Cobalt-catalysed reactions carbonylation

Not unexpectedly, alkylation of the double carbonylated complex proceeds via a base-catalysed interfacial enolization step, but it is significant that the initial double carbonylation step also involves an interfacial reaction, as it has been shown that no pyruvic acid derivatives are obtained at low stirring rates. Further evidence comes from observations of the cobalt-catalysed carbonylation of secondary benzyl halides [8], where the overall reaction is more complex than that indicated by Scheme 8.3. In addition to the expected formation of the phenylacetic and phenylpyruvic acids, the reaction with 1-bromo-l-phenylethane also produces 3-phenylpropionic acid, 2,3-diphenylbutane, ethylbenzene and styrene (Scheme 8.4). The absence of secondary carbonylation of the phenylpropionylcobalt tetracarbonyl complex is consistent with the less favourable enolization of the phenylpropionyl group, compared with the phenylacetyl group. 

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. 

Although the acylcobalt tetracarbonyls react with hydroxide ion under phase-transfer conditions, in the presence of alkenes and alkynes they form o-adducts rapidly via an initial interaction with the ir-electron system. Subsequent extrusion of the organometallic group as the cobalt tetracarbonyl anion leads to a,(J-unsaturated ketones (see Section 8.4). In contrast, the cobalt carbonyl catalysed reaction of phenylethyne in the presence of iodomethane forms the hydroxybut-2-enolide (5) in... 

A cobalt catalysed carbonylation reaction converts A-substituted 1-aza-1,3-dienes into A-allylacetamides by a reductive acylation process [31]. Acetamides are byproducts of the reaction. In contrast, Schiff bases undergo a double A,C-acetylation under the same conditions producing a-acetamido ketones and A,A-disubstituted acetamides [32],... 

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... 

Catalysis by cobalt(III) has been the subject of several papers.185-187 The N.N-bis(sahcyldene)ethylnediaminocobalt(III)-catalysed oxidative carbonylation of o-, m-and -substituted primary aromatic amines in MeOH gives ureas, isocyanates, carbamates, and azo derivatives. A Hammett p value of —0.5 for the reaction indicates that electrophilic attack of CO at a nitrogen anion complexed to Co in the TS is... 

Reports of nucleophilic vinylic photosubstitution reactions, which occur via the S l mechanism, are conspicuously scarce. One such example is the cobalt carbonyl catalysed photostimulated carbonylation of vinylic halides339. By this method 1-bromo and 1-chlorocyclohexene are converted into 1-cyclohexenecarboxylic acid in 98 and 97% yield, respectively. In a prototype vinylic S l reaction, of / -bromostyrene with the enolate anion CH2COCMe3, an ionic elimination-addition route seems to be followed along with the S l route340. 

Hydroformylation (or the Oxo-process) is the conversion of alkenes to aldehydes (reaction 26.17). It is catalysed by cobalt and rhodium carbonyl complexes and has been exploited as a manufacturing process since World War II. 

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 . 

In the presence of a phase-transfer catalyst the cobalt carbonyl-catalysed reaction of dienes with methyl iodide and carbon monoxide (room temp., 1 atm) produces dienones with high regioselectivity. 1-Vinylcyclohexene undergoes acylation only at the least substituted carbon atom of the diene to give the E-isomer (26) in 42% yield. With isoprene acylation occurs at the terminal carbon... 

A synergic effect has been observed in autoxidation reactions with mixed catalysts for example autoxidation of p-nitrotoluene to />-nitrobenzoic acid is rapidly effected with the catalyst Co Mn Br (1 0.005—0.01 1— 2). Bis(n-butyl-AT-salicylideneiminato)cobalt(n) catalyses reaction (20). Cyclohexanone, labelled at the carbonyl with C or C, undergoes Co(OAc)3-catalysed oxidation with >90% retention of the label in the glutaric and succinnic... 

Cobalt. The rate law for carbonylation of Schiff bases, catalysed by Co2(CO)8, has been reported. Dicobalt octacarbonyl also catalyses reaction between aldehydes, for instance formaldehyde or acetaldehyde, amides, for example acetamide or benzamide, and carbon monoxide. The products are iV-acyl-amino-acids. The main product from the reaction of acetylene with carbon monoxide in the presence of CoH(CO)4 is ethyl acrylate. Characterization of the intermediates permits suggestions to be made as to the mechanism of this reaction. Initial reactions between the acetylene and two molecules of catalyst may give (106), in equilibrium with its isomer (107) the carbon monoxide inserts into the cobalt-carbon bonds of the latter. Further information about Coa(CO)8-catalysed hydro-formylation of acrylonitrile and of 3-methyl[3- H]hex-l-ene has led... 

Chemical reactions that are catalysed by carbonyl complexes (whether or not new CO-containing species are identified) are to be found in the section dealing with that particular metal. The cobalt carbonyls are usually well represented in this sphere and 2000 maintained that trend, although other metals do figure in this type of reaction. 

