Lead compounds nitrogen-coordinated products

One of the major problems in the chemistry of three-coordinated boron-nitrogen compounds is their relative instability towards hydrolysis 79>8°). This feature reduces their possible applications in many areas such as in the medicinal field or utilization for polycondensation-products. However, steric hindrance by bulky substituents on the borazine ring leads to compounds with enhanced hydrolytic stability, particularly when no solvent is present in which they may dissolve. This observation has resulted in extensive research on sterically hindered boron-nitrogen ring compounds. 

With lithiated imidazoles, only bis(carbene) complexes are formed, although careful adjustment of the conditions can lead to a compound which contains carbene ligands resulting from both alkylation and protonation411. A similar methodology is applicable with isothiazolyl lithium. In the product the nitrogen atom occupies a position remote from the coordinated carbon (equation 93)412. 

In this section examples of polyazamacrocyclic products synthesised by the interaction of simple ligsons, such as hydrazine and its derivatives with mono- and dicarbonyl compounds, are discussed. The main feature of hydrazines as ligsons is the presence of two lone pairs of electrons in the functional groups. Coordination of hydrazines to the metal ion leads to the loss of nucleophilic properties of only one functionality, because steric restraints will not permit the second nitrogen donor to coordinate to a metal at the same time. As a result the nucleophilic properties of the non-coordinated amino groups can be exploited to carry out ring-closure reactions. 

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