Polyphosphorus Compounds—New Results and Perspectives

In contrast to the numerous known and often technically important mono‐ and diphosphorus compounds with phosphorus in its maximum oxidation state, polyphosphorus compounds led only a shadowy existence up to about twenty years ago. One of the reasons for this was the properties of such compounds, which made their handling and structural characterization difficult. This problem was solved by the development of modern preparative techniques and, especially, by the further methodological development of nuclear magnetic resonance spectroscopy. Thus, a fascinating new branch of phosphorus chemistry has been opened up in recent years. The first comprehensive review on this subject was published five years ago. Since then, research on this “element‐near” chemistry of phosphorus has produced further impressive advances with the result that a surprisingly large variety of compounds with skeletons consisting of chains or rings of phosphorus atoms is known today. However, the recent observation of the spontaneous formation of the “aromatic” pentaphosphacyclopentadienide ion, P   5 − , during the synthesis of phosphorus‐richer polyphosphides from phosphorus‐poorer compounds in solution and the discovery of the inversion of phosphorus in tetra‐ and pentacyclic organophosphanes demonstrate that this field is still capable of producing surprises.