Metathesis or Salt Elimination Reactions

Metal cluster anions can be employed in place of the mononuclear metal carbonylate anions. Complexes that have been used include [Fe2(CO)8]2, 107 [Fe3(CO)n]2, 92,132 [Fe4(CO)13]2-,132 227233 [HRu3(CO)u]-,124,136,137 

In some reactions, halide ions may be retained at E.512 This is potentially useful as the residual halide becomes a functionality that may allow for further reactions. Examples are given in Eqs. (13)53 71 and (14).72 

The polarity of the displacement reaction can be reversed where suitable reagents are available. Thus, metal halides can be treated with anionic main group fragments. This has been an important method for extending the E-M chemistry to the earlier transition metals for which fewer readily accessible metal-carbonyl complexes are known. Examples for production 

Metal complexes of E fragments that contain E-H bonds may be deproto-nated by strong bases. The E atoms in these complexes are often highly negatively charged and consequently very basic. When these complexes are subjected to reactions involving the ionic displacement strategy, the site of reaction is often at E as exemplified in Eqs. (27)282 and (28).282 

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This procedure, sometimes referred to as transmetallation or (metathesis or salt-elimination) reaction, is by far the most versatile synthetic method for a wide range of d-and p-block metal alkoxide complexes. The alkali metal (usually sodium or potassium) alkoxide is treated in the presence of excess alcohol with the corresponding metal(loid) halide either in a hydrocarbon (generally benzene) or an ether solvent (Eq. 2.41) ... 

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