Phosphorus‐Nitrogen Heterocycles Derived from Chelating <i>N</i> ‐Donor Ligands: Historical Advances, Recent Highlights, and Outlook

The exploration of phosphorus-nitrogen heterocycles derived from chelating N-donor ligands is an area of research that has lagged behind the development of similar heterocycles based on other main group elements, most notably boron. The fact that phosphorus and nitrogen are both group 15 elements and that their compounds are most commonly viewed as Lewis bases likely contributes to this observation. However, through judicious ligand design and creative use of phosphorus sources that render phosphorus as Lewis acidic and/or electron poor, a variety of heterocyclic architectures are possible. In this article, we highlight selected examples of phosphorus adducts of bidentate, tridentate, and tetradentate N-donor ligands that have shown utility as functional molecular materials, in small molecule activation and catalysis, and as therapeutics and diagnostics in chemical biology. Finally, we look forward to the future of this emerging area and provide commentary on the unique opportunities available to researchers working within the field of phosphorus-nitrogen heterocycle chemistry.