A Stable Phosphinidene Radical Anion as a Multielectron Reducing Agent

Abstract

The diagonal relationship between carbon and phosphorus has long inspired comparisons between the chemistries of carbenes and phosphinidenes. However, while carbene chemistry has flourished over the past three decades, isolable phosphinidenes remain exceptionally rare, and their one-electron reduction products, phosphinidene radical anions, are unknown. Here, we report the synthesis and isolation of a crystalline phosphinidene radical anion through one-electron reduction of a ring-strained phosphanorcaradiene, a phosphinidene equivalent. Structural, spectroscopic, and computational studies reveal a monocoordinate phosphorus center where the unpaired electron is predominantly localized, in line with a highly reduced phosphorus center. The radical anion exhibits multielectron redox reactivity, including radical addition to an arylalkyne, sulfur atom transfer from isothiocyanate, elemental chalcogen activation, and stepwise oxidation to high-valent P(V) compounds through an overall five-electron process, integrating formal paramagnetic P(0)/P(II)/P(IV) radicals and diamagnetic P(I)/P(III)/P(V) derivatives.