ELECTRON-TRANSFER CATALYSIS IN THE ACTIVATION OF C-H BONDS BY RUTHENIUM COMPLEXES

Ruthenium(II) dimethyl complexes, [Ru(Me)(2)(eta(6)-C(6)Me(6))(PR(3))] (R = Ph 1a, R(3) = MePh(2) 1b, R(3) = Me(2)Ph 1c, R = Me 1d, R = Et 1 e), react with C-H bonds of benzene or toluene under severe conditions (85-105 degrees C depending on the phosphine ligand) to give methane and the new methyl aryl derivatives [Ru(Me)(Ar)(eta(6)-C(6)Me(6))(PR(3 ))]. The methyl tolyl complexes are formed as a 2/1 mixture of meta an d para isomers. In contrast the reaction of 1a-1e with arenes, in the presence of [FeCp(2)]PF6, proceeds rapidly at room temperature: the co rresponding methyl aryl derivatives [Ru(Me)(Ar)(eta(6)-C(6)Me(6))(PR(3 ))] (Ar = Ph, Tol) and/or the intramolecular reaction products [Ru(C(6 )H(4)PR(2))(Me)(eta(6)-C(6)Me(6))] are formed depending on the steric hindrance of the phosphine. The fact that electrochemistry and ESR spe ctroscopy show that on oxidation the ruthenium(II) complexes give stab le ruthenium(III) congeners suggests that the catalytic reaction trigg ered by ferrocenium ions proceeds through a different redox pathway.