EPR and DFT Studies of the Structure of Phosphinyl Radicals Complexed by a Pentacarbonyl Transition Metal

Paramagnetic complexes M(CO)5P(C6H5)2, with M = Cr, Mo, W, have been trapped in irradiated crystals of M(CO)5P(C6H5)3 (M = Cr, Mo, W) and M(CO)5PH(C6H5)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)5P(C6H5)2, is consistent with both the number of EPR sites and the crystal structures. The g and 31P hyperfine tensors measured for M(CO)5P(C6H5)2 present some of the characteristics expected for the diphenylphosphinyl radical. However, compared to Ph2P•, the 31P 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)5P(C6H5)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.