Paramagnetic complexes M(CO) 5 P(C 6 H 5 ) 2 , with M ) Cr, Mo, W, have been trapped in irradiated crystals of M(CO) 5 P(C 6 H 5 ) 3 (M ) Cr, Mo, W) and M(CO) 5 PH(C 6 H 5 ) 2 (M ) Cr, W) and studied by EPR. The radiolytic scission of a P-C or a P-H bond, responsible for the formation of M(CO) 5 P(C 6 H 5 ) 2 , is consistent with both the number of EPR sites and the crystal structures. The g and 31 P hyperfine tensors measured for M(CO) 5 P-(C 6 H 5 ) 2 present some of the characteristics expected for the diphenylphosphinyl radical. However, compared to Ph 2 P • , the 31 P isotropic coupling is larger, the dipolar coupling is smaller, and for Mo and W compounds, the g-anisotropy is more pronounced. These properties are well predicted by DFT calculations. In the optimized structures of M(CO) 5 P(C 6 H 5 ) 2 (M ) Cr, Mo, W), the unpaired electron is mainly confined in a phosphorus p-orbital, which conjugates with the metal d xz orbital. The trapped species can be described as a transition metal-coordinated phosphinyl radical.

(5.VII.93)Single crystals of 1-[2,4,6-tri(wrt -butyl)phenyl]-2-phenylphosphaetbene (PPPE) and of 'D-and "C-enriched PPPE were studied by ESR after X-ray irradiation. Two phosphorus-centered radicals were trapped in the crystals. The first one was characterized by its 3'P, 'H-, and '3C-hyperfine tensors, the second one exhibited coupling with "P only. Comparison of these parameters with those predicted by ub initio calculations on some phosphinyl species indicates that these two radicals probably result, on the one hand, from an addition of a H-atom to the C-atom of the P=C bond and, on the other, from a cyclization of the parent molecule. The proposed mechanisms are consistent with the mutual orientations of the hyperfine eigenvectors and bond directions in the undamaged molecule. A C-centered radical which results from an addition of a H-atom to the P-atom of the phosphaethylene bond is also detected.

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have been studied by EPR and have been identified, from their 31P hyperfine tensors, as being phosphoniumyl radical cations. The spectra modifications caused by I3C or 2D enrichment of the phosphaalkene moiety show that these species result from an intramolecular cyclization which can lead to two possible conformations of the radical. The experimental 3iP, I3C, and 'H hyperfine tensors are compared with those predicted by ab initio calculations on model phosphoniumyl radical cations. These calculations show that these interactions are very sensitive to the geometry of the radical and that their measurement can yield precise structural information

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