Free Radical Forming Activity of the Grubbs Catalyst and Related Organometallics

When (PCy)2RuCl2CHPh, RuCl2(PPh3)3, or RhCl(PPh3)3 is added in CH2C12 solution to p-benzoquinone strong persistent concentrations of the quinone radical-anion are found. The epr spectra show that in each case only one species is formed, and the very well resolved hyperfine splittings are accurately simulated on the basis that the four hydrogen atoms are inequivalent because of close engagement with the metal donor complexes, thereby removing the two orthogonal symmetry axes present in the free radical anions. The results are therefore not only of great theoretical interest but they also demonstrate a sensitive means of estimating the basicities of the metal complexes.