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Updated: Jan 4, 2026

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of PhosphorusI
Published on: November 22, 2016
A strong organic electron donor incorporating highly π-donating triphenylphosphonium ylidyl substituents
Morgan M Burgoyne1, Thomas M MacDougall1, Zachary N Haines1
1Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada. cadyker@unb.ca.
Abstract:
The π-electron donor strength of a triphenylphosphonium ylidyl group (Ph3P[double bond, length as m-dash]CH-) was explored through its substitution onto a bispyridinylidene (BPY) scaffold. Electrochemical studies revealed that the new triphenylphosphonium ylidyl-substituted BPY is the most reducing di-substituted derivative reported to date (E1/2 = -1.55 V vs. SCE). By using a previously established correlation between the redox potential of the substituted BPYs and the corresponding substituent, a Hammett constant for the Ph3P[double bond, length as m-dash]CH- group was determined (σp+ = -2.33), establishing it as the most donating neutral substituent currently quantified. The BPY is readily oxidized by hexachloroethane to produce the corresponding dicationic bipyridinium salt as a mixture of isomers owing to hindered Cylidyl-Cpyridyl bond rotation. In preliminary tests of the BPY as a reductant, dichlorotricyclohexylphosphorane and chlorodiphenylphosphine were reduced to the corresponding phosphine and diphosphine, respectively.
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