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Updated: Nov 9, 2025

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of PhosphorusI
Published on: November 22, 2016
Bis(Iminophosphorano)-Substituted Pyridinium Ions and their Corresponding Bispyridinylidene Organic Electron Donors
Brandon L Frenette1, Nadine Arsenault1, Sarah L Walker1
1Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada.
Abstract:
Optimized synthetic procedures for pyridinium ions featuring iminophosphorano (-N=PR3 ; R=Ph, Cy) π-donor substituents in the 2- and 4- positions are described. Crystallographic and theoretical studies reveal that the strongly donating substituents severely polarize the π-electrons of the pyridyl ring at the expense of aromaticity. Moreover, the pyridinium ions are readily deprotonated to generate powerful bispyridinylidene (BPY) organic electron donors. Electrochemical studies show exceptionally low redox potentials for the two-electron BPY/BPY2+ couples, ranging from -1.71 V vs the saturated calomel electrode for 3PhPh (with four Ph3 P=N- groups) to -1.85 V for 3CyCy (with four Cy3 P=N- groups). These new compounds represent the most reducing neutral organic electron donors (OEDs) currently known. Some preliminary reductions involving 3CyCy showed enhanced capability owing to its low redox potential, such as the thermally activated reduction of an aryl chloride, but purification challenges were often encountered.
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