Redox-Active Complexes Containing Group 8 Metal Centers Linked by C2 Bridges

A series of complexes containing dicarbon ligands bridging redox-active group 8 metal−ligand fragments M(dppe)Cp‘ (M = Fe, Ru, Os; Cp‘ = Cp, Cp*) have been prepared. These complexes give up to four one-electron anodic processes at a platinum electrode, with separations of successive oxidation potentials of ca. 850 mV, giving rise to large comproportionation constants, KC (ca. 1012). Examples of the 36-electron neutral, 35-electron monocationic, and 34-electron dicationic species, together with some related monoprotonated complexes, have been isolated. Structural studies of the 36-, 35-, and 34-electron species derived from the dicarbon complex featuring two Ru(dppe)Cp end-caps (7) show that shortening of the M−C and lengthening of the C−C bonds occur upon oxidation. A complementary spectroelectrochemical investigation has revealed an intense band near 14 300 cm-1 associated with [7]PF6, which is tentatively attributed to a Ru(d)−[Ru(d)/C2(π)]* transition, rather than a genuine IVCT band. These observations have been rationalized using DFT calculations and collectively indicate that the frontier orbitals are delocalized over both group 8 metal centers and the carbon chain.