Recent studies on the low-coordinate species of the heavier main group elements, such as silylenes and germylenes, have shown that they can behave similarly to the transition metal complexes. Phosphenium ions, derivatives of divalent phosphorus which have both vacant 3p-orbital and lone pair electrons, are intrinsically highly reactive. The stabilization methods of phosphenium ions can be categorized into thermodynamic and kinetic stabilization. Thermodynamic stabilization is achieved by coordinating electrons with 3p-orbitals of phosphenium ions. Moreover, 3p-orbitals of phosphenium ions can be kinetically stabilized by steric protection with bulky substituents. So far, the most widely used synthetic method for phosphenium ions is the halogen abstraction from the neutral halophosphine precursor, which can be accomplished by strongly electrophilic halide scavengers. Phosphenium ions exhibit both Lewis acid and Lewis base chemical properties. In recent years, nitrogen-substituted phosphenium ions based on the ferrocenyl frameworks have attracted substantial attention due to their stable redox behavior. However, since the highest occupied molecular orbital (HOMO) of such species is predominantly located on the iron atom of ferrocenyl group, it is considered that the central phosphorus atom is not involved in the redox process. From the perspective of studying the redox behavior of phosphenium ions, the review indicates that phosphenium ions with bulky ferrocenyl groups can be kinetically stabilized and the frontier orbitals can be located on the central phosphorus atom. The design and synthesis of phosphenium ions with stable redox behavior, high reactivity, and kinetic stability will become the research trend in this field.

Key words: low-coordinate main group species, phosphenium ions, kinetic stabilization, redox behavior, ferrocenyl group