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.
a b s t r a c tA radical species characterized by a large g-anisotropy and a clearly resolved hyperfine structure with 95/97 Mo and 31 P nuclei is formed, at 77 K, by radiolysis of a single crystal of Mo(CO) 5 PPh 3 . The corresponding EPR signals disappear irreversibly with increasing temperature and the angular dependence of the various coupling constants imply a spin delocalization of $60% and $4% on the molybdenum and the phosphorus atoms, respectively and are, a priori, consistent with the trapping of a one-electron deficient centre. The ability of DFT to predict the EPR tensors for a 17-electron Mo (I) species is verified by calculating the g-tensor and the various 14 N and 13 C coupling tensors previously reported by Hayes for [Mo(CN) 5 NO] 3À . Calculations at the B3LYP/ZORA/SOMF level of theory show that, in contrast to Mo(CO) 5 PH 3 , one-electron oxidation of Mo(CO) 5 PPh 3 causes an appreciable change in the geometry of the complex. The g-tensor and the 95/97 Mo and 31 P isotropic and anisotropic coupling constants calculated for [Mo(CO) 5 PPh 3 ] + Á confirm the trapping of this species in the irradiated crystal of Mo(CO) 5 PPh 3 ; they also show that the conformational modifications induced by the electron release are probably hindered by the nearby complexes.
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