Using organometallics to make organic molecules

Halogen-metal exchange tolls the knell of one appealing way to make carbon-carbon bonds. It may already have occurred to you that we might make a Grignard or organo-lithium reagent and combine it with another alkyl halide to make a new carbon-carbon a bond. 

This reaction does not work because of transmetallation. The two alkyl bromides and their Grignard reagents will be in equilibrium with each other so that, even if the coupling were successful, three coupled products will be formed. 

You will see later that transition metals are needed for this sort of reaction. The only successful reactions of this kind are couplings between metal derivatives of alkynes and alkyl halides. These do not exchange the metal as the alkynyl metal is much more stable than the alkyl metal. 

A good example is the synthesis of a substituted alkyne starting from acetylene (ethyne) itself. One alkylation uses NaNH2 as the base to make sodium acetylide and the other uses BuLi to make a iithium acetylide. 

Organolithiums can be converted to other types of organometallic reagents by transmetallation—simply treating with the salt of a less electropositive metal. The more electropositive Mg or Li goes into solution as an ionic salt, while the less electropositive metal such as In takes over the alkyl group. 

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Using organometallic reagents to make organic molecules... 

For organic molecules, the lifetime of the singlet state ranges from tens of picoseconds to hundreds of nanoseconds, whereas the triplet lifetime is much longer (microseconds to seconds). However, such a difference cannot be used to make a distinction between fluorescence and phosphorescence because some inorganic compounds (for instance, uranyl ion) or organometallic compounds may have a long lifetime. 

It is obviously of importance for these studies to have a variety of means available for the incorporation of tritium into organic molecules. This is done using catalytic systems and is where the subject takes on a particular interest to the organometallic chemist. Indeed, the high sensitivity of H NMR makes it an ideal tool for the study of surface catalysis, an area of research which has already been reviewed, " or for the mechanistic study of metal catalyzed reactions. Tritiation can be carried out with... 

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