Carbonation of organometallics

Organometallic compounds or carbanions undergo a number of reactions in which the carbanion or carbanion-like moiety of the organometallic compound acts as a nucleophilic displacing agent. Examples are the formation of hydrocarbons from alkyl halides, alkyl halides from halogens, and ketones from acid chlorides or esters. The latter two reactions are closely related to the base-catalyzed condensations and are perhaps additions as well as displacement reactions. Related addition reactions are the carbonation of organometallic compounds and the addition to ketones or aldehydes. 

Hard carbon nucleophiles of organometallic compounds react with 7r-allyl-palladium complexes. A steroidal side-chain is introduced regio- and stereo-selectively by the reaction of the steroidal 7T-allylpalladium complex 319 with the alkenylzirconium compound 320[283]. 

In addition, a catalytic version of Tt-allylpalladium chemistry has been devel-oped[6,7]. Formation of the Tr-allylpalladium complexes by the oxidative addition of various allylic compounds to Pd(0) and subsequent reaction of the complex with soft carbon nucleophiles are the basis of catalytic allylation. After the reaction, Pd(0) is reformed, and undergoes oxidative addition to the allylic compounds again, making the reaction catalytic.-In addition to the soft carbon nucleophiles, hard carbon nucleophiles of organometallic compounds of main group metals are allylated with 7r-allylpalladium complexes. The reaction proceeds via transmetallation. These catalytic reactions are treated in this chapter. 

The stereochemistry of the Pd-catalyzed allylation of nucleophiles has been studied extensively[5,l8-20]. In the first step, 7r-allylpalladium complex formation by the attack of Pd(0) on an allylic part proceeds by inversion (anti attack). Then subsequent reaction of soft carbon nucleophiles, N- and 0-nucleophiles proceeds by inversion to give 1. Thus overall retention is observed. On the other hand, the reaction of hard carbon nucleophiles of organometallic compounds proceeds via transmetallation, which affords 2 by retention, and reductive elimination affords the final product 3. Thus the overall inversion is observed in this case[21,22]. 

The properties of organometallic compounds are much different from those of the other classes we have studied to this point Most important many organometallic com pounds are powerful sources of nucleophilic carbon something that makes them espe cially valuable to the synthetic organic chemist For example the preparation of alkynes by the reaction of sodium acetylide with alkyl halides (Section 9 6) depends on the presence of a negatively charged nucleophilic carbon m acetylide ion... 

Organohthium and organomagnesium compounds are stable species when prepared m suitable solvents such as diethyl ether They are strongly basic however and react instantly with proton donors even as weakly acidic as water and alcohols A proton is transferred from the hydroxyl group to the negatively polarized carbon of the organometallic compound to form a hydrocarbon... 

Carbon-Carbon Bond-Forming Reactions of Organometallic Reagents... 

The major problem in the produchon of semiconductors by the decomposition of organometallics appears to be the unwanted carbon contaminahon of the products. 

At the start of this Chapter, an essay by Peter Day was quoted in which he lauds the use of soft chemistry , exemplifying this by citing the use of organometallic precursors for making thin films of various materials used in microelectronics. The same approach, but without the softness, is increasingly used to make ceramic fibres here, ceramic includes carbon (sometimes regarded as almost an independent state of matter because it is found in so many forms). 

House investigated the role of cuprous ions in the conjugate addition of organometallic reagents. He found that the catalytic effect can be explained by the intervention of a methyl copper derivative, which reacts rapidly with the carbon-carbon double bonds of the conjugated system. 

The processes of reversible adsorption of the coordination" inhibitors (including the adsorption of organometallic compounds) result in an increase in the lifetime of the transition metal-carbon bond. It is possible that due to this, in the case of propylene polymerization by two-component catalysts based on TiCU, at low temperatures a long-term increase of molecular weight with time was observed (192,193). 

Stabilization of intermediates by strong adsorption will frequently be a necessary precondition for synthesis. Thus, in the case of the Kolbe reaction, further oxidation of the radicals is prevented the formation of metal-carbon bonds in the reduction of alkyl halides (Fleischmann et al., 1971a Galli and Olivani, 1970) or oxidation of Grignard reagents (Fleischmann et al., 1972c) is shown by the isolation of organometallic... 

For lists of organometallic reagents that react with epoxides, see Wardell, J.L. Paterson, E.S. in Hartley Patai. The Chemistry of the Metal-Carbon Bond, vol. 2 Wiley NY, 1985, p. 307 Ref. 568, p. 512. 

For reviews of the addition of organometallic compounds to carbonyl groups, see Eicher, T. in Patai, Ref. 2, p. 621 Kharasch, M.S. Reinmuth, O. Grignard Reactions of Nonmetallic Substances, Prentice-Hall Englewood Cliffs, NJ, 1954, p. 138. For a review of reagents that extend carbon chains by three carbons, with some functionality at the new terminus, see Stowell, J.C. Chem. Rev., 1984, 84, 409. 

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