The Nucleophilic Organometallic Partner

The preparations of the various types of organometallic compounds that can be used as cross-coupling parmers are described earlier in this chapter. Most magnesium and zinc compounds have to be prepared, then used, as needed. However, boronates (i.e. boronic acids and esters), stannanes and silanes are much more stable to air and water, and many of them can be stored for long periods. 

A large number of heterocyclic boronates and, to a lesser degree, stannanes are available conunercially. Included in the suppliers lists are many compounds, the preparations and properties of which do not appear in the literature. They are often noted in papers just as reagents for syntheses of libraries for biological testing and, although this may be a practical approach, it is scientifically unsatisfactory because there is no trail of characterization, particularly as some of these compounds, for example azine a-boronates, are significant from a theoretical viewpoint. 

Other than ability to perform the required reaction, factors to be taken into consideration when choosing the organometallic include functional group compatibility, selectivity and reaction conditions. When considering scale-up, disposal of metal residues, particularly tin and zinc, and by-products of other additives, such as fluoride, can be significant problems. 

Carbanionic reagents, such as enolates and cyanide can also be used in place of the organometallic component. 

There are a number of named reactions , which are specific to the organometallic used and, in chronological order of introduction, these are  

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