The Higher Oligopyridines and their Metal Complexes

The series of oligopyridine ligands has increasingly become one of the most popular ligands in coordination chemistry. While the lower members of this series, 2,2'-bipyridine (bpy) and 2,2':6',2''- terpyridine (tpy), are mostly used due to their easy synthetic accessibility and predictable coordination behaviour, the higher members have also attracted chemists' interest. The higher the number of pyridine ring is, the lower is the solubility. Though some aromatic rests were attached to pyridine rings to increase the solubility. In addition, the higher oligopyridines may react, depending on metal ions, in different manners, e.g. they can be divided into subunits. This may be a drawback, however, this property was used to prepare fascinating metal complexes. These two properties make them as attractive and challenging synthetic molecules for chemists and material scientists. In this paper the synthetic strategies used to prepare the higher oligopyridine ligands are reviewed comprehensively.