Remarkably flexible 2,2′:6′,2″-terpyridines and their group 8–10 transition metal complexes – Chemistry and applications

The main purpose of this article is to focus on the diversity created by substitution on pyridine rings of 2,2′:6′,2″-terpyridines (tpy) allowing a fine-tuning of the ligand properties and offering substantial scope for tailoring the properties and applications of their corresponding metal complexes. The various substituents on tpys include nitrogen-, phosphorus-, halogen-, oxygen-, sulfur-and silicon-based functionalities and tpys have directly N-bound metals. These tpys have been recognized as unique chelating ligand systems with widespread exposure primarily because of their excellent complexing properties of N-donor atoms towards various main-group, transition, and f-metals. Owing to the considerable variety of these functionalized ligands available, the structural range of these complexes possessing mono-, di-, tri-, oligomeric- and polynuclear metal complexes is very diverse and describes the formation of unexpected shapes and further leading to the supra-molecular architectures. The remarkable flexibility of the tpy-metal complexes facilitates the synthesis of a wide range of organometallic complexes and the catalytic applications for organic transformations ranging from homogeneous to heterogeneous catalysis and the development of materials science. The special properties of these metal complexes have led to the production of different luminescent metal compounds, sensitizers for photovoltaic appliances, and electrochemical sensors based on ditopic terpyridyl units. Furthermore, these tpy based metal complexes exhibit applications in pharmaceutical and agrochemical fields. Since the sustained interest for tpy ligands has been motivated to lay the foundation for future synthetic endeavors, the present review compiles the synthesis, coordination ability, rich organometallic chemistry, and promising applications of Group 8–10 transition metal complexes of various tpy derivatives.