Cobalt carbonyl carboxylation reactions

Naphthaleneacetic acid has also been prepared by the carbonyl-insertion reaction of 1-chloromethylnaphthalene cataly2ed by carbonyl cobalt cation (90,91). Carboxylation of 1-chloromethylnaphthalene in the presence of the catalyst Pd[P(CgH )2]2Cl2 under phase-transfer conditions gave 1-naphthaleneacetic acid in 78% yield (92). 

If cobalt carbonylpyridine catalyst systems are used, the formation of unbranched carboxylic acids is strongly favored not only by reaction of a-olefins but also by reaction of olefins with internal double bonds ( contrathermo-dynamic double-bond isomerization) [59]. The cobalt carbonylpyridine catalyst of the hydrocarboxylation reaction resembles the cobalt carbonyl-terf-phos-phine catalysts of the hydroformylation reaction. The reactivity of the cobalt-pyridine system in the hydrocarboxylation reaction is remarkable higher than the cobalt-phosphine system in the hydroformylation reaction, especially in the case of olefins with internal double bonds. This reaction had not found an industrial application until now. 

Organomercury compounds undergo a similar reaction. Alkyl and aryl Grignard reagents can be converted to carboxylic esters with Fe(CO)5 instead of CO. Amides have been prepared by the treatment of trialkyl or triarylboranes with CO and an imine, in the presence of catalytic amounts of cobalt carbonyl ... 

Nickel carbonyl is the more widely known catalyst for the carboxylation reaction dicobalt octacarbonyl has the disadvantage of giving side reactions (15). Dicobalt octacarbonyl has been used in the presence of tributyl phosphine for the reaction of ethylene, carbon monoxide, water, and ethanol. Besides ethyl acetate, acetaldehyde and diethyl ketone were found (136). Hydrogen has been found to increase the rate of reaction (78), presumably by the formation of cobalt hydrocarbonyl. However, this can lead to the formation of aldehydes, as in the reaction of acetyl bromide when an 89.4% yield of aldehyde was obtained in spite of the presence of water (95). 

Heck (59) has suggested that the first step in the carboxylation reaction is the formation of cobalt hydrocarbonyl, which can be formed from dicobalt octacarbonyl and solvent (55). Alkylation and carbonylation then produce an acylcobalt carbonyl. Reaction of the acylcobalt carbonyl with the compound containing active hydrogen then regenerates cobalt hydrocarbonyl, e.g.,... 

Carbonylation with iron carbonyls parallels that of cobalt carbonyls. Benzylic chlorides and bromides are carbonylated with Fe(CO)5 in the presence of base. Esters are realized when carbonylation is performed in alcohols under 1 atm of CO with catalytic amounts of iron pentacarbonyl415. Under phase transfer conditions, two predominant routes are available. With catalytic amounts of iron under a CO atmosphere and strongly basic conditions, the carboxylic acids are realized in reasonable yields415,416, whereas mild bases [Ca(OH)2l, stoichiometric amounts of iron carbonyl and the omission of CO give dibenzyl ketones417. In at least a few cases, it is possible to prepare unsymmetrical methyl benzyl ketones418, des Abbayes and coworkers have observed the formation of acyltetracarbonyl anion (52) under the reaction conditions, and have proposed the catalytic cycle in Scheme 8 for the ketone formation418. 

Amidocarbonylation is a recently developed, organometallic-catalyzed route to amino acid generation - particularly A(-acyl a-amino acids - using either aldehydes or alkenes as starting materials and synthesis gas as an integral building block. The two principal classes of reaction are illustrated in eqs. (1) and (2). Both syntheses offer the opportunity to introduce two functionalities, amido and carboxylate, simultaneously where an amide is the co-reactant. Homogeneous amidocarbonylation catalysts are typically cobalt carbonyl-based, or utilize transition-metal binary systems, e. g. cobalt-rhodium, cobalt-palladium, and cobalt-iron. 

Other metal catalysts which have been utilized for biphasic carbonylation of ben-zylic halides to carboxylic acids under phase-transfer conditions, besides cobalt carbonyl [11], include palladium(O) complexes [12] and water-soluble nickel cyanide complexes [13], Although not investigated in detail, it must be assumed that catalysis takes place in all these reactions in the organic phase. 

The insertion of carbon monoxide into a C—M bond is a common reaction for alkyl derivatives of the late transition elements. It has been reported for Mo, Mn, Fe, Co, Ni, Pd, and Pt compounds. The insertion of CO into the C —Co bond of cobalt carbonyl derivatives is a key step in the 0x0 reaction and catalytic carboxylation processes (see Section IV,D). The CO insertion reaction is frequently reversible but sometimes only the reverse reaction, CO elimination, is known, e.g.,... 

