Cobalt-catalyzed carbonylations species involved

A rather different approach to carbonylation of aliphatic halides involves the carbonyl anion [Co(CO)4] which, being a kinetically stable 18-electron species, attacks the halide by nucleophilic displacement rather than by undergoing oxidative addition. A probable catalytic cycle for cobalt-catalyzed carbonylation of benzyl chloride is shown in Scheme 6. ... 

Cobalt complexes have been used to catalyze the carbonylation of chloroarenes to the corresponding carboxylic acids and their esters (Sect. 3.3). Some complexes of cobalt in the oxidation state -1 activate the Ar-Cl bond via an SRN1-type mechanism [2] involving single electron transfer from the metal to chloro-arene, followed by elimination of Cl . The simplest Co(-I) carbonyl species, [Co(CO)4] , is not electron-rich enough to react with haloarenes. However, its reactivity has been shown to enhance tremendously in the presence of Caubere s complex bases, mixtures of NaH and NaOAlk [23,66,67]. For instance, the stoichiometric carbonylation of chlorobenzene has been performed with the... 

Other Octacarbonyidicobalt-Catalyzed Reactions. A retro-Diels-Alder reaction catalyzed by Co2(CO)8 was observed in which a barrelene derivative loses a C2H2 fragment (eq 30). An analogous cleavage accompanies the cyclopentenone synthesis (see below) when norbomadiene reacts in certain solvents with alkynehexacarbonyldicobalts, as shown by the formation of dicarbonylcyclopentadienylcobalt, whereas a Diels-Alder addition catalyzed by a cobalt carbonyl species is involved when the same reaction is applied to cyclohexadiene. ... 

The above studies indicate that metal ions catalyze the hydrolysis of amides and peptides at pH values where the carbonyl-bonded species (25) is present. At higher pH values where deprotonated complexes (26) can be formed the hydrolysis is inhibited. These conclusions have been amply confirmed in subsequent studies involving inert cobalt(III) complexes (Section 61.4.2.2.2). Zinc(II)-promoted amide ionization is uncommon, and the first example of such a reaction was only reported in 1981.103 Zinc(II) does not inhibit the hydrolysis of glycylglycine at high pH, and amide deprotonation does not appear to occur at quite high pH values. Presumably this is one important reason for the widespread occurrence of zinc(Il) in metallopeptidases. Other metal ions such as copper(II) would induce amide deprotonation at relatively low pH values leading to catalytically inactive complexes. 

The amidocarbonylation reaction was discovered by Wakamatsu [1], who demonstrated the synthesis of a range of A -acyl amino acids through the cobalt carbonyl-catalyzed reactions of various combinations of aldehyde plus amide, with carbon monoxide (eq. (1)). Some aspects of the mechanism of aliphatic aldehyde amidocarbonylation have been examined by both Pino and co-workers [2] and by Getman [3], Magnus and Slater [4] subsequently investigated the scope of this synthesis for variety of A -substituted amide co-reactants and C-sub-stituted aldehydes. Further mechanistic revisions were proposed involving acyl-iminium species. 

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