Acylcobalt derivatives

Alkali Metal Derivatives of Metal Carbonyls, 2, 1S7 Alkyl and Aryl Derivatives of Transition Metals, 7, 1S7 Alkyl cobalt and Acylcobalt Tetracarbonyls, 4, 243 Allyl Metal Complexes, 2, 32S... 

Evidence for the insertion of an olefin group between an acyl group and a cobalt atom has been obtained more directly by analyzing the decomposition products of co-unsaturated acylcobalt tetracarbonyls (CHjp=CH(CH2) COCo(CO)4). The products of thermal decomposition of these complexes depend upon the value of n. When n = 0 or 2 the compounds form relatively stable cyclic olefin 7r-complexes which may be isolated as monotriphenylphosphine derivatives (47). The ir-acrylyl-cobalt tricarbonyl (n o) gives an amorphous polymer on heating (37), whereas the... 

This hydride then may add an acetylene molecule to form the vinyl derivative. A carbon monoxide insertion will produce the acrylyl nickel compound which can yield acrylate esters by either of two routes. Direct alcoholysis of the acyl nickel group may take place, as occurs with acylcobalt compounds (42) or, an acyl halide (or other acyl derivative, e.g., acyl alkanoate) may be eliminated. Alcoholysis of the acyl halide would then complete the catalytic cycle (35). 

When a large excess of olefin was used, the cobalt hydrocarbonyl was completely used up in Eq. (2), and Eq. (3) did not occur. In this case the products have been recovered as the triphenylphosphine derivatives, or as the esters by reaction of the acylcobalt carbonyls with iodine and an alcohol. 

Cobalt complexes derived from Schiff bases 388 catalyzed the hydroxyacylation of electron-deficient alkenes (Fig. 90) [431, 432]. Thus, methyl acrylate 387 reacted with aliphatic aldehydes 386 in the presence of 5 mol% of the in situ generated catalyst, molecular oxygen, and acetic anhydride to 2-acyloxy-4-oxoesters 389 in 56-77% yield. When acetic anhydride was omitted, the yields of products were lower and mixtures of the free hydroxy compounds and acylated compounds resulting from Tishchenko reactions were obtained. Electron-rich alkenes did not undergo the transformation, since the addition of the acyl radical is much slower. The acylcobalt species inserts oxygen instead and acts as an epoxidation catalyst. 

When the acylcobalt species is derived from a compound containing halogen on an activated carbon (e.g. an a-halo ester or nitrile) an elimination may occur to introduce an exocyclic double bond in the final product. This sequence, leading to lactones of pentadienoic acids, is general for both terminal and internal alkynes in the presence of amine bases (equation 17). ... 

Although butadiene reacts with Co2(CO)8 to yield the diene complexes (diene)C02(CO)o and (diene)2Co2(CO)4 (268), with alkyl- or acylcobalt tetracarbonyls it produces only the Tr-allylic species, 1-alkyl- or 1-acylmethyl-TT-allylcobalt tricarbonyls (281). These will react, in turn, with P(C3Hb)3 which displaces one CO ligand to form monotriphenyl-phosphine derivatives (281). 

Acylmetal complexes generally react with conjugated dienes to produce useful organic compounds. For example, acylcobalt carbonyls add to butadiene, producing 1 -acylmethyl-7r-allylcobalt derivatives, which then undergo elimination of the elements of HCo(CO)3 on treatment with base to give 1-acyl-diene u6). This reaction can be made catalytic with respect to the cobalt catalyst under proper reaction conditions. 

This chapter reviews the methods of preparation and the chemistry of the alkylcobalt and acylcobalt tetracarbonyis. These compounds are among the most thoroughly studied of the organo-substituted transition metal carbonyl derivatives. Recent evidence suggests that the mechanisms of reaction of the various transition metal compounds are closely related. Consequently, the information obtained from the alkylcobalt and acylcobalt tetracarbonyis should provide a basis for predicting the reactions of other transition metal compounds. 

The coordinated carbonyl groups of the alkylcobalt and acylcobalt tetracarbonyls may be replaced by other ligands. When alkylcobalt tetracarbonyls react with ligands, they generally form acylcobalt tricarbonyl derivatives. 

The formation of acylcobalt tetracarbonyls from alkylcobalt tetracarbonyls and carbon monoxide described above is an example of this type of reaction. The similar reactions with triarylphosphines and phosphite esters have been thoroughly studied because the equilibria are far on the side of the acyl compounds and the products are convenient derivatives to prepare from the alkylcobalt tetracarbonyls (7,10), The triarylphosphine and phosphite ester derivatives are much more thermally and oxidatively stable than the alkylcobalt tetracarbonyls themselves. 

