Bidentate 1,2-diaminoethane

Examples of bidentate ligands include the oxalate ion (Cp/) and 1,2-diaminoethane. 

A simple chelating ligand is 1,2-diaminoethane (H2NCH2CH2NH2 also called ethylene-diamine), whose binding to a metal ion is shown in the margin. We say that ethylenediamine is bidentate because it binds to the metal through two ligand atoms. 

The chelate effect is well known in coordination chemistry and relates to the observation that metal complexes of bidentate ligands (such as 1,2-diaminoethane, en) are significantly more stable than closely... 

Rhodium(III) complexes typically contain anunine, halo, or aqua ligands, or the important bidentate ligands 1,2-diaminoethane (en), oxalato, or pentane-2,4-dionato (acac) and are invariably octahedral. Their wide variety is in part a reflection of the slow reactions, which take place at the low-spin d centers, which allow many intermediates, and geometrical or chiral isomers, to be isolated. It is fairly difficult to oxidize rhodium(III) complexes, but they may be reduced to rhodium(l) species in the presence of suitable ligands. However, there is little current work being carried out on the classical rhodium(III) complexes and even less on the higher oxidation states. 

Utility. Many asymmetric syntheses have been developed using vicinal diamines as the source of chirality. The major interest lies in their use as precursors for the synthesis of a broad family of bidentate ligands. Many reactions have also been described using the N-alkyl derivatives of these diamines as chiral auxiliaries and protecting groups of aldehydes. Most of these applications generally use the framework of l,2-diphenyl-l,2-diaminoethane (7) or 1,2-diaminocyclohexane (8), whose preparations have been fully described. ... 

These reactions have been studied for a variety of bidentate Ugands, including 1,2-diaminoethane, pentane-2,4-dionate, and 1,10-phenanthroline. The quantum yield of the racemisation reaction is of the order of 1-2 % in each case, indicating similar pathways for aU of those complexes [2]. 

However, the lUPAC system also makes it possible to use the prefix amino-, with the location of the -NH2 group being indicated by numbering the carbon atoms in the chain. This method is most often used when the number of carbon atoms in the chain is four or more. Examples (Figure 10.41) of the application of this system are 2-aminopentane, l,2-diaminoethane (an example of a bidentate ligand, see Chapter 13) and l,6-diaminohexane (often used in the laboratory preparation of nylon-6,6). 

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