Nucleophilic Attack on Co-ordinated Nitriles

Many of the reactions which have been reported for carbonyl compounds (hydration, alcoholysis, aminolysis, etc.) are also shown by co-ordinated nitrile ligands. The reaction of a nucleophile with a nitrile is a two-stage process, which may involve one or two molecules of the incoming nucleophile (Fig. 4-6). 

In the case of water as a nucleophile, the initially produced hydroxyimine may tauto-merise to an amide, which in turn generates a carboxylic acid upon further hydrolysis. Hydrolysis of a nitrile is, of course, one of the standard classical methods for the synthesis of carboxylic acids (Fig. 4-7). 

4 Other Reactions of Co-ordinated Ligands with Nucleophiles 

The metal-promoted reactions with nucleophiles generally yield metal complexes of the intermediate imino species and it is quite unusual to observe the carboxylate products derived from the attack of a second equivalent of nucleophile. A wide variety of products have been observed. The ligands may be monodentate O- or A-bonded species, or exhibit a didentate N,0-mode. The ligands may be in the amide or the hydroxyimine tautomeric forms, and may be neutral or deprotonated (Fig. 4-8). 

Particularly well-studied examples of the hydration of nitriles are seen with the chelating ligands 2-cyano-1,10-phenanthroline (4.1) or 2-cyano-8-hydroxyquinoline (4.2). The products of the reactions are the appropriate amides, and the rate of hydration is enhanced by up to ten million times on co-ordination to nickel(n), copper(n) or cobalt(m). 

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