Stable phosphorus radicals

Stable and persistent phosphorus radicals are phosphorus-centred radicals that are isolable and can exist for at least short periods of time.^[1] Radicals consisting of main group elements are often very reactive and undergo uncontrollable reactions, notably dimerization and polymerization.^[2] The common strategies for stabilising these phosphorus radicals usually include the delocalisation of the unpaired electron over a pi system or nearby electronegative atoms, and kinetic stabilisation with bulky ligands. Stable and persistent phosphorus radicals can be classified into three categories: neutral, cationic, and anionic radicals. Each of these classes involve various sub-classes, with neutral phosphorus radicals being the most extensively studied. Phosphorus exists as one isotope ³¹P (I = 1/2) with large hyperfine couplings relative to other spin active nuclei, making phosphorus radicals particularly attractive for spin-labelling experiments.^[1]