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 [3a]~-. The oxidation of this anion with elemental iodine causes an intramolecular rearrangement reaction to give a bicyclic 1,3,2-diazaphospho-lenium 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 [3a]~-. Theoretical calculations suggest that phosphinidene species are involved in the rearrangement processes.
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