Formation of Other Organometallics

The chemistry of alkyne complexes is somewhat more complicated than that of alkene complexes because of the greater possibilities for -n bonding by alkynes and the tendency of some of die complexes to act as intermediates in the formation of other organometallic compounds. 

One previous synthesis of ferrocene-containing condensation polymers via interfacial methods at room temperature has been reported by Knobloch and Rauscher, who formed low molecular weight polyamides and polyesters by reacting l,l -bis(chloro-formyl)ferrocene with various diamines and diols. Further, Carraher and co-workers have utilized interfacial techniques in the formation of other types of organometallic polymers. 

The reaction products depend on pH and other factors such as the presence of ferrous ions, epithiospecifier protein, and the nature of the glucosinolate side chain. Epithiospecifier protein has recently been independently purified and characterized7,8 and appears to require ferrous ions indicating the formation of an organometallic (FeN - aglycone) intermediate that leads to die formation of a thiirane ring. 

As shown in a model study (Fig. 60), extension of the Barbier procedure to carboxylic acids is unsatisfactory for ketone synthesis. On the other hand, lithium carboxylates and lithium and alkyl chlorides lead to good to excellent yields when sonicated in THF. An application of such a procedure to the preparation of long chain alkyl ketones is given in Ch. 9, p. 361. The use of chlorides is required. The reason seems to be the necessity of a rapid formation of the organometallic (p. 217). When this formation is slow, with bromides or iodides, complex electron transfers take place and imexpected couplings result. 

Because of the complexity of the full mechanism, most theoretical studies concentrate on particular steps of the catalytic cycle. This chapter is thus organized by the different steps of the mechanism, rather than by reaction. Oxidative addition and reduction elimination have been studied also in the context of other organometallic reactions. Transmetalation is on the other hand specific of C-C bond formation processes, and because of this, it will be discussed in more detail. Our intention in this contribution is to review the present state of the research in the area. As wiU be seen, a significant part of the articles mentioned have been published after 2003, indicating the current high activity on the topic. Because of this, it is impossible to provide a definitive mechanistic picture. This is rather a progress report on a very active research field. This paper complements a recent review by some of us that focused on cross-coupling [19]. 

Formation of ketones. Ketones can be prepared by the carbonylation of halides and pseudo-halides in the presence of various organometallic compounds of Zn, B, Al, Sn, Si, and Hg, and other carbon nucleophiles, which attack acylpalladium intermediates (transmetallation and reductive elimination). 

Carbanions are very useful intermediates in the formation of carbon-carbon bonds. This is true both for unstabilized structures found in organometallic reagents and stabilized structures such as enolates. Carbanions can participate as nucleophiles both in addition and in substitution reactions. At this point, we will discuss aspects of the reactions of carbanions as nucleophiles in reactions that proceed by the 8 2 mechanism. Other synthetic aj lications of carbanions will be discussed more completely in Part B. 

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