Oxygenates carbon bond mechanism

Presumably the complex forms by electrophilic attack of the C02 carbon on the electron-rich metal center, followed by a similar electrophilic attack of the second C02 on the more basic oxygen of the coordinated C02, forming an oxygen-carbon bond. The metallocycle ring closing then completes the complex formation. Support for this mechanism comes from infrared spectra implicating a mono-C02 adduct that is observed when the starting metal complex reacts with less than two equivalents of C02. 

Mechanism The mechanism of the aliphatic side-chain oxidation as shown in Scheme 7.34 probably involves manganese-oxygen-carbon bonding with subsequent reduction of manganese and oxidation of carbon to yield aldehyde, which is much more vulnerable to oxidation with permanganate. 

In order to consider a generalized mechanism for the Michaelis-Arbu-zov reaction, it is necessary to regard each of the two steps as involving a band of mechanisms ranging from pure SNl to pure SN2. The more stable the carbonium ion which can be formed by dissociation of the alkyl halide or by dissociation of an oxygen-carbon bond in the intermediate, the greater will be the SNl character of the first or second steps, respectively. 

Mechanisms available for the aquation of carboxylato-cobalt(in) complexes have been considered, with the discussion covering such topics as cobalt-oxygen versus oxygen-carbon bond breaking, dechelation of multidentate carboxylate ligands, and stereochemistry. ... 

The mechanism of conjugate addition reactions probably involves an initial complex between the cuprate and enone.51 The key intermediate for formation of the new carbon-carbon bond is an adduct formed between the enone and the organocopper reagent. The adduct is formulated as a Cu(III) species, which then undergoes reductive elimination. The lithium ion also plays a key role, presumably by Lewis acid coordination at the carbonyl oxygen.52 Solvent molecules also affect the reactivity of the complex.53 The mechanism can be outlined as occurring in three steps. 

Although the high reactivity of metal-chalcogen double bonds of isolated heavy ketones is somewhat suppressed by the steric protecting groups, Tbt-substituted heavy ketones allow the examination of their intermolecular reactions with relatively small substrates. The most important feature in the reactivity of a carbonyl functionality is reversibility in reactions across its carbon-oxygen double bond (addition-elimination mechanism via a tetracoordinate intermediate) as is observed, for example, in reactions with water and alcohols. The energetic basis... 

Furthermore, the data from Table 2 allow us to draw several valuable conclusions regarding the mechanism of hydride addition to carbon-oxygen double bonds. 

Alternative mechanisms for carbon-oxygen double bond hydrogenation and methanol synthesis are shown in Schemes 4 and 5. 

Figure 27. Mechanism of radiation induced chain scission in PMMA. Homolysis of the mainchain-carbonyl carbon bond is indicated as the initial step. Acylcarbon-oxygen, sigma bond homolysis also occurs but rapid decarbonylation ultimately leads to the same indicated products.

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