Redox‐Triggered Reversible Interconversion of a Monocyclic and a Bicyclic Phosphorus Heterocycle

Molecules which change their structures significantly and reversibly upon an oxidation or reduction process have potential as future components of smart materials. A prerequisite for such an application is that the molecules should undergo the redox‐coupled transformation within a reasonable electrochemical window and lock into stable redox states. Sodium phosphaethynolate reacts with two equivalents of dicyclohexylcarbodiimide (DCC) to yield an anionic, imino‐functionalized 1,3,5‐diazaphosphinane [ 3 a ] − . The oxidation of this anion with elemental iodine causes an intramolecular rearrangement reaction to give a bicyclic 1,3,2‐diazaphospholenium cation [ 6 ] + . This umpolung of electronic properties from non‐aromatic to highly aromatic is reversible, and the cation [ 6 ] + is reduced with elemental magnesium to reform the 1,3,5‐diazaphosphinanide anion [ 3 a ] − . Theoretical calculations suggest that phosphinidene species are involved in the rearrangement processes.