The acylcobalt tetracarbonyls react with ligands by losing carbon monoxide, producing the same acylcobalt tricarbonyl derivatives as obtained from the alkylcobalt tetracarbonyls and the same ligands (7). 

Acylcobalt carbonyl derivatives are cleaved by sodium methoxide to esters and sodium salts of the corresponding carbonyl anions. By means of this reaction, acetyl[bis(trimethylolpropane phosphite)]cobalt dicarbonyl has been converted into sodium [bis(trimethylolpropane phosphite)]cobalt dicarbonyl. The latter compound is readily alkylated by methyl iodide to form the methylcobalt derivative and this compound in turn reacts with another mole of the phosphite ester, in the same way that methylcobalt tetracarbonyl does, to form acetyl[tris(trimethylolpropane phosphite)]-cobalt carbonyl ... 

Mixed phosphite ester-phosphine coordinated acylcobalt carbonyl derivatives have also been prepared. Methyl(triphenylphosphine)cobalt tricarbonyl, which cannot be produced by a simple ligand replacement reaction, can be obtained by another method. Hieber and Lindner (21) found that bis(triphenylphosphine)dicobalt hexacarbonyl reacts with sodium amalgam to form sodium(triphenylphosphine)cobalt tricarbonyl and that this compound reacted with methyl iodide to form methyl-(triphenylphosphine)cobalt tricarbonyl. 

The same reaction occurs much more rapidly and without gas evolution with alkylcobalt tetracarbonyls and conjugated dienes (14). Thus, the reaction probably involves the addition of an acylcobalt tricarbonyl to the diene, perhaps by way of a w complex, either 1 2 or 1 4 and then a cyclization to the TT-allyl derivative. 

Insertion reactions of alkylcobalt or acylcobalt tetracarbonyls with saturated aldehydes or ketones have not been observed. Carbonyl insertions do occur in some unsaturated carbonyl systems, however. The cyclization of the intermediate acylacrylylcobalt tricarbonyls, formed from acetylenes and alkylcobalt or acylcobalt tetracarbonyls, to butenolactone derivatives, as described above, is one example of the reaction. Another example is the addition of alkylcobalt or acylcobalt tetracarbonyls to a, -unsaturated aldehydes or ketones. In this reaction an acyl group from the cobalt compound is added to a carbonyl oxygen and the cobalt carbonyl group forms a iT-allyl system with the carbonyl carbon and the double bond 19). 

By the addition of a phosphine to an alkylcobalt tetracarbonyl, the phosphine-substituted acylcobalt carbonyl can be prepared (182,183). In the case of (methoxycarbonyl)methylcobalt tetracarbonyl as a model compound, some details of the reaction have been revealed. Adding a phosphine to this complex, the kinetically controlled formation of a phosphine-substituted acylcobalt carbonyl is observed that can be converted to the thermodynamically more stable phosphine -substituted derivative. 

Water and alcohols cleave some acyl-metal bonds to give carboxylic acid derivatives and a metal hydride, another example of an inverse cleavage. This reaction has been studied with acylcobalt carbonyl derivatives such as... 

The insertion of an olefin into a C—M bond is a critical step in some olefin dimerization and polymerization reactions (Section IV,D), but studies of this reaction have not been very fruitful. The insertion of isobutylene into the C—Ti bond of CH3TiCl3 to give a neopentyl derivative is one of the few straightforward examples of this reaction (133). Olefin, diene, and acetylene insertion in acylcobalt compounds have been reported by Heck in an elegant series of papers sununarized in his review of this area (3). These insertions are often quite complex, as illustrated by the butadiene insertion. 

Some interesting syntheses 236) have been carried out utilizing alternately the reactions of alkylcobalt carbonyl derivatives with tricovalent phosphorus derivatives and the cleavage of acylcobalt carbonyl derivatives to the corresponding anions with methanolic sodium methoxide, e.g. 

Some kinetic studies involving the reactions of various cobalt carbonyl derivatives with triphenylphosphine have recently been reported. The rate constants were measured for the reactions of a variety of acylcobalt tetra-carbonyl derivatives with triphenylphosphine according to the following equation 237)... 

The reaction was found to be first order with respect to the acylcobalt tetra-carbonyl derivative. The rate of the reaction was increased by an increase in the size of the acyl group and decreased by an increase in the electron-withdrawing tendencies of the acyl group. 

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