Other Reactions of Esters and Amides with Co-ordinated Nucleophiles

9 Other Reactions of Esters and Amides with Co-ordinated Nucleophiles 

Transesterification or transamination are metal-directed reactions which are commonly encountered. We have discussed transamination processes in Section 5.5.2 and also in Chapter 3. The key step involves the attack of a co-ordinated alcohol or alkoxy group upon the carbonyl of a co-ordinated ester or amide. Many Lewis acidic metal ions have been shown to be effective catalysts for transesterification reactions for example, heating diethyl picolinate with copper(n) salts in methanol results in rapid and clean transesterification (Fig. 5-86). In the absence of the metal ion, the rate of reaction is vanishingly slow. 

5 Stabilisation of Anions and the Reactions of Co-ordinated Ligands with Electrophiles 

In this reaction, the incoming alkoxide group is almost certainly co-ordinated to the metal centre in the key stages of the reaction. A particularly elegant demonstration of this is seen in the zinc(n) catalysed transesterification of 4-nitrophenyl picolinate with HO(CH2)2NH(CH2)2NH2 (Figs. 5-87 and 5-88). In the initial step of the reaction, an intermediate complex 5.38 may be isolated (Fig. 5-87). 

Buckingham in Biological Aspects of Inorganic Chemistry , (eds. A.W. Addison, W.R. Cullen, D. Dolphin, B.R. James), Wiley, New York, 1976. 

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