Organic halides reaction patterns

Carbonylation is an exceedingly broad subject, but the main reaction patterns can be easily rationalized by recalling the classification used earlier for coupling reactions involving (a) metallacycles (b) hydride-promoted reactions and (c) oxidative addition of organic halides to zero-valent nickel. In fact, one or other of these steps is necessary to form a species able to undergo carbonylation. 

Allenes undergo facile carbopalladation and are used extensively in organic synthesis. The general reaction patterns of allenes with aryl halides are as follows. In carbopalladation of allene, an Ar group attacks the central sp carbon of the allene system to generate 367 and then the 7r-allylpalladium 368 as an intermediate. Then the attack of a nucleophile mainly on a less substituted terminus yields the alkene 369. Thus 1,2-addition to one of the double bonds in the allene occurs. In the absence of nucleophiles, y3-H elimination gives 2-substituted 1,3-dienes... 

In conclusion, do the similarities and differences in the reactivity patterns for these reactive species with organic halides indicate a basic relationship or are these similarities fortuitous and does nature provide distinct pathways of comparable energy. Of the three mechanistic possibilities considered for radical anions, electron transfer, radical-like and nucleophic substitution, electron transfer is indicated for highly exothermic reactions, and a radical-like process is likely for the less... 

The value of alkyl halides as starting materials for the preparation of a variety of organic functional groups has been stressed many times In our earlier discussions we noted that aryl halides are normally much less reactive than alkyl halides m reactions that involve carbon-halogen bond cleavage In the present chapter you will see that aryl halides can exhibit their own patterns of chemical reactivity and that these reac tions are novel useful and mechanistically interesting... 

The organic analogues of the reactions to be discussed here are the borane reductions of aldehydes and ketones and the addition of metal alkyls across ketonic carbonyls, equation 15. In contrast to the ease of these organic reactions, qualitative data which has accumulated in our laboratory over the last decade demonstrates that the carbonyl group in organometallies is fairly resistant to addition across CO. For example, many stable adducts of organometallie carbonyls with aluminum alkyls are known, eq. lc, but under similar conditions a ketone will quickly react by addition of the aluminum alkyl across the CO bond. A similar reactivity pattern is seen with boron halides. 

Close inspection of m T plots for aquation of metal ammine- or amine-halide complexes reveals that there is some pattern in the (relatively small) scatter of points about the best straight line. Usually rate constants for acetone-water mixtures lie on the opposite side of the line from those for alcohol-water mixtures the rate constants for aquation in acetone-water mixtures vary slightly less with solvent Y values than expected. It is possible to accommodate this pattern by the use of a more sophisticated equation, such as that [equation (1)] established for organic reactions. ... 

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