyst system. Other studies have suggested that use of this reagent to form palladium salts may have useful applications in the reductive carbonylation of nitroaromatic compounds to give isocyanates via initial carbamate formation (eq 2). ... 

Aryl halides can be carbonylated to give the corresponding carboxylic acids (Scheme 138) under very mild conditions in presence of inorganic bases (like alkaline metal hydroxides, carbonates, acetates etc.) and certain palladium catalysts (like Pd(OAc)2, K PdCl, Pd(NH3) Cl, PdCl2(PPh3)2 etc.). Best results are obtained with simple palladium salt using K2CO3 as base (Scheme 138). 

Ethylene reacts with carbon monoxide and water in the presence of nickel carbonyl to give propionic acid in high yield. If care is taken to maintain a high concentration of propionic acid in the reaction mixture and the temperature, which is normally 300 in the propionic acid synthesis, is decreased to 240 °C propionic acid anhydride is formed in high yield in the presence of Ni(CO)4. Propionic acid ethyl ester is the main product in the reaction of ethylene, carbon monoxide and water (low water concentration must be applied) with cobalt carbonyls instead of Ni(CO)4. The conversion of ethylene with carbon monoxide in dilute alkaline medium with the aid of potassium nickel cyanide gives propionyl propionic acid [403-405]. At higher temperatures and without pH correction in the same reaction mainly polyketones with the sequences -(CHg-CHg-CO)- are formed. If the reaction is carried out in absence of water or alcohols and in presence of palladium iodide as catalyst, a mixture of hexenolide isomers is the main product. Colorless polyketones of the same structure are obtained if an excess of ethylene is treated with carbon monoxide in the presence of complex palladium salts as catalysts in an alcoholic hydrogen halide solution at 100 °C and 700 atm [406]. 

Enone Formation. The transformation of saturated carbonyl compounds into their ajS-unsaturated analogues by a process of homogeneous liquid-phase oxidative dehydrogenation has been described use of oxygen or air in the presence of a palladium(ii) catalyst and a co-catalyst, usually copper(ii) salts or quinone, gives good yields based on ketone consumed, though overall conversion is low. 

Reduction of unsaturated carbonyl compounds to the saturated carbonyl is achieved readily and in high yield. Over palladium the reduction will come to a near halt except under vigorous conditions (73). If an aryl carbonyl compound, or a vinylogous aryl carbonyl, such as in cinnamaldehyde is employed, some reduction of the carbonyl may occur as well. Carbonyl reduction can be diminished or stopped completely by addition of small amounts of potassium acetate (i5) to palladium catalysts. Other effective inhibitors are ferrous salts, such asferroussulfate, at a level of about one atom of iron per atom of palladium. The ferrous salt can be simply added to the hydrogenation solution (94). Homogeneous catalysts are not very effective in hydrogenation of unsaturated aldehydes because of the tendencies of these catalysts to promote decarbonylation. 

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