Carbonylation and decarbonylation reactions of alkyl complexes in catalytic cycles have been reviewed . A full account of the carbonylation and homologation of formic and other carboxylic acid esters catalysed by Ru/CO/I systems at 200 C and 150-200 atm CO/H2 has appeared. In a novel reaction, cyclobutanones are converted to disiloxycyclopentenes with hydrosilane and CO in the presence of cobalt carbonyl (reaction 4) . The oxidative addition of Mel to [Rh(CO)2l2] in aprotic solvents (MeOH, CHCI3, THF, MeOAc), the rate determining step in carbonylation of methyl acetate and methyl halides, is promoted by iodides, such as Bu jN+I", and bases (eg 1-methylimidazole) . A further kinetic study of rhodium catalysed methanol carbonylation has appeared . The carbonylation of methanol by catalysts prepared by deposition of Rh complexes on silica alumina or zeolites is comparable with the homogeneous analogue . 

However, the reaction proceeded only under drastic conditions (pressure 700 upward to 900 atm) in the presence of mineral acids, BFg or metal halogenides. At that time metal carbonyls had been regarded as catalyst poisons. However, Reppe could prove that olefins react with carbon monoxide and water in the presence of metal carbonyls. The reaction products are saturated carboxylic acids. Whereas Ni(CO)4 is the preferred catalyst in the carbonylation of acetylenes, cobalt, rhodium and ruthenium catalysts are equivalent or superior in olefin carbonylation. Also palladium and hydrochloric acid containing catalyst systems are of special activity in hydrocarboxylation [469-471]. Iron has an accelerating effect [472]. Addition of boric acid to Ni or Co catalysts increases the catalyst life and suppresses the formation of insoluble polymer products [473]. 

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

In spite of the general lack of detailed understanding of mechanism, the procedure is superior to that using the cobalt catalyst both in the overall yields and in the specificity of the reaction to produce only mono-carbonylation products. Prolonged reaction times may lead, however, to the formation of benzyl esters of the acids, as a result of a catalysed reaction of the halide with the carboxylate anion. 

Aryl methyl ketones have been obtained [4, 5] by a modification of the cobalt-catalysed procedure for the synthesis of aryl carboxylic acids (8.3.1). The cobalt tetracarbonyl anion is converted initially by iodomethane into the methyltetra-carbonyl cobalt complex, which reacts with the haloarene (Scheme 8.13). Carboxylic acids are generally obtained as by-products of the reaction and, in several cases, it is the carboxylic acid which predominates. Unlike the carbonylation of haloarenes to produce exclusively the carboxylic acids [6, 7], the reaction does not need photoinitiation. Replacement of the iodomethane with benzyl bromide leads to aryl benzyl ketones in low yield, e.g. 1-bromonaphthalene produces the benzyl ketone (15%), together with the 1-naphthoic acid (5%), phenylacetic acid (15%), 1,2-diphenylethane (15%), dibenzyl ketone (1%), and 56% unchanged starting material [4,5]. a-Bromomethyl ketones dimerize in the presence of cobalt octacarbonyl and... 

Precipitation of the catalyst from the reaction medium, followed by filtration, as in the cobalt-based hydroformylation process (see Section 5.4). Here cobalt is removed from the reaction products in the form of one of its salts or as the sodium salt of the active carbonyl catalyst. The aqueous salts can be recycled directly, but sometimes they are first converted into an oil-soluble long-chain carboxylic acid salt, such as the corresponding naphthenate, oleate, or 2-ethylhexanoate. 

It is important to note that even certain phase-transfer catalysts can be carbonylated to carboxylic acids, not by cobalt tetracarbonyl anion catalysis, but by acetylcobalt tetracarbonyl. This is a slow but high-yield reaction that occurs for quaternary ammonium salts that are capable of forming reasonably stable free radicals. For example, phenylacetic acid is formed in 95% yield from benzyltriethylammonium chloride (benzyl radi-... 

Some insight into the mechanisms of the iodine-promoted carbonylation has been obtained by radioactive tracer techniques [17] and low-temperature NMR spectroscopy [18]. The mechanism involves the formation of HI, which in a series of reactions forms with rhodium a hydrido iodo complex which reacts with ethylene to give an ethyl complex. Carbonylation and reductive elimination yield propionic acid iodide. The acid itself is then obtained after hydrolysis. The rate of carboxylation was reported to be accelerated by the addition of minor amounts of iron, cobalt, or manganese iodide [19]. The rhodium catalyst can be stabilized by triphenyl phosphite [20]. However, it is doubtful whether the ligand itself would meet the requirements of an industrial-scale process. 

In combination with the incremental advances concerning reaction conditions in recent years, especially for low-pressure carbonylations, there is a trend toward increasing use of this chemistry to synthesize advanced building blocks. In this respect carboxylation of alkenes with an appropriate alcohol or amine function leads to the formation of lactones or lactams. Thus, cobalt, rhodium, or palladium chloride/copper chloride catalysts convert allyl and homoallyl alcohols or amines to the corresponding butyrolactones or butyrolactams, respectively [15]. 

The hydroxycarbonylations (carboxylations) of alkyl, aryl, benzyl and allyl halides are from a retrosynthetic and mechanistic standpoint closely related. This type of reaction is widely used in organic synthesis [6], although a stoichiometric amount of salt by-product makes these methods less attractive on a large scale. The use of water-soluble catalysts for carbonylation of organic halides was scarcely studied in the past. Up to now palladium, cobalt, and nickel compounds in combination with water-soluble ligands have been used as catalysts for various carboxylations. 

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