Organometallic compounds carbenes, reactions with

Carbene transfer reactions with participation of organometallic compounds bearing heterocyclic substituents 99CSR315. 

The majority of gold(I) carbene complexes are pure organometallic compounds and the are out of the scope of this work. Some halide or triphenylphosphine carbene complexes are known and they will be considered here. Nucleophilic addition of alcohols or amines to gold-coordinated isocyanides is one of the best-established methods to obtain gold carbene derivatives. The reaction of H[Au(CN)2] with propene oxide and estirene oxide yields (cyano)carbene complexes (380) avoiding the intermediate step.2257 A cyclic carbene compound is obtained by reaction of a dinuclear isocyanide with amine (Scheme 32).2258... 

In a somewhat intriguing sequence of reactions, the organometallic compound (56) on treatment with methyllithium afforded the rearranged product (57), as shown in equation (118).265 While the mechanism of this transformation is not known, it has been speculated that the initially formed carbene rearranges to a spirocyclopropene intermediate via a novel ring contraction. 

The problem with many of these reactions is that they require strong bases—either the organometallic compound itself is basic or a base must be used to create the carbanion. Carbenes are so unstable that they must be formed n the presence of the compound they are intended to react with, and this can be a problem if that compound is base-sensitive. For dichlorocarbene, a way round the problem is to make the carbanion by losing CO2 instead of a metal or a proton. Decarboxylation of sodium trichloroacetate is ideal as it happens at about 80 °C in solution. 

In this chapter, we have considered just a few types of reactions of organometallic compounds, principally the replacement of CO by other ligands and the reactions involved in syntheses of carbene and carbyne complexes. Additional types of reactions will be discussed in Chapter 14. We conclude this chapter with two examples of how spectral data may be used in the characterization of organometallic compounds. Further examples can be found in the problems at the end of this chapter and in Chapter 14. 

In certain cases it has been shown that the rate of reaction of the a-haloalkyl derivative with a second reagent, such as an olefin or diazoalkane, is dependent upon the concentrations of both reactants (Blanchard and Simmons, 1964 Bethell and Brown, 1967). Such observations are consistent either with a one-step bimolecular reaction of the organometallic compound as such and the other reagent or with a rapid preequilibrium forming an intermediate, followed by a slow reaction of this intermediate with the second reactant. The latter alternative is represented in equation (14), in which A b[olefin]Rate-determining reaction of an intermediate carbene... 

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