As indicated in Chapter 8, the production of alkanes, as by-products, frequently accompanies the two-phase metal carbonyl promoted carbonylation of haloalkanes. In the case of the cobalt carbonyl mediated reactions, it has been assumed that both the reductive dehalogenation reactions and the carbonylation reactions proceed via a common initial nucleophilic substitution reaction and that a base-catalysed anionic (or radical) cleavage of the metal-alkyl bond is in competition with the carbonylation step [l]. Although such a mechanism is not entirely satisfactory, there is no evidence for any other intermediate metal carbonyl species. 

Carbonylation of phenethyl bromide catalysed by Co2(CO)8 alone or modified either with tppts or tppms yielded products of double- and mono-carbonylation, (benzylpyruvic and benzylacetic acid, respectively) at a concentration of 8 mol% cobalt, 85°C and 20 bar CO under basic conditions in an H20/tBuOH (14/1) solvent mixture (Figure 13).475>476 The reaction rates exhibited by Co2(CO)8 were comparable with the Co2(CO)6(tppts)2 catalyst but replacement of tppts by tppms gave rise to a dramatic decrease in catalytic activity.475 Substantially different double/mono carbonylation (d/m ratios) were observed with Co2(CO)8, Co2(CO)e(tppts)2 and Co2(CO)6(tppms)2 7.3, 2.1 and 0.3, respectively, which... 

Metal-ion catalysis has been extensively reviewed (Martell, 1968 Bender, 1971). It appears that metal ions will not affect ester hydrolysis reactions unless there is a second co-ordination site in the molecule in addition to the carbonyl group. Hence, hydrolysis of the usual types of esters is not catalysed by metal ions, but hydrolysis of amino-acid esters is subject to catalysis, presumably by polarization of the carbonyl group (Kroll, 1952). Cobalt (II), copper (II), and manganese (II) ions promote hydrolysis of glycine ethyl ester at pH 7-3-7-9 and 25°, conditions under which it is otherwise quite stable (Kroll, 1952). The rate constants have maximum values when the ratio of metal ion to ester concentration is unity. Consequently, the most active species is a 1 1 complex. The rate constant increases with the ability of the metal ion to complex with amines. The scheme of equation (30) was postulated. The rate of hydrolysis of glycine ethyl... 

T. Mizoroki Yuki Gosei Kagaku Kyokai Shi 28, 697 (1970) Carbonylation reactions catalysed by metal carbonyls 11 (60) Japan. Esp. cobalt and nickel ... 

Isomerisation of olefins catalysed 11 by palladium and other transi- (34) tion-metal complexes Hydrogenation reaction with 10 cobalt carbonyl hydride as a (29) hydrogenation agent 7r-Complex adsorption in hydrogen 27 exchange on Group VIII transi- (45) tion metal catalysts... 

Intermediates in the cobalt carbonyl-catalysed carbonylation of o-substituted benzyl halides have been identified by H and 13C NMR.1142 High-pressure 13C and 31P NMR spectra were used to detect intermediates during hydro-formylation of 1-pentene in the presence of Co2(CO)6[P(OPh )3]2.1143 Time-dependent NMR spectra followed the reactions of benzyl-, heteroaromatic-,... 

The mechanism of the reaction which takes place in the presence of nickel as well as certain other of the metal catalysts, has been explained by assuming that metallic carbonyls are formed by the action of carbon monoxide on the metal and that these compounds represent intermediate products in the catalyses. Evidence in support of this theory has been brought forward by Mond, Langer and Quinke,0- who studied the decomposition of carbon monoxide in contact with nickel at temperatures between 350° and 450° C. In examining the carbonized nickel catalyst at the end of the experiment these investigators discovered that when heated, it gave off a volatile inflammable nickel compound which could be condensed to a liquid and which was later identified as nickel carbonyl. Metals, such as nickel, cobalt, and iron, which form distinct metallic carbonyls are particularly active catalysts for the decomposition, a fact which adds weight to this theory. 

Other Zinc Enzymes. Studies aimed at elucidating the mechanism of dimeric alcohol dehydrogenase enzymes have also been reported. Cobalt(n) can replace zinc(ii) at the two catalytic and non-catalytic sites in the liver enzyme, LADH. Reduction of pyridinealdehyde derivatives by the yeast enzyme has been examined. In acetonitrile solution, reduction by NADH analogues is catalysed by metal ions and mechanistic studies of the reaction have been carried out. Biomimetic studies of zinc-catalysed carbonyl reduction have also been reported. ... 

A similar mechanism may operate in related reactions, such as a vinylation of azoles 3.48 using an economical cobalt catalyst (Scheme 3.25), generated in as well as a ruthenium-catalysed carbonylative... 

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