Schiff base and non-Schiff base macrocyclic ligands and complexes incorporating the pyridine moiety – The first 50 years

• A recent 50-years history of synthesis of [1+1] and [2+2] Schiff base and non-Schiff base macrocycles.
• Developments in the design and synthesis of pyridine containing macrocycles.
• The preparation of functionalized ligands containing pendant arms.
• A summary of the new approach of these compounds such as mechanically interlocked molecules is reviewed.
• The catalytic properties and cofactors and artificial metalloenzymes are also included.

In this paper, there is an attempt to review the developments in the design and synthesis of pyridine containing [1+1] and [2+2] macrocyclic Schiff base ligands, formed by condensations of 2,6-diacylpyridine or 2,6-diformylpyridine and appropriate polyamines, which utilize the templating capability of different metal ions to direct the synthetic pathway. The reduction of the cyclic Schiff bases to their related amine derivatives is also considered since this leads to more flexible ligands capable of structural elaboration through donor groups. Attention is mainly paid to the synthetic and structural aspects of the resulting metal complexes, particularly to the role of the coordination preferences of the different metal ions in directing the synthesis totally or preferentially toward mono-, di- or poly-nuclear entities. The preparation of functionalized ligands, containing pendant arms, capable of promoting rapid complexation and decomplexation and their use in selective metal ion transportation and separation are also paid attention to. Furthermore, a summary of the new approach of these compounds such as mechanically interlocked molecules, catalytic properties and cofactors and artificial metalloenzymes is reviewed.