Single Crystal EPR Studies of Radicals Produced by Radiolysis of Organophosphorus Compounds

Abstract

The main radical species produced by radiolysis of organophosphorus compounds are described in this chapter. Their identification is generally based on an analysis of the g and hyperfine tensors obtained from EPR experiments performed on irradiated single crystals. Special emphasis is placed on the properties of the 31P hyperfine tensor, which is often decisive in determining the structure of these radicals. Radiogenic species mentioned in the beginning of this review correspond to simple phosphorus-centered radicals (PR2, PR3 −, PR4, PR3 +, and R2PO). Then, more delocalized systems are reported (allylic structures, captodatively stabilized radicals, symmetrical radical ions containing a P–P bond). The effects of radiolysis on compounds containing low-coordinate phosphorus atoms (e.g. phosphaalkenes) are also described as well as the formation of radical pairs in irradiated phosphated sugars. The last part of the chapter deals with metallated radicals formed by radiolysis of metallic complexes M(CO)5P(H)Ph2 (with M = Mo, Cr, W). In some cases, phosphorus-centered radicals are compared with their arsenic analogues. For several systems the focus lies on dynamical effects; this is the case, for example, for the triptycenephosphinyl radical, which undergoes internal rotation around a P–C bond. Molecular rearrangements after radiolysis of some organophosphorus compounds (e.g. diphosphenes) are also